Interactions Between the Endoplasmic Reticulum Mitochondria Plasma Membrane and Other Sub Cellular...

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The International Journal of Biochemistry & Cell Biology 41 (2009) 18051816

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The International Journal of Biochemistry& Cell Biology

j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / b i o c e l

Review

Interactions between the endoplasmic reticulum, mitochondria, plasmamembrane and other subcellular organelles

Magdalena Lebiedzinska a, Gyrgy Szabadkai b, Aleck W.E. Jones b,Jerzy Duszynski a, Mariusz R. Wieckowski a,

a Nencki Institute of Experimental Biology, Dept. of Biochemistry, Warsaw, Polandb University College London, Department of Cell and Developmental Biology, Mitochondrial Biology Group, London, United Kingdom

a r t i c l e i n f o

Article history:

Available online 5 March 2009

Keywords:

Organelle interaction

Mitochondria-associated membranes

(MAM)

Plasma membrane-associated membranes

(PAM)

Lipid metabolism

Ca2+ signaling

a b s t r a c t

Several recent works show structurally and functionally dynamic contacts between mitochondria, the

plasma membrane, the endoplasmic reticulum, and other subcellular organelles. Many cellular processes

require proper cooperationbetweenthe plasmamembrane, the nucleus and subcellularvesicular/tubular

networks such as mitochondria and the endoplasmic reticulum. It has been suggested that such contacts

are crucial for the synthesis and intracellular transport of phospholipids as well as for intracellular Ca2+

homeostasis, controlling fundamental processes like motility and contraction, secretion, cell growth,

proliferation and apoptosis. Close contacts between smooth sub-domains of the endoplasmic reticulum

and mitochondria have been shown to be required also for maintaining mitochondrial structure. The

overall distance between the associating organelle membranes as quantified by electron microscopy is

small enough to allow contact formation by proteins present on their surfaces, allowing and regulating

their interactions. In this review we give a historical overview of studies on organelle interactions, and

summarize the present knowledge and hypotheses concerning their regulation and (patho)physiological

consequences.

2009 Elsevier Ltd. All rights reserved.

Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1806

1.1. Interaction of the endoplasmic reticulum with mitochondriathe MAM fraction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1806

1.1.1. Th e role of MA M fraction in lipid syn thesis an d t raf fickin g . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1806

1.1. 2. Th e MAM a s a center of non- vesicle interorganelle lipid traffi cking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1808

1.1.3. The role of MAM in the transmission of physiological and pathological Ca2+ signals from endoplasmic reticulum to

mitochondria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1808

2. Interaction of the ER with plasma membrane: the PAM fraction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1809

2.1. The role of PAM in the lipid synthesis and trafficking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1809

2.2. The role of PAM in non-vesicular cholesterol transport . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1809

2.3. The role of PAM in capacitative calcium influx . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1809

2.4. The role of MAM and PAM in the cellular response to oxidative stress: the p66Shc protein as a MAM and PAM resident

redox regulator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18103. Molecular characterization of MAM and PAM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1810

3.1. Phospholipid composition of MAM and PAM fractions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1810

3.2. Molecular composition of protein complexes that cross-link endoplasmic reticulum with mitochondria. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1810

3.3. Molecular components of PMER junctions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1812

Abbreviations: ER, endoplasmic reticulum; GSLs,glicerolosphingolipids;IMS, intermembranespace; IP3R, inositol 1,4,5-triphosphate receptor; MAM, mitochondria-

associated membranes; Mfn, mitofusin; OSBP, oxysterol binding protein; PAM, plasma membrane-associated membranes; PEMT, PtdEtn N-metyltransferase; PKC, protein

kinase C; PM, plasma membrane; PSS, phosphatidylserine synthase; PtdCho, phosphatidylcholine; PtdEtn, phosphatidylethanolamine; PtdSer, phosphatidylserine; VAMP,

vesicle-associatedmembrane protein;VAP, vesicle-associatedmembrane protein-associated protein;VDAC, voltage-dependentanion channel;VLDL, very low densityprotein. Corresponding author at: Laboratory of Bioenergetic and Biomembranes, Department of Biochemistry, Nencki Institute of Experimental Biology, Pasteura 3 Dt., 02-093

Warsaw, Poland.

E-mail address: [email protected] (M.R. Wieckowski).

1357-2725/$ see front matter 2009 Elsevier Ltd. All rights reserved.

doi:10.1016/j.biocel.2009.02.017
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1806 M. Lebiedzinska et al. / The International Journal of Biochemistry & Cell Biology 41 (2009) 18051816

4. ERGolgi, nuclear, lysosomal and peroxisomal interactions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1813

5. Concluding remarks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1814

Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1814

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1814

1. Introduction

Theendoplasmicreticulum (ER)extends fromthe nucleus acrossthe entire intracellular space, reaching to the plasma membrane

(PM), therefore is spatially intertwined with virtually all cellu-

lar organelles, including the mitochondria, peroxisomes and the

Golgi. Since the early 1960s, many groups have studied contact sites

between the apposing membranes of these organelles with the

intention of determining their function in the context of cell phys-

iology and pathology. While this research has identified a number

of different contact sites, only two contacts-enriched subcellular

fractions have been physically isolated: (i) the mitochondria-

associated membranes fraction, containing unique regions of ER

membranes attached to the outer mitochondrial membrane, and

(ii) the PM-associated membranes fraction, containing many types

of intracellular membranes (mainly ER and mitochondria) that

co-isolate with the PM. The importance of these membrane con-tacts has been corroborated by a series of findings proving that

functional interplay, essential for cell life and death, relies upon

structural interactions between the protein and lipid components

of the organelle membranes in an evolutionarily conserved man-

ner (Ardail et al., 2003; Camiciand Corazzi, 1995; Gaigget al., 1995;

Shiaoet al.,1995; Vance, 1990,2003; Vance andSteenbergen, 2005;

Vance andVance, in press). Inour reviewwewillfirstfocus upon the

structuralfunctional analysis of the most studied mitochondria-

and PM-associated membrane fractions, followed by a description

of their molecular determinants, and in conclusion briefly summa-

rize the accumulating knowledge on interactions between the ER

and other organelles.

1.1. Interaction of the endoplasmic reticulum withmitochondriathe MAM fraction

The first described association of intracellular organelles refers

to the ER and mitochondria. In 1959 Copeland and Dalton (1959)

reported the occurrence of a tubular form of the ER in association

with mitochondria in pseudobranch gland cells. In the early 1970s

various groups using different microscopy techniques observed

the apposition of the outer mitochondrial membrane and the ER

in rat liver (Lewis and Tata, 1973; Morre et al., 1971) and cul-

tured rat hepatocytes (Franke and Kartenbeck, 1971) (see Fig. 1).

At the same time, Dennis and Kennedy found that the interme-

diate fraction (unwashed mitochondrial pellet, many years later

named as the crude mitochondrial fraction) isolated from rat liver,

contained enzymes involved in phospholipid synthesis (e.g. thephosphatidylserine synthase (PSS)) (Dennis and Kennedy, 1972).

Still, 20 years hadto pass until separationand detailed characteriza-

tion of this fraction, performed by the group of Vance, first showed

that the crude mitochondrial preparation from rat liver contains an

X fraction with a high similarity to the ER (Vance, 1990). SDS-

PAGE of the X fraction has revealed distinct differences, as well

as similarities, to the mitochondria and both rough and smooth ER.

This ER-like fraction, named by Vance as an ERsub-fraction associ-

ated with mitochondria, or a mitochondria-associated membranes

fraction (the name used at present and abbreviated MAM), usu-

ally co-sediments with mitochondria during cell fractionation, and

can be separated by an additional centrifugation on Percoll gradi-

ent (Vance, 1990). Finally, structural and functional interaction of

mitochondria with the ER has been demonstrated for rat (Vance,

1990) and mouse (Ardail et al., 1993) liver, rat brain (Camici and

Corazzi, 1995) and Chinese hamster ovary cells (Shiao et al., 1995).

A similar membrane fraction was isolated from yeast ( Zinseret al., 1991) and characterized by biochemical means (Gaigg et

al., 1995). More detailed morphological studies, carried out by

Achleitner et al. (1999), indicated that the distance between the

ER and mitochondria in the area of interaction varied between 10

and 60nm. Importantly, a direct fusion between membranes of the

ER and mitochondria was not observed in any case, and the mem-

branes invariably maintained their separate structures. The authors

of this pioneering paper proposedthat a distance of less than 30nm

between the two organelles could be considered as an association,

their assumption based on the fact that proteins mediating associ-

ation of organelles may have a diameter of 445 nm (hypothetical

protein size around 300 amino acids). Achleitner et al. observed

that in yeast association of the ER with mitochondria (80110 con-

tacts/cell) occurred more often than with other organelles, e.g.the nucleus (6 contacts/cell), vacuoles (10 contacts/cell) or per-

oxisomes (30 contacts/cell) (Achleitner et al., 1999). Moreover,

Rizzuto and coworkers calculated that in living HeLa cells approxi-

mately 20% of the mitochondrial surface could be in direct contact

withtheER(Rizzuto et al.,1998a,b). Finally, the electron microscopy

studies of Mannela provided several lines of evidence concerning

the real structure of sub-cellular organelles and the existence of

numerous physical links between them (see Fig. 1) (Csords et al.,

2006; Hsieh et al., 2002; Mannella et al., 1998; Renken et al., 2009).

1.1.1. The role of MAM fraction in lipid synthesis and trafficking

Phospholipid biosynthesis and transport from the site of syn-

thesis to the destination organelle(s) is highly important for

establishing and maintaining membrane structure and cell func-tionality. Significantly, a large number of enzymes involved in

phospholipid biosynthesis have been found in the ER and some

in mitochondria. Moreover, it has been repeatedly demonstrated

that the MAM fraction is enriched in several lipid-synthesizing

enzymes, including diacylglycerol acyltransferase, PSS and acyl-

CoA:cholesterol acyltransferase (Rusinol et al., 1994), as compared

to the bulk of ER.

The best example for functional crosstalk between the ER and

mitochondria is related to the synthesis of phosphatidylcholine

(PtdCho) (see Fig.2), where it wasdemonstrated thatthe MAM frac-

tion mediates the transfer of newly synthesized phospholipids to

mitochondrial compartments (Ardail et al., 1993; Achleitner et al.,

1999;Shiao et al.,1995;Vance, 2003, 2004; Vance and Steenbergen,

2005; Vance and Vance, 2004; Voelker, 1993). The first step in Ptd-Chosynthesis is catalyzed by PtdSer synthase. It is important tonote

that yeast and mammalian cells have different PtdSer biosynthetic

machinery. In yeast PSS requires CDP-diacylglycerol to synthesize

PtdSer, whereasin mammaliancells PtdSer synthesisis based on an

exchange reaction in which choline or ethanolamine (from PtdCho

or PtdEtn, respectively) is exchanged for serine. There exists con-

tradictory data relating to the intracellular localization of PtdSer

synthase. Early studies by Dennisand Kennedy pointed to the ER as

the site of PtdSer synthesis (Dennis and Kennedy, 1972). Later, two

isoforms (PSS1 and PSS2) of the PtdSer synthase with distinct sub-

strate specificity were discovered (Kuge et al., 2001). Accordingly, it

was proposed by Stone and Vance that both PSS1 (in vivo using Ptd-

Choas thedonor of thephosphatidyl group)and PSS2(usingPtdEtn)

were highly enrichedin the MAM fraction. Additionally, theypostu-


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M. Lebiedzinska et al. / The International Journal of Biochemistry & Cell Biology 41 (2009) 18051816 1807

Fig. 1. Association of the endoplasmic reticulum with a mitochondrion. Electron micrograph of a sample field (26.000 ) made by Mariusz R. Wieckowski (left hand panel)

with the corresponding traced profiles of mitochondrion and ER (right hand panel).

latedthe existence of a third ER-specific isoform of PtdSer synthase,

which could also explain synthesis of PtdSer in the ER ( Stone and

Vance, 2000; Vance, 2003, 2004; Vance and Steenbergen, 2005;

Vance and Vance, 2004).

The newly formed PtdSer is next transported to the mito-chondrial intermembrane space (IMS) where it undergoes

decarboxylation by PtdSer decarboxylase (an enzyme of the inner

mitochondrial membrane IMM), resulting in the synthesis of

phosphatidylethanolamine (PtdEtn). Two different isoforms of

PtdSer decarboxylase have been described in yeast. The first is

present in the IMM (PtdSer decarboxylase 1) (Trotter et al., 1993),

whereas the second (PtdSer decarboxylase 2) has been found in

the Golgi compartment (Trotter and Voelker, 1995; Vance and

Vance, 2004). In contrastto yeast, mammaliancells containonly the

mitochondrial-specific PtdSer decarboxylase 1 isoform (Voelker,

1985; Wu and Voelker, 2002). When the mitochondrial PtdSer

decarboxylase 1 is inhibited, e.g. by hydroxylamine, accumulation

of PtdSer in the MAM fraction is observed, which directly indicates

the transport of PtdSer from ER to mitochondria occurs through

the MAM compartment (Daum and Vance, 1997; Vance and Shiao,

1996).

Depending on the organism, PtdEtn is exported either frommitochondria or the Golgi to the ER, where its sequential methy-

lation, catalyzed by two isoforms of phosphatidylethanolamineN-methyltransferase (PEMT1 or PEMT2) results in the conversion

of PtdEtn to PtdCho. Interestingly, with the exception of hepato-

cytes, mammalian cells do not contain PEMT2 and are incapable

of synthesizing significant amounts of PtdCho from PtdEtn (as was

observed in liver). Moreover, it has been found that the MAM frac-

tion isolated from ratliver is enrichedin this unique form of PEMT2,

and immunogold electron microscopy has confirmed thatPEMT2 is

present in ER regions localizedin closevicinity to mitochondria (Cui

et al., 1993). It therefore seems that the MAMis an important cellu-

lar compartment that may be involved in the biosynthesis of both

Fig.2. Schematicview of interorganellephospholipidtransport and phosphatidylcholinesynthesisshown as a compositeof reactionsoccurring in bothyeastand mammalian

cells.PtdSeris synthesizedin theER andMAM byisozymesof PtdSersynthase (1a, 1b and1c).The PtdSercanbe transported tothe mitochondriaor tothe Golgi compartment.

In mitochondria or in the Golgi the PtdSer is decarboxylated by PtdSer decarboxylase (isozyme 1) or (isozyme 2) respectively. The PtdEtn formed can be exported to the ER

where it is methylated to the phosphatidylcholine (PtdCho) by the methyltransferase enzymes (PEMT1 and PEMT2). Some characteristic proteins were highlighted: p66Shc

(found in cytosol, mitochondria, MAM and PAM), STIM and ORAi that interacts in PAM region. Possible contact sites between organelles are marked in pink. For details see

corresponding paragraphs. PtdSer, phosphatidylserine; PtdEtn, phosphatidylethanolamine; PtdCho, phosphatidylcholine.


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PtdSer and PtdCho. Elegant experiments supporting thisconclusion

were based upon purification of mitochondria and ER, followed by

the reconstitution of a unique system for phospholipid biosynthe-

sis and transport by addition of the MAM fraction to the mixture of

mitochondria and ER (Ardail et al., 1993). Other studies suggested

that the MAM fraction can also play an important role in ceramide

metabolism, since it has the ability to synthesize ceramide (Merril,

2002; Vance and Vance, 2004). More recently, Bionda et al. (2004)

documented the presence of the activities of both ceramide syn-

thase and reverse ceramidase in thisfraction. The MAM fractioncan

also be involved in the biosynthesis of glycosphingolipids (GSLs),

since it contains highly active sphingolipid-specific glycosyltrans-

ferases (Ardail et al., 2003).

1.1.2. The MAM as a center of non-vesicle interorganelle lipid

trafficking

Aside from the important contribution of the MAM to lipid

synthesis, participation of this structure in the cellular lipid traf-

ficking was also proposed. Several different models have been put

forward to explain the complexity of intracellular phospholipid

transfer, and they usually are based either on vesicle-mediated

transport or assume a direct contact of organelle membranes pro-

viding fast transfer of lipids to the respective organelles. However,

importantly, the importance of specific lipid transport proteinsin this process has also been highlighted. In the literature, the

MAM, since it is enriched in phospholipid synthesis enzymes, has

often been described as a center of non-vesicular interorganelle

lipid trafficking. In 1997, Vances group published a seminal paper

enabling a better understanding of lipid trafficking and its role

in cell physiology (Vance et al., 1997). The authors described the

molecular basis of the human neurodegenerative disease neu-

ronal ceroid lipofuscinosis (NCL) by studying a related animal

model (mnd/mnd mouse). The abnormal accumulation of lipids

and proteins in storage bodies in this disease appeared to be

the consequence of impaired interorganelle transport, specifically

reduced transport betweenthe ER andmitochondria. Indeed, analy-

sis of cellular fractions obtained from mnd/mnd mouse liver clearly

showed that the affected lipid trafficking was associated withreduced amount of MAM. Additionally, specific activities of both

PtdSer synthase and PtdEtn methyltransferase in the MAM frac-

tion were significantly decreased, while cytidyltransferase was not

affected (Vance et al., 1997). These and other well-documented

data emphasize that a close apposition of ER and mitochon-

drial membranes is crucial for phospholipid transport, and equally

highlight the unique function of MAM in both the transfer of

PtdSer from the ER to mitochondria and in phospholipid synthe-

sis (Ardail et al., 1993; Shiao et al., 1995; Trotter and Voelker,

1994).

In yeast, PtdSer transport from MAM to mitochondria can be

regulated by the Met30p protein, an ubiquitin ligase subunit. Three

hypotheses concerning the action of Met30p on PtdSer transport

were described in a review by Voelker (2005). In brief: (i) dock-ing of MAM to the mitochondrial surface might be dependent

upon ubiquitination of as yet unknown surface proteins of both

mitochondria and MAM; (ii) ubiquitination of a PtdSer transport

inhibitor (localized to the MAM or mitochondrial surface) induces

its degradation,resultingin theactivation of phospholipidtransport

at mitochondria-ER contact sites; or (iii) ubiquitination of the tran-

scription factor Met4p carried out by E3 ubiquitin ligase containing

Met30p causes inactivation of Met4p, which alters the transcrip-

tion of factor(s) involved in phospholipid transport. On the other

hand, in mammalian cells the rate of phospholipid transport from

MAMto mitochondria is regulatedby S100B,an EF-hand Ca2+ bind-

ing protein. Whether S100B is directly involved in the translocation

process or may stabilize mitochondria-MAM contact sites is still

unclear, and the mechanistic details of how this protein increases

the rate of phospholipid transport are yet to be clarified (Kuge et

al., 2001; Voelker, 2005).

Another potential role in lipid trafficking attributed to the MAM

fraction comes from the observations that it contains apolipopro-

teins suchas apoE, apoB and apoC (Rusinol et al., 1994; Schmitt and

Grand-Perret, 1999; Vance, 1990). Thus, in this respect, the MAM

can also be described as a component of the secretory pathway,

supplying lipids for assembly into very low-density lipoproteins

(VLDL). Along these lines, the MAM can be considered as a post-

rough ER and pre-Golgi compartment of this secretory route. The

existence of an intermediate compartment between the ER and

Golgi was previously proposed at the beginning of the 1990s, and

a 58 kDa protein (p58) characteristic of this fraction was identified

(Saraste and Svensson, 1991). The enrichment of p58 in MAM, as

compared to the ER and the Golgi, suggests that MAM has some of

the properties of this intermediate compartment (Rusinol et al.,

1994). Moreover, a high activity of diacylglycerol acyltransferase

in MAM suggests that this fraction could also be involved in the

formation of triacylglycerol-rich lipid storage droplets (Rusinol et

al., 1994). Nascent VLDL particles previously detected in the MAM

fraction seem to support this idea (Born et al., 1990). Thus, Rusinol

and coworkers suggested that some complete assembly of VLDL

or exchange of phospholipids between VLDL and organelles dur-

ing passage through the secretory pathway may occur in the MAM(Rusinol et al., 1994).

1.1.3. The role of MAM in the transmission of physiological and

pathological Ca2+ signals from endoplasmic reticulum to

mitochondria

The ER and mitochondria are endomembrane networks which

not only control different aspects of cellular metabolism but,

through their dynamic interaction, are also directly involved in sig-

nalling pathways. Of these pathways, Ca2+ signalling, notably that

concerning Ca2+-dependent cell death pathways, is best character-

ized(Berridgeet al.,2003; Brough et al.,2005a,b;Ferri andKroemer,

2001; Szabadkai and Rizzuto, 2004; Yi et al., 2004). Mitochon-

dria can efficiently accumulate Ca2+ due to their highly negative

(inside) membrane potential (m), triggering an increase in theirmetabolic activity. Excessive Ca2+ influx induces necrosis or apop-

tosis, usually accompanied by the opening of the permeability

transition pore. Close apposition of inositol 1,4,5-trisphosphate

(IP3)-gated channels (IP3 receptors) to the mitochondrial surface

enables the uptake of Ca2+ by mitochondria via the low affinity

calcium uniporter in an efficient manner, as it can be exposed

to a concentration of Ca2+ higher than is usually present in the

bulk cytosol during cell stimulation. Proteins present in the zones

of organelle association may make possible selective release and

uptake of calcium from ER and mitochondria, respectively. Numer-

ous proteins have been proposed to participate in the interaction

between mitochondria and ER. It was shown that the voltage-

dependent anion channel 1 (VDAC1) is present in ER-mitochondrial

contacts sites as a prominent member of the association, caninteract with several mitochondrial and ER proteins and is respon-

sible for exposing the calcium uniporter to large [Ca2+] gradients

(Gincel et al., 2001; Rapizzi et al., 2002). In addition, such VDAC1

localization enables formation of ATP microdomains close to the

sarco-endoplasmic reticulum Ca2+ ATPase (SERCA), thus maintain-

ing Ca2+ uptake by the ER (Vendelin et al., 2004; Ventura et al.,

2004). Thesefunctionalaspectsof ER-mitochondrial signalling have

been recently reviewed extensively (Hajnczky et al., 2006, 2007;

Rizzutoand Pozzan,2006; Szabadkai andDuchen, 2008;Walter and

Hajnczky, 2005), and we will cover further molecular details in

Section 3. Interestingly, an increased degree of apposition between

mitochondria and the ER might cause mitochondrial Ca2+ over-

load following Ca2+ release from the ER, which could result in

permeabilization of the outer mitochondrial membrane through


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opening of the permeability transition pore (PTP) (Bernardi, 1999;

Green and Kroemer, 2004; Rasola and Bernardi, 2007). In contrast,

decreased ER-mitochondria coupling might impair mitochondrial

Ca2+-dependent metabolism. Csords et al. (2006) speculated that

the improperly decreased distance between the ER and mitochon-

dria seems to be an important parameter in several mechanisms

of cell death. More information about the role of mitochondria-

ER contact sites may be found in the review of Giorgi et al. (this

issue).

2. Interaction of the ER with plasma membrane: the PAM

fraction

Analysis of serial ultrathin electron microscopy sections per-

formed by Pichler and coworkers indicated that a significant

amount of the ER is located in the proximity of the PM (Pichler et

al., 2001). Three-dimensional image reconstruction performed by

this group showed that there are specialized ER domains preferen-

tially associated with PM. Based on the assumption that a distance

of less than 30 nm constitutes an association between ER and PM,

approximately 1100 contact sites in an average series of sections

was calculated (Pichler et al., 2001). Strikingly, this is a muchhigher

number than that of the ER-mitochondria contact sites (80110 peryeast cell) calculated by Achleitner et al. (1999), indicating a funda-

mental functional role of PMER communication in cell physiology.

Opportunely, a reproducible isolation protocol for the PAM fraction

hasbeendescribedforyeastby Pichleret al.(2001), boostingfurther

studies. Indeed, more recently it has been shown that the distance

between ER and PM varies between 10 and 25nm and that the dis-

tance of less than 30nm between the organelles canbe regarded as

a true association (Wuet al., 2006), confirming the previous results

(Pichler et al., 2001).

2.1. The role of PAM in the lipid synthesis and trafficking

The PM of both yeast and higher eukaryotic cells represents themost sterol rich cellular compartment and contains all species of

glycerophospholipids, yet, in the majority of cases, lipid synthesiz-

ing enzymes are absent. In the light of this fact, the PAM can be

considered as an efficient machinery for supplying the PM with

necessary constituents and signaling compounds. For a long time,

no specific marker of the PAM was known, but more recent studies

have demonstrated that its function is related to the synthesis and

transportof phospholipids (phosphatidylserine and phosphatidyli-

nositol) within the cell. Thus, similar to MAM, the PAM was shown

to containa significant amount of PtdSer synthase. In addition, it has

been also proposed that,apartfromthe ability to synthesize PtdSer,

PAM may also be involved in the transferof this phospholipidto the

PM (Vance, 2003; Vance and Steenbergen, 2005; Vance and Vance,

2004; Voelker, 2003). There is strong evidence that two derivativesof phospatydylinositol, namely PtdIns 4-phosphate (PtdIns4P) and

PtdIns (4,5)-bisphosphate (PtdIns4,5P), play an important role in

the regulation of PtdSer transport, but it remains unclear whether

PtdSer must first be transported to the PM before reaching the

Golgi/vacuole compartment. In addition, Voelker hasproposedPAM

to be the compartment involved in the translocation of PtdSer to

the Golgi (Vance, 2003; Vance and Steenbergen, 2005; Voelker,

2003), despite the mechanism of such transport being unknown.

A further role attributed to PAM is the synthesis and export of

phospholipids for maintaining the proper functionality of insect

photoreceptors. In his excellent review, Levine described trafficking

of PtdIns from the ER to the PM mediated by PtdIns-transfer pro-

tein(PITPs)in thefly photoreceptorRdgB (Levine,2004; Cockcroft,

2007).

2.2. The role of PAM in non-vesicular cholesterol transport

It has been estimated that around 6580% of total cellular

cholesterol is present in PM, whereas only 0.12% is located

in the ER. Cycling of cholesterol between ER and PM is highly

dynamic, with a half-time of 40min. In both yeast and mam-

malian cells, sterol trafficking occurs in a non-vesicular way

(Baumann et al., 2005; Li and Prinz, 2004). Non-vesicular trans-

port of these membrane compounds may be mediated by the

oxysterol binding protein (OSBP), which also plays the role of

an intracellular sterol sensor (Perry and Ridgway, 2006). While

earlier data suggested that OSBP binds only relatively water-

soluble oxysterols, further investigations demonstrated that the

complex of OSBP with extracellular-signal-regulated kinase (ERK)

can also contain cholesterol. Therefore, OSBP can act as a sterol

transfer/binding protein. Interestingly, binding of cholesterol is

necessary for phosphatase-dependent inactivation of ERK, while

oxysterol has the opposite effect (Wang et al., 2005a,b). The spe-

cial structure of these oxysterol-binding proteins, along with their

localization in the vicinity to membrane contact sites, enables fast

and efficient cholesterol transport between organelles. OSBP has

two targeting domains (to the ER and Golgi compartments) and a

C-terminal domain responsible for lipid binding (Hynynen et al.,

2005; Kvam et al., 2005; Sullivan et al., 2006). The recruitmentof OSBP protein to destination membranes is regulated by PtdIns

(4)P and PtdIns (4,5)P, while dissociation of OSBP from membranes

is regulated by AAA-ATPases (Wang et al., 2005a,b). However, the

precise roleof thesetransport proteins and theirlipid and non-lipid

regulators remains an outstanding question in the field.

In yeast, three homologues of OSBP (named Osh proteins) have

been described. Osh1p contains ER and nucleus-vacuole junction

targeting domains, while Osh2p and Osh3p have ERPM targeting

domains (Johansson et al., 2005). The presence of such organelle

targeting domainsenablessimultaneousbindingbothto theER and

PM, and, by stabilizing membrane interactions, it facilitates sterol

transport between the ER and PM (see review Levine, 2004; Levine

and Rabouille, 2005; Levine and Loewen, 2006). Altogether, PAM

appears to be a good candidate for the site of action of OSBP dur-ing sterol trafficking both to and from the PM in an evolutionary

conserved manner. More about the characteristics of OSBP may be

found in the review ofYan and Olkkonen (2008).

2.3. The role of PAM in capacitative calcium influx

Studies on Jurkat cells (human lymphoidal T cells) suggested

that PAM could also play a role in cellular Ca2+ homeostasis, par-

ticularly in capacitative Ca2+ entry (CCE). During cell activation,

close apposition of ER and mitochondria to the PM is important

in the initiation and regulation of Ca2+ fluxes. Antigen-dependent

activation of Jurkat cell leads to a transient increase in [Ca 2+]cwhich in part depends on Ca2+ influx from the extracellular space.

Several models have been put forward to describe the nature ofcommunication between ER and PM during CCE, and have been

extensively reviewed elsewhere (for review see: Chakrabarti and

Chakrabarti, 2006; Jones et al., 2008; Parekh, 2006; Parekh and

Putney, 2005). The attractive conformational coupling model is

based onthe assumption that proteins, one from theER (STIM1) and

a secondfrom thePM (ORAi), maintainthe structural association of

these organelles by a direct interactionfollowingcell stimulation by

Ca2+ mobilizing agonists (Firth, 2008; Frischauf et al., 2008; Penna

et al., 2008). This model has found support in the observation that

upon Ca2+ release from the ER, a discrete domain of the ER moves

to the cell periphery, where it can interact with the PM (Frieden

et al., 2005). Wu et al. (2006) observed that Ca2+ release from the

ER results in an increase of the number of contacts between the

ER and PM (one third of junctions were newly formed, while two


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thirds of were preexisting in unstimulated cells). However, despite

thecrucialrole of PAM in signalingER Ca2+ depletionto thePM, this

fraction should not be considered to contain only interaction sites

between the PM and ER. The PAM fraction can also contain other

intracellular membranes, e.g. mitochondria. It has been presented

that, upon antigen stimulation of the T-cell, mitochondria move

to the PM region. After formation of the immunological synapse,

mitochondria migrate to a position no further than 1m from PM.This close vicinity of mitochondria to the PM facilitates Ca2+ entry

by Ca2+ release-activated calcium (CRAC) channels (Frieden et al.,

2005). By buffering calcium ions in the vicinity of SOC channels,

mitochondria prevent feed-back inactivation of CCE. Moreover,sus-

tained activity of SOC requires translocation of mitochondria to

the PM and where they appear to fulfill further, although poorly

defined, signaling roles, indicating the importance of PAM in the

Ca2+-dependent immunological answer, such as cytokine produc-

tion and release (Quintana et al., 2006, 2007; Varadi et al., 2004).

On the role of mitochondria in CCE we refer the reader to recent

detailed reviews (Duszynski et al., 2006; Parekh, 2006; Parekh and

Putney, 2005).

2.4. The role of MAM and PAM in the cellular response to

oxidative stress: the p66Shc protein as a MAM and PAM resident

redox regulator

Since both the MAM and PAM fractions are dynamic mem-

brane domainsmediating theinteractions andtransportof proteins,

lipids, ions and metabolites between intracellular organelles, it is

not surprising that recent studies have aimed to reveal how their

function intertwines with major cellular signalling routes. Here

we will briefly discuss the role of MAM and PAM in redox sig-

nalling. Since the pioneering studies of Pellicis group, it has been

proposed that mammalian life span might be controlled by the

p66Shc proteinthrough regulation of thecellularresponseto oxida-

tive stress (Migliaccio et al., 1999). Following further studies by

the groups of Pellici and Rizzuto, p66Shc is now recognized as a

mediator of the oxygen free radical theory of ageing (Giorgio et

al., 2005, 2007). This protein, together with p52Shc and p46Shcproteins, belongs to the ShcA family, all of which consist of three

functionally identical domains (the carboxy terminal Src homol-

ogy domain (SH2), the central proline-rich domain (CH1) and

the N-terminal phosphotyrosine-binding domain (PTB)). In addi-

tion, p66Shc contains an N-terminal proline-rich domain (CH2)

with a phosphorylation site at serine 36; phosphorylation of this

residue is a trigger for the initiation of a multistep process lead-

ing cell death upon oxidative stress. Briefly, oxidative conditions in

the cell activate protein kinase C (PKC), which phosphorylatesp66Shc at Ser36 (Pinton et al., 2007). Such phosphorylated p66Shc

is in turn recognized by the prolyl-isomerase Pin1. Subsequent

dephosphorylation of p66Shc by phosphatase 2A directly precedes

its translocation to the mitochondria where, after import into

the matrix, p66Shc causes perturbions in mitochondrial function,including alterations of mitochondrial Ca2+ responses, fragmen-

tation of the mitochondrial network and permeabilization of the

outer or both mitochondrial membranes, triggering the mitochon-

drial route of apoptosis (Kroemer et al., 2007; Pinton et al., 2007).

Although many years have passed since the discovery of Shc

proteins, their intracellular localization still represents an open

question. Lotti et al. (1996) observed that in 3T3fibroblastsShc pro-

teins are located mainly in the ER,especially on the cytosolicside of

the rough ER. EGF-dependent activation of tyrosine kinase recep-

tors (TRK) caused redistribution of Shc proteins to the periphery of

cell and their association with PM and endocytic structures. More

recently, evidence has accumulated showing that a sub-fraction

of the cellular p66Shc pool can also be localized to the cytosolic

and mitochondrial compartments. Initially it was suggested that

the mitochondrial pool of p66Shc protein is present in the mito-

chondrial matrix, and interacts with mtHsp70 (grp75) (Orsini et

al., 2004). Later on, the same group re-evaluated this observation,

and proposed that p66Shc is rather present in the intermembrane

space, where it interacts with cytochrome c and functions as an

oxidoreductase, shuttling electrons from cytochrome c to molecu-

lar oxygen, thus participating in superoxide production (Giorgio et

al., 2005). The partial mitochondrial localisation of this protein has

been explained by the finding that it contains an internally located

mitochondrial targeting sequence (Ventura et al., 2004). Indeed, in

mammalian fibroblasts about 20% of p66Shc is localized in mito-

chondria (Nemoto et al., 2006; Orsini et al., 2004). Moreover, our

recentdataindicate that a quitesignificantportionof p66Shcis also

present in MAM and PAM fractions (Lebiedzinska et al., 2009).

Under conditions of oxidative stress, an increased amount of

either the cytosolic or mitochondrial form of p66Shc has been

observed (Pacini et al., 2004; Trinei et al., 2002). At the same

time, Orsini and coworkers did not detect any relevant translo-

cation of p66Shc to the mitochondria, in spite of demonstrating

the interaction of this protein with TIM/TOM protein complexes

(Orsini et al., 2004). Additionally, p66Shc has been shown to be

excluded from isolated mitochondria (Ventura et al., 2004). How-

ever, more recent studies showed that in MEF cells responding to

oxidative stress, a portion of the cytosolic pool of p66Shc translo-cates to the crude mitochondrial fraction (containing MAM and

PAM elements) (Pinton et al., 2007). Purification of the crude

mitochondrial fraction, resulting in the isolation of highly puri-

fied mitochondria and MAM, showed that most p66Shc was found

in MAM, while highly purified mitochondria contained only a low

amount of the protein (Wieckowski et al., unpublished). This impli-

cates the MAM as the origin of the mitochondrial p66Shc pool, and

partially explains the earlier contradictory observations. Similar

results were obtained after fractionation of MEFs and HeLa cells.

This strongly suggests that MAM and PAM, due to their charac-

teristic composition, can also be involved in signal transduction

pathways transmitting different signals to mitochondria.

3. Molecular characterization of MAM and PAM

3.1. Phospholipid composition of MAM and PAM fractions

Detailed analysis of the lipid composition of subcellular mem-

branes was performed many years ago by both Daums and Vances

groups. Studies using yeast showed that mitochondria and the PM

containedlower amounts of phosphatydyloinositol thanthe ER and

PAM fractions. The major phospholipid constituents of the PAM

fraction were PtdCho and PtdEtn, while, the ER, mitochondria and

PM were rich in PtdSer. Interestingly, in yeastthe lipid composition

of the PAM fraction also differs significantly from that of the PM

(Pichler et al., 2001).

A detailed analysis of lipid composition in subcellular fractions

(unfortunately excluding the PAM) isolated from rat liver was car-ried out by Vance andcoworkers. In this case the content of PtdCho

was the highest in MAM fraction. The relative amount of phospho-

lipids in subcellular fractions isolatedfrom yeast andrat liver (based

on datapresented by Pichler et al. (2001) and Vance (1990) is shown

in Fig. 3.

3.2. Molecular composition of protein complexes that cross-link

endoplasmic reticulum with mitochondria

The mitochondria and the ER are dynamic organelles which

undergo continuous membrane remodeling, fusion and fission, as

well as redistribution in the intracellular space. This suggests that

their interaction is also a transient phenomenon. However, the

sites of Ca2+

signal transmission between the ER and mitochon-


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Fig. 3. Phospholipid composition of subcellular fractions isolated from yeast and rat liver. The diagrams show the relative amount of phospholipids in the ER, mitochondria,

plasma membrane, MAM and PAM fractions in yeast (based on Pichler et al., 2001; data originally presented as % of total phospholipids) and in the ER, mitochondria

and MAM fraction in rat liver (based on Vance, 1990; data originally presented in nmol of phospholipid/mg protein). ER, endoplasmic reticulum; MAM, mitochondria-

associated membranes; PAM, plasma membrane-associated membranes; PM, plasma membrane; PtdCho, phosphatidylcholine; PtdEtn, phosphatidylethanolamine; PtdIns,

phosphatidylinosytol; PtdSer, phosphatidylserine.

dria appear to be preserved, at least in the timescale of minutes,

in HeLa cells (Filippin et al., 2003), and a significant amount of

ER membranes can be co-isolated with mitochondria (MAM frac-

tion) by subcellular fractionation from a wide range of tissues andcell types. Indeed, a plethora of recent works have exploited in

vivo fluorescent labeling, immunofluorescence and cell fraction-

ation methods to study the protein composition, function and

dynamic regulation of this membrane fraction, other than in lipid

synthesis and transfer (see above). These studies were mainly

focused upon proteins related to (i) physiological and pathological

Ca2+ transfer between the organelles, (ii) mitochondrial dynamics

and membrane trafficking, and (iii) endogenous and viral pro-

teins regulating mitochondrial membrane permeabilization during

apoptosis/necrosis.

The IP3R (inositol 1,4,5-triphosphate receptor) (types 1, 2 and 3)

is a large homo- or heterotetramer, with a C-terminal Ca 2+ chan-

nel domain embedded in the ER membrane and a vast N-terminal

domain forming protruding arms on the cytosolic surface of theorganelle. Thus it is not surprising that the IP3R has been identified

as an anchor for a number of protein interactors, in part related to

the regulation of its channel function, but also forming signaling

complexes not directly associated with Ca2+ signaling (Mikoshiba,

2007). IP3Rs havebeen shownto be localizedin thevicinity of mito-

chondria (Mendes et al., 2005), but whether it is indeed enriched

in the MAM fraction or in any hitherto identified ER sub-domain is

a matter of present debate. Its co-localization (Rapizzi et al., 2002)

and interaction with the OMM resident VDAC have been recently

shown (Szabadkai et al., 2006), in concert with the current view

that VDAC is responsible for Ca2+ channeling through the OMM

(Bthori et al., 2000; Colombini, 2007; Rapizzi et al., 2002; Tan and

Colombini, 2007), allowing Ca2+ to reach the IMM localized mito-

chondrial Ca2+ uniporter (MCU), mediating uptake of Ca2+ into the

matrix space (forreview see Bernardi and Forte, 2007; Bernardi and

Rasola, 2007; Szabadkai and Duchen, 2008). Intriguingly, ER and

mitochondria resident stress related chaperones have been shown

to mediate the assembly of IP3R-VDAC complexes. Hayashi and Sureported that sigma-1 receptors (Sig1R) are enriched in the MAM

and recruit the Ca2+ binding chaperone grp78, ankyrin-B and type 3

IP3R (Hayashi and Su, 2001; Hayashi and Su, 2007; Wu and Bowen,

2008). From the mitochondrial side, an OMM associated fraction

of the matrix chaperone grp75 bridges the gap between the IP3R

and VDAC, interacting with both Ca2+ channels (Schwarzer et al.,

2002; Szabadkai et al., 2006). Thesilencing of both Sig1R and grp75

leads to impaired ER-mitochondrial Ca2+ transfer, while their over-

expression or induction by ER stress promotes mitochondrial Ca2+

loading, with parallel Ca2+ depletion of the ER. Interestingly, ER

stress also leads to the accumulation of an alternatively spliced

truncated form of the type 1 SERCA (Chami et al., 2001) in the

MAM, which, in contrast to the function of the full-length form

(ATP-dependent Ca2+

pumping into the ER), promotes Ca2+

leak,and consequently mitochondrial Ca2+ overload (Chamiet al., 2008).

Along these lines, increased association of the ER and mitochon-

dria have been shown to accompany ER Ca2+ depletion and ER

stress (Chami et al., 2008; Csords et al., 2006), further supporting

redistribution of Ca2+ from the ER to mitochondria. Further Ca2+

binding ER resident chaperones have repeatedly been found in the

MAM, e.g. calnexin (CNX), calreticulin and ERp44, which interact

with the MAM-enriched IP3R and SERCA2b, respectively (Higo et

al., 2005; John et al., 1998; Roderick et al., 2000). Still, how their

function relates to ER-mitochondrial association has not yet been

characterized in detail, aside from an observation that calreticulin

overexpression impairs mitochondrial function.

The above example of ER stress related plasticity in the MAM

fraction also suggests that its components, and thus the interac-


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tion between the ER and mitochondria, are a valuable target of

cellular signaling pathways, regulating both ER and mitochondrial

function and cell fate. Indeed, recent reports shed light on multi-

ple mechanisms of crosstalk between stress activated pathways and

the ER-mitochondrial axis,and we can envisage further advances in

thistopic.Ca2+ signalingitself appears to regulateER-mitochondrial

association in different ways. Increased [Ca2+]c blocks the motil-

ity of both organelles, at least partially by binding to the EF hands

domains of the mitochondrial rhoGTPases (Miro-1,2) (Fransson et

al., 2006; Saotome et al., 2008), enhancing theirinteraction (Brough

et al., 2005a; Chami et al., 2008; Yi et al., 2004 ). Similarly, the

group of Nabi described a biphasic regulation by Ca2+ of the inter-

action of an ER sub-compartment (characterized by the presence of

autocrine mobility factor receptor (AMFR), able to bind to the 3F3A

monoclonal antibody, and partially overlappingwith theMAM frac-

tion) with mitochondria (Goetz et al., 2007; Goetz and Nabi, 2006;

Wang et al., 2000).

The multifunctional cytosolic sorting protein PACS-2 has been

shown to reside partially in the MAM, and maintain its integrity

(Simmen et al., 2005). To achieve this, PACS-2 interacts with CNX,

which resides in a complex with SERCA2b, and the interaction is

regulated by multiple phosphorylation by protein kinase C (PKC),

extracellular-signal regulated kinase-1 (ERK-1) and protein kinase

CK2 (Chevet et al., 1999; Myhill et al., 2008; Roderick et al.,2000). CNX and PACS-2 also interact with the MAM resident ER

cargo receptor BAP31 and regulate its cleavage during apoptosis

(Breckenridge et al., 2003; Groenendyk et al., 2006; Zuppini et al.,

2002), which triggers mitochondrial OMM permeabilization (OMP)

through the recruitment of the proapoptotic Bcl-2 family proteins

Bax and Bak (Kroemer et al., 2007). Accordingly, antiapoptotic Bcl-

2 and Bcl-XL have also been found in the MAM, providing another

level of regulation of ER-mitochondrial Ca2+ transport through

interactions with both the IP3R and VDAC (Pinton and Rizzuto,

2006). Further functional and morphological evidence of the regu-

lation of ER-mitochondrial association and Ca2+ transfer by TGF-,the MAPK pathway and PKCs has also been presented recently, but

the presumably MAM resident targets of these pathways have not

yet been identified (Pacher et al., 2008; Pinton et al., 2004; Szandaet al., 2008). A recent work bythe group of L. Scorrano may provide

a hint, since they have shown that homo- and hetero-oligomers

of the mitochondrial and ER localized mitofusins 1 and 2 GTPases,

bearing a p21ras motif, anchor the ER to mitochondria (Martins de

Brito and Scorrano, 2008).

Ardail et al. (1993) proposed that ER can interact with mito-

chondria at mitochondrial contact sites. These special docking

sites on mitochondria are formed by two different types of con-

tacts between OMM and IMM. The first, described by Brdiczkas

and Cromptons groups, contains VDAC, ANT and cyclophylin D

as the main protein constituents, and has been proposed to be

involved in the formation of mitochondrial permeability transition

pores (MPTP) (Wieckowski et al., 2000) (for reviewsee: Brdiczka et

al., 2006; Crompton, 2000; Grimm and Brdiczka, 2007; Shoshan-Barmatz et al., 2006). The functional significance of this interaction

is represented by the finding that close apposition of the MPTP to

the ER can sensitize mitochondria to calcium signals (Wieckowski

etal.,2006) (forreviewsee: Sptet al.,2008; Szabadkai andDuchen,

2008). The second type of protein complex present in mitochon-

drial contact sites is known to participate in protein import into

mitochondria, and consists of complexes associated with both the

outer and inner mitochondrial membranes (TOM and TIM, respec-

tively, for reviews see Mokranjac and Neupert, 2009; Neupert and

Herrmann,2007). The factthat adriamycindisruptsboth PtdSer and

protein import intomitochondria (presumably via its specific inter-

actions with cardiolipin) indicates that mitochondrial contact sites

contribute to various aspects of mitochondrial function (Eilers et

al., 1989).

Finally, the functional significance of regulation of ER-

mitochondrial cross-talk by MAM resident complexes is further

supported by the finding that several viral proteins, such as the

human cytomegalovirus vMIA (Bozidis et al., 2008) and the p7 and

NS5B proteins of hepatitis C virus (Sheikh et al., 2008), are targeted

to the MAM and exert either anti or pro-apoptotic effects, respec-

tively. The HIV-1 component Nef has been shown to associate with

PACS-2, triggering a signalling cascade which results in cell surface

MHC-I down-regulation, but whether this interaction takes place

in the MAM has not been verified (Atkins et al., 2008). Studying the

protein compositionof the MAM, it is possible to conclude that this

fraction may be examined from both the mitochondrial and the ER

sides. As described above, MAM is formed by special regions of ER.

As MAM can be isolated from crude mitochondrial fraction, similar

purification of crude ER was performedby Vance (1990). Unexpect-

edly, a special membranefraction, equivalent to MAM and localized

at the same Percoll density gradient, was isolated. Further analysis

showed that this MAM-like fractionwas more similar tothe ER than

totheMAM(Vance, 1990). Moreover,the presence of glycosyltrans-

ferases in the MAM means this fraction can also be considered as a

pre-Golgi compartment. Therefore, the question of whether clas-

sic MAM is similar to the fraction involved in the non-vesicular

ceramide trafficking mediated by CERT between the ER and Golgi

remains open.

3.3. Molecular components of PMER junctions

In contrast to the MAM fraction, the molecular composition

of the PAM fraction is much less well studied. Information about

the strength of the interaction between ER and PM comes indi-

rectly from cell fractionation experiments. Based on Pichlers

experiments, it seems obvious that ER proteins are present in

relatively high quantities even in carefully purified PM fraction

(Pichler et al., 2001), suggesting that ERPM interactions are quite

strong. Apart from the above described complexes of STIM1 and

ORAi, involved in capacitative calcium influx and OSBP, solu-

ble N-ethylmaleimidesensitive factor attachment protein receptors

(SNAREs) are another set of candidates which allow interaction ofER with PM. These proteins (with fusogenic activity), together with

lipids exposed at the surface of ER and PM, can cross-link these

membranes through ionic interactions (Camici and Corazzi, 1997).

Observation that contacts between PAM and PM can be destroyed

by treatment of isolated fractions with a buffer at pH 6.0, supports

this hypothesis (Pichler et al., 2001).

An interesting, althoughrather specialized, type of PMER asso-

ciation can be found in muscle cells, named as triad-junctions.

Proteins responsible for bridging this contact site have been

identified and classified as junctophilins (Kakizawa et al., 2008;

Takeshima, 2001; Takeshima et al., 2000). Interestingly, muscle

function is affected in mice lacking junctophilins, suggesting an

important functional role in PMER contact sites (Komazaki et al.,

2002). Unfortunately, the PM resident interactors of these proteinshave not been described. In other cell types, the ER-membrane

resident vesicle-associated membrane protein-associated protein

(VAP) can form complexes with peripheral PM proteins, possibly

providing an anchor between the ER and PM. VAP can also bind

membrane proteins from other organelles, as described below for

the ERGolgi interaction (Loewen et al., 2003).

Finally, a few sets of data indicate that at the PMER contact

sites proteins and enzymes involved in signal transduction path-

ways arealso present.So far, thebest characterized is theinteraction

of protein tyrosine phosphatase 1B (PTP1B), an ER membrane resi-

dent protein, with the insulin receptor localized in the PM (Anderie

et al., 2007; Goldstein et al., 2000). Moreover, using fluorescence

and bioluminescence resonance energy transfer techniques, it was

demonstrated that PTP1B can interact directly with other cell sur-


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Table 1

Subcellular distribution of marker enzymes and proteins in isolated cellular fractions.

MAM PAM Mitochondria Golgi ERa PH

PSS (nmol/(h-mgprotein))

6.8 0.8 (c) 21.93.4 (c) 3.32 0.30 (c) 0.6 40.30 (c)

14.8 6.3 (d) 2.010.21 (d) 6.92 1.83 (d)

2.7 0.9 (e) 0.14 0.07 (e)

25.3 7.1 (f) 6.7 1.1 (f)

PSD (nmol/(min-mg protein)) 0.04 0.02 (e) X 0.3 0.1 (e) X 0.04 0.01 (e) X

PEMT (nmol/(min-mgprotein))4.12 0.11 (d) 1.470.2 9 (d) 5.03 0.21 (d)2.74 0.62 (e) X 0.25 0.12 (e) X

2.17 0.62 (f) 5.68 0.33 (f)

NADPH-cyt c reductase (nmol/(min-mg protein))

14.1 2.8 (a)

X

0.7 0.1 (a) 3.10.8 (a) 35.2 8.2 (a)

0.7 0.1 (b)

13.5 3.3 (d) 8.51.3 (d) 53.1 7.9 (d)

9.77 3.15 (e) 0.90 0.66 (e) 27.6 7.2 (e)

0.9 (i)

Cyt c oxidase (nmol/(min-mgprotein)

17.3 2.5 (b)

X

427 23 (a) 25.64.0 (a) 43.3 5.5 (a)

X77.0 44.9 (e) 388 119 (e) 35.0 15.4 (e)

1877.9 (g)

Glucose-6P-phosphatase (molPi/(h-mg protein)

298.5 76.2 (b) 23.8 2.7 (b) 139 33 (b)

X325.1 106.0 (e) X 27.5 5.0 (e) 179.9 40.2 (e)

32.00.8 (g)

Relative amount of selected proteins in subcellular fractions

ANT (c)

Kex2 (c) ND ND

Galactozyl-transferase (a) X ND X

ATPase NA+ /K+ (c) ND ND

p66Shc (h) X

ANT, mitochondrial adenine nucleotide translocase; Kex2, calcium-dependent serine protease; MAM, mitochondria-associated membranes; PAM, plasma membrane-

associated membranes; PEMT, PtdEtn N-metyltransferase; PM, plasma membrane; PSD, PtdSer decarboxylase; PSS, phosphatidylserine synthase; X = data not available;

ND = not determined;

Marker enzymes activity values have been described by: (a) Ardail et al. (2003); (b) Bionda et al. (2004); (c) Pichler et al. (2001); (d) Rusinol et al. (1994); (e) Vance (1990);

(f) Vance et al. (1997); (g) Vance and Vance (1988); (h) Lebiedzinska et al. (2009); (i) Zinser et al. (1991).a ER, smooth endoplasmic reticulum microsomes 30.000g.

face receptors, and that dephosphorylation mediated by PTP1B is

important for their transport to the cell surface or during endocy-

tosis (Hernndez et al., 2006).

Information regarding the subcellular distribution of marker

enzymes and some selected proteins in isolated cellular fractions

is presented in Table 1, based on both the large amount of data

available in the literature and our own studies.

4. ERGolgi, nuclear, lysosomal and peroxisomal

interactions

Non-vesicular lipid transport between the ER and the Golgi

membranes has been proposed to maintain the characteris-

tic lipid composition of the Golgi compartment. Based onelectron tomography studies, it was observed that in mam-

malian tissues a specialized trans-ER region (continuous with

the entire ER network) interacts with trans-cisternal Golgi mem-

branes (Ladinsky et al., 1999; Marsh et al., 2001; Marsh, 2005).

These stable contacts are proposed to be involved in the

non-vesicular transport of ceramide between both organelles

(Ladinsky et al., 1999; Mogelsvang et al., 2004). The ceramide

binding protein (CERT), responsible for ceramide trafficking,

links the ER and Golgi membranes in a similar way to that

described above for OSBP, due to their similar domain struc-

ture (Hanada et al., 2007; Kawano et al., 2006). More recently,

Peretti et al. (2008) described non-vesicular lipid trafficking

at ERGolgi contact sites as a coordinated cooperation of the

lipid-binding/transfer proteins OSBP, CERT and Nir2 phosphatidyli-

nositol/phosphatidylcholine (PI/PC)-transfer protein. OSBP, CERT

and Nir2 proteins all contain an FFAT motif (two phenylala-

nines in an acidic tract) that mediates their interactions with

integral ER-membrane proteins of the vesicle-associated mem-

brane protein-associated protein (VAP) family (VAP-A and VAP-B)

(Hanada, 2006). Recruitment of VAPs to the ERGolgi contact sites

by 25-hydroxycholesterol enhances movement Nir2 to Golgi com-

partment.

The double membrane structure of the nuclear envelope is

continuous with the rest of the ER membranes, but may also be

connected with other organelles by membrane contacts. For exam-

ple, in yeast, junctions between the vacuole (equivalent to the

lysosome of mammalian cells) and nucleus were observed. The

molecular structure of protein complexes present in the vacuole-nucleus contact sites has been proposed by Pan and coworkers.

In this model the armadillo repeat protein Vac8p from the vac-

uolar membrane interacts with the cytoplasmic domain of Nvj1p,

an integral membrane protein of the nuclear envelope) ( Pan et

al., 2000). According to Levine (2004) and Levine and Loewen

(2006), the junctions between the nucleus and vacuole can be

compared to the ER-endosome/lysosome contacts found in higher

eukaryotes, where cooperation between peroxisomes and the ER

in some phospholipid biosynthetic processes has been observed.

Similarly, nuclear-vacuole junctions in yeast contain enzymes

involved in lipid trafficking, for example a lipid synthase subunit

(Tsc13p) involved in very long chain fatty acid synthesis and the

oxysterol-binding protein homolog (Osh1p), related to the human

OSBP.


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5. Concluding remarks

Recent awareness in metabolism and signaling research has

been raised on compartmentalization of metabolic and signaling

networks, which appears to have a fundamental role in maintain-

ing their integrity. Still, given its importance, relatively few studies

have focused on the intracellular membrane domains providing

a platform for the massive metabolic and signaling events occur-

ringin thesecompartments. Wereviewed the available information

on interactorymembrane surfaces between intracellularorganelles

and the PM, and we conclude that they represent such a platform

for compartmentalized metabolism and signaling. Our selection of

recent work might have been weighted by our own experience,

thus we apologize for works which have not been cited, and look

forward to further discussion. We intended to highlight that much

further effortis neededto better characterize the nature and molec-

ular composition of these domains. Improvement in markers and

separation will combine with detailed proteomic cataloging of the

membrane fractions, and underlie studies on interaction between

membrane and protein components, to determine the function and

malfunction of those compartmentsas partof cellular life anddeath

signaling networks.

Acknowledgments

The authors thank Prof. Lech Wojtczak for his suggestions and

helpful discussions. This work was supported by the Polish State

Committee for ScientificResearch grant N301 092 32/3407and Pol-

ish Mitochondrial Network to M.L., J.D. and M.R.W. This work was

also partly supported by a University College London startup grant

to G.S. andby a Medical Research Council (MRC, UK) PhD fellowship

to A.J.

We apologize to the authors whose research articles could not

be cited due to space constraints.

References

Achleitner G, Gaigg B, Krasser A, Kainersdorfer E, Kohlwein SD, Perktold A, et al.Association betweenthe endoplasmic reticulumand mitochondriaof yeast facil-itates interorganelle transport of phospholipidsthroughmembranecontact.Eur

J Biochem 1999;264:54553.Anderie I, Schulz I, Schmid A. Direct interaction between ER membrane-bound

PTP1B and its plasma membrane-anchored targets. Cell Signal 2007;19:58292.

Ardail D, Gasnier F, Lerme F, Simonot C, Louisot P, Gateau-Roesch O. Involvementof mitochondrial contact sites in the subcellularcompartmentalizationof phos-pholipid biosynthetic enzymes. J Biol Chem 1993;268:2598592.

Ardail D, Popa I, Bodennec J, Louisot P, Schmitt D, Portoukalian J. The mitochondria-associated endoplasmic-reticulum subcompartment (MAM fraction) of rat livercontains highly active sphingolipid-specific glycosylotransferases. Biochem J2003;371:10139.

Atkins KM, Thomas L, Youker RT, Harriff MJ, Pissani F, You H, et al. HIV-1 Nef bindsPACS-2 to assemble a multi-kinase cascade that triggers major histocompatibil-ity complex class I (MHC-I) down-regulation: analysis using short interferingRNA and knock-out mice. J Biol Chem 2008;283:1177284.

Bthori G, ParoliniI, SzabI, TombolaF, Messina A, Oliva M, et al. Extramitochondrial

porin: facts and hypotheses. J Bioenerg Biomembr 2000;32:7989.Baumann N, Sullivan D, Ohvo-Rekila H, Simonot C, Pottekat A, Klaassen Z, et al.

Transport of newly synthesized sterol to the sterol-enriched plasma membraneoccurs via non-vesicular equilibration. Biochemistry 2005;44:581626.

Bernardi P. Mitochondrial transport of cations: channels, exchangers, and perme-ability transition. Physiol Rev 1999;79:112755.

Bernardi P, Forte M. The mitochondrialpermeability transitionpore. NovartisFoundSymp 2007;287:15764 [discussion 1649].

Bernardi P, Rasola A. Calcium and cell death: the mitochondrial connection. SubcellBiochem 2007;45:481506.

Berridge MJ, Bootman MD, Roderick HL. Calcium signalling: dynamics, homeostasisand remodeling. Nat Rev Mol Cell Biol 2003;4:51729.

Bionda C, Portoukalian J, Schmitt D, Rodriguez-Lafrasse C, Ardail D. Subcellularcompartmentalizationof ceramide metabolism:MAM (mitochondriaassociatedmembrane) and/or mitochondria. Biochem J 20 04;382:52733.

Born J, WettestenM, Sjberg A, ThorlinT, BondjersG, Wiklund O, etal. Theassemblyand secretion of apoB 100 containing lipoproteins in Hep G2 cells. Evidencefor different sites for protein synthesis and lipoprotein assembly. J Biol Chem

1990;265:1055664.

Bozidis P, Williamson CD, Colberg-Poley AM. Mitochondrial and secretory humancytomegalovirus UL37 proteins traffic into mitochondrion-associated mem-branes of human cells. J Virol 2008;82:271526.

Brdiczka DG, Zorov DB, Sheu SS. Mitochondrial contact sites: their role in energymetabolism and apoptosis. Biochim Biophys Acta 20 06;1762:14863.

Breckenridge DG, Stojanovic M, Marcellus RC, Shore GC. Caspase cleavage prod-uct of BAP31 induces mitochondrial fission through endoplasmic reticulumcalcium signals, enhancing cytochrome c release to the cytosol. J Cell Biol2003;160:111527.

Brough D, Schell MJ, Irvine RF. Agonist-induced regulation of mitochondrial andendoplasmic reticulum motility. Biochem J 20 05a;392:2917.

Brough D, Sim Y, Thorn P, Irvine RF. The structural integrity of the endoplasmicreticulum, and its possible regulation by inositol 1,3,4,5-tetrakisphosphate. CellCalcium 2005b;38:1539.

Camici O, Corazzi L. Import of phosphatidylethanolamine for the assembly of ratbrain mitochondrial membranes. J Membr Biol 1995;148:16976.

Camici O, Corazzi L. Phosphatidylserine translocation into brain mitochondria:involvement of a fusogenic protein associated with mitochondrial membranes.Mol Cell Biochem 1997;175:718.

Chakrabarti R, Chakrabarti R. Calcium signaling in non-excitable cells: Ca 2+ releaseand influx are independent events linked to two plasma membrane Ca2+ entrychannels. J Cell Biochem 2006;99:150316.

Chami M, Gozuacik D, Lagorce D, Brini M, Falson P, Peaucellier G, et al. SERCA1truncated proteins unable to pump calcium reduce the endoplasmic retic-ulum calcium concentration and induce apoptosis. J Cell Biol 2001;153:130114.

Chami M, Ouls B, Szabadkai G, Tacine R, Rizzuto R, Paterlini-Brchot P. Role ofSERCA1 truncatedisoform in the proapoptoticcalcium transferfrom ER to mito-chondria during ER stress. Mol Cell 20 08;32:64151.

Chevet E, Wong HN, Gerber D, Cochet C, Fazel A, Cameron PH, et al. Phosphoryla-

tion by CK2 and MAPK enhances calnexin association with ribosomes. EMBO J1999;18:365566.

CockcroftS. Trafficking of phosphatidylinositol by phosphatidylinositol transferpro-teins. Biochem Soc Symp 2007;74:25971.

Colombini M. Measurement of VDAC permeability in intact mitochondria and inreconstituted systems. Methods Cell Biol 2007;80:24160.

Copeland DE, Dalton AJ. An association between mitochondria and the endoplasmicreticulum in cells of the pseudobranch gland of a teleost. J Biophys Biochem1959;5:3939.

Crompton M. Mitochondrial intermembrane junctional complexes and their role incell death. J Physiol 200 0;529:1121.

Csords G, Renken C, Vrnai P, Walter L, Weaver D, Buttle KF, et al. Structural andfunctional features and significance of the physical linkage between ER andmitochondria. J Cell Biol 2006;174:91521.

Cui Z, Vance JE, Chen MH, Voelker DR, Vance DE. Cloning and expression of anovel phosphatidylethanolamine N-methyltransferase. A specific biochemicaland cytological marker for a unique membrane fraction in rat liver. J Biol Chem1993;268:1665563.

Daum G, Vance JE. Import of lipids into mitochondria. Prog Lipid Res 1997;36(23):10330.Dennis EA, Kennedy EP. Intracellular sites of lipid synthesis and biogenesis of mito-

chondria. J Lipid Res 1972;13:2637.Duszynski J, Koziel R, Brutkowski W, Szczepanowska J, Zablocki K. The regula-

tory role of mitochondria in capacitative calcium entry. Biochim Biophys Acta2006;1757:3807.

Eilers M, EndoT, Schatz G. Adriamycin, a drug interacting with acidicphospholipids,blocks import of precursor proteins by isolated yeast mitochondria. J Biol Chem1989;264:294550.

Filippin L, Magalhes PJ, Di Benedetto G, Colella M, Pozzan T. Stable interactionsbetween mitochondria and endoplasmic reticulum allow rapid accumula-tion of calcium in a subpopulation of mitochondria. J Biol Chem 2003;278:3922434.

Ferri KF, Kroemer G. Mitochondriathe suicide organelle. Bioessays 2001;23:1115.

Firth AL. Fine tuning ICRAC: the interactions of STIM-1 and Orai. J Physiol2008;587:156.

FrankeWW,KartenbeckJ. Dense cytoplasmic aggregatesassociatedwith Golgiappa-

ratus cisternae of rat hepatocytes. Protoplasma 1971;73:3541.Fransson S, Ruusala A, Aspenstrm P. The atypical Rho GTPases Miro-1 and Miro-2

have essentialroles in mitochondrialtrafficking. Biochem Biophys ResCommun2006;344:50010.

Frieden M, Arnaudeau S, Castelbou C, Demaurex N. Subplasmalemmal mitochon-dria modulate the activity of plasma membrane Ca2+-ATPases. J Biol Chem2005;280:43198208.

Frischauf I, Schindl R, Derler I, Bergsmann J, Fahrner M, Romanin C. The STIM/Oraicoupling machinery. Channels (Austin) 2008;2:2618.

Gaigg B, Simbeni R, Hrastnik C, Paltauf F, Daum G. Characterization of a micro-somal subfraction associated with mitochondria of the yeast, Saccharomycescerevisiae. Involvementin synthesisand import of phospholipids intomitochon-dria. Biochim Biophys Acta 1995;1234:21420.

Gincel D, Zaid H, Shoshan-Barmatz V. Calcium binding and translocation by thevoltage-dependent anion channel: a possible regulatory mechanism in mito-chondrial function. Biochem J 2001;358:14755.

Giorgi C, De Stefani D, Bononi A, Rizzuto R, Pinton P. Structural and functional linkbetween the mitochondrial network and the endoplasmic reticulum. The Inter-national Journal of Biochemistry & Cell Biology; this issue.


11/12


Giorgio M, Migliaccio E, Orsini F, Paolucci D, Moroni M, Contursi C, et al. Electrontransfer between cytochrome c and p66Shc generates reactive oxygen speciesthat trigger mitochondrial apoptosis. Cell 2005;122:22133.

Giorgio M, Trinei M, Migliaccio E, Pelicci PG. Hydrogen peroxide: a metabolicby-product or a common mediator of ageing signals? Nat Rev Mol Cell Biol2007;8:7228.

Goetz JG, Genty H, St-Pierre P, Dang T, Joshi B, Sauv R, et al. Reversible interac-tionsbetween smooth domains of theendoplasmic reticulumand mitochondriaare regulated by physiological cytosolic Ca2+ levels. J Cell Sci 2007;120:355364.

Goetz JG, Nabi IR. Interaction of the smooth endoplasmic reticulum and mitochon-

dria. Biochem Soc Trans 2006;34:3703.Goldstein BJ, Bittner-Kowalczyk A, White MF, Harbeck M. Tyrosine dephospho-

rylation and deactivation of insulin receptor substrate-1 by protein-tyrosinephosphatase 1B. Possible facilitation by the formationof a ternary complex withthe Grb2 adaptor protein. J Biol Chem 2000;275:42839.

Green DR, Kroemer G. The pathophysiology of mitochondrial cell death. Science2004;305:6269.

Grimm S, Brdiczka D. The permeability transition pore in cell death. Apoptosis2007;12:84155.

Groenendyk J, Zuppini A, Shore G, Opas M, Bleackley RC, Michalak M. Caspase 12 incalnexin-deficient cells. Biochemistry 2006;45:1321926.

Hajnczky G, Csords G, Das S, Garcia-Perez C, Saotome M, Sinha Roy S, et al.Mitochondrial calcium signalling and cell death: approaches for assessingthe role of mitochondrial Ca2+ uptake in apoptosis. Cell Calcium 2006;40:55360.

Hajnczky G, Saotome M, Csords G, Weaver D, Yi M. Calcium signalling and mito-chondrial motility. Novartis Found Symp 2007;287:10517.

Hanada K, Kumagai K, Tomishige N, Kawano M. CERT and intracellular trafficking ofceramide. Biochim Biophys Acta 2007;1771:64453.

Hanada K. Discovery of the molecular machinery CERT for endoplasmic reticulum-to-Golgi trafficking of ceramide. Mol Cell Biochem 2006;286:2331.

HayashiT, Su TP. Regulatingankyrindynamics:Roles of Sigma-1 receptors. ProcNatlAcad Sci USA 2001;98:4916.

Hayashi T, Su TP. Sigma-1 receptor chaperones at the ER-mitochondrion interfaceregulate Ca2+ signaling and c ell survival. Cell 2007;131:596610.

HernndezMV, Sala MG,Balsamo J, LilienJ, Arregui CO.ER-bound PTP1B is targetedto newly forming cell-matrix adhesions. J Cell Sci 2006;119:123343.

Higo T, Hattori M, Nakamura T, Natsume T, Michikawa T, Mikoshiba K. Subtype-specific and ER lumenal environment-dependent regulation of inositol 1,4,5-trisphosphate receptor type 1 by ERp44. Cell 2005;120:8598.

Hsieh CE, Marko M, Frank J, Mannella CA. Electron tomographic analysis of frozen-hydrated tissue sections. J Struct Biol 2002;138:6373.

Hynynen R,LaitinenS, KakelaR, TanhuanpaaK, Lusa S,Ehnholm C,et al.Overexpres-sion of OSBP-related protein 2 (ORP2) induces changes in cellular cholesterolmetabolism and enhances endocytosis. Biochem J 2005;390:27383.

Johansson M, Lehto M, Tanhuanpaa K, Cover TL, OlkkonenVM. Theoxysterol-bindingprotein homologue ORP1L interacts with Rab7 and alters functional properties

of late endocytic compartments. Mol Biol Cell 2005;16:548092.John LM, Lechleiter JD, Camacho P. Differential modulation of SERCA2 isoforms bycalreticulin. J Cell Biol 1998;142:96373.

Jones BF, Boyles RR, Hwang SY, Bird GS, Putney JW. Calcium influx mecha-nisms underlying calcium oscillations in rat hepatocytes. Hepatology 2008;48:127381.

Kakizawa S, MoriguchiS, IkedaA, IinoM, Takeshima H. Functional crosstalkbetweencell-surface and intracellular channels mediated by junctophilins essential forneuronal functions. Cerebellum 2008;7:38591.

Kawano M, Kumagai K, Nishijima M, Hanada K. Efficient trafficking of ceramidefrom the endoplasmic reticulum to the Golgi apparatus requires a VAMP-associated protein-interacting FFAT motif of CERT. J Biol Chem 2006;281:3027988.

KomazakiS, ItoK, Takeshima H, NakamuraH. Deficiencyof triad formationin devel-oping skeletal muscle cells lacking junctophilin type 1. FEBS Lett 2002;524:2259.

Kroemer G, Galluzzi L, Brenner C. Mitochondrial membrane permeabilizationin celldeath. Physiol Rev 2007;87:99163.

KugeO, Yamakawa Y,NishijimaM. Enhancement oftransport-dependentdecarboxy-

lation of phosphatidylserineby S100B proteinin permeabilized Chinesehamsterovary cells. J Biol Chem 2001;276:237006.

KvamE, GableK, DunnTM, GoldfarbDS. Targeting of Tsc13pto nucleus-vacuolejunc-tions: a rolefor very-long-chain fattyacids in thebiogenesis of microautophagicvesicles. Mol Biol Cell 2005;16:398798.

Ladinsky MS, Mastronarde DN, McIntoshJR, Howell KE,Staehelin LA. Golgistructurein three dimensions: functional insights from the normal rat kidney cell. J CellBiol 1999;144:113549.

Lebiedzinska M, Duszynski J, Rizzuto R, Pinton P, Wieckowski MR. Agerelatedchanges in levels of p66Shc and serine 36phosphorylated p66Shc in organsand mouse tissues. Arch Biochem Biophys 2009, in press.

Levine T, Loewen C. Inter-organellemembranecontact sites: through a glass, darkly.Curr Opin Cell Biol 2006;18:3718.

Levine T, Rabouille C. Endoplasmic reticulum: one continuous network compart-mentalized by extrinsic cues. Curr Opin Cell Biol 2005;17:3628.

Levine T. Intracellular trafficking of small molecules across endoplasmic reticulumjunctions. Trends Cell Biol 2004;14:48390.

Lewis JA, Tata JR. A rapidly sedimenting fraction of rat liver endoplasmic reticulum.J Cell Sci 1973;13:44759.

Li Y, Prinz WA. ATP-binding cassette (ABC) transporters mediate nonvesicular, raft-modulated sterol movement from the plasma membrane to the endoplasmicreticulum. J Biol Chem 2004;279:4522634.

LoewenCJ, Roy A, LevineTP. A conservedER targetingmotif in three families of lipidbinding proteins and in Opi1p binds VAP. EMBO J 2003;22:202535.

Lotti LV, Lanfrancone L, Migliaccio E, Zompetta C, Pelicci G, Salcini AE, et al. Shc pro-teins are localized on endoplasmic reticulum membranes and are redistributedafter tyrosine kinase receptor activation. Mol Cell Biol 1996;16:194654.

Mannella CA, Buttle K, Rath BK, Marko M. Electron microscopic tomography ofrat-liver mitochondria and their interaction with the endoplasmic reticulum.Biofactors 1998;8:2258.

Marsh BJ, Mastronarde DN, Buttle KF, Howell KE, McIntosh JR. Organellar relation-ships in the Golgi region of the pancreatic beta cell line, HIT-T15, visualized byhigh resolution electron tomography. PNAS 2001;98:2399406.

Marsh BJ. Lessons from tomographic studies of the mammalian Golgi. Biochim Bio-phys Acta 2005;1744:27392.

Martins de Brito O, Scorrano L. Mitofusin 2 tethers endoplasmic reticulum to mito-chondria. Nature 2008;456:60510.

Mendes CC, Gomes DA, Thompson M, Souto NC, Goes TS, Goes AM, et al. The typeIII inositol 1,4,5-trisphosphate receptor preferentially transmits apoptotic Ca2+

signals into mitochondria. J Biol Chem 2005;280:40892900.Merril Jr AH. De novo sphingolipid biosynthesis: a necessary, but dangerous, path-

way. J Biol Chem 2002;277:258436.Migliaccio E, Giorgio M, Mele S, Pelicci G, Reboldi P, Pandolfi PP, et al. The p66Shc

adaptor protein controls oxidative stress response and life span in mammals.Nature 1999;402:30913.

Mikoshiba K. IP3 receptor/Ca2+ channel: from discovery to new signaling concepts.J Neurochem 2007;102(5):142646.

Mogelsvang S, Marsh BJ, Ladinsky MS, Howell KE. Predicting function from struc-ture: 3D structure studies of the mammalian Golgi complex. Traffic 2004;5:

33845.Mokranjac D, Neupert W. Thirty years of protein translocation into mitochondria:

unexpectedly complex and still puzzling. Biochim Biophys Acta 2009;1793:3341.

Morre DJ, Merritt WD, LembiCA. Connections between mitochondria and endoplas-mic reticulum in rat liver and onion stem. Protoplasma 1971;73:439.

Myhill N, Lynes EM, Nanji JA, Blagoveshchenskaya AD, Fei H, Carmine Simmen K, etal. The subcellular distribution of calnexin is mediated by PACS-2. Mol Biol Cell2008;19:277788.

Nemoto S, Combs CA, French S, Ahn BH, Ferguson MM, Balaban RS, et al. Themammalian longevity-associatedgene product p66Shcregulates mitochondrialmetabolism. J Biol Chem 2006;281:1055560.

Neupert W, Herrmann JM. Translocation of proteins into mitochondria. Ann RevBiochem 2007;76:72349.

Orsini F, Migliaccio E, Moroni M, Contursi C, Raker VA, Piccini D, et al. The life spandeterminant p66Shc localizes to mitochondria where it associates with mito-chondrial heat shock protein 70 and regulates trans-membrane potential. J BiolChem 2004;279:2568995.

PacherP, SharmaK, Csords G, ZhuY, Hajnczky G. Uncoupling of ER-mitochondrialcalcium communication by transforming growth factor-. Am J Physiol RenalPhysiol 20 08;295:F130312.

Pacini S, Pellegrini M, Migliaccio E, Patrussi L, Ulivieri C, Ventura A, et al. p66SHCpromotesapoptosis and antagonizes mitogenicsignalingin T cells. Mol Cell Biol2004;24:174757.

PanX, RobertsP,ChenY, Kvam E,Shulga N,HuangK, etal. Nucleus-vacuolejunctionsin Saccharomyces cerevisiae are formed through the direct interaction of Vac8pwith Nvj1p. Mol Biol Cell 2000;11:244557.

Parekh AB. On the activation mechanism of store-operated calcium channels.Pflugers Arch 2006;453:30311.

Parekh B, Putney Jr JW. Store-operated calcium channels. Physiol Rev 2005;85:757810.

Penna A, Demuro A, Yeromin AV, Zhang SL, Safrina O, Parker I, et al. The CRAC chan-nel consists of a tetramer formed by Stim-induced dimerization of Orai dimers.Nature 2008;456:11620.

Peretti D, Dahan N, Shimoni E, Hirschberg K, Lev S. Coordinated lipid trans-fer between the endoplasmic reticulum and the Golgi complex requires theVAP proteins and is essential for Golgi-mediated transport. Mol Biol Cell

2008;19:387184.Perry RJ, Ridgway ND. Oxysterol-binding protein and VAMP-associated protein are

required for sterol-dependent activation of the ceramide transport protein. MolBiol Cell 2006;17:260416.

Pichler H, Gaigg B, Hrastnik C, Achleitner G, Kohlwein SD, Zellnig G, et al. Asubfraction ofthe yeast endoplasmic reticulumassociateswiththe plasma mem-brane and has a high capacity to synthesize lipids. Eur J Biochem 2001;268:235161.

Pinton P, Leo S, Wieckowski MR, Di Benedetto G, Rizzuto R. Long-term modula-tion of mitochondrial Ca2+ signals by protein kinase C isozymes. J Cell Biol2004;165:22332.

Pinton P, Rimessi A, Marchi S, Orsini F, Migliaccio E, Giorgio M, et al. Protein kinaseC beta and prolyl isomerase 1 regulate mitochondrial effects of the life-spandeterminant p66Shc. Science 2007;315:65963.

Pinton P, Rizzuto R. Bcl-2 and Ca2+ homeostasis in the endoplasmic reticulum. CellDeath Differ 2006;13:140918.

QuintanaA, SchwarzEC, Schwindling C, LippP, KaestnerL, HothM. Sustainedactivityof calcium release-activated calcium channels requires translocation of mito-chondria to the plasma membrane. J Biol Chem 2006;281:403029.


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