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MBB 306 - 2013-2014
VIRUSES and INFECTIONS of
HUMANS
LECTURE:THE HUMAN HERPESVIRUSES
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CLASSIFICATION of the HUMAN HERPESVIRUSES
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ALPHAHERPESVIRUSES: --Epidermo-neurotropic viruses with a wide host range.
Type 1 herpes simplex virus (HSV-1) HHV-1Type 2 herpes simplex virus (HSV-2) HHV-2
Varicella-Zoster virus (VZV) HHV-3
BETAHERPESVIRUSES:-- Slow growing viruses with a narrow host range; grow in
T-lymphocytes and/or leukocytes.
Human cytomegalovirus (HCMV) HHV-5
Human herpesvirus 6 HHV-6
Human herpesvirus 7 HHV-7
GAMMAHERPESVIRUSES:-- These viruses have a predilection for B-lymphocytes.
Epstein-Barr virus (EBV) HHV-4
Kaposis sarcoma virus (KSHV) HHV-8
[Herpesviruses infecting very many vertebrate animals, including other primates, frogs andelephants have been identified].
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VIRUS
NUMBER
COMMON NAME DISEASE
HHV-1 Herpes simplex virus
type 1 (HSV-1)
Oropharyngeal herpes;
Encephalitis.
HHV-2 Herpes simplex virus
type 2 (HSV-2)
Genital herpes; Encephalitis
HHV-3 Varicella-Zoster virus
(VZV)
Chickenpox and shingles
HHV-4 Epstein-Barr virus
(EBV)
Glandular fever/Infectious
mononucleosis;
Burkittslymphoma
HHV-5 Human Cytomegalovirus
(HCMV)
Cytomegalic inclusion disease (CID) in
utero, in newborns and in the
immunocompromised.
DISEASES caused by the IMPORTANT
HUMAN HERPESVIRUSES
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SCHEMATICREPRESENTATION of
a HERPESVIRUS
PARTICLE
ELECTRON MICROGRAPH OF A
HERPESVIRUS PARTICLE
Viral nucleocapsid
containing the DNA
and ICP0 protein
Viral tegument containing
VP16 and ICP4 proteins
Lipid envelope ofthe virus
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CYTOPATHIC EFFECTPRODUCED by HERPES
SIMPLEX VIRUS (HSV) in CELL
CULTURE
THE
HSV GENOME
The linear 152kbp genome contains 3
origins of DNA replication and about 80ORFs.
HSV DNA replication is by a rolling circle
mechanism which takes place in discreet
HSV replication compartments.
Replication generates long progeny HSV
DNA concatamers which are cleaved and
packaged into progeny viral particles.
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HSV CAPSID
+ DNA
HSV
Glycoproteins
gB -
Fusogen
gH + gL -
Fusion Regulator
Host Cell
gDFusion Trigger
gB -
Receptors
gH + gL -
Receptors
gD
Receptors
ENTRY of HSV-1
into HOST CELLS
gBfusogen; essential
for cell entry
gD- essential for cellfusion and
penetration
gH+gLcomplexessential for
fusion and cell entry
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HSV PROTEINS regulating or operating against
HOST CELL METABOLISMImmediately after entering the cell the HSV-1 tegument protein, vhs, becomes free in the
cell cytoplasm.
The vhsprotein:-
a). accelerates decay of host cell mRNA
b). disrupts pre-existing host cell polysomes
Replication of the HSV genome commences with transcription and expression of the HSV IEproteins. Activation and accumulation of these proteins drives transcription of the other
viral genes and subverts host gene expression. In particular,
a). ICP0an E3 ubiquitin ligase destabilising specific cellular proteins that would
otherwise inhibit the HSV life cycle. Creates a cellular environment
favourable for HSV DNA transcription
b). ICP 27 - inhibits the host cell splicing of pre-mRNA
All the IE proteins contribute to a redirection of cell metabolism from synthesis of
host proteins to synthesis of viral proteins, and develop an active and robustenvironment.
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PROGRESSION of HSV and VIRAL DNA to CELL
NUCLEUS
After penetration into the cell cytoplasm, the viralenvelope is lost.
VP16 (500-1000 molecules) and the other tegument
proteins are freed into the cytoplasm.
The capsid containing the viral DNA and remnants of the
tegument is transported to the nuclear membrane along
the microtubule network.
The capsid docks at the nuclear pore and this facilites
release of the viral DNA into the nucleus.
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EMINTRACYTOPLASMIC HERPES SIMPLEX
VIRIONS
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Chromatin is a complex of DNA and histonesthe
nucleosome - through which DNA is structured and
manoeuvered in the cell nucleus.
Modifications of chromatin permit transcription
processes.
A nucleosome has a core of 8 histones, withDNA wrapped around the outside, and a single
molecule of histone H1 to stabilise the complex.
Two types of chromatin are recognised:-
Heterochromatin- highly condensed; DNAassociated with it is inaccessible and therefore
genetically inactive.
Euchromatin- much less condensed allowing
transcription of the associated DNA.
CHROMATIN and HSV DNA REPLICATION
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HCF is a co-activator unable to bind DNA alone. With activated
histone acetyl transferases (HATs), HCF causes chromatinmodifications that increase gene expression by binding to an
activator having a DNA binding domain such as HSV VP16.
The chromatin modifications involving HCF are acetylationandmethylationof the nucleosome histone core.
HCF/HAT activity opens the nucleosomes in the control regions of the
promoters close to the enhancers, by relaxing the connections
between the histones and associated DNA. High levels of acetylation
make the chromatin more active, allowing transcription.
With low or absent HCF, transcription is reduced as the promoters
and enhancers cannot be accessed by transactivating factors. 12
HOST CELL FACTOR (HCF-1), CHROMATIN
and HSV LYTIC INFECTION
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VIRAL GENE CASCADE in LYTIC HSV INFECTION
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The entire process of HSV replication takes 18-20h in fully permissive
cell cultures.
Immediate Early () - genes -- transcribed and expressed from input viral DNA, inducedby VP16 (-TIF) and responsible for synthesis of the 5 proteins (expressed 2-4h p.i.)
Early () and Late () - genes -- Only transcribed after expression of the genes.(Maximal expression at 5-7h p.i.)
Early () - genes -- Transcription and expression of the genes is notstimulated by viral DNA replication.
Late (-1 and -2)genes -- -1 genes are transcribed and expressed (at low levels) even in the absence of viral DNA replication, but are
greatly stimulated when viral DNA is replicating.
-- -2 genes are not transcribed or expressed in theabsence of viral DNA replication.
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INITIATION of LYTIC HSV INFECTION in
EPITHELIAL CELLSNUCLEUS
CYTOPLASM
TAATGARAT (R = purine) sequences-Immediate early promoterHSV DNA
HCF
Oct-1
VP16
HATs
Histone (H3K9) -
acetylation groupsform Euchromatin
around the HSV
DNA
Transcription of HSV DNA using
host cell RNA polymerase II
HCF
VP16
HATs HATsHATsHATs
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RELEASE of HERPES SIMPLEX
VIRUS FROM HOST CELLGolgi
Viral nucleic acidEmpty viral capsid
NUCLEUS
CYTOPLASM
Precursor viralglycoproteins
Endoplasmic
reticulum
Cytoplasmic
vesicle
Cytoplasmic
vesicle
EXTERIOR ENVIRONMENT
Nuclear membrane
Viral glycoproteins modified
and matured in the Golgi
Nucleocapsid +
tegument
Association of nucleocapsid
+ tegument with membrane
of vesicle bearing viral
glycoproteins
+Viral nucleocapsid
Cell membrane
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EMs showing BUDDING of IMMATURE HSV
PARTICLE from NUCLEAR MEMBRANE
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REGULATION of VIRAL GENE EXPRESSION
during LYTIC HSV-1 INFECTION
Viral entry to cellcytoplasm
Viral DNA
transported to
nucleus
VP16
transported
to nucleus
Immediate Early
gene expression
ICP4 ICP27 ICP0 ICP22/Us1.5 ICP47
X Immune evasion
Assembly of virions
and releaseX
Essential
in vitro
Non-essential
in vitro
Late geneexpression
Early gene
expression
Viral DNA replication
Viral structural proteins
Both ICP4 and ICP27
must be expressed for
the lytic cycle to proceed
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ACUTE PRIMARY HERPETIC
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ACUTE, PRIMARY HERPETIC
GINGIVISTOMATITIS RECURRENT HERPETICLESIONSCOLD SORES
HERPETIC WHITLOW
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2111
NATURAL HISTORY of HERPES SIMPLEX VIRUS
INFECTIONS
PRIMARY INFECTION
PASIVE IMMUNITY
FROM MATERNALANTIBODY IN INFANCY
SOURCE OF VIRUS
SKIN LESIONS
SALIVA
(usually Type 1 virus)
SOURCE OF VIRUS
GENITAL LESIONS
GENITAL SECRETIONS
(usually Type 2 virus)
ASYMPTOMATIC
(90%-99%)
SYMPTOMATIC
(1%-10%)
NO IMMUNITY
ESTABLISHMENT OF
LATENT INFECTION
REACTIVATION OF
LATENT VIRUS AND
RECURRENT INFECTION
IMMUNE RESPONSES
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VARICELLA-ZOSTER VIRUS (VZV)
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Size120-250nm diameter;
typical herpesvirus structure
dsDNAlinear in virion,circular in the infected nucleus.
72 open reading frames (ORFs)
Latent infection in neurones.
Genetically stable
VIRAL PROPERTIESPatient with chickenpox
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VARICELLA-ZOSTER VIRUS (VZV)
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Highly infectious disease usually
occurring in children.
Virus spread from the upper
respiratory tract prior toappearance of rash.
Virus present in skin lesions (asmuch as 10101011virions/ml).
VZV causes severe infections in the
immunocompromised.
EPIDEMIOLOGYShingles in elderly patient
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The most common disease caused by EBV is
infectious mononucleosis (glandular fever).
About 70% of the worlds population are infected.
Often asymptomatic, but symptoms can include
sore throat, swollen cervical lymph nodes and mild
fever. May run a prolonged, episodic, course over 1-
2 years.
Associated with the cancer, BurkittsLymphoma in
some parts of the world.
THE EPSTEIN-BARR VIRUS (EBV)
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PATIENT with INFECTIOUS
MONONUCLEOSIS
(GLANDULAR FEVER)
EM of the EPSTEIN-
BARR VIRUS (EBV)
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END of LECTURE
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INITIATION f LYTIC HSV INFECTION i
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INITIATION of LYTIC HSV INFECTION in
EPITHELIAL CELLS
TAATGARAT sequences-Immediate early promoterHSV DNA
HATsHistone (H3K9) -
acetylation formingEuchromatin
SETs
Histone methylation
forming
Heterochromatin
Transcription of HSV DNA involvinghost cell RNA polymerase II
NUCLEUS
Oct-1
CYTOPLASM
HCF
VP16VP16
HCF
VP16HCF
Oct-1
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Oct-1
VP16
HCF
VP16HCF
SETs
Histone methylation
forming
Heterochromatin
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