Wnt Signaling in Cancercshperspectives.cshlp.org/content/4/5/a008052.full.pdf · Wnt Signaling in...

Wnt Signaling in Cancer

Paul Polakis

Genentech, Inc., South San Francisco, California 94608

Correspondence: [email protected]

Aberrant regulation of the Wnt signaling pathway is a prevalent theme in cancer biology.From the earliest observation that Wnt overexpression could lead to malignant transforma-tion of mouse mammary tissue to the most recent genetic discoveries gleaned from tumorgenome sequencing, the Wnt pathway continues to evolve as a central mechanism in cancerbiology. This article summarizes the evidence supporting a role for Wnt signaling in humancancer. This includes a review of the genetic mutations affecting Wnt pathway components,as well as some of epigenetic mechanisms that alter expression of genes relevant to Wnt. Ialso highlight some research on the cooperativity of Wnt with other signaling pathways incancer. Finally, some emphasis is placed on laboratory research that provides a proof ofconcept for the therapeutic inhibition of Wnt signaling in cancer.

The starting point of the field was the discov-ery that mammary tumors arising in mice

infected with the murine mammary tumor vi-rus was often caused by the activation of themurine int-1 gene, later called Wnt1. It was latershown that the Wnt gene resembled the flywingless gene, a secreted factor controlling asignaling cascade that included GSK3 and ar-madillo, the fly version of mammalian b-cate-nin. The importance of this pathway in humancancer became very clear when the human tu-mor suppressor adenomatous polyposis coli(APC) protein was found in association withb-catenin. The finding that APC could down-regulate b-catenin and Wnt-1 could upregulateit, provided further support for the Wnt cancerconnection. Ultimately, the TCF transcriptionfactors that associated with b-catenin complet-ed the understanding of a basic signaling path-way that could account for the potent tumori-

genic effects of Wnt (reviewed by Klaus andBirchmeier 2008).

ONCOGENES AND TUMOR SUPPRESSORS

As in many other oncogenic signaling pathways,constituents of Wnt signaling can roughly besubdivided into positive and negatively actingcomponents. By and large, the negatively act-ing, suppressing components are found mutat-ed to a loss of function status in cancer, whilethe positive components are activated (Fig. 1).Among the suppressing components of Wntsignaling, APC stands as the most frequentlymutated gene in human cancers. Genetic defectsin APC are the cause of familial adenomatouspolyosis, a heritable syndrome in which affectedindividuals develop hundreds of polyps in thelarge intestine at an early age and ultimatelysuccumb to colorectal cancer (Clements et al.

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2003). APC is also mutated in the vast majorityof all sporadic colorectal cancers. Loss of func-tion in both alleles is required for tumorigenesisand that loss is structurally linked to the pro-tein’s ability to regulateb-catenin protein stabil-ity (Polakis 2007).

Specifically, the truncating mutations inAPC remove all binding sites for Axin, a scaffoldthat also binds b-catenin and recruits the pro-tein kinases GSK3 and CKI, both essential formarking b-catenin for destruction facilitated bythe E3 ubiquitin ligase b-TRCP (Fig 1). Axins Iand II are also tumor suppressors found mutat-

ed in both sporadic cancers, particularly he-patocellar and some colorectal, as well as insome familial cancer syndromes (Lammi et al.2004; Salahshor and Woodgett 2005; Marvinet al. 2011). Regulation of b-catenin also failswhen b-catenin itself contains mutations thatprevent it from being marked for destructionby the kinases (Polakis 2007). These mutationsare found with significant frequency in hepato-cellular cancers and medulloblastoma.

More recently, WTX has joined APC, Axin,and b-TrCP as a part of the so-called b-catenindestruction complex (Major et al. 2007). This is

Nucleus

β-cat

CBP

TCF

LEF

bcl9

pygo

APC

WTX1 Cytoplasm

PM

AXIN

AXIN

GSK3

GSK3

dvl

Wnt

porcn

Wntfzd

Wnt

LRP

5/6

CKla

CKlg

TANK

β-cat

β-trcp

Figure 1. Tumor suppressors and oncogenes in the Wnt pathway. Diagram of a basic Wnt signaling pathway inwhich oncogenes are depicted in green and tumor suppressors in red.

P. Polakis

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particularly intriguing as WTX is a tumor sup-pressor associated with the pediatric renalcancer Wilm’s tumor, which is also commonlyassociated with b-catenin mutations (Huff2011). That both WTX and b-catenin muta-tions coexist in some Wilm’s tumors suggeststhe two genes are not strictly functionally redun-dant (Ruteshouser et al. 2008). In a recent devel-opmental study in mice, germline inactivationof WTX resulted in the accumulation of multi-potent mesenchymal precursor cells resultingfrom aberrant b-catenin activation (Moisanet al. 2011). Although these animals did notdevelop renal tumors, it was proposed that theexpansion of these mesenchymal progenitorscould increase the target population of cells sus-ceptible to transformation by additional geneticinsults.

One might expect the occurrence of inacti-vating mutations in the GSK3 genes as theyare critical to b-catenin regulation. Althoughmutations in the alleles coding for GSK3a andb have not been associated with cancer, the Ja-mieson lab found an in-frame splice deletionaffecting the kinase domain of GSK3b in chron-ic mylogenous leukemia (Abrahamsson et al.2009). Aberrant splicing has also been describedfor the Wnt coreceptor LRP5 in parathyroidand breast cancers. Here missplicing deletesthe region of LRP5 that interacts with the se-creted Wnt signaling repressor DDK1 (Bjork-lund et al. 2009).

Frameshift mutations in the 30 region of thegene encoding the b-catenin-binding tran-scription factor TCF4 are extremely commonin colorectal cancers with microsatellite insta-bility (Cuilliere-Dartigues et al. 2006). Thesemutations were proposed to be activating asthey ablate binding of the transcriptional repres-sor CtBP to TCF4. Paradoxically, mutations inTCF4, identified through genomic sequencingefforts of colorectal cancers, appear to be inac-tivating by compromising its ability to represscell growth (Sjoblom et al. 2006; Tang et al.2008). This is consistent with recent findingsfrom the Cappechi laboratory in which TCF4haploinsuffciency promotes cell proliferationin the mouse intestine and enhances tumorigen-esis in an APC mutant mouse model (Angus-

Hill et al. 2011). In a colorectal cancer genomesequencing effort, the Meyerson laboratory re-cently reported a rare, but recurring rearrange-ment in which the TCF4 gene TCFL72 was fusedto VTI1A (Bass et al. 2011). The specific functionof the VTI1A-TCF7L2 fusion was not elucidated,but knockdown of the transcript inhibited an-chorage independent cell growth, indicative of apositive acting tumorigenic function.

Mutations in the gene coding for the CREBbinding protein (CREBBP/CBP) have beenidentified in acute lypmhoblastic leukemia andB-cell lymphoma (Mullighan et al. 2011; Pas-qualucci et al. 2011). This is of interest to Wntsignaling as CBP associates directly with the car-boxy-terminal sequence in b-catenin and CBP/b-catenin mediated transcription has been pro-posed to be critical for stem cell/progenitor cellmaintenance and proliferation (Teo and Kahn2011). Accordingly, CBP is currently a clinicaltarget for small molecule inhibition in Wnt-driven cancers. CBP is a transcriptional coacti-vator with histone acetyltransferase activity andassociates with a wide variety of transcriptionfactors in controlling facets of developmentand cellular homeostasis. Given this pleiotropy,the relevance of the CBP mutations to Wnt sig-naling, per se, is difficult to gauge. Moreover, themutations identified in the hematopoietic can-cers impair the histone acetyltransferase activi-ty, which seem inconsistent with a role in facil-itating active Wnt signaling. Table 1 summarizessome of the salient DNA and mRNA aberrationsthat potentially contribute to Wnt-driven tu-morigenesis.

EPIGENETIC MODULATION OFWnt SIGNALING

Recurrent mutations in a gene that alter theproducts’ function in a relevant manner typical-ly offer the clearest evidence for its involvementin oncogenic transformation. Nevertheless, it isapparent that epigenetic modifications in DNAand chromatin also play a role in tumor progres-sion by modulating the suppressor or activatorcomponents of a signaling pathway (Rodriguez-Paredes and Esteller 2011). The impact of DNAmethylation on Wnt-driven tumorigenesis was


Cite this article as Cold Spring Harb Perspect Biol 2012;4:a008052 3



reported by Laird et al., who found that ge-netic depletion and pharmacological suppres-sion of DNA methyl transferase effectivelyreduced the tumor burden in the APC minmouse (Laird et al. 1995). Subsequent studieswith this model revealed that deficiency of themethyl–CpG binding repressor Mbd2 also se-verely repressed tumor formation by attenuat-ing Wnt signaling (Sansom et al. 2003; Phesseet al. 2008). These studies point to the silencingof Wnt antagonists by DNA hypermethylation.Indeed, genome-wide analysis of promotorDNA methylation in human medulloblastoma,colon, and pancreatic cancers showed that Wntpathway inhibitors are common targets of thismechanism of gene repression (Kongkham et al.2010; Vincent et al. 2011; Suzuki et al. 2002). Inparticular, the promotor region of the genecoding for the secreted frizzled related protein1 (sFRP1), that binds to and inhibits Wnt li-gands, was commonly identified in these stud-ies. Members of the sFRP family have also beenreported to be silenced by DNA methylationin numerous other cancers including hepato-cellular cancer, breast cancer, and melanoma(Suzuki et al. 2008; Takagi et al. 2008; Ekstromet al. 2011).

In addition to the direct methylation ofDNA, many Wnt signaling genes and targetsundergo chromatin modifications that affectgene transcription. Considering that DNA hy-permethylation of promotor regions is frequentlyaccompanied by chromatin modifications, it isnot surprising that the sSFRP1 gene is also atarget of chromatin modifying factors (McGar-vey et al. 2006). In the case of AML, it was pro-posed that chromatin modification resulted fromthe targeting of the sFRP1 gene by the RUNX-ETO fusion protein (Cheng et al. 2011b). ARUNX binding site was identified in the 50 regu-latory region of the sFRP1 gene and this regionwas also detected in chromatin immunoprecipi-tated with antibodies specific to ETO. The ETOportion of this fusion recruits multiple chroma-tin modifying factors that can repress gene acti-vation and, in the case of sFRP1, drive Wnt sig-naling and cell proliferation.

An additional epigenetic mechanism un-derlying the suppression of numerous Wnt an-tagonists in hepatocellular cancer was reportedby Cheng et al (2011a). In this study, chromatinimmunoprecipitation/microarray analysis wasused to show that many genes coding for Wntinhibitors, including sFRP5, Axin2, and NKD2

Table 1. Genetic alterations in Wnt signaling in cancer

Affected gene

DNA/mRNA

alteration Functional outcome Cancer type Reference

CTNNBl (b-catenin)

Missense/in-framedeletion

Enhanced proteinstability

Hepatocellular/Medulloblastoma

Polakis 2007

APC (APC) Truncation Reduced regulatoryactivity

Colorectal/gastric Clements et al. 2003

Axins (Axin I,Axin II)

Truncation/missense

Reduced regulatoryactivity

Hepatocellular/colorectal

Salahshor andWoodgett 2005

CREBP(CBP) Truncation/missense

Inactiveacetyltransferase

Lymphoma/leukemia

Teo and Kahn 2011

GSK3b Missplicing, in-frame deletion

Inactive kinase Leukemia Abrahamssonet al. 2009

LRP5 Missplicing, in-frame deletion

Loss of repression byDKK1

Breast/parathyroid Bjorklund et al. 2009

TCF7L2 (TCF4) Missense/deletion/truncation

Loss of repression Colorectal Cuilliere-Dartigueset al. 2006

TCF7L2 (TCF4) Fusion with VT11Agene

Unclear Colorectal Bass 2011

FAB123B (WTX) Truncation/deletion

Loss of function Wilm’s tumor Ruteshouseret al. 2008

P. Polakis




were occupied by EZH2, a subunit of the poly-comb repressor complex 2 (PRC2). EZH2 is amethyl transferase that deposits the repressiveH3K27me3 marks on chromatin (Rodriguez-Paredes and Esteller 2011). Knockdown ofEZH2 in HCC cells resulted in increased expres-sion of NKD2 and a concomitant reduction inWnt reporter signaling. This is particularly in-triguing because somatic mutations in EZH2, aswell as another H3k27 methyltransferase, UTX,have been detected in a variety of human can-cers (van Haaften et al. 2009; Morin et al. 2011).

DACT3 is an additional inhibitor of Wntsignaling that is repressed in colon cancers byhistone modification (Jiang et al. 2008). DACT3is a member of the FDO/DPR gene family thatinhibits Wnt signaling by interacting with DVLproteins. Derepression of DACT3 inhibited Wntsignaling and promoted apoptosis of colorectalcancer cells, an effect that could be rescued byknockdown of DACT3 mRNA. Unlike sFRP1 incolon cancer cells, the DACT3 DNA promotorregion does not appear to be hypermethylated.Thus, DACT3 derepression might not requirereversal of DNA methylation, but perhaps mayrespond singularly to treatment with an inhib-itor of histone modification such as that repre-sented by the Trichostatin A compound.

In contrast to gene silencing, modificationof chromatin can also enable gene activation.The carboxyl terminus of b-catenin is knownto recruit numerous chromatin-remodeling sub-units, such as set1 and paf1, that mediate theH3K4me3 histone marks associated with highlyactive genes (Willert and Jones 2006). Althoughmany of these sorts of modifiers are commonlyassociated with gene activation by transcriptionfactors, the Clevers laboratory reported thatthe MLLT10/AF10-DOT1L complex was prin-cipally dedicated to Wnt signaling (Mahmoudiet al. 2011). They discovered that this leukemia-associated chromatin-modifying complex wasrecruited to Wnt target genes in a b-catenin/TCF4-dependent manner. DOT1L is a methyltransferase responsible for H3K79me3 modifi-cation associated with gene activation. The studyshowed a requirement for MLLT10/AF10-DOT1L in Wnt target gene expression in coloncancer cells and in normal intestinal homeo-

stasis. MLLT10/AF10 expression was localizedto the proliferative compartment of the intes-tine and its knockdown rescued defects inAPC mutant zebrafish. On the basis of thisspecificity, the investigators concluded that theDOT1L enzyme might represent a colon cancertarget.

COOPERATIVITY WITH OTHERSIGNALING PATHWAYS

Studies involving the use genetically engineeredmouse models of cancer, as well as expansivehuman studies on nonsteroidal anti-inflam-matory drugs (NSAIDS) and cancer risk, havefirmly established a role for prostaglandin sig-naling in colorectal tumorigenesis (Oshima andTaketo 2002; Chan et al. 2007). The cyclooxy-genase 2 (COX2) enzyme, which catalyzesthe production of PGE2 is targeted by NSAIDSand its deletion in the APCmin mouse negative-ly impacts tumor burden. Mechanistic propos-als for the interaction between prostaglandinand Wnt signaling include COX2 as a directtarget gene of Wnt signaling, PPARDelta as aconvergent focal point for the two pathways,and stimulation of the Wnt pathway by crosstalkfrom the EP2 prostaglandin receptor (Arakiet al. 2003; Wang et al. 2004; Castellone et al.2005). The levels of PGE2 are downregulatedby 15-Hydroxyprostaglandin dehydrogenase(15-PGDH), which catalyzes the rate-limitingstep in prostaglandin degradation. Therefore, itacts opposite to COX2, and knockout of 15-PGDH in the APCmin mouse dramatically in-creases tumor burden, further fortifying the casefor prostaglandins as intestinal tumor promo-tors (Myung et al. 2006). In human cancers, 15-PGDH is consistently downregulated, althoughit is highly expressed in normal human intestinalepithelium. In a recent study, the Paraskeva laboffered an additional mechanism for the inter-action of the prostaglandin and Wnt signals byshowing that the 15-PGDH gene is a target ofb-catenin-dependent repression (Smartt et al.2011). This study documented 15-PGDH genepromotor occupancy by b-catenin/TCF4, invivo activation of 15-PDGH expression by con-ditional knockdown of b-catenin, and inhibition





of 15-PGDH expression in cultured cells treatedwith Wnt ligand.

Cooperativity between the androgen recep-tor (AR) and Wnt signaling was proposed as amechanism for the potentiation of EGF recep-tor tyrosine kinase family signaling in ER-/Her2þ breast cancers (Ni et al. 2011). In thisstudy, the Wnt7b gene was occupied and acti-vated by AR on stimulation of breast cancer cellswith DHT. This led to activation of canonicalWnt signaling in which the stabilized b-catenincooperated with AR to turn on the Her3 gene.Her3 is the ligand binding receptor that part-ners with the catalytically active Her2 tyrosinekinase to activate the Pi3K pathway. The papershowed that the upregulation of HER3, activa-tion of HER2/HER3 signaling and enhance-ment of cell growth by AR activation was de-pendent on b-catenin.

The EGF receptor tyrosine kinase has had along history of cooperating with Wnt signaling,resulting in a litany of mechanisms to accountfor their interaction. These include direct bind-ing of b-catenin to EGFR, modulation of thecadherin-b-catenin interface by EGFR, activa-tion ofb-catenin-dependent signaling by EGFRthrough PI3K signaling as well as the EGFR geneitself as a Wnt target (review by Hu and Li2011). However, in a very surprising findingby the Lu lab, the M2 splice form of pyruvatekinase (PKM2) was found to translocate to thenucleus in response to EGFR signaling, where itbinds to tyrosine phosphorylated of b-cateninand activates b-catenin-dependent target genes(Fig. 2A) (Yang et al. 2011b). PKM2 has receivedconsiderable attention lately, although mainlybecause of a renewed interest in the role ofmetabolism and aerobic glycolysis in cancer(Christofk et al. 2008). However, in the Lu study,knockdown of PKM2 reduced tumor cell pro-liferation by EGFR, which correlated with a fail-ure to activate the myc and cyclin D1 genes,both targets of Wnt signaling. Moreover, chro-matin immunoprecipitation was used to showbinding of PKM2 to the cyclin D1 promotor ina b-catenin-dependent manner. Nevertheless,PKM2 deficiency did interfere with the activa-tion of cyclin D1 by Wnt ligands. Thus, EGFand Wnt receptors both employ b-catenin to

activate some common target genes, yet engageindependent effectors in route to the nucleus.

Another surprise from the Lu study was thatthe tyrosine phosphorylation of b-catenin re-sulting from EGFR activation was mediated bysrc and occurred on b-catenin residue Y-333.Previously, EGFR-mediated phoshorylation ofb-catenin on Y-654 had been reported to affectits interaction with cadherins and also correlat-ed with an increase inb-catenin-mediated tran-scriptional activity (Lilien and Balsamo 2005).The relevance of Y-654 phosphorylation was fi-nally tested in vivo by the Smits laboratory,who corroborated its importance in bindingof cadherin to b-catenin, but also found a pos-itive impact on Wnt signaling (van Veelen et al.2011). When the constitutive phosphorylationwas mimicked by knocking in the Y654E muta-tion, the homozygotes were embryonic lethal,whereas 38% of the heterozygotes presentedwith intestinal tumors by 16–18 months ofage. On the background of a germline APC mu-tation, the compound heterozygotes were em-bryonic lethal, suggesting that half of a dose ofwildtype APC was not sufficient to regulate theexcess signaling produced by a single Y654E b-catenin allele. An intestine-specific allele of theY654E b-catenin mutant was then generatedand when crossed to an APC mutant mouse,increased intestinal tumor multiplicity was ob-served in male animals.

Given the interplay between morphogenicsignals in developing embryos, the interactionof these pathways might be expected in cancer.In a particularly intriguing example of Wnt andnotch pathway cooperativity, Fre et al. (2009)showed that the expansion of intestinal progen-itor cells by constitutive Notch signaling wasdependent on Wnt. Notch and Wnt signalingalso synergized to induce intestinal adenomasin compound mice, with a dramatic increase incolonic tumors, which are typically rare in micedeficient only in APC. The impact of Notch inthe intestine was consistent with previous workshowing that its activation or inhibition in-creased or decreased the population of pro-liferating/progenitor cells, respectively, at theexpense of the differentiated population (Freet al. 2005; van Es et al. 2005). The Srivastava

P. Polakis




laboratory recently offered an unexpected me-chanism for cooperativity between Wnt andNotch signaling (Kwon et al. 2011). Here theICD domain of Notch was shown to directlyassociate with and thereby titrate the unphos-phorylated pool of activeb-catenin, rendering itunavailable for transcriptional activity. Accord-ingly, the knockdown of Notch1 exacerbated theactivation of Wnt target genes, whereas chemi-cal inhibition of g-secretase or expression of anoncleavable Notch1 mutant, was inhibitory toWnt signaling. It was concluded that the activeb-catenin associated with Notch was ultimatelydirected to the lysosome for destruction in aNumb-dependent manner.

EXPERIMENTAL EVIDENCE FOR A CRITICALROLE FOR Wnt IN HUMAN CANCER

Avariety of preclinical experiments suggest thatinhibition of Wnt signaling can thwart tumorcell growth and survival. One of the first suchexperiments involved the induced expressionof wild type APC in a colorectal cancer cellline harboring only mutant alleles. On induc-tion, the growth of cultured HT29 cells was in-hibited by the wild-type APC, which was attrib-uted to an increase in apoptosis (Morin et al.1996). Similarly, ectopic expression of Axin1,an additional tumor suppressor in the Wntpathway, promoted apoptosis in colorectal and

PGE2

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EG

FR

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EP2

PKM2 src

srcPKM2

PKM2

P

P

PMGsα

Gsα

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β-cat

β-cat

β-cat

Cyclin D1

TCFON

HDAC3

β-cat

GSK3

AA

PGE2

COX2

PGDH

Inactive

TCF TCF OFFONCOX2 PGDH

AXIN

A B

PGE2nt

fzdfz

Gs

Figure 2. Signaling pathways that cooperate with Wnt signaling. (A) Wnt and prostaglandin signaling. Activa-tion of canonical Wnt signaling drives expression of COX2, which catalyzes production of PGE2, and repressionof 15-PDGH, which catalyzes the inactivation of PGE2. PGE2 activates the prostaglandin GPCR receptor EP2releasing the Gsa subunnit that displaces GSK3 form Axin, resulting in the stabilization of b-catenin. (B)Activation of b-catenin by EGFR. EGFR activity promotes the activation of src and the translocation ofPKM2 into the nucleus, in which src phosphorylates residue Y333 on b-catenin. The phosphorylated b-cateninbinds PKM2 and the resulting complex associates with TCF in which kinase-active PKM2 displaces HDAC3 toturn on the cyclin D1 target gene.





hepatocellular cancer cell lines containing mu-tations in either b-catenin, APC or Axin1 (Sa-toh et al. 2000). Although encouraging, the re-animation of wild-type tumor suppressors isinferior to a proof of principle in which a pos-itive acting element is interfered with. Early ex-amples of this included the ectopic expressionof a dominant negative TCF-4. This amino-ter-minally deleted TCF-4 binds Wnt target genesnonproductively as a result of its inability toassociate with b-catenin. Consequently, inhibi-tion of target gene activation in colorectal can-cer cells expressing the dominant negative TCF4resulted in their growth arrest (Tetsu and Mc-Cormick 1999; van de Wetering et al. 2002).

Based on the genetics of Wnt signaling incancer, b-catenin would be considered a highvalue drug target. Two tumor suppressors, Axinand APC, negatively regulate b-catenin, and b-catenin itself is oncogenically activated by gain-of-function mutations. Accordingly, interferingwith b-catenin, by various methods, producesantitumorigenic affects. Gottardi et al. (2001),exploited the mutually exclusive binding of b-catenin to E-cadherin and the TCF transcrip-tion factors by expressing cadherin chimerasthat block the latter interaction. This was ac-companied by growth inhibition of SW480 co-lorectal cancer cells. Suppression of b-cateninby antisense oligonucleotides was also foundto inhibit tumorgenicity of colon cancer cellsin vitro and in vivo (Green et al. 2001; Rohet al. 2001). Kim et al. (2002) employed a so-matic cell gene targeting strategy to show thatb-catenin expression was essential for clonalgrowth of the APC mutant and b-catenin mu-tant colorectal cancer lines, DLD-1 and SW48,respectively. Curiously, a second b-catenin mu-tant cell line, HCT116, was unaffected by thegene targeting.

The advent of interfering RNA technologiesushered in further validation of b-catenin as apotential cancer target. In one of the first exam-ples of this, siRNA knockdown of b-catenin re-duced b-catenin-dependent transcription anddiminished the anchorage independent growthof colon cancer cells and their ability to generatetumors in mice (Verma et al. 2003). Unlike thegene targeting approach, the tumorigenecity of

the HCT116 cell line was negatively impacted bythe siRNA. In a separate study, knockdown ofb-catenin by inducible shRNA strongly inhibitedproliferation of HCT116 and Ls174t colorectalcancer cells, both of which harbor mutant b-catenin alleles (Mologni et al. 2010). However,induction of apoptosis was insignificant withknockdown of either b-catenin or K-ras indi-vidually, whereas the combination produced astrong effect. The effect of this combination onin vivo tumor growth was again far more effec-tive than knockdown of either transcript alone.

In addition to its role in gene activation,b-catenin is essential to cadherin function informing cell–cell contacts. To some extent thiscomplicates the interpretation of b-cateninmRNA knockdown experiments. To overcomethis, Cong et al. (2003), devised a fusion pro-tein that artificially recruited the E3 ubiquitinligase b-TrCP to b-catenin. This resulted in theselective destruction of the Wnt signaling pool,but not the cadherin-bound fraction. Coloncells expressing this construct lost their tumor-igenic potential, including their ability to formtumors in mice.

Inhibitors of Wnt signaling might also beeffective in hepatocellular cancers, where muta-tions in Wnt pathway components are relativelycommon. In the HepG2 human hepatoma cellline, RNAi mediated knockdown of b-catenindecreased cell viability, proliferation and growthin soft agar (Zeng et al. 2007). Although theHepG2 cell line carries a mutant b-catenin al-lele, a second cell line, Hep3b, is wild type, yetsimilar inhibitory effects were observed with it.Ashihara et al. (2009) provided an additionalexample in which interference with Wnt signal-ing impaired the tumorigencity of cancer cellslacking Wnt pathway mutations. Here, siRNAknockdown of b-catenin significantly reducedthe tumor burden resulting from the inocula-tion of RPMI8226 myeloma cells in irradiatednude mice. Thus, interference with Wnt signal-ing in cancers lacking pathway mutations can beeffective and suggests that aberrant activation ofWnt receptors should also be entertained as anoncogenic mechanism.

Mammary cancer is a prominent example inwhich Wnt pathway mutations are very rare, yet

P. Polakis




hyperactive signaling is apparent, particularly incancers classified as basal-like or triple negativetype (Lin et al. 2000; Chung et al. 2004; Howeand Brown 2004; Khramtsov et al. 2010; Geyeret al. 2011). Expression of the Wnt receptorFZD7 is characteristic of these types of breastcancer (Sorlie et al. 2003). Accordingly, Yang,et al. recently reported a proof of principle ex-periment in which knockdown of FZD7, in cellline models of triple negative breast cancer, re-duced expression of Wnt target genes, inhibitedtumorigenesis in vitro and greatly retarded thecapacity of the MDA-MD-231 cell line to formtumors in mice (Yang et al. 2011a). This sug-gests that Wnt ligands might drive certain breastcancers and is consistent with previous workfrom the Hynes laboratory (Matsuda et al.2009). Here the secreted frizzled related pro-tein (sFRP1), which binds to and effectivelycompetes with FZD receptors for Wnt ligands,was ectopically expressed in the MDA-MB-231cell line. The sFRP1 expressing cells struggled toform tumors upon inoculation into the mam-mary fat pads of mice and their propensityto metastasize to lung was greatly impaired.The source of Wnt ligand in these studies couldarise from either host cells and/or the cancercells, themselves. The latter possibility was firstmade apparent by Bafico et al. (2004), whenthey reported autocrine Wnt signaling in a pan-el of breast and ovarian cancer cell lines, MDA-MB-231 among them. These cells were identi-fied by the presence of a signaling pool of un-complexedb-catenin, a hallmark of Wnt signal-ing. This pool of b-catenin, as well as the signalfrom a Wnt reporter gene, was reduced on ex-pression or addition of the soluble Wnt inhi-bitors sFRP1 or DKK1. These investigatorssubsequently reported autocrine signaling innon-small cell lung cancers, as well (Akiri etal. 2009).

Work from the Massague laboratory en-courages us to target Wnt signaling in lung can-cer, which again typically lacks pathway muta-tions (Nguyen et al. 2009). In this study, a Wnttarget gene signature was associated with meta-static lesions derived from human lung cancermodels grown in mice. Expression of dominantnegative TCF4 or TCF1 in the metastasis-prone

derivatives of the PC9 and H2030 nonsmalllung cancer lines provided a proof-of-principle.The expression of these dominant negativetranscription factors had little impact on thegrowth rate of the pulmonary tumors, but re-tarded their metastatic spread to bone andbrain.

Although the knockdown of FZD7 or theectopic expression of sFRP1 implicate Wnt li-gands and in cancer, they still involve geneticmanipulation, and thus remain one step re-moved from a pharmacological proof of concept.A more pharmacologically relevant approachwas provided by De Almeida et al. (2007),whom injected tumor-bearing mice with a fu-sion protein consisting of the Fc region IgG fusedto the extra cellular domain of the FZD8(FZD8CRD) Wnt receptor. That the FZD8CRDmolecule was active in vivo was initially shown byits dramatic inhibitory effect in the MMTV-Wnt-1 model of mammary cancer. Secondly,the FZD8CRD showed significant tumor inhibi-tion of two nonengineered cancer cell lines, theN-TERA2 human testicular cancer and the PA1human ovarian cancer cell line. The PA1 wasamong those cells identified by Bafico et al.(2004) as having autocrine Wnt signaling. Inan additional pharmacological test, You et al.(2004), inhibited the growth of a human mela-noma xenograft model by administering amonoclonal antibody to Wnt2.

The impact ofb-catenin knockdown in can-cers without identifiable genetic lesions in Wntsignaling could relate to the purported role ofWnt in the establishment and maintenance ofso-called cancer stem cells (CSCs) (Reya andClevers 2005; Malanchi and Huelsken 2009).There is considerable evidence for this in he-matopoetic cancers, in which evidence for a cel-lular hierarchy is well established. Granulocytic-macrophage progenitors isolated from CMLpatients show attributes of excessive Wnt signal-ing relative to normal progenitors and the in-troduction of the Wnt pathway inhibitor Axindecreased their capacity for proliferation andself-renewal (Jamieson et al. 2004). In a mousemodel of CML, introduction of BCR-ABL intomarrow cells from conditional b-catenin2/2

knockout animals significantly reduced the onset





of CML-like disease relative to that observedwith wild-type marrow cells (Zhao et al.2007). Nevertheless, recipients of the trans-formed b-catenin2/2 cells went on to developdisease resembling acute lymphoblastic leuke-mia. In another mouse model of leukemia, ini-tiated by expression of a mixed lineage leukemia(MLL) fusion protein, the conditional ablationof the b-catenin gene prevented preleukemicstem cells from inducing leukemia in graftedanimals (Wang et al. 2010). In this same study,shRNA knock down of b-catenin in leukemiastem cells severely delayed the onset of leukemiain recipient hosts.

Recent evidence also points to a role for Wntsignaling in cutaneous cancer stem cells. TheHuelsken laboratory found many similaritiesbetween normal skin stem cells and cancerstem cells isolated from murine epidermal tu-mors induced by carcinogens (Malanchi et al.2008). The cancer stem cells appeared enrichedfor Wnt signaling and conditional knockdownof b-catenin effectively eliminated this popula-tion of cells resulting in complete regression ofthe epidermal tumors. Although this shows thata mouse epidermal tumor is indeed impactedby inhibition of Wnt signaling, the investigatorsalso provided some evidence that Wnt signal-ing is exacerbated in human squamous cell car-cinomas.

SUMMARY

Wnt signaling clearly contributes to human tu-mor progression. This is best defined by germ-line and somatic mutations in Wnt pathwaycomponents that deregulate signaling. The rap-idly evolving field of epigenetics also continuesto implicate Wnt signaling in cancer by identi-fying suppressors and activators whose expres-sion is modulated by DNA and chromatin mod-ifications. New mechanisms of cooperativitybetween Wnt signaling and other pathways un-derscore the flexibility available to cancer cellsfor maintaining growth and survival. Finally, alarge body of experimental evidence stronglyencourages us to develop therapies that specif-ically interfere with Wnt signaling in the cancerclinic.

REFERENCES

Abrahamsson AE, Geron I, Gotlib J, Dao KH, Barroga CF,Newton IG, Giles FJ, Durocher J, Creusot RS, Karimi M,et al. 2009. Glycogen synthase kinase 3b missplicing con-tributes to leukemia stem cell generation. Proc Natl AcadSci 106: 3925–3929.

Akiri G, Cherian MM, Vijayakumar S, Liu G, Bafico A,Aaronson SA. 2009. Wnt pathway aberrations includingautocrine Wnt activation occur at high frequency in hu-man non-small-cell lung carcinoma. Oncogene 28: 2163–2172.

Angus-Hill ML, Elbert KM, Hidalgo J, Capecchi MR. 2011.T-cell factor 4 functions as a tumor suppressor whosedisruption modulates colon cell proliferation and tumor-igenesis. Proc Natl Acad Sci 108: 4914–4919.

Araki Y, Okamura S, Hussain SP, Nagashima M, He P, ShisekiM, Miura K, Harris CC. 2003. Regulation of cyclooxy-genase-2 expression by the Wnt and ras pathways. CancerRes 63: 728–734.

Ashihara E, Kawata E, Nakagawa Y, Shimazaski C, Kuroda J,Taniguchi K, Uchiyama H, Tanaka R, Yokota A, TakeuchiM, et al. 2009. b-catenin small interfering RNA success-fully suppressed progression of multiple myeloma in amouse model. Clin Cancer Res 15: 2731–2738.

Bafico A, Liu G, Goldin L, Harris V, Aaronson SA. 2004. Anautocrine mechanism for constitutive Wnt pathway acti-vation in human cancer cells. Cancer Cell 6: 497–506.

Bass AJ, Lawrence MS, Brace LE, Ramos AH, Drier Y, Ci-bulskis K, Sougnez C, Voet D, Saksena G, Sivachenko A,et al. 2011. Genomic sequencing of colorectal adenocar-cinomas identifies a recurrent VTI1A-TCF7L2 fusion.Nat Genet 43: 964–968.

Bjorklund P, Svedlund J, Olsson AK, Akerstrom G, Westin G.2009. The internally truncated LRP5 receptor presents atherapeutic target in breast cancer. PLoS ONE 4: e4243.

Castellone MD, Teramoto H, Williams BO, Druey KM, Gut-kind JS. 2005. Prostaglandin E2 promotes colon cancercell growth through a Gs-axin-b-catenin signaling axis.Science 310: 1504–1510.

Chan AT, Ogino S, Fuchs CS. 2007. Aspirin and the risk ofcolorectal cancer in relation to the expression of COX-2.N Engl J Med 356: 2131–2142.

Cheng AS, Lau SS, Chen Y, Kondo Y, Li MS, Feng H, ChingAK, Cheung KF, Wong HK, Tong JH, et al. 2011a. EZH2-mediated concordant repression of Wnt antagonists pro-motes b-catenin-dependent hepatocarcinogenesis. Can-cer Res 71: 4028–4039.

Cheng CK, Li L, Cheng SH, Ng K, Chan NP, Ip RK, WongRS, Shing MM, Li CK, Ng MH. 2011b. Secreted-frizzledrelated protein 1 is a transcriptional repression target ofthe t(8;21) fusion protein in acute myeloid leukemia.Blood 118: 6638–6648.

Christofk HR, Vander Heiden MG, Harris MH, Ramana-than A, Gerszten RE, Wei R, Fleming MD, Schreiber SL,Cantley LC. 2008. The M2 splice isoform of pyruvatekinase is important for cancer metabolism and tumourgrowth. Nature 452: 230–233.

Chung GG, Zerkowski MP, Ocal IT, Dolled-Filhart M, KangJY, Psyrri A, Camp RL, Rimm DL. 2004. b-Catenin andp53 analyses of a breast carcinoma tissue microarray.Cancer 100: 2084–2092.

P. Polakis




Clements WM, Lowy AM, Groden J. 2003. Adenomatouspolyposis coli/b-catenin interaction and downstreamtargets: Altered gene expression in gastrointestinal tu-mors. Clin Colorectal Cancer 3: 113–120.

Cong F, Zhang J, Pao W, Zhou P, Varmus H. 2003. A proteinknockdown strategy to study the function ofb-catenin intumorigenesis. BMC Mol Biol 4: 10.

Cuilliere-Dartigues P, El-Bchiri J, Krimi A, Buhard O, Fon-tanges P, Flejou JF, Hamelin R, Duval A. 2006. TCF-4isoforms absent in TCF-4 mutated MSI-H colorectal can-cer cells colocalize with nuclear CtBP and repress TCF-4-mediated transcription. Oncogene 25: 4441–4448.

DeAlmeida VI, Miao L, Ernst JA, Koeppen H, Polakis P,Rubinfeld B. 2007. The soluble Wnt receptor Friz-zled8CRD-hFc inhibits the growth of teratocarcinomasin vivo. Cancer Res 67: 5371–5379.

Ekstrom EJ, Sherwood V, Andersson T. 2011. Methylationand loss of Secreted Frizzled-Related Protein 3 enhancesmelanoma cell migration and invasion. PLoS ONE 6:e18674.

Fre S, Huyghe M, Mourikis P, Robine S, Louvard D, Arta-vanis-Tsakonas S. 2005. Notch signals control the fate ofimmature progenitor cells in the intestine. Nature 435:964–968.

Fre S, Pallavi SK, Huyghe M, Lae M, Janssen KP, Robine S,Artavanis-Tsakonas S, Louvard D. 2009. Notch and Wntsignals cooperatively control cell proliferation and tu-morigenesis in the intestine. Proc Natl Acad Sci 106:6309–6314.

Geyer FC, Lacroix-Triki M, Savage K, Arnedos M, LambrosMB, MacKay A, Natrajan R, Reis-Filho JS. 2011. b-Cat-enin pathway activation in breast cancer is associatedwith triple-negative phenotype but not with CTNNB1mutation. Mod Pathol 24: 209–231.

Gottardi CJ, Wong E, Gumbiner BM. 2001. E-cadherin sup-presses cellular transformation by inhibiting b-cateninsignaling in an adhesion-independent manner. J CellBiol 153: 1049–1060.

Green DW, Roh H, Pippin JA, Drebin JA. 2001. b-cateninantisense treatment decreases b-catenin expression andtumor growth rate in colon carcinoma xenografts. J SurgRes 101: 16–20.

Howe LR, Brown AM. 2004. Wnt signaling and breast can-cer. Cancer Biol Ther 3: 36–41.

Hu T, Li C. 2011. Convergence between Wnt-b-catenin andEGFR signaling in cancer. Mol Cancer 9: 236.

Huff V. 2011. Wilms’ tumours: About tumour suppressorgenes, an oncogene and a chameleon gene. Nat Rev Can-cer 11: 111–121.

Jamieson CH, Ailles LE, Dylla SJ, Muijtjens M, Jones C,Zehnder JL, Gotlib J, Li K, Manz MG, Keating A, et al.2004. Granulocyte-macrophage progenitors as candidateleukemic stem cells in blast-crisis CML. N Engl J Med351: 657–667.

Jiang X, Tan J, Li J, Kivimae S, Yang X, Zhuang L, Lee PL,Chan MT, Stanton LW, Liu ET, et al. 2008. DACT3 is anepigenetic regulator of Wnt/b-catenin signaling in colo-rectal cancer and is a therapeutic target of histone mod-ifications. Cancer Cell 13: 529–541.

Khramtsov AI, Khramtsova GF, Tretiakova M, Huo D, Olo-pade OI, Goss KH. 2010. Wnt/b-catenin pathway acti-

vation is enriched in basal-like breast cancers and predictspoor outcome. Am J Pathol 176: 2911–2920.

Kim JS, Crooks H, Foxworth A, Waldman T. 2002. Proof-of-principle: oncogenic b-catenin is a valid molecular targetfor the development of pharmacological inhibitors. MolCancer Ther 1: 1355–1359.

Klaus A, Birchmeier W. 2008. Wnt signalling and its impacton development and cancer. Nat Rev Cancer 8: 387–398.

Kongkham PN, Northcott PA, Croul SE, Smith CA, TaylorMD, Rutka JT. 2010. The SFRP family of WNT inhibitorsfunction as novel tumor suppressor genes epigeneticallysilenced in medulloblastoma. Oncogene 29: 3017–3024.

Kwon C, Cheng P, King IN, Andersen P, Shenje L, Nigam V,Srivastava D. 2011. Notch post-translationally regulatesb-catenin protein in stem and progenitor cells. Nat CellBiol 13: 1244–1251.

Laird PW, Jackson-Grusby L, Fazeli A, Dickinson SL, JungWE, Li E, Weinberg RA, Jaenisch R. 1995. Suppression ofintestinal neoplasia by DNA hypomethylation. Cell 81:197–205.

Lammi L, Arte S, Somer M, Jarvinen H, Lahermo P, ThesleffI, Pirinen S, Nieminen P. 2004. Mutations in AXIN2cause familial tooth agenesis and predispose to colorectalcancer. Am J Hum Genet 74: 1043–1050.

Lilien J, Balsamo J. 2005. The regulation of cadherin-medi-ated adhesion by tyrosine phosphorylation/dephosphor-ylation of b-catenin. Curr Opin Cell Biol 17: 459–465.

Lin SY, Xia W, Wang JC, Kwong KY, Spohn B, Wen Y, PestellRG, Hung MC. 2000. b-catenin, a novel prognosticmarker for breast cancer: Its roles in cyclin D1 expressionand cancer progression. Proc Natl Acad Sci 97: 4262–4266.

Mahmoudi T, Boj SF, Hatzis P, Li VS, Taouatas N, Vries RG,Teunissen H, Begthel H, Korving J, Mohammed S, et al.2011. The leukemia-associated Mllt10/Af10-Dot1l areTcf4/b-catenin coactivators essential for intestinal ho-meostasis. PLoS Biol 8: e1000539.

Major MB, Camp ND, Berndt JD, Yi X, Goldenberg SJ,Hubbert C, Biechele TL, Gingras AC, Zheng N, MaccossMJ, et al. 2007. Wilms tumor suppressor WTX negativelyregulates WNT/b-catenin signaling. Science 316: 1043–1046.

Malanchi I, Huelsken J. 2009. Cancer stem cells: Never Wntaway from the niche. Curr Opin Oncol 21: 41–46.

Malanchi I, Peinado H, Kassen D, Hussenet T, Metzger D,Chambon P, Huber M, Hohl D, Cano A, Birchmeier W,et al. 2008. Cutaneous cancer stem cell maintenance isdependent onb-catenin signalling. Nature 452: 650–653.

Marvin ML, Mazzoni SM, Herron CM, Edwards S, GruberSB, Petty EM. 2011. AXIN2-associated autosomal dom-inant ectodermal dysplasia and neoplastic syndrome. AmJ Med Genet A 155A: 898–902.

Matsuda Y, Schlange T, Oakeley EJ, Boulay A, Hynes NE.2009. WNTsignaling enhances breast cancer cell motilityand blockade of the WNT pathway by sFRP1 suppressesMDA-MB-231 xenograft growth. Breast Cancer Res 11:R32.

McGarvey KM, Fahrner JA, Greene E, Martens J, Jenuwein T,Baylin SB. 2006. Silenced tumor suppressor genes reacti-vated by DNA demethylation do not return to a fullyeuchromatic chromatin state. Cancer Res 66: 3541–3549.





Moisan A, Rivera MN, Lotinun S, Akhavanfard S, CoffmanEJ, Cook EB, Stoykova S, Mukherjee S, Schoonmaker JA,Burger A, et al. 2011. The WTX tumor suppressor regu-lates mesenchymal progenitor cell fate specification. DevCell 20: 583–596.

Mologni L, Dekhil H, Ceccon M, Purgante S, Lan C, Cleris L,Magistroni V, Formelli F, Gambacorti-Passerini CB. 2010.Colorectal tumors are effectively eradicated by combinedinhibition of fbg-catenin, KRAS, and the oncogenictranscription factor ITF2. Cancer Res 70: 7253–7263.

Morin PJ, Vogelstein B, Kinzler KW. 1996. Apoptosis andAPC in colorectal tumorigenesis. Proc Natl Acad Sci 93:7950–7954.

Morin RD, Johnson NA, Severson TM, Mungall AJ, An J,Goya R, Paul JE, Boyle M, Woolcock BW, Kuchenbauer F,et al. 2011. Somatic mutations altering EZH2 (Tyr641) infollicular and diffuse large B-cell lymphomas of germi-nal-center origin. Nat Genet 42: 181–185.

Mullighan CG, Zhang J, Kasper LH, Lerach S, Payne-TurnerD, Phillips LA, Heatley SL, Holmfeldt L, Collins-Under-wood JR, Ma J, et al. 2011. CREBBP mutations in re-lapsed acute lymphoblastic leukaemia. Nature 471:235–239.

Myung SJ, Rerko RM, Yan M, Platzer P, Guda K, Dotson A,Lawrence E, Dannenberg AJ, Lovgren AK, Luo G, et al.2006. 15-Hydroxyprostaglandin dehydrogenase is an invivo suppressor of colon tumorigenesis. Proc Natl AcadSci 103: 12098–12102.

Nguyen DX, Chiang AC, Zhang XH, Kim JY, Kris MG, La-danyi M, Gerald WL, Massague J. 2009. WNT/TCF sig-naling through LEF1 and HOXB9 mediates lung adeno-carcinoma metastasis. Cell 138: 51–62.

Ni M, Chen Y, Lim E, Wimberly H, Bailey ST, Imai Y, RimmDL, Liu XS, Brown M. 2011. Targeting androgen receptorin estrogen receptor-negative breast cancer. Cancer Cell20: 119–131.

Oshima M, Taketo MM. 2002. COX selectivity and animalmodels for colon cancer. Curr Pharm Des 8: 1021–1034.

Pasqualucci L, Dominguez-Sola D, Chiarenza A, Fabbri G,Grunn A, Trifonov V, Kasper LH, Lerach S, Tang H, Ma J,et al. 2011. Inactivating mutations of acetyltransferasegenes in B-cell lymphoma. Nature 471: 189–195.

Phesse TJ, Parry L, Reed KR, Ewan KB, Dale TC, Sansom OJ,Clarke AR. 2008. Deficiency of Mbd2 attenuates Wntsignaling. Mol Cell Biol 28: 6094–6103.

Polakis P. 2007. The many ways of Wnt in cancer. Curr OpinGenet Dev 17: 45–51.

Reya T, Clevers H. 2005. Wnt signalling in stem cells andcancer. Nature 434: 843–850.

Rodriguez-Paredes M, Esteller M. 2011. Cancer epigeneticsreaches mainstream oncology. Nat Med 17: 330–339.

Roh H, Green DW, Boswell CB, Pippin JA, Drebin JA. 2001.Suppression of b-catenin inhibits the neoplastic growthof APC-mutant colon cancer cells. Cancer Res 61:6563–6568.

Ruteshouser EC, Robinson SM, Huff V. 2008. Wilms tumorgenetics: Mutations in WT1, WTX, and CTNNB1 ac-count for only about one-third of tumors. Genes Chro-mosomes Cancer 47: 461–470.

Salahshor S, Woodgett JR. 2005. The links between axin andcarcinogenesis. J Clin Pathol 58: 225–236.

Sansom OJ, Berger J, Bishop SM, Hendrich B, Bird A, ClarkeAR. 2003. Deficiency of Mbd2 suppresses intestinal tu-morigenesis. Nat Genet 34: 145–147.

Satoh S, Daigo Y, Furukawa Y, Kato T, Miwa N, Nishiwaki T,Kawasoe T, Ishiguro H, Fujita M, Tokino T, et al. 2000.AXIN1 mutations in hepatocellular carcinomas, andgrowth suppression in cancer cells by virus-mediatedtransfer of AXIN1. Nat Genet 24: 245–250.

Sjoblom T, Jones S, Wood LD, Parsons DW, Lin J, Barber TD,Mandelker D, Leary RJ, Ptak J, Silliman N, et al. 2006. Theconsensus coding sequences of human breast and colo-rectal cancers. Science 314: 268–274.

Smartt HJ, Greenhough A, Ordonez-Moran P, Talero E,Cherry CA, Wallam CA, Parry L, Al Kharusi M, RobertsHR, Mariadason JM, et al. 2011. b-catenin represses ex-pression of the tumour suppressor 15-prostaglandin de-hydrogenase in the normal intestinal epithelium andcolorectal tumour cells. Gut doi: 10.1136/gutjnl-2011-300817.

Sorlie T, Tibshirani R, Parker J, Hastie T, Marron JS, Nobel A,Deng S, Johnsen H, Pesich R, Geisler S, et al. 2003. Re-peated observation of breast tumor subtypes in indepen-dent gene expression data sets. Proc Natl Acad Sci 100:8418–8423.

Suzuki H, Gabrielson E, Chen W, Anbazhagan R, van Enge-land M, Weijenberg MP, Herman JG, Baylin SB. 2002. Agenomic screen for genes upregulated by demethylationand histone deacetylase inhibition in human colorectalcancer. Nat Genet 31: 141–149.

Suzuki H, Toyota M, Carraway H, Gabrielson E, Ohmura T,Fujikane T, Nishikawa N, Sogabe Y, Nojima M, Sonoda T,et al. 2008. Frequent epigenetic inactivation of Wnt an-tagonist genes in breast cancer. Br J Cancer 98: 1147–1156.

Takagi H, Sasaki S, Suzuki H, Toyota M, Maruyama R, No-jima M, Yamamoto H, Omata M, Tokino T, Imai K, et al.2008. Frequent epigenetic inactivation of SFRP genes inhepatocellular carcinoma. J Gastroenterol 43: 378–389.

Tang W, Dodge M, Gundapaneni D, Michnoff C, Roth M,Lum L. 2008. A genome-wide RNAi screen for Wnt/b-catenin pathway components identifies unexpected rolesfor TCF transcription factors in cancer. Proc Natl Acad Sci105: 9697–9702.

Teo JL, Kahn M. 2011. The Wnt signaling pathway in cellularproliferation and differentiation: A tale of two coactiva-tors. Adv Drug Deliv Rev 62: 1149–1155.

Tetsu O, McCormick F. 1999. b-catenin regulates expressionof cyclin D1 in colon carcinoma cells. Nature 398: 422–426.

van de Wetering M, Sancho E, Verweij C, de Lau W, Oving I,Hurlstone A, van der Horn K, Batlle E, Coudreuse D,Haramis AP, et al. 2002. The b-catenin/TCF-4 compleximposes a crypt progenitor phenotype on colorectal can-cer cells. Cell 111: 241–250.

van Es JH, van Gijn ME, Riccio O, van den Born M, VooijsM, Begthel H, Cozijnsen M, Robine S, Winton DJ, RadtkeF, et al. 2005. Notch/g-secretase inhibition turns prolif-erative cells in intestinal crypts and adenomas into gobletcells. Nature 435: 959–963.

van Haaften G, Dalgliesh GL, Davies H, Chen L, Bignell G,Greenman C, Edkins S, Hardy C, O’Meara S, Teague J,et al. 2009. Somatic mutations of the histone H3K27

P. Polakis




demethylase gene UTX in human cancer. Nat Genet 41:521–523.

van Veelen W, Le NH, Helvensteijn W, Blonden L, TheeuwesM, Bakker ER, Franken PF, van Gurp L, Meijlink F, vander Valk MA, et al. 2011. b-catenin tyrosine 654 phos-phorylation increases Wnt signalling and intestinal tu-morigenesis. Gut 60: 1204–1212.

Verma UN, Surabhi RM, Schmaltieg A, Becerra C, GaynorRB. 2003. Small interfering RNAs directed against b-cat-enin inhibit the in vitro and in vivo growth of coloncancer cells. Clin Cancer Res 9: 1291–1300.

Vincent A, Omura N, Hong SM, Jaffe A, Eshleman J, Gog-gins M. 2011. Genome-wide analysis of promoter meth-ylation associated with gene expression profile in pancre-atic adenocarcinoma. Clin Cancer Res 17: 4341–4354.

Wang D, Mann JR, DuBois RN. 2004. WNT and cyclooxy-genase-2 cross-talk accelerates adenoma growth. CellCycle 3: 1512–1515.

Wang Y, Krivtsov AV, Sinha AU, North TE, Goessling W, FengZ, Zon LI, Armstrong SA. 2010. The Wnt/b-cateninpathway is required for the development of leukemiastem cells in AML. Science 327: 1650–1653.

Willert K, Jones KA. 2006. Wnt signaling: Is the party in thenucleus? Genes Dev 20: 1394–1404.

Yang L, Wu X, Wang Y, Zhang K, Wu J, Yuan YC, Deng X,Chen L, Kim CC, Lau S, et al. 2011a. FZD7 has a criticalrole in cell proliferation in triple negative breast cancer.Oncogene 43: 4437–4446.

Yang W, Xia Y, Ji H, Zheng Y, Liang J, Huang W, Gao X,Aldape K, Lu Z. 2011b. Nuclear PKM2 regulates b-cat-enin transactivation upon EGFR activation. Nature 480:118–122.

You L, He B, Xu Z, Uematsu K, Mazieres J, Mikami I, Reg-uart N, Moody TW, Kitajewski J, McCormick F, et al.2004. Inhibition of Wnt-2-mediated signaling inducesprogrammed cell death in non-small-cell lung cancercells. Oncogene 23: 6170–6174.

Zeng G, Apte U, Cieply B, Singh S, Monga SP. 2007. siRNA-mediated b-catenin knockdown in human hepatomacells results in decreased growth and survival. Neoplasia9: 951–959.

Zhao C, Blum J, Chen A, Kwon HY, Jung SH, Cook JM,Lagoo A, Reya T. 2007. Loss of b-catenin impairs therenewal of normal and CML stem cells in vivo. CancerCell 12: 528–541.





March 20, 20122012; doi: 10.1101/cshperspect.a008052 originally published onlineCold Spring Harb Perspect Biol

Paul Polakis Wnt Signaling in Cancer

Subject Collection Wnt Signaling

Wnt Signaling in Vertebrate Axis SpecificationHiroki Hikasa and Sergei Y. Sokol

-Catenin Destruction ComplexβThe Jennifer L. Stamos and William I. Weis

ActivatorsSecreted and Transmembrane Wnt Inhibitors and

Cristina-Maria Cruciat and Christof Niehrsand DiseaseWnt Signaling in Skin Development, Homeostasis,

Xinhong Lim and Roel Nusse

HematopoiesisWnt Signaling in Normal and Malignant

et al.William Lento, Kendra Congdon, Carlijn Voermans,

Making Stronger Bone with WntsWnt Signaling in Bone Development and Disease:

Williams, et al.Jean B. Regard, Zhendong Zhong, Bart O.

Signaling-CateninβFrizzled and LRP5/6 Receptors for Wnt/

Bryan T. MacDonald and Xi He

Targeting Wnt Pathways in Disease

J. ChienZachary F. Zimmerman, Randall T. Moon and Andy

TCF/LEFs and Wnt Signaling in the NucleusKen M. Cadigan and Marian L. Waterman Fates and Combinatorial Signaling

Wnt Signaling in Mammary Glands: Plastic Cell

Fakhraldeen, et al.Caroline M. Alexander, Shruti Goel, Saja A.

Alternative Wnt Pathways and ReceptorsRenée van Amerongen

Wnt Signaling and Injury Repair

HelmsJemima L. Whyte, Andrew A. Smith and Jill A.

Teaching an Old Dog a New Trick:C. elegans-Catenin-Dependent Wnt Signaling in β

Belinda M. Jackson and David M. Eisenmann

Wnt Signaling and Forebrain DevelopmentSusan J. Harrison-Uy and Samuel J. Pleasure

The Evolution of the Wnt PathwayThomas W. Holstein Development

Wnt Signaling in Neuromuscular Junction

Kate Koles and Vivian Budnik

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