Ubiquitin E3 ligase WWP1 as an oncogenic factor in human prostate cancer

The genefor E3 ubiquitinligaseWWP1is locatedat8q21, a region frequently amplified in human cancers,includingprostatecancer.RecentstudieshaveshownthatWWP1negativelyregulatestheTGFb tumorsuppressorpathway by inactivating its molecular components,including Smad2, Smad4 and TbR1. These findingssuggestanoncogenicroleofWWP1incarcinogenesis,butdirectsupportingevidencehasbeenlacking.Inthisstudy, we examined WWP1 for gene dosage, mRNAexpression,mutationandfunctionsinanumberofhumanprostatecancersamples.WefoundthattheWWP1 genehadcopynumbergainin15of34(44%)xenograftsandcelllinesfromprostatecancerand15of49(31%)clinicalprostatecancersamples.Consistently,WWP1 wasover-expressed in 60% of xenografts and cell lines fromprostate cancer. Mutation of WWP1 occurred infre-quently in prostate cancer. Functionally, WWP1 over-expression promoted colony formation in the 22Rv1prostatecancercellline.InPC-3prostatecancercells,WWP1 knockdownsignificantlysuppressedcellprolifera-tion and enhanced TGFb-mediated growth inhibition.ThesefindingssuggestthatWWP1 isanoncogenethatundergoes genomic amplification at 8q21 in humanprostatecancer,andWWP1 overexpressionisacommonmechanisminvolvedintheinactivationofTGFb functioninhumancancer.Oncogene(2007)26,2386–2394.doi:10.1038/sj.onc.1210021;publishedonline2October2006Keywords: WWP1;amplification;overexpression;prostatecancer;KLF5;TGFbIntroductionProstatecancerisoneofthemostcommonsolidtumorsinmen.Themolecularbasisofprostatecancerisnotwellunderstood,althoughithasbeenrecognizedthatidentifyingmolecularalterationsunderlyingthedeve-lopment and progression of prostate cancer will benecessary for improving its detection and treatment.Copy number gain or loss is a common geneticalterationinsolidtumors.Manychromosomalregionshave been identified for such changes in cancer bycomparativegenomichybridization(CGH)andotherapproaches,yettheunderlyingtargetgenesremaintobeidentifiedandcharacterizedformostcancers.Theq21band of chromosome 8 (8q21) shows frequent copynumbergaininprostatecancer,andthegainat8q21isoftenassociatedwithaggressivebehaviorsofprostatecancer.Forexample,inmenwithclinicallylocalizedprostatecancer,gainof8q21isassociatedwithpooroutcomeandmetastasis(Nupponenet al.,1998;vanDekkenetal.,2003;Rubinetal.,2004).Therefore,8q21isbelievedtoharboranimportantoncogeneforprostatecancer.Many important molecules involved in cell proli-feration,differentiationandcarcinogenesisaretightlycontrolledbydifferentmechanisms,includingubiquitinproteasomepathway(UPP)-mediatedproteindegrada-tion.ManyE3ubiquitinligasesintheUPPhavebeenimplicatedincellcyclecontrolanduncontrolledcellproliferation. Some E3 ligases such as MDM2 andSKP2,whichtargetp53andCDKN1A/CDKN1B,areconsideredoncoproteins(Leiteet al.,2001;Luet al.,2002;Drobnjaketal.,2003),whilesomeotherE3ligasesare considered tumor suppressors. WWP1 is an E3ubiquitinligasethatcontainsfourtandemWWdomainsandaHECTdomain.PublishedstudiessuggestthatWWP1 plays a role in different biological processesincluding regulation of epithelial sodium channels,viral budding, receptor trafficking and transcription(Malbert-Colas et al., 2003; Ingham et al., 2004;Zhang et al., 2004). With regard to a role incell proliferation and carcinogenesis, it has been