BackgroundInformation | Theepidermalgrowthfactorreceptor(EGFR;ErbB-1;HER1inhumans)isthecell-surfacereceptorformembersoftheepidermalgrowthfactorfamily(EGF-family)ofextracellularproteinligands.TheepidermalgrowthfactorreceptorisamemberoftheErbBfamilyofreceptors,asubfamilyoffourcloselyrelatedreceptortyrosinekinases:EGFR(ErbB-1),HER2/c-neu(ErbB-2),Her3(ErbB-3)andHer4(ErbB-4).MutationsaffectingEGFRexpressionoractivitycouldresultincancer.EGFR(epidermalgrowthfactorreceptor)existsonthecellsurfaceandisactivatedbybindingofitsspecificligands,includingepidermalgrowthfactorandtransforminggrowthfactorα(TGFα).Uponactivationbyitsgrowthfactorligands,EGFRundergoesatransitionfromaninactivemonomericformtoanactivehomodimer.Inadditiontoforminghomodimersafterligandbinding,EGFRmaypairwithanothermemberoftheErbBreceptorfamily,suchasErbB2/Her2/neu,tocreateanactivatedheterodimer.ThereisalsoevidencetosuggestthatclustersofactivatedEGFRsform,althoughitremainsunclearwhetherthisclusteringisimportantforactivationitselforoccurssubsequenttoactivationofindividualdimers. EGFRdimerizationstimulatesitsintrinsicintracellularprotein-tyrosinekinaseactivity.Asaresult,autophosphorylationoffivetyrosine(Y)residuesintheC-terminaldomainofEGFRoccurs.TheseareY992,Y1045,Y1068,Y1148andY1173.Thisautophosphorylationelicitsdownstreamactivationandsignalingbyseveralotherproteinsthatassociatewiththephosphorylatedtyrosinesthroughtheirownphosphotyrosine-bindingSH2domains.Thesedownstreamsignalingproteinsinitiateseveralsignaltransductioncascades,principallytheMAPK,AktandJNKpathways,leADIngtoDNAsynthesisandcellproliferation.Suchproteinsmodulatephenotypessuchascellmigration,adhesion,andproliferation.ThekinasedomainofEGFRcanalsocross-phosphorylatetyrosineresiduesofotherreceptorsitisaggregatedwith,andcanitselfbeactivatedinthatmanner. |