mTOR信号通路中raptor蛋白功能介绍

Cell,Vol.110,163–175,July26,2002,Copyright2002byCellPressmTORInteractswithRaptortoFormaNutrient-SensitiveComplexthatSignalstotheCellGrowthMachinerypathwayregulatesavarietyofprocessescontributingtocellgrowth,includinginitiationofmRNAtranslation,ribosomesynthesis,expressionofmetabolism-relatedgenes,autophagy,andcytoskeletalreorganization(re-centlyreviewedbySchmelzleandHall,2000,andbyGin-Do-HyungKim,1DosD.Sarbassov,1SirajM.Ali,1JessieE.King,1RobertR.Latek,1HediyeErdjument-Bromage,2PaulTempst,2andDavidM.Sabatini1,31WhiteheadInstituteforBiomedicalResearchgrasetal.,2001).Byinterferingwiththefunctionofmam-NineCambridgeCentermalianTOR,rapamycininhibitsprogressionthroughtheCambridge,Massachusetts02142G1phaseofthecellcycleinvariouscelltypes.Because2MolecularBiologyProgramoftheseantiproliferativeeffects,rapamycinisaclinicallyMemorialSloan-KetteringCancerCentervaluabledrugthatiscurrentlyusedtoblockimmunerejec-NewYork,NewYork10021tionoftransplantedorgans(Saundersetal.,2001)andintrialsforthetreatmentofcancer(Dudkinetal.,2001;Hi-dalgoandRowinsky,2000)andforthepreventionofreste-nosisafterangioplasty(Sousaetal.,2001).SummaryMammalianTOR,mTOR(alsoknownasRAFT1orFRAP),phosphorylatesatleasttworegulatorsofproteinmTOR/RAFT1/FRAPisthetargetoftheimmunosup-synthesis:S6K1(formerlycalledp70ribosomalS6ki-pressivedrugrapamycinandthecentralcomponentofnase)andaninhibitoroftranslationinitiation,theeIF-anutrient-andhormone-sensitivesignalingpathway4Ebindingprotein1(4E-BP1)(Brunnetal.,1997;Burnettthatregulatescellgrowth.WereportthatmTORformsetal.,1998;Haraetal.,1997;Isotanietal.,1999).Inastoichiometriccomplexwithraptor,anevolutionarilymammaliancells,aminoaciddeprivationleadstotheconservedproteinwithatleasttworolesinthemTORdephosphorylationofbothS6K1and4E-BP1andtopathway.Raptorhasapositiveroleinnutrient-stimu-decreasedratesofproteinsynthesis,effectsthatarelatedsignalingtothedownstreameffectorS6K1,rapidlyreversedbythereadditionofaminoacids(Foxetmaintenanceofcellsize,andmTORproteinexpres-al.,1998;Haraetal.,1998).Amongaminoacids,changesinsion.TheassociationofraptorwithmTORalsonega-leucinelevelsalonearesufficienttoregulatethephos-tivelyregulatesthemTORkinaseactivity.Conditionsphorylationstateandactivityofbothdownstreamcom-thatrepressthepathway,suchasnutrientdeprivationponentsofthemTORpathway(Haraetal.,1998;Lynchandmitochondrialuncoupling,stabilizethemTOR-etal.,2000).Inadditiontoaminoacidlevelinthemedia,raptorassociationandinhibitmTORkinaseactivity.mitochondrialfunction(Xuetal.,2001),glycolysis(Den-Weproposethatraptorisamissingcomponentofnisetal.,2001),andcellstress(ParrottandTempleton,themTORpathwaythatthroughitsassociationwith1999)regulateS6K1,asdogrowthfactorssuchasinsu-mTORregulatescellsizeinresponsetonutrientlevels.lin(LawrenceandBrunn,2001).Despiteextensiveefforts,hownutrientsregulatetheIntroductionmTORsignalingpathwayremainspoorlyunderstood.Inparticular,stimulithatactivate(e.g.,aminoacids)orIncreasingevidenceindicatesthatineukaryotes,cellinhibit(e.g.,mitochondrialuncouplers)downstreamef-growth(massaccumulation)isfinelyregulatedinre-fectorsofmTOR,suchasS6K1and4E-BP1,failtosponsetoenvironmentalanddevelopmentalconditionschangetheinvitrokinaseactivityofmTOR(Dennisetandcanbederangedinhumandiseasessuchascanceral.,2001;Haraetal.,1997).Thisdiscrepancyhasledusanddiabetes(reviewedbyDixonandFordham-Skelton,tohypothesizethatinvivomTORexistsasacomplex1998;JohnstonandGallant,2002;Katsoetal.,2001;withoneormoreproteinsthatarelostduringisolationKozmaandThomas,2002;SchmelzleandHall,2000).ofmTORforinvitroassays.SeverallinesofevidenceTherateofmassaccumulationiscontrollednotsimplysupportthenotionthatmTORassociateswithotherbytheavailabilityofnutrients,butbysignalingpathwaysproteins:mTORcontainsHEATrepeats,whicharethatcoordinatetheactivityofthecellgrowthmachineryknowntobeprotein-proteininteractionmotifs;itmi-withnutritional,hormonal,andmitogenicsignals.Stud-gratesatadisproportionatelylargeapparentmoleculariesintothemechanismofactionofrapamycin,animmu-weight(1.5–2.0mDa)ingelfiltrationchromatographynosuppressiveandanticancerdrug,ledtothediscovery(D.M.S.,unpublisheddata);andtheexpressionintrans-ofanevolutionarilyconservedregulatorofcellgrowth,fectedcellsofmTORfragmentslackingthecatalytictheTOR(targetofrapamycin)pathway(Brownetal.,sitehasdominant-negativeeffectsonthepathway(data1994;Chiuetal.,1994;Kunzetal.,1993;Oldhametal.,notshown).However,conventionalbiochemicalat-2000;Sabatinietal.,1994;Sabersetal.,1995;ZhangettemptstopurifymTOR-interactingproteinshavebeenal.,2000).Thecomplexofrapamycinwithitsreceptor,fruitless,asmightbeexpectedifmTOR-containingcom-FKBP12,bindsdirectlytoTORandperturbsitsfunctionplexeswereunstableunderstandardpurificationcondi-inapoorlyunderstoodfashion(Brownetal.,1995;Burnetttions.Therefore,wedevisedapurificationschemethatetal.,1998;Petersonetal.,2000;Zhengetal.,1995).usesareversiblechemicalcrosslinkertostabilizeputa-StudiesinseveralorganismshaveshownthattheTORtivemTOR-containingcomplexes.Usingthisstrategy,wehavediscoveredraptor(regulatoryassoci