BackgroundInformation | I.TESTPRINCIPLE TheUPSTATE®colorimetricSTAR(SignalTransductionAssayReaction)ELISAkitisasolidphasesandwichenzymelinkedimmunosorbentassaythatprovidesafast,sensitivemethodtodetectspecificlevelsofsignalingtargetsinwholecellextracts.TheIRS1plateiscoatedwithaspecificmousemonoclonalcaptureantibodyonthemicrowellsofthe96-wellclearplate.SamplelysateorthestandardincludedinthekitareincubatedinthemicrowellsallowingIRS1antigentobecapturedintheplatewells.Theplateisthenwashedtoremoveanyunboundnon-specificmaterial.Thewellsarethenincubatedwithaspecificrabbitanti-phospho-IRS1(Ser312)antibodytodetectthecapturedIRS1ontheplatewellthatisphosphorylatedonSer312.TheunbounddetectionantibodyiswashedawayfollowedbyincubationwithanHRP-conjugatedanti-rabbitantibody.Thisallowsforasensitiveenzymaticdetectionofthesample.AftertheadditionofTMBsubstrateandstopsolutiontheabsorbanceismeasuredat450nmusingaplatereader. Theentireassaytakeslessthan5hourstocompletewithminimalhands-ontime.Manyofthereagentsaresuppliedinready-touseformulationsforeaseofuse.Thekitalsoincludesastandardthatisrunasbothapositivecontrolandtodevelopastandardcurve.
II.IRS1BACKGROUND IRS(InsulinReceptorSubstrate)proteinsaretheeffectorsofbothInsulinandIGF-initiatedsignaling.Insulin,inadditiontoworkingverysimilarlytoagrowthfactorinstimulatingreceptortyrosinekinases,isessentialformaintainingglucosehomeostasisandregulatingcarbohydrate,lipid,andproteinmetabolism.Thesignalingeventsofinsulinaremediatedviaavastandhighlyintegratednetworkofmoleculesthatcontrolsseveralprocesses.Thereare4IRSproteins,1-4.Itisbelievedthattheseproteinsservecomplementaryfunctionsindifferenttissues.ThetwoprominentplayersareIRS1andIRS2withIRS1playingimportantrolesinskeletalmuscleandIRS2intheliver.TheIRSproteinslinktheinsulinreceptorwithmanysignalingpathwaysincludingthePI3Kinase/Akt/mTORandtheMAPKinasepathways.ThePI3K/Akt/mTORpathwayisinvolvedwithmanymetabolicactionsofinsulinsignaling.MAPKisinvolvedintheregulationofsomegenesandworkswithPI3Kinasetocontrolcellgrowthanddifferentiation.InadditiontotheinsulinreceptortyrosinekinaseactivityintypeIIdiabetespatientsandmice,studieshaveshownagreaterdefectincomponentsoftheinsulinsignalingpathwayincludingInsulinReceptorSubstrate(IRS)phosphorylationortheactivationofPhosphoinositide3-Kinase(PI3Kinase).Insulinstimulatesthesignalingcascadebybindingtotheinsulinreceptorthroughitsextracellularαsubunits.Thisstimulatesthetyrosinekinaseactivityoftheβsubunitsofthereceptor.ThereceptorthenautophosphorylatesitselfandphosphorylatestheIRS(InsulinReceptorSubstrate)proteinsthatareveryimportantmodulatorsofinsulinsignaling.IRSbindstothephosphorylatedtyrosinesoftheβsubunitoftheinsulinreceptor.TheysharePHandPTBdomainsneartheirN-termini,andmultipleTyrphosphorylationmotifsintheirC-terminalregions.Proteinswhichbindtotyrosine-phosphorylatedIRS-proteinsincludePI3Kinasep85,GRB2,SHP2,Nck,Crk,andFyn.IRS1appearstobeprincipallyinvolvedinIGF-signalingandcytoskeletalgrowth.IRS2appearstobethecriticalmediatorofInsulinsignaling,asgeneticablationresultsintypeIIdiabetes.IRS3isexpressedprimarilyinADIpocytesandisanunusuallypotentactivatorofPI3Kinase.IRS4lacksthetyrosineresidueswhichintheotherIRS-proteinsbindstoSHP2. |