Type:Protein
SpeciesReactivity:M
B=Bovine;Ca=Cat;Ch=Chicken;D=Dog;EQ=Equine;GP=GuineaPig;H=Human;M=Mouse;P=Porcine;Pr=Primate;R=Rat;Rb=Rabbit;Y=Yeast;Xe=Xenopus;Ze=Zebrafish;;;;NA-NotApplicable;STP=Step-TactinProteins;AllInsulin-likegrowthfactorI(alsoknownassomatomedinCandsomatomedinA)andinsulin-likegrowthfactorII(multiplicationstimulatingactivityorMSA)belongtothefamilyofinsulin-likegrowthfactorsthatarestructurallyhomologoustoproinsulin.MatureIGF-IandIGF-IIshareapproximately70%sequenceidentity.BothIGF-IandIGF-IIareexpressedinmanytissuesandcelltypesandmayhaveautocrine,paracrineandendocrinefunctions.MatureIGF-IandIGF-IIarehighlyconserved(100%identitybetweenhuman,bovineandporcineproteins)andexhibitcross-speciesactivity.
IGF-IIisapotentmitogenicgrowthfactor.However,unlikeIGF-Iwhichhasimportantpostnatalroles,thegrowth-promotingfunctionofIGF-IIislimitedtoembryonicdevelopment.
TwospecificcellsurfacereceptorsthatbindIGF-IandIGF-IIhavebeenidentified.ThetypeIIGFreceptorthatparticipatesinIGFsignalingisstructurallyrelatedtotheinsulinreceptor.Itisadisulfide-linkedheterotetramerictransmembraneglycoproteinwithanintracellulartyrosinekinasedomain.TypeIIGFreceptorbindsIGF-IwithhigheraffinitythanIGF-II.ThetypeIIIGFreceptorwhichbindsIGF-IIwithmuchhigheraffinitythanIGF-Iisalsothecation-independentmannose6-phosphatereceptor.Atthepresenttime,itisnotknownifthetypeIIIGFreceptorparticipatesintheIGFsignalingpathway.AnadditionalunknownreceptorwhichmediatesIGF-IIsignalinghasalsobeenproposed.CirculatingIGFsexistincomplexesboundtoIGFbindingproteins.Currently,atleastsixhighaffinitybindingproteinshavebeenidentified.
