Insulin-likegrowthfactorI,alsoknownassomatomedinC,isthedominanteffectorofgrowthhormoneandisstructurallyhomologoustoproinsulin.HumanIGF-IissynthesizedastwoprecursorisoformswithN-andalternateC-terminalpropeptides(1).Theseisoformsaredifferentiallyexpressedbyvarioustissues(1).The7.6kDamatureIGF-IisidenticalbetweenisoformsandisgeneratedbyproteolyticremovaloftheN-andC-terminalregions.MaturehumanIGF-Ishares94%and96%aasequenceidentitywithmouseandratIGF-I,respectively(2),andexhibitscross-speciesactivity.Itshares64%aasequenceidentitywithmaturehumanIGF-II.CirculatingIGF-Iisproducedbyhepatocytes,whilelocalIGF-Iisproducedbymanyothertissuesinwhichithasparacrineeffects(1).IGF-Iinducestheproliferation,migration,anddifferentiationofawidevarietyofcelltypesduringdevelopmentandpostnatally(3).IGF-Iregulatesglucoseandfattyacidmetabolism,steroidhormoneactivity,andcartilageandbonemetabolism(4-7).Itplaysanimportantroleinmuscleregenerationandtumorprogression(1,8).IGF-IbindsIGF-IR,IGF-IIR,andtheinsulinreceptor,althoughitseffectsaremediatedprimarilybyIGF-IR(9).IGF-IassociationwithIGFbindingproteinsincreasesitsplasmahalf-lifeandmodulatesitsinteractionswithreceptors(10).

References:

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