Insulin receptor substrate 1 mediates insulin and insulin-like growth factor I-stimulated maturation of Xenopus oocytes.
Insulin and insulin-like growth factor I (IGF-I) initiate cellular functions by activating their homologous tyrosine kinase receptors. In most mammalian cell types, this results in rapid tyrosine phosphorylation of a high-molecular-weight substrate termed insulin receptor substrate 1 (IRS-1). Previous studies suggest that IRS-1 may act as a "docking" protein that noncovalently associates with certain signal-transducing molecules containing src homology 2 domains; however, direct evidence for the role of IRS-1 in the final biological actions of these hormones is still lacking. We have developed a reconstitution system to study the role of IRS-1 in insulin and IGF-I signaling, taking advantage of the fact that Xenopus oocytes possess endogenous IGF-I receptors but have little or no IRS-1, as determined by immunoblotting with anti-IRS-1 and antiphosphotyrosine antibodies. After microinjection of IRS-1 protein produced in a baculovirus expression system, tyrosyl phosphorylation of injected IRS-1 is stimulated by both insulin and IGF-I in a concentration-dependent manner, with IGF-I more potent than insulin. Furthermore, after IRS-1 injection, both hormones induce a maturation response that correlates well with the amount of injected IRS-1. By contrast, overexpression of human insulin receptors in the Xenopus oocytes does not enhance either IRS-1 phosphorylation or oocyte maturation response upon insulin stimulation. These results demonstrate that IRS-1 serves a critical role in linking IGF-I and insulin to their final cellular responses.
Chuang
L M
LM
Research Division, Joslin Diabetes Center, Boston, MA 02215.
Myers
M G
MG
Seidner
G A
GA
Birnbaum
M J
MJ
White
M F
MF
Kahn
C R
CR
D000818:Animals; D005260:Female; D015870:Gene Expression; D006801:Humans; D007328:Insulin / Q000494:pharmacology*; D055504:Insulin Receptor Substrate Proteins; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D009865:Oocytes / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D010750:Phosphoproteins / Q000235:genetics / Q000494:pharmacology*; D019000:Phosphotyrosine; D017526:Receptor, IGF Type 1 / Q000187:drug effects / Q000502:physiology*; D011972:Receptor, Insulin / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D011994:Recombinant Proteins / Q000494:pharmacology; D014162:Transfection; D014443:Tyrosine / Q000031:analogs & derivatives / Q000378:metabolism; D029867:Xenopus Proteins; D014982:Xenopus laevis
C526292:IRS1 protein, human; D007328:Insulin; D055504:Insulin Receptor Substrate Proteins; D010750:Phosphoproteins; D011994:Recombinant Proteins; D029867:Xenopus Proteins; C526294:irs1 protein, Xenopus; D019000:Phosphotyrosine; D014443:Tyrosine; D007334:Insulin-Like Growth Factor I; D017526:Receptor, IGF Type 1; D011972:Receptor, Insulin