Insulin-like growth factor-I-induced DNA synthesis in insulin-secreting cell line RINm5F is associated with phosphorylation of the insulin-like growth factor-I receptor and the insulin receptor substrate-2.
A proliferative effect of insulin-like growth factor-I (IGF-I) was previously shown in pancreatic islets. However, the mechanism under which IGF-I actions are exerted in insulin-secreting cells is not clear. The rat insulinoma cell line, RINm5F, was shown to have both IGF-I receptors and IGF-Il/mannose-6-phosphate receptors. IGF-I binding to cell surface receptors stimulated phosphorylation of 97 kDa and 93 kDa subunits of the IGF-I receptor and incorporation of [3H]thymidine into RINm5F cells. Both the IGF-I-induced protein phosphorylation and [3H]thymidine incorporation were abolished in the presence of the tyrosine kinase inhibitor, genistein. Under basal conditions, IGF-I did not induce insulin release or changes in cytosolic free Ca2+ concentration. Immunoprecipitation of proteins from RINm5F cells, using phosphotyrosine antibodies, followed by western blotting using antibody against IRS-1 revealed no distinct band of phosphorylated insulin receptor substrate (IRS)-1. Instead, tyrosine-phosphorylated IRS-2 was detected and stimulated by IGF-I when western blotting was performed using antibody against IRS-2. These results indicate that IRS-1 is not likely to be involved in IGF-I signalling in RINm5F cells. Hence, IGF-I stimulated DNA synthesis in RINm5F cells was associated with phosphorylation of IGF-I receptors and IRS-2.
Zhang
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Department of Molecular Medicine, Rolf Luft Center for Diabetes Research, Karolinska Institute, Stockholm, Sweden.
Berggren
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PO
Hansson
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A
Tally
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D000818:Animals; D002118:Calcium / Q000378:metabolism; D004247:DNA / Q000096:biosynthesis*; D019833:Genistein / Q000494:pharmacology; D007328:Insulin / Q000378:metabolism; D055504:Insulin Receptor Substrate Proteins; D000078790:Insulin Secretion; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D007340:Insulinoma / Q000378:metabolism*; D047908:Intracellular Signaling Peptides and Proteins; D010750:Phosphoproteins / Q000378:metabolism*; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors; D051381:Rats; D017526:Receptor, IGF Type 1 / Q000378:metabolism*; D013936:Thymidine / Q000378:metabolism; D014407:Tumor Cells, Cultured
D007328:Insulin; D055504:Insulin Receptor Substrate Proteins; D047908:Intracellular Signaling Peptides and Proteins; C526299:Irs2 protein, rat; D010750:Phosphoproteins; D007334:Insulin-Like Growth Factor I; D004247:DNA; D019833:Genistein; D011505:Protein-Tyrosine Kinases; D017526:Receptor, IGF Type 1; D002118:Calcium; D013936:Thymidine