Molecular cloning of rat SH2-containing inositol phosphatase 2 (SHIP2) and its role in the regulation of insulin signaling

SH2-containing inositol 5'-phosphatase (SHIP) plays a negative regulatory role in hematopoietic cells. We have now cloned the rat SHIP isozyme (SHIP2) cDNA from skeletal muscle, which is one of the most important target tissue of insulin action. Rat SHIPS cDNA encodes a 1183-amino-acid protein that is 45% identical with rat SHIP. Rat SHIPS contains an aminoterminal SH2 domain, a central 5'-phosphoinositol phosphatase activity domain, and a phosphotyrosine binding (PTB) consensus sequence and a proline-rich region at the carboxyl tail. Specific antibodies to SHIPS were raised and the function of SHIPS was studied by stably overexpressing rat SHIPS in Rat1 fibroblasts expressing human insulin receptors (HIRc). Endogenous SHIPS underwent insulin-mediated tyrosine phosphorylation and phosphorylation was markedly increased when SHIPS was overexpressed. Although overexpression of SHIPS did not affect insulin-induced tyrosine phosphorylation of the insulin receptor P-subunit and Shc, subsequent association of Shc with Grb2 was inhibited, possibly by competition between the SH2 domains of SHIPS and Grb2 for the Shc phosphotyrosine. As a result, insulin-stimulated MAP kinase activation was reduced in SHIP2-over-expressing cells. Insulin-induced tyrosine phosphorylation of IRS-1, IRS-1 association with the p85 subunit of PI3-kinase, and PI3-kinase activation were not affected by overexpression of SHIPS. Interestingly, although both PtdIns-(3,4,5)P3 and PtdIns(3,4)P2 have been implicated in the regulation of Akt activity in vitro, overexpression of SHIPS inhibited insulin-induced Akt activation, presumably by its 5'-inositol phosphatase activity. Furthermore, insulin-induced thymidine incorporation was decreased by overexpression of SHIPS. These results indicate that SHIPS plays a negative regulatory role in insulin-induced mitogenesis, and regulation of the Shc Grb2 complex and of the downstream products of PI3-kinase provides possible mechanisms of SHIPS action in insulin signaling. (C) 1999 Academic Press.