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Impact of Src Homology 2-Containing Inositol 5'-Phosphatase 2 Gene Polymorphisms Detected in a Japanese Population on Insulin Signaling

Department of Clinical Pharmacology (S.K., T.S., S.Y., H.T., S.K., I.K.) and First Department of Internal Medicine (S.M., K.F., T.W., M.K.), Toyama Medical and Pharmaceutical University, Toyama 930-0194, Japan; and Sainou Hospital (H.I.), Toyama 930-0887, Japan

Address all correspondence and requests for reprints to: Toshiyasu Sasaoka, M.D., Ph.D., Department of Clinical Pharmacology, Toyama Medical and Pharmaceutical University, 2630 Sugitani, Toyama 930-0194, Japan. E-mail: tsasaoka-tym{at}umin.ac.jp.

Src homology 2-containing 5'-inositol phosphatase 2 (SHIP2) is known to be one of lipid phosphatases converting PI(3,4,5)P₃ to PI(3,4)P₂ in the negative regulation of insulin signaling with the fundamental impact on the state of insulin resistance. To clarify the possible involvement of SHIP2 in the pathogenesis of human type 2 diabetes, we examined the relation of human SHIP2 gene polymorphisms to type 2 diabetes in a Japanese population. We identified 10 polymorphisms including four missense mutations. Among them, single nucleotide polymorphism (SNP)3 (L632I) was located in the 5'-phosphatase catalytic region, and SNP5 (N982S) was adjacent to the phosphotyrosine binding domain binding consensus motif in the C terminus. SNP3 was found more frequently in control subjects than in type 2 diabetic patients, suggesting that this mutation might protect from insulin resistance. Transfection study showed that expression of SNP3-SHIP2 inhibited insulin-induced PI(3,4,5)P₃ production and Akt2 phosphorylation less potently than expression of wild-type SHIP2 in CHO-IR cells. Insulin-induced tyrosine phosphorylation of SNP5-SHIP2 was decreased compared with that of wild-type SHIP2, resulting in increased Shc/Grb2 association and MAPK activation. These results indicate that the polymorphisms of SHIP2 are implicated, at least in part, in type 2 diabetes, possibly by affecting the metabolic and/or mitogenic insulin signaling in the Japanese population

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