Association of SH2-Containing Inositol Phosphatase 2 With the Insulin Resistance of Diabetic db/db Mice
- Hiroyuki Hori1,
- Toshiyasu Sasaoka2,
- Hajime Ishihara1,
- Tsutomu Wada1,
- Shihou Murakami1,
- Manabu Ishiki1 and
- Masashi Kobayashi1
- 1First Department of Internal Medicine, Toyama Medical & Pharmaceutical University, Toyama, Japan
- 2Department of Clinical Pharmacology, Toyama Medical & Pharmaceutical University, Toyama, Japan
SH-2-containing inositol 5′-phosphatase 2 (SHIP-2) is a physiologically important lipid phosphatase that functions to hydrolyze phosphatidylinositol (PI) 3-kinase product PI(3,4,5)P3 to PI(3,4)P2 in the negative regulation of insulin signaling. We investigated whether SHIP-2 is associated with the insulin resistance of diabetic db/db mice. The amount of SHIP-2 protein was elevated in quadriceps muscle and epididymal fat tissue, but not in the liver, of db/db mice relative to that in control db/+m mice. In accordance with the enhanced expression of SHIP-2, its localization at the membrane preparation was increased in the skeletal muscle and fat tissue of db/db mice. Insulin stimulation of PI 3-kinase activity was modestly decreased in skeletal muscle, fat tissue, and liver of db/db mice compared with that of db/+m mice. In addition to the modest decrease at the level of PI 3-kinase, the activity of Akt and protein kinase C (PKC)-ζ/λ, which are downstream molecules of PI 3-kinase, was more severely reduced in the skeletal muscle and fat tissue, but not in liver of db/db mice. Treatment with the insulin-sensitizing agent rosiglitazone decreased the elevated expression of SHIP-2 in the skeletal muscle and fat tissue of db/db mice. Insulin-induced Akt activation and PKC-ζ/λ phosphorylation were restored to the control level, although insulin-stimulated PI 3-kinase activation was minimally affected in the skeletal muscle and fat tissue of db/db mice. These results indicate that SHIP-2 is a novel molecule associated with insulin resistance in the skeletal muscle and fat tissue, and that insulin-induced activity of the downstream molecules of PI 3-kinase is decreased, at least in part, by the elevated expression of SHIP-2 in diabetic db/db mice.
Address correspondence and reprint requests to Dr. Toshiyasu Sasaoka, Department of Clinical Pharmacology, Toyama Medical & Pharmaceutical University, 2630 Sugitani, Toyama, 930-0194, Japan. E-mail:.
Received for publication 19 November 2001 and accepted in revised form 6 May 2002.
DTT, dithiothreitol; ECL, enhanced chemiluminescence; HES, HEPES EDTA sucrose; IRS, insulin receptor substrate; PI, phosphatidylinositol; PKC, protein kinase C; PMSF, phenylmethylsulfonyl fluoride; PVDM, polyvinylidene difluoride membrane; SHIP-2, SH-2−containing inositol 5′-phosphatase 2.