The period immediately after exercise is characterized by enhanced insulin action in skeletal muscle, and on the molecular level, by a marked increase in insulin-stimulated, phosphotyrosine-associated phosphatidylinositol (PI) 3-kinase activity. Because the increase in PI 3-kinase activity cannot be explained by increased insulin receptor substrate (IRS)-1 signaling, the present study examined whether this effect is mediated by enhanced IRS-2 signaling. In wild-type (WT) mice, insulin increased IRS-2 tyrosine phosphorylation (∼2.5-fold) and IRS-2−associated PI 3-kinase activity (∼3-fold). Treadmill exercise, per se, had no effect on IRS-2 signaling, but in the period immediately after exercise, there was a further increase in insulin-stimulated IRS-2 tyrosine phosphorylation (∼3.5-fold) and IRS-2−associated PI 3-kinase activity (∼5-fold). In IRS-2−deficient (IRS-2−/−) mice, the increase in insulin-stimulated, phosphotyrosine-associated PI 3-kinase activity was attenuated as compared with WT mice. However, in IRS-2−/− mice, the insulin-stimulated, phosphotyrosine-associated PI 3-kinase response after exercise was slightly higher than the insulin-stimulated response alone. In conclusion, IRS-2 tyrosine phosphorylation and associated PI 3-kinase activity are markedly enhanced by insulin in the immediate period after exercise. IRS-2 signaling can partially account for the increase in insulin-stimulated phosphotyrosine-associated PI 3-kinase activity after exercise.
Address correspondence and reprint requests to Laurie J. Goodyear, Metabolism Section, Joslin Diabetes Center, One Joslin Pl., Boston, MA 02215. E-mail:.
Received for publication 20 June 2001 and accepted in revised form 1 November 2001.
2DG, 2-deoxy-glucose; IRS, insulin receptor substrate; MAP, mitogen-activated protein; PI, phosphatidylinositol; PMSF, phenylmethylsulfonyl fluoride; WT, wild-type.