REGULATION OF PHOSPHATIDYLINOSITOL 3,4,5-TRISPHOSPHATE 5'-PHOSPHATASEACTIVITY BY INSULIN

Polyphosphoinositides are thought to be mediators of cellular signalin g pathways as well as regulators of cytoskeletal elements and membrane trafficking events. It has recently been demonstrated that a class of phos phatidylinositol (PI) 3,4,5-P-3 5'-phosphatases contains SH2 dom ains and proline-rich regions, which are present in many signaling pro teins. We report here that insulin stimulation of Chinese hamster ovar y cells (CHO-T) expressing human insulin receptors causes an 8-10-fold increase in PI 3,4,5-P-3 5'-phosphatase activity in anti-phosphotyros ine immunoprecipitates of the cell lysates, This insulin-sensitive pol yphosphoinositide 5'-phosphatase did not catalyze dephosphorylation of PI 4,5-P-2. No change in 5'-phosphatase activity was detected in insu lin receptor or IRS-1 immune complexes in response to insulin. However , insulin treatment of CHO-T cells markedly increased the PI 3,4,5-P-3 5'-phosphatase activity associated with She and Grb2. The insulin-reg ulated polyphosphoinositide 5'-phosphatase was not immunoreactive with antibody raised against the recently cloned SHIP 5'-phosphatase repor ted to associate with She and Grb2 in B lymphocytes. These data demons trate that insulin causes formation of complexes containing a PI 3,4,5 -P-3 5'-phosphatase, and Shc or Grb2, or both, suggesting an important role of this enzyme in insulin signaling.