Dissociation of pp70 ribosomal protein S6 kinase from insulin-stimulated glucose transport in 3T3-L1 adipocytes.

Overview

The metabolic and mitogenic actions of insulin have been proposed to be mediated by cellular serine/threonine kinases such as the ribosomal protein S6 kinases pp70-S6 (pp70-S6 kinase) and pp90rsk and the erk-encoded mitogen-activated protein kinases (pp42mapk and pp44mapk). Rapamycin completely blocked activation of pp70-S6 kinase by insulin in 3T3-L1 adipocytes, but did not inhibit insulin-stimulated glucose transport, translocation of GLUT4 to the cell surface, or activation of pp90rsk or pp44mapk by insulin. Concordant with the inhibition of kinase activity, rapamycin prevented the insulin-induced decrease in mobility of pp70-S6 kinase visualized by SDS-polyacrylamide gel electrophoresis, reflecting a reduction in the hormone-stimulated phosphorylation of the enzyme. The structurally related macrolide, FK506, had no effect on pp70-S6 kinase or hexose uptake. These data demonstrate that rapamycin blocks insulin activation of pp70-S6 kinase in 3T3-L1 adipocytes and that pp70-S6 kinase is not required in the signaling pathway leading to insulin-stimulated glucose transport.