Differential effect of PKC isoform on insulin- and phorbol ester-stimulated glucose uptake mechanism in rat adipocytes

Insulin stimulates glucose uptake in association with phosphatidylinositol (PI) 3-kinase activation mechanisms in rat adipocytes. Insulin stimulated g lucose uptake to 6.5-fold, and 12-o-tetradecanoyl phorbol 13-acetate (TPA) also stimulated glucose uptake to 4.5-fold in rat adipocytes. We examined t hese differences in glucose uptake, PKC zeta activation, and PI 3-kinase ac tivation after stimulation with insulin and TPA. TPA stimulated PI 3-kinase activity and increased the p85 subunit of PI 3-kinase immunoreactivity in anti-phosphotyrosine antibody-immunoprecipitated protein. Insulin and TPA p rovoked increases in membrane PKC zeta immunoreactivity. The PI 3-kinase in hibitor, wortmannin, suppressed insulin-induced increases in glucose uptake , PI 3-kinase activity, and PKC zeta activation. Wortmannin also suppressed TPA-induced PI 3-kinase activity and PKC zeta activation but suppressed TP A-induced glucose uptake to only a small extent. The PKC inhibitor, Go6976, which only inhibits conventional PKC alpha and -, suppressed TPA-induced g lucose uptake, but suppressed insulin-induced glucose uptake to only a smal l extent. On the other hand, the PKC inhibitor, RO32-0432, which inhibits c onventional, novel, and atypical PKCs, markedly suppressed both insulin- an d TPA-induced glucose uptake. These results suggest that insulin-induced gl ucose uptake is mainly mediated by PI 3-kinase-PKC zeta signaling, whereas phorbol ester-induced glucose uptake is mainly mediated by conventional PKC despite PI 3-kinase and PKC zeta activations.