Involvement of Phosphatidylinositol 3 Kinase in the Progesterone-Induced Oocyte Maturation in Rana dybowskii

Previously, we observed that 70-kDa ribosomal protein S6 kinase (p70s6k) plays an essential role during the early phase of oocyte maturation in Rana dybowskii. To investigate further the early signal transduction components involved in this process, the possible role of phosphatidylinositol- 3 kinase (PI3 kinase) during oocyte maturation was examined. Progesterone-induced oocyte maturation was significantly inhibited by wortmannin and LY294002, specific inhibitors of PI3 kinase. In contrast, protein kinase C activator 12-0-tetradecanoylphorbol-13- acetate-induced oocyte maturation was not inhibited by wortmannin. Protein synthesis was also significantly suppressed by wortmannin treatment during oocyte maturation. Moreover, PI3 kinase inhibitor suppressed progesterone- induced phosphorylation of S6 kinase in a dose-dependent manner. Likewise, PI3 kinase inhibitors significantly inhibited the phosphorylation of mitogenactivated protein (MAP) kinase which was increased during oocyte maturation. Finally, progesterone-induced H1 kinase activity was also inhibited by PI3 kinase inhibitors in a dose-dependent manner. Taken together, these results suggest that PI3 kinase is an initial component of the signal transduction pathway which precedes p70s6k,MAP kinase, and MPF production during progesteroneinduced maturation of amphibian oocyte