Oncogenic Ras-induced germinal vesicle breakdown is independent of phosphatidylinositol 3-kinase in Xenopus oocytes

• Published in: FEBS letters 1999-05, Vol.451 (3), p.284-288
• Main Authors: López-Hernández, Eva, Santos, Eugenio
• Format: Article
• Language: English
• Subjects: Androstadienes - pharmacology; Animals; Cell Nucleus - metabolism; Chromones - pharmacology; Enzyme Inhibitors - pharmacology; Germinal vesicle breakdown; Hypoglycemic Agents - pharmacology; Insulin; Insulin - pharmacology; Insulin Antagonists - pharmacology; Meiosis; Morpholines - pharmacology; Oocytes - cytology; Oocytes - metabolism; Phosphatidylinositol 3-kinase; Phosphatidylinositol 3-Kinases - metabolism; Ras; ras Proteins - metabolism; Signal transduction; Signal Transduction - drug effects; Wortmannin; Xenopus; Xenopus oocyte
• ISSN: 0014-5793; 1873-3468
• DOI: 10.1016/S0014-5793(99)00595-5

A number of reports have identified phosphatidylinositol 3-kinase as a downstream effector of Ras in various cellular settings, in contrast to others supporting the notion that phosphatidylinositol 3-kinase acts upstream of Ras. Here, we used Xenopus oocytes, a model of Ras-mediated cell cycle progression (G2/M transition) to analyze the contribution of phosphatidylinositol 3-kinase to insulin/Ras-dependent signaling pathways leading to germinal vesicle breakdown and to ascertain whether phosphatidylinositol 3-kinase acts upstream or downstream of Ras in those signaling pathways. We analyzed the process of meiotic maturation induced by progesterone, insulin or micro-injected oncogenic Ras (Lys12) proteins in the presence and absence of specific inhibitors of phosphatidylinositol 3-kinase activity. As expected, the progesterone-induced maturation was independent of phosphatidylinositol 3-kinase since similar rates of germinal vesicle breakdown were produced by the hormone in the presence and absence of wortmannin and LY294002. In contrast, insulin-induced germinal vesicle breakdown was completely blocked by pre-incubation with the inhibitors prior to insulin treatment. Interestingly, similar rates of germinal vesicle breakdown were obtained in Ras (Lys12)-injected oocytes, independently of whether or not they had been pre-treated with phosphatidylinositol 3-kinase inhibitors. The effect of wortmannin or LY294002 on MAPK and Akt activation by progesterone, insulin or Ras was also analyzed. Whereas insulin activated those kinases in a phosphatidylinositol 3-kinase-dependent manner, progesterone and Ras were able to activate those kinases in the absence of phosphatidylinositol 3-kinase activity. Since Ras is a necessary and sufficient downstream component of insulin signaling pathways leading to germinal vesicle breakdown, these observations demonstrate that phosphatidylinositol 3-kinase is not a downstream effector of Ras in insulin/Ras-dependent signaling pathways leading to entry into the M phase in Xenopus oocytes.