The classical progesterone receptor associates with p42 MAPK and is involved in phosphatidylinositol 3kinase signaling in Xenopus oocytes

The induction of Xenopus laevis oocyte maturation by progesterone is a striking example of a steroid hor-mone-mediated event that does not require transcrip-tion. Here we have investigated the role of the classical progesterone receptor in this nongenomic signaling. The Xenopus progesterone receptor (XPR) was pre-dominantly cytoplasmic; however, a significant frac-tion (5%) of one form of the receptor (p82 XPR) was associated with the plasma membrane-containing P-10,000 fraction, compatible with the observation that membrane-impermeant derivatives of progesterone can induce maturation. XPR co-precipitated with ac-tive phosphatidylinositol 3-kinase. The phosphatidyli-nositol 3-kinase (PI3-K) inhibitor wortmannin delayed progesterone-induced maturation and completel