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(203) GONADOTROPIN-INDUCED DEPHOSPHORYLATION OF EXTRACELLULAR-SIGNAL REGULATED KINASES AUGMENTS STEROIDOGENESIS IN BOVINE GRANULOSA AND THECA CELLS. Tajima, Kimihisa1, Yoshii, Kumiko1, Fukuda, Shin1, Orisaka, Makoto1, Amsterdam, Abraham2, Kotsuji, Fumikazu1, 1 University of Fukui, Fukui, Japan2 The Weizmann Institute of Science, Rehovot, Israel ABSTRACT- It has been reported that gonadotropins promoted the phosphorylation of extracellular-signal regulated kinase (ERK) in rat and human granulosa cells. In the present work we demonstrate that bovine granulosa cells obtained from small vesicular ovarian follicle (3-5 mm in diameter) respond to FSH as well as to forskolin in dephosphorylation of ERK. Addition of H89 (PKA inhibitor) and sodium orthovanadate (protein tyrosine phosphatases inhibitor) to the cell culture attenuated the dephosphorylation of ERK but Okadaic acid (protein phosphatase 1 ,2A inhibitor) had no effect on it. Moreover, the potent MAPK inhibitors, PD98059 and U0126, augmented progesterone production in these cell cultures concomitantly with specific elevation of intracellular steroidogenic acute regulatory protein (StAR). Intracellular levels of the cytochrome P450 side-chain cleavage enzyme system were not affected by the MAPK inhibitors. Similar observations were made with bovine theca cells stimulated with LH or forskolin. Elevation of StAR expression by the MAPK inhibitors involved elevation of StAR mRNA, as demonstrated by RT-PCR in the granulosa and theca cells. Immunocytochemical studies using specific antibodies to StAR demonstrated a higher content of mitochondrial StAR in control as well as in gonadotropin-stimulated cells in the presence of U0126 compared with cells not treated with U0126. Thus, inactivation of the MAPK cascade by gonadotropins may serve as a novel mechanism to regulate steroidogenesis via augmentation of StAR expression. Moreover, it is suggested that the balance between kinases and phoshatases modulates ERK activity in the regulation of StAR expression and the mode of modulation is different among species. KEY WORDS: theca, StAR, granulosa, ERK |
