PROSTAGLANDIN-F2-ALPHA ACTIVATES PROTEIN-KINASE-C IN HUMAN OVARIAN-CELLS

Recent studies in several non-primate species have suggested that prostaglandin F2alpha (PGF2alpha) inhibits luteal cell progesterone production by activating the calcium and phospholipid-dependent protein kinase, protein kinase C (PKC). This study investigated the presence of PKC in human ovarian cells and assessed the ability of PGF2alpha and its structural analogue, cloprostenol, to generate inositol polyphosphates and activate PKC. PKC was detected in cultured human granulosa-lutein cells and human luteal cells (from mid-late luteal phase). The major proportion of PKC detected was cytosol-associated in both cell types. Cloprostenol increased the generation of inositol polyphospates in cultured human granulosa-lutein cells in a dose- and time-dependent manner. In addition both cloprostenol and PGF2alpha activated PKC (as assessed by redistribution of enzyme activity from a principally cytosol-associated form to a membrane-associated form) in both granulosa-lutein and luteal cells. Short-term exposure of both cell types to phorbol myristate acetate (4beta-PMA) activated PKC, whilst prolonged exposure of human granulosa-lutein cells to 4beta-PMA led to a > 85% loss of total PKC activity. The inactive phorbol ester, 4alpha-PMA, had no effect on PKC activity when exposed to cells for up to 20 h. These results demonstrate the presence of PKC in human ovarian cells and the ability of PGF2alpha to induce translocation/activation of this kinase. The reported capacity of tumour promoting phorbol esters to mimic the inhibitory actions of PGF2alpha leads us to suggest that the activation of PKC is an essential component of the mechanism by which this eicosanoid inhibits lutropin (LH)-stimulated ovarian steroidogenesis.