Although many of the effects of luteinizing hormone (LH) in the corpus luteum are thought to be mediated by cAMP, the exact mechanism of action of LH is unknown. It is presumed that the LH-induced events in ovarian tissues mediated by cAMP occur via cAMP-dependent protein kinases. Fluxes in cellular calcium may also have a mediatory role in the action of LH in ovarian tissues. Like cAMP, calcium may regulate cellular function through phosphorylation of endogenous substrate proteins. Phosphorylation of proteins is one of the major post-translational mechanisms by which cellular functions are regulated. Receptor-mediated alterations in phospholipid metabolism are also known to control cellular activity, including steroidogenesis in endocrine tissues. A new species of cyclic nucleotide-independent protein kinase has been discovered in a number of tissues. This protein kinase is selectively activated by the simultaneous presence of calcium and phospholipid. Research from this laboratory has confirmed the presence of this phospholipid-sensitive, calcium-dependent protein kinase in rat ovarian tissues and bovine corpora lutea. The objectives of the proposed research are to further characterize this new protein kinase and evaluate its physiological significance in rat and bovine corpora lutea. Utilizing information gathered from experiments on crude enzyme preparations, the enzyme will be partially purified and the specific calcium and phospholipid requirements will be determined. The physiological role for this enzyme will be examined by 1) determining whether or not enzyme activity varies throughout the life span of the corpus luteum and 2) determining if enzyme activity is regulated by LH or or others factors known to regulate luteal function. These studies will be carried out by monitoring the phosphorylation of both exogenous and endogenous substrate proteins. The proposed studies on the ovarian phospholipid-sensitive, calcium-dependent protein kinase may provide new insight into the mechanism of LH action and establish a link between hormonally-induced changes in phospholipid metabolism and corpus luteum function.
