CORPORA LUTEAL CA 2+ AND LIPID DEPENDENT PROTEIN KINASE

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.