HORMONAL CONTROL OF C-KINASE AND CORPUS LUTEUM FUNCTION

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.
Phosphorylation of proteins is one of the major post-translational
mechanisms by which cellular functions are regulated. We have recently
described another important messenger system in ovarian tissues which is
linked to protein phosphorylation. Receptor-mediated increases in second
messengers derived from phosphoinositide metabolism (diacylglycerol and
inositol phosphates) lead to the activation of a calcium- and
phospholipid-dependent protein kinase (C-kinase). The regulation of
phosphoinositide metabolism by LH and other hormones and the presence of
C-kinase in the corpus luteum suggest that the control of C-kinase activity
is related to the function of the corpus luteum. The specific aims of the
proposed research are to purify and further characterize this new protein
kinase and evaluate its physiological significance in rat and bovine
corpora lutea. The enzyme will be purified with the objectives of 1)
determining the specific co-factors required for C-kinase activity, 2)
producing monoclonal antibodies to C-kinase for the purpose of detection
and quantitation of C-kinase, and 3) determining the substrate specificity
of C-kinase. The physiological role for C-kinase 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 other factors known to regulate luteal function. The possible
involvement of C-kinase in the regulation of luteal function will be
determined by examining its role in 1) gonadotropin binding, 2) receptor
phosphorylation, 3) adenylate cyclase activation, and 4) progesterone
synthesis. These studies will be carried out by monitoring the
phosphorylation of both exogenous and endogenous substrate proteins. The
proposed studies on the ovarian C-kinase may provide new insight into the
mechanism of LH action and establish a link between hormonally-induced
changes in C-kinase activation and corpus luteum function.