Members of the protein kinase C (PKC) family of serine/threonine kinases play critical roles in the regulation of cellular differentiation and proliferation of diverse cell types. Protein kinase C (PKC) is the major phorbol ester receptor. Parker et al. (1986) purified this protein from bovine brain and through the use of oligonucleotide probes based on partial amino acid sequence, derived cDNA clones from bovine
cDNA libraries. Thus, the complete amino acid sequence of bovine protein kinase C was determined, revealing a
domain structure. Activation of PKC by calcium ions and the second messenger diacylglycerol is thought to play a
central role in the induction of cellular responses to a variety of ligand-receptor systems and in the regulation of cellular
responsiveness to external stimuli.
General function
Intracellular signaling cascade
Comment
Peters CA, et al 1999 reported that treatment of luteinized rat granulosa cells with phorbol myristate acetate, a known activator of PKC, promoted a 7-fold increase in HSP-27 phosphorylation by PKC delta. Similarly, immunoreactivity with the phospho-epitope-specific PKC delta antibody was increased in extracts prepared from luteinized granulosa cells treated with phorbol myristate acetate or following in vitro activation of recombinant PKC delta.
Cellular localization
Cytoplasmic
Comment
Ovarian function
Luteinization, Oocyte maturation
Comment
Cutler RE Jr et al reported the regulation of delta protein kinase C during rat ovarian
differentiation.
Hydroxyapatite (HAP) column chromatography of rat luteal tissue revealed the presence of multiple forms of PKC (alpha, beta, delta, zeta).
Identification of the PKC isoforms was based upon elution positions from HAP
column chromatography and immunoreactivity. The delta PKC isoform was
identified as the major Ca(2+)-independent form of PKC present in rat luteal
tissue. The Ca(2+)-independent, lipid-dependent phosphorylation of the 80-kDa
delta PKC was readily detectable in soluble luteal extracts and was shown to
reflect autophosphorylation of delta PKC. To evaluate the regulation of PKC
isoforms during ovarian differentiation, PKC protein levels were compared
between preovulatory follicle-enriched ovaries and corpora lutea obtained on day
16 of pregnancy. Levels of delta PKC protein were greatly elevated in corpora
lutea compared to levels in preovulatory follicles. Levels of delta PKC mRNA were also
higher in corpora lutea than in preovulatory follicles.
Peters CA, et al 2000 reported that PRL/ rat placental lactogen (rPL-10 induction of relaxin expression in cultured rat granulosa-luteal cells
required protein kinase C (PKC) delta, based on the ability of the
preferential PKC delta inhibitor rottlerin to abolish induction of relaxin
expression. Direct activation of PKC by phorbol myristate acetate, however,
was not sufficient to promote induction of relaxin mRNA expression. Their results demonstrate that PRL/rPL-1
promotes relaxin expression in luteal cells and that this event is mediated,
at least in part, via PKC delta.
Maizels ET et al reported that immunoblot
analysis confirmed that luteal levels of PKC delta were increased by estrogen
treatment.
Ovarian localization
Oocyte, Granulosa, Luteal cells
Comment
Peluso JJ, et al reported that basic fibroblast growth factor maintains calcium homeostasis
and granulosa cell viability by stimulating calcium efflux via
a PKC delta-dependent pathway.
Previous studies have demonstrated that basic fibroblast growth factor
prevents granulosa cell apoptosis. Granulosa cells, as well as spontaneously immortalized
granulosa cells, were shown to express PKC delta, -lambda, and -zeta. Finally,
the PKC delta -specific inhibitor, rottlerin, blocked basic fibroblast growth
factor's antiapoptotic action in granulosa cells and spontaneously
immortalized granulosa cells. These studies suggest that basic fibroblast
growth factor regulates intracellular free calcium through a PKC delta
-dependent mechanism and that a sustained increase in intracellular free
calcium is sufficient to induce and is required for granulosa cell apoptosis.
Characterization of Protein Kinase C-{delta} in Mouse Oocytes Throughout Meiotic Maturation and Following Egg Activation.
Viveiros MM,et al .
Changes in protein kinase C (PKC) activity influence the progression of meiosis; however, the specific function of the various PKC isoforms in female gametes is not known. In the current study, the protein expression and subcellular distribution profile of PKC-delta (PKC-delta), a novel isoform of the PKC family, was determined in mouse oocytes undergoing meiotic maturation and following egg activation. The full-length protein was observed as a doublet (76 and 78 kDa) on Western blot analysis. A smaller (47 kDa) carboxyl-terminal fragment, presumably the truncated catalytic domain of PKC-delta, was also strongly expressed. Both the full-length protein and the catalytic fragment became phosphorylated coincident with the resumption of meiosis and remained phosphorylated throughout metaphase II (MII) arrest. Immunofluorescence staining showed PKC-delta distributed diffusely throughout the cytoplasm of oocytes during maturation and associated with the spindle apparatus during the first meiotic division. Discrete foci of the protein also localized with the chromosomes in some mature eggs. Following the completion of meiosis, PKC-delta became dephosphorylated within 2 h of in vitro fertilization or parthenogenetic activation. The protein also accumulated in the nuclei of early embryos and was phosphorylated during M-phase of the initial mitotic cleavage division. By the two-cell stage, expression of the truncated catalytic fragment was minimal. These data demonstrate that the subcellular distribution and posttranslational modification of PKC-delta is cell cycle dependent, suggesting that its activity and/or function likely vary with the progression of meiosis and egg activation.