Regulation of δ protein kinase C during rat ovarian differentiation

Abstract

Studies were undertaken to classify protein kinase C (PKC) forms present in rat corpora lutea and to begin to evaluate their regulation during ovarian differentiation. Hydroxyapatite (HAP) column chromatography of rat luteal tissue revealed the presence of multiple forms of PKC (α, β, δ, ζ). Identification of the PKC isoforms was based upon elution positions from HAP column chromatography and immunoreactivity. The δ 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 δ PKC was readily detectable in soluble luteal extracts and was shown to reflect autophosphorylation of δ 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 δ PKC protein were greatly elevated in corpora lutea compared to levels in preovulatory follicles. In contrast, levels of α and β PKC protein remained constant while levels of ζ PKC were slightly higher in the follicular than the luteal extract. Levels of δ PKC mRNA were also higher in corpora lutea than in preovulatory follicles. These results are the first to demonstrate the physiological regulation of δ PKC with follicular differentiation into corpora lutea and implicate a role for this prominent PKC form in the corpus luteum during pregnancy.