Regulation of PKC δ expression by estrogen and rat placental lactogen-1 in luteinized rat ovarian granulosa cells

Protein kinase C (PKC) δ is dramatically upregulated in the corpus luteum in the second half of pregnancy in the rat. To gain insight into the hormonal regulation of PKC δ expression, studies were undertaken to analyze the regulation of PKC δ expression in a luteinized rat granulosa cell model. PKC δ protein expression was evaluated in luteinized granulosa cells, isolated from human (h)CG-treated immature female rats 7 h after the injection of an ovulatory dose of hCG and cultured up to 12 days. Cytochrome P450 cholesterol side chain cleavage enzyme expression was observed throughout the culture period, and a majority of the cells expressed steroidogenic acute regulatory protein and responded to rat placental lactogen (rPL)-1 by exhibiting hypertrophy, consistent with maintenance of the luteal phenotype. Both PKC δ protein and mRNA expression increased 3.5–4-fold with time of culture, and PKC δ mRNA expression could be eliminated by treatment of cells with the PKC inhibitor GF109203X. E 2 caused a specific dose- and time-dependent increase in expression of PKC δ protein of twofold, whereas PKC δ mRNA was unaffected by E 2 over a 12-day culture period. Treatment of cells with 500 ng/ml rPL-1 for the final 4 days of a 12-day culture in the absence of E 2 had no effect on PKC δ protein or mRNA expression, while treatment with 500 or 3000 ng/ml rPL-1 in the presence of E 2 significantly enhanced both PKC δ protein and mRNA expression (up to threefold). These results show that two of the major regulators of luteal function in the second half of pregnancy in the rat, E 2 and rPL-1, cooperate to regulate PKC δ expression in luteinized granulosa cells.