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

Protein kinase C (PKC) delta is dramatically upregulated in the corpus lute um in the second half of pregnancy in the rat. To gain insight into the hor monal regulation of PKC delta expression, studies were undertaken to analyz e the regulation of PKC delta expression in a luteinized rat granulosa cell model. PKC delta 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. Cytochro me P350 cholesterol side chain cleavage enzyme expression was observed thro ughout the culture period, and a majority of the cells expressed steroidoge nic acute regulatory protein and responded to rat placental lactogen (rPL)- 1 by exhibiting hypertrophy, consistent with maintenance of the luteal phen otype. Both PKC delta protein and mRNA expression increased 3.5-4-fold with time of culture, and PKC delta mRNA expression could be eliminated by trea tment of cells with the PKC inhibitor GF109203X. E-2 caused a specific dose - and time-dependent increase in expression of PKC delta protein of twofold , whereas PKC delta 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 delta protein or mRNA ex pression, while treatment with 500 or 3000 ng/ml rPL-1 in the presence of E -2 significantly enhanced both PKC delta 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. E2 and rPL-1, cooperat e to regulate PKC delta expression ill luteinized granulosa cells. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.