Hormonal regulation of PKC-δ protein and mRNA levels in the rabbit corpus luteum

Abstract

We have previously reported that rabbit corpora lutea exhibit a prominent phosphorylated substrate protein at 76 kDa which corresponds to the autophosphorylated form of protein kinase C (PKC) δ and that the expression of PKC-δ protein is increased in rabbit corpora lutea of pseudopregnancy at least 2-fold when serum estrogen levels are raised by the presence of an estrogen implant inserted at the time of human chorionic gonadotropin (hCG)-induced ovulation. The purpose of the experiments described herein was to evaluate further the hormonal regulation of PKC-δ in the rabbit corpus luteum. Results demonstrate that luteal PKC-δ protein and mRNA are concomitantly induced some 5-fold within 48 h in response to an ovulatory surge of hCG; that, as in corpora lutea of pseudopregnancy, luteal PKC-δ expression is relatively constant during the life span of the corpus luteum following a fertile mating; that exogenous estrogen does not modulate the induction of luteal PKC-δ during luteinization but promotes an additional two-fold increase in steady state PKC-δ mRNA (and protein) levels in corpora lutea by day 10 of pseudopregnancy; and that luteal PKC-δ expression can be abruptly and reversibly modulated upon withdrawal and subsequent replacement of an estrogen implant to pseudopregnant rabbits. These results demonstrate that an ovulatory surge of luteinizing hormone induces the expression of PKC-δ mRNA and protein in rabbit corpora lutea, and that once the corpus luteum becomes estrogen responsive, estrogen then regulates expression of PKC-δ mRNA and protein.