Progesterone Pretreatment Inhibits the Expression of c-ski mRNA and Epithelial Cell Proliferation Induced by Estrogen in the Rat Uterus.

Progesterone has been shown to inhibit the proliferative action of estrogen in the uterine epithelial cells. We have previously reported that the expression of cellular protooncogene, c-ski, is induced by estrogen treatment in the uterine epithelial cells of ovariectomized rats, and suggested its role in the proliferation of uterine epithelial cells. In the present study, we examined whether progesterone pretreatment would affect the estrogen-induced expression of c-ski mRNA in the uterine epithelial cells. In situ hybridization analysis revealed that estrogen-induced expression of c-ski mRNA was attenuated by progesterone pretreatment in the uterine luminal epithelial cells, accompanied by the decrease in the number of proliferating cell nuclear antigen-positive cells among the luminal epithelial cells. The results obtained further support our hypothesis that c-ski plays a role in proliferation of uterine epithelial cells and mediates the proliferative action of estrogen.