Growth factor control of cultured rat uterine stromal cell proliferation is progesterone dependent

Uterine stromal cells undergo mitosis and differentiate into the decidua just prior to the expected time of implantation in humans and rodents. We have utilized a culture system that will be suitable for study of the molecular mechanisms regulating stromal cell proliferation. Stromal cells were isolated from the uteri of ovariectomized rats and were cultured in chemically defined medium. Cultured cells express the mesenchymal markers vimentin and desmin. They do not express the epithelial marker cytokeratin. Serum-starved stromal cells were stimulated to proliferate in a time frame consistent with the cell cycle through addition of a panel of growth factors (basic fibroblast growth factor [bFGF], epidermal growth factor, platelet-derived growth factor, transforming growth factor alpha, insulin-like growth factor I) and hormones to the culture medium. None of the growth factors tested significantly stimulated proliferation in the absence of progesterone. Furthermore, progesterone was the only steroid of those tested that stimulated mitosis in the presence of growth factors. Stromal cell proliferation in response to progesterone and bFGF was dose dependent and saturable. Addition of the progesterone receptor antagonist mifepristone (RU486) and an inhibitor of tyrosine kinase receptor activation (suramin) abolished stromal cell mitosis. Progesterone receptors and fibroblast growth factor receptor 1 (FGFR1) were identified by immunoblot analysis in proliferating stromal cells. Taken together, these results show that cultured stromal cells maintain progesterone-dependent cell cycle control that is mediated via progesterone receptors. Moreover, the data indicate that bFGF control of stromal cell proliferation is modulated via a specific isoform of FGFR1 containing the three-loop immunoglobulin-like domain.