The endogenous progesterone metabolite, 5a-pregnane-3,20-dione, decreases cell-substrate attachment, adhesion plaques, vinculin expression, and polymerized F-actin in MCF-7 breast cancer cells.

Tumorous human breast tissue readily converts progesterone to 5alpha-pregnane-3,20-dione (5alphaP), and this metabolite has been shown to stimulate proliferation and to decrease adhesion of MCF-7 breast cancer cells. To determine the mechanisms of action of 5alphaP on cell adhesion, MCF-7 cells were grown without or with 5alphaP (10(-9)-10(-5) M), and the effects on cell and nuclear morphology, adhesion plaques, vinculin and actin expression, actin polymerization, and microfilament distribution were examined by immunohistochemistry, morphometry (using confocal microscopy and digital computer imaging analysis), and Western blotting. Treatment of cells with 10(-9)-10(-6) M 5alphaP resulted in dose-dependent decreases in cell area, cell-to-cell contacts, and attachment to the substratum, and increases in variation in nuclear area. These changes in the 5alphaP-treated cells were accompanied by decreases in vinculin-containing adhesion plaques, vinculin expression, polymerized actin stress fibers, and decreases in insoluble and increases in soluble actin fractions. The results suggest that the observed decreases in adhesion and increases in cell proliferation following 5alphaP treatment may be owing to depolymerization of actin and decreased expression of actin and vinculin. We conclude that the endogenous progesterone metabolite, 5alphaP, may be involved in promoting breast neoplasia and metastasis by affecting adhesion and cytoskeletal molecules.