Membrane 5α-pregnane-3,20-dione (5αP) receptors in MCF-7 and MCF-10A breast cancer cells are up-regulated by estradiol and 5αP and down-regulated by the progesterone metabolites, 3α-dihydroprogesterone and 20α-dihydroprogesterone, with associated cha

Previous studies have shown that the progesterone metabolite, 5α-pregnane-3,20-dione (5αP), exhibits mitogenic and metastatic activity in breast cell lines and that specific, high affinity receptors for 5αP are located in the plasma membrane fractions of tumorigenic (ER/PR-positive) MCF-7 cells. The aim of this study was to determine the effects of the mitogenic (estradiol; 5αP) and anti-mitogenic (3α-hydroxy-4-pregnen-20-one, 3αHP; 20α-hydroxy-4-pregnen-3-one, 20αHP) endogenous steroid hormones on 5αP receptor (5αP-R) numbers and on cell proliferation and adhesion of MCF-7 and MCF-10A cells. Exposure of MCF-7 cells for 24 h to estradiol or 5αP resulted in significant (p < 0.05-0.001) dose-dependent increases in 5αP-R levels. Conversely, treatment with 3αHP or 20αHP resulted in significant (p < 0.05-0.01) dose-dependent decreases in 5αP-R levels. Treatment with one mitogenic and one anti-mitogenic hormone resulted in inhibition of the mitogen-induced increases, whereas treatment with two mitogenic or two anti-mitogenic hormones resulted in additive effects on 5αP-R numbers. Treatments with cycloheximide and actinomycin D indicate that changes in 5αP-R levels depend upon transcription and translation. The non-tumorigenic breast cell line, MCF-10A, was also shown to posses specific, high affinity plasma membrane receptors for 5αP that were up-regulated by estradiol and 5αP and down-regulated by 3αHP. Estradiol binding was demonstrated in MCF-10A cell membrane fractions and may explain the estradiol action in these cells that lack intracellular ER. In both MCF-7 and MCF-10A cells, the increases in 5αP-R due to estradiol or 5αP, and decreases due to 3αHP or 20αHP correlate with respective increases and decreases in cell proliferation as well as detachment. These results show distribution of 5αP-R in several cell types and they provide further evidence of the significance of progesterone metabolites and their novel membrane-associated receptors in breast cancer stimulation and control. The findings that 3αHP and 20αHP down-regulate 5αP-R and suppress mitogenic and metastatic activity suggest that these endogenous anti-mitogenic progesterone metabolites deserve considerations in designing new breast cancer therapeutic agents.