Characteristics of steroid hormone receptors in cultured MC3T3-E1 osteoblastic cells and effect of steroid hormones on cell proliferation.

We examined the binding characteristics of three kinds of steroid hormones--estrogen, androgen, and glucocorticoid--in cultured MC3T3-E1 mouse osteoblastic cells by whole-cell binding assay. The binding studies revealed the presence of a single class of high-affinity binding sites for [3H]17 beta-estradiol, [3H]mibolerone (a synthetic androgen), and [3H]triamcinolone acetonide (a synthetic glucocorticoid). The numbers of binding sites for these steroid hormones were found to be 4534 +/- 819, 14312 +/- 1884, and 24898 +/- 655 sites/cell; and the Kd values were 8.57 +/- 0.62 x 10(-10) M, 1.12 +/- 0.19 x 10(-9) M, and 6.08 +/- 1.24 x 10(-10) M, respectively. We also examined the effects of steroid hormones on the proliferation of MC3T3-E1 cells. 17 beta-estradiol significantly stimulated the proliferation of the cells (130-150% of control). Dihydrotestosterone also significantly stimulated the proliferation of the cells (115% of control); the effect was, however, much less potent than that of 17 beta-estradiol, although the number of binding sites was approximately three times more than that of 17 beta estradiol. Triamcinolone acetonide and dexamethasone had no effect on cell proliferation. These results suggest that estrogen and androgen act directly on osteoblastic cells through a receptor-mediated mechanism, and that androgen is much less potent than estrogen in stimulating the proliferation of MC3T3-E1 osteoblastic cells.