Effect of Retinoic Acid on Proliferation of Estrogen-responsive Transformed Murine Leydig Cells in Serum-free Culture

Abstract

B-1 F cells, one of the sublines established from mouse Leydig cell tumor, have been found to be maintained as an estrogen-responsive cell line under the serum-free culture conditions. Reported results that retinoids have action mechanisms similar to those of estrogen prompted us to examine the effect of retinoids on the proliferation of B-1 F cells.

Stimulation of B-1 F cell growth by retinoic acid in a dose-dependent manner was observed, whereas retinoic acid did not promote but inhibited the proliferation of MCF-7 cells (estrogen- and retinoic acid receptor-positive human breast cancer cells). To elucidate the mechanism of retinoic acid-dependent cell growth, simultaneous treatment with retinoic acid and estradiol was carried out. The result did not show the additive effect on B-1 F cell growth. Hydroxytamoxifen, a potent antiestrogen, inhibited not only estradiol-dependent but also retinoic acid-dependent cell growth. However, retinoic acid failed to be associated with estrogen receptor, suggesting that retinoic acid induced enhancement of B-1 cell growth through its interaction with retinoic acid receptor. Northern blot analyses of polyadenylated RNA with complementary DNA probes for human retinoic acid receptor α, β, and γ revealed the presence of transcripts encoded by retinoic acid receptor α gene in B-1 F cells.

These results would suggest that enhancement of the B-1 F cell growth is mediated through interaction of retinoic acid with retinoic acid receptor α. This stimulatory activity is inhibited by estrogen receptor complexed with hydroxytamoxifen.