Estrogen and the selective estrogen receptor modulator (SERM) protection against cell death in estrogen receptor alpha and beta expressing U2OS cells

In the current work, we compared the ability of 17β-estradiol (E2) and the selective estrogen receptor modulators (SERMs), tamoxifen (Tam), raloxifene (Ral) and ospemifene (Osp) to promote the survival of osteoblast-derived cells against etoposide-induced apoptosis. In order to compare the roles of the two estrogen receptor (ER) isotypes, we created a U2OS human osteosarcoma cell line stably expressing either ERalpha (ERα) or ERbeta (ERβ). Transfection with either of the ERs was able to render the U2OS cells sensitive to E2. We show that E2 opposed etoposide-induced apoptosis and that the effect was mediated via both ER isotypes. The ER isotype selective agonists propyl-pyrazole-triol (PPT) and diarylpropionitrile (DPN) had the same effect in U2OS/ERα and U2OS/ERβ cells, respectively. Osp also opposed apoptosis at least in U2OS/ERα cells. Tam and Ral were not able to protect against etoposide-induced cell death. In order to evaluate the protective effects of E2 and Osp upon etoposide challenge, we studied the expression of two E2-regulated, osteoblast-produced cytokines, IL-6 and OPG in E2 and SERM-treated U2OS/ERα and U2OS/ERβ cells. Etoposide strongly increased expression of IL-6 and decreased that of OPG. E2 opposed IL-6 increase only in U2OS/ERα cells and OPG decrease primarily in ERβ cells. Osp opposed the effect of etoposide on OPG primarily in U2OS/ERβ cells but interestingly, it had little effect on IL-6 expression. E2, PPT, DNP and Osp also inhibited etoposide-induced death and cytokine changes in SAOS-2 osteosarcoma cells expressing endogenous ERα and ERβ. Collectively, our results suggest that the osteoblast protective anti-apoptotic effects of E2 are mediated by both ERα and ERβ but those of Osp primarily by ERα. In addition, E2 and Osp opposed the etoposide-induced increase of IL-6 and decrease of OPG which changes would increase osteoclastic activity. These anti-resorptive effects of E2 and Osp upon etoposide challenge differed from each other and they seemed to be differentially mediated in ERα and ERβ expressing osteoblast-derived U2OS cells.