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 17 beta-estradiol (E-2) and the selective estrogen receptor modulators (SERMs), tamoxifen (Tam), raloxifene (Ral) and ospemifene (Osp) to promote the survival of osteoblast-derived cells against etoposide-incluced 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 (ER alpha) or ERbeta (ER beta). Transfection with either of the ERs was able to render the U2OS cells sensitive to E-2. 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/ER alpha and U20S/ER beta cells, respectively. Osp also opposed apoptosis at least in U2OS/ERa cells. Tam and Ral were not able to protect against etoposide-induced cell death. In order to evaluate the protective effects of E-2 and Osp upon etoposide challenge, we studied the expression of two E-2-regulated, osteoblast-produced cytokines, IL-6 and OPG in E-2 and SERM-treated U2OS/ER alpha and U2OS/ER beta cells. Etoposide strongly increased expression of IL-6 and decreased that of OPG. E-2 opposed IL-6 increase only in U2OS/ER alpha cells and OPG decrease primarily in ER beta cells. Osp opposed the effect of etoposide on OPG primarily in U2OS/ER beta 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 ER alpha and ER beta. Collectively, our results suggest that the osteoblast protective anti-apoptotic effects of E-2 are mediated by both ER alpha and ER beta but those of Osp primarily by ER alpha. In addition, E-2 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 E-2 and Osp upon etoposide challenge differed from each other and they seemed to be differentially mediated in ER(x and ER beta expressing osteoblast-derived U2OS cells. (C) 2008 Elsevier Ireland Ltd. All rights reserved.