Stimulation of creatine kinase specific activity in human osteoblast and endometrial cells by estrogens and anti-estrogens and its modulation by calciotropic hormones

We have previously demonstrated sex-specific stimulation of creatine kinase specific activity (CK) in bone cells both in vivo and in vitro, in primary culture cells derived from rat and human bone and in established human bone-derived cell lines. We found that the female-derived cell Line, SaOS-2, responded to 17 beta-estradiol (E(2)) by increased CK specific activity. The effects of E, on the CK activity in SaOS-2 cells was inhibited by 100-fold excess of 4-hydroxytamoxifen (Tam) as well as by the other antiestrogen, ICI 164,384. Tam by itself had some stimulatory effect whereas ICI 164,384 showed no estrogenic activity. We also demonstrated the estrogenic-like effect of another anti-estrogen, raloxifene (Ral), which is agonist only in the SaOS-2 osteoblast-like cells but not in the human endometrial, Ishikawa cell line. Ishikawa cells respond to E, and to Tam by increased CK activity. In both osteoblasts and endometrial cell lines, Ral and Tam were inhibitory in the presence off,. The effects off, on SaOS-2 cells are at least partially mediated by the estrogen receptor (ER) at the level of transcription as demonstrated by transient transfection experiments using the human creatine kinase promoter chloramphenicol acetyltransferase in these cells. Pretreatment of SaOS-2 with calcitropic hormones, either 1,25 dihydroxyvitamin D-3 (1,25(OH)(2)D-3) or human parathyroid hormone (1-34) (hPTH(1-34)) increased the stimulation of CK by E(2) by 40-60% relative to E(2) alone and significantly increased the sensitivity of the cells to E(2) by lowering the effective hormonal dose needed for stimulation of CK by E(2) by 100-fold. This stimulatory effect of pretreatment of the cells with 1,25(OH)(2)D-3 was due to a 2.5-fold increase in the level of ER expression as measured directly by enzyme immunoassay in the SaOS-2/1 subline. The increase in the responsiveness to E(2) by hPTH(1-34) was not due to an increase in ER level in the cells, We can conclude that in cell cultures as in vivo, Ral shows different effects depending on the cell type, namely estrogenic-like activity in skeletal cells but not in uterine cells. We can also conclude that as with rat-derived cells, in bone cells derived. From human bone 1,25(OH)(2)D-3 increased the sensitivity to E(2) due to an increase in the number of ER in the cells,whereas PTH(1-34) augmented the response to E(2) without increasing ER, by another, as yet unknown, mechanism. These studies suggest that the treatment of pathological bone disorders may be improved by combined hormone therapy.