STIMULATION OF CREATINE-KINASE SPECIFIC ACTIVITY IN HUMAN OSTEOBLAST AND ENDOMETRIAL CELLS BY ESTROGENS AND ANTIESTROGENS AND ITS MODULATION BY CALCIOTROPIC HORMONES

We have previously demonstrated sex-specific stimulation of creatine k inase specific activity (CK) in bone cells both in vivo and in vitro, in primary culture cells derived from rat and human bone and in establ ished 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 c ells was inhibited by 100-fold excess of 4-hydroxytamoxifen (Tam) as w ell 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-estrog en, raloxifene (Ral), which is agonist only in the SaOS-2 osteoblast-l ike cells but not in the human endometrial, Ishikawa cell line. Ishika wa cells respond to E, and to Tam by increased CK activity. In both os teoblasts and endometrial cell lines, Ral and Tam were inhibitory in t he presence off,. The effects off, on SaOS-2 cells are at least partia lly mediated by the estrogen receptor (ER) at the level of transcripti on as demonstrated by transient transfection experiments using the hum an 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% rel ative to E(2) alone and significantly increased the sensitivity of the cells to E(2) by lowering the effective hormonal dose needed for stim ulation of CK by E(2) by 100-fold. This stimulatory effect of pretreat ment of the cells with 1,25(OH)(2)D-3 was due to a 2.5-fold increase i n the level of ER expression as measured directly by enzyme immunoassa y 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 eff ects depending on the cell type, namely estrogenic-like activity in sk eletal cells but not in uterine cells. We can also conclude that as wi th 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 numb er 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 s tudies suggest that the treatment of pathological bone disorders may b e improved by combined hormone therapy.