title: Evidence that estrogens modulate activity and increase the number of 1,25-dihydroxyvitamin D receptors in osteoblast-like cells (ROS 17/2.8).
abstract: A detailed understanding of the mechanism of action of estrogen on bones is still lacking. The present study was designed to examine possible modulation by 17 beta-estradiol (E2) on the effects of 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3] and on vitamin D receptors (VDR) in the ROS 17/2.8 osteoblast-like cell line. Cells were grown in phenol-red free medium supplemented with charcoal-stripped fetal calf serum (FCS). Total cellular VDR were measured in cell homogenates after extraction with a KCl hypertonic buffer. VDR-binding capacity doubled in the presence of 10 nM E2 (16.2 +/- 2.3 vs. 7.0 +/- 1.3 fmol/mg protein, respectively; P less than 0.01), while the Kd for 1,25-(OH)2D3 did not change (approximately 0.1 nM). Tamoxifen alone had no effect on VDR, while it completely abolished the E2-induced increase in VDR, indicating that the effect was specific for E2 and estrogen receptor mediated. 1,25-(OH)2D3 inhibited cell proliferation, determined by [3H] thymidine incorporation to DNA, in a dose-dependent fashion between 0.01-100 nM. The inhibitory effect of 1,25-(OH)2D3 on cell proliferation was significantly augmented in the presence of E2 (10 nM). 1,25-(OH)2D3 increased osteocalcin secretion to the medium by the cells in a dose-dependent fashion between 0.01-100 nM. In the presence of E2 (10 nM), maximal osteocalcin secretion in response to 1,25-(OH)2D3 was 3.5-fold higher than that in response to 1,25-(OH)2D3 alone. These results indicate that E2 modulates 1,25-(OH)2D3 activity in osteoblast-like cells, and that this effect can be attributed to an increase in VDR.
authors.affiliation: Department of Medicine, Soroka University Hospital, Beer-Sheva, Israel.
authors.forename: Y
authors.initials: Y
authors.lastname: Liel
authors.forename: S
authors.initials: S
authors.lastname: Kraus
authors.forename: J
authors.initials: J
authors.lastname: Levy
authors.forename: S
authors.initials: S
authors.lastname: Shany
mesh_terms: D000818:Animals; D002117:Calcitriol / Q000378:metabolism* / Q000494:pharmacology; D002460:Cell Line; D003600:Cytosol / Q000378:metabolism; D004261:DNA Replication / Q000187:drug effects; D004958:Estradiol / Q000494:pharmacology*; D007700:Kinetics; D010006:Osteoblasts / Q000187:drug effects / Q000378:metabolism*; D015675:Osteocalcin / Q000378:metabolism; D012516:Osteosarcoma; D051381:Rats; D018167:Receptors, Calcitriol; D011987:Receptors, Steroid / Q000187:drug effects / Q000378:metabolism*; D013936:Thymidine / Q000378:metabolism
chemical_list: D018167:Receptors, Calcitriol; D011987:Receptors, Steroid; D015675:Osteocalcin; D004958:Estradiol; D002117:Calcitriol; D013936:Thymidine