Characterization of the progestin receptors in the human TE85 and murine MC3T3-E1 osteoblast-like cell lines

Abstract

Progestins are believed to exert positive effects on bone density through receptors located in osteoblasts. In the present studies, the binding characteristics and regulation of the progestin receptors in two osteoblast-like cell lines were compared with those in human breast lines. Human TE85 and murine MC3T3-E1 osteoblast-like cells contain a single, high-affinity progestin binding site whose affinity and concentration are lower than in human breast cells. The osteoblastic progestin binding sites showed the expected steroid specificity and associated with the cell nuclei when occupied by ligand. The progestin receptors in osteoblastic cells also had sedimentation coefficients similar to those receptors in breast cells. The regulation of the progestin receptor in the osteoblast-like cells was explored by treating them with estradiol. In contrast to the large, rapid change seen in the breast cells, the progestin receptor levels in the MC3T3-E1 cells showed only a small, delayed up-regulation with estradiol treatment. The progestin receptor number in the TE85 cells was unaffected by estradiol. Down-regulation of the progestin receptors was explored by treating the cells with the progestin, norethindrone (NET). NET administration produced a rapid drop in progestin binding sites in the breast cells and a smaller, more gradual decline in MC3T3-E1 progestin binding. While the maximal decrease in receptor number occurred within 24 h in the breast cells, the receptor number was still continuing to fall after 72 h in the MC3T3-E1 cells. The data presented here demonstrate that both human and murine osteoblastlike cells contain a functional progestin receptor whose binding characteristics and regulation are similar, but not identical, to those receptors in other progestin target tissues such as the breast.

Human Osteoblasts' Proliferative Responses to Strain and 17β-Estradiol Are Mediated by the Estrogen Receptor and the Receptor for Insulin-Like Growth Factor I

“…Baylink (Loma Linda University, Loma Linda, CA, USA). These cells exhibit typical osteoblastic characteristics, (12) possess ERs (13) and have been used in a number of previous studies (8–10) …”

“…The experiments reported here were designed to establish whether human osteoblastic cells (HOBs) show similar responses to strain and estrogen as those observed in rat cells, and, thus, whether the mechanisms that these responses suggest are similar in these two species. To do this, we have used monolayer cultures of first‐passage primary HOBs (fHOBs) derived from female human bone salvaged from surgical procedures and the human osteosarcoma‐derived TE85 osteoblastic cell line (8–10) . We investigated the proliferative responses of these cells to a single, short period of cyclic mechanical strain and/or 17β‐estradiol in the presence and absence of the ER modulators ICI 182,780 and tamoxifen; monoclonal neutralizing antibody (MNAb) to IGF‐I and IGF‐II; and αIR‐3, a well‐characterized blocking antibody to the IGF‐I receptor.…”

Functional glass slides for in vitro evaluation of interactions between osteosarcoma TE85 cells and mineral-binding ligands

“…[29][30][31] They have been widely used as experimental models for investigating osteoblast functions. [32][33][34][35][36][37][38] Optical images acquired at 6 h after initial seeding (Fig. 4) showed that TE85 cells attached to and spread over all surfaces examined.…”