Glucocorticoid Receptors and Inhibition of Bone Cell Growth in Primary Culture¹²

Abstract

We have previously identified glucocorticoid binding proteins in cytosol of cells dispersed from fetal rat calvaria by collagenase digestion. The present study, employing primary culture of these cells, provides further evidence that these binding proteins represent glucocorticoid receptors. [3H]Dexamethasone bound to cytoplasmic extracts of cultured cells with an apparent Kdiss of 6.8 nM and exhibited approximately 8500 binding sites/cell. Nuclear translocation of [3H]dexamethasone was demonstrated with approximately 50% of bound steroid extractable from the nuclear pellet after incubation at 37 C; little nuclear transfer occurred at 0 C. The specificity of these binding site was characterized by competition studies with other steroids in whole cells, the order of affinities being: triamcinolone acetonide greater than dexamethasone greater than progesterone greater than cortisol greater than corticosterone = cortexolone. Non-glucocorticoids except progesterone competed only poorly. Sedimentation analysis of [3H]dexamethasone-protein complexes on sucrose gradients revealed a cytoplasmic peak of 6.5 S in salt-free gradients and 3.8 S in 0.3 M KCl gradients. Dexamethasone addition to the culture medium resulted in a dose-dependent inhibition of cell growth with approximately 40% reduction in cell number at 13 nM. That this inhibition was receptor mediated was substantiated by the partial blockade of the dexamethasone effect in the presence 1.3 microM progesterone. Functionally, dexamethasone inhibits the growth of these cells. These data provide evidence for receptor mediated inhibitory effects of glucocorticoids directly at the level of the bone cell.

The growth‐supportive effect of thrombospondin (TSP1) and the expression of TSP1 by human MG‐63 osteoblastic cells are both inhibited by dexamethasone

“…By contrast, interleukin-l/I up-regulates a,/&-integrin expression in MG-63 cells [24], resulting in cell growth inhibition of interleukin-l/I treated MG-63 cells [25]. Besides its effect on TSP expression, dexamethasone inhibits growth of human MG-63 osteoblastic cells (this study) as has been previously reported for cultured mouse osteoblastlike cells [8,9]. We have previously suggested that the growth-supportive effect of TSP could depend of a mechanism whereby cell surface-bound TSP stimulates secretion of prostaglandins which, in turn, allow cell proliferation to proceed [6].…”

“…Glucocorticoid-induced osteoporosis primarily involves decreased width of trabecular bone, suggesting reduction of trabecular osteoblast proliferation [7]. Osteoblastic cells have receptors for glucocorticoids [8], and cultured mouse MC3T3-El osteoblastic cells have been used to show that the glucocorticoid, dexamethasone, inhibits DNA synthesis and prostaglandin synthesis [9]. In addition, glucocorticoids also affect the expression of bone extracellular matrix proteins including type I collagen [lo], osteocalcin [11,12], alkaline phosphatase [12,13], osteopontin [14], bone sialoprotein [15], and fibronectin [ 161.…”

Cortisol Inhibits Acid-Induced Bone Resorption In Vitro

“…Glucocorticoids have been shown to inhibit bone cell proliferation (43) and have a biphasic effect on type I collagen synthesis, a principal function of the osteoblast (16,44 -46). In addition to being dose-and treatment time-dependent, the effects of glucocorticoids also seem to depend on the stage of osteoblast differentiation.…”

Effects of dexamethasone on proliferation, activity, and cytokine secretion of normal human bone marrow stromal cells: possible mechanisms of glucocorticoid-induced bone loss

“…In addition, both stimulation and inhibition of cell proliferation by glucocorticoids have been reported in these organ cultures (Tenenbaum & Heersche 1985, McCulloch & Tenenbaum 1986, Kream et al 1997. In isolated osteoblast-like cell populations, glucocorticoids decrease cell proliferation but increase alkaline phosphatase activity (Chen et al 1977, Wong et al 1990, Cheng et al 1994. The effects of glucocorticoids on collagen expression in osteoblast-like cells, however, remain controversial.…”