title: The growth-supportive effect of thrombospondin (TSP1) and the expression of TSP1 by human MG-63 osteoblastic cells are both inhibited by dexamethasone.
abstract: Thrombospondin (TSP) is a 450-kDa extracellular matrix glycoprotein which supports the growth of human MG-63 osteoblastic cells [Abbadia et al., FEBS Lett., 329 (1993) 341-346]. In this study, we describe the effect of the glucocorticoid, dexamethasone, on cell proliferation and TSP expression by MG-63 cells. Using a serum-free mitogenesis assay, dexamethasone (25 to 500 nM) caused a dose-dependent decrease in [3H]thymidine incorporation by MG-63 cells in culture, reaching 40% inhibition of cell proliferation at a concentration of 250 nM. Similarly, the stimulatory effect of TSP (500 ng/ml) on proliferation of MG-63 cells was totally abolished in the presence of dexamethasone (250 nM). In situ hybridization indicated that TSP mRNA level in dexamethasone-treated MG-63 cells decreased compared to quiescent cells. As judged by fluorescence-activated cell sorting analysis, dexamethasone treatment of MG-63 cells resulted in a 50 to 70% decrease in TSP cell surface expression compared to quiescent cells. Secretion of TSP in the culture fluid of dexamethasone-treated MG-63 cells also decreased by 40% while, under similar experimental conditions, a 180% increase in alkaline phosphatase activity was observed in dexamethasone-treated cells. Because glucocorticoids induce osteoporosis in vivo and reduce proliferation of osteoblasts in vitro, our results argue for an important role of TSP during bone formation.
authors.affiliation: INSERM Research Unit 234, Pavillon F, Hôpital E. Herriot, Lyon, France.
authors.forename: Z
authors.initials: Z
authors.lastname: Abbadia
authors.forename: J
authors.initials: J
authors.lastname: Amiral
authors.forename: M C
authors.initials: MC
authors.lastname: Trzeciak
authors.forename: P D
authors.initials: PD
authors.lastname: Delmas
authors.forename: P
authors.initials: P
authors.lastname: Clezardin
mesh_terms: D000469:Alkaline Phosphatase / Q000378:metabolism; D002455:Cell Division / Q000187:drug effects; D002460:Cell Line; D002469:Cell Separation; D003907:Dexamethasone / Q000494:pharmacology*; D004789:Enzyme Activation; D004797:Enzyme-Linked Immunosorbent Assay; D005434:Flow Cytometry; D006801:Humans; D017403:In Situ Hybridization; D008562:Membrane Glycoproteins / Q000096:biosynthesis / Q000187:drug effects / Q000502:physiology*; D010006:Osteoblasts / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D019699:Thrombospondins
chemical_list: D008562:Membrane Glycoproteins; D019699:Thrombospondins; D003907:Dexamethasone; D000469:Alkaline Phosphatase