title: Regulation of osteocalcin secretion by human primary bone cells and by the human osteosarcoma cell line MG-63.
abstract: We present evidence that the regulation of osteocalcin secretion by PTH and PGE2 in normal human bone cells can be produced in the human osteoblast-like cell line MG-63. Both cell cultures showed time- and dose-dependent stimulation of osteocalcin secretion in response to 1,25(OH)2D3. Bovine parathyroid hormone (PTH) amino acid fragment 1-34 (40 nM) and prostaglandin E2 (PGE2, 5 nM) significantly inhibited 1,25(OH)2D3-induced osteocalcin secretion by these cells. The inhibition reached 20 and 36%, respectively. In contrast, PTH 3-34 had no effect on osteocalcin secretion. Both cell cultures produced cAMP in response to PTH. Dexamethasone (Dex) (100 nM) potentiated PTH-induced (40 nM) cAMP synthesis in subconfluent MG-63 cells (1.5-fold increase, P less than 0.05). This treatment with Dex resulted in a greater inhibition of 1,25(OH)2D3-induced osteocalcin secretion (-30%, P less than 0.005) by PTH in MG-63 cells as compared to cells exposed to PTH and 1,25(OH)2D3 alone. Pretreatment of subconfluent MG-63 cells with Dex (100 nM) for 48 h also increased 1,25(OH)2D3-induced osteocalcin secretion by 40% (P less than 0.025). In contrast, treatments of confluent MG-63 cells with Dex inhibited osteocalcin secretion regardless of the 1,25(OH)2D3 doses used. Forskolin (10(-7)-10(-5) M) and dibutyryl cAMP (10(-6)-(10(-3) M) both reproduced the effects observed with PTH and PGE2 in the two cell cultures. Forskolin's action was time-dependent: addition of forskolin (10(-6) M) 12 h after 1,25(OH)2D3 (50 nM) resulted in a progressively weaker inhibition of osteocalcin secretion. Increasing the extracellular calcium concentration of the incubation media resulted in a dose-dependent increase in osteocalcin secretion (P less than 0.01). These results indicate that PTH and PGE2 inhibit osteocalcin secretion by a mechanism involving cAMP production. In contrast, an increase in extracellular calcium stimulated osteocalcin release. Thus the human osteosarcoma cell line MG-63 is a useful osteoblast-like cell model to study the regulation of osteocalcin secretion. Furthermore, a factor (or factors) between hormone-receptor coupling and gene induction can regulate the expression of the osteocalcin gene or affect pre- or posttranslational mechanisms implicated in osteocalcin synthesis and secretion.
authors.affiliation: National Institute of Health, National Institute on Aging, Gerontology Research Center, Francis Scott Key Medical Center, Baltimore, MD.
authors.forename: D
authors.initials: D
authors.lastname: Lajeunesse
authors.forename: G M
authors.initials: GM
authors.lastname: Kiebzak
authors.forename: C
authors.initials: C
authors.lastname: Frondoza
authors.forename: B
authors.initials: B
authors.lastname: Sacktor
mesh_terms: D001842:Bone and Bones / Q000187:drug effects / Q000378:metabolism*; D003994:Bucladesine / Q000494:pharmacology; D002117:Calcitriol / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000096:biosynthesis; D003907:Dexamethasone / Q000494:pharmacology; D015232:Dinoprostone / Q000494:pharmacology; D006801:Humans; D010006:Osteoblasts / Q000187:drug effects / Q000378:metabolism; D015675:Osteocalcin / Q000378:metabolism*; D012516:Osteosarcoma / Q000378:metabolism*; D010281:Parathyroid Hormone / Q000494:pharmacology; D014407:Tumor Cells, Cultured
chemical_list: D010281:Parathyroid Hormone; D015675:Osteocalcin; D005576:Colforsin; D003994:Bucladesine; D003907:Dexamethasone; D000242:Cyclic AMP; D002117:Calcitriol; D015232:Dinoprostone; D002118:Calcium