Effects of transforming growth factor beta 1 on the regulation of osteocalcin synthesis in human MG-63 osteosarcoma cells

• Published in: Journal of bone and mineral research Vol. 9; no. 10; p. 1635
• Main Authors: Pirskanen, A, Jääskeläinen, T, Mäenpää, P H
• Format: Journal Article
• Language: English
• Published: United States 01-10-1994
• Subjects: 1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine; Base Sequence; Bone Neoplasms - pathology; Calcitriol - pharmacology; Cell Division - drug effects; Dexamethasone - pharmacology; Dose-Response Relationship, Drug; Drug Interactions; Gene Expression Regulation, Neoplastic - drug effects; Gene Expression Regulation, Neoplastic - genetics; Humans; Isoquinolines - pharmacology; Molecular Sequence Data; Oligonucleotide Probes - chemistry; Osteocalcin - antagonists & inhibitors; Osteocalcin - biosynthesis; Osteocalcin - genetics; Osteosarcoma - pathology; Phosphorylation; Piperazines - pharmacology; Protein Kinase C - antagonists & inhibitors; Receptors, Calcitriol - metabolism; RNA, Messenger - genetics; RNA, Messenger - metabolism; Transcription, Genetic - drug effects; Transcription, Genetic - genetics; Transforming Growth Factor beta - pharmacology; Tretinoin - pharmacology; Tumor Cells, Cultured; Vitamin D-Binding Protein - genetics; Vitamin D-Binding Protein - metabolism
• ISSN: 0884-0431

Treatment of human MG-63 osteosarcoma cells with human recombinant transforming growth factor beta 1 (TGF-beta 1) was found to inhibit cell proliferation. In addition, 1,25-dihydroxyvitamin D3 [1,25(OH)2D3]-induced osteocalcin synthesis was greatly influenced by TGF-beta 1. Dose- and time-dependent inhibition was seen both in medium osteocalcin and the corresponding mRNA concentrations. Furthermore, TGF-beta 1 decreased osteocalcin synthesis modulated negatively by dexamethasone or positively by retinoic acid. The stability of osteocalcin mRNA was not decreased by the TGF-beta 1 treatment, but in vitro transcription assays demonstrated diminished osteocalcin gene transcription caused by the TGF-beta 1 treatment. Binding of vitamin D receptor (VDR) to an oligonucleotide probe containing the osteocalcin vitamin D response element (VDRE) was not influenced by TGF-beta 1, however. Incubation of the cells with the serine/threonine kinase inhibitor H-7 did not block the ability of TGF-beta 1 to decrease osteocalcin synthesis but caused a further inhibition. Also, the 1,25(OH)2D3-induced osteocalcin synthesis was decreased by H-7 treatment, suggesting that phosphorylation as such is involved in the transcriptional activation mechanism of VDR. These results demonstrate that TGF-beta 1 is a strong inhibitor of the synthesis of osteocalcin, a calcium binding protein participating in bone mineralization, by counteracting the stimulatory effects of other hormones on its synthesis. We further suggest that TGF-beta 1 affects the synthesis of osteocalcin at the level of transcription through mechanism(s) different from the serine/threonine kinase pathway.