Effects of transforming growth factor beta 1 on the regulation of osteocalcin synthesis in human MG-63 osteosarcoma cells.
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.
Pirskanen
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Department of Biochemistry and Biotechnology, University of Kuopio, Finland.
Jääskeläinen
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Mäenpää
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D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine; D001483:Base Sequence; D001859:Bone Neoplasms / Q000473:pathology; D002117:Calcitriol / Q000494:pharmacology; D002455:Cell Division / Q000187:drug effects; D003907:Dexamethasone / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects / Q000235:genetics; D006801:Humans; D007546:Isoquinolines / Q000494:pharmacology; D008969:Molecular Sequence Data; D015345:Oligonucleotide Probes / Q000737:chemistry; D015675:Osteocalcin / Q000037:antagonists & inhibitors* / Q000096:biosynthesis / Q000235:genetics; D012516:Osteosarcoma / Q000473:pathology; D010766:Phosphorylation; D010879:Piperazines / Q000494:pharmacology; D011493:Protein Kinase C / Q000037:antagonists & inhibitors; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D018167:Receptors, Calcitriol / Q000378:metabolism; D014158:Transcription, Genetic / Q000187:drug effects / Q000235:genetics; D016212:Transforming Growth Factor beta / Q000494:pharmacology*; D014212:Tretinoin / Q000494:pharmacology; D014407:Tumor Cells, Cultured; D014809:Vitamin D-Binding Protein / Q000235:genetics / Q000378:metabolism
D007546:Isoquinolines; D015345:Oligonucleotide Probes; D010879:Piperazines; D012333:RNA, Messenger; D018167:Receptors, Calcitriol; D016212:Transforming Growth Factor beta; D014809:Vitamin D-Binding Protein; D015675:Osteocalcin; D014212:Tretinoin; D003907:Dexamethasone; D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine; D011493:Protein Kinase C; D002117:Calcitriol