Parathyroid Hormone Inhibits Collagen Synthesis at Both Ribonucleic Acid and Protein Levels in Rat Osteogenic Sarcoma Cells

Publisher Website
Google Scholar
Abstract
Cells of the clonal rat osteogenic sarcoma cell line, UMR 106-01, were used to investigate the regulation of collagen synthesis by PTH in osteoblastic cells. Monolayer cultures of cells were labeled with [3H] proline in order to determine both collagen type and rates of production. Analysis of labeled extracellular polypeptides on sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed that UMR 106-01 cells synthesized predominantly type I collagen, accounting for 45.48 .+-. 2.09% of the radioactivity incorporated into total protein. After 24-h treatment with bovine PTH (1-34, 10-8 M), collagen synthesis (i.e. collagenase-digestible protein) was decreased to 29.45 .+-. 1.39% of total protein production. This decrease was first observed 12 h after addition of hormone and greatest inhibition was achieved at 24 h. The effect of PTH was dose dependent, with half-maximal inhibition of collagen synthesis occurring at 5 .times. 1010 M after 24-h treatment. In contrast, when steady levels of mRNA for type I collagen chains were examined by Northern blot analysis, the concentration of PTH that reduced collagen synthesis by 35-45% (10-8 M), caused a net decrease of approximately 80-96% in the number of procollagen transcripts; a small reduction in .beta.-actin mRNA levels was also observed. The effect of the hormone on procollagen message level was dose dependent, with significant inhibition observed at 1010 M PTH and, as with collagen synthesis, maximal after 24 h. However, the markedly greater decline in mRNA level compared with the change in the rate of protein synthesis indicates that transcriptional regulation cannot be solely responsible for the control of collagen synthesis by PTH and suggests that events operating at both the pretranslational and translational levels are likely involved in the process.