Hormonal regulation of collagen synthesis in a clonal rat osteosarcoma cell line

Collagen synthesis in rat osteosarcoma cell line 17/2 (ROS 17/2) was assessed by measuring the incorporation of [³H]proline into collagenase-digestible protein and the formation of [³H]hydroxyproline. PTH and 1,25-dihydroxyvitamin D₃ [1,25-(OH)₂D₃] inhibited collagen synthesis in ROS 17/2 cells in a time- and dose-dependent manner. PTH reduced collagen synthesis after a 3-h incubation, whereas the effect of 1,25-(OH)₂D₃ was somewhat slower. Maximal and half-maximal inhibition of collagen synthesis occurred at approximately 1 and 0.1 nm of each hormone, respectively. At confluency, ROS 17/2 cells synthesized 96% type I and 4% type III collagen. PTH reduced the synthesis of type I, but not type III, collagen. PTH and 1,25-(OH)₂D₃ also reduced procollagen mRNA levels, as determined by a dot blot hybridization assay. Thus, ROS 17/2 cells are a convenient model system for studying the hormonal regulation of collagen metabolism and gene expression in a cloned cell line with the osteoblastic phenotype.