Partial characterization of a parathyroid hormone-stimulated resorption factor(s) from osteoblast-like cells

PTH stimulates osteoblast-like cells to produce a product(s) capable of increasing cellular bone resorption. We have investigated this phenomenon using primary cultures of osteoblasts and the clonal osteoblast-like cell line ROS 17/2. Conditioned medium from PTH-stimulated populations of either culture increases bone resorption compared to conditioned medium measured in three independent assay systems; the isolated osteoclast assay system, elicited macrophages, and the fetal bone rudiment system. Characterization of the factor(s) of PTH-stimulated osteoblast-like cell (ROS 17/2) suggests that the compound(s) is not prostaglandin (no inhibition by indomethacin; not extractable in diethylacetate). Rather, it is heat and protease sensitive. In addition, secretion of the product is sensitive to cycloheximide. These findings lead us to the conclusion that the factor(s) is protein. Further work demonstrates the necessity for a divalent cation for retention of factor activity. Finally, we have estimated the molecular radius of the factor as about 110,000 daltons and perhaps a second at about 70,000 daltons using a sizing column. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis of [35S]methionine-labeled PTH-stimulated ROS culture supernatants reveals relatively increased secretion of proteins with these approximate molecular radii.