Stimulation of creatine kinase BB activity by parathyroid hormone and by prostaglandin E₂ in cultured bone cells

1. Bone cells in culture responded to parathyroid hormone (PTH) and prostaglandin E₂ (PGE₂) by a 2-fold increase in creatine kinase (CK) activity. Combined treatment resulted in a higher response than with PTH alone. Calcitonin (CT) failed to stimulate CK activity, did not affect the response of CK to PTH, but inhibited slightly the increase in CK activity by PGE₂. 2. Bone-cell cultures grown in low [Ca²⁺] (0.125 mM), enriched in PTH-responsive osteoblast-like cells, responded to PTH, but not to PGE₂ or CT, by increased CK activity. In both normal and low [Ca²⁺] cultures, 8-bromo cyclic AMP did not affect CK activity, nor did it change the response of the cells to PTH, PGE₂ or CT. 3. The increase in CK activity was time- and dose-dependent and inhibited both by cycloheximide and by actinomycin D. The isoenzyme of CK stimulated was the CKBB form, the isoenzyme induced by other hormones. 4. This appears to be the first report of the stimulation of CK activity by a polypeptide hormone or a prostaglandin. We suggest that stimulation of CKBB can serve as a marker for the action of a variety of hormones and growth promoters.