Activation of Adenosine 3', 5'-Monophosphate-Dependent Protein Kinase in Normal and Malignant Bone Cells by Parathyroid Hormone, Prostaglandin E₂, and Prostacyclin

Hormonal activation of cAMP-dependent protein kinase has been studied in cultured cells derived from a rat osteogenic sarcoma and in osteoblast-rich cells grown from newborn rat calvaria. Both cell strains contain adenylate cyclase activities which respond to parathyroid hormone (PTH) and a variety of prostanoids. PTH, prostaglandin E ₂ (PGE ₂), and prostacyclin (PGI ₂) were all capable of activating cAMP-dependent protein kinase (s) in suspensions of the two cell types. Activation was very rapid in all cases, being detectable at 10 sec and maximal between 30-60 sec. Using saturating concentrations of hormones, the protein kinase activity ratio remained elevated (between 0.6-0.9) for up to 35 min after the start of PGE ₂ stimulation, but declined toward basal activity ratio 5-10 min after stimulation with PTH or PGI₂. Each of the hormones caused a dose-dependent increase in activation of cAMP-dependent protein kinase in both cell types. Half-maximal activation of the enzyme occurred at 2 × 10 ^-9 M bovine PTH for calvarial cells, at 10^-8 M bPTH for osteogenic sarcoma cells, and at 2-4 × 10^-8 M PGE₂2 and 1-3 × 10^-7 M PGI₂2 for both cell types. Maximal activation of protein kinase occurred before maximal _cAMP accumulated, implying that only a fraction of cAMP is biologically significant. These two cell strains provide a useful means of analyzing postreceptor events in the hormonal regulation of bone cells.