Selective hormonal activation of cyclic AMP-dependent protein kinase isoenzymes in normal and malignant osteoblasts

The pattern of cyclic AMP-dependent protein kinase isoenzyme response to acute hormonal activation has been studied in cultured cells derived from rat osteogenic sarcoma and osteoblast-rich cells grown from newborn rat calvaria. Using multiple small anion exchange columns and a batch elution technique, a rapid method of separating the isoenzymes of cyclic AMP-dependent protein kinase was developed and the acute activation by parathyroid hormone and prostaglandin E ₂ of each isoenzyme was studied. Activation was rapid, being detectable at 5 s, maximal at 15-30 s, and persisting for up to 6 h. Both hormones showed a dose-dependent activation of each isoenzyme in both cell types, but the patterns of response differed. Parathyroid hormone predominantly stimulated isoenzyme I in the clonal osteogenic sarcoma cells but showed equivalent activation of each isoenzyme in calvarial cells. Prostaglandin E ₂ also predominantly stimulated isoenzyme I in the malignant cells, whereas in the calvarial strain there was a major effect on isoenzyme II with almost no stimulation of isoenzyme I. Half-maximal stimulation of cyclic AMP-dependent protein kinase in the malignant cell strain was achieved for both hormones at concentrations an order of magnitude lower than those in the normal strain. These studies demonstrate selective activation of cyclic AMP-dependent protein kinase isoenzymes by hormones. Furthermore, the nature of the response differs between the normal and the corresponding neoplastic cell types for the same hormone stimulus.