Modulation of parathyroid hormone-sensitive adenylate cyclase in ROS 17/2.8 cells by dexamethasone 1,25-dihydroxyvitamin D 3 and protein kinase C

Abstract

We tested whether the protein kinase C (PKC) modulation of PTH-sensitive adenylate cyclase in ROS 17/2.8 cells is affected by the glucocorticoid dexamethasone and the vitamin D hormone 1,25-dihydroxyvitamin D 3 [l,25(OH) 2D 3]. Basal and PTH- and forskolin-stimulated adenylate cyclase activities were determined in the presence or absence of 100 nM phorbol 12-myristate 13-acetate (PMA), the activator of PKC, in ROS 17/2.8 cells that had been previously cultured with or without dexamethasone or l,25(OH) 2D 3. Dexamethasone treatment increased the basal, PMA-, PTH-, (PTH + PMA)- and (forskolin + PMA)-sensitive adenylate cyclase while l,25(OH) 2D 3 decreased these effects. The stimulatory and inhibitory effects were dose-dependent with respect to dexamethasone and l,25(OH) 2D 3, respectively. Dexamethasone increased, while 1,25(OH) 2D 3 decreased the maximal activity of both PTH-sensitive and PKC-modulated PTH-sensitive adenylate cyclase without affecting the half-maximal concentration (ED 50) of PTH required for the activation of the enzyme. Additionally, dexamethasone, l,25(OH) 2D 3 and PKC did not affect each other's ED 50. Our results suggest that the effects of dexamethasone, l,25(OH) 2D 3 and PKC on PTH-sensitive adenylate cyclase in ROS 17/2.8 cells are independent of each other.