REGULATION OF PARATHYROID-HORMONE MESSENGER-RNA LEVELS BY PROTEIN KINASE-A AND KINASE-C IN BOVINE PARATHYROID CELLS

Secretion of parathyroid hormone (PTH) is regulated by Ca2+ as well as by protein kinases A and C, In this study we report that protein kina ses A and C regulate PTH messenger RNA levels in vitro in dispersed bo vine parathyroid cells, Incubation of bovine parathyroid cells with ch olera toxin (10(-9) M), which activates adenylate cyclase and indirect ly stimulates protein kinase A, increased PTH mRNA levels about 2-fold after 3 and 7 h incubation, but not at 24 h, Incubation with pertussi s toxin (5 x 10(-9) M), which blocks the high-calcium-mediated inhibit ion of cyclic adenosine monophosphate accumulation in these cells, als o reversed the inhibition of PTH mRNA levels at high Ca2+ (2.0 mM) wit h a marked increase in PTH mRNA levels, Pertussis toxin also increased PTH mRNA at a low extracellular Ca2+ concentration (0.7 mM) (5-fold i ncrease) and a normal concentration (1.25 mM) (2-fold increase), Inhib ition of protein kinase C both by staurosporine (1 x 10(-8) M) and by prolonged incubation with the phorbol ester phorbol 12-myristate 13-ac etate (PMA) (1 x 10(-7) M), decreased PTH mRNA levels at 24 h, reachin g approximately 40% and 5% of control, respectively, Staurosporine and PMA had no effect on PTH mRNA levels at 3 h, The inactive phorbol est er, phorbol 12-13-dibutyrate (PDBu), had no effect on PTH mRNA levels at 1 and 24 h, There were no changes in a control gene 18S RNA in thes e studies, PMA at 24 h, which may down-regulate protein kinase C activ ity, decreased PTH mRNA levels, suggesting that protein kinase C is ne cessary for normal PTH gene expression, These results suggest that bot h protein kinase A and C are involved in the regulation of PTH gene ex pression.