Stimulation of specific types of Gs-stimulated adenylyl cyclases by phorbol ester treatment

Abstract

Regulation of adenylyl cyclases by protein kinase C was studied. Types 1-6 were transiently expressed in 293 cells. The cells were treated with 4 beta-phorbol 12-myristate 13-acetate (PMA), and adenylyl cyclase activity was measured. PMA treatment of untransfected or vector-transfected cells resulted in a 35% (mean) increase in basal and forskolin-stimulated activity. PMA treatment of type 2 enzyme-transfected cells showed a 3-fold increase in basal activity. This stimulation varied with Mg2+ concentration with up to 4.5-fold increases at low Mg2+. PMA treatment resulted in about a 60% increase in fluoride or GTP gamma S (guanosine 5'-O-(thiotriphosphate))-stimulated activity in type 2 enzyme-transfected cells. Expression of the type 1 and 3 enzymes resulted in pronounced Ca2+/calmodulin stimulation, which was significantly increased upon pretreatment with PMA. No effects of PMA treatment were observable on other activities of the type 1 enzyme, whereas all activities of the type 3 enzymes were stimulated. Expressed types 4, 5, and 6 enzymes showed modest (approximately 30%) or no increases in basal and forskolin-stimulated activities upon PMA treatment. These data indicate that specific types of adenylyl cyclases can be functional targets for protein kinase C. The pronounced effects on the basal activity of the type 2 enzyme suggest this adenylyl cyclase could in the appropriate environment be an intracellular signal generator for external signals not routed through the activation of Gs.