Role of protein kinase C in ethanol-induced activation of adenylyl cyclase

Ethanol is known to enhance the activity of adenylyl cyclase (AC) in a numb er of cells and tissues. Recent work has suggested that the various isoform s of AC show differential sensitivity to ethanol, with Type VII AC being mo st sensitive. However, the mechanism of action of ethanol is unclear. In th e present work, we investigated the effect of ethanol on AC activity in the human erythroleukemia (HEL) cell line, platelets, and AC VII-transfected H EK 293 cells, The HEL cells contain abundant amounts of mRNA for Type VII A C, We found that both ethanol and phorbol dibutyrate (PDBu) treatment enhan ced agonist (prostaglandin E-1; PGE(1))-stimulated AC activity in HEL cells , as well as in platelets and HEK 293 cells transfected with AC VII, Inhibi tors of protein kinase C (PKC) blocked the stimulatory effects of both etha nol and PDBu, However, the effects of ethanol and PDBu on AC activity were additive, suggesting that the mechanisms of action of ethanol and PDBu were not identical. Furthermore, a 30-min exposure of HEL cells to ethanol atte nuated (desensitized) the ability of ethanol, but not PDBu, to enhance agon ist-activated AC activity. On the other hand, a 30-min pretreatment with PD Bu attenuated the AC response to the phorbol ester, but not to ethanol; but , after a 20 hr preincubation with phorbol ester, the ability of both PDBu and ethanol to enhance prostaglandin E-1-stimulated AC activity was complet ely eliminated, Finally, pretreatment of HEL cells with pertussis toxin blo cked the effect of PDBu, but not ethanol, on AC activity. The results suppo rt the involvement of phorbol ester-sensitive PKC(s) in ethanol's enhanceme nt of agonist-activated activity of AC in HEL cells, but suggest that the m echanism of ethanol's action is different from that of PDBu, The findings w ith pertussis toxin suggest that PDBu activation of PKC(s) may affect AC ac tivity through phosphorylation of a G(i) protein, whereas ethanol may act b y promoting phosphorylation of a different substrate (e,g,, AC VII).