Potentiation of mitogen-activated protein kinase by ethanol in embryonic liver cells

Ethanol modulates agonist responses in liver cells, which are the major site of ethanol metabolism. Mitogen-activated protein kinases (MAPKs) are involved in the integration of multiple signaling pathways leading to cellular responses. However, the effect of ethanol on liver MAPK is not known. To this end, we studied the activation of MAPK in a normal mouse embryonic liver cell line (BNLCL2) after acute and chronic exposure to ethanol. Acute exposure to ethanol (0-400 mM) for 1 hr had no effect on either basal or serum- and phorbol-12-myristate-13-acetate (PMA)-stimulated MAPK activity. Chronic exposure to ethanol (0-400 mM) for 24 hr potentiated the stimulation of MAPK by serum, PMA, or thrombin. Maximum potentiation was observed with 200 mM ethanol (2- to 3-fold higher than control cells). Chronic exposure had no significant effect on epidermal growth factor-stimulated MAPK activity. In-gel MAPK assay of cytosolic extracts and of immunoprecipitates obtained with MAPK antibody demonstrated that ethanol potentiated the activation of both p42 and p44 MAPKs. When cells were pretreated with pertussis toxin, the potentiation by ethanol was abolished. It is concluded that ethanol potentiates MAPK in fetal liver cells by a pertussis toxin-sensitive G-protein-dependent mechanism.