Role of Ras in ethanol modulation of angiotensin II activated p42/p44 MAP kinase in rat hepatocytes

Abstract

Angiotensin II plays a role in both liver cell proliferation and liver injury but the effects of ethanol on angiotensin II signaling in liver are not clearly understood. We have investigated the role of Ras in ethanol modulation of p42/p44 mitogen-activated protein kinase (MAPK) stimulated by angiotensin II (Ang II) in primary cultures of rat hepatocytes. Hepatocytes were incubated with ethanol (100 mM) for 24 h, then stimulated with Ang II (100 nM). The level of p42/p44 MAPK phosphorylation was measured by Western blot analysis and Ras activation was assessed by specific binding of Ras-GTP (activated form) to a GST-RBD fusion protein containing Ras-binding domain (RBD) of Raf-1. Ethanol potentiated p42/p44 MAPK activation by Ang II, whereas ethanol alone did not significantly affect phosphorylation of p42/p44 MAPK. Ang II increased Ras activity by about 2 fold. Ethanol exposure increased Ang II stimulated Ras activity by an additional about 2 fold. Ethanol alone elicited a small increase in basal Ras activity. Pretreatment with manumycin A (10 μM), a Ras farnesylation inhibitor, partially blocked both Ang II-activated and ethanol-potentiated MAPK activities. These data provided the first evidence that ethanol potentiation of Ang II stimulated p42/p44 MAPK is mediated, in part, by Ras in hepatocytes.