Ethanol differentially regulates guanine nucleotide-binding protein alpha subunit expression in NG108-15 cells...

Recent work has suggested that chronic ethanol treatment induces heterologous desensitization of adenylate cyclase in a number of cell lines maintained in culture and that this phenomenon is mediated by adenosine. It has been proposed that ethanol induces the accumulation of extracellular adenosine, which then down-regulates the Gs alpha protein and leads to heterologous desensitization. Here we investigated the effects of chronic ethanol treatment on the expression of Gs alpha, Gi alpha, and Go alpha, as well as cAMP signal transduction, in NG108-15 cells and further examined the role of adenosine in mediating these effects. Pretreatment of NG108-15 cells with 200 mM ethanol for 2 days reduced membrane levels of Gs alpha and Gi alpha and increased those of Go alpha. However, ethanol did not reduce the levels of Gs alpha and Gi alpha 2 mRNA in these cells. The ability of ethanol to alter alpha subunit expression was not reversed by removal of extracellular adenosine and could not be mimicked by an adenosine agonist. Chronic ethanol treatment increased both basal and agonist-stimulated cAMP accumulation in NG108-15 cells. Whereas the increase in basal cAMP was abolished by acute addition of adenosine deaminase, the increase in agonist-stimulated cAMP accumulation was not. Morphological examination of the cells indicated that ethanol inhibited cell division and promoted the apparent differentiation of the cells. These results indicate that ethanol induces complex alterations in guanine nucleotide-binding protein alpha subunit expression and cAMP signal transduction in NG108-15 cells and that it is unlikely that these effects are mediated simply by adenosine.