Ethanol inhibits palmitoylation of G protein G alpha(s).
Neurobiological actions of ethanol have been linked to perturbations in cyclic AMP (cAMP)-dependent signaling processes. Chronic ethanol exposure leads to desensitization of cAMP production in response to physiological ligands (heterologous desensitization). Ethanol-induced alterations in neuronal expression of G proteins G(s) and G(i) have been invoked as a cause of heterologous desensitization. However, effects of ethanol on G protein expression vary considerably among different experimental protocols, various brain regions and diverse neuronal cell types. Dynamic palmitoylation of G protein alpha subunits is critical for membrane localization and protein-protein interactions, and represents a regulatory feature of G protein function. We studied the effect of ethanol on G alpha(s) palmitoylation. In NG108-15 rat neuroblastoma x glioma hybrid cells, acute exposure to pharmacologically relevant concentrations of ethanol (25-100 mm) inhibited basal and prostaglandin E1-stimulated incorporation of palmitate into G alpha(s). Exposure of NG108-15 cells to ethanol for 72 h induced a shift in G alpha(s) to its non-palmitoylated state, coincident with an inhibition of prostaglandin E1-induced cAMP production. Both parameters were restored following 24 h of ethanol withdrawal. Chronic ethanol exposure also induced the depalmitoylation of G alpha(s) in human embryonic kidney (HEK)293 cells that overexpress wild-type G alpha(s) and caused heterologous desensitization of adenylyl cyclase. By contrast, HEK293 cells that express a non-palmitoylated mutant of G alpha(s) were insensitive to heterologous desensitization after chronic ethanol exposure. In summary, the findings identify a novel effect of ethanol on post-translational lipid modification of G alpha(s), and represent a mechanism by which ethanol might affect adenylyl cyclase activity.
Hallak
Hazem
H
Department of Pathology, Anatomy and Cell Biology, Jefferson Medical College, Thomas Jefferson University, Philadelphia, Pennsylvania 19107-5541, USA. hazem.hallak@jefferson.edu
Rubin
Raphael
R
D000262:Adenylyl Cyclases / Q000378:metabolism; D000818:Animals; D002460:Cell Line; D000431:Ethanol / Q000494:pharmacology*; D019205:GTP-Binding Protein alpha Subunits, Gs / Q000187:drug effects* / Q000378:metabolism*; D006801:Humans; D006822:Hybrid Cells; D007668:Kidney / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D009447:Neuroblastoma / Q000378:metabolism; D010169:Palmitic Acids / Q000378:metabolism*; D011499:Protein Processing, Post-Translational / Q000187:drug effects; D021122:Protein Subunits / Q000187:drug effects / Q000378:metabolism; D051381:Rats; D013997:Time Factors
D010169:Palmitic Acids; D021122:Protein Subunits; D000431:Ethanol; D019205:GTP-Binding Protein alpha Subunits, Gs; D000262:Adenylyl Cyclases