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EDITORIAL FOCUS

Acute and chronic ethanol consumption differentially impact pathways limiting hepatic protein synthesis

Department of Cellular and Molecular Physiology, The Pennsylvania State University College of Medicine, Hershey, Pennsylvania

Submitted 15 January 2008 ; accepted in final form 10 March 2008

ABSTRACT

This review identifies the various pathways responsible for modulating hepatic protein synthesis following acute and chronic alcohol intoxication and describes the mechanism(s) responsible for these changes. Alcohol intoxication induces a defect in global protein synthetic rates that is localized to impaired translation of mRNA at the level of peptide-chain initiation. Translation initiation is regulated at two steps: formation of the 43S preinitiation complex [controlled by eukaryotic initiation factors 2 (eIF2) and 2B (eIF2B)] and the binding of mRNA to the 40S ribosome (controlled by the eIF4F complex). To date, alcohol-induced alterations in eIF2 and eIF2B content and activity are best investigated. Ethanol decreases eIF2B activity when ingested either acutely or chronically. The reduced eIF2B activity most likely is a consequence of twofold increased phosphorylation of the -subunit of eIF2 on Ser⁵¹ following acute intoxication. The increase in eIF2 phosphorylation after chronic alcohol consumption is the same as that induced by acute ethanol intoxication, and protein synthesis is not further reduced by long-term alcohol ingestion despite additional reduced expression of initiation factors and elongation factors. eIF2 phosphorylation alone appears sufficient to maximally inhibit hepatic protein synthesis. Indeed, pretreatment with Salubrinal, an inhibitor of eIF2(P) phosphatase, before ethanol treatment does not further inhibit protein synthesis or increase eIF2 phosphorylation, suggesting that acute ethanol intoxication causes maximal eIF2 phosphorylation elevation and hepatic protein synthesis inhibition. Ethanol-induced inhibition of hepatic protein synthesis is not rapidly reversed by cessation of ethanol consumption. In conclusion, sustained eIF2 phosphorylation is a hallmark of excessive alcohol intake leading to inhibition of protein synthesis. Enhanced phosphorylation of eIF2 represents a unique response of liver to alcohol intoxication, because the ethanol-induced elevation of eIF2(P) is not observed in skeletal muscle or heart.

mRNA translation initiation; alcohol; eukaryotic initiation factor 2B; eukaryotic initiation factor 2

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				P. E. Molina Alcohol--intoxicating roadblocks and bottlenecks in hepatic protein and lipid metabolism Am J Physiol Endocrinol Metab, July 1, 2008; 295(1): E1 - E2. [Full Text] [PDF]