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Am J Physiol Endocrinol Metab (March 11, 2008). doi:10.1152/ajpendo.00026.2008
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Submitted on January 15, 2008
Accepted on March 10, 2008

Acute and Chronic Ethanol Consumption Differentially Impact Pathways Limiting Hepatic Protein Synthesis

Anne MacLeod Karinch1*, Jonathan H. Martin1, and Thomas C. Vary1

1 Cellular & Molecular Physiology, Penn State University College of Medicine, Hershey, Pennsylvania, United States

* To whom correspondence should be addressed. E-mail: akarinch{at}psu.edu.

This review identifies pathways responsible for modulating hepatic protein synthesis following acute and chronic alcohol intoxication and describes mechanism(s) responsible for these changes. Alcohol intoxication induces a defect in global protein synthesis that impairs mRNA translation at the level of peptide-chain initiation. Initiation is regulated at formation of the 43S pre-initiation complex (controlled by eukaryotic initiation factors 2 (eIF2) and eIF2B) and mRNA binding to the 40S ribosome (controlled by eIF4F complex). Alcohol-induced alterations in eIF2 and eIF2B content and activity are best investigated. Ethanol decreases eIF2B activity when ingested acutely or chronically. Reduced eIF2B activity most likely is a consequence of increased eIF2{alpha} phosphorylation on Ser51 following acute intoxication. The increase in eIF2{alpha} 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 and elongation factors. eIF2{alpha} phosphorylation appears sufficient to maximally inhibit hepatic protein synthesis. Pretreatment with Salubrinal, which inhibits eIF2{alpha}(P) phosphatase, before ethanol treatment does not further inhibit protein synthesis or increase eIF2{alpha} phosphorylation, suggesting acute ethanol intoxication causes maximal eIF2{alpha} phosphorylation elevation and hepatic protein synthesis inhibition. Cessation of ethanol consumption does not rapidly reverse ethanol-induced inhibition of hepatic protein synthesis. Therefore, sustained eIF2{alpha} phosphorylation is a hallmark of excessive alcohol intake leading to inhibition of protein synthesis. Enhanced phosphorylation of eIF2{alpha} represents a unique response of liver to alcohol intoxication as ethanol-induced elevation of eIF2{alpha}(P) is not observed in skeletal muscle or heart.







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