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Acute alcohol intoxication enhances myocardial eIF4G phosphorylation despite reducing mTOR signaling

¹Department of Cellular and Molecular Physiology, The Pennsylvania State University College of Medicine, Hershey; and ²Department of Biology, Lebanon Valley College, Annville, Pennsylvania

Submitted 11 May 2004 ; accepted in final form 14 September 2004

Acute alcohol intoxication impairs myocardial protein synthesis in rats, secondary to a diminished mRNA translational efficiency. Decreased mRNA translational efficiency occurs through altered regulation of peptide chain initiation. The purpose of the present set of experiments was to determine whether acute alcohol intoxication alters the phosphorylation state of eukaryotic initiation factor (eIF) 4G, eIF4G·eIF4E complex formation, and the mammalian target of rapamycin (mTOR) signaling pathway in the heart. Acute alcohol intoxication was induced by injection of alcohol (75 mmol/kg body wt ip). Control animals received an equal volume of saline. Alcohol administration enhanced phosphorylation of eIF4G (Ser¹¹⁰⁸) approximately threefold. Alcohol administration lowered formation of the active eIF4G·eIF4E complex by >90%, whereas it increased the abundance of the inactive 4E-binding protein 1 (4E-BP1)·eIF4E complex by 160%. Phosphorylation of mTOR on Ser²⁴⁴⁸ and Ser²⁴⁸¹ was decreased by 50%. Reduced mTOR phosphorylation did not result from decreased phosphorylation of PKB. Phosphorylation of 4E-BP1 and S6 kinase 1 (Thr³⁸⁹), downstream targets of mTOR, were also reduced after acute alcohol administration. These data suggest that acute alcohol-induced impairments in myocardial mRNA translation initiation result, in part, from marked decreases in eIF4G·eIF4E complex formation, which appear to be independent of changes in phosphorylation of eIF4G but dependent on mTOR.

cardiomyopathy; peptide-chain initiation; eukaryotic initiation factor 4E; 4E-binding protein 1; heart; translational efficiency; p70 S6 kinase; protein kinase B

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