Impaired myocardial protein synthesis induced by acute alcohol intoxication is associated with changes in eIF4F

Abstract

The purpose of the present study was to examine potential mechanisms for the known inhibitory effect of acute alcohol exposure on myocardial protein synthesis. Rats were injected intraperitoneally with either ethanol (75 mmol/kg) or saline, and protein synthesis was measured in vivo 2.5 h thereafter by use of the flooding-dosel-[3H]phenylalanine technique. Rates of myocardial protein synthesis and translational efficiency in alcohol-treated rats were decreased compared with control values. Free (nonpolysome bound) 40S and 60S ribosomal subunits were increased 50% after alcohol treatment, indicating an impaired peptide-chain initiation. To identify mechanisms responsible for this impairment, several eukaryotic initiation factors (eIF) were analyzed. Acute alcohol intoxication did not significantly alter the myocardial content of eIF2α or eIF2Bɛ, the extent of eIF2α phosphorylation, or the activity of eIF2B. Acute alcohol exposure increased the binding of 4E-binding protein 1 (4E-BP1) to eIF4E (55%), diminished the amount of eIF4E bound to eIF4G (70%), reduced the amount of 4E-BP1 in the phosphorylated γ-form (40%), and decreased the phosphorylation of p70S6 kinase and the ribosomal protein S6. There was no significant difference in either the plasma insulin-like growth factor (IGF) I concentration (total or free) or expression of IGF-I or IGF-II mRNA in heart between the two groups. These data suggest that the acute alcohol-induced impairment in myocardial protein synthesis results, in part, from an inhibition in peptide-chain initiation, which is associated with marked changes in eIF4E availability and p70S6 kinase phosphorylation but is independent of changes in the eIF2/2B system and IGFs.