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Departments of Cellular and Molecular Physiology, and Surgery, Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033
The present study examined potential cellular
mechanisms responsible for the inhibition of protein synthesis in liver
after chronic alcohol consumption. Rats were maintained on an
alcohol-containing diet for 14 wk; control animals were fed
isocalorically. Hepatic ATP content was not different in alcohol-fed
and control animals. No alcohol-induced reduction in total hepatic RNA
content (an estimate of ribosomal RNA) was detected, suggesting that
alcohol decreased translational efficiency. Alcohol feeding increased the proportion of 40S and 60S ribosomal subunits in the
nonpolysome-associated fraction by 30%. To identify mechanisms
responsible for the impairment in initiation, several eukaryotic
initiation factors (eIF) were analyzed. Alcohol feeding decreased
hepatic eIF2B activity by 36%. This reduction was associated with a
20% decrease in eIF2B
content and a 90% increase in eIF2
phosphorylation. Alcohol also dramatically influenced the distribution
of eIF4E. Compared with pair-fed control values, alcohol feeding
increased the amount of eIF4E present in the inactive 4E-binding
protein 1 (4E-BP1) · eIF4E complex by 80% and
decreased binding of eIF4G to eIF4E by 70%. However, the
phosphorylation status of 4E-BP1 and eIF4E was not altered by alcohol.
Although the plasma concentrations of threonine, proline, and
citrulline were mildly decreased, the circulating amount of total amino
acids was not altered by alcohol feeding. In summary, these data
suggest that chronic alcohol consumption impairs translation initiation
in liver by altering eIF2B activity as well as eIF4F function via
changes in eIF4E availability.
eukaryotic initiation factor 2; eukaryotic initiation factor 4E; ribosomal subunits; amino acids; liver; rats
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