The present study examined potential mechanisms for the inhibition of protein synthesis in skeletal muscle after chronic alcohol consumption. Rats were maintained on an alcohol-containing diet for 14 wk; control animals were pair fed. Alcohol-induced myopathy was confirmed by a reduction in lean body mass as well as a decrease in the weight of the gastrocnemius and psoas muscles normalized for tibial length. No alcohol-induced decrease in total RNA content (an estimate of ribosomal RNA) was detected in any muscle examined, suggesting that alcohol reduced translational efficiency but not the capacity for protein synthesis. To identify mechanisms responsible for regulating translational efficiency, we analyzed several eukaryotic initiation factors (eIF). There was no difference in the muscle content of either total eIF2α or the amount of eIF2α in the phosphorylated form between alcohol-fed and control rats. Similarly, the relative amount of eIF2Bε in muscle was also not different. In contrast, alcohol decreased eIF2B activity in psoas (fast-twitch) but not in soleus or heart (slow-twitch) muscles. Alcohol feeding also dramatically influenced the distribution of eIF4E in the gastrocnemius (fast-twitch) muscle. Compared with control values, muscle from alcohol-fed rats demonstrated1) an increased binding of the translational repressor 4E-binding protein 1 (4E-BP1) with eIF4E,2) a decrease in the phosphorylated γ-form of 4E-BP1, and 3) a decrease in eIF4G associated with eIF4E. In summary, these data suggest that chronic alcohol consumption impairs translation initiation in muscle by altering multiple regulatory sites, including eIF2B activity and eIF4E availability.
- peptide-chain initiation
- translation initiation
- eukaryotic initiation factors 2, 4E, and 4G
- 4E-binding protein 1
- adenosine 5′-triphosphate
Address for reprint requests and other correspondence: C. H. Lang, Dept. of Cell. Molec. Physiology (H166), Penn State College of Medicine, Hershey, PA 17033-0850 (E-mail:).
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- Copyright © 1999 the American Physiological Society