Inhibition of muscle protein synthesis by alcohol is associated with modulation of eIF2B and eIF4E.
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 eIF2alpha or the amount of eIF2alpha in the phosphorylated form between alcohol-fed and control rats. Similarly, the relative amount of eIF2Bepsilon 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 demonstrated 1) an increased binding of the translational repressor 4E-binding protein 1 (4E-BP1) with eIF4E, 2) a decrease in the phosphorylated gamma-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.
Lang
C H
CH
Departments of Cellular and Molecular Physiology and Surgery, Pennsylvania State College of Medicine, Hershey, Pennsylvania 17033, USA. clang@psghs.edu
Wu
D
D
Frost
R A
RA
Jefferson
L S
LS
Kimball
S R
SR
Vary
T C
TC
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D001823:Body Composition / Q000187:drug effects; D000431:Ethanol / Q000494:pharmacology*; D020717:Eukaryotic Initiation Factor-2B; D039561:Eukaryotic Initiation Factor-4E; D020662:Guanine Nucleotide Exchange Factors; D007328:Insulin / Q000097:blood; D008297:Male; D009124:Muscle Proteins / Q000037:antagonists & inhibitors* / Q000096:biosynthesis; D009132:Muscles / Q000033:anatomy & histology; D009929:Organ Size / Q000187:drug effects; D010448:Peptide Initiation Factors / Q000378:metabolism*; D010725:Phosphocreatine / Q000378:metabolism; D020033:Protein Isoforms / Q000378:metabolism; D011506:Proteins / Q000378:metabolism*; D012313:RNA / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D012269:Ribosomal Proteins / Q000378:metabolism
D020717:Eukaryotic Initiation Factor-2B; D039561:Eukaryotic Initiation Factor-4E; D020662:Guanine Nucleotide Exchange Factors; D007328:Insulin; D009124:Muscle Proteins; D010448:Peptide Initiation Factors; D020033:Protein Isoforms; D011506:Proteins; D012269:Ribosomal Proteins; D010725:Phosphocreatine; D000431:Ethanol; D012313:RNA; D000255:Adenosine Triphosphate