The effect of dietary protein on the initiation of mRNA translation was examined in rats starved for 18 h and then refed isocaloric diets containing either 20% protein (20P) or no added protein (0P). In 18-h fasted rats, the amount of eukaryotic initiation factor eIF4E present in an inactive complex with the eIF4E binding protein, 4E-BP1, was significantly increased compared to freely fed animals. One h after refeeding the 20P diet, the amount of 4E-BP1 bound to eIF4E was reduced to control values. Decreased association of the two proteins was the result of increased phosphorylation of 4E-BP1. Refeeding a 20P diet also stimulated the binding of eIF4G to eIF4E to form the active eIF4F complex. In contrast, refeeding a 0P diet had no effect on the binding of eIF4E to either eIF4G or 4E-BP1 or on the phosphorylation of 4E-BP1. All of these effects were observed in both liver and skeletal muscle and the effects were similar in magnitude. Refeeding a 20P diet also resulted in partial dephosphorylation of eIF4E in both tissues. In liver, but not muscle, refeeding a 0P diet also resulted in partial dephosphorylation of eIF4E. Finally, plasma insulin concentrations were the same following refeeding either diet, suggesting that insulin alone does not affect the association of eIF4E with 4E-BP1 or eIF4G. Instead a combination of dietary protein and increased plasma insulin concentration is required to stimulate translation initiation.
|Published - Dec 1 1997
All Science Journal Classification (ASJC) codes
- Molecular Biology