Yoshizawa F, Kimball S R, Vary T C, Jefferson L S
Department of Cellular and Molecular Physiology, Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033, USA.
Am J Physiol. 1998 Nov;275(5):E814-20. doi: 10.1152/ajpendo.1998.275.5.E814.
The effect of dietary protein on the initiation of mRNA translation was examined in rats starved for 18 h and then fed isocaloric diets containing either 20% protein (20P) or no added protein (0P). Feeding the 20P diet, but not the 0P diet, stimulated protein synthesis in skeletal muscle and liver by 38 and 41%, respectively. The stimulation was associated with reduced binding of eukaryotic initiation factor (eIF) 4E to the translational repressor 4E-BP1, increased formation of the active eIF4E-eIF4G complex, and increased phosphorylation of 4E-BP1. In contrast, feeding a 0P diet had no effect on any of these parameters. Feeding a 20P diet resulted in partial dephosphorylation of eIF4E in both tissues. In liver, refeeding a 0P diet also resulted in partial eIF4E dephosphorylation, suggesting that the phosphorylation state of eIF4E is not important in the stimulation of protein synthesis under these conditions. Finally, plasma insulin concentrations were the same in rats fed either diet (14.8 +/- 4.9 vs. 15.5 +/- 4.5 microU/ml for 20P and 0P groups, respectively), suggesting that feeding-induced changes in plasma insulin are not sufficient to stimulate protein synthesis. Instead, a combination of dietary protein and insulin may be required to stimulate translation initiation.
在饥饿18小时后再喂食等热量饮食（含20%蛋白质的20P饮食或无添加蛋白质的0P饮食）的大鼠中，研究了膳食蛋白质对mRNA翻译起始的影响。喂食20P饮食而非0P饮食分别使骨骼肌和肝脏中的蛋白质合成增加了38%和41%。这种刺激与真核起始因子（eIF）4E与翻译抑制因子4E - BP1的结合减少、活性eIF4E - eIF4G复合物的形成增加以及4E - BP1的磷酸化增加有关。相比之下，喂食0P饮食对这些参数均无影响。喂食20P饮食导致两个组织中的eIF4E部分去磷酸化。在肝脏中，重新喂食0P饮食也导致eIF4E部分去磷酸化，这表明在这些条件下eIF4E的磷酸化状态对蛋白质合成的刺激并不重要。最后，两种饮食喂养的大鼠血浆胰岛素浓度相同（20P组和0P组分别为14.8±4.9与15.5±4.5微单位/毫升），这表明喂食引起的血浆胰岛素变化不足以刺激蛋白质合成。相反，可能需要膳食蛋白质和胰岛素共同作用来刺激翻译起始。
