Department of Biochemistry, College of Pharmacy, Nihon University, 7-7-1, Narashinodai, Funabashi, Chiba 274-8555, Japan.
Biochem Biophys Res Commun. 2011 Nov 4;414(4):647-52. doi: 10.1016/j.bbrc.2011.09.086. Epub 2011 Sep 21.
Y-box-binding protein 1 (YB-1) binds to mRNAs and affects translation. In this study, we focused on skeletal muscle, in which YB-1 expression is restricted to the early postnatal period, and found that YB-1 binds to acetylcholine receptor α-subunit (AChR α) mRNA. Although transcription of the AChR α gene is known to be regulated by myogenic transcription factors, translational control of the mRNA in response to neuromuscular transmission has not been examined. In undifferentiated C2C12 myoblasts, expression of AChR α remained at a low level. However, translation of the mRNA was increased by knockdown of YB-1. Continued overexpression of YB-1 prevented the cells from differentiating. In myotubes, which show clustering of AChRs, translation of the mRNA was induced within 3h after treatment with nicotine. The effect of nicotine was inhibited by α-bungarotoxin, and in the presence of cycloheximide the level of AChR α was reduced, even after nicotine treatment. Sucrose gradient analysis revealed that in nicotine-treated myotubes, YB-1-containing polysomes were shifted to the heavier-sedimenting fractions, and showed an apparent decrease in the amount of YB-1 bound to AChR α mRNA. These results suggest that in skeletal muscle cells, neural activity reduces the molar ratio of YB-1 relative to its binding AChR α mRNA, leading to an increase of ribosome binding to the mRNA, and thus activating translation. Furthermore, in postnatal growing mice, as has already been shown, the level of AChR α mRNA declined during the early period with maturation of neuromuscular synapses, but the translation level was found to increase transiently at postnatal day 10, when the level of YB-1 was markedly reduced. It is suggested that although the level of AChR α mRNA is reduced, the translation can be induced by alteration of the ratio of YB-1 protein to the mRNA.
Y 盒结合蛋白 1（YB-1）与 mRNA 结合并影响翻译。在这项研究中，我们专注于骨骼肌，其中 YB-1 的表达仅限于出生后的早期阶段，并且发现 YB-1 与乙酰胆碱受体 α 亚基（AChRα）mRNA 结合。虽然已知 AChRα 基因的转录受成肌转录因子调节，但尚未检查 mRNA 的翻译是否响应神经肌肉传递而受到调节。在未分化的 C2C12 成肌细胞中，AChRα 的表达保持在低水平。然而，YB-1 的敲低会增加 mRNA 的翻译。YB-1 的持续过表达阻止了细胞分化。在肌管中，AChR 聚集，用尼古丁处理后 3 小时内诱导 mRNA 的翻译。尼古丁的作用被α-银环蛇毒素抑制，并且在存在环己酰亚胺的情况下，即使在用尼古丁处理后，AChRα 的水平也降低。蔗糖梯度分析表明，在用尼古丁处理的肌管中，含有 YB-1 的多核糖体向较重的沉降部分转移，并且与 AChRα mRNA 结合的 YB-1 的量明显减少。这些结果表明，在骨骼肌细胞中，神经活动降低了 YB-1 与其结合的 AChRαmRNA 的摩尔比，导致核糖体与 mRNA 的结合增加，从而激活翻译。此外，在出生后生长的小鼠中，正如已经显示的那样，AChRαmRNA 的水平在神经肌肉突触成熟的早期阶段下降，但在出生后第 10 天，当 YB-1 的水平明显降低时，发现翻译水平短暂增加。这表明，尽管 AChRαmRNA 的水平降低，但通过改变 YB-1 蛋白与 mRNA 的比例可以诱导翻译。
