Leucine limitation induces autophagy and activation of lysosome-dependent proteolysis in C2C12 myotubes through a mammalian target of rapamycin-independent signaling pathway
Leucine limitation induces autophagy and activation of lysosome-dependent proteolysis in C2C12 myotubes through a mammalian target of rapamycin-independent signaling pathway
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DOI：
10.1074/jbc.m003633200
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发表时间：
2000-09-22
影响因子：
4.8
通讯作者：
Ferrara, M
中科院分区：
文献类型：
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作者：
Mordier, S;Deval, C;Ferrara, M
肌肉质量的损失通常表征不同的病理（败血症，癌症，创伤），也发生在正常衰老过程中。肌肉萎缩的一个原因与食物摄入量减少有关。本研究探讨了亮氨酸作为小鼠C2 C12肌管中蛋白质分解的调节剂的作用，旨在确定哪些细胞反应调节该过程。蛋白质分解速率的测定表明，亮氨酸是肌管中该过程的一个关键调节因子，因为这种氨基酸的饥饿占总氨基酸饥饿产生的总增加的30-40%。亮氨酸限制以剂量依赖性方式迅速加速蛋白质分解速率（饥饿1小时后+11至15%（p < 0.001））。通过使用各种抑制剂，提供的证据表明，蛋白质催化的加速主要是由于诱导自噬，激活溶酶体依赖性蛋白水解，而不改变编码溶酶体组织蛋白酶B、L或D的mRNA水平。这些结果表明，自噬是食物剥夺后增加肌肉中蛋白质分解的必要细胞反应。自噬的诱导先于亮氨酸饥饿3小时后发生的整体蛋白质合成减少（约20%至约30%（p < 0.001））。抑制哺乳动物雷帕霉素靶蛋白（mTOR）活性并不能消除亮氨酸饥饿的作用，磷酸化核糖体S6蛋白的水平也不受亮氨酸戒断的影响。这些后面的数据提供了明确的证据，表明mTOR信号传导途径不参与亮氨酸对C2 C12肌管中蛋白质合成和降解的调节。
Loss of muscle mass usually characterizes different pathologies (sepsis, cancer, trauma) and also occurs during normal aging. One reason for muscle wasting relates to a decrease in food intake. This study addressed the role of leucine as a regulator of protein breakdown in mouse C2C12 myotubes and aimed to determine which cellular responses regulate the process. Determination of the rate of protein breakdown indicated that leucine is one key regulator of this process in myotubes because starvation for this amino acid is responsible for 30-40% of the total increase generated by total amino acid starvation. Leucine restriction rapidly accelerates the rate of protein breakdown (+11 to 15% (p < 0.001) after 1 h of starvation) in a dose-dependent manner. By using various inhibitors, evidence is provided that acceleration of protein catabolism results mainly from an induction of autophagy, activation of lysosome-dependent proteolysis, without modification of mRNA levels encoding the lysosomal cathepsins B, L, or D. Those results suggest that autophagy is an essential cellular response for increasing protein breakdown in muscle following food deprivation, Induction of autophagy precedes a decrease in global protein synthesis (-20% to -30% (p < 0.001)) that occurs after 3 h of leucine starvation. Inhibition of the mammalian target of rapamycin (mTOR) activity does not abolish the effect of leucine starvation and the level of phosphorylated ribosomal S6 protein is not affected by leucine withdrawal. These latter data provide clear evidence that the mTOR signaling pathway is not involved in the mediation of leucine effects on both protein synthesis and degradation in C2C12 myotubes.