S6 kinase inactivation impairs growth and translational target phosphorylation in muscle cells maintaining proper regulation of protein turnover
S6 kinase inactivation impairs growth and translational target phosphorylation in muscle cells maintaining proper regulation of protein turnover
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DOI：
10.1152/ajpcell.00499.2006
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发表时间：
2007-08-01
影响因子：
5.5
通讯作者：
Pende, Mario
中科院分区：
文献类型：
--
作者：
Mieulet, Virginie;Roceri, Mila;Pende, Mario
蛋白质周转缺陷是多种形式的细胞萎缩的基础。由于S6激酶(S6K)缺陷的细胞很小，对营养和生长因子的可获得性反应迟钝，我们假设突变细胞萎缩可能是由全球蛋白质合成的变化触发的。通过使用针对哺乳动物靶标雷帕霉素(MTOR)/S6K通路的小鼠遗传学和药物抑制剂，我们评估了mTOR/S6K通路对骨骼肌和肝脏组织中翻译靶标磷酸化和蛋白质周转的控制。在肌肉细胞中，核糖体蛋白S6(RpS6)、真核细胞起始因子-4B(EIF4B)和真核细胞延伸因子-2(EEF2)的磷酸化主要受mTOR调控。相反，在肝脏中，MAPK和磷脂酰肌醇3-激酶通路也发挥着重要作用，这表明了一种组织特异性调控。肌肉中S6K的缺失模拟了mTOR抑制剂雷帕霉素对rpS6和eIF4B磷酸化的影响，而不影响eEF2的磷酸化。为了深入了解这些修饰的功能后果，我们评估了肌细胞中蛋氨酸的掺入和多聚体的分布。在S6K缺陷的肌肉细胞中，整体翻译启动的速率和雷帕霉素的敏感性没有改变。此外，蛋白质降解的两条主要途径--自噬和肌肉萎缩相关的E3泛素连接酶的表达--不受S6K缺失的影响。我们的结果不支持全局翻译调控在S6K缺失导致的生长缺陷中所起的作用，提示了mTOR下游特定的生长控制和翻译靶调控模式。
A defect in protein turnover underlies multiple forms of cell atrophy. Since S6 kinase (S6K)-deficient cells are small and display a blunted response to nutrient and growth factor availability, we have hypothesized that mutant cell atrophy may be triggered by a change in global protein synthesis. By using mouse genetics and pharmacological inhibitors targeting the mammalian target of rapamycin (mTOR)/S6K pathway, here we evaluate the control of translational target phosphorylation and protein turnover by the mTOR/S6K pathway in skeletal muscle and liver tissues. The phosphorylation of ribosomal protein S6 (rpS6), eukaryotic initiation factor-4B (eIF4B), and eukaryotic elongation factor-2 (eEF2) is predominantly regulated by mTOR in muscle cells. Conversely, in liver, the MAPK and phosphatidylinositol 3-kinase pathways also play an important role, suggesting a tissue-specific control. S6K deletion in muscle mimics the effect of the mTOR inhibitor rapamycin on rpS6 and eIF4B phosphorylation without affecting eEF2 phosphorylation. To gain insight on the functional consequences of these modifications, methionine incorporation and polysomal distribution were assessed in muscle cells. Rates and rapamycin sensitivity of global translation initiation are not altered in S6K-deficient muscle cells. In addition, two major pathways of protein degradation, autophagy and expression of the muscle-specific atrophy-related E3 ubiquitin ligases, are not affected by S6K deletion. Our results do not support a role for global translational control in the growth defect due to S6K deletion, suggesting specific modes of growth control and translational target regulation downstream of mTOR.