The tuberous sclerosis protein TSC2 is not required for the regulation of the mammalian target of rapamycin by amino acids and certain cellular stresses
The tuberous sclerosis protein TSC2 is not required for the regulation of the mammalian target of rapamycin by amino acids and certain cellular stresses
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DOI：
10.1074/jbc.m414499200
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发表时间：
2005-05-13
影响因子：
4.8
通讯作者：
Proud, CG
中科院分区：
文献类型：
--
作者：
Smith, EM;Finn, SG;Proud, CG
氨基酸通过哺乳动物雷帕霉素靶蛋白（mTOR）积极调节信号传导。最近的研究表明，结节性硬化症蛋白TSC2对胰岛素调控mTOR的重要性。TSC2含有GTPase-activator结构域，可促进与Rheb结合的GTP水解，从而正向调节mTOR信号传导。一些研究表明，TSC2也介导氨基酸对mTOR的控制。在缺乏TSC2的细胞中，氨基酸退出仍然会导致S6K1、核糖体蛋白S6、真核起始因子4e结合蛋白和延伸因子2激酶的去磷酸化。通过抑制蛋白质合成或添加回氨基酸来减少氨基酸退出的影响。这些研究表明，氨基酸对mTOR的信号传导独立于TSC2发生，并涉及额外的未知输入。虽然mTOR的氨基酸控制不需要TSC2，但氨基酸停用确实降低了Rheb处于活性gtp结合状态的比例。在这里，我们还表明Rheb和mTOR形成稳定的复合物，然而，氨基酸退出不会破坏。不能结合GTP或GDP的Rheb突变体可以与mTOR复合物相互作用。我们还表明过氧化氢和山梨醇的作用，细胞应激损害mTOR信号，是独立于TSC2的。最后，我们发现能量消耗（损害TSC2（+/+）细胞中的mTOR信号传导）增加真核延伸因子2磷酸化的能力也独立于TSC2。这可能涉及延伸因子-2激酶被amp激活的蛋白激酶磷酸化。
Amino acids positively regulate signaling through the mammalian target of rapamycin ( mTOR). Recent work demonstrated the importance of the tuberous sclerosis protein TSC2 for regulation of mTOR by insulin. TSC2 contains a GTPase-activator domain that promotes hydrolysis of GTP bound to Rheb, which positively regulates mTOR signaling. Some studies have suggested that TSC2 also mediates the control of mTOR by amino acids. In cells lacking TSC2, amino acid withdrawal still results in dephosphorylation of S6K1, ribosomal protein S6, the eukaryotic initiation factor 4E-binding protein, and elongation factor-2 kinase. The effects of amino acid withdrawal are diminished by inhibiting protein synthesis or adding back amino acids. These studies demonstrate that amino acid signaling to mTOR occurs independently of TSC2 and involves additional unidentified inputs. Although TSC2 is not required for amino acid control of mTOR, amino acid withdrawal does decrease the proportion of Rheb in the active GTP-bound state. Here we also show that Rheb and mTOR form stable complexes, which are not, however, disrupted by amino acid withdrawal. Mutants of Rheb that cannot bind GTP or GDP can interact with mTOR complexes. We also show that the effects of hydrogen peroxide and sorbitol, cell stresses that impair mTOR signaling, are independent of TSC2. Finally, we show that the ability of energy depletion (which impairs mTOR signaling in TSC2(+/+) cells) to increase the phosphorylation of eukaryotic elongation factor 2 is also independent of TSC2. This likely involves the phosphorylation of the elongation factor-2 kinase by the AMP-activated protein kinase.