Regulation of targets of mTOR (mammalian target of rapamycin) signalling by intracellular amino acid availability
Regulation of targets of mTOR (mammalian target of rapamycin) signalling by intracellular amino acid availability
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DOI：
10.1042/bj20021266
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发表时间：
2003-06-01
影响因子：
4.1
通讯作者：
Proud, CG
中科院分区：
文献类型：
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作者：
Beugnet, A;Tee, AR;Proud, CG
在哺乳动物细胞中，氨基酸影响参与mRNA翻译的几种蛋白质的磷酸化状态和功能，这些蛋白质通过雷帕霉素敏感性mTOR（雷帕霉素的哺乳动物靶蛋白）途径进行调节。这些包括核糖体蛋白S6激酶，S6 K1和真核起始因子4 E结合蛋白，4 E-BP 1。氨基酸，特别是支链氨基酸，如亮氨酸，促进4 E-BP 1和S6 K1的磷酸化，并允许胰岛素进一步增加其磷酸化。然而，目前尚不清楚这些作用是由细胞外还是细胞内氨基酸发挥的。预期蛋白质合成的抑制会增加氨基酸的细胞内水平，而抑制蛋白质水解具有相反的效果。我们在本研究中表明，通过测试的几种蛋白质合成抑制剂中的任何一种抑制蛋白质合成，可以使胰岛素调节氨基酸剥夺细胞中的4 E-BP 1或S6 K1，向培养基中添加氨基酸也是如此。特别是，胰岛素激活S6 K1和促进起始因子复合物组装在氨基酸剥夺细胞与蛋白质合成抑制剂处理，但不能这样做，在没有这些化合物。它们的作用发生在与其抑制蛋白质合成的浓度相称的浓度下，而不是由于应激激活激酶级联的激活。蛋白质分解（自噬）的抑制损害了胰岛素在这种条件下调节4 E-BP 1或S6 K1的能力。目前研究中提供的这些和其他数据与细胞内氨基酸水平调节mTOR信号传导的想法一致。
In mammalian cells, amino acids affect the phosphorylation state and function of several proteins involved in mRNA translation that are regulated via the rapamycin-sensitive mTOR (mammalian target of rapamycin) pathway. These include ribosomal protein S6 kinase, S6K1, and eukaryotic initiation factor 4E-binding protein, 4E-BP1. Amino acids, especially branched-chain amino acids, such as leucine, promote phosphorylation of 4E-BP1 and S6K1, and permit insulin to further increase their phosphorylation. However, it is not clear whether these effects are exerted by extracellular or intracellular amino acids. Inhibition of protein synthesis is expected to increase the intracellular level of amino acids, whereas inhibiting proteolysis has the opposite effect. We show in the present study that inhibition of protein synthesis by any of several protein synthesis inhibitors tested allows insulin to regulate 4E-BP1 or S6K1 in amino-acid-deprived cells, as does the addition of amino acids to the medium. In particular, insulin activates S6K1 and promotes initiation factor complex assembly in amino-acid-deprived cells treated with protein synthesis inhibitors, but cannot do so in the absence of these compounds. Their effects occur at concentrations commensurate with their inhibition of protein synthesis and are not due to activation of stress-activated kinase cascades. Inhibition of protein breakdown (autophagy) impairs the ability of insulin to regulate 4E-BP1 or S6K1 under such conditions. These and other data presented in the current study are consistent with the idea that it is intracellular amino acid levels that regulate mTOR signalling.