Activation of the mammalian target of rapamycin complex 1 is both necessary and sufficient to stimulate eukaryotic initiation factor 2Bε mRNA translation and protein synthesis
Activation of the mammalian target of rapamycin complex 1 is both necessary and sufficient to stimulate eukaryotic initiation factor 2Bε mRNA translation and protein synthesis
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DOI：
10.1016/j.biocel.2008.04.010
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发表时间：
2008-01-01
影响因子：
4
通讯作者：
Jefferson, Leonard S.
中科院分区：
文献类型：
--
作者：
Kubica, Neil;Crispino, Jamie L.;Jefferson, Leonard S.
在先前的研究中，我们证明了在响应抗阻运动的骨骼肌中刺激eIF 2B mRNA翻译需要mTORC 1的激活。尽管该研究确定了mTORC 1激活的必要性。所用的实验模型并不容易解决mTORC 1活化是否足以产生应答的问题。因此，本研究旨在使用Rat 2成纤维细胞培养物来解决mTORC 1活化的充分性，其中mTORC 1信号传导被血清/亮氨酸耗尽抑制并被亮氨酸和/或IGF-1补充刺激。补充亮氨酸和IGF-1导致eIF 2B β mRNA转移到积极翻译的多聚核糖体中，并刺激新的eIF 2B β蛋白的合成，但对编码其他四个eIF 2B亚基的mRNA没有影响。通过用mTORC 1抑制剂雷帕霉素预处理逆转eIF 2B β翻译的刺激。FLAG-Rheb（mTORC 1的近端激活剂）的外源性过表达也引起eIF 2B β的重新分布。mRNA进入多核糖体和刺激eIF 2B β蛋白合成。eIF 2B β mRNA翻译的刺激发生在对eIF 2B β mRNA丰度没有任何影响的情况下。RNAi介导的eIF 2B抑制导致细胞增殖减少，这一结果表型模仿了mTORC 1抑制的已知细胞抑制作用。总体而言，结果表明，mTORC 1的激活是必要的，足以刺激eIF 2B β mRNA翻译，这种反应可能代表了一种新的机制，通过mTORC 1可以影响mRNA翻译起始，蛋白质合成速率和细胞生长/增殖。(C)2008爱思唯尔有限公司保留所有权利。
In a previous study we demonstrated a requirement for activation of mTORC1 in the stimulation of eIF2B epsilon mRNA translation in skeletal muscle in response to resistance exercise. Although that study established the necessity of mTORC1 activation. the experimental model used did not lend itself readily to address the question of whether or not mTORC1 activation was sufficient to produce the response. Therefore, the present study was designed to address the sufficiency of mTORC1 activation, using cultures of Rat2 fibroblasts in which mTORC1 signaling was repressed by serum/leucine-depletion and stimulated by repletion of leucine and/or IGF-1. Repletion with leucine and IGF-1 caused a shift of eIF2B epsilon mRNA into actively translating polysomes and a stimulation of new eIF2B epsilon protein synthesis, but had no effect on mRNAs encoding the other four eIF2B subunits. Stimulation of eIF2B epsilon translation was reversed by pre-treatment with the mTORC1 inhibitor rapamycin. Exogenous overexpression of FLAG-Rheb, a proximal activator of mTORC1, also caused a re-distribution of eIF2B epsilon. mRNA into polysomes and a stimulation of eIF2B epsilon protein synthesis. The stimulation of eIF2B epsilon mRNA translation occurred in the absence of any effect on eIF2B epsilon mRNA abundance. RNAi-mediated knockdown of eIF2B epsilon resulted in reduced cellular proliferation, a result that phenocopied the known cytostatic effect of mTORC1 repression. Overall the results demonstrate that activation of mTORC1 is both necessary and sufficient to stimulate eIF2B epsilon mRNA translation and that this response may represent a novel mechanism through which mTORC1 can affect mRNA translation initiation, rates of protein synthesis, and cellular growth/proliferation. (C) 2008 Elsevier Ltd. All rights reserved.