mTOR kinase-dependent, but raptor-independent regulation of downstream signaling is important for cell cycle exit and myogenic differentiation.
mTOR kinase-dependent, but raptor-independent regulation of downstream signaling is important for cell cycle exit and myogenic differentiation.
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DOI：
10.4161/15384101.2014.941747
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发表时间：
2014
期刊：
影响因子：
--
通讯作者：
Morley SJ
中科院分区：
文献类型：
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作者：
Pollard HJ;Willett M;Morley SJ
C2 C12成肌细胞模型系统中的成肌分化反映了细胞退出细胞周期后转录和翻译的协调和受控激活。以前，我们已经表明，mTORC 1信号传导抑制剂，RAD 001，降低蛋白质合成速率，延迟C2 C12成肌细胞分化，降低p70 S6 K活性，但不影响4 E-BP 1的过度修饰。在这里，我们进一步研究了在细胞退出细胞周期的分化早期阶段4 E-BP 1的修饰，使用靶向mTOR激酶的抑制剂和siRNA来消除raptor和rictor的表达。正如所预测的，mTOR激酶活性的抑制阻止了p70 S6 K，4 E-BP 1磷酸化，并与肌源性分化的抑制有关。令人惊讶的是，raptor的大量消耗不影响p70 S6 K或4 E-BP 1磷酸化，但促进mTORC 2活性的增加（如Akt Ser 473磷酸化增加所证明的）。这些数据表明，mTOR激酶依赖性，但猛禽非依赖性的下游信号调节是重要的肌源性分化。
Myogenic differentiation in the C2C12 myoblast model system reflects a concerted and controlled activation of transcription and translation following the exit of cells from the cell cycle. Previously we have shown that the mTORC1 signaling inhibitor, RAD001, decreased protein synthesis rates, delayed C2C12 myoblast differentiation, decreased p70S6K activity but did not affect the hypermodification of 4E-BP1. Here we have further investigated the modification of 4E-BP1 during the early phase of differentiation as cells exit the cell cycle, using inhibitors to target mTOR kinase and siRNAs to ablate the expression of raptor and rictor. As predicted, inhibition of mTOR kinase activity prevented p70S6K, 4E-BP1 phosphorylation and was associated with an inhibition of myogenic differentiation. Surprisingly, extensive depletion of raptor did not affect p70S6K or 4E-BP1 phosphorylation, but promoted an increase in mTORC2 activity (as evidenced by increased Akt Ser473 phosphorylation). These data suggest that an mTOR kinase-dependent, but raptor-independent regulation of downstream signaling is important for myogenic differentiation.