Institute for Ageing and Health, Newcastle University, Campus for Ageing and Vitality, Newcastle upon Tyne, UK.
Sci Signal. 2012 Mar 27;5(217):ra25. doi: 10.1126/scisignal.2002469.
The kinase mammalian target of rapamycin (mTOR) exists in two multiprotein complexes (mTORC1 and mTORC2) and is a central regulator of growth and metabolism. Insulin activation of mTORC1, mediated by phosphoinositide 3-kinase (PI3K), Akt, and the inhibitory tuberous sclerosis complex 1/2 (TSC1-TSC2), initiates a negative feedback loop that ultimately inhibits PI3K. We present a data-driven dynamic insulin-mTOR network model that integrates the entire core network and used this model to investigate the less well understood mechanisms by which insulin regulates mTORC2. By analyzing the effects of perturbations targeting several levels within the network in silico and experimentally, we found that, in contrast to current hypotheses, the TSC1-TSC2 complex was not a direct or indirect (acting through the negative feedback loop) regulator of mTORC2. Although mTORC2 activation required active PI3K, this was not affected by the negative feedback loop. Therefore, we propose an mTORC2 activation pathway through a PI3K variant that is insensitive to the negative feedback loop that regulates mTORC1. This putative pathway predicts that mTORC2 would be refractory to Akt, which inhibits TSC1-TSC2, and, indeed, we found that mTORC2 was insensitive to constitutive Akt activation in several cell types. Our results suggest that a previously unknown network structure connects mTORC2 to its upstream cues and clarifies which molecular connectors contribute to mTORC2 activation.
哺乳动物雷帕霉素靶蛋白激酶（mTOR）存在于两个多蛋白复合物（mTORC1 和 mTORC2）中，是生长和代谢的中央调节剂。胰岛素通过磷酸肌醇 3-激酶（PI3K）、Akt 和抑制性结节性硬化复合物 1/2（TSC1-TSC2）激活 mTORC1，启动负反馈环，最终抑制 PI3K。我们提出了一个基于数据的动态胰岛素-mTOR 网络模型，该模型整合了整个核心网络，并利用该模型研究了胰岛素调节 mTORC2 的机制，这些机制目前了解较少。通过分析针对网络中几个层次的扰动的计算机模拟和实验影响，我们发现，与当前的假设相反，TSC1-TSC2 复合物不是 mTORC2 的直接或间接（通过负反馈环作用）调节剂。尽管 mTORC2 的激活需要活性的 PI3K，但这不受负反馈环的影响。因此，我们提出了一种通过对调节 mTORC1 的负反馈环不敏感的 PI3K 变体激活 mTORC2 的途径。这个假定的途径预测 mTORC2 将对 Akt 不敏感，Akt 抑制 TSC1-TSC2，实际上，我们发现 mTORC2 在几种细胞类型中对组成性 Akt 激活不敏感。我们的结果表明，一个以前未知的网络结构将 mTORC2 与其上游线索连接起来，并阐明了哪些分子连接器有助于 mTORC2 的激活。
