Wang Bin, Jie Zuliang, Joo Donghyun, Ordureau Alban, Liu Pengda, Gan Wenjian, Guo Jianping, Zhang Jinfang, North Brian J, Dai Xiangpeng, Cheng Xuhong, Bian Xiuwu, Zhang Lingqiang, Harper J Wade, Sun Shao-Cong, Wei Wenyi
Department of Gastroenterology, Institute of Surgery Research, Daping Hospital, Third Military Medical University, Chongqing 400042, China.
Department of Pathology, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, Massachusetts 02215, USA.
Nature. 2017 May 18;545(7654):365-369. doi: 10.1038/nature22344. Epub 2017 May 10.
The mechanistic target of rapamycin (mTOR) has a key role in the integration of various physiological stimuli to regulate several cell growth and metabolic pathways. mTOR primarily functions as a catalytic subunit in two structurally related but functionally distinct multi-component kinase complexes, mTOR complex 1 (mTORC1) and mTORC2 (refs 1, 2). Dysregulation of mTOR signalling is associated with a variety of human diseases, including metabolic disorders and cancer. Thus, both mTORC1 and mTORC2 kinase activity is tightly controlled in cells. mTORC1 is activated by both nutrients and growth factors, whereas mTORC2 responds primarily to extracellular cues such as growth-factor-triggered activation of PI3K signalling. Although both mTOR and GβL (also known as MLST8) assemble into mTORC1 and mTORC2 (refs 11, 12, 13, 14, 15), it remains largely unclear what drives the dynamic assembly of these two functionally distinct complexes. Here we show, in humans and mice, that the K63-linked polyubiquitination status of GβL dictates the homeostasis of mTORC2 formation and activation. Mechanistically, the TRAF2 E3 ubiquitin ligase promotes K63-linked polyubiquitination of GβL, which disrupts its interaction with the unique mTORC2 component SIN1 (refs 12, 13, 14) to favour mTORC1 formation. By contrast, the OTUD7B deubiquitinase removes polyubiquitin chains from GβL to promote GβL interaction with SIN1, facilitating mTORC2 formation in response to various growth signals. Moreover, loss of critical ubiquitination residues in GβL, by either K305R/K313R mutations or a melanoma-associated GβL(ΔW297) truncation, leads to elevated mTORC2 formation, which facilitates tumorigenesis, in part by activating AKT oncogenic signalling. In support of a physiologically pivotal role for OTUD7B in the activation of mTORC2/AKT signalling, genetic deletion of Otud7b in mice suppresses Akt activation and Kras-driven lung tumorigenesis in vivo. Collectively, our study reveals a GβL-ubiquitination-dependent switch that fine-tunes the dynamic organization and activation of the mTORC2 kinase under both physiological and pathological conditions.
雷帕霉素作用的分子靶点（mTOR）在整合各种生理刺激以调节多种细胞生长和代谢途径中起关键作用。mTOR主要作为两种结构相关但功能不同的多组分激酶复合物——mTOR复合物1（mTORC1）和mTOR复合物2（参考文献1,2）中的催化亚基发挥作用。mTOR信号失调与多种人类疾病相关，包括代谢紊乱和癌症。因此，mTORC1和mTORC2激酶活性在细胞中受到严格控制。mTORC1由营养物质和生长因子激活，而mTORC2主要响应细胞外信号，如生长因子触发的PI3K信号激活。尽管mTOR和GβL（也称为MLST8）都组装到mTORC1和mTORC2中（参考文献11,12,13,14,15），但在很大程度上仍不清楚是什么驱动了这两种功能不同的复合物的动态组装。在这里，我们在人和小鼠中表明，GβL的K63连接的多聚泛素化状态决定了mTORC2形成和激活的稳态。从机制上讲，TRAF2 E3泛素连接酶促进GβL的K63连接多聚泛素化，这破坏了它与mTORC2独特组分SIN1的相互作用（参考文献12,13,14），从而有利于mTORC1的形成。相比之下，OTUD7B去泛素酶从GβL上去除多聚泛素链，以促进GβL与SIN1的相互作用，促进mTORC2在各种生长信号响应下的形成。此外，通过K305R/K313R突变或与黑色素瘤相关的GβL(ΔW297)截短导致GβL中关键泛素化残基的缺失，会导致mTORC2形成增加，这部分通过激活AKT致癌信号促进肿瘤发生。为了支持OTUD7B在激活mTORC2/AKT信号中具有生理关键作用，小鼠中Otud7b的基因缺失在体内抑制了Akt激活和Kras驱动的肺癌发生。总的来说，我们的研究揭示了一个依赖于GβL泛素化的开关，它在生理和病理条件下微调mTORC2激酶的动态组织和激活。
