Department of Molecular Oncology, British Columbia Cancer Research Centre, Vancouver, BC, Canada.
Faculty of Medicine, University of British Columbia, Vancouver, BC, Canada.
EMBO Rep. 2023 Dec 6;24(12):e56815. doi: 10.15252/embr.202356815. Epub 2023 Oct 17.
HACE1 is a HECT family E3 ubiquitin-protein ligase with broad but incompletely understood tumor suppressor activity. Here, we report a previously unrecognized link between HACE1 and signaling complexes containing mammalian target of rapamycin (mTOR). HACE1 blocks mTORC1 and mTORC2 activities by reducing mTOR stability in an E3 ligase-dependent manner. Mechanistically, HACE1 binds to and ubiquitylates Ras-related C3 botulinum toxin substrate 1 (RAC1) when RAC1 is associated with mTOR complexes, including at focal adhesions, leading to proteasomal degradation of RAC1. This in turn decreases the stability of mTOR to reduce mTORC1 and mTORC2 activity. HACE1 deficient cells show enhanced mTORC1/2 activity, which is reversed by chemical or genetic RAC1 inactivation but not in cells expressing the HACE1-insensitive mutant, RAC1 . In vivo, Rac1 deletion reverses enhanced mTOR expression in KRas -driven lung tumors of Hace1 mice. HACE1 co-localizes with mTOR and RAC1, resulting in RAC1-dependent loss of mTOR protein stability. Together, our data demonstrate that HACE1 destabilizes mTOR by targeting RAC1 within mTOR-associated complexes, revealing a unique ubiquitin-dependent process to control the activity of mTOR signaling complexes.
HACE1 是一种 HECT 家族 E3 泛素蛋白连接酶，具有广泛但不完全了解的肿瘤抑制活性。在这里，我们报告了 HACE1 与包含雷帕霉素靶蛋白（mTOR）的信号复合物之间以前未被识别的联系。HACE1 通过以 E3 连接酶依赖的方式降低 mTOR 的稳定性来阻断 mTORC1 和 mTORC2 的活性。在机制上，当 RAC1 与包括焦点黏附在内的 mTOR 复合物结合时，HACE1 结合并泛素化 Ras 相关 C3 肉毒杆菌毒素底物 1（RAC1），导致 RAC1 的蛋白酶体降解。这反过来又降低了 mTOR 的稳定性，从而降低了 mTORC1 和 mTORC2 的活性。缺乏 HACE1 的细胞显示增强的 mTORC1/2 活性，这可以通过化学或遗传 RAC1 失活来逆转，但在表达 HACE1 不敏感突变体 RAC1 的细胞中则不会逆转。在体内，Rac1 缺失逆转了 Hace1 小鼠中 KRas 驱动的肺肿瘤中增强的 mTOR 表达。HACE1 与 mTOR 和 RAC1 共定位，导致 RAC1 依赖性 mTOR 蛋白稳定性丧失。总之，我们的数据表明，HACE1 通过靶向 mTOR 相关复合物中的 RAC1 来使 mTOR 不稳定，揭示了一种独特的依赖泛素的过程来控制 mTOR 信号复合物的活性。
