Departments of Cell Biology and Neuroscience, Yale University School of Medicine, New Haven, CT 06510.
Mol Biol Cell. 2019 Oct 15;30(22):2750-2760. doi: 10.1091/mbc.E19-03-0146. Epub 2019 Sep 18.
Stable localization of the Rheb GTPase to lysosomes is thought to be required for activation of mTOR complex 1 (mTORC1) signaling. However, the lysosome targeting mechanisms for Rheb remain unclear. We therefore investigated the relationship between Rheb subcellular localization and mTORC1 activation. Surprisingly, we found that Rheb was undetectable at lysosomes. Nonetheless, functional assays in knockout human cells revealed that farnesylation of the C-terminal CaaX motif on Rheb was essential for Rheb-dependent mTORC1 activation. Although farnesylated Rheb exhibited partial endoplasmic reticulum (ER) localization, constitutively targeting Rheb to ER membranes did not support mTORC1 activation. Further systematic analysis of Rheb lipidation revealed that weak, nonselective, membrane interactions support Rheb-dependent mTORC1 activation without the need for a specific lysosome targeting motif. Collectively, these results argue against stable interactions of Rheb with lysosomes and instead that transient membrane interactions optimally allow Rheb to activate mTORC1 signaling.
雷帕霉素靶蛋白复合物 1（mTORC1）信号的激活被认为需要 Rheb GTPase 在溶酶体上的稳定定位。然而，Rheb 的溶酶体靶向机制仍不清楚。因此，我们研究了 Rheb 亚细胞定位与 mTORC1 激活之间的关系。令人惊讶的是，我们发现 Rheb 在溶酶体上无法检测到。尽管如此，在敲除的人类细胞中的功能测定表明，Rheb 上 C 末端 CaaX 基序的法尼基化对于 Rheb 依赖性 mTORC1 激活是必不可少的。尽管法尼基化的 Rheb 表现出部分内质网（ER）定位，但将 Rheb 持续靶向 ER 膜并不能支持 mTORC1 激活。对 Rheb 脂质化的系统分析表明，弱的、非选择性的膜相互作用支持 Rheb 依赖性 mTORC1 激活，而不需要特定的溶酶体靶向基序。总的来说，这些结果表明 Rheb 与溶酶体之间不存在稳定的相互作用，而是 Rheb 与膜的短暂相互作用最有利于激活 mTORC1 信号。
