Institute of Biochemistry II, Goethe University School of Medicine, 60590 Frankfurt am Main, Germany.
Institute of Biophysical Chemistry and Center for Biomolecular Magnetic Resonance, Goethe University, 60438 Frankfurt am Main, Germany.
Mol Cell. 2015 Mar 19;57(6):995-1010. doi: 10.1016/j.molcel.2014.12.040. Epub 2015 Feb 12.
The small Rho GTPase RAC1 is an essential regulator of cellular signaling that controls actin rearrangements and cell motility. Here, we identify a novel CUL3 RING ubiquitin ligase complex, containing the substrate adaptors KBTBD6 and KBTBD7, that mediates ubiquitylation and proteasomal degradation of TIAM1, a RAC1-specific GEF. Increasing the abundance of TIAM1 by depletion of KBTBD6 and/or KBTBD7 leads to elevated RAC1 activity, changes in actin morphology, loss of focal adhesions, reduced proliferation, and enhanced invasion. KBTBD6 and KBTBD7 employ ATG8 family-interacting motifs to bind preferentially to GABARAP proteins. Surprisingly, ubiquitylation and degradation of TIAM1 by CUL3(KBTBD6/KBTBD7) depends on its binding to GABARAP proteins. Our study reveals that recruitment of CUL3(KBTBD6/KBTBD7) to GABARAP-containing vesicles regulates the abundance of membrane-associated TIAM1 and subsequently spatially restricted RAC1 signaling. Besides their role in autophagy and trafficking, we uncovered a previously unknown function of GABARAP proteins as membrane-localized signaling scaffolds.
小 Rho GTPase RAC1 是细胞信号转导的必需调节剂，控制肌动蛋白重排和细胞迁移。在这里，我们鉴定了一种新型的 CUL3 RING 泛素连接酶复合物，包含底物接头 KBTBD6 和 KBTBD7，介导 TIAM1 的泛素化和蛋白酶体降解，TIAM1 是 RAC1 特异性的鸟苷酸交换因子。通过耗尽 KBTBD6 和/或 KBTBD7 增加 TIAM1 的丰度会导致 RAC1 活性升高、肌动蛋白形态改变、焦点黏附丧失、增殖减少和侵袭增强。KBTBD6 和 KBTBD7 通过 ATG8 家族相互作用基序优先结合 GABARAP 蛋白。令人惊讶的是，CUL3（KBTBD6/KBTBD7）对 TIAM1 的泛素化和降解依赖于其与 GABARAP 蛋白的结合。我们的研究揭示了 CUL3（KBTBD6/KBTBD7）与含有 GABARAP 的囊泡的募集调节了膜相关 TIAM1 的丰度，随后空间限制了 RAC1 信号。除了它们在自噬和运输中的作用外，我们还揭示了 GABARAP 蛋白作为膜定位信号支架的先前未知功能。
