Díaz Jorge, Mendoza Pablo, Ortiz Rina, Díaz Natalia, Leyton Lisette, Stupack Dwayne, Quest Andrew F G, Torres Vicente A
Institute for Research in Dental Sciences, Faculty of Dentistry, Universidad de Chile, Calle Sergio Livingstone 943, Santiago, Chile Center for Molecular Studies of the Cell, Faculty of Medicine, Universidad de Chile, Avenida Independencia 1027, Santiago, Chile Advanced Center for Chronic Diseases (ACCDiS), Faculty of Medicine, Universidad de Chile, Avenida Independencia 1027, Santiago, Chile.
Institute for Research in Dental Sciences, Faculty of Dentistry, Universidad de Chile, Calle Sergio Livingstone 943, Santiago, Chile.
J Cell Sci. 2014 Jun 1;127(Pt 11):2401-6. doi: 10.1242/jcs.141689. Epub 2014 Mar 21.
Rab5 is a small GTPase that regulates early endosome trafficking and other cellular processes, including cell adhesion and migration. Specifically, Rab5 promotes Rac1 activation and cancer cell migration, but little is known about the upstream regulators of Rab5. We have previously shown that the scaffolding protein Caveolin-1 (CAV1) promotes Rac1 activation and migration of cancer cells. Here, we hypothesized that CAV1 stimulates Rab5 activation, leading to increased Rac1 activity and cell migration. Expression of CAV1 in B16-F10 mouse melanoma and HT-29(US) human colon adenocarcinoma cells increased the GTP loading of Rab5, whereas shRNA-mediated targeting of endogenous CAV1 in MDA-MB-231 breast cancer cells decreased Rab5-GTP levels. Accordingly, shRNA-mediated downregulation of Rab5 decreased CAV1-mediated Rac1 activation, cell migration and invasion in B16-F10 and HT-29(US) cells. Expression of CAV1 was accompanied by increased recruitment of Tiam1, a Rac1 guanine nucleotide exchange factor (GEF), to Rab5-positive early endosomes. Using the inhibitor NSC23766, Tiam1 was shown to be required for Rac1 activation and cell migration induced by CAV1 and Rab5. Mechanistically, we provide evidence implicating p85α (also known as PIK3R1), a Rab5 GTPase-activating protein (GAP), in CAV1-dependent effects, by showing that CAV1 recruits p85α, precluding p85α-mediated Rab5 inactivation and increasing cell migration. In summary, these studies identify a novel CAV1-Rab5-Rac1 signaling axis, whereby CAV1 prevents Rab5 inactivation, leading to increased Rac1 activity and enhanced tumor cell migration and invasion.
Rab5是一种小GTP酶，可调节早期内体运输及其他细胞过程，包括细胞黏附和迁移。具体而言，Rab5促进Rac1激活和癌细胞迁移，但关于Rab5的上游调节因子知之甚少。我们之前已表明，支架蛋白小窝蛋白-1（CAV1）促进Rac1激活和癌细胞迁移。在此，我们假设CAV1刺激Rab5激活，导致Rac1活性增加和细胞迁移。在B16-F10小鼠黑色素瘤细胞和HT-29（美国）人结肠腺癌细胞中表达CAV1可增加Rab5的GTP负载，而在MDA-MB-231乳腺癌细胞中，shRNA介导的内源性CAV1靶向作用则降低了Rab5-GTP水平。相应地，shRNA介导的Rab5下调降低了B16-F10和HT-29（美国）细胞中CAV1介导的Rac1激活、细胞迁移和侵袭。CAV1的表达伴随着Rac1鸟嘌呤核苷酸交换因子（GEF）Tiam1向Rab5阳性早期内体的募集增加。使用抑制剂NSC23766表明，Tiam1是CAV1和Rab5诱导的Rac1激活和细胞迁移所必需的。从机制上讲，我们通过表明CAV1募集p85α（也称为PIK3R1），一种Rab5 GTP酶激活蛋白（GAP），参与CAV1依赖性效应，从而排除p85α介导的Rab5失活并增加细胞迁移。总之，这些研究确定了一种新的CAV1-Rab5-Rac1信号轴，通过该轴CAV1可防止Rab5失活，导致Rac1活性增加以及肿瘤细胞迁移和侵袭增强。
