Ambra1 spatially regulates Src activity and Src/FAK-mediated cancer cell invasion via trafficking networks

Here, using mouse squamous cell carcinoma cells, we report a completely new function for the autophagy protein Ambra1 as the first described ‘spatial rheostat’ controlling the Src/FAK pathway. Ambra1 regulates the targeting of active phospho-Src away from focal adhesions into autophagic structures that cancer cells use to survive adhesion stress. Ambra1 binds to both FAK and Src in cancer cells. When FAK is present, Ambra1 is recruited to focal adhesions, promoting FAK-regulated cancer cell direction-sensing and invasion. However, when Ambra1 cannot bind to FAK, abnormally high levels of phospho-Src and phospho-FAK accumulate at focal adhesions, positively regulating adhesion and invasive migration. Spatial control of active Src requires the trafficking proteins Dynactin 1 and IFITM3, which we identified as Ambra1 binding partners by interaction proteomics. We conclude that Ambra1 is a core component of an intracellular trafficking network linked to tight spatial control of active Src and FAK levels, and so crucially regulates their cancer-associated biological outputs.

本研究以小鼠鳞状细胞癌细胞为实验模型，首次揭示自噬蛋白Ambra1的全新功能：其作为首个被报道的‘空间变阻器（spatial rheostat）’，可调控Src/黏着斑激酶（Focal Adhesion Kinase，FAK）信号通路。Ambra1可将活化的磷酸化Src（phospho-Src）从黏着斑（focal adhesions）靶向转运至自噬结构，而癌细胞可通过此类自噬结构抵御黏附应激以维持存活。在癌细胞中，Ambra1可同时结合FAK与Src。当FAK存在时，Ambra1会被招募至黏着斑，进而促进FAK介导的癌细胞方向感知与侵袭能力。但若Ambra1无法与FAK结合，则磷酸化Src与磷酸化FAK会在黏着斑处异常积累，进而正向调控细胞黏附与侵袭性迁移。对活化Src的空间调控需要依赖转运蛋白动力蛋白激活蛋白1（Dynactin 1）与干扰素诱导跨膜蛋白3（IFITM3）；本研究通过相互作用蛋白质组学（interaction proteomics）鉴定出二者均为Ambra1的结合伴侣。综上，Ambra1是细胞内转运网络的核心组成部分，该网络可精准调控活化Src与FAK的空间分布及蛋白水平，进而关键调控其与癌症发生发展相关的生物学效应。