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 one 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. DOI: http://dx.doi.org/10.7554/eLife.23172.001
eLife digest In animal bodies, a mesh of proteins – known the extracellular matrix – holds cells together to give the body shape and make it more stable. Cells bind to the matrix using structures called focal adhesions. However, cells do not always stay in one place: in young animals, certain cells need to move around the body to reach their final destination. Adult animals also have some cells that are able to move, for example, to close wounds. The cells move when the focal adhesions that hold these cells in place are taken apart and then rebuilt. These processes are very dynamic and happen all the time when cells move. They are normally tightly controlled to ensure that cells only migrate under appropriate conditions. However, focal adhesions are less well regulated in cancer cells, allowing the cells to migrate away from a tumour to form new tumours elsewhere in the body. Focal adhesions are large structures that contain many proteins. These proteins include FAK and Src, which are particularly important and have been well studied. In order to better understand how focal adhesions are taken apart, Schoenherr et al. wanted to discover new proteins that interact with FAK in skin cancer cells from mice. The experiments show that FAK binds to a protein called Ambra1, which is known to control how other proteins move around inside cells. Ambra1 and FAK work together to regulate the movement of Src away from focal adhesions and into the cell. Furthermore, Ambra1 belongs to a larger network of proteins within the cancer cells that regulates the location of Src. By changing the levels of Src and FAK at focal adhesions, Ambra1 and its other binding partners can control whether the cancer cells are attached to the extracellular matrix or are free to migrate. Overall this work shows that the location and activity of Src within cells needs to be carefully controlled to stop the cells from moving at the wrong time. Further experiments will aim to understand which other proteins are involved in this network and how they contribute to the growth of cancer cells and the spread of tumours around the body. DOI: http://dx.doi.org/10.7554/eLife.23172.002