CMG2 interaction with actin is required for growth factor-induced chemotaxis in endothelial cells

Capillary morphogenesis gene 2 (CMG2/ANTXR2) is a cell surface receptor that contributes to corneal angiogenesis and is essential for orienting endothelial cell chemotaxis in growth factor gradients. However, the mechanism by which CMG2 transmits signals to orient endothelial cells is unknown. Here, we use affinity proteomics to identify proteins that interact with CMG2. This led us to investigate CMG2 interaction with F-actin in the context of serum and individual growth factors (bFGF/PDGF/VEGF) in both primary and immortalized endothelial cells. We also measured different matrix-protein-mediated changes in chemotaxis. We find that CMG2 function is matrix dependent, and that CMG2-actin interaction is required for serum- and growth-factor-induced chemotaxis. Inhibiting chemotaxis with CMG2 antagonists (collagen 6, penta-galloyl-glucose, or anthrax toxin protective antigen; PA) leads to the release of actin cytoskeleton from CMG2. Furthermore, CMG2 co-localizes with actin at the leading edge during live migration. This colocalization is disrupted by PA, which also disrupts directional movement. Finally, we demonstrate that the conserved actin binding domain of CMG2 directly binds to F-actin in vitro where it bundles F-actin, suggesting a mechanism by which it enables directional migration.