Annexin A2 modulates phospholipid membrane composition upstream of Arp2 to control angiogenic sprout initiation

The intersection of protein and lipid biology is of growing importance for understanding how cells address structural challenges during adhesion and migration. While protein complexes engaged with the cytoskeleton play a vital role, support from the phospholipid membrane is crucial for directing localization and assembly of key protein complexes. During angiogenesis, it is well observed that dramatic cellular remodeling is necessary for endothelial cells to shift from a stable monolayer to invasive structures. However, the molecular dynamics between lipids and proteins during endothelial invasion are not defined. Here, we utilized cell culture, immunofluorescence, and lipidomic analyses to identify a novel role for the membrane binding protein Annexin A2 (ANXA2) in modulating the composition of specific membrane lipids necessary for cortical F-actin organization and adherens junction stabilization. In the absence of ANXA2, there is disorganized cortical F-actin, reduced junctional Arp2, excess sprout initiation, and ultimately failed sprout maturation. Further, we observed reduced filipin III labeling of membrane cholesterol in cells with reduced ANXA2, suggesting there is an alteration in phospholipid membrane dynamics. Lipidomic analyses reveal that 42 lipid species are altered with loss of ANXA2, including an accumulation of phosphatidylcholine (16:0_16:0). We find that supplementation of phosphatidylcholine (16:0_16:0) in wild-type endothelial cells mimics the ANXA2 knock-down phenotype, indicating that ANXA2 regulates the phospholipid membrane upstream of Arp2 recruitment and organization of cortical F-actin. Altogether these data indicate a novel role for ANXA2, and show that proper lipid modulation is a critical component of endothelial sprouting. Summary StatementAnnexin A2 modulates composition of select phospholipid species in endothelial cells needed for F-actin organization and Arp2 recruitment to endothelial adherens junctions. These events simultaneously temper sprout initiation and support sprout maturation to maintain the integrity of sprouting structures during angiogenesis