Phactr4 Regulates Macrophage Effector Functions via Interactions with Arp2/3 and Ezrin 4005

Abstract Description Macrophages are innate immune cells that maintain tissue homeostasis, clear phagocytic targets, and modulate immune activation. These processes require dynamic actin cytoskeleton reorganization but many molecular details remain unclear. Phosphatase and actin regulator 4 (Phactr4) is an understudied protein that binds protein phosphatase 1 (PP1) and actin and leads to impaired neural crest cell migration when mutated. Ezrin is a phosphoregulated linker that connects the actin cytoskeleton to the plasma membrane. After Ezrin mediated actin-membrane decoupling, the Arp2/3 complex generates branched actin for migration-associated protrusions. We hypothesize that Phactr4 plays a role in migration and membrane protrusion in macrophages by regulating Arp2/3 and ezrin. In line with our hypothesis, Phactr4 physically interacts with active Arp2/3 and binds Ezrin, but does so during different phases of cell spreading. Phactr4 localizes to migratory lamellipodia and iC3b phagocytic cups, and its knockdown impairs macrophage migration and phagocytosis, due to altered Arp2/3-dependent membrane protrusions. Phactr4 knockdown also leads to Ezrin hyperphosphorylation, suggesting that the PP1-phactr4 complex regulates its activity level in migrating cells. These preliminary data suggest that Phactr4 regulates Arp2/3 and Ezrin activity, influencing macrophage function. These findings offer molecular insight into macrophage biology, and may help clarify disease-relevant migratory phenotypes. Funding Sources NIH RO1 GM134104 Topic Categories Cellular Adhesion, Migration, and Inflammation (CAM)