Rho-Kinase and Myosin-II Control Phagocytic Cup Formation during CR, but Not FcγR, Phagocytosis

Abstract

Phagocytosis through Fcγ receptor (FcγR) or complement receptor 3 (CR) requires Arp2/3 complex-mediated actin polymerization, although each receptor uses a distinct signaling pathway [1]. Rac and Cdc42 are required for actin and Arp2/3 complex recruitment during FcγR phagocytosis, while Rho controls actin assembly at CR phagosomes [2, 3]. To better understand the role of Rho in CR phagocytosis, we tested the idea that a known target of Rho, Rho-kinase (ROK), might control phagocytic cup formation and/or engulfment of particles. Inhibitors of ROK (dominant-negative ROK and Y-27632) and of the downstream target of ROK, myosin-II (ML7, BDM, and dominant-negative myosin-II), were used to test this idea. We found that inhibition of the Rho → ROK → myosin-II pathway caused a decreased accumulation of Arp2/3 complex and F-actin around bound particles, which led to a reduction in CR-mediated phagocytic engulfment. FcγR-mediated phagocytosis, in contrast, was independent of Rho or ROK activity and was only dependent on myosin-II for particle internalization, not for actin cup formation. While myosins have been previously implicated in FcγR phagocytosis [4–6], to our knowledge, this is the first demonstration of a role for myosin-II in CR phagocytosis.