F-actin flashes on phagosomes mechanically deform contents for efficient digestion in macrophages

Abstract

The mechanism and role of transient F-actin recruitment or F-actin “flashes” on phagosomes remains enigmatic. Here we provide a comprehensive characterization of F-actin flashing dynamics on phagosomes including receptor and signaling involvement. F-actin flashes predominate during the integrin-driven CR-mediated phagocytosis. F-actin flashes begin shortly after internalization and persist on phagosomes for ∼3 minutes before disassembling and reassembling several times within the first hour. Strikingly, the appearance of F-actin flashes on phagosomes coincides with RBC morphological deformation, lysis and occasional fission events. The cadence of flashes depends on particle stiffness and the F-actin networks on phagosomes are enriched in mechanosensitive components including focal adhesion proteins, RhoA and actomyosin. Inhibiting Arp2/3 and myosin IIA activity significantly reduces the frequency at which phagosome cargo becomes deformed during transient F-actin accumulation. At later time points, post-F-actin flashing, an enhanced degradation of phagosome contents is observed, compared to non-flashing phagosomes. Together these data suggest that actomyosin-driven phagosome contractions serve to physically disrupt malleable particles, a process akin to mastication, to enhance later enzymatic digestion.