WASH-driven actin polymerization is required for efficient mycobacterial phagosome maturation arrest

Abstract

SummaryPathogenic mycobacteria survive in phagocytic host cells primarily as a result of their ability to prevent fusion of their vacuole with lysosomes, thereby avoiding a bactericidal environment. The molecular mechanisms to establish and maintain this replication compartment are not well understood. By combining molecular and microscopical approaches we show here that after phagocytosis the actin nucleation-promoting factor WASH associates and generates F-actin on the mycobacterial vacuole. Disruption of WASH or depolymerization of F-actin leads to the accumulation of the protonpumping V-ATPase around the mycobacterial vacuole, its acidification and reduces the viability of intracellular mycobacteria. This effect is observed for M. marinum in the model phagocyte Dictyostelium but also for M. marinum and M. tuberculosis in mammalian phagocytes. This demonstrates an evolutionarily conserved mechanism by which pathogenic mycobacteria subvert the actin-polymerization activity of WASH to prevent phagosome acidification and maturation, as a prerequisite to generate and maintain a replicative niche.

Neurons Are Host Cells for Mycobacterium tuberculosis

“…Moreover, it was established that entry of M. tuberculosis bacilli into epithelial cells was dependent on microtubules, which could be inhibited by administration of colchicine and nocodazole, known to cause microtubule depolymerization (43). Our findings do not exclude cytoskeletal concentration around bacilli residing within phagosomes, as others have shown actin nucleation around mycobacterial phagosomes (44,45). The role of cytoskeletal concentration around bacilli is controversial, and its complexity is highlighted by contrasting reports.…”

“…The role of cytoskeletal concentration around bacilli is controversial, and its complexity is highlighted by contrasting reports. Kolonko and colleagues (45) suggest that actin polymerization protects M. tuberculosis bacilli from delivery to a bactericidal environment, whereas Anes and colleagues (44) propose that actin assembly promotes killing of pathogenic mycobacteria.…”

The autophagic machinery ensures nonlytic transmission of mycobacteria

“…Using the Dictyostelium-M. marinum system (9,17,18) to further dissect the mechanism of ejectosome formation and function, we demonstrate an unexpected role for autophagic membranes in both mycobacteria egress and concomitant cell-tocell transmission.…”

Drosophila WASH is required for integrin-mediated cell adhesion, cell motility and lysosomal neutralization

“…Lysosomal neutralization requires a functional WASH-VCA domain, suggesting that Arp2/3-mediated actin polymerization is essential for the V-ATPase retrieval . Further studies in Dictyostelium and in mammalian cells suggest a conserved role of WASH in regulating the lysosomal network required for efficient phagocytic and autophagic digestion (Kolonko et al, 2014;King et al, 2013;Gomez et al, 2012). Dictyostelium cells lacking WASH are unable to digest their cytoplasm in order to survive phases of starvation (King et al, 2013).…”