Direct recruitment of H⁺-ATPase from lysosomes for phagosomal acidification

The nascent phagosome progressively establishes an acidic milieu by acquiring a proton pump, the vacuolar-type ATPase (V-ATPase). However, the origin of phagosomal V-ATPase remains poorly understood. We found that phagosomes were enriched with the V-ATPase a3 subunit, which also accumulated in late endosomes and lysosomes. We modified the mouse Tcirg1 locus encoding subunit a3, to express an a3-GFP fusion protein. Live-cell imaging and immunofluorescence microscopy revealed that nascent phagosomes received the a3-GFP from tubular structures extending from lysosomes located in the perinuclear region. Macrophages from a3-deficient mice exhibited impaired acidification of phagosomes and delayed digestion of bacteria. These results show that lysosomal V-ATPase is recruited directly to the phagosomes via tubular lysosomes to establish the acidic environment hostile to pathogens.