Cell Biology Membrane Biology
Vacuolar ATPase in Phagosome-Lysosome Fusion

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The vacuolar H+-ATPase (v-ATPase) complex is instrumental in establishing and maintaining acidification of some cellular compartments, thereby ensuring their functionality. Recently it has been proposed that the transmembrane V0 sector of v-ATPase and its a-subunits promote membrane fusion in the endocytic and exocytic pathways independent of their acidification functions. Here, we tested if such a proton-pumping independent role of v-ATPase also applies to phagosome-lysosome fusion. Surprisingly, endo(lyso)somes in mouse embryonic fibroblasts lacking the V0 a3 subunit of the v-ATPase acidified normally, and endosome and lysosome marker proteins were recruited to phagosomes with similar kinetics in the presence or absence of the a3 subunit. Further experiments used macrophages with a knockdown of v-ATPase accessory protein 2 (ATP6AP2) expression, resulting in a strongly reduced level of the V0 sector of the v-ATPase. However, acidification appeared undisturbed, and fusion between latex bead-containing phagosomes and lysosomes, as analyzed by electron microscopy, was even slightly enhanced, as was killing of non-pathogenic bacteria by V0 mutant macrophages. Pharmacologically neutralized lysosome pH did not affect maturation of phagosomes in mouse embryonic cells or macrophages. Finally, locking the two large parts of the v-ATPase complex together by the drug saliphenylhalamide A did not inhibit in vitro and in cellulo fusion of phagosomes with lysosomes. Hence, our data do not suggest a fusion-promoting role of the v-ATPase in the formation of phagolysosomes.

Background: The vacuolar H+-ATPase complex is thought to contribute to membrane fusion.

Results: v-ATPase complex knock-out experiments in mice revealed that its absence does not affect phagosome-lysosome fusion.

Conclusion: Participation of v-ATPase in phagosome-lysosome fusion is unlikely.

Significance: Fusion between lysosomes/late endosomes and phagosomes is not controlled by the v-ATPase.

vacuolar ATPase
phagocytosis
lysosome
membrane fusion
ATP6AP2
phagosome maturation
lysosomal acidification

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This work was supported by Deutsche Forschungsgemeinschaft Grants GRK1459 (to P. S. and S. K.) and SPP1580 (to A. H., G. G., and P. S).

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Both authors equally contributed to this work.