Abstract
The protozoan Leishmania parasitizes macrophages and evades the microbicidal consequences of phagocytosis through the inhibition of phagolysosome biogenesis. In this study, we investigated the impact of this parasite on LC3-associated phagocytosis, a non-canonical autophagic process that enhances phagosome maturation and functions. We show that whereas internalization of L. major promastigotes by macrophages promoted LC3 lipidation, recruitment of LC3 to phagosomes was inhibited through the action of the parasite surface metalloprotease GP63. Reactive oxygen species generated by the NOX2 NADPH oxidase are necessary for LC3-associated phagocytosis. We found that L. major promastigotes prevented, in a GP63-dependent manner, the recruitment of NOX2 to phagosomes through a mechanism that does not involve NOX2 cleavage. Moreover, we found that the SNARE protein VAMP8, which regulates phagosomal assembly of the NADPH oxidase NOX2, was down-modulated by GP63. In the absence of VAMP8, recruitment of LC3 to phagosomes containing GP63-deficient parasites was inhibited, indicating that VAMP8 is involved in the phagosomal recruitment of LC3. These findings reveal a role for VAMP8 in LC3-associated phagocytosis and highlight a novel mechanism exploited by L. major promastigotes to interfere with the host antimicrobial machinery.
Highlights
Phagocytosis plays a central role in linking innate and adaptive immunity [1, 2]
Growing evidence supports the notion that the autophagy machinery lends a hand to phagocytosis in eliminating intracellular pathogens, in a process known as LC3-associated phagocytosis (LAP)
Protozoan parasites of the Leishmania genus use surface virulence factors such as lipophosphoglycan and the metalloprotease GP63 to interfere with phagolysosome biogenesis and sabotage macrophage antimicrobial functions
Summary
Phagocytosis plays a central role in linking innate and adaptive immunity [1, 2] During this process, pathogens are internalized in a vacuole, the phagosome, which engages in a maturation program involving sequential interactions with various cellular compartments [1]. Phagolysosome biogenesis represents an important means of controlling infections, but several pathogenic microorganisms have evolved mechanisms to subvert this process and cause disease [5] Upon their internalization by host phagocytes, promastigote forms of the protozoan parasite Leishmania turn off key antimicrobial and immune functions through the inhibition of phagolysosome biogenesis [6, 7]. Targeting of VAMP8 through GP63 enables Leishmania promastigotes to inhibit assembly of the NOX2 complex on phagosomes, thereby impairing the ability of infected cells to process antigens for cross-presentation and to activate T cells [7, 17]
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