MUNC13-4 Protein Regulates the Oxidative Response and Is Essential for Phagosomal Maturation and Bacterial Killing in Neutrophils

• Published in: The Journal of biological chemistry 2012-12, Vol.287 (53), p.44603-44618
• Main Authors: Monfregola, Jlenia, Johnson, Jennifer Linda, Meijler, Michael M., Napolitano, Gennaro, Catz, Sergio Daniel
• Format: Article
• Language: English
• Subjects: Animals; Bacterial Killing; Cells, Cultured; Humans; Immunology; Innate Immunity; Intracellular Trafficking; Membrane Proteins - genetics; Membrane Proteins - immunology; Mice; Mice, Inbred C57BL; Mice, Knockout; MUNC13-4; Myeloperoxidase; Neutrophil; Neutrophil Extracellular Traps; Neutrophils - immunology; Oxidative Stress; Phagocytosis; Phagosomes - immunology; Pseudomonas aeruginosa - immunology; Pseudomonas aeruginosa - physiology; Pseudomonas Infections - genetics; Pseudomonas Infections - immunology; Pseudomonas Infections - microbiology; Rab Proteins; RAB27A; Reactive Oxygen Species - immunology
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M112.414029

Neutrophils use diverse mechanisms to kill pathogens including phagocytosis, exocytosis, generation of reactive oxygen species (ROS), and neutrophil extracellular traps. These mechanisms rely on their ability to mobilize intracellular organelles and to deliver granular cargoes to specific cellular compartments or into the extracellular milieu, but the molecular mechanisms regulating vesicular trafficking in neutrophils are not well understood. MUNC13-4 is a RAB27A effector that coordinates exocytosis in hematopoietic cells, and its deficiency is associated with the human immunodeficiency familial hemophagocytic lymphohistiocytosis type 3. In this work, we have established an essential role for MUNC13-4 in selective vesicular trafficking, phagosomal maturation, and intracellular bacterial killing in neutrophils. Using neutrophils from munc13-4 knock-out (KO) mice, we show that MUNC13-4 is necessary for the regulation of p22phox-expressing granule trafficking to the plasma membrane and regulates extracellular ROS production. MUNC13-4 was also essential for the regulation of intracellular ROS production induced by Pseudomonas aeruginosa despite normal trafficking of p22phox-expressing vesicles toward the phagosome. Importantly, in the absence of MUNC13-4, phagosomal maturation was impaired as observed by the defective delivery of azurophilic granules and multivesicular bodies to the phagosome. Significantly, this mechanism was intact in RAB27A KO neutrophils. Intracellular bacterial killing was markedly impaired in MUNC13-4 KO neutrophils. MUNC13-4-deficient cells showed a significant increase in neutrophil extracellular trap formation but were unable to compensate for the impaired bacterial killing. Altogether, these findings characterize novel functions of MUNC13-4 in the innate immune response of the neutrophil and have direct implications for the understanding of immunodeficiencies in patients with MUNC13-4 deficiency. MUNC13-4 regulates vesicular trafficking, and its deficiency causes immunodeficiency in humans. MUNC13-4 regulates ROS production, phagosomal maturation, and bacterial killing in neutrophils. MUNC13-4 is essential for the neutrophil-dependent innate immune response. This study identifies MUNC13-4 as a potential target for therapeutic intervention during bacterial infections.