The Rab27a Effectors JFC1/Slp1 and Munc13‐4 Regulate Exocytosis of Neutrophil Granules

Department of Molecular and Experimental Medicine, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, CA 92037, USA.
Traffic (Impact Factor: 4.35). 11/2008; 9(12):2151-64. DOI: 10.1111/j.1600-0854.2008.00838.x
Source: PubMed


Neutrophil granules contain secretory molecules that contribute to the implementation of all neutrophil functions. The molecular components that regulate the exocytosis of neutrophil granules have not been characterized. In this study, using small interfering RNA gene-targeting approaches and granulocytes from genetically modified mice, we characterized the Rab27a effectors JFC1/Slp1 and Munc13-4 as components of the exocytic machinery of granulocytes. Using total internal reflection fluorescence microscopy analysis, we show that Rab27a and JFC1 colocalize in predocked and docked vesicles in granulocytes. Next, we demonstrate that JFC1-downregulated granulocytes have impaired myeloperoxidase secretion. Using immunological interference, we confirm that JFC1 plays an important role in azurophilic granule exocytosis in human neutrophils. Interference with Rab27a but not with JFC1 impaired gelatinase B secretion in neutrophils, suggesting that a different Rab27a effector modulates this process. In similar studies, we confirmed that Munc13-4 regulates gelatinase secretion. Immunofluorescence analysis indicates that Munc13-4 localizes at secretory organelles in neutrophils. Using neutrophils from a Munc13-4-deficient mouse model (Jinx), we demonstrate that Munc13-4 plays a central role in the regulation of exocytosis of various sets of secretory organelles. However, mobilization of CD11b was not affected in Munc13-4-deficient neutrophils, indicating that secretory defects in these cells are limited to a selective group of exocytosable organelles.

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    • "Munc13-4 (also known as UNC13D) is highly expressed in neutrophils and interacts with Rab27, which is the Rab that direct granules to dock at the plasma membrane. Munc13-4 tethers granules to the plasma membrane for exocytosis via two calcium-sensitive lipid bind C2 domains (Figure 4) (113). Neutrophil subfractionation revealed that high levels of Munc13-4 rapidly translocate from the cytosol to granules upon stimulation with a secretagogue like fMLF (114). "
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    • "True colocalization was further demonstrated by the similar temporal distribution of JFC1 and Rab27a molecules (Brzezinska et al., 2008) and direct interaction by co-immunoprecipitation analysis (Munafo et al., 2007). A role for Slp1/JFC1 in the regulation of azurophilic granule exocytosis was demonstrated in human neutrophils (Brzezinska et al., 2008), neutrophil-like HL-60 cells (Munafo et al., 2007; Brzezinska et al., 2008) and in JFC1-null murine primary neutrophils (Johnson et al., 2012). In this way, using inhibitory antibodies in permeabilized human neutrophils, and shRNA-mediated JFC1-downregulation in human granulocytic cells, Brzezinska and colleagues showed that interference with JFC1 function inhibits azurophilic granule exocytosis (Brzezinska et al., 2008) while other work showed impaired azurophilic granule exocytosis in JFC1-KO murine primary granulocytes (Sytl "
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