Rab27a and Rab27b regulate neutrophil azurophilic granule exocytosis and NADPH oxidase activity by independent mechanisms.
Neutrophils rely on exocytosis to mobilize receptors and adhesion molecules and to release microbicidal factors. This process should be strictly regulated because uncontrolled release of toxic proteins would be injurious to the host. In vivo studies showed that the small GTPase Rab27a regulates azurophilic granule exocytosis. Using mouse neutrophils deficient in Rab27a (Rab27a(ash/ash)), Rab27b [Rab27b knockout (KO)] or both [Rab27a/b double KO (DoKo)], we investigated the role of the Rab27 isoforms in neutrophils. We found that both Rab27a and Rab27b deficiencies impaired azurophilic granule exocytosis. Rab27a(ash/ash) neutrophils showed upregulation of Rab27b expression which did not compensate for the secretory defects observed in Rab27a-deficient cells, suggesting that Rab27 isoforms play independent roles in neutrophil exocytosis. Total internal reflection fluorescence microscopy analysis showed that Rab27a(ash/ash) and Rab27b KO neutrophils have a decreased number of azurophilic granules near the plasma membrane. The effect was exacerbated in Rab27a/b DoKo neutrophils. Rab27-deficient neutrophils showed impaired activation of the reduced nicotinamide adenine dinucleotide phosphate (NADPH) oxidase at the plasma membrane although intraphagosomal reactive oxygen species (ROS) production was not affected. Exocytosis of secretory vesicles in Rab27-deficient neutrophils was functional, suggesting that Rab27 GTPases selectively control the exocytosis of neutrophil granules.
Johnson
Jennifer L
JL
Department of Molecular and Experimental Medicine, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, CA 92037, USA.
Brzezinska
Agnieszka A
AA
Tolmachova
Tanya
T
Munafo
Daniela B
DB
Ellis
Beverly A
BA
Seabra
Miguel C
MC
Hong
Hong
H
Catz
Sergio D
SD
D000818:Animals; D005089:Exocytosis; D051379:Mice; D018345:Mice, Knockout; D019255:NADPH Oxidases / Q000378:metabolism; D009504:Neutrophils / Q000201:enzymology*; D022142:Secretory Vesicles / Q000378:metabolism; D020691:rab GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D000075745:rab27 GTP-Binding Proteins
D000075745:rab27 GTP-Binding Proteins; D019255:NADPH Oxidases; C512958:Rab27b protein, mouse; C512962:Rab27a protein, mouse; D020691:rab GTP-Binding Proteins