title: An essential role for Rab27a GTPase in eosinophil exocytosis.
abstract: Eosinophil degranulation has been implicated in inflammatory processes associated with allergic asthma. Rab27a, a Rab-related GTPase, is a regulatory intracellular signaling molecule expressed in human eosinophils. We postulated that Rab27a regulates eosinophil degranulation. We investigated the role of Rab27a in eosinophil degranulation within the context of airway inflammation. Rab27a expression and localization in eosinophils were investigated by using subcellular fractionation combined with Western blot analysis, and the results were confirmed by immunofluorescence analysis of Rab27a and the granule membrane marker CD63. To determine the function of eosinophil Rab27a, we used Ashen mice, a strain of Rab27a-deficient animals. Ashen eosinophils were tested for degranulation in response to PAF and calcium ionophore by measuring released EPX activity. Airway EPX release was also determined by intratracheal injection of eosinophils into mice lacking EPX. Rab27a immunoreactivity colocalized with eosinophil crystalloid granules, as determined by subcellular fractionation and immunofluorescence analysis. PAF induced eosinophil degranulation in correlation with redistribution of Rab27a(+) structures, some of which colocalized with CD63(+) crystalloid granules at the cell membrane. Eosinophils from mice had significantly reduced EPX release compared with normal WT eosinophils, both in vitro and in vivo. In mouse models, Ashen mice demonstrated reduced EPX release in BAL fluid. These findings suggest that Rab27a has a key role in eosinophil degranulation. Furthermore, these findings have implications for Rab27a-dependent eosinophil degranulation in airway inflammation.
authors.affiliation: 2.559 HMRC, Department of Medicine, University of Alberta, Edmonton, AB, T6G 2S2, Canada. paige.lacy@ualberta.ca.
authors.forename: John Dongil
authors.initials: JD
authors.lastname: Kim
authors.forename: Lian
authors.initials: L
authors.lastname: Willetts
authors.forename: Sergei
authors.initials: S
authors.lastname: Ochkur
authors.forename: Nutan
authors.initials: N
authors.lastname: Srivastava
authors.forename: Rudolf
authors.initials: R
authors.lastname: Hamburg
authors.forename: Anooshirvan
authors.initials: A
authors.lastname: Shayeganpour
authors.forename: Miguel C
authors.initials: MC
authors.lastname: Seabra
authors.forename: James J
authors.initials: JJ
authors.lastname: Lee
authors.forename: Redwan
authors.initials: R
authors.lastname: Moqbel
authors.forename: Paige
authors.initials: P
authors.lastname: Lacy
mesh_terms: D000818:Animals; D001249:Asthma / Q000201:enzymology / Q000235:genetics / Q000276:immunology* / Q000473:pathology; D015550:Cell Degranulation / Q000235:genetics / Q000276:immunology*; D004195:Disease Models, Animal; D004804:Eosinophils / Q000201:enzymology / Q000276:immunology* / Q000473:pathology; D005260:Female; D015971:Gene Expression Regulation, Enzymologic / Q000235:genetics / Q000276:immunology; D018922:HL-60 Cells; D006801:Humans; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D060149:Tetraspanin 30 / Q000235:genetics / Q000276:immunology; D020691:rab GTP-Binding Proteins / Q000096:biosynthesis / Q000235:genetics / Q000276:immunology*; D000075745:rab27 GTP-Binding Proteins
chemical_list: C554586:CD63 protein, human; C554587:Cd63 protein, mouse; D060149:Tetraspanin 30; D000075745:rab27 GTP-Binding Proteins; C066694:RAB27A protein, human; C512962:Rab27a protein, mouse; D020691:rab GTP-Binding Proteins
keywords: Ashen mice; IL-5 transgenic mice; allergic asthma; degranulation; hE2 transgenic mice; subcellular fractionation