title: Munc13-4 interacts with syntaxin 7 and regulates late endosomal maturation, endosomal signaling, and TLR9-initiated cellular responses.
abstract: The molecular mechanisms that regulate late endosomal maturation and function are not completely elucidated, and direct evidence of a calcium sensor is lacking. Here we identify a novel mechanism of late endosomal maturation that involves a new molecular interaction between the tethering factor Munc13-4, syntaxin 7, and VAMP8. Munc13-4 binding to syntaxin 7 was significantly increased by calcium. Colocalization of Munc13-4 and syntaxin 7 at late endosomes was demonstrated by high-resolution and live-cell microscopy. Munc13-4-deficient cells show increased numbers of significantly enlarged late endosomes, a phenotype that was mimicked by the fusion inhibitor chloroquine in wild-type cells and rescued by expression of Munc13-4 but not by a syntaxin 7-binding-deficient mutant. Late endosomes from Munc13-4-KO neutrophils show decreased degradative capacity. Munc13-4-knockout neutrophils show impaired endosomal-initiated, TLR9-dependent signaling and deficient TLR9-specific CD11b up-regulation. Thus we present a novel mechanism of late endosomal maturation and propose that Munc13-4 regulates the late endocytic machinery and late endosomal-associated innate immune cellular functions.
authors.affiliation: Department of Molecular and Experimental Medicine, Scripps Research Institute, La Jolla, CA 92037.
authors.forename: Jing
authors.initials: J
authors.lastname: He
authors.affiliation: Department of Molecular and Experimental Medicine, Scripps Research Institute, La Jolla, CA 92037.
authors.forename: Jennifer L
authors.initials: JL
authors.lastname: Johnson
authors.affiliation: Department of Molecular and Experimental Medicine, Scripps Research Institute, La Jolla, CA 92037.
authors.forename: Jlenia
authors.initials: J
authors.lastname: Monfregola
authors.affiliation: Department of Molecular and Experimental Medicine, Scripps Research Institute, La Jolla, CA 92037.
authors.forename: Mahalakshmi
authors.initials: M
authors.lastname: Ramadass
authors.affiliation: Cancer Center Microscopy Shared Resource, University of California, San Diego, La Jolla, CA 92093.
authors.forename: Kersi
authors.initials: K
authors.lastname: Pestonjamasp
authors.affiliation: Department of Molecular and Experimental Medicine, Scripps Research Institute, La Jolla, CA 92037.
authors.forename: Gennaro
authors.initials: G
authors.lastname: Napolitano
authors.affiliation: Department of Molecular and Experimental Medicine, Scripps Research Institute, La Jolla, CA 92037.
authors.forename: Jinzhong
authors.initials: J
authors.lastname: Zhang
authors.affiliation: Department of Molecular and Experimental Medicine, Scripps Research Institute, La Jolla, CA 92037 scatz@scripps.edu.
authors.forename: Sergio D
authors.initials: SD
authors.lastname: Catz
mesh_terms: D000818:Animals; D039481:CD11b Antigen / Q000378:metabolism; D002118:Calcium / Q000378:metabolism; D011992:Endosomes / Q000378:metabolism*; D057809:HEK293 Cells; D006801:Humans; D007113:Immunity, Innate; D008565:Membrane Proteins / Q000502:physiology*; D008810:Mice, Inbred C57BL; D009504:Neutrophils / Q000378:metabolism; D025941:Protein Interaction Mapping; D050765:Qa-SNARE Proteins / Q000378:metabolism*; D050683:R-SNARE Proteins / Q000378:metabolism; D015398:Signal Transduction; D051217:Toll-Like Receptor 9 / Q000502:physiology*
chemical_list: D039481:CD11b Antigen; D008565:Membrane Proteins; D050765:Qa-SNARE Proteins; D050683:R-SNARE Proteins; C495370:Tlr9 protein, mouse; D051217:Toll-Like Receptor 9; C520225:Unc13d protein, mouse; C491831:Vamp8 protein, mouse; D002118:Calcium