title: Protein-tyrosine kinase Syk is required for pathogen engulfment in complement-mediated phagocytosis.
abstract: The protein tyrosine kinase Syk plays a central role in Fcgamma receptor-mediated phagocytosis in the adaptive immune system. We show here that Syk also plays an essential role in complement-mediated phagocytosis in innate immunity. Macrophage-like differentiated HL60 cells and C3bi-opsonized zymosan comprised the pathogen-phagocyte system. C3bi-opsonized zymosan particles promptly attached to the cells and were subsequently engulfed via complement receptor 3. During this process, Syk became tyrosine phosphorylated and accumulated around the nascent phagosomes. The transfer of Syk-siRNA or dominant-negative Syk (DN-Syk) into HL60 cells resulted in impaired phagocytosis. Quenching assays using fluorescent zymosan revealed that most of the attached zymosan particles were located inside parental HL60 cells, whereas few were ingested by the mutant cells. These data indicated that Syk is required for the engulfment of C3bi-opsonized zymosan. During C3bi-zymosan-induced phagocytosis, actin accumulation occurred around phagosomes and was followed by depolymerization, and further RhoA was activated together with tyrosine phosphorylation of Vav. These responses including the actin remodeling were suppressed in Syk-siRNA- or DN-Syk-expressing cells. Our results demonstrated that Syk plays an indispensable role in complement-mediated phagocytosis by regulating both actin dynamics and the RhoA activation pathway and that these functions of Syk lead to phagosome formation and pathogen engulfment.
authors.affiliation: Department of Genome Sciences, Kobe University Graduate School of Medicine, Kobe 650-0017, Japan.
authors.forename: Yuhong
authors.initials: Y
authors.lastname: Shi
authors.forename: Yumi
authors.initials: Y
authors.lastname: Tohyama
authors.forename: Tomomi
authors.initials: T
authors.lastname: Kadono
authors.forename: Jinsong
authors.initials: J
authors.lastname: He
authors.forename: S M Shahjahan
authors.initials: SM
authors.lastname: Miah
authors.forename: Ryoichi
authors.initials: R
authors.lastname: Hazama
authors.forename: Chisato
authors.initials: C
authors.lastname: Tanaka
authors.forename: Kaoru
authors.initials: K
authors.lastname: Tohyama
authors.forename: Hirohei
authors.initials: H
authors.lastname: Yamamura
mesh_terms: D000199:Actins / Q000378:metabolism; D003165:Complement System Proteins / Q000276:immunology*; D018922:HL-60 Cells; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism / Q000502:physiology*; D016177:Macrophage-1 Antigen / Q000378:metabolism; D010587:Phagocytosis; D010588:Phagosomes / Q000378:metabolism; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000378:metabolism / Q000502:physiology*; D000072377:Syk Kinase; D015054:Zymosan / Q000378:metabolism; D020742:rhoA GTP-Binding Protein / Q000378:metabolism
chemical_list: D000199:Actins; D047908:Intracellular Signaling Peptides and Proteins; D016177:Macrophage-1 Antigen; D003165:Complement System Proteins; D015054:Zymosan; D011505:Protein-Tyrosine Kinases; C000606896:SYK protein, human; D000072377:Syk Kinase; D020742:rhoA GTP-Binding Protein