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Blood, 1 June 2006, Vol. 107, No. 11, pp. 4554-4562.
Prepublished online as a Blood First Edition Paper on January 31, 2006; DOI 10.1182/blood-2005-09-3616.
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Submitted September 8, 2005
Accepted January 17, 2006
Protein-tyrosine kinase, Syk is required for pathogen engulfment in complement-mediated phagocytosis
Yuhong Shi, Yumi Tohyama*, Tomomi Kadono, Jinsong He, S M Miah, Ryoichi Hazama, Chisato Tanaka, Kaoru Tohyama, and Hirohei Yamamura
Department of Genome Sciences, Kobe University Graduate School of Medicine, Kobe, Hyogo, Japan
Department of Laboratory Medicine and Clinical Pathology, Kawasaki Medical School, Kurashiki, Okayama, Japan
* Corresponding author; email: ytohyama{at}med.kobe-u.ac.jp.
The protein-tyrosine kinase, Syk, plays a central role in Fc 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 receptor3. 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 RhoA-activation pathway and that these functions of Syk lead to phagosome formation and pathogen engulfment.
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