EGF receptor pathway substrate No.8 facilitates phagocytosis by increasing TLR4-MyD88 interaction in LPS-stimulated macrophages

• Main Authors: Yen-JenChen, 陳彥任
• Other Authors: Tzeng-Horng Leu
• Format: Others
• Language: en_US
• Published: 2012
• Online Access: http://ndltd.ncl.edu.tw/handle/65011821006273951097

博士 === 國立成功大學 === 基礎醫學研究所 === 100 === Macrophage-mediated phagocytosis and subsequent degradation of pathogens by macrophages play a pivotal role in host innate immune responses to microbial infection. Recent studies have shown that Toll-like receptors (TLRs) play an important role in promoting the clearance of bacteria by up-regulating the phagocytic activity of macrophages under LPS stimulation. However, the underlying mechanism is not well defined. In the present study, we demonstrated the induction of Src in LPS-treated macrophages was TLR4- and MyD88-dependent and attenuation of Src by src-specific siRNA reduced LPS-promoted phagocytosis. And reintroduction of siRNA-resistant Src could restore the defect. Interestingly, we observed Eps8 was also up-regulated under LPS stimulation in a Src-dependent manner and Eps8 knockdown or overexpression of PH-truncated Eps8 (i.e. 261-p97Eps8) decreased LPS-mediated macrophage phagocytosis. In addition, confocal microscopy indicated Eps8 and TLR4 were colocolized in the cytosol and at the phagosome in RAW264.7 cells. Consistently, both Eps8 and TLR4 immunoprecipitated together from the lysates of RAW264.7 cells with or without LPS stimulation. This Eps8-TLR4 complex formation was required for LPS-induced TLR4-MyD88 interaction and the following activation of Src, FAK, and p38 MAPK. Importantly, Eps8 knockdown reduced bacterium killing ability of macrophages. Thus, Eps8 is a key protein regulating LPS-stimulated TLR4-MyD88 interaction and the following macrophage phagocytosis.