MyD88-independent activation of a novel actin-Cdc42/Rac pathway is required for Toll-like receptor-stimulated phagocytosis.
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. However, information regarding the signaling mechanism of TLR-mediated phagocytosis is still limited. Here, we provide evidence that the stimulation of TLR4 with LPS leads to activation of multiple signaling pathways including MAP kinases, phosphatidylinositide 3-kinase (PI3K), and small GTPases in the murine macrophage-like cell line RAW264.7. Specific inhibition of Cdc42/Rac or p38 MAP kinase, but not PI3K, reduced TLR4-induced phagocytosis of bacteria. Moreover, we have found that either inhibition of actin polymerization by cytochalasin D or the knockdown of actin by RNAi markedly reduced the activation of Cdc42 and Rac by LPS. TLR4-induced activation of Cdc42 and Rac appears to be independent of MyD88. Taken together, our results described a novel actin-Cdc42/Rac pathway through which TLRs can specifically provoke phagocytosis.
Kong
Ling
L
Institute of Health Science, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences and Shanghai Jiao-Tong University School of Medicine, Shanghai 200032, China.
Ge
Bao-Xue
BX
D000199:Actins / Q000378:metabolism*; D000818:Animals; D004926:Escherichia coli / Q000276:immunology; D008070:Lipopolysaccharides / Q000276:immunology; D017737:Macrophages, Peritoneal / Q000276:immunology*; D051379:Mice; D053594:Myeloid Differentiation Factor 88 / Q000378:metabolism; D010587:Phagocytosis; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D015398:Signal Transduction; D051197:Toll-Like Receptor 4 / Q000276:immunology* / Q000378:metabolism; D020764:cdc42 GTP-Binding Protein / Q000378:metabolism; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
D000199:Actins; D008070:Lipopolysaccharides; D053594:Myeloid Differentiation Factor 88; D051197:Toll-Like Receptor 4; D051057:Proto-Oncogene Proteins c-akt; D048051:p38 Mitogen-Activated Protein Kinases; D020764:cdc42 GTP-Binding Protein