title: Pivotal role of ADP-ribosylation factor 6 in Toll-like receptor 9-mediated immune signaling.
abstract: CpG oligodeoxynucleotide (CpG ODN) cellular uptake into endosomes, the rate-limiting step of Toll-like receptor 9 (TLR9) signaling, is critical in eliciting innate immune responses. ADP-ribosylation factor 6 (ARF6) is a member of the Ras superfamily, which is critical to a wide variety of cellular events including endocytosis. Here, we found that inhibition of ARF6 by dominant mutants and siRNA impaired CpG ODN-mediated responses, whereas cells expressing the constitutively active ARF6 mutant enhanced CpG ODN-induced cytokine production. Inhibition of ARF6 impaired TLR9 trafficking into endolysosomes, thereby inhibiting proceed functional cleavage of TLR9. Additional studies showed that CpG ODN uptake was increased in ARF6-activated cells but impaired in ARF6-defective cells. Furthermore, cells pretreated with CpG ODN but not GpC ODN had increased CpG ODN uptake due to CpG ODN-induced ARF6 activity. Further studies with ARF6-defective and ARF6-activated cells demonstrated that class III phosphatidylinositol 3-kinases (PI3K) was required for downstream ARF6 regulation of CpG ODN uptake. Together, our findings demonstrate that a novel class III PI3K-ARF6 axis pathway mediates TLR9 signaling by regulating the cellular uptake of CpG ODN.
authors.affiliation: Institute of Cellular and System Medicine, National Health Research Institutes, Zhunan, Miaoli 35053, Taiwan.
authors.forename: Jing-Yiing
authors.initials: JY
authors.lastname: Wu
authors.forename: Cheng-Chin
authors.initials: CC
authors.lastname: Kuo
mesh_terms: D000089982:ADP-Ribosylation Factor 6; D020727:ADP-Ribosylation Factors / Q000235:genetics / Q000276:immunology* / Q000378:metabolism; D000818:Animals; D002460:Cell Line; D004789:Enzyme Activation / Q000187:drug effects / Q000235:genetics / Q000276:immunology; D006801:Humans; D007113:Immunity, Innate / Q000187:drug effects / Q000502:physiology*; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D009154:Mutation; D009838:Oligodeoxyribonucleotides / Q000494:pharmacology; D019869:Phosphatidylinositol 3-Kinases / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D034741:RNA, Small Interfering / Q000235:genetics; D015398:Signal Transduction / Q000187:drug effects / Q000235:genetics / Q000276:immunology*; D051217:Toll-Like Receptor 9 / Q000235:genetics / Q000276:immunology* / Q000378:metabolism
chemical_list: D000089982:ADP-Ribosylation Factor 6; D020727:ADP-Ribosylation Factors; D009838:Oligodeoxyribonucleotides; D019869:Phosphatidylinositol 3-Kinases; D034741:RNA, Small Interfering; D051217:Toll-Like Receptor 9; C408982:CPG-oligonucleotide; C495371:TLR9 protein, human; C495370:Tlr9 protein, mouse; C000715348:ARF6 protein, human; C000715727:Arf6 protein, mouse