title: Raftlin Controls Lipopolysaccharide-Induced TLR4 Internalization and TICAM-1 Signaling in a Cell Type-Specific Manner.
abstract: The clathrin-dependent endocytic pathway is crucial for endosomal TLR3- and TLR4-mediated Toll-IL-1R domain-containing adaptor molecule-1 (TICAM-1) signaling. TLR4 uses a different signaling platform, plasma membrane and endosomes, for activation of TIRAP-MyD88 and TICAM-2-TICAM-1, respectively. LPS-induced endocytosis of TLR4 is mandatory for TICAM-1-mediated signaling including IFN-β production. Several molecules/mechanisms such as CD14, clathrin, and phosphatidylinositol metabolism have been reported to act as inducers of TLR4 translocation. However, the molecular mechanism of spatiotemporal regulation of TLR4 signaling remains unresolved. We have previously shown that Raftlin is essential for clathrin-dependent endocytosis of TLR3 ligand in human epithelial cells and myeloid dendritic cells (DCs). In this article, we demonstrate that Raftlin also mediated LPS-induced TLR4 internalization and TICAM-1 signaling in human monocyte-derived DCs and macrophages (Mo-Mϕs). When Raftlin was knocked down, LPS-induced TLR4-mediated IFN-β promoter activation, but not NF-κB activation, was decreased in HEK293 cells overexpressing TLR4/MD-2 or TLR4/MD-2/CD14. LPS-induced IFN-β production by monocyte-derived DCs and Mo-Mϕs was significantly decreased by knockdown of Raftlin. Upon LPS stimulation, Raftlin moved from the cytoplasm to the plasma membrane in Mo-Mϕs, where it colocalized with TLR4. Raftlin associated with clathrin-associated adaptor protein-2 in resting cells and transiently bound to TLR4 and clathrin at the cell surface in response to LPS. Thus, Raftlin appears to modulate cargo selection as an accessary protein of clathrin-associated adaptor protein-2 in clathrin-mediated endocytosis of TLR3/4 ligands.
authors.affiliation: Department of Microbiology and Immunology, Hokkaido University Graduate School of Medicine, Kita-ku, Sapporo 060-8638, Japan;
authors.forename: Megumi
authors.initials: M
authors.lastname: Tatematsu
authors.affiliation: Department of Microbiology and Immunology, Hokkaido University Graduate School of Medicine, Kita-ku, Sapporo 060-8638, Japan;
authors.forename: Ryuji
authors.initials: R
authors.lastname: Yoshida
authors.affiliation: Laboratory of Animal Experiment, Institute for Genetic Medicine, Hokkaido University, Sapporo 060-8638, Japan; and.
authors.forename: Yuka
authors.initials: Y
authors.lastname: Morioka
authors.affiliation: Department of Microbiology and Immunology, Hokkaido University Graduate School of Medicine, Kita-ku, Sapporo 060-8638, Japan;
authors.forename: Noriko
authors.initials: N
authors.lastname: Ishii
authors.affiliation: Department of Microbiology and Immunology, Hokkaido University Graduate School of Medicine, Kita-ku, Sapporo 060-8638, Japan;
authors.forename: Kenji
authors.initials: K
authors.lastname: Funami
authors.affiliation: Department of Microbiology and Immunology, Hokkaido University Graduate School of Medicine, Kita-ku, Sapporo 060-8638, Japan;
authors.forename: Ayako
authors.initials: A
authors.lastname: Watanabe
authors.affiliation: Department of Biochemistry, Juntendo University School of Medicine, Tokyo 113-8421, Japan.
authors.forename: Kazuko
authors.identifier: 0000-0003-1205-8261
authors.initials: K
authors.lastname: Saeki
authors.affiliation: Department of Microbiology and Immunology, Hokkaido University Graduate School of Medicine, Kita-ku, Sapporo 060-8638, Japan;
authors.forename: Tsukasa
authors.initials: T
authors.lastname: Seya
authors.affiliation: Department of Microbiology and Immunology, Hokkaido University Graduate School of Medicine, Kita-ku, Sapporo 060-8638, Japan; matumoto@pop.med.hokudai.ac.jp.
authors.forename: Misako
authors.initials: M
authors.lastname: Matsumoto
mesh_terms: D033942:Adaptor Proteins, Vesicular Transport / Q000378:metabolism*; D000818:Animals; D002966:Clathrin / Q000378:metabolism; D004705:Endocytosis; D004847:Epithelial Cells / Q000502:physiology*; D057809:HEK293 Cells; D006801:Humans; D016899:Interferon-beta / Q000378:metabolism; D008070:Lipopolysaccharides / Q000276:immunology; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D022423:Myeloid Cells / Q000502:physiology*; D009928:Organ Specificity; D015398:Signal Transduction; D051197:Toll-Like Receptor 4 / Q000378:metabolism
chemical_list: D033942:Adaptor Proteins, Vesicular Transport; D002966:Clathrin; D008070:Lipopolysaccharides; D008565:Membrane Proteins; C476398:RFTN1 protein, human; C470409:TICAM1 protein, human; D051197:Toll-Like Receptor 4; C000621721:raftlin protein, mouse; D016899:Interferon-beta