Lipopolysaccharide (LPS)-binding protein stimulates CD14-dependent Toll-like receptor 4 internalization and LPS-induced TBK1-IKKα-IRF3 axis activation

Hiroki Tsukamoto, Shino Takeuchi, Kanae Kubota, Yohei Kobayashi, Sao Kozakai, Ippo Ukai, Ayumi Shichiku, Misaki Okubo, Muneo Numasaki, Yoshitomi Kanemitsu, Yotaro Matsumoto, Tomonori Nochi, Koui Chi Watanabe, Hisashi Aso, Yoshihisa Tomioka

Research output: Contribution to journalArticlepeer-review

20 Citations (Scopus)

Abstract

Toll-like receptor 4 (TLR4) is an indispensable immune receptor for lipopolysaccharide (LPS), a major component of the Gram-negative bacterial cell wall. Following LPS stimulation, TLR4 trnsmits the signal from the cell surface and becomes internalized in an endosome. However, the spatial regulation of TLR4 signaling is not fully understood. Here, we investigated the mechanisms of LPS-induced TLR4 internalization and clarified the roles of the extracellular LPS-binding molecules, LPSbinding protein (LBP), and glycerophosphatidylinositol-anchored protein (CD14). LPS stimulation of CD14-expressing cells inducedTLR4internalization in the presence of serum, and an inhibitory anti-LBP mAb blocked its internalization. Addition of LBP to serum-free cultures restored LPS-induced TLR4 internalization to comparable levels of serum. The secretory form of the CD14 (sCD14) induced internalization but required a much higher concentration than LBP. An inhibitory antisCD14mAbwas ineffective for serum-mediated internalization. LBP lacking the domain for LPS transfer to CD14 and a CD14 mutant with reduced LPS binding both attenuated TLR4 internalization. Accordingly, LBP is an essential serum molecule for TLR4 internalization, and its LPS transfer to membrane-anchored CD14 (mCD14) is a prerequisite. LBP induced the LPSstimulated phosphorylation of TBK1, IKKϵ, and IRF3, leading to IFN-β expression. However, LPS-stimulated late activation of NF-κB or necroptosis were not affected. Collectively, our results indicate that LBP controls LPS-induced TLR4 internalization, which induces TLR adaptor molecule 1 (TRIF)-dependent activation of the TBK1-IKKϵ-IRF3-IFN-β pathway. In summary, we showed that LBP-mediated LPS transfer to mCD14 is required for serum-dependent TLR4 internalization and activation of the TRIF pathway.

Original languageEnglish
Pages (from-to)10186-10201
Number of pages16
JournalJournal of Biological Chemistry
Volume293
Issue number26
DOIs
Publication statusPublished - 2018 Jun 29

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology

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