title: Co-operation of TLR4 and raft proteins in LPS-induced pro-inflammatory signaling.
abstract: Toll-like receptor 4 (TLR4) is activated by lipopolysaccharide (LPS), a component of Gram-negative bacteria to induce production of pro-inflammatory mediators aiming at eradication of the bacteria. Dysregulation of the host responses to LPS can lead to a systemic inflammatory condition named sepsis. In a typical scenario, activation of TLR4 is preceded by binding of LPS to CD14 protein anchored in cholesterol- and sphingolipid-rich microdomains of the plasma membrane called rafts. CD14 then transfers the LPS to the TLR4/MD-2 complex which dimerizes and triggers MyD88- and TRIF-dependent production of pro-inflammatory cytokines and type I interferons. The TRIF-dependent signaling is linked with endocytosis of the activated TLR4, which is controlled by CD14. In addition to CD14, other raft proteins like Lyn tyrosine kinase of the Src family, acid sphingomyelinase, CD44, Hsp70, and CD36 participate in the TLR4 signaling triggered by LPS and non-microbial endogenous ligands. In this review, we summarize the current state of the knowledge on the involvement of rafts in TLR4 signaling, with an emphasis on how the raft proteins regulate the TLR4 signaling pathways. CD14-bearing rafts, and possibly CD36-rich rafts, are believed to be preferred sites of the assembly of a multimolecular complex which mediates the endocytosis of activated TLR4.
authors.affiliation: Laboratory of Molecular Membrane Biology, Nencki Institute of Experimental Biology, 3 Pasteur St., 02-093, Warsaw, Poland.
authors.forename: Agnieszka
authors.initials: A
authors.lastname: Płóciennikowska
authors.affiliation: Laboratory of Molecular Membrane Biology, Nencki Institute of Experimental Biology, 3 Pasteur St., 02-093, Warsaw, Poland.
authors.forename: Aneta
authors.initials: A
authors.lastname: Hromada-Judycka
authors.affiliation: Laboratory of Molecular Membrane Biology, Nencki Institute of Experimental Biology, 3 Pasteur St., 02-093, Warsaw, Poland.
authors.forename: Kinga
authors.initials: K
authors.lastname: Borzęcka
authors.affiliation: Laboratory of Molecular Membrane Biology, Nencki Institute of Experimental Biology, 3 Pasteur St., 02-093, Warsaw, Poland. k.kwiatkowska@nencki.gov.pl.
authors.forename: Katarzyna
authors.initials: K
authors.lastname: Kwiatkowska
mesh_terms: D033942:Adaptor Proteins, Vesicular Transport / Q000378:metabolism; D001424:Bacterial Infections / Q000276:immunology*; D006801:Humans; D007249:Inflammation / Q000276:immunology* / Q000378:metabolism; D018950:Lipopolysaccharide Receptors / Q000378:metabolism; D008070:Lipopolysaccharides / Q000378:metabolism*; D021962:Membrane Microdomains / Q000378:metabolism*; D008565:Membrane Proteins / Q000378:metabolism*; D008958:Models, Molecular; D053594:Myeloid Differentiation Factor 88 / Q000378:metabolism; D015398:Signal Transduction / Q000276:immunology*; D051197:Toll-Like Receptor 4 / Q000276:immunology*
chemical_list: D033942:Adaptor Proteins, Vesicular Transport; D018950:Lipopolysaccharide Receptors; D008070:Lipopolysaccharides; C507779:MYD88 protein, human; D008565:Membrane Proteins; D053594:Myeloid Differentiation Factor 88; C470409:TICAM1 protein, human; C495345:TLR4 protein, human; D051197:Toll-Like Receptor 4