Selective use of TRAM in lipopolysaccharide (LPS) and lipoteichoic acid (LTA) induced NF-kappaB activation and cytokine production in primary human cells: TRAM is an adaptor for LPS and LTA signaling.
TLR signal via Toll-IL-1R (TIR) homology domain-containing adaptor proteins. One of these adaptors, Toll-IL-1R domain-containing adaptor inducing IFN-beta-related adaptor molecule (TRAM), has been shown to be essential for TLR4 signaling in TRAM(-/-) mice and cell lines. Previously, we showed that MyD88 or Mal dominant-negative constructs did not inhibit LPS induction of cytokines in primary human M-CSF-derived macrophages. A possible explanation was redundancy of the adaptors during LPS signaling. TRAM is a suitable candidate to compensate for these adaptors. To investigate a potential role for TRAM in LPS signaling in human M-CSF-derived macrophages, we engineered an adenoviral construct expressing dominant-negative TRAM-C117H (AdTRAMdn). Synovial fibroblasts (SF) and human umbilical endothelial cells (HUVECs) were used as a nonmyeloid comparison. AdTRAMdn inhibited LPS-induced signaling in SFs and HUVECs, reducing NF-kappaB activation and cytokine production, but did not inhibit LPS signaling in M-CSF-derived human macrophages. Further investigation of other TLR ligands showed that AdTRAMdn was also able to inhibit signaling initiated by lipoteichoic acid, a TLR2 ligand, in SFs and HUVECs and lipoteichoic acid and macrophage-activating lipopeptide 2 signaling was also inhibited in TRAM(-/-) murine embryonic fibroblasts. We conclude that TRAM is an adaptor protein for both TLR4 and TLR2/6 signaling in SFs, HUVECs, and murine embryonic fibroblasts, but cannot demonstrate a role in human macrophages.
Sacre
Sandra M
SM
Kennedy Institute of Rheumatology Division, Faculty of Medicine, Imperial College of Science, Technology and Medicine, London, United Kingdom.
Lundberg
Anna M C
AM
Andreakos
Evangelos
E
Taylor
Corinne
C
Feldmann
Marc
M
Foxwell
Brian M
BM
D048868:Adaptor Proteins, Signal Transducing; D033942:Adaptor Proteins, Vesicular Transport / Q000276:immunology*; D000818:Animals; D002478:Cells, Cultured; D004622:Embryo, Mammalian / Q000166:cytology / Q000276:immunology; D042783:Endothelial Cells / Q000166:cytology / Q000276:immunology*; D005347:Fibroblasts / Q000166:cytology / Q000276:immunology*; D006801:Humans; D008070:Lipopolysaccharides / Q000494:pharmacology*; D008264:Macrophages / Q000166:cytology / Q000276:immunology*; D051379:Mice; D018345:Mice, Knockout; D016328:NF-kappa B / Q000276:immunology*; D009928:Organ Specificity / Q000276:immunology; D018123:Receptors, Interleukin / Q000172:deficiency / Q000276:immunology; D015398:Signal Transduction / Q000187:drug effects* / Q000276:immunology; D013045:Species Specificity; D013583:Synovial Membrane / Q000166:cytology / Q000276:immunology; D013682:Teichoic Acids / Q000494:pharmacology*; D051195:Toll-Like Receptor 2 / Q000276:immunology; D051197:Toll-Like Receptor 4 / Q000276:immunology; D051216:Toll-Like Receptor 6 / Q000276:immunology; D014470:Umbilical Cord / Q000166:cytology / Q000276:immunology
D048868:Adaptor Proteins, Signal Transducing; D033942:Adaptor Proteins, Vesicular Transport; D008070:Lipopolysaccharides; D016328:NF-kappa B; D018123:Receptors, Interleukin; C480228:TICAM2 protein, human; C495342:TLR2 protein, human; C495345:TLR4 protein, human; C495368:TLR6 protein, human; D013682:Teichoic Acids; C476416:Ticam2 protein, mouse; D051195:Toll-Like Receptor 2; D051197:Toll-Like Receptor 4; D051216:Toll-Like Receptor 6; C009900:lipoteichoic acid