title: Regulation of lipopolysaccharide-induced translation of tumor necrosis factor-alpha by the toll-like receptor 4 adaptor protein TRAM.
abstract: Lipopolysaccharide (LPS)-induced production of tumor necrosis factor (TNF)-α requires the recruitment of two pairs of adaptors to the Toll-like receptor 4 cytoplasmic domain. The contribution of one pair - Toll-interleukin-1 receptor domain-containing adaptor inducing interferon-β (TRIF) and TRIF-related adaptor molecule (TRAM) - to TNF-α expression is not well understood. To clarify this issue, we studied TRAM knockout bone marrow-derived macrophages (BMDM). LPS-stimulated TRAM-deficient BMDM had decreased TNF-α protein expression even at times when TNF-α mRNA levels were normal, suggesting impaired translation. Consistent with this idea, knockdown of TRAM in RAW264.7 macrophages decreased translation of a reporter controlled by the TNF-α 3' untranslated region, while transfection of TRAM in HEK293T cells increased translation of this reporter. Also consistent with a role for TRAM in TNF-α translation, LPS-induced activation of MK2, a kinase involved in this process, was impaired in TRAM-deficient BMDM. TRIF did not increase translation of the TNF-α 3' untranslated region reporter when expressed in HEK293T cells. However, BMDM that lacked functional TRIF produced reduced levels of TNF-α protein in response to LPS despite normal amounts of the mRNA. Unlike BMDM, LPS-stimulated TRAM-deficient peritoneal macrophages displayed equivalent reductions in TNF-α protein and mRNA. Our results indicate that TRAM- and TRIF-dependent signals have a previously unappreciated, cell type-specific role in regulating TNF-α translation.
authors.affiliation: Mucosal Immunology Laboratory, Division of Pediatric Gastroenterology, Massachusetts General Hospital, Charlestown, Mass., USA.
authors.forename: Lijian
authors.initials: L
authors.lastname: Wang
authors.forename: Estela
authors.initials: E
authors.lastname: Trebicka
authors.forename: Ying
authors.initials: Y
authors.lastname: Fu
authors.forename: Lisa
authors.initials: L
authors.lastname: Waggoner
authors.forename: Shizuo
authors.initials: S
authors.lastname: Akira
authors.forename: Katherine A
authors.initials: KA
authors.lastname: Fitzgerald
authors.forename: Jonathan C
authors.initials: JC
authors.lastname: Kagan
authors.forename: Bobby J
authors.initials: BJ
authors.lastname: Cherayil
mesh_terms: D033942:Adaptor Proteins, Vesicular Transport / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D057809:HEK293 Cells; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism; D008070:Lipopolysaccharides / Q000276:immunology* / Q000378:metabolism; D008264:Macrophages / Q000276:immunology / Q000378:metabolism* / Q000473:pathology; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D014176:Protein Biosynthesis; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D018123:Receptors, Interleukin / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D015398:Signal Transduction / Q000235:genetics / Q000276:immunology; D019076:Transgenes / Q000235:genetics; D014409:Tumor Necrosis Factor-alpha / Q000276:immunology / Q000378:metabolism*; D000099190:MAP-Kinase-Activated Kinase 2
chemical_list: D033942:Adaptor Proteins, Vesicular Transport; D047908:Intracellular Signaling Peptides and Proteins; D008070:Lipopolysaccharides; D017346:Protein Serine-Threonine Kinases; D018123:Receptors, Interleukin; D014409:Tumor Necrosis Factor-alpha; D000099190:MAP-Kinase-Activated Kinase 2; C476286:Ticam1 protein, mouse; C476416:Ticam2 protein, mouse