title: Tribbles 2 (Trib2) is a novel regulator of toll-like receptor 5 signaling.
abstract: BACKGROUND
  Toll-like receptors (TLRs) are expressed by a variety of cells, including intestinal epithelia. However, the full spectrum of regulators modulating innate responses via TLRs has not been delineated. Tribbles (Trib) have been identified as a highly conserved family of kinase-like proteins. We sought to clarify the role of Trib2 in the TLR signaling pathway.
  
  
  METHODS
  Trib2 mRNA and protein levels were analyzed by quantitative polymerase chain reaction (PCR) and western blot, respectively. Immunohistochemical staining was used to determine the expression of Trib2 in human tissue. Involvement of Trib2 in nuclear factor kappa B (NF-κB) pathways was assessed in epithelial cells by NF-κB reporter assay. Proteins that interacted with Trib2 were identified by mass spectrometry and confirmed by immunoprecipitation. The domain essential for Trib2 function was mapped using truncated constructs.
  
  
  RESULTS
  Trib2 expression is decreased in active inflamed tissue from patients with inflammatory bowel disease (IBD). Trib2 is expressed in human and mouse colonic epithelium as well as immune cells, and its expression in epithelium is inducible in a ligand-dependent manner by TLR5 ligand stimulation. Trib2 inhibits TLR5-mediated activation of NF-κB downstream of TRAF6. Trib2 selectively modulates mitogen-activated protein kinase (MAPK) pathways p38 and Jun N-terminal kinase (JNK) but not p44/p42 (ERK1/2). NF-κB2 (p100) was identified as a Trib2 binding partner in regulating the TLR5 signaling pathway that leads to inhibition of NF-κB activity. Residues 158-177 in the Trib2 kinase-like domain are required for Trib2 function.
  
  
  CONCLUSIONS
  These observations indicate that Trib2 is a novel regulator in the TLR5 signaling pathway and altered expression of Trib2 may play a role in IBD.
authors.affiliation: Gastrointestinal Unit and Center for the Study of Inflammatory Bowel Disease, Massachusetts General Hospital, Boston, Massachusetts 02114, USA.
authors.forename: Shu-Chen
authors.initials: SC
authors.lastname: Wei
authors.forename: Ian M
authors.initials: IM
authors.lastname: Rosenberg
authors.forename: Zhifang
authors.initials: Z
authors.lastname: Cao
authors.forename: Alan S
authors.initials: AS
authors.lastname: Huett
authors.forename: Ramnik J
authors.initials: RJ
authors.lastname: Xavier
authors.forename: Daniel K
authors.initials: DK
authors.lastname: Podolsky
mesh_terms: D000818:Animals; D015153:Blotting, Western; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D002478:Cells, Cultured; D005786:Gene Expression Regulation; D006801:Humans; D007124:Immunoenzyme Techniques; D047468:Immunoprecipitation; D015212:Inflammatory Bowel Diseases / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D047908:Intracellular Signaling Peptides and Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D008156:Luciferases / Q000378:metabolism; D051379:Mice; D020928:Mitogen-Activated Protein Kinases / Q000235:genetics / Q000378:metabolism; D016328:NF-kappa B / Q000235:genetics / Q000378:metabolism; D052003:NF-kappa B p52 Subunit / Q000235:genetics / Q000378:metabolism; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics; D034741:RNA, Small Interfering / Q000235:genetics; D060888:Real-Time Polymerase Chain Reaction; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D051198:Toll-Like Receptor 5 / Q000235:genetics / Q000378:metabolism*
chemical_list: D047908:Intracellular Signaling Peptides and Proteins; D016328:NF-kappa B; D052003:NF-kappa B p52 Subunit; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D051198:Toll-Like Receptor 5; C515847:tribbles 2 protein, mouse; D008156:Luciferases; D017346:Protein Serine-Threonine Kinases; D017871:Calcium-Calmodulin-Dependent Protein Kinases; C489044:TRIB2 protein, human; D020928:Mitogen-Activated Protein Kinases