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.
Subject(s)
Gene Expression Regulation , Inflammatory Bowel Diseases/metabolism , Intracellular Signaling Peptides and Proteins/metabolism , Protein Serine-Threonine Kinases/antagonists & inhibitors , Toll-Like Receptor 5/metabolism , Animals , Blotting, Western , Calcium-Calmodulin-Dependent Protein Kinases , Cells, Cultured , Humans , Immunoenzyme Techniques , Immunoprecipitation , Inflammatory Bowel Diseases/genetics , Inflammatory Bowel Diseases/pathology , Intracellular Signaling Peptides and Proteins/antagonists & inhibitors , Intracellular Signaling Peptides and Proteins/genetics , Luciferases/metabolism , Mice , Mitogen-Activated Protein Kinases/genetics , Mitogen-Activated Protein Kinases/metabolism , NF-kappa B/genetics , NF-kappa B/metabolism , NF-kappa B p52 Subunit/genetics , NF-kappa B p52 Subunit/metabolism , Phosphorylation , Protein Serine-Threonine Kinases/genetics , Protein Serine-Threonine Kinases/metabolism , RNA, Messenger/genetics , RNA, Small Interfering/genetics , Real-Time Polymerase Chain Reaction , Reverse Transcriptase Polymerase Chain Reaction , Signal Transduction , Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization , Toll-Like Receptor 5/geneticsABSTRACT
Discs large homolog 1 (DLGH1), a founding member of the membrane-associated guanylate kinase family of proteins containing PostSynaptic Density-95/Discs large/Zona Occludens-1 domains, is an ortholog of the Drosophila tumor suppressor gene Discs large. In the mammalian embryo, DLGH1 is essential for normal urogenital morphogenesis and the development of skeletal and epithelial structures. Recent reports also indicate that DLGH1 may be a critical mediator of signals triggered by the antigen receptor complex in T lymphocytes by functioning as a scaffold coordinating the activities of T-cell receptor (TCR) signaling proteins at the immune synapse. However, it remains unclear if DLGH1 functions to enhance or attenuate signals emanating from the TCR. Here, we used Dlgh1 gene-targeted mice to determine the requirement for DLGH1 in T-cell development and activation. Strikingly, while all major subsets of T cells appear to undergo normal thymic development in the absence of DLGH1, peripheral lymph node Dlgh1(-/-) T cells show a hyper-proliferative response to TCR-induced stimulation. These data indicate that, consistent with the known function of Discs large proteins as tumor suppressors and attenuators of cell division, in T lymphocytes, DLGH1 functions as a negative regulator of TCR-induced proliferative responses.
