Edinburgh Napier University

  Background & Aims The mechanisms by which specific mutations in NOD2/CARD15 increase the risk for Crohn's disease (CD) are unclear. We identified proteins that interact with {NOD2} and investigated them by expression, genetic, and functional analyses. Methods By using a yeast 2-hybrid screen of an intestinal epithelial library, we identified proteins that interact with {NOD2} and confirmed the interactions in mammalian cells using co-immunoprecipitation. We used microarray analysis to analyze gene expression patterns in 302 intestinal biopsy samples (129 from patients with ulcerative colitis [UC], 106 with CD, and 67 controls). Eighty single-nucleotide polymorphisms within the genes that encoded 6 interacting proteins were genotyped in a discovery cohort (869 cases of inflammatory bowel disease [IBD], 885 controls) and a replication cohort (504 patients with IBD, 713 controls). We investigated interaction between transducin-like enhancer of split 1 (TLE1) and {NOD2} in {HEK293} cells. Results We identified 6 NOD2-interacting proteins (TLE1, UDP-N-acetyl-alpha-D-galactosamine:polypeptide N-acetylgalactosaminyltransferase 2 [GALNT2], HIV-1 Tat interactive protein [HTATIP], Vimentin, fission 1 (mitochondrial outer membrane) homolog [FIS1], and protein phosphatase 2, regulatory subunit B′, epsilon isoform [PPP2R5E]). Of these, expression of {GALNT2} (CD, P = .004) and vimentin (CD, P = .006; UC, P = .0025) was altered in patients with {IBD} compared with controls. Single-nucleotide polymorphisms within {TLE1} were associated with susceptibility to CD, specifically with ileal disease (rs6559629, P = 3.1 × 10−5; odds ratio, 1.45). The {TLE1} risk allele is required for susceptibility to {CD} in carriers of {NOD2} mutations. In cells, {TLE1} and {NOD2} co-localized around the nuclear membrane and {TLE1} inhibited activation of nuclear factor-κB by NOD2. Conclusions Epistatic and biological interactions between {TLE1} and {NOD2} are involved in {IBD} pathogenesis. {NOD2} might be involved in a series of pathways such as epigenetic regulation of expression (via {TLE1} and HTATIP), biosynthesis of mucin (via GALNT2), apoptosis (via {PPP2R5E} and FIS1), and integrity of the intracellular cytoskeleton (vimentin).