Phosphorylation of CBP by IKKα links intestinal homeostasis

[Speaker] Yi-Ting Lin:1
[Co-author] Yu-Hua Hsu:2, Yan-Zhang Lee:2, Chieh-Chang Chen:5, Chi Liu:1, Chia-Tung Shun:3,4, Chia-Hung Tu:5, Ming-Shiang Wu:5, Shi-Chuen Miaw:2, Ching-Chow Chen:1
1:Department of Pharmacology, College of Medicine, National Taiwan University, Taiwan, 2:Graduate Institute of Immunology, College of Medicine, National Taiwan University, Taiwan, 3:Graduate Institute of Forensic Medicine, College of Medicine, National Taiwan University, Taiwan, 4:Department of Pathology, National Taiwan University Hospital, Taiwan, 5:Division of Gastroenterology, Department of Internal Medicine, National Taiwan University Hospital, Taiwan

Background and Aims: Immune dysregulation and intestinal barrier impairment due to host genetic and gut microbiota interaction leads to inflammatory bowel disease (IBD). Whole genome analysis revealed a decrease of CREB-binding protein (CBP) gene in colonic biopsy of patients with ulcerative colitis and Crohn's disease. CREB-binding protein (CBP) is a transcriptional coactivator participating in the regulation of DNA access for transcription factors. We demonstrated that human CBP phosphorylation by IKKα at serines 1382/1386 suppresses p53-mediated gene expression and plays a critical role in regulating cell fates. The effect of serines 1383/1387 mutation to alanine is evaluated by generation of knockin mice (AA mice).
Methods: The expression of phosphorylated CBP was determined by immunohistochemistry and Western blot analysis. Intestinal barrier permeability was measured by FITC-dextran in an Ussing Chamber system. Apoptosis was detected by TUNEL assay. Experimental colitis was induced by dextran sulfate sodium (DSS), and severity was assessed by body weight, stool consistency and hemoccult. Translocation of luminal microbes was measured by agar culturing. Immune cells were detected by flow cytometry. The bacteria 16S rRNA gene was examined by high-throughput DNA-sequencing.
Results: Impaired phosphorylation of CBP (Ser1382/1386) is positively correlated with human clinical samples. The deficiency of phosphorylated CBP leads AA mice to early changes at the age of 4 weeks exhibiting intestinal epithelial hyper-permeability and an increase of p53 level. Spontaneous colitis at young adult age is shown to be accompanied with infiltration of neutrophil and macrophage and apoptosis of epithelial cells. Upon chemical induction, AA mice show deteriorated colitis with severe disease activity index and mucosal inflammation, as well as enhanced translocation of viable bacteria from colon to spleen. Elevated immune cells in mesenteric lymph nodes with infiltration of neutrophil and macrophage are also more prominent. AA mice harbor a greater abundance of colitogenic strain (Proteobacteria phyla).
Conclusions: Impaired phosphorylation of CBP causes spontaneous colitis through mediating epithelial hyper-permeability, intestinal epithelial cell apoptosis and gut dysbiosis. This study elaborates the pathophysiological mechanism of IBD and brings novel insights for management of bowel disorder.

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