From Inflammation to Tumorigenesis: Mechanisms of Action of the Transcription Factor Kaiso in Murine Intestinal Pathologies

Abstract

Colorectal Cancer (CRC) is the third most prevalent cancer and the second leading cause of cancer-related mortality worldwide. Patients who suffer from inflammatory bowel disease (IBD) have a greater risk of developing IBD-associated CRC, also known as Colitis-associated colorectal cancer (CAC). While CAC accounts for ~ 2% of all CRC cases, it is listed as the cause of death in 10–15% of patients with IBD, of which there are currently over 4 million. However, the molecular mechanisms underlying the progression from IBD to CAC remains to be fully determined as there are few in vivo mouse models that effectively recapitulate IBD and CAC. Our lab has previously shown that murine intestinal-specific overexpression of the transcription factor Kaiso disturbs epithelial barrier stability, induces a chronic intestinal inflammatory phenotype, and promotes Wnt-mediated intestinal tumorigenesis. However, the molecular mechanisms and signalling networks involved have not been fully elucidated. Notably, loss of Kaiso’s binding partner and transcriptional inhibitor, p120-catenin (p120ctn), in murine intestines results in intestinal inflammation and adenoma formation. These findings suggest that Kaiso and p120ctn play opposing roles in intestinal inflammation and tumorigenic processes. However, the mechanisms by which Kaiso and p120ctn regulate intestinal inflammation, and their potential roles in the IBD to CAC transition have yet to be established. The goals of this study were to further characterize the Kaiso-mediated intestinal inflammatory phenotype, identify the signalling networks involved in Kaiso-mediated intestinal inflammation, and determine the role(s) that Kaiso and p120ctn play in IBD development and its subsequent progression to CAC. To delineate the molecular mechanism and signalling networks involved in the Kaiso overexpressing transgenic mouse chronic inflammatory phenotype, transcriptomic profiling was conducted. RNA extracted from whole intestinal ileal tissues of 6-week-old Kaiso transgenic (KaisoTg) and non-transgenic (Non-Tg) mice were subjected to RNA sequencing and differential gene expression analysis. 788 genes were identified as differentially expressed that were robust to sex and parental origin. Functional annotation assigning biological meaning and function to these genes identified a significant enrichment in the innate immune response specifically driven by interferon signalling. Importantly, we demonstrated that Kaiso associated with the endogenous promoter region of the interferon regulatory factor 7 (IRF7), a master transcriptional activator responsible for initiating and driving IFN signalling and interferon-stimulated gene expression. Kaiso also activated the minimal IRF7 promoter-reporter construct in a Kaiso binding site (KBS)-specific but methyl-CpG-independent manner. We also investigated whether Kaiso overexpression in conjunction with p120ctn depletion would induce an IBD-like phenotype that subsequently progresses to CAC. Thus, we generated a Kaiso-overexpressing, p120ctn conditional-depleted mice model (KaisoTg ;p120cKO) and characterized the resultant progeny. Using a tamoxifen-inducible mouse model (Vil-Cre-ERT2;p120fl/fl), we observed an ~15% of p120ctn depletion in the intestinal epithelium. However, loss of p120ctn (~5%) was only observed in the small intestine at 2 months post injection, while the depletion (~10%) persisted until study endpoint in the large intestine. Intriguingly, KaisoTg and KaisoTg;p120cKO mice presented with small intestinal tumours at endpoint that were associated with decreased Kaiso, E-cadherin and p120ctn expression, independent of p120ctn depletion. Our findings suggest that Kaiso potentiates tumour formation in murine intestines and p120ctn depletion did not enhance Kaiso's tumorigenic effect. Collectively, these findings unveiled a new molecular signalling pathway (Type 1 IFN) in Kaiso-mediated intestinal inflammation and implicates Kaiso as a driver of tumour formation in murine intestines.