Background: High levels of pro-inflammatory cytokines are present in the gut of patients with inflammatory bowel disease (IBD) and have a crucial role in the dysfunction of mucosal homeostasis. Caudal-related homeobox transcription factor 2 (CDX2) is an essential regulator of intestinal epithelium homeostasis. When expressed, CDX2 modulates a diverse set of processes, including cell proliferation and differentiation, and cell adhesion and migration. In addition to these critical cellular processes, there is increasing indications (such as involvement in pro-inflammatory pathways and regulation of genes of importance for intestinal homeostasis) linking CDX2 to intestinal inflammation.
Aim: The overall objective of this PhD thesis was to explore the role of CDX2 in the colonic epithelium of patients with IBD and to investigate the impact of pro-inflammatory pathways on the expression of CDX2 and its target genes.
Methods: Initially, a literature research was conducted to review the importance of CDX2 in epithelial homeostasis and its potential role in mucosal inflammation. Expression of CDX2 was measured in colonic biopsies of patients with IBD, and the effects of pro-inflammatory cytokines and anti-TNF-α treatment (infliximab) were examined in Caco-2 cells. The role of CDX2 in the transcriptional regulation of MEP1A and the β-catenin degradation complex genes APC, AXIN2, and GSK3β were investigated in Caco-2 cells. Finally, the intracellular signalling pathways involved in the TNF-α-mediated down-regulation of CDX2 were investigated.
Results: The expression of CDX2 was decreased in the epithelium of patients with ulcerative colitis (UC), and the expression was inversely correlated with the level of TNF-α. The endogenous expression of CDX2 in Caco-2 cells was decreased by TNF-α through NF-κB and p38 MAPK pathways. High levels of TNF-α affected the expression of CDX2 target genes and reduced the binding of CDX2 to gene regulatory regions of these targets in Caco-2 cells. Finally, TNF-α increased the expression of well-known Wnt target genes.
Conclusions: These findings indicate that the CDX2 expression is decreased in UC, and moreover, the studies in Caco-2 cells have shed light on some of the molecular pathways of importance in the inhibitory effect of TNF-α. In addition, these studies have provided novel insight into the CDX2-mediated regulation of genes involved in the β-catenin degradation complex and in response to the pro-inflammatory cytokine, TNF-α. In particular, these findings indicate that CDX2 is involved in the crosstalk between TNF-α and the Wnt signalling pathway, which might be of importance in understanding the link between intestinal inflammation and tumourigenesis.