Involvement of CDX2 in the cross talk between TNF-α and Wnt signaling pathway in the colon cancer cell line Caco-2

Tumor necrosis factor-alpha (TNF-alpha) is highly upregulated in inflammation and reduces the expression of the intestinal transcription factor, Caudal-related homeobox transcription factor 2 (CDX2). Wnt/beta-catenin signaling is critical for intestinal cell proliferation, but a decreased CDX2 expression has influence on the Wnt signaling-related genes and progression of colorectal cancer. Although several inflammatory signaling pathways, including TNF-alpha, have been reported to promote Wnt/beta-catenin activity and development of cancer, the underlying molecular mechanisms remain unclear. The aim was to investigate the signaling pathways involved in the TNF-alpha-mediated downregulation of CDX2, and its influence on Wnt/beta-catenin signaling components in colon cancer cells. The expression of TNF-alpha and CDX2 at the invasive front were evaluated by immunohistochemical staining and showed reduced CDX2-positive cells in tumor buddings in areas with TNF-alpha expression in the surrounding inflammatory cells. In vitro studies revealed that TNF-alpha treatment showed a dose-dependent decrease of CDX2 messenger RNA (mRNA) and protein expression in Caco-2 cells. Inhibition of nuclear factor-kappaB or p38 pathways showed that these are involved in the TNF-alpha-dependent downregulation of CDX2. Furthermore, TNF-alpha-mediated downregulation of CDX2 was found to significantly decrease the mRNA levels of adenomatous polyposis coli (APC), axis inhibition protein 2 (AXIN2) and glycogen synthase kinase-3 beta (GSK3 beta), whereas the mRNA levels of Wnt targets were significantly elevated in TNF-alpha-treated Caco-2 cells. These findings were associated with reduced binding of CDX2 to promoter or enhancer regions of APC, AXIN2 and GSK3 beta. In conclusion, it was found that TNF-alpha induces the expression of Wnt signaling components through a downregulation of the CDX2 expression that might have a tumor-promoting effect on colon cancer cells.