The Adenomatous Polyposis Coli Tumor Suppressor Gene Suppresses Deoxycholic Acid Induction of the Chemotactic Cytokine CXCL8 in Human Colorectal Cancer

Abstract

Elevated deoxycholic acid (DCA) and mutations in the Adenomatous Polyposis Coli (APC) tumor suppressor gene have been associated with increased risk of colorectal cancer (CRC). Chronic inflammation has also been associated with increased risk of CRC. It is unclear if DCA mediates inflammation in the normal or transformed colonic mucosa. The status of APC was manipulated in human CRC cell lines to study the role of DCA mediated inflammation. The chemotactic cytokine, CXCL8, was used as a marker of inflammation. Addition of DCA to the HT29-parental cell line with mutant-APC increased the steady state mRNA and protein levels of CXCL8. Conversely, addition of DCA to the HT29-APC cell line with wild type-APC was protective for increased steady state RNA and protein levels of CXCL8. DCA activated transcription factors which had binding regions in the CXCL8 5’-promoter. To elucidate the mechanism of induction, the 5’-promoter of CXCL8 was investigated. DCA increased promoter-reporter activity of the CXCL8 gene in HT29-parental cell line but wild type-APC blocked this effect. Chromatin immunoprecipitation (ChIP) revealed that DCA activated transcription factors, AP-1 and NF-κB were bound to the 5’-promoter of CXCL8. The transcription factor, β-catenin, was also bound to the 5’-promoter of CXCL8. Phenotypic effects were measured. Increased CXCL8 lead to matrix metalloproteinase-2 (MMP-2) production and increased invasion by HT29-parental cells on laminin coated filters. The DCA-mediated invasion was blocked by antibody directed against CXCL8 and wild type- APC. Therefore DCA-mediated inflammation occurs in transformed colonic epithelium and increases the invasive phenotype of CRC cells by CXCL8.