Inferred inactivation of the CFTR gene in the duodena of mice exposed to hexavalent chromium (Cr(VI)) in drinking water supports its tumor-suppressor status and implies its potential role in Cr(VI)-induced carcinogenesis of the small intestines
Hexavalent chromium [Cr (VI)] compounds are used in metallurgical, chemical and refractory industries. Their carcinogenicity has been supported by a number of epidemiological and animal studies; however, their carcinogenic mode of action is still incompletely understood. To identify mechanisms involved in cancer development from toxicologically relevant exposures to Cr(VI), we analyzed gene expression data from duodena of mice (a target of carcinogenic transformation following oral exposure) exposed for 7 or 90 days to Cr(VI) in drinking water at concentrations of 0.3-520 mg/L. This analysis included (i) identification of upstream regulatory molecules that are likely responsible for the observed gene expression changes, (ii) identification of annotated gene expression data from public repositories that correlate with gene expression changes in duodena of Cr(VI)-exposed mice, and (iii) identification of hallmark and oncogenic signature gene sets from the Molecular Signatures Database (MSigDB) relevant to these data. We identified the inactivated CFTR gene (Cystic fibrosis transmembrane conductance regulator) among the top scoring upstream regulators, and found positive correlations between the expression data from duodena of Cr(VI)-exposed mice and other datasets in public repositories associated with the inactivation of the CFTR gene. In addition, we found enrichment of signatures for oncogenic signaling, sustained cell proliferation, impaired apoptosis and tissue remodeling in the duodena of mice exposed to Cr(VI) in drinking water. Our results support the tumor-suppressor role of the CFTR gene, which was previously suggested for intestinal carcinogenesis in humans and mice. Furthermore, our results support human relevance of the Cr(VI)-mediated carcinogenesis observed in the small intestines of exposed mice and suggest possible groups that may be more vulnerable to the adverse outcomes associated with the inactivation of CFTR by hexavalent chromium or other agents. Lastly, our findings indicate, for the first time, the role of CFTR inactivation in chemical carcinogenesis and expand the range of plausible mechanisms that may be operative in Cr(VI)-mediated carcinogenesis of intestinal and possibly other tissues.