The roles of KCNQ1 (potassium voltage-gated channel, KQT-like subfamily, Member 1) and CFTR (cystic fibrosis transmembrane conductance regulator) in mouse and human GI cancers

Abstract

The ion-channel genes <italic>Kcnq1<italic> and <italic>Cftr<italic> were identified as gastrointestinal (GI) tract cancer susceptibility genes in multiple <italic>Sleeping Beauty<italic> DNA transposon-based forward genetic screens in mice. <italic>Kcnq1<italic> encodes for the pore-forming alpha subunit of a voltage-gated potassium channel and <italic>Cftr<italic> encodes for the chloride conductance channel. These ion channels act together to maintain ion homeostasis in the cellular and extracellular environment. To confirm that <italic>Kcnq1<italic> and <italic>Cftr<italic> have a functional role in GI tract cancer, mouse models in which targeted mutant alleles of <italic>Kcnq1<italic> and <italic>Cftr<italic> were intogressed into the intestinal tumor susceptible <italic>Apc<super>Min<super><italic> strain of mice. Results demonstrated that <italic>Kcnq1<italic> mutant mice developed significantly more intestinal tumors, especially in the proximal small intestine and colon, with some of these tumors in the proximal small intestine progressing to adenocarcinomas. Gross tissue abnormalities and neoplasia were also observed in the rectum, pancreas and stomach. Similarly, <italic>Cftr<italic> mutant mice developed significantly more intestinal tumors, both in the colon and the entire small intestine. Colon organoid formation was significantly increased in organoids created from <italic>Kcnq1<italic> mutant and <italic>Cftr<italic> mutant mice compared with wildtype littermate controls, suggesting a role for <italic>Kcnq1<italic> and <italic>Cftr<italic> in regulation of the intestinal crypt stem cell compartment. To identify gene expression changes due to loss of <italic>Kcnq1<italic> and <italic>Cftr<italic>, we carried out microarray studies in the colon and proximal small intestine. We identified an overlapping set of altered genes involved in innate immune responses, goblet and Paneth cell function, ion channels, intestinal stem cells, EGFR and other growth regulatory signaling pathways. We also found genes implicated in inflammation and in cellular detoxification. Pathway analysis using Ingenuity Pathway Analysis (IPA) and gene set enrichment analysis (GSEA) confirmed the importance of these gene clusters and further identified significant overlap with genes regulated by <italic>MUC2<italic>, another important regulator of intestinal homeostasis. To investigate the role of <italic>KCNQ1<italic> in human colorectal cancer (CRC) we measured protein levels of KCNQ1 by immunohistochemistry in tissue microarrays containing samples from CRC patients with liver metastases who had undergone hepatic resection. Results showed that low expression of KCNQ1 expression was significantly associated with poor overall survival (OS). Our results indicate that both <italic>KCNQ1<italic> and <italic>CFTR<italic> are potent tumor suppressor genes in GI cancer. Defining the mechanisms of action of <italic>KCNQ1<italic> and <italic>CFTR<italic>, and elucidating the nature of their interactions in GI cancer can lead to their use as prognostic biomarkers and potential therapeutic targets for human cancers.