Regulation of UGT1A1 and HNF1 transcription factor gene expression by DNA methylation in colon cancer cells

Gel retardation assays revealed that methylation of CpG-4 directly affect the interaction of USF1/2 with its cognate sequence without altering the binding for HNF1-alpha. Luciferase assays sustained a role for USF1/2 and HNF1-alpha in UGT1A1 regulation in colon cancer cells. Based on the differential expression profiles of HNF1A gene in colon cell lines, we also assessed whether methylation affects its expression. In agreement with the presence of CpG islands in the HNF1A promoter, treatments of UGT1A1-negative HCT116 colon cancer cells with a DNA methyltransferase inhibitor restore HNF1A gene expression, as observed for UGT1A1.This study reveals that basal UGT1A1 expression in colon cells is positively regulated by HNF1-alpha and USF, and negatively regulated by DNA methylation. Besides, DNA methylation of HNF1A could also play an important role in regulating additional cellular drug metabolism and transporter pathways. This process may contribute to determine local inactivation of drugs such as the anticancer agent SN-38 by glucuronidation and define tumoral response.Irinotecan (CPT-11) is a topoisomerase I inhibitor and one of the main cytotoxic agent for treatment of advanced metastatic colorectal cancer [1-3]. In vivo, irinotecan is converted to 7-ethyl-10-hydroxycamptothecin (SN-38), by a carboxylesterase-mediated hydrolysis, a metabolite ~1000-fold more active as topoisomerase I inhibitor than irinotecan [4,5]. The elimination pathway of the active metabolite SN-38 is primarily through glucuronidation, which is mainly mediated by the UDP-glucuronosyltransferase (UGT) 1A1 enzyme [6-8]. Low rates of SN-38 glucuronidation in tumor sites increase the level of the active compound that could lead to higher sensitivity to irinotecan. In contrast, high levels of UGT activity and expression were associated with an increase of SN-38 resistance in colon cancer cells [9]. Therefore, the regulation of UGT1A gene expression together with other mechanisms altering its prote