Regulation of the human mucin MUC4 by taurodeoxycholic and taurochenodeoxycholic bile acids in oesophageal cancer cells is mediated by hepatocyte nuclear factor 1α

MUC4 (mucin 4) is a membrane-bound mucin overexpressed in the early steps of oesophageal carcinogenesis and implicated in turnout progression. We previously showed that bile acids, main components of gastro-oesophageal reflux and tumour promoters, up-regulate MUC4 expression [Mariette, Perrais, Leteurtre, Jonckheere, Hemon, Pigny, Batra, Aubert, Triboulet and Van Seuningen (2004) Biochem. J. 377, 701-708]. HNF (hepatocyte nuclear factor) 1 alpha and HNF4 alpha transcription factors are known to mediate bile acid effects, and we previously identified cis-elements for these factors in MUC4 distal promoter. Our aim was to demonstrate that these two transcription factors were directly involved in MUC4 activation by bile acids. MUC4, HNF1 alpha and HNF4a expressions were evaluated by immunohistochemistry in human oesophageal tissues. Our results indicate that MUC4, HNF1 alpha and HNF4 alpha were co-expressed in oesophageal metaplastic and adenocarcinomatous tissues. Studies at the mRNA, promoter and protein levels indicated that HNF1 alpha a regulates endogenous MUC4 expression by binding to two cognate cis-elements respectively located at - 3332/- 3327 and - 3040/ - 3028 in the distal promoter. We also showed by siRNA (small interfering RNA) approach, co-transfection and site-directed mutagenesis that HNF1 alpha mediates taurodeoxycholic and taurochenodeoxycholic bile acid activation of endogenous MUC4 expression and transcription in a dose-dependent manner. In conclusion, these results describe a new mechanism of regulation of MUC4 expression by bile acids, in which HNF1 alpha is a key mediator. These results bring new insights into MUC4 up-regulation in oesophageal carcinoma associated with bile reflux.