Increased expression of caudal-related homeobox gene CDX2 in response to bile acid exposure in esophageal cell lines

A48

Purpose: To further investigate critical early molecular alterations in esophageal premalignancy, we studied the expression of caudal-related homeobox gene 2 (CDX2) in human esophageal cell lines exposed to three clinically-relevant bile acids. These in vitro studies follow our recent observation of aberrant expression of CDX2, a nuclear transcription factor implicated intestinal development, in human Barrett esophagus, an acquired condition predisposed by chronic gastroduodenoesophageal reflux, in which normal esophageal squamous epithelium is replaced by a specialized metaplastic columnar cell-lined epithelium.
 >Methods: Two esophageal adenocarcinoma cell lines (Bic-1, Seg-1) and Het-1A, an immortalized normal esophageal epithelial cell line, were exposed in culture to cholic acid (CA), taurocholic acid (TCA), and glycocholic acid (GCA), at concentrations ranging from 5 µM to 1000µM for 24 hours. Following extraction of total RNA, quantitative PCR was used to evaluate the effect of bile acids on CDX2 RNA expression. Western blot analysis was used to study CDX2 protein expression.
 >Results: Relative to baseline CDX2 RNA expression in untreated Bic-1 cells, exposure to low levels (100-200 µM ) of CA, TA and GCA resulted in overexpression (2.5-3.8 fold) of CDX2 RNA. By contrast, Seg 1 and Het-1A cells required relatively higher bile acid concentration (500 µM) to achieve significant CDX2 RNA overexpression, which ranged from 3.6 fold following CA exposure in Seg 1 to 63 fold overexpression following GCA exposure in Het 1A. All bile acids were toxic to all cells at concentrations of 1000µM.
 >Conclusions: The induced expression of CDX2 in human esophageal cell lines by CA, TCA, and GCA at physiologically-relevant concentrations, supports the hypothesis that bile acid exposure may be important in the pathobiology of Barrett esophagus, specifically by initiating metaplastic transformation through up-regulation of CDX2.