Bile Acids Induce Ectopic Expression of Intestinal Guanylyl Cyclase C Through Nuclear Factor-κB and Cdx2 in Human Esophageal Cells

Abstract

Background & Aims: Although progression to adenocarcinoma at the gastroesophageal junction reflects exposure to acid and bile acids associated with reflux, mechanisms mediating this transformation remain undefined. Guanylyl cyclase C (GC-C), an intestine-specific tumor suppressor, may represent a mechanism-based marker and target of transformation at the gastroesophageal junction. The present studies examine the expression of GC-C in normal tissues and tumors from esophagus and stomach and mechanisms regulating its expression by acid and bile acids. Methods: Gene expression was examined by reverse-transcription polymerase chain reaction, promoter analysis, immunohistochemistry, immunoblotting, and functional analysis. Promoter transactivation was quantified by using luciferase constructs and mutational analysis. DNA binding of transcription factors was examined by electromobility shift analysis. Results: GC-C mRNA and protein were ectopically expressed in ∼80% of adenocarcinomas arising in, but not in normal, esophagus and stomach. Similarly, in OE19 human esophageal cancer cells, deoxycholate and acid induced expression of GC-C. This was associated with the induction of expression of Cdx2, a transcription factor required for GC-C expression. In turn, induction of Cdx2 expression by deoxycholate was mediated by binding sites in the proximal promoter for nuclear factor κB (NF-κB). Furthermore, deoxycholate increased NF-κB activity, associated with nuclear translocation and Cdx2 promoter binding of the NF-κB subunit p50. Moreover, a dominant negative construct for NF-κB prevented deoxycholate-induced p50 nuclear translocation and activation of the Cdx2 promoter. Conclusions: Transformation associated with reflux at the gastroesophageal junction reflects activation by bile acid and acid of a transcriptional program involving NF-κB and Cdx2, which mediate intestinal metaplasia and ectopic expression of GC-C. © 2006 American Gastroenterological Association Institute.