Does Bile Reflux Influence the Progression of Barrett's Esophagus to Adenocarcinoma? (Gastroenterology 2013;145:1300-1311)

Abstract

In recent times, the incidence of esophageal adenocarcinoma (EAC) in Western countries is increasing. Barrett's esophagus (BE) is characterized by the replacement of the squamous epithelium by metaplastic columnar epithelium in the lower esophagus. It is a premalignant lesion that is detected in a majority of patients with EAC. Gastroesophageal reflux disease (GERD) and bile reflux are known to cause BE and EAC.1 Caudal-related homologue 2 (CDX2), is a homeodomain transcription factor that regulates normal intestinal cell differentiation by functioning as a tumor suppressor protein, and its expression levels are associated with the prognosis of adenocarcinomas. Moreover, decreased levels of CDX2 are reported during the progression of BE to metaplasia, dysplasia and EAC.2 However, little is known about the molecular mechanism that downregulates CDX2 in the carcinogenesis of BE. The inhibitor p27Kip1, a member of the Cip/Kip family of cyclin-dependent kinase (CDK) inhibitors has been reported to stabilize CDX2 protein by blocking its phosphorylation and degradation.3 Matsuzaki et al4 designed this study to investigate whether bile acids affect the expression of microRNA-221 and microRNA-222 (miR-221 and miR-222), which bind to p27Kip1 mRNA and facilitate the degradation of CDX2 in the esophagus. In the biopsy samples of BE and EAC, obtained from 11 patients, the levels of miR-221 and miR-222 were increased, as indicated by quantitative reverse transcriptase PCR, whereas the levels of p27Kip1 and CDX2 protein were decreased, as indicated by immunohistochemistry, in the areas of EAC when compared to areas of BE. Levels of miR-221 and miR-222 increased along with the activity of farnesoid X receptor (FXR) when EAC cells (OE33) or human esophageal squamous epithelial cells transfected with a CDX2 transgene (HET1A + Cdx2) were exposed to bile acids (cholic acids or chenodeoxycholic acid). When the cells were incubated with bile acids, the degradation of CDX2 increased. However, this process was attenuated when the cells were incubated with proteasome inhibitors. Overexpression of miR-221 and miR-222 reduced the levels of p27Kip1 and CDX2, whereas the knockdown of these miRNAs increased the levels of these proteins in the cultured cells. Inhibitors of miR-221 and miR-222 increased the levels of p27Kip1 and CDX2 in the EAC cells and reduced the growth of human EAC xenograft tumors in NOD/SCID/IL-2Rγnull (NOG) mice. The degradation of CDX2 was enhanced by the increased levels of miR-221 and miR-222 during exposure to bile acids via FXR activation in human esophageal epithelial cells. The findings of this study suggest that the FXR pathway could emerge as a therapeutic target and implicate the therapeutic potential of FXR antagonists or inhibitors of miRNAs as a treatment option for BE and EAC.