Notch signaling pathway and Cdx2 expression in the development of Barrett's esophagus

Cdx2 expression in esophageal stem cells induced by reflux bile acids may be an important factor for development of Barrett's esophagus, whereas Notch signaling is a molecular signaling pathway that plays an important role in the determination of cell differentiation. ATOH1 (a factor associated with Notch signaling) plays an important role in differentiation of stem cells into goblet cells. However, the relationship between the Notch signaling pathway and Cdx2 expression in the development of Barrett's esophagus has not been explored. The aim of this study was to investigate the interrelationship between Notch signaling and Cdx2 in esophageal epithelial cells. The expressions of Cdx2, MUC2, and intracellular signaling molecules related to Notch signaling (Notch1, Hes1, and ATOH1) were examined using real-time polymerase chain reaction (PCR) and immunohistochemical staining with biopsy specimens obtained from esophageal intestinal metaplasia (IM) with goblet cells (IM⁺) and columnar epithelium not accompanied by goblet cells (IM⁻). For in vitro experiments, we employed human esophageal epithelial cell lines (OE33, OE19, and Het-1A). After forced Cdx2 expression by applying a Cdx2 expression vector to the cells, changes in the expressions of Notch1, Hes1, ATOH1, Cdx2, and MUC2 were analyzed by real-time PCR and western blot analysis. Changes in expressions of Notch1, Hes1, ATOH1, Cdx2, and MUC2 in cells were analyzed following stimulation with bile acids in the presence or absence of Cdx2 blocking with Cdx2-siRNA. Suppressed Hes1 and enhanced ATOH1 and MUC2 expressions were identified in IM⁺ specimens. Forced expression of Cdx2 in cells suppressed Hes1, and enhanced ATOH1 and MUC2 expressions, whereas bile acids suppressed Hes1, and enhanced ATOH1, Cdx2, and MUC2 expressions. On the other hand, these effects were blocked by siRNA-based Cdx2 downregulation. Enhanced expression of Cdx2 by stimulation with bile acids may induce intestinal differentiation of esophageal columnar cells by interaction with the Notch signaling pathway.