S1634 Bone Morphogenetic Protein-4 Has an Important Role in the Transformation of Normal Esophageal Cells to an Intestinal Phenotype in Barrett's Esophagus via CDx2 Pathway

Background & Aims: Barrett's esophagus (BE) is a metaplastic condition in which normal squamous esophageal epithelium is replaced by columnar epithelium. A recent study has shown that bone morphogenetic protein 4 (BMP-4), a member of the transforming growth factor-β superfamily, is uniquely overexpressed in BE. The mechanisms of the BMP signaling pathway in the metaplastic transformation in BE, however, remain unclear. The aim of this study was to examine the role of the BMP signaling pathway in the metaplastic transformation of normal squamous cells into columnar cells. Methods: The expression of BMP signaling related molecules, including BMP-4, ID2, SMAD4 in biopsy samples was assessed. Samples were taken fromBE (16 cases), with or without reflux esophagitis, and fromnormal esophagus (12 cases) and assayed by immunohistochemistry and real-time PCR. In addition, the In Vitro effects of acid and/or bile acid on BMP-4 expression were analyzed in HET1A, an immortalized human esophageal squamous cell line, and OE33, a human esophageal adenocarcinoma cell line. These cells were treated with recombinant human BMP-4 (10-100 ng/ mL), and cell biological changes were examined by immunoblot analysis and real-time PCR. Cell proliferation was assessed by MTS assay. Results: Immunohistochemistry of biopsy specimens demonstrated that the expression of BMP-4 protein was observed in all the cases of BE, but not in normal squamous epithelium. Consistent with the immunohistochemistry results, BMP-4 mRNA expression was 13 fold greater in BE as compared with normal squamous epithelium. Up-regulation of BMP-4 expression was more evident in BE with reflux esophagitis. In Vitro, acid (pH4) and bile acid exposure synergistically induced BMP4 expression in both HET1A and OE33 cells. Treatment of these cells with recombinant BMP-4 resulted in increased expression of the intestine-specific transcription factor, CDX2. Blocking BMP signalling by preincubating cells with the BMP antagonist Noggin before treatment with BMP-4, resulted in decreased expression of CDX2. In addition, Noggin also blocked the proliferation of OE33 cells. Conclusion: These results suggest that the BMP signaling pathway is activated in BE, and that BMP-4 has an important role in the process of transformation of squamous epithelium toward a mucosa that resembles columnar metaplasia. The results suggest that transformation occurs via a CDX2-dependent pathway, and that this process might be promoted in the inflamed condition. We propose that the premalignant metaplastic development of BE is mediated by BMP-4, and that inhibition of BMP-4 signaling offers a novel therapeutic approach for this disease.