ABSTRACT
TP63 gene is a member of TP53 tumor suppressor gene family that encodes several protein isoforms involved in the process of epithelial stratification and in epithelial-mesenchyme interactions. TP63 is amplified in a significant proportion of squamous cell carcinoma of the esophagus (ESCC), resulting in the hyper-expression of DeltaNp63 as the major p63 isoform. To better understand the contribution of this high expression to tumorigenesis, we have analyzed the impact of intraepithelial p63 expression on the expression of cell adhesion complexes in normal esophagus and in ESCC cell lines. Cells expressing p63 showed an adhesion pattern characterized by lack of tight junctions and presence of adherens junctions. Cell differentiation was accompanied by a decrease in p63 and by a shift to adhesion patterns involving tight junctions. Silencing of p63 mRNA in ESCC cell lines resulted in a similar shift, characterized by increased expression of component of tight junctions, decreased cell-to-cell communication and downregulation of cell proliferation. These results indicate that DeltaNp63 may contribute to esophageal squamous carcinogenesis by maintaining cell adhesion patterns compatible with cell proliferation.
Subject(s)
Carcinoma, Squamous Cell/metabolism , Cell Adhesion Molecules/metabolism , Esophageal Neoplasms/metabolism , Esophagus/metabolism , Tumor Suppressor Protein p53/metabolism , Cell Adhesion , Cell Line , Cell Line, Tumor , Cell Proliferation , Humans , Intestinal Mucosa/metabolism , Protein Isoforms/metabolism , RNA InterferenceABSTRACT
p63 is a member of the p53 protein family that regulates differentiation and morphogenesis in epithelial tissues and is required for the formation of squamous epithelia. Barrett's mucosa is a glandular metaplasia of the squamous epithelium that develops in the lower esophagus in the context of chronic, gastroesophageal reflux and is considered as a precursor for adenocarcinoma. Normal or squamous cancer esophageal cells were exposed to deoxycholic acid (DCA, 50, 100, or 200 microM) and chenodeoxycholic and taurochenodeoxycholic acid at pH 5. p63 and cyclooxygenase-2 (COX-2) expressions were studied by Western blot and RT-PCR. DCA exposure at pH 5 led to a spectacular decrease in the levels of all isoforms of the p63 proteins. This decrease was observed within minutes of exposure, with a synergistic effect between DCA and acid. Within the same time frame, levels of p63 mRNA were relatively unaffected, whereas levels of COX-2, a marker of stress responses often induced in Barrett's mucosa, were increased. Similar results were obtained with chenodeoxycholic acid but not its taurine conjugate at pH 5. Proteasome inhibition by lactacystin or MG-132 partially blocked the decrease in p63, suggesting a posttranslational degradation mechanism. These results show that combined exposure to bile salt and acid downregulates a critical regulator of squamous differentiation, providing a mechanism to explain the replacement of squamous epithelium by a glandular metaplasia upon exposure of the lower esophagus to gastric reflux.
