Bile Salts Differentially Sensitize Esophageal Squamous Cells to CD95 (Fas/Apo-1 Receptor) Mediated Apoptosis

Abstract

The role of nonacidic reflux contents on the pathophysiology of Barrett's esophagus remains poorly understood. We hypothesized that esophageal squamous epithelium differs from Barrett's columnar epithelium in response to bile salts with respect to subsequent changes in the cell surface expression of CD95 (Fas/Apo-1) and sensitivity to CD95-mediated apoptosis. Immortalized esophageal squamous cells (HET-1A) and Barrett's esophagus cells (BAR-T), and esophageal adenocarcinoma cells (Flo-1) were treated with toxic and nontoxic bile salts at concentrations observed in gastroesophageal refluxate. CD95 cell-surface expression and apoptotic response to activating anti-CD95 antibody treatment was determined by FACScan analysis. Bile salt exposure resulted in a dose-dependent increase in CD95 cell-surface expression in HET-1A cells, but not BAR-T or Flo-1 cells. This response occurred rapidly, within a time-frame inconsistent with de novo protein synthesis and was blocked by protein kinase C (PKC) inhibition. Surprisingly, PKC inhibition in Flo-1 cells resulted in an increase in CD95 cell surface expression. Following bile salt exposure, a corresponding increase in the induction of CD95-mediated apoptosis was observed in HET-1A cells; PKC inhibition sensitized Flo-1 cells to apoptosis. Our findings suggest that esophageal squamous cells are sensitized to CD95-mediated apoptosis following bile salt exposure. This differential response, compared with columnar epithelial cells, could exert a selection pressure that contributes to the pathophysiology of Barrett's esophagus.