Loss of p53, rather than beta-catenin overexpression, induces survivin-mediated resistance to apoptosis in an esophageal cancer cell line

Abstract

Survivin, an important inhibitor of apoptosis, is overexpressed in esophageal cancer and negatively affects survival. The complex regulation of survivin transcription involves enhancement by beta-catenin and repression by p53. The purpose of this study is to test whether inhibition of beta-catenin or overexpression of p53 can decrease survivin expression and render esophageal cancer cells more susceptible to apoptosis. Studies were performed in normal human esophageal epithelial cells and the human esophageal cancer cell line TE7. Levels of beta-catenin, survivin, and p53 were measured by Western blot. Apoptosis was induced after treatment with camptothecin and measured by release of caspase 3 and morphologic criteria. The roles of survivin and beta-catenin in preventing apoptosis were tested by their silencing with specific small interfering RNA molecules. The effect of p53 overexpression on survivin promoter activity was measured using a survivin promoter-luciferase reporter construct and by real-time polymerase chain reaction measurement of survivin mRNA levels. Both beta-catenin and survivin are overexpressed in TE7 cells, whereas p53 expression is negligible. TE7 cells demonstrate resistance to camptothecin-induced apoptosis (P < .01). This effect is significantly reduced by inhibition of survivin, but not of beta-catenin (P < .01). Overexpression of p53 in TE7 cells reduces survivin transcription and mRNA levels (P < .01), without reducing survivin protein levels. Survivin plays a critical role in TE7 cell resistance to camptothecin-induced apoptosis. This effect is not dependent on beta-catenin expression. Overexpression of p53 decreases survivin transcription but does not decrease levels of survivin protein, suggesting posttranscriptional control of survivin expression.