Based on its marked overexpression in multiple
malignancies and its roles in promoting cell survival and proliferation,
survivin is an attractive candidate for targeted
therapy. Toward this end, a detailed understanding of the mechanisms regulating
survivin expression in different
cancer cells will be critical. We have previously shown that the
RNA-binding protein (RBP) CUG-BP1 is overexpressed in
esophageal cancer cells and post-transcriptionally regulates
survivin in these cells. The objective of this study was to investigate the role of
microRNAs (miRs) in regulating
survivin expression in
esophageal cancer cells. Using miR expression profiling analysis, we found that miR-214-3p is one of the most markedly downregulated miRs in two esophageal squamous
cancer cell lines compared with esophageal epithelial cells. Interestingly, using miR target prediction programs, both
survivin and CUG-BP1
mRNA were found to contain potential binding sites for miR-214-3p. Forced expression of miR-214-3p in
esophageal cancer cells leads to a decrease in the
mRNA and
protein levels of both
survivin and CUG-BP1. This effect is due to decreased mRNA stability of both targets. By contrast, silencing miR-214-3p in esophageal epithelial cells leads to an increase in both
survivin and CUG-BP1
mRNA and
protein. To determine whether the observed effect of miR-214-3p on
survivin expression was direct, mediated through CUG-BP1, or both, binding studies utilizing
biotin pull-down assays and heterologous
luciferase reporter constructs were performed. These demonstrated that the
mRNA of
survivin and CUG-BP1 each contain two functional miR-214-3p-binding sites as confirmed by mutational analysis. Finally, forced expression of miR-214-3p enhances the sensitivity of
esophageal cancer cells to
cisplatin-induced apoptosis. This effect is abrogated with rescue expression of
survivin or CUG-BP1. These findings suggest that miR-214-3p acts as a
tumor suppressor and that its downregulation contributes to chemoresistance in
esophageal cancer cells by targeting both
survivin and CUG-BP1.