Resveratrol-induced p53-independent apoptosis of human nasopharyngeal carcinoma cells is correlated with the downregulation of ΔNp63

Delta Np63, the N-terminal truncated isoform of p63, has been found to be overexpressed in several human epithelial cancers, including nasopharyngeal carcinomas (NPCs), suggesting a function in carcinogenesis. Trans-resveratrol (RSV) has been shown to exert proapoptotic activities through a p53-dependent or p53-independent pathway in various cancer cells. However, the effects of RSV on NPC are still unexplored. In this study, we investigated the apoptotic effects of RSV on Delta Np63-overexpressing NPC cell lines. We showed that RSV (12-100 mu M) induced dose-dependent growth suppression, cell-cycle arrest in the S phase and caspase-dependent apoptosis in NPC-TW076 and NPC-TW039 cells. The RSV effect was accompanied by the downregulation of Delta Np63 and the upregulation of p53 protein in a dose-dependent manner. By using small-interfering RNA (siRNA) technology, we found that the targeted silencing of Delta Np63 induced apoptosis and sensitized the NPC cells to RSV-induced apoptosis through caspase-3 activation, whereas suppression of p53 by siRNA did not inhibit RSV-induced apoptosis. Furthermore, transfection with p53 siRNA or pretreatment with caspase inhibitors (Z-VAD-fmk or Z-DEVD-fmk) had no influence on the RSV downregulation of Delta Np63. Interestingly, ecoptic expression of Delta Np63 did not significantly block RSV-induced cell death and was also downregulated after RSV treatment. Downregulation of Delta Np63 by RSV was shown to occur at the mRNA transcript and post-translational levels. Importantly, RSV enhanced chemotheraptic drug-induced apoptosis in NPC and two human carcinoma cell lines, HT1376 and Hep3B cells. These results suggested that Delta Np63, but not p53, is a molecular target of RSV-induced apoptosis and the regulation of Delta Np63 expression by RSV may provide a therapeutic effect of RSV in human NPC. Cancer Gene Therapy (2010) 17, 872-882; doi: 10.1038/cgt.2010.44; published online 20 August 2010