Bcl-xL inhibits p53- but not apoptin-induced apoptosis in head and neck squamous cell carcinoma cell line.

Nonfunctional p53 and especially upregulation of Bcl-x(L) result in advanced disease and poor prognosis of patients suffering head and neck squamous cell carcinoma (HNSCC). Aberrancies of Bcl-x(L) and/or p53 in HNSCC lead to inability of anticancer drugs to induce apoptosis. Bcl-x(L) and/or mutated p53 inhibit the apoptotic process by preventing the mitochondrial release of cytochrome c and/or activation of execution caspases. Here, we report that expression of the avian virus-derived apoptin protein resulted in induction of apoptosis in the HNSCC-derived cell line UMSSC-14B despite the presence of nonfunctional p53. Apoptin activated the execution caspase 3 and induced the release of mitochondrial cytochrome c. Upregulation of Bcl-x(L) in UMSCC-14B cells did not interfere with the apoptin-induced apoptosis, whereas it clearly negatively affected the p53-induced one. Bcl-x(L) significantly decreased the p53-induced cytochrome c release, but not the apoptin-triggered one. Our data demonstrate that apoptin induces apoptosis independent of Bcl-x(L) and p53 and may constitute a potential therapeutic agent for treatment of HNSCC.