Direct gene transfer of adenoviral-mediated interferon α into human bladder cancer cells but not the bystander factors produced induces endoplasmic reticulum stress-related cytotoxicity

We have previously shown that adenoviral-mediated interferon alpha (Ad-IFN alpha) is cytotoxic both to cells that are sensitive to recombinant interferon alpha (IFN alpha) and to cells which are resistant to IFN alpha. The cancer cell-specific cytotoxic effects of Ad-IFN alpha involve three different mechanisms: 1. The direct effect of IFN alpha production causing cancer cell death in IFN alpha sensitive cells (1); 2. The direct effect of Ad-IFN alpha infection and high levels of IFN alpha expression in IFNa resistant cancer cells (2); and 3. The indirect effect of the Ad-IFN alpha bystander factors produced (2-4). After Ad-IFN alpha infection, the cells produce a large amount of perinuclear localized IFN protein. This protein over-load could be a major factor in the direct cancer cell death of those cells infected with Ad-IFN alpha compared with the indirect cytotoxic effects of the bystander factors produced. Here, we investigated whether a component of Ad-IFN-induced cell death involves protein overload-induced endoplasmic reticulum (ER) stress, using an IFN alpha-resistant human bladder cancer cell line (KU7), and the normal human urothelial cell line, TERT-NHUC, as preclinical models. We found that the two ER stress response pathways examined were activated in KU7 cells. In contrast, following treatment of the normal TERT-NHUC cells with Ad-IFN alpha, no ER stress signals were observed. In addition, no ER stress related changes were seen, when KU7 cells were exposed to conditioned medium from Ad-IFN alpha-treated KU7 cells, indicating that bystander produced cytotoxicity did not involve ER stress. After 24 h of Ad-IFN alpha infection, the KU7 cancer cells produced spliced X-box binding protein 1 and activating transcription factor 6 protein (ATF6), evoking an ER stress response that could contribute to Ad-IFN alpha induced apoptosis in these cancer cells. In addition, GADD153/CHOP, GADD34 and BAX were also subsequently modified following activation of the ER stress pathways, thereby signaling downstream effectors in a pro-apoptotic manner. Cancer Gene Therapy (2011) 18, 260-264; doi:10.1038/cgt.2010.76; published online 24 December 2010