Autophagy is induced by adenoviral-mediated interferon α treatment in interferon resistant bladder cancer and normal urothelial cells as a cell death protective mechanism but not by the bystander factors produced

Abstract

We have previously shown that adenoviral-mediated interferon α (Ad-IFNα) treatment is highly cytotoxic to tumor cells which are resistant to the interferon α̣ protein. We now report that autophagy is produced after Ad-IFNα treatment of either interferon resistant bladder cancer cells (UC-9 and KU7) or the normal urothelial cell line (TERT-NHUC). After Ad-IFNα infection autophagesomes, an early stage of autophagy, were seen in cancer cells whereas autophagolysosomes, a later stage of autophagy, were observed mostly in normal cells by electron microscopy. Conditioned medium from either normal or bladder cancer cells, however, produced no autophagy when placed on the bladder cancer cells, although again marked cytotoxicity was observed. This indicated that the autophagy seen was related to the direct effect of Ad-IFNα transfection and expression rather than to the bystander factors produced. In addition, autophagic changes were seen using LysoTracker Red DND99 in both normal and cancer cells. We also documented that Ad-IFNα treatment produces the autophagic protein form, LC3-II, in cancer cells but not normal cells, which in turn was inhibited by the autophagic inhibitor, 3-methyladenine (3-MA). This inhibition of autophagy resulted in a significant increase in apoptotic cell death as measured by the sub-G1 population. We hypothesize that the autophagy seen in normal urothelial cells is a protective response and is allowed to be completed, providing a survival mechanism following Ad-IFN treatment, whereas the autophagy produced in interferon resistant cancer cells is not allowed to be completed and is insufficient to significantly suppress cytotoxicity.