Direct cytotoxicity produced by adenoviral-mediated interferon α gene transfer in interferon-resistant cancer cells involves ER stress and caspase 4 activation

Over the past several years we have obtained considerable evidence indicating that adenoviruses-expressing interferon alpha (Ad-IFN alpha) can overcome resistance to the IFN alpha protein itself. Since cancer cells infected with Ad-IFN alpha also show high perinuclear cytoplasmic IFNa expression, we were interested in whether endoplasmic reticulum (ER) stress and cleavage of caspase 4 could have a major role in Ad-IFN alpha-produced cancer cell death. Indeed, procaspase 4 was upregulated and cleaved as early as 12 h after Ad-IFN alpha infection of the cancer cells, which co-localized with IFN alpha staining and ER tracker. In contrast, immortalized normal human urothelial cells, although exhibiting similar perinuclear IFN alpha staining, showed no cleaved caspase 4. Caspase 4 cleavage was not blocked by the caspase 8 specific inhibitor zIETD, indicating that caspase 4 activation was independent of caspase 8 activation. Blocking caspase 4 also inhibited activation of caspase 3 in Ad-IFN alpha containing cells. Finally, the cleaved form of caspase 4 (p10) was detected in Ad-IFN alpha-positive cancer cells from the urine of a patient following intravesical Ad-IFN alpha/Syn3 treatment. Therefore, ER stress and activation of caspase 4 appears to be an important mechanism involved in the direct cancer cell death produced by Ad-IFN alpha and also occurs in the clinical setting. Cancer Gene Therapy (2011) 18, 609-616; doi:10.1038/cgt.2011.26; published online 17 June 2011