Role of IRF-1 and Caspase-7 in IFN-gamma Enhancement of Fas-mediated Apoptosis in ACHN Renal Cell Carcinoma Cells

Caspases exist as zymogens, and are activated by various extracellular stimuli, leading to apoptosis. One such stimulus is Fas/CD95, a member of the tumor necrosis factor receptor family, providing one means of cytotoxic T lymphocyte (CTL)-mediated cell lysis. Clinical evidence has shown that administration of cytokine leads to regression in selected patients with renal cell carcinomas (RCCs). Interferon-gamma (IFN-gamma) indicates its contribution to anti-tumor activity of immune cells. IFN-gamma elicits its effect through the transcription factor signal transducer and activator of transcription-1 (STAT-1), and through interferon regulatory factor-1 (IRF-1), one of the target genes of STAT-1. Our previous study demonstrated an increase in the susceptibility of ACHN cells, established from RCC, to Fas-mediated apoptosis by IFN-gamma, and the inhibition of this effect by the caspase-3 and -7 inhibitor, DEVD-CHO. We demonstrated the following phenomena in IFN-gamma-treated ACHN cells: 1) enhanced transcription of caspase-1, 3 and 7 mRNAs without any change in cleavage of their substrates; 2) increased cleavage DEVD (specific for caspase-3 and 7), but not YVAD (for caspase-1) or DMQD (for caspase-3), after anti-Fas/CD95 MAb treatment; 3) activation of the STAT-1 and IRF-1 pathway; and 4) partial abrogation of the IFN-gamma-induced increase in Fas-mediated apoptosis by antisense IRF-1 oligodeoxynucleotide. These results suggest that IRF-1 plays a pivotal role in the IFN-gamma-mediated-enhancement of Fas/CD95-mediated apoptosis, through regulation of DEVD-CHO-sensitive caspases, most likely caspase-7.