Role of IRF‐1 and caspase‐7 in IFN‐γ enhancement of Fas‐mediated apoptosis in ACHN renal cell carcinoma cells

Abstract 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‐γ (IFN‐γ) indicates its contribution to anti‐tumor activity of immune cells. IFN‐γ 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‐γ, and the inhibition of this effect by the caspase‐3 and ‐7 inhibitor, DEVD‐CHO. We demonstrated the following phenomena in IFN‐γ‐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‐γ‐induced increase in Fas‐mediated apoptosis by antisense IRF‐1 oligodeoxynucleotide. These results suggest that IRF‐1 plays a pivotal role in the IFN‐γ‐mediated‐enhancement of Fas/CD95‐mediated apoptosis, through regulation of DEVD‐CHO‐sensitive caspases, most likely caspase‐7. © 2003 Wiley‐Liss, Inc.