Interferon-alpha induces TRAIL expression and cell death via an IRF-1-dependent mechanism in human bladder cancer cells.

Apoptosis induced by interferon-alpha (IFNalpha) is associated with induction of TRAIL in a number of different cell types. Here we examined whether or not TRAIL was required for apoptosis in a model human bladder cancer cell line (UM-UC-12) and defined the molecular mechanisms involved in IFNalpha-induced TRAIL expression. Exposure to IFNalpha resulted in concentration-dependent induction of TRAIL and apoptosis. Inhibition of TRAIL or downstream components of the TRAIL cell death pathway (FADD, caspase-8) via siRNA-mediated knockdown attenuated IFNalpha-induced cell death, thereby implicating TRAIL in the response. IFNalpha induced rapid STAT-1 phosphorylation and DNA binding activity and subsequent accumulation of IRF-1. Transfection with siRNAs directed against STAT-1 or IRF-1 inhibited IFNalpha-induced TRAIL production and cell death, and chromatin immunprecipitation (ChIP) analyses demonstrated that IFNalpha induced direct, time-dependent binding of both transcription factors to the TRAIL promoter. Together, our results demonstrate that IFNalpha induces TRAIL expression via a STAT-1/IRF-1-dependent mechanism in human bladder cancer cells, and this induction of TRAIL plays an important role in IFNalpha-induced cell killing.