Abstract
LIGHT is a member of tumor necrosis factor (TNF) superfamily, and previous studies have indicated that in the presence of interferon‐γ (IFN‐γ), LIGHT through LTβR signaling can induce cell death with features unlike classic apoptosis. In present study, we investigated the mechanism of LIGHT/IFN‐γ‐induced cell death in HT‐29 cells, where the cell death was profoundly induced when sub‐toxic concentrations of LIGHT and IFN‐γ were co‐treated. LIGHT/IFN‐γ‐induced cell death was accompanied by DNA fragmentation and slight LDH release. This effect was not affected by caspase, JNK nor cathepsin B inhibitors, but was partially prevented by p38 mitogen‐activated protein kinase (MAPK) and poly (ADP‐ribose) polymerase (PARP) inhibitors, and abolished by aurintricarboxylic acid (ATA), which is an inhibitor of endonuclease and STATs signaling of IFN‐γ. Immunobloting reveals that LIGHT/IFN‐γ could induce p38 MAPK activity, Bak and Fas expression, but down‐regulate Mcl‐1. Besides, LIGHT/IFN‐γ could not activate caspase‐3 and ‐9, but decreased mitochrondrial membrane potential. Although LIGHT could not affect IFN‐γ‐induced STAT1 phosphorylation and transactivation activity, which was required for the sensitization of cell death, survival NF‐κB signaling of LIGHT was inhibited by IFN‐γ. These data suggest that co‐presence of LIGHT and IFN‐γ can induce an integrated interaction in signaling pathways, which lead to mitochondrial dysfunction and mix‐type cell death, not involving caspase activation. © 2004 Wiley‐Liss, Inc.