Mechanism of LIGHT/interferon-gamma-induced cell death in HT-29 cells

LIGHT is a member of tumor necrosis factor (TNF) superfamily, and previous studies have indicated that in the presence of interferon-gamma (IFN-gamma), LIGHT through LTbetaR signaling can induce cell death with features unlike classic apoptosis. In present study, we investigated the mechanism of LIGHT/IFN-gamma-induced cell death in HT-29 cells, where the cell death was profoundly induced when sub-toxic concentrations of LIGHT and IFN-gamma were co-treated. LIGHT/IFN-gamma-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-gamma. Immunobloting reveals that LIGHT/IFN-gamma could induce p38 MAPK activity, Bak and Fas expression, but down-regulate Mcl-1. Besides, LIGHT/IFN-gamma could not activate caspase-3 and -9, but decreased mitochondrial membrane potential. Although LIGHT could not affect IFN-gamma-induced STAT1 phosphorylation and transactivation activity, which was required for the sensitization of cell death, survival NF-kappaB signaling of LIGHT was inhibited by IFN-gamma. These data suggest that co-presence of LIGHT and IFN-gamma can induce an integrated interaction in signaling pathways, which lead to mitochondrial dysfunction and mix-type cell death, not involving caspase activation.