Mechanism of LIGHT and IFN-g Synergistic Effect to Induce Cell Apoptosis

• Main Authors: Yang-Chieh Chou, 周楊捷
• Other Authors: Shie-Liang Hsieh
• Format: Others
• Language: zh-TW
• Published: 2002
• Online Access: http://ndltd.ncl.edu.tw/handle/26446507801229943312

碩士 === 國立陽明大學 === 微生物暨免疫學研究所 === 90 === LIGHT is a member of TNF superfamily and binds to LTbR, HVEM and DcR3. LIGHT is expressed on activated T cells and serves as a costimulatory factor to enhance IFN-g production by activated T cells. In cojunction with IFN-g, LIGHT induces cell death via apoptosis. However, the underlying mechanism for LIGHT/IFN-g mediated apoptosis is not illustrated yet. In order to investigate the role of LTbR in LIGHT-mediated apoptosis, we designed a LIGHT mutant that retained its binding ability to LTbR but not to HVEM. A three-dimensional model of LIGHT based on the crystallographic struncture of LT-a and TNFR1 complex was generated to predict residues that are likely involoved in receptor binding. One mutant, LIGHT-R228E, of which 228th arginine is replaced by glutamic acid, exhibits specific binding to LTR and fails to bind with HVEM. Receptor neutralization assay and surface plasmon resonance analysis were performed to elucidate the specific binding ability of LIGHT-R228E to LTbR, HVEM, and DcR3 respectively. The lost of LIGHT-R228E’s binding to HVEM was further confirmed by its inactivity to trigger T cell proliferation. This result further confirm previous hypothesis that the apoptotic ability of LIGHT is via LTbR, and HVEM is dispensible for LIGHT-mediated apoptosis. Moreover, caspase-3 activation, decreased mitochondria membrane potential, and release of cytochrome c and Smac/DIABLO from mitochondria were also observed in LIGHT/IFN-g or LIGHT-R228E/IFN-g-mediated apoptosis in Hep3BT2 cells, indicating the involvement of mitochondria pathway in LIGHT-mediated apoptosis. However, over-expression of non-caspase-3-cleavable Bcl-2 cannot fully rescue Hep3BT2 cells from apoptosis. Based on this study, we concluded that both mitochondria dependent and independent pathways are involved in LIGHT-mediated apoptosis.