Anti-apoptotic activities of GAGE-7C, a gene expressed in multiple tumors

GAGE-7C belongs to GAGE family of cancer testis antigens that are expressed in a variety of tumors but are silent in normal tissues except testis. We have previously reported that GAGE overexpression in HeLa cells can render them resistant to radio- and chemotherapeutic agents, Taxol and gamma-radiation, and apoptotic agents Fas and Interferon-gamma. In this study we investigated the mechanism by which GAGE protects cells from Fas and IFN-gamma induced cell death. GAGE protects HeLa cells from Fas-induced apoptosis and effect of GAGE is mapped downstream of caspase-8 cleavage. GAGE overexpression result in inhibition of cytochrome c release from the mitochondria that result in inhibition of cleavage of apoptotic substrates leading to survival of the cells upon treatment with Fas. GAGE overexpression also renders HeLa and HEK293 cells resistant to IFN-gamma induced cell death. GAGE overexpression in HeLa cells result in downregulation of the tumor suppressor IRF-1 that is sufficient to address the survival of cells upon GAGE overexpression. We have also uncovered relevant binding partners of GAGE in this study. Among others GAGE binds to nucleophosmin/B23/numatrin and result in elevated expression of NPM/B23 by stabilization of the NPM/B23 protein. GAGE and NPM/B23 also bind to IRF1 and result in its downregulation. Downregulation of IRF-1 is a post-transcriptional event and is accompanied by downregulation of its pro-apoptotic targets. A peptide derived from GAGE protein causes cell death in GAGE expressing cells such as HeLa and HT-1080, however GAGE null HEK293 and Fibroblasts are resistant to killing induced by this peptide at lower doses. Thereby, this peptide could be used as a therapeutic agent to specifically kill GAGE expressing tumor cells while sparing GAGE null normal cells. Overall, we have discovered the mechanism by which a tumor antigen GAGE can rescue cells from Fas and Interferon induced cell death thereby predisposing the cells to tumorigenesis.