Abstract 2013: Interferon gamma receptor 2 (IFNgR2) has a ligand (IFNg)-independent activity as a Bax inhibitor in cancer cells
Authors: Ngo Justine , Chen Joseph , Wu Mengzhi , Almasan Alexander , Morita Hajime , Jang Kuen-Young , Danielpour David , Borden Ernest , Matsuyama Shigemi 
Published: August 2012

Abstract
Bax is a pro-apoptotic member of Bcl-2 family proteins playing a pivotal role in cell death induction of cancer cells. Using a yeast-based functional screening system, we identified interferon gamma receptor 2 (IFNgR2) as a novel Bax suppressor. IFNgR2 is known to heterodimerize with IFNgR1 to form a functional IFNg receptor complex. In addition to this function, we showed that the C-terminal cytoplasmic domain of IFNgR2 can bind to Bax and inhibit the conformational change that is required for Bax activation. Furthermore, this anti-Bax activity does not require IFNgR1 or Jak-STAT signaling, which suggests that IFNgR2 has a previously unrecognized biological identity as an apoptosis inhibitor that is independent to its function as an IFNg receptor subunit. In this study, the physiological significance of anti-Bax activity of IFNgR2 was determined in prostate cancer and melanoma. Using immunocytochemistry and subcellular cell fractionation, we found that IFNgR2 was mainly detected in the intracellular membranes (i.e. ER, mitochondria, and Golgi apparatus), whereas IFNgR2 expression in the plasma membrane was barely detectable in all of the cancer cell lines (8 cell lines) examined. Strong immunostaining of IFNgR2 localizing in the intracellular space of malignant cells was also observed in prostate cancer and melanoma tissue sections. We examined the expression levels of IFNgR2, IFNgR1, Bax, and Bcl-2 by Western blot and ELISA. The approximate concentrations were IFNgR2=100-600 pg/ug total protein, IFNgR1=0.1-1 pg/ug total protein, Bax=100-800 pg/ug total protein, and Bcl-2=30-100 pg/ug total protein. IFNgR2 expression levels were significantly higher than IFNgR1, much more than the 1:1 ratio required for functional IFNg receptors. Importantly, IFNgR2 levels were comparable to that of Bax and Bcl-2. These results suggest that there are abundant IFNgR2 molecules free from IFNgR1 in cancer cells, and IFNgR2 is expressed at a sufficiently high level to function as a Bax inhibitor. Furthermore, short hairpin-RNA-mediated knockdown of IFNgR2 significantly stimulated apoptosis induction triggered by taxol, cisplatin, doxorubicin, and ABT-737 (Bcl-2 inhibitor) in prostate cancer (PC3) and melanoma cell lines (WM164 and A375). These results support our hypothesis that IFNgR2 has a physiological role as a Bax inhibitor in cancer cells. We propose that (1) IFNgR2 may become an useful diagnostic marker to predict cell death resistance of prostate cancer and melanoma, and that (2) new technologies suppressing the anti-apoptotic activity of IFNgR2 may be able to improve efficiency of apoptosis induction in these cancer cells.
Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2013. doi:1538-7445.AM2012-2013