Presentation Abstract

Abstract Number: 1023
Presentation Title: Cytoplasmic domain of interferon-gamma receptor beta chain (IFNγR2) has an antiapoptotic activity as a Bax inhibitor
Presentation Time: Monday, Apr 19, 2010, 9:00 AM -12:00 PM
Location: Exhibit Hall A-C, Poster Section 2
Poster Section: 2
Poster Board Number: 4
Author Block: Jose Gomez1, Weiyong Sun2, Vivian Gama1, Dagmar Hajkova1, Tomoyuki Yoshida1, Zhengrong Wu3, John Pink1, Mark Jackson1, Masaru Miyagi1, Shigemi Matsuyama1. 1Case Western Reserve Univ., Cleveland, OH; 2Daiichi Sankyo Research Institute, Edison, NJ; 3Ohio State University, Columbus, OH
Abstract Body: Bax is a pro-apoptotic protein mediating intrinsic cell death signal. New Bax inhibitor was searched by using yeast-based functional screening, and Interferon Gamma Receptor Beta chain (IFNγR2) was cloned as a Bax suppressor. IFNγR2 is a receptor protein, which is a part of the IFNγ receptor complex with IFNγR1, involved in the Jak/STAT signaling pathway. Upon IFNγ binding a conformational change in the receptor complex occurs, followed by activation of Jak kinases, and STAT1. We found that the C-terminus region of IFNγR2 amino acids 296-337 (IFNγR2296-337) contains the novel Bax inhibiting domain. This portion does not contain the Jak2 binding domain, therefore IFNγR2 anti-apoptotic function is independent of the well characterized JAK/STAT signaling. IFNγR2296-337 rescued human cells from apoptosis induced by overexpression of Bax, but not Bak. Overexpression of IFNγR2 (wild type and IFNγR2296-337) rescued cells from apoptosis induced by Etoposide and Staurosporine that are known to activate Bax-mediated cell death. Interestingly, IFNγR2 inhibited apoptosis induced by the BH3 only protein Bim-EL, suggesting that IFNγR2 inhibits Bax activation by BH3 protein. The binding of Bax and the C-terminus of IFNγR2 was confirmed by co-immunoprecipitation using cell lysate and binding experiments using purified recombinant proteins. Interestingly, recombinant Bcl-2 protein competed with IFNγR2 to bind Bax in cell lysates, suggesting that IFNγR2 and Bcl-2 share a similar mechanism to bind Bax. We found that the C-terminal fragment (cytoplasmic domain) of IFNγR2 is expressed in the cytosol of transformed, and in some human prostate cancer cell lines (PC3, and DAMI cells). Our preliminary study suggests that the cytoplasmic IFNγR2 C-terminal fragment is produced by proteolytic cleavage of IFNγR2 at the plasma membrane. The cytoplasmic IFNγR2 fragment may have a certain role to confer cancer cells resistant to apoptotic stress. The discovery of anti-Bax activity of the cytoplasmic domain of INFγR2 may shed new light on the mechanism of how cell survival is controlled by IFNγ and Bax.