Abstract
Apoptotic cytochrome c (Cytc) release follows the transcription dependent and independent pathways that p53 activates expression of proapoptotic BH3-only Noxa and BH1-4 Bax proteins, and p53 DBD binds to antiapoptotic Bcl-XL in the mitochondria (MT), respectively. The proposed Cytc-releasing pore models (Bax oligomers, Bax/VDAC complex, supramolecular pore) remain controversial. We studied the Bax (Bak)/VDAC complex formation and its role in Cytc release after 5 Gy in p53/Bax-expressing apoptosis-sensitive cells and Bak/Bcl-2-expressing resistant cells. The protein crosslinking approach for isolated MT showed time-dependent formation of Bax di- and tetramers as well as Bax/VDAC di- and tetramers. By immunofluorescent microscopy, clotorimazol which displaces hexokinase recruited Bax to VDAC in MT and released Cytc. Further, DIDS as a VDAC inhibitor blocked the clustering of Bax on MT, Cytc release and apoptosis after IR. Contrary, although Bak/Bcl-2-expressing IR apoptosis-resistant cells formed the Bak/VDAC heterodimer independently of post-IR time, they released no Cytc. Thus we suggest the Bax/VDAC channel, most likely its heterotetramer, may be responsible for Bax-mediated Cytc release from cellular MT in the p53/Bax-mediated apoptosis. [J Radiat Res 44:446 (2003)]
