Differential Sensitivity Of Normal Liver And Hepatocarcinoma Tissues To Tbid Induced Apoptosis Is Determined By The Abundance Of Vdac2

A conserved step in extrinsic apoptosis is the outer mitochondrial membrane (OMM) permeabilization by truncated Bid (tBid) that is generated from Bid upon cleavage by Caspase-8 activated at death receptors. tBid directly or indirectly activate proapoptotic proteins i.e. Bak in OMM and/ or Bax in cytosol which is followed by a change in their conformation and oligomerization, leading to a pore formation in the OMM. To better understand the mitochondrial phase of this pathway we applied tBid to semi-permeabilized cells and isolated mitochondria. We monitored cytochrome c release, and the ensuing mitochondrial membrane potential collapse, using immunoblotting and fluorimetry as the markers for mitochondrial cell death. We found that normal liver tissue and normal hepatocytes (Rat, Mouse or Human) are unexpectedly resistant to tBid, whereas hepatocellular carcinoma (HCC) tissues and cell lines (e.g. PLC, Huh7) are greatly sensitized. Considering that the effect of tBid is most effectively mediated through Bak, its abundance in the mitochondria was tested. Bak level is significantly higher in tumor tissue/cell lines, whereas OMM-bound tBid and Bax levels are similar in both cancerous and normal tissue. Since we have recently found that voltage dependent anion channel 2 (V2), a pore forming OMM protein, is specifically required for Bak targeting to OMM, the abundance of V2 was also measured. V2 showed significant upregulation in HCC tissue/cell lines. Rescue studies using V2 sensitized normal hepatocytes and liver mitochondria to tBid. We propose that V2 might be the main regulator for the differential tBid sensitivity in normal liver and hepatocellular carcinoma. Citation Format: Shamim Naghdi, Soumya Sinha Roy, Ludivine Walter, Gyorgy Hajnoczky. Differential sensitivity of normal liver and hepatocarcinoma tissues to tBid induced apoptosis is determined by the abundance of VDAC2. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 3492.