Abstract 3707: Moonlighting function of mitochondrial protein VDAC2 provides a potent pharmacological strategy against selective killing of hepatocellular carcinoma

Abstract

Abstract Voltage dependent anion channels (VDACs) family of proteins are the most abundant proteins in the outer mitochondrial membrane (OMM). There are three isoforms of VDAC, that are structurally and functionally conserved as far as their ion transport function is concerned. However, there are isoform-specific functions that support distinct pathways. For VDAC2 isoform, an established isoform-specific function is the targeting of the pro-apoptotic Bak protein to the OMM, which stabilizes Bak, leading to its elevated cellular levels. On the surface of OMM, activation and oligomerization of Bak and Bax, another pro-apoptotic protein leads to OMM perforation and release of pro-apoptotic proteins from intermembrane space to the cytoplasm. This is an irreversible step that stimulates the downstream events of apoptotic pathway. Hepatocellular carcinoma (HCC) ranks third in cancer mortality and in the advanced stages is associated with poor prognosis. We observed that unexpectedly, HCC cells are vastly more sensitive to tBid induced apoptosis compared to normal hepatocytes. tBid is a BH3-only pro-apoptotic Bcl-2 family protein, the effect of which is primarily mediated by Bak. We have shown that, in the absence of VDAC2, the Bid-Bak apoptosis pathway is suppressed. VDAC2 protein expression is the lowest in liver and lung among different tissues. We also determined the protein abundances in the HCC lines and normal hepatocytes and found elevated VDAC2 and Bak levels in HCC. Our findings are in line with multiple datasets that show an elevation of VDAC2/Bak expression in human HCC suggesting a potential clinical relevance. We found that combination of an inhibitor of the anti-apoptotic proteins (S63845, a selective Mcl-1 inhibitor), which normally suppresses Bak activation, with an activator of the tBid pathway (TRAIL) enhanced the death of hepatocarcinoma cells with little effect on normal hepatocytes. This treatment strategy was also effective at reducing tumor growth in vivo, but only in tumors expressing VDAC2. Thus, we postulate that increased VDAC2 expression in HCC leads to elevated Bak recruitment to the OMM, which in turn sensitizes HCC to tBid. Therefore, this differential expression provides an excellent opportunity for selective elimination of HCC cells. Citation Format: Piyush Mishra. Moonlighting function of mitochondrial protein VDAC2 provides a potent pharmacological strategy against selective killing of hepatocellular carcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3707.