Hexokinase II (HXK II) controls the first step in glycolysis, phosphorylating glucose to glucose-6-phosphate (G-6-P). Cancer cells over-express HXK II with the majority being bound to the mitochondria through an interaction with VDAC-1 (voltage dependent anion carrier), an abundant outer mitochondrial membrane protein (OMM). The enhanced binding of HXK II to mitochondria in cancer cells accelerates the rate of glycolysis, thus providing an ample supply of precursors for amino, nucleic and fatty acid synthesis. Mitochondria have emerged as an important component of the cell death pathway in both apoptosis and necrosis, with the release of mitochondrial intermembrane space proteins being critical in the execution and ultimate demise of cellular viability. Proapoptotic proteins such as Bax, Bid and Bim induce mitochondrial dysfunction, possibly by interacting with VDAC-1, thereby provoking the release of intermembrane space proteins. For this proposal our working hypothesis is that the increased binding of HXK II to mitochondria is critical for providing cancer cells with the necessary metabolic profile for maintaining their accelerated rate of proliferation. Additionally, HXK II binding to mitochondria aids in the survival and resistance of cancer cells to chemotherapeutic agents by preventing proapoptotic proteins such as Bax, Bim and Bid from inducing mitochondrial dysfunction. The localization of HXK II to mitochondria is controlled in part by the activity of the PBR and glycogen synthase kinase 3P (GSKP). These hypotheses are supported by the preliminary results demonstrating the ability of recombinant HXK II to prevent Bax from binding to and releasing cytochrome c from isolated mitochondria and the enhanced sensitivity exhibited by transformed cells to a range of chemotherapeutic agents upon the detachment of mitochondrial bound HXK II. Inhibition of PBR mediated cholesterol uptake and phosphorylation of VDAC-1 by GSK3? resulted in a detachment of HXK II from mitochondria with the subsequent development of enhanced sensitivity to chemotherapy induced cell death. The general goals of this project are to provide a deeper understanding of the mechanism(s) by which mitochondrial bound HXK II increases the proliferation and survival of cancer cells and to elucidate how HXK II binding to mitochondria is regulated and maintained, with the goal of exploiting the binding of HXK II to mitochondria as an anti-cancer target.
