Abstract
4343
Many cancer cells exhibit mitochondrial respiratory dysfunction due to multiple factors including mitochondrial DNA (mtDNA) mutations, hypoxia in tumor tissues, and oncogenic signals. An important consequence of mitochondrial respiration defect in cancer cells is a decrease of ATP generation in the mitochondria and an increase of aerobic glycolysis in the cytosol (the Warburg effect). However, the precise relationship between mitochondrial dysfunction and cancer cell survival remain elusive, and the potential therapeutic implications remain to be investigated. To study underlying mechanisms and test new therapeutic approaches, a novel model system harboring a dominant negative form of mitochondrial DNA polymerase gamma (POLGdn) was expressed in the T-ReX293 tetracycline inducible cell system (tet/on system). Mitochondrial dysfunctions, including a significant decrease in mtDNA content, mtDNA-encoded RNA/protein expression, and oxygen consumption, were observed upon POLGdn expression (tet/on). Increased glycolysis was also observed, as evidenced by elevated glucose uptake, lactate production, and HKII protein expression. Importantly, NOX activation was observed in this model system two days after POLGdn expression. Detail analysis revealed an increased expression of NOXA1 and p47, associated with an increase in NOX activity and increased ROS generation compared with the non-induced (tet/off) cells. Upon treatment of the cells with DPI, a NOX inhibitor, tet/on cells exhibited a decrease in glucose uptake and ATP level, but showed a slight increase in lactate production. In contrast, the tet/off cells showed no change in glucose uptake and ATP level but had a significant increase in lactate production. Tet/on cells showed resistance to gemcitabine and taxol treatment, but sensitive to DPI treatment. Further analysis by comparing immortalized ovarian epithelial T72 cells with the Ras transformed tumorigenic T72-Ras cells showed that the transformed cells had increased NOX activity, increased gene expression of NOX1, NOX2 and p47, and more sensitive to DPI treatment especially under hypoxic condition while mitochondrial respiration was suppressed. These data together suggest that mitochondrial dysfunction leads to NOX activation, and that NOX inhibition might have potential implications in cancer therapeutics.
99th AACR Annual Meeting-- Apr 12-16, 2008; San Diego, CA