Abstract 1538: Role of mitochondrial dysfunction in GPX regulation and glutathione metabolism

Abstract

Abstract Many cancer cells exhibit mitochondrial respiratory dysfunction, which is associated with metabolic alterations, change in cellular redox states, and drug resistance. It is also known that elevated glutathione in cancer cells may promote their survival and resistance to anticancer agents. However, the exact relationship between mitochondrial dysfunction and alterations in cell redox states and viability remain elusive, and the underlying regulatory mechanisms are unclear. In this study, we used a dominant negative form of mitochondrial DNA polymerase γ (POLGdn) expressed in a T-Rex293 tet/on system as a model to induce mitochondrial dysfunction, and showed that suppression of mitochondrial respiration caused a significant increase in ROS generation. Mitochondrial dysfunction also led to a significant increase in glutathione, along with an elevated expression of its rate-limiting enzyme GCLC and the upstream transcription factor Nrf-2. Interestingly, the mRNA expression of glutathione peroxidases GPX1 and GPX4 remain the same, while the GPX proteins and enzyme activity were significantly increased in the mitochondrial defective cells. Since GPX1 and GPX4 are selenium-containing enzymes, they require selenocysteine-tRNA for their protein synthesis. We further demonstrated that selenocysteine-tRNA expression and its transcription factor ZNF143 protein were significantly increased after induction of mitochondrial dysfunction. Furthermore, siRNA knockdown of ZNF143 led to a decrease of GPX activity, an increase in ROS, and a reduction in cell viability in the mitochondrial defective cells. Similarly, a knockdown of GPX1 by shRNA in the mitochondrial defective cells also compromised cell survival. We also observed that ZNF143 protein level was decreased in the GPX1-knockdown cells, suggesting that GPX1 has a positive feedback role in regulating ZNF143 expression. These data suggest that mitochondrial dysfunction led to an activation of glutathione synthesis and an increase in GPX activity through upregulation of the transcription factors Nrf-2 and ZNF143, respectively, and that mitochondrial dysfunction in cancer cells seems to set a new balance between the increase in ROS generation and the elevation in glutathione antioxidant system to maintain cell survival. As such, targeted inhibition of selenocysteine-tRNA, selenoenzymes, or glutathione synthesis may be potential therapeutic strategies for cancer treatment. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1538.