MnSOD detoxifies superoxide and impacts tumor biology by generating H2O2 which can diffuse through the mitochondrial membrane and affect metabolism and apoptosis. The selenium-dependent enzyme GPx-1 localizes to both the cytoplasm and the mitochondria and reduces H2O2 to water and may therefore modulate the impact of MnSOD on carcinogenesis. A val to ala polymorphism in codon 16 of the MnSOD gene has been shown to be associated with increased prostate cancer risk in men with the lowest level of dietary antioxidant intake and individuals who consumed less dietary antioxidants, including selenium, had the greatest risk of prostate cancer (Li et al, 2005). A polymorphism in the GPx-1 gene resulting in a leucine (L) instead of a proline (P) at position 198 has frequently been reported to be associated with elevated cancer risk. To examine the molecular mechanism behind the epidemiological observation that genotypes in GPx-1 gene modify elevated risk of cancer associated with MnSOD genotypes, MCF-7 human breast cancer cells null for GPx-1 and having negligible levels of endogenous MnSOD were transfected with GPx-1 and MnSOD allele-specific expression constructs to determine outcomes related to cellular signaling and metabolism. MnSOD and GPx-1 alleles differentially interacted to modulate the expression of the anti-oxidant stress response regulator Nrf2, the cell adhesion protein E-Cadherin, the cell signaling protein pAkt, the anti-apoptotic protein Bcl-2 and the mitochondria located deacetylase Sirt3. Also, co-expression of the GPx-1A7L and either MnSODval or MnSODala increased oxidative phosphorylation as measured by O2 uptake using the Seahorse XF24 XF analyzer, which simultaneously determines relative mitochondrial respiration and glycolysis. In order to assess whether GPx-1 and MnSOD allelic variants modulate mitochondrial membrane potential, CMX-ROS fluorescence was measured. Independent and irrespective of which allele was evaluated, MnSOD and GPx-1 individually decreased mitochondrial potential as compared to that seen using MCF-7 control cells. In addition, co-expression of GPx-1A7L with either MnSODval or MnSODala further decreased membrane potential above that observed for either MnSOD and GPx-1 alone. In order to determine if MnSOD and GPx-1 levels are associated with a higher risk for biochemical recurrence of prostate cancer after radical prostatectomy, immunohistochemistry of human prostate tissue cores will be performed. Preliminary results indicate that a high MnSOD/ GPx-1 ratio was observed in prostate cancer tissue compared to adjacent normal tissue.
Citation Format: Dede N. Ekoue, Soumen Bera, Emmanuel Ansong, Peter Hart, Virgilia Macias, Andre Kajdacsy-Balla, Marcelo Bonini, Alan M. Diamond. Allelic variations in MnSOD and GPx-1 affect metabolism, mitochondrial membrane potential and expression of signaling proteins. [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 225.