Increasing discordant antioxidant protein levels and enzymatic activities contribute to increasing redox imbalance observed during human prostate cancer progression

A metabolomics study demonstrated a decrease in glutathione and an increase in cysteine (Cys) levels in human prostate cancer (PCa) tissues as Gleason scores increased, indicating redox imbalance with PCa progression. These results were extended in the present study by analyzing the redox state of the protein thioredoxin 1 (Trx1) and sulfinylation (SO₃) of peroxiredoxins (Prxs) (PrxSO₃) in PCa tissues and cell lines. Lysates of paired human PCa tissues with varying degrees of aggressiveness and adjacent benign (BN) tissues were used for analysis. Redox Western blot analysis of Trx1 demonstrated low levels of reduced and high levels of oxidized Trx1 (functional and nonfunctional, respectively) in high-grade PCa (Gleason scores 4+4 to 4+5) in comparison to intermediate-grade PCa (Gleason scores 3+3 to 3+4) or BN tissues. PrxSO₃ were increased in high-grade PCa. Oxidized Trx1 and PrxSO₃ are indicators of oxidative stress. To study whether redox imbalance may potentially affect enzyme activities of antioxidant proteins (APs), we determined the levels of selected APs in PCa tissues by Western blot analysis and found that mitochondrial manganese superoxide dismutase (MnSOD), Prx3, and Trx1 were increased in high-grade PCa tissues compared with BN tissues. Enzyme activities of MnSOD in high-grade PCa tissues were significantly increased but at a lower magnitude compared with the levels of MnSOD protein (0.5-fold vs 2-fold increase). Trx1 activity was not changed in high-grade PCa tissues despite a large increase in Trx1 protein expression. Further studies demonstrated a significant increase in posttranslational modifications of tyrosine and lysine residues in MnSOD protein and oxidation of Cys at the active site (Cys32 and Cys35) and the regulatory site (Cys62 and Cys69) of Trx1 in high-grade PCa compared to BN tissues. These discordant changes between protein levels and enzyme activities are consistent with protein inactivation by redox imbalance and/or posttranslational modifications. In contrast, the protein level and activity of extracellular superoxide dismutase were significantly decreased in high-grade PCa compared with adjacent BN tissues. Results from cell lines mirror those from PCa tissues. Knowledge of redox-state profiles in specific cancers may help to predict the behavior and response of each cancer to chemotherapeutic drugs and radiation.