(A) Inhibition of PC3 cell invasion by overexpression of ECSOD and inhibition of xCT expression was reversed by treatment with 10,000 Units of CAT. (B) Inhibition of MMP2/9 activities by overexpression of ECSOD and inhibition of xCT expression was reversed by treatment with 10,000 Units of CAT. #p-value ≤ 0.05 when compared with Non-Catalase treatment. (C) Proposed mechanism by which ECSOD and xCT regulate PCa invasion. A decrease in ECSOD (1) results in an elevation of extracellular O2•− and OONO• (2), while an increase in xCT (3) results in an imbalance of extracellular thiol couples, e.g. an increased level of extracellular Cys (4) and a decreased level of extracellular CySS. These changes in the extracellular redox state are likely to have a profound effect on the activation of migration/invasion-related proteins (e.g., MMPs) (5), resulting in migration/invasion/metastasis of PCa. (Green arrows = increased levels, Red arrow = decreased levels).