Abstract Microarray profiling and analysis of in vivo-selected metastatic bladder cancer has revealed a strong association between manganese superoxide dismutase (Sod2) expression and invasiveness. However, whether increased Sod2 expression contributes to progression from transitional cell carcinoma (TCC) to invasive bladder cancer has not been established. To test this hypothesis we evaluated the impact of Sod2 overexpression on invasive and migratory properties of two distinct TCC cell lines (UC3 and UC6). Sod2 overexpression increased wound healing and matrigel transwell migration of UC6 while inhibiting these activities in the UC3 cell line. Increases or decreases in invasiveness were accompanied by parallel shifts in the levels of matrix metalloproteinases and VEGF. The opposing effects of Sod2 on TCC invasion and the secretory phenotype were associated with differential Erk activation. Sod2-dependent suppression of Erk activation and MMP-1 expression was reversed by EGF activation in UC3 cells while Erk inhibition blocked the Sod2-mediated elevation in ERK activity, MMP-1 and VEGF levels. Activation or inhibition of Erk by Sod2 in the UC6 and UC3 cell lines, respectively, was driven by superoxide (O2−.) and not H2O2. Increasing mitochondrial superoxide by treatments with complex I or III inhibitors reversed the effects of Sod2 overexpression in both cell lines. Sod2-dependent inhibition of invasion in vitro was associated with impairment in growth of orthotopically implanted tumors. These findings unveil distinct redox regulated attributes of TCC that participate in controlling their invasiveness both in vitro and in vivo. In addition, we have identified the ERK signaling network as a primary target for controlling divergent tumorigenic responses to Sod2 overexpression. 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 74.