Fredrik Pontén

Abstract A10: Peroxiredoxin-1 and oxidative stress: Controlling the balance between oncogenic and endocrine signalling in estrogen receptor-positive breast cancer

Introduction: Peroxiredoxin-1 (PRDX1) is a multifunctional protein, acting as a hydrogen peroxide (H2O2) scavenger, molecular chaperone and immune mediator. Differential expression of PRDX1 has been described in many tumor types, including lung and ovarian carcinoma. Despite the wealth of knowledge about PRDX1 functionality, its role in human breast cancer has not been fully elucidated. Preclinical studies suggest that PRDX1 may be protective against oncogene-induced mammary carcinogenesis, indicating that it may be an important biomarker. In this study, we describe PRDX1 as a robust prognostic biomarker in estrogen receptor α (ER)-positive breast cancer and propose a molecular mechanism which explains this observation. Materials and Methods: The anti-PRDX1 antibody was validated in breast cancer cell lines using Western blotting, immunohistochemistry and reverse phase protein array (RPPA) technology following exogenous overexpression or shRNA-mediated knockdown of PRDX1. PRDX1 protein expression was evaluated using two independent breast cancer cohorts: a 512 patient tissue microarray (TMA) and a 712 patient RPPA cohort. Increase in cellular content of H2O2 was accomplished via treatment of cell lines with exogenous (H2O2) or activation of oncogenic pathways (611CTF-HER2 overexpression). Western blotting and RPPA were used to assess changes in ERα and oncogenic signaling proteins in cell lines and a third breast cancer cohort, consisting of 410 patients. Results: High expression of PRDX1 protein was associated with a favorable outcome in ER-positive, but not ER-negative breast cancer cases across both cohorts (evaluable data for 975 patients total; log-rank p-value: TMA=0.022; RPPA=0.002). Exogenous treatment with (H2O2) or induction of oncogenic signaling suppressed ERα protein and stimulated phosphorylation/activation of Akt kinase in ER-positive cell lines. Knockdown of PRDX1 further sensitized the cells to the (H2O2)-mediated effect whilst overexpression protects against it. These observations were further validated in an additional cohort of ER-positive tumor samples, where PRDX1 protein levels correlated with ERα (positive) and pAkt-473 protein expression (negative). Conclusions: Our findings provide robust evidence of the importance of PRDX1 as a biomarker of favorable prognosis in ER-positive breast cancer. We suggest that PRDX1 acts as a shielding mechanism for ERα protein by counteracting (H2O2)-mediated suppression of this molecule in ER-positive tumors, and suppressing phosphorylation of Akt kinase under these oxidative stress conditions. This strongly implies that (H2O2) and PRDX1 are important role players in the crosstalk between oncogenic (e.g. HER2- or PI3K-induced) and ER-driven signaling pathways in breast cancer. Understanding the mechanisms underlying the regulation of oxidative stress response in ER-positive breast cancer can allow for better tailoring the management of this disease.