Peroxiredoxin (Prdx) proteins are thiol-specific antioxidants that protect cells from oxidative stress in many normal and disease states. There are six Prdx proteins expressed in mammals, each with a characteristic tissue expression, subcellular distribution and substrate specificity. Recent studies have revealed elevated Prdx levels in many cancers, suggesting a protective role for these proteins in cancer cell survival. The present study is the first to investigate the function of all six Prdx proteins in the MCF-7 breast cancer cell line. We show that these cells have both higher resistance to doxorubicin-induced toxicity and significantly elevated Prdx levels, compared to the non-cancer MCF-10A cells. Using transient siRNA transfections, we show that Prdx3 suppression leads to decreased MCF-7 cell survival in the absence of doxorubicin. We further demonstrate that individual suppression of four of six of the Prdx proteins leads to increased doxorubicin-induced toxicity by apoptosis. Finally, we show that clonal selection of a doxorubicin-resistant MCF-7 subline by 2-week culture in 0.1 µM doxorubicin resulted in a marked elevation in the expression of several Prdx proteins. Together, these data reveal a protective function for peroxiredoxins in MCF-7 cell survival, and suggest that Prdx overexpression in breast cancer may play a role in doxorubicin-resistance in these, and possibly other, breast cancer cells. This study is the first to investigate the function of the entire Prdx family in a breast cancer cell line.

The Peroxiredoxin (Prdx) family of genes encodes thiol-specific antioxidant proteins that protect cells from oxidative stress. Mammalian cells express six different Prdx proteins, and these proteins play a role in cell signaling, proliferation and apoptosis. Recent studies have shown that Prdx levels are elevated in many cancers, suggesting that Prdx upregulation may be an advantageous adaptation to the cancerous state. In the present study we investigated the expression and function of different Prdx proteins in untreated and doxorubicin-treated MCF-7 breast cancer cells, as well as noncancerous MCF-10A cells. We used real-time PCR and western blotting to examine Prdx expression in both cell lines, and also measured Prdx protein expression in doxorubicin-treated MCF-7 cells. In addition, we suppressed Prdx expression using transiently transfected siRNA and measured cell proliferation and apoptosis. Our results show that MCF-7 cells are significantly more resistant to cell death induced by the chemotherapy agent doxorubicin. We also found that five of the six Prdxs are overexpressed in MCF-7 cells at the mRNA and protein levels, and that serum deprivation reduced Prdx expression. Treatment of MCF-7 cells with doxorubicin altered expression of specific Prdxs, demonstrating a specific effect on these antioxidants. Transient transfection of MCF-7 cells with Prdx6 siRNA resulted in a marked reduction in Prdx6 suppression, with no change in other Prdx proteins. Suppression of Prdx6 in these cells led to reduced cell proliferation and increased susceptibility to doxorubicin-induced death. Similar studies are currently underway for the other Prdx proteins. Together, these findings suggest that Prdx overexpression in MCF-7 cells may be cytoprotective and that Prdxs may contribute to doxorubicin-resistance in these and other breast cancer cells. Citation Format: Caitlin McDonald, Gregg Perlmutter, Kekoa Taparra, Jillian Muhlbauer, Julie Passarelli, Shelley A. Phelan. Function and regulation of peroxiredoxin proteins in doxorubicin-treated MCF-7 breast cancer cells. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2908. doi:10.1158/1538-7445.AM2013-2908

Peroxiredoxin (Prdx) proteins are thiol-specific antioxidants that protect cells from oxidative stress in various normal and disease states. There are six different Prdx proteins expressed in mammals, each possessing a characteristic tissue and subcellular distribution. Recent studies have revealed elevated Prdx levels in many cancers, suggesting a protective role for these proteins in cancer cell survival. In the present study we analyzed Prdx levels in several human breast tumor samples, and also investigated the function of Prdx proteins in the MCF-7 breast cancer cell line. Analysis of breast tumor and adjacent normal breast tissue from almost 20 patients showed elevated levels of most Prdx proteins in tumor tissue from the majority of patients. To address the role of Prdxs in breast cancer, we used transient siRNA transfections of MCF-7 cells and examined resulting cell viability in the absence and presence of doxorubicin treatment. Our data show that individual suppression of four of six of the Prdx proteins leads to increased cell death, as well as increased sensitivity to doxorubicin-induced toxicity. Finally, we show that clonal selection of doxorubicin-resistant MCF-7 cells by two-week culture in 0.1uM doxorubicin resulted in a marked elevation in the expression of several Prdx proteins. Similar studies are currently underway in the highly metastatic MDA cell line, and possible upstream regulators of Prdx overexpression in these lines are being investigated. Together, these data show a strong protective role for Peroxiredoxins in breast cancer cell survival, and suggest that Prdx overexpression in breast cancer may play a role in chemotherapy-resistance. Citation Format: Jillian Muhlbauer, Gregg Perlmutter, Caitlin McDonald, Harry Cintineo, Caterina Aiello, Shelley A. Phelan. Elevated peroxiredoxin expression in breast cancer and its protective role in doxorubicin-resistance. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2262. doi:10.1158/1538-7445.AM2014-2262