NF-E2-related factor 2 (Nrf2) is an important transcription factor that activates the expression of cellular detoxifying enzymes. Nrf2 expression is largely regulated through Nrf2 association with Kelch-like ECH-associated protein 1 (Keap1), which results in cytoplasmic Nrf2 degradation. Conversely, little is known concerning the regulation of Keap1 expression. Until now, a regulatory role for microRNAs (miRs) in controlling Keap1 gene expression had not been characterized. By using miR array-based screening, we observed miR-200a silencing in breast cancer cells and demonstrated that upon re-expression, miR-200a targets the Keap1 3′ untranslated region (3′UTR) leading to Keap1 mRNA degradation. Loss of this regulatory mechanism may contribute to the dysregulation of Nrf2 activity in breast cancer. Previously, we have identified epigenetic repression of miR-200a in breast cancer cells. Here, we find that treatment with epigenetic therapy, the histone deacetylase (HDAC) inhibitor suberoylanilide hydroxamic acid (SAHA), restored miR-200a expression and reduced Keap1 levels. This reduction in Keap1 levels corresponded with Nrf2 nuclear translocation and activation of Nrf2-dependent NAD(P)H-quinone oxidoreductase 1 (NQO1) gene transcription. Moreover, we found that Nrf2 activation inhibited the anchorage-independent growth of breast cancer cells. Finally, our in vitro observations were confirmed in a model of carcinogen-induced mammary hyperplasia in vivo. In conclusion, our study demonstrates that miR-200a regulates the Keap1/Nrf2 pathway in mammary epithelium and we find that epigenetic therapy can restore miR-200a regulation of Keap1 expression, therefore re-activating the Nrf2-dependent antioxidant pathway in breast cancer.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2302. doi:1538-7445.AM2012-2302