Abstract 3138: FOXC1 represses estrogen receptor-α expression via increasing NF-κB activity in breast cancer: A novel mechanism to explain antiestrogen resistance

Abstract

Abstract The Forkhead-box transcription factor FOXC1 has recently been identified as a critical marker for human basal-like breast cancer, which lacks or under-expresses estrogen receptor-α (ERα). Here we show a consistent inverse correlation between FOXC1 expression and ERα expression in multiple cDNA microarray data sets of human breast cancer. Overexpression of FOXC1 in ERα-positive breast cancer cells induces cell growth, migration, and invasion, but downregulates ERα mRNA and protein levels and consequently reduces cellular responses to estradiol and tamoxifen. This could explain why tamoxifen-refractory breast cancer cells exhibit higher FOXC1 levels as compared with tamoxifen-sensitive parental cells. We also found that FOXC1 induces NF-κB activation, which is known to be associated with ER-negative breast cancer, by increasing Pin1-mediated p65 protein stability and thus p65 protein levels. NF-κB mediates, at least in part, the regulation of ERα by FOXC1, because inhibition of NF-κB by an IκBα super-repressor and small-molecule inhibitors attenuated the suppression of ERα expression by FOXC1. Furthermore, the importance of the NF-κB pathway in FOXC1-stimulated cell growth was demonstrated by increased cell sensitivity to pharmacologic inhibition of NF-κB. Taken together, these results reveal a novel ERα-regulating mechanism that may explain the loss or low expression of ERα in basal-like breast cancer and also may provide new insight into mechanisms for antiestrogen resistance in breast cancer. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 3138. doi:10.1158/1538-7445.AM2011-3138