Reciprocal regulation of ZEB1 and AR in triple negative breast cancer cells.

Abstract

Abstract Abstract #3054 Introduction: Approximately 60-80% of breast tumors are positive for androgen receptor (AR) and negative for estrogen receptor (ER) and progesterone (PR) (Isola et al. J Pathol. 1993). This suggests that AR may function independently of ER and PR to cross-talk with other factors such as Zinc-finger enhancer binding protein (ZEB1). ZEB1 is a transcription factor involved in the progression of breast cancer primarily through promoting epithelial to mesenchymal transition (EMT). ZEB1 represses the expression of E-cadherin by binding to E-box sequences in the promoter, thus decreasing epithelial differentiation and promotes cell migration.
 Methods: We established a stable control and ZEB1 knockdown using shRNA in MDA-MB-231 cells, a highly metastatic triple negative breast cancer cell line with mesechymal morphology. The stable cell lines were characterized by immunoblot and RT-PCR analysis and were stimulated with synthetic androgens or an androgen antagonist and cell growth and migration were monitored.
 Results: ZEB1 regulated the expression of AR in triple breast cancer cell lines. AR promoter contains two E-boxes, which may be critical to the transcriptional regulation of this gene. ZEB1 suppression by stably transfecting shRNA in MDA-MB-231 cells resulted in a decrease of AR mRNA, protein and AR downstream targets. In addition, ZEB1 suppression reduced the protein expression of Cyclin D1 and decreased cell proliferation. Conversely, blockade of AR signaling with bicalutamide resulted in suppression of ZEB1 protein expression in two triple negative breast cancer cell lines. ZEB1 knockdown in MDA-MB-231 cells sensitized the cells to bicalutamide by inducing a greater amount of cell death and a reduction in migration compared to the control cells.
 Conclusions: Taken together, these results indicate that ZEB1 and AR regulate each other to promote cell growth and cell migration in triple negative breast cancer cells. Inhibition of AR signaling could decrease cell proliferation via ZEB1 in a subset of triple negative breast cancers. The growth of triple negative breast cancers that express ZEB1 and AR could be inhibited by antiandrogen treatment. Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 3054.