ERE-independent ERα target genes differentially expressed in human breast tumors

The classical pathway for estrogen receptor (ER) signaling is mediated by ER binding to an estrogen response element (ERE) in DNA. ER alpha can also act via a nonclassical pathway by altering the activities of other transcription factors (e.g., Sp1 AP-1, or NF-kappa B) at their cognate sites on DNA. We previously generated a mutant form of ER alpha (E207A/G208A) that does not bind to EREs, and therefore lacks signaling via the classical pathway but retains signaling via the nonclassical pathway. In the Current study, we introduce this mutant ERa into MDA-MB231 ER alpha-negative breast carcinoma cells to identify nonclassical pathway genes that respond to 17 beta-estradiol (E2), selective estrogen receptor modulators (SERMs) tamoxifen (TAM) or raloxifene (RAL), or the estrogen antagonist ICI 182,780 (ICI). Consistent with a role for nonclassical signaling in SERM action, microarray analyses identify 268 responsive nonclassical ER alpha pathway target genes. ICI elicits the largest number of nonclassical genes, followed by RAL, TAM, and E2. Custom microarrays containing identified nonclassical ERa responsive genes are used to compare gene expression in human breast tumor (n = 34) and normal mammary epithelial cell (n = 9) samples. A subset of nonclassical genes (n = 32) are differentially expressed in breast tumors. In summary, we show that nonclassical ERa pathway target genes exhibit a range of transcriptional responses to SERMs and identify targets of this pathway as potentially relevant to breast cancer. The identification of nonclassical ERa target genes offers new insight into estrogen receptor signaling and cross talk with pathways that mediate breast tumor response to SERM therapy. (c) 2005 Elsevier Ireland Ltd. All rights reserved.