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C-Jun/AP-1 overexpression reprograms ERα signaling related to tamoxifen response in ERα-positive breast cancer [ChIP-seq]

ABSTRACT: A critical mechanism for transcription regulation by estrogen receptor α (ER) is the tethering of ER to DNA via other transcription factors, such as AP-1. However, genome-wide assessment of the overlap in chromatin binding repertoires of these two transcription factors has not been reported. Here, we show that the AP-1 transcription factor c-Jun interacts with ER and is recruited globally to ER binding regions. Interestingly, we identify differential motif enrichment between unique ER binding regions and unique c-Jun binding regions, with FoxA1 motif enriched in both sets of binding regions, whereas GATA3 motif only specifically enriched in the unique ER binding regions but not in the unique Jun binding regions. We demonstrate that the primary mechanism for estrogen/ER-dependent transcriptional responses is the tethering of ER to DNA under conditions where it cooperates with AP-1. We provide evidence that c-Jun overexpression causes reduced sensitivity to tamoxifen in ER+ breast cancer cells. Integrated omics data reveal TGFBI as one of the most perturbed genes regulated by c-Jun. TGFBI knockdown suppresses the growth of breast cancer cells and is critical for increasing the sensitivity of tamoxifen-resistant cells to tamoxifen. We show that TGFBI expression is elevated in breast cancer than in normal breast and the basal-like tumors express high levels of TGFBI. TGFBI expression is associated with poor patient survival in ER+ breast cancer receiving endocrine therapy, highlighting a role of AP-1 via TGFBI signaling as a major determinant of endocrine response in ER+ breast tumor.

ORGANISM(S): Homo sapiens

PROVIDER: GSE102410 | GEO | 2018/03/02

REPOSITORIES: GEO

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Project description:Estrogen receptor positive breast cancer is the most prevalent form of breast cancer. Although a number of available drugs are highly effective at blocking estrogen mediated receptor activity, thousands of patients die every year from ER positive breast cancers because the disease progresses to a stage at which these drugs are no longer effective. Thus, it is crucial to establish a comprehensive understanding of the biology of the estrogen receptor (ER) in ER:positive breast cancers that progress despite hormone therapy, a gap in knowledge that remains a serious impediment to successful treatment of patients with ER positive breast cancer. A key question that must be answered is how the estrogen receptor retains the capacity to activate transcription in the absence or near absence of estrogen. We have found a partial answer to this question upon investigating the effect of amplification and overexpression of Wolf Hirschhorn Syndrome Candidate 1:Like 1 (WHSC1L1), a gene that is amplified in 15% of breast cancers that codes for a histone:lysine methyltransferase. WHSC1L1 lies in the 8p11:p12 amplicon, a region of gene amplification that is strongly associated with breast cancer. In this study, we performed shRNA knockdown of the catalytically inactive short isoform of WHSC1L1 in SUM44PE breast cancer cells and found that expression of the short isoform of WHSC1L1 is necessary for expression of the estrogen receptor in this highly ER:positive cell line. In addition, we found that the estrogen receptor binds chromatin extensively in the absence of exogenous estrogen, including several actively transcribed canonical ER target genes, indicating that estrogen receptor signaling is active in SUM44 cells in estrogen free conditions. These findings represent a novel model for ER biology in luminal B breast cancers harboring amplification of WHSC1L1 and provide insight into the mechanisms by which ER: positive breast cancers become unresponsive to SERMs or aromatase inhibitors.

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C-Jun/AP-1 overexpression reprograms ERα signaling related to tamoxifen response in ERα-positive breast cancer [ChIP-seq]

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