RAC1 plays an essential role in estrogen receptor alpha function in breast cancer cells

AbstractThe activity of Rho family GTPase protein, RAC1, which plays important normal physiological functions, is dysregulated in multiple cancers. RAC1 is expressed in both estrogen receptor alpha (ER)-positive and ER-negative breast cancer (BC) cells. However, ER-positive BC is more sensitive to RAC1 inhibition. We have determined that reducing RAC1 activity, using siRNA or EHT 1864 (a small molecule Rac inhibitor), leads to rapid ER protein degradation. RAC1 interacts with ER within the ER complex and RAC1 localizes to chromatin binding sites for ER upon estrogen treatment. RAC1 activity is important for RNA Pol II function at both promoters and enhancers of ER target genes and ER-regulated gene transcription is blocked by EHT 1864, in a dose-dependent manner. Having identified that RAC1 is an essential ER cofactor for ER protein stability and ER transcriptional activity, we report that RAC1 inhibition could be an effective therapeutic approach for ER-positive BC.

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Physiologically Relevant Estrogen Receptor Alpha Pathway Reporters for Single-Cell Imaging-Based Carcinogenic Hazard Assessment of Estrogenic Compounds

Toxicological Sciences ◽

10.1093/toxsci/kfab037 ◽

2021 ◽

Author(s):

Britt Duijndam ◽

Annabel Goudriaan ◽

Tineke van den Hoorn ◽

Wanda van der Stel ◽

Sylvia Le Dévédec ◽

...

Keyword(s):

Estrogen Receptor ◽

Single Cell ◽

Cell Lines ◽

Estrogen Receptor Alpha ◽

Target Genes ◽

Dependent Manner ◽

Reporter Cell ◽

Estrogenic Compounds ◽

Receptor Alpha ◽

17Β Estradiol

Abstract Estrogen receptor alpha (ERα) belongs to the nuclear hormone receptor family of ligand-inducible transcription factors and regulates gene networks in biological processes such as cell growth and proliferation. Disruption of these networks by chemical compounds with estrogenic activity can result in adverse outcomes such as unscheduled cell proliferation, ultimately culminating in tumor formation. To distinguish disruptive activation from normal physiological responses, it is essential to quantify relationships between different key events leading to a particular adverse outcome. For this purpose, we established fluorescent protein MCF7 reporter cell lines for ERα-induced proliferation by bacterial artificial chromosome-based tagging of 3 ERα target genes: GREB1, PGR, and TFF1. These target genes are inducible by the non-genotoxic carcinogen and ERα agonist 17β-estradiol in an ERα-dependent manner and are essential for ERα-dependent cell-cycle progression and proliferation. The 3 GFP reporter cell lines were characterized in detail and showed different activation dynamics upon exposure to 17β-estradiol. In addition, they demonstrated specific activation in response to other established reference estrogenic compounds of different potencies, with similar sensitivities as validated OECD test methods. This study shows that these fluorescent reporter cell lines can be used to monitor the spatial and temporal dynamics of ERα pathway activation at the single-cell level for more mechanistic insight, thereby allowing a detailed assessment of the potential carcinogenic activity of estrogenic compounds in humans.

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ERRF is essential for Estrogen-Estrogen Receptor alpha signaling pathway in ER positive breast cancer cells

Biochemical and Biophysical Research Communications ◽

10.1016/j.bbrc.2016.04.132 ◽

2016 ◽

Vol 474 (2) ◽

pp. 400-405 ◽

Cited By ~ 4

Author(s):

Ang Luo ◽

Xuan Zhang

Keyword(s):

Breast Cancer ◽

Estrogen Receptor ◽

Cancer Cells ◽

Signaling Pathway ◽

Breast Cancer Cells ◽

Estrogen Receptor Alpha ◽

Receptor Alpha ◽

Er Positive ◽

Positive Breast Cancer

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Pharmacological Inhibition of CBP/p300 Blocks Estrogen Receptor Alpha (ERα) Function through Suppressing Enhancer H3K27 Acetylation in Luminal Breast Cancer

Cancers ◽

10.3390/cancers13112799 ◽

2021 ◽

Vol 13 (11) ◽

pp. 2799

Author(s):

Aaron Waddell ◽

Iqbal Mahmud ◽

Haocheng Ding ◽

Zhiguang Huo ◽

Daiqing Liao

Keyword(s):

Breast Cancer ◽

Estrogen Receptor ◽

Drug Targets ◽

Estrogen Receptor Alpha ◽

Target Genes ◽

Acquired Resistance ◽

Standard Of Care ◽

Luminal Breast Cancer ◽

Receptor Alpha ◽

Standard Of Care Treatment

Estrogen receptor alpha (ER) is the oncogenic driver for ER+ breast cancer (BC). ER antagonists are the standard-of-care treatment for ER+ BC; however, primary and acquired resistance to these agents is common. CBP and p300 are critical ER co-activators and their acetyltransferase (KAT) domain and acetyl-lysine binding bromodomain (BD) represent tractable drug targets, but whether CBP/p300 inhibitors can effectively suppress ER signaling remains unclear. We report that the CBP/p300 KAT inhibitor A-485 and the BD inhibitor GNE-049 downregulate ER, attenuate estrogen-induced c-Myc and Cyclin D1 expression, and inhibit growth of ER+ BC cells through inducing senescence. Microarray and RNA-seq analysis demonstrates that A-485 or EP300 (encoding p300) knockdown globally inhibits expression of estrogen-regulated genes, confirming that ER inhibition is an on-target effect of A-485. Using ChIP-seq, we report that A-485 suppresses H3K27 acetylation in the enhancers of ER target genes (including MYC and CCND1) and this correlates with their decreased expression, providing a mechanism underlying how CBP/p300 inhibition downregulates ER gene network. Together, our results provide a preclinical proof-of-concept that CBP/p300 represent promising therapeutic targets in ER+ BC for inhibiting ER signaling.

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