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C/EBP? mediates the growth inhibitory effect of progestins on breast cancer cells.

ABSTRACT: Steroid hormones are key gene regulators in breast cancer cells. While estrogens stimulate cell proliferation, progestins activate a single cell cycle followed by proliferation arrest. Here, we use biochemical and genome-wide approaches to show that progestins achieve this effect via a functional crosstalk with C/EBP?. Using ChIP-seq, we identify around 1,000 sites where C/EBP? binding precedes and helps binding of progesterone receptor (PR) in response to hormone. These regions exhibit epigenetic marks of active enhancers, and C/EBP? maintains an open chromatin conformation that facilitates loading of ligand-activated PR. Prior to hormone exposure, C/EBP? favors promoter-enhancer contacts that assure hormonal regulation of key genes involved in cell proliferation by facilitating binding of RAD21, YY1, and the Mediator complex. Knockdown of C/EBP? disrupts enhancer-promoter contacts and decreases the presence of these architectural proteins, highlighting its key role in 3D chromatin looping. Thus, C/EBP? fulfills a previously unknown function as a potential growth modulator in hormone-dependent breast cancer.

SUBMITTER: Nacht AS

PROVIDER: S-EPMC6745496 | biostudies-literature | 2019 Sep

REPOSITORIES: biostudies-literature

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C/EBPα mediates the growth inhibitory effect of progestins on breast cancer cells.

Nacht A Silvina AS Ferrari Roberto R Zaurin Roser R Scabia Valentina V Carbonell-Caballero José J Le Dily Francois F Quilez Javier J Leopoldi Alexandra A Brisken Cathrin C Beato Miguel M Vicent Guillermo P GP

The EMBO journal 20190802 18

Steroid hormones are key gene regulators in breast cancer cells. While estrogens stimulate cell proliferation, progestins activate a single cell cycle followed by proliferation arrest. Here, we use biochemical and genome-wide approaches to show that progestins achieve this effect via a functional crosstalk with C/EBPα. Using ChIP-seq, we identify around 1,000 sites where C/EBPα binding precedes and helps binding of progesterone receptor (PR) in response to hormone. These regions exhibit epigenet ...[more]

PMID: 31373033

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Project description:BackgroundNumerous studies have implicated the aryl hydrocarbon receptor (AhR) as a potential therapeutic target for several human diseases, including estrogen receptor alpha (ER?) positive breast cancer. Aminoflavone (AF), an activator of AhR signaling, is currently undergoing clinical evaluation for the treatment of solid tumors. Of particular interest is the potential treatment of triple negative breast cancers (TNBC), which are typically more aggressive and characterized by poorer outcomes. Here, we examined AF's effects on two TNBC cell lines and the role of AhR signaling in AF sensitivity in these model cell lines.MethodsAF sensitivity in MDA-MB-468 and Cal51 was examined using cell counting assays to determine growth inhibition (GI50) values. Luciferase assays and qPCR of AhR target genes cytochrome P450 (CYP) 1A1 and 1B1 were used to confirm AF-mediated AhR signaling. The requirement of endogenous levels of AhR and AhR signaling for AF sensitivity was examined in MDA-MB-468 and Cal51 cells stably harboring inducible shRNA for AhR. The mechanism of AF-mediated growth inhibition was explored using flow cytometry for markers of DNA damage and apoptosis, cell cycle analysis, and ?-galactosidase staining for senescence. Luciferase data was analyzed using Student's T test. Three-parameter nonlinear regression was performed for cell counting assays.ResultsHere, we report that ER?-negative TNBC cell lines MDA-MB-468 and Cal51 are sensitive to AF. Further, we presented evidence suggesting that neither endogenous AhR expression levels nor downstream induction of AhR target genes CYP1A1 and CYP1B1 is required for AF-mediated growth inhibition in these cells. Between these two ER? negative cell lines, we showed that the mechanism of AF action differs slightly. Low dose AF mediated DNA damage, S-phase arrest and apoptosis in MDA-MB-468 cells, while it resulted in DNA damage, S-phase arrest and cellular senescence in Cal51 cells.ConclusionsOverall, this work provides evidence against the simplified view of AF sensitivity, and suggests that AF could mediate growth inhibitory effects in ER?-positive and negative breast cancer cells, as well as cells with impaired AhR expression and signaling. While AF could have therapeutic effects on broader subtypes of breast cancer, the mechanism of cytotoxicity is complex, and likely, cell line- and tumor-specific.

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C/EBP? mediates the growth inhibitory effect of progestins on breast cancer cells.

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C/EBPα mediates the growth inhibitory effect of progestins on breast cancer cells.

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