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Synergistic epigenetic reactivation of estrogen receptor-α (ERα) by combined green tea polyphenol and histone deacetylase inhibitor in ERα-negative breast cancer cells.

Li Y, Yuan YY, Meeran SM, Tollefsbol TO - Mol. Cancer (2010)

Bottom Line: We also found that EGCG can lead to remodeling of the chromatin structure of the ERα promoter by altering histone acetylation and methylation status thereby resulting in ERα reactivation.A decreased binding of the transcription repressor complex, Rb/p130-E2F4/5-HDAC1-SUV39H1-DNMT1, in the regulatory region of the ERα promoter also contributes to ERα transcriptional activation through treatment with EGCG and/or TSA.Collectively, these studies show that green tea EGCG can restore ERα expression by regulating epigenetic mechanisms, and this effect is enhanced when combined with an HDAC inhibitor.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Biology, University of Alabama at Birmingham, 1300 University Boulevard Birmingham, AL 35294, USA.

ABSTRACT

Background: The status of estrogen receptor-α (ERα) is critical to the clinical prognosis and therapeutic approach in breast cancer. ERα-negative breast cancer is clinically aggressive and has a poor prognosis because of the lack of hormone target-directed therapies. Previous studies have shown that epigenetic regulation plays a major role in ERα silencing in human breast cancer cells. Dietary green tea polyphenol, (-)-epigallocatechin-3-gallate (EGCG), is believed to be an anticancer agent in part through its regulation of epigenetic processes.

Results: In our current studies, we found that EGCG can reactivate ERα expression in ERα-negative MDA-MB-231 breast cancer cells. Combination studies using EGCG with the histone deacetylase (HDAC) inhibitor, trichostatin A (TSA), revealed a synergistic effect of reactivation of ERα expression in ERα-negative breast cancer cells. Reactivation of ERα expression by EGCG and TSA treatment was found to sensitize ERα-dependent cellular responses to activator 17β-estradiol (E2) and antagonist tamoxifen in ERα-negative breast cancer cells. We also found that EGCG can lead to remodeling of the chromatin structure of the ERα promoter by altering histone acetylation and methylation status thereby resulting in ERα reactivation. A decreased binding of the transcription repressor complex, Rb/p130-E2F4/5-HDAC1-SUV39H1-DNMT1, in the regulatory region of the ERα promoter also contributes to ERα transcriptional activation through treatment with EGCG and/or TSA.

Conclusions: Collectively, these studies show that green tea EGCG can restore ERα expression by regulating epigenetic mechanisms, and this effect is enhanced when combined with an HDAC inhibitor. This study will facilitate more effective uses of combination approaches in breast cancer therapy and will help to explore more effective chemotherapeutic strategies toward hormone-resistant breast cancer.

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Schematic representation of a mechanism of EGCG-induced ERα reactivation in ERα-negative breast cancer cells. In this model, EGCG and TSA can affect chromatin modifications as well as the binding alteration of a transcription repressor complex, Rb/p130-E2F4/5-HDAC1-DNMT1-SUV39H1, to the ERα promoter, resulting in ERα reactivation in ERα-negative breast cancer cells.
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Figure 5: Schematic representation of a mechanism of EGCG-induced ERα reactivation in ERα-negative breast cancer cells. In this model, EGCG and TSA can affect chromatin modifications as well as the binding alteration of a transcription repressor complex, Rb/p130-E2F4/5-HDAC1-DNMT1-SUV39H1, to the ERα promoter, resulting in ERα reactivation in ERα-negative breast cancer cells.

Mentions: Many studies have shown that transcription factors play a crucial role in regulating gene expression by interacting with epigenetic modulators. For example, HDAC/DNMT1 involves a series of gene silencing through recruiting transcriptional repressors to the gene promoter [26,27]. Moreover, histone methyltransferase, SUV39H1, is another important epigenetic factor for transcriptional silencing [28]. A recent study has shown that a multimolecular complex, pRb2/p130-E2F4/5-HDAC1-DNMT1-SUV39H1, binding to the ERα promoter, is associated with ERα transcriptional repression in ERα-negative breast cancer MDA-MB-231 cells [29]. Further, the switching of DNMT1 to p300 in this complex will induce ERα transcription. We therefore sought to explore whether EGCG can affect the binding of this transcriptional complex to the ERα promoter. Using chromatin immunoprecipitation (ChIP) techniques, we observed that EGCG treatment can significantly decrease the binding of all the transcription factors of the repressor complex to the ERα promoter and this effect was greater for transcription factors such as SUV39H1 and Rb/p130 when EGCG was combined with TSA suggesting SUV39H1 and Rb/p130 may play an important role to assemble other transcription factors to the ERα promoter (Figures 4A and 4B). In particular, EGCG alone can induce a pronounced reduction of binding of HDAC1 and DNMT1 by 20 and 12.5 fold, respectively, further suggesting that epigenetic control plays a crucial role in EGCG-induced ERα reactivation. However, no difference has been found in the binding alteration of p300 in response to EGCG and/or TSA treatment indicating an alternative mechanism may involve p300-induced estrogen gene activation. To identify the direct mechanism of EGCG on ERα transcription regulation, we performed western-blotting to examine the protein expression of the related epigenetic factors induced by EGCG. As indicated in Figure 4C, the protein level of HDAC and SUV39H1 were decreased significantly, whereas p300 was increased prominently by EGCG, especially when EGCG was combined with TSA. However, no significant changes were found in protein levels of DNMT1 (data not shown), which may explain the less response of DNA methylation alteration in the ERα promoter. Collectively, these results suggest that the binding alterations of repressor complex to the promoter and/or direct expression regulation of key epigenetic factors contributed to the reactivation of ERα by the botanical compound EGCG (Figure 5).


Synergistic epigenetic reactivation of estrogen receptor-α (ERα) by combined green tea polyphenol and histone deacetylase inhibitor in ERα-negative breast cancer cells.

Li Y, Yuan YY, Meeran SM, Tollefsbol TO - Mol. Cancer (2010)

Schematic representation of a mechanism of EGCG-induced ERα reactivation in ERα-negative breast cancer cells. In this model, EGCG and TSA can affect chromatin modifications as well as the binding alteration of a transcription repressor complex, Rb/p130-E2F4/5-HDAC1-DNMT1-SUV39H1, to the ERα promoter, resulting in ERα reactivation in ERα-negative breast cancer cells.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2967543&req=5

Figure 5: Schematic representation of a mechanism of EGCG-induced ERα reactivation in ERα-negative breast cancer cells. In this model, EGCG and TSA can affect chromatin modifications as well as the binding alteration of a transcription repressor complex, Rb/p130-E2F4/5-HDAC1-DNMT1-SUV39H1, to the ERα promoter, resulting in ERα reactivation in ERα-negative breast cancer cells.
Mentions: Many studies have shown that transcription factors play a crucial role in regulating gene expression by interacting with epigenetic modulators. For example, HDAC/DNMT1 involves a series of gene silencing through recruiting transcriptional repressors to the gene promoter [26,27]. Moreover, histone methyltransferase, SUV39H1, is another important epigenetic factor for transcriptional silencing [28]. A recent study has shown that a multimolecular complex, pRb2/p130-E2F4/5-HDAC1-DNMT1-SUV39H1, binding to the ERα promoter, is associated with ERα transcriptional repression in ERα-negative breast cancer MDA-MB-231 cells [29]. Further, the switching of DNMT1 to p300 in this complex will induce ERα transcription. We therefore sought to explore whether EGCG can affect the binding of this transcriptional complex to the ERα promoter. Using chromatin immunoprecipitation (ChIP) techniques, we observed that EGCG treatment can significantly decrease the binding of all the transcription factors of the repressor complex to the ERα promoter and this effect was greater for transcription factors such as SUV39H1 and Rb/p130 when EGCG was combined with TSA suggesting SUV39H1 and Rb/p130 may play an important role to assemble other transcription factors to the ERα promoter (Figures 4A and 4B). In particular, EGCG alone can induce a pronounced reduction of binding of HDAC1 and DNMT1 by 20 and 12.5 fold, respectively, further suggesting that epigenetic control plays a crucial role in EGCG-induced ERα reactivation. However, no difference has been found in the binding alteration of p300 in response to EGCG and/or TSA treatment indicating an alternative mechanism may involve p300-induced estrogen gene activation. To identify the direct mechanism of EGCG on ERα transcription regulation, we performed western-blotting to examine the protein expression of the related epigenetic factors induced by EGCG. As indicated in Figure 4C, the protein level of HDAC and SUV39H1 were decreased significantly, whereas p300 was increased prominently by EGCG, especially when EGCG was combined with TSA. However, no significant changes were found in protein levels of DNMT1 (data not shown), which may explain the less response of DNA methylation alteration in the ERα promoter. Collectively, these results suggest that the binding alterations of repressor complex to the promoter and/or direct expression regulation of key epigenetic factors contributed to the reactivation of ERα by the botanical compound EGCG (Figure 5).

Bottom Line: We also found that EGCG can lead to remodeling of the chromatin structure of the ERα promoter by altering histone acetylation and methylation status thereby resulting in ERα reactivation.A decreased binding of the transcription repressor complex, Rb/p130-E2F4/5-HDAC1-SUV39H1-DNMT1, in the regulatory region of the ERα promoter also contributes to ERα transcriptional activation through treatment with EGCG and/or TSA.Collectively, these studies show that green tea EGCG can restore ERα expression by regulating epigenetic mechanisms, and this effect is enhanced when combined with an HDAC inhibitor.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Biology, University of Alabama at Birmingham, 1300 University Boulevard Birmingham, AL 35294, USA.

ABSTRACT

Background: The status of estrogen receptor-α (ERα) is critical to the clinical prognosis and therapeutic approach in breast cancer. ERα-negative breast cancer is clinically aggressive and has a poor prognosis because of the lack of hormone target-directed therapies. Previous studies have shown that epigenetic regulation plays a major role in ERα silencing in human breast cancer cells. Dietary green tea polyphenol, (-)-epigallocatechin-3-gallate (EGCG), is believed to be an anticancer agent in part through its regulation of epigenetic processes.

Results: In our current studies, we found that EGCG can reactivate ERα expression in ERα-negative MDA-MB-231 breast cancer cells. Combination studies using EGCG with the histone deacetylase (HDAC) inhibitor, trichostatin A (TSA), revealed a synergistic effect of reactivation of ERα expression in ERα-negative breast cancer cells. Reactivation of ERα expression by EGCG and TSA treatment was found to sensitize ERα-dependent cellular responses to activator 17β-estradiol (E2) and antagonist tamoxifen in ERα-negative breast cancer cells. We also found that EGCG can lead to remodeling of the chromatin structure of the ERα promoter by altering histone acetylation and methylation status thereby resulting in ERα reactivation. A decreased binding of the transcription repressor complex, Rb/p130-E2F4/5-HDAC1-SUV39H1-DNMT1, in the regulatory region of the ERα promoter also contributes to ERα transcriptional activation through treatment with EGCG and/or TSA.

Conclusions: Collectively, these studies show that green tea EGCG can restore ERα expression by regulating epigenetic mechanisms, and this effect is enhanced when combined with an HDAC inhibitor. This study will facilitate more effective uses of combination approaches in breast cancer therapy and will help to explore more effective chemotherapeutic strategies toward hormone-resistant breast cancer.

Show MeSH
Related in: MedlinePlus