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Single CpG site methylation controls estrogen receptor gene transcription and correlates with hormone therapy
Kouki Tsuboi1, Takamasa Nagatomo1, Tatsuyuki Gohno1
1Department of Molecular and Functional Dynamics, Graduate School of Medicine, Tohoku University, Aoba-ku, Sendai, 980-8575, Japan.
Abstract:
Hormone therapy is the most effective treatment for patients with estrogen receptor α-positive breast cancers. However, although resistance occurs during treatment in some cases and often reflects changed estrogen receptor α status, the relationship between changes in estrogen receptor α expression and resistance to therapy are poorly understood. In this study, we identified a mechanism for altered estrogen receptor α expression during disease progression and acquired hormone therapy resistance in aromatase inhibitor-resistant breast cancer cell lines. Subsequently, we investigated promoter switching and DNA methylation status of the estrogen receptor α promoter, and found marked changes of methylation at a single CpG site (CpG4) in resistant cells. In addition, luciferase reporter assays showed reduced transcriptional activity from this methylated CpG site. This CpG region was also completely conserved among species, suggesting that it acts as a methylation-sensitive Ets-2 transcription factor binding site, as confirmed using chromatin immunoprecipitation assays. In estrogen receptor α-positive tumors, CpG4 methylation levels were inversely correlated with estrogen receptor α expression status, suggesting that single CpG site plays an important role in the regulation of estrogen receptor α transcription.
Insights
A specific DNA methylation change in estrogen receptor alpha (ERα) promoter can lead to hormone therapy resistance in breast cancer. This finding reveals a new mechanism for ERα regulation and potential therapeutic targets.
Area of Science:
- Oncology
- Molecular Biology
- Genetics
Background:
- Hormone therapy is a primary treatment for estrogen receptor alpha-positive breast cancer.
- Acquired resistance to hormone therapy, often linked to altered estrogen receptor alpha status, is a significant clinical challenge.
- The precise mechanisms linking estrogen receptor alpha expression changes to therapy resistance remain incompletely understood.
Purpose of the Study:
- To elucidate the molecular mechanisms underlying altered estrogen receptor alpha expression in acquired hormone therapy resistance.
- To investigate the role of promoter alterations and DNA methylation in estrogen receptor alpha regulation during disease progression.
Main Methods:
- Utilized aromatase inhibitor-resistant breast cancer cell lines to study acquired resistance.
- Analyzed DNA methylation status at the estrogen receptor alpha promoter, focusing on specific CpG sites.
- Performed luciferase reporter assays to assess transcriptional activity.
- Conducted chromatin immunoprecipitation assays to identify transcription factor binding.
Main Results:
- Identified significant changes in DNA methylation at a single CpG site (CpG4) within the estrogen receptor alpha promoter in resistant cells.
- Demonstrated reduced transcriptional activity from the methylated CpG4 site.
- Confirmed CpG4 as a conserved, methylation-sensitive transcription factor (Ets-2) binding site.
- Observed an inverse correlation between CpG4 methylation levels and estrogen receptor alpha expression in patient tumors.
Conclusions:
- A single CpG site (CpG4) methylation in the estrogen receptor alpha promoter is a key mechanism driving reduced estrogen receptor alpha expression and acquired hormone therapy resistance.
- CpG4 methylation represents a critical regulatory point for estrogen receptor alpha transcription in breast cancer.
- Targeting this methylation mechanism could offer novel therapeutic strategies for hormone-resistant breast cancer.