The role of erna M6A modification in ligand-independent ER activation and breast cancer progression

The National Cancer Institute awarded the University of Texas at El Paso $573,746 on September 1, 2026, under the Cancer Biology Research program (CFDA 93.396) to investigate the role of N6-methyladenosine (M6A) modification in estrogen receptor activation and breast cancer progression.

The research examines how M6A modification of enhancer RNAs facilitates phase-separated condensation of estrogen receptors, which is critical for assembling enhancer transcriptional machinery and regulating gene expression in breast cancer cells. The project focuses on understanding ligand-independent estrogen receptor activation driven by mutations in the ligand-binding domain, particularly the Y537S and D538G variants associated with endocrine resistance and metastatic progression. The investigators will evaluate whether inhibiting M6A modification or disrupting M6A binding to the nuclear reader protein YTHDC1 can dissolve estrogen receptor condensates and reduce transcriptional activity in endocrine-resistant breast cancer models. These findings are expected to inform new therapeutic approaches targeting hormone receptor signaling in aggressive, treatment-resistant breast cancer.

The award period runs through August 31, 2031. Work is performed in San Antonio, Texas.

Abstract

The role of erna M6A modification in ligand-independent ER activation and breast cancer progression estrogens (E2) and estrogen receptor (ERΑ) are essential for the normal function of the mammary gland. Aberrant regulation of ERΑ signaling is closely linked to breast cancer progression, making endocrine therapies using aromatase inhibitors, tamoxifen, and fulvestrant crucial for treating ER+ breast cancer. However, despite initial efficacy, many tumors develop resistance and advance to a lethal metastatic state. Recent findings highlight mutations in the ligand-binding domain (LBD) of the ERΑ gene as significant contributors to endocrine resistance and metastatic progression. Understanding the impact of these ERΑ LBD mutations is vital for developing new therapeutic approaches for aggressive breast cancer. N6- methyladenosine (M6A) modification, a common RNA modification, plays significant roles in normal biological processes and cancer. Although METTL3-catalyzed M6A modification is known to have oncogenic roles in breast cancer, its impact on ERΑ signaling, particularly in endocrine-resistant breast cancer, remains unclear. Our data reveal that phase-separated condensation of hormone receptors is critical for assembling enhancer transcriptional machinery, with ERΑ condensate formation facilitated by M6A modification on enhancer rnas (ernas) and the nuclear M6A reader YTHDC1. Inhibiting M6A modification or disrupting M6A binding to YTHDC1 leads to the dissolution of ERΑ condensates, decreased chromatin binding of ERΑ and its cofactors, and reduced transcriptional activity. Our preliminary studies on endocrine-resistant ERΑ mutants (Y537S and D538G) show that these mutations enable chromatin binding and transcriptional activation independent of E2. Unlike wild-type ERΑ, which only forms condensates upon E2 stimulation, these constitutively active ERΑ mutants form condensates without E2. Our findings further demonstrate that inhibiting M6A modification and disrupting condensation could suppress the ligand-independent activation of ERΑ mutants, suggesting that M6A-mediated ERΑ condensation drives the constitutively active signaling observed in advanced breast cancer. Thus, these findings lead US to propose an ERΑ signaling activation model linking M6A modification of erna, ERΑ condensation, enhancer assembly, and transactivation. We hypothesize that targeting M6A modification could inhibit the constitutive activation of these ERΑ mutants and overcome breast cancer progression. To test this hypothesis, we propose three specific aims: 1). Determine the role of M6A-ernas in E2-independent activation of endocrine-resistant ERΑ mutants. 2). Elucidate the mechanisms by which M6A- ernas promote E2-indpendent enhancer activation. 3). Evaluate the potential of targeting M6A modification as a therapeutic approach to combat constitutively active ERΑ signaling and tumor progression. Successful completion of these studies will have a broad impact by elucidating the role of erna M6A modification in ERΑ signaling activation and offering a novel therapeutic strategy to treat aggressive breast cancer by targeting M6A modification and mutant ER enhancer condensates to inhibit constitutive activation of mutant ERΑ.