Nuclear receptor ESRRA promotes ERα-positive breast cancer through dual action on super enhancers and promoters to regulate gene transcriptional programs.

Estrogen-Related Receptor Alpha (ESRRA) is an orphan nuclear receptor that plays a pivotal role in regulating cellular metabolism, mitochondrial biogenesis, and energy homeostasis through transcriptional control. It has been implicated in diverse physiological processes and diseases, including cancer. However, the transcriptional programs governed by ESRRA and the underlying molecular mechanisms remain incompletely understood. Here, we demonstrate that ESRRA serves as a central regulator in orchestrating the transcriptional activation of estrogen receptor α(ERα)-occupied super enhancers (ERSEs) and cognate ERα -target genes. In parallel, ESRRA represses the expression of cytosolic RNA sensors RIG1 and MDA5, thereby attenuating type I interferon (IFN) signaling and type I IFN-stimulated genes. In terms of mechanism, ESRRA is recruited to ERSEs together with ERα in response to estrogen and their binding to ERSEs occurs in a mutually dependent manner. In contrast, ESRRA directly binds to the promoter regions of RIG1 and MDA5 to suppress their expression. Consistent with these findings, pharmacological inhibition of ESRRA using its inverse agonist XCT790 suppressed estrogen/ERα-induced gene transcription while enhancing type I IFN pathway and antitumor immunity, thereby restraining ERα-positive breast cancer cell growth both in vitro and in vivo. Combination treatment with XCT790 and endocrine therapies, including the ERα antagonist Tamoxifen or degrader Fulvestrant, produced synergistic antitumor effects. Furthermore, co-treatment with XCT790 and tamoxifen re-sensitized Tamoxifen-resistant ERα-positive breast cancer cells to Tamoxifen treatment. In addition, XCT790 treatment augmented the therapeutic efficacy of chemotherapeutic agents such as Doxorubicin in suppressing ERα-positive breast cancer cell growth both in vitro and in vivo. In summary, our findings reveal that ESRRA is a pivotal regulator of ERSEs and estrogen/ERα-target gene activation, as well as the type I IFN signaling pathway, highlighting its potential as a promising therapeutic target in ERα-positive breast cancer in the clinic.