Activation of ERß hijacks the splicing machinery to trigger R-loop formation in triple-negative breast cancer.

Triple-negative breast cancer (TNBC) is a subtype of breast cancer with aggressive behavior and poor prognosis. Current therapeutic options available for TNBC patients are primarily chemotherapy. With our evolving understanding of this disease, novel targeted therapies, including poly ADP-ribose polymerase (PARP) inhibitors, antibody-drug conjugates, and immune-checkpoint inhibitors, have been developed for clinical use. Previous reports have demonstrated the essential role of estrogen receptor ß (ERß) in TNBC, but the detailed molecular mechanisms downstream ERß activation in TNBC are still far from elucidated. In this study, we demonstrated that a specific ERß agonist, LY500307, potently induces R-loop formation and DNA damage in TNBC cells. Subsequent interactome experiments indicated that the residues 151 to 165 of U2 small nuclear RNA auxiliary factor 1 (U2AF1) and the Trp439 and Lys443 of ERß were critical for the binding between U2AF1 and ERß. Combined RNA sequencing and ribosome sequencing analysis demonstrated that U2AF1-regulated downstream RNA splicing of 5-oxoprolinase (OPLAH) could affect its enzymatic activity and is essential for ERß-induced R-loop formation and DNA damage. In clinical samples including 115 patients from The Cancer Genome Atlas (TCGA) and 32 patients from an in-house cohort, we found a close correlation in the expression of ESR2 and U2AF1 in TNBC patients. Collectively, our study has unraveled the molecular mechanisms that explain the therapeutic effects of ERß activation in TNBC, which provides rationale for ERß activation-based single or combined therapy for patients with TNBC.

The genomic and immunogenomic landscape of mechanics pathway informs clinical prognosis and response to mechanotherapy.

Mechanics shape cell and tissue plasticity and maintain their homeostasis. In cancers, mechanical signals regulate cancer hallmarks via mechanotransduction pathways, such as proliferation, metastasis and metabolic reprogramming. However, comprehensive characterization of mechanotransduction pathway genes and their clinical relevance across different cancer types remains untouched. Herein, we systematically portrayed the alterations of mechanotransduction pathway genes across 31 cancer types using The Cancer Genome Atlas (TCGA) databases. All the cancer types could be categorized into 6 subtypes based upon the transcriptional pattern of mechanics pathway genes. Each subtype has its own unique molecular expression pattern, mutation landscapes, immune infiltrates, and patient clinical outcome. We further found that the responses of two subtypes of cancers, one with the optimal outcome and the other with the worst prognosis, to a classical mechanotherapeutic agent (Fasudil, RhoA/ROCK inhibitor) were totally different, indicating that our cancer stratification system based upon mechanotransduction pathway genes could inform clinical responses of patients to mechanotherapeutic agents. Collectively, our study provides a novel pan-cancer landscape of the mechanotransduction pathways and underscores its potential clinical significance in the prediction of clinical prognosis and therapeutic responses to mechanotherapy among cancer patients.