HELZ-BRCA2 complex resolves R-loops to drive transcription-coupled homologous recombination.

Abstract

R-loops are transcription-induced, three-stranded nucleic acid structures that, if not properly resolved, can disrupt DNA repair and compromise genome stability. BRCA2, a tumor suppressor vital for homologous recombination (HR), also contributes to R-loop regulation, though the underlying mechanisms remain poorly understood. Here, we identify HELZ as a direct BRCA2 interactor and characterize it as an ssRNA-specific R-loop resolvase. BRCA2 enhances HELZ helicase activity and promotes its recruitment to R-loops. Importantly, HELZ resolves R-loops at DNA double-strand breaks, enabling efficient DNA end resection and HR, particularly within transcriptionally active genomic regions. We further demonstrate that HELZ is critical for R-loop clearance in cancers with elevated transcriptional activity and R-loop accumulation, such as estrogen receptor-positive breast cancer, where it becomes essential for cell survival under estrogen-induced transcriptional stress. These findings establish HELZ as a BRCA2-dependent regulator of R-loop homeostasis and identify it as a potential biomarker and therapeutic target in R-loop-driven malignancies.