Stalled replication forks, susceptible to nucleolytic threats, necessitate protective mechanisms involving pivotal factors such as the tumor suppressors BRCA1 and BRCA2. Here, we demonstrate that, upon replication stress, RNA polymerase II (RNAPII) is recruited to stalled forks, actively promoting the transient formation of RNA-DNA hybrids. These hybrids act as safeguards, preventing premature engagement by the DNA2 nuclease and uncontrolled DNA2-mediated degradation of nascent DNA. Furthermore, we provide evidence that DExD box polypeptide 39A (DDX39A), serving as an RNA-DNA resolver, unwinds these structures and facilitates regulated DNA2 access to stalled forks. This orchestrated process enables controlled DNA2-dependent stalled fork processing and restart. Finally, we reveal that loss of DDX39A enhances stalled fork protection in BRCA1/2-deficient cells, consequently conferring chemoresistance. Our results suggest that the dynamic regulation of RNA-DNA hybrid formation at stalled forks by RNAPII and DDX39A precisely governs the timing of DNA2 activation, contributing to stalled fork protection, processing, and restart, ultimately promoting genome stability.
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http://dx.doi.org/10.1016/j.molcel.2024.11.034 | DOI Listing |
Mol Cell
December 2024
Department of Gynecology, The Second Affiliated Hospital, Zhejiang University School of Medicine, 310058 Hangzhou, China; Department of Cell Biology, Zhejiang University School of Medicine, 310058 Hangzhou, China. Electronic address:
Stalled replication forks, susceptible to nucleolytic threats, necessitate protective mechanisms involving pivotal factors such as the tumor suppressors BRCA1 and BRCA2. Here, we demonstrate that, upon replication stress, RNA polymerase II (RNAPII) is recruited to stalled forks, actively promoting the transient formation of RNA-DNA hybrids. These hybrids act as safeguards, preventing premature engagement by the DNA2 nuclease and uncontrolled DNA2-mediated degradation of nascent DNA.
View Article and Find Full Text PDFMol Cell
December 2024
Department of Radiation Medicine, School of Basic Medical Sciences, Peking University International Cancer Institute, Institute of Advanced Clinical Medicine, State Key Laboratory of Molecular Oncology, Peking University Health Science Center, Beijing 100191, China; Department of Gastrointestinal Translational Research, Peking University Cancer Hospital, Beijing 100142, China. Electronic address:
Safeguarding replication fork stability in transcriptionally active regions is crucial for precise DNA replication and mutation prevention. Here, we discover the pervasive existence of replication fork-associated RNA-DNA hybrids (RF-RDs) in transcriptionally active regions of human cells. These hybrids function as protective barriers, preventing DNA2-mediated nascent DNA degradation and replication fork collapse under replication stress.
View Article and Find Full Text PDFMethods Mol Biol
December 2024
Genome Integrity and Cancers, UMR 9019 CNRS, Université-Paris-Saclay, Gustave Roussy, Villejuif, France.
Homologous recombination (HR) is a high-fidelity DNA repair pathway that uses a homologous DNA sequence as a template. Recombinase proteins are the central HR players in the three kingdoms of life. RecA/RadA/Rad51 assemble on ssDNA, generated after the processing of double-strand breaks or stalled replication forks into an active and dynamic presynaptic helical nucleofilament.
View Article and Find Full Text PDFPNAS Nexus
December 2024
Amity Institute of Biotechnology, Amity University Haryana, Gurgaon, Haryana 122413, India.
In , RecA plays a central role in the rescue of stalled replication forks, double-strand break (DSB) repair, homologous recombination (HR), and induction of the SOS response. While the RecA-dependent pathway is dominant, alternative HR pathways that function independently of RecA do exist, but relatively little is known about the underlying mechanism. Several studies have documented that a variety of proteins act as either positive or negative regulators of RecA to ensure high-fidelity HR and genomic stability.
View Article and Find Full Text PDFCell Rep
December 2024
Department of Oncology, Faculty of Medicine & Dentistry, University of Alberta, 11560 University Avenue, Edmonton, AB T6G 1Z2, Canada; Biophysics Department, Faculty of Science, Cairo University, Giza 12613, Egypt. Electronic address:
Uncontrolled degradation and collapse of stalled replication forks (RFs) are primary sources of genomic instability, yet the molecular mechanisms for protecting forks from degradation/collapse remain to be fully elaborated. Here, we show that polynucleotide kinase-phosphatase (PNKP) localizes at stalled forks and protects stalled forks from excessive degradation. The loss of PNKP results in nucleolytic degradation of nascent DNA at stalled RFs.
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