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cGAS restricts PARP1-mediated microhomology-mediated end joining by suppressing poly-ADP-ribosylation

Cell Death & Differentiation (2025)Cite this article

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Abstract

Repair of DNA double-strand breaks (DSBs) is essential for cells to maintain genome stability and cell survival. While cyclic GMP-AMP synthase (cGAS) is best known for its role in innate immunity, emerging evidence reveals that it plays regulatory roles in DNA damage response. In this study, we demonstrate that cGAS suppresses PARP1-mediated poly(ADP-ribose) (PAR) formation at both double-stranded DNA (dsDNA) and DNA:RNA hybrids. As a result, cGAS deficiency enhances PARP1-mediated microhomology-mediated end joining (MMEJ). Since MMEJ competes with transcription-coupled homologous recombination (TC-HR) at actively transcribed genomic regions, cGAS-mediated suppression of MMEJ consequently leads to efficient TC-HR with increased recruitment of RAD52 and RAD51. Mechanistically, the zinc finger domain of cGAS binds PAR, inhibiting PARP1 activation. In prostate cancer cells, loss of cGAS increases dependency on PARP1, rendering them more sensitive to PARP inhibitors. Collectively, our findings uncover a noncanonical role for cGAS in negatively regulating PARP1-mediated MMEJ and suggest its potential as a therapeutic biomarker in prostate cancer.

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Fig. 1: cGAS negatively regulates PARP1-mediated PARylation and MMEJ repair.
Fig. 2: The zinc finger mediated PAR binding of cGAS is required to prevent PARP1 activation and MMEJ.
Fig. 3: cGAS indirectly promotes TC-HR through inhibiting PARP1-medidated MMEJ.
Fig. 4: Loss of cGAS impairs resolution of γH2AX and R-Loops at DSBs at transcriptionally active sites.
Fig. 5: cGAS deficiency creates vulnerability in prostate cancer cells.
Fig. 6: A working model for suppression of PARP1 activation by cGAS at transcriptionally active genomic regions.

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All data is contained within the manuscript and/or supplementary files. The original western blot images are provided in the Supplementary File.

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Acknowledgements

This work was supported by grants from National Institutes of Health R01CA262524 (LJ), R01CA279410 (LJ), R01CA282939 (LL); Department of Defense W81XWH-22-1-0477 (LJ).

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Authors and Affiliations

  1. Department of Urology, Brigham and Women’s Hospital & Harvard Medical School, Boston, MA, USA

    Haibo Yang, Jing Luo, Fu Gui & Li Jia

  2. Departments of Molecular Genetics and Microbiology, School of Medicine, Duke University, Durham, NC, USA

    Boya Gao, Laiyee Phoon & Li Lan

  3. Department of Biochemistry and Structural Biology, University of Texas Health Science Center at San Antonio, San Antonio, TX, USA

    Bo Wu, Wenjing Li & Weixing Zhao

  4. Center for Immunology and Inflammatory Diseases, Division of Rheumatology, Allergy, and Immunology, Massachusetts General Hospital, Harvard Medical School, Boston, MA, USA

    Xueping Zhu

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Contributions

HY conducted the major experiments and data analysis. BG, BW, WL, XZ, LP, JL, and FG participated in the experiments and data analysis. WZ participated in experimental design and data analysis. LJ and LL provided overall experimental guidance. All authors acknowledge their specific contributions and have reviewed the manuscript.

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Yang, H., Gao, B., Wu, B. et al. cGAS restricts PARP1-mediated microhomology-mediated end joining by suppressing poly-ADP-ribosylation. Cell Death Differ (2025). https://doi.org/10.1038/s41418-025-01637-x

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