Topoisomerase IIβ-binding protein 1 (TOPBP1) participates in DNA replication and DNA damage response; however, its role in DNA repair and relevance for human cancer remain unclear. Here, through an unbiased small interfering RNA screen, we identified and validated TOPBP1 as a novel determinant whose loss sensitized human cells to olaparib, an inhibitor of poly(ADP-ribose) polymerase. We show that TOPBP1 acts in homologous recombination (HR) repair, impacts olaparib response, and exhibits aberrant patterns in subsets of human ovarian carcinomas. TOPBP1 depletion abrogated RAD51 loading to chromatin and formation of RAD51 foci, but without affecting the upstream HR steps of DNA end resection and RPA loading. Furthermore, TOPBP1 BRCT domains 7/8 are essential for RAD51 foci formation. Mechanistically, TOPBP1 physically binds PLK1 and promotes PLK1 kinase-mediated phosphorylation of RAD51 at serine 14, a modification required for RAD51 recruitment to chromatin. Overall, our results provide mechanistic insights into TOPBP1's role in HR, with potential clinical implications for cancer treatment.

Danish Cancer Society Research Center DK 2100 Copenhagen Denmark

Danish Cancer Society Research Center DK 2100 Copenhagen Denmark Department of Medical Biochemistry and Biophysics Science For Life Laboratory Division of Translational Medicine and Chemical Biology Karolinska Institute 17121 Solna Sweden

Danish Cancer Society Research Center DK 2100 Copenhagen Denmark Institute of Molecular and Translational Medicine Faculty of Medicine and Dentistry Palacky University 779 00 Olomouc Czech Republic

Danish Cancer Society Research Center DK 2100 Copenhagen Denmark Institute of Molecular and Translational Medicine Faculty of Medicine and Dentistry Palacky University 779 00 Olomouc Czech Republic Department of Medical Biochemistry and Biophysics Science For Life Laboratory Division of Translational Medicine and Chemical Biology Karolinska Institute 17121 Solna Sweden

Danish Cancer Society Research Center DK 2100 Copenhagen Denmark Novo Nordisk Foundation Center for Protein Research University of Copenhagen DK 2200 Copenhagen Denmark

Department of Biology University of Copenhagen DK 2200 Copenhagen Denmark

Department of Pathology Familial and Hereditary Cancer Unit University Hospital 35010 Las Palmas de Gran Canaria Spain

The Sir William Dunn School of Pathology University of Oxford Oxford OX1 3RE England UK

J Cell Biol. 2016 Feb 1;212(3):263-6. doi: 10.1083/jcb.201601028. PubMed

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