Liquid-liquid phase separation in DNA double-strand breaks repair

Abstract

DNA double-strand breaks (DSBs) are the fatal type of DNA damage mostly induced by exposure genome to ionizing radiation or genotoxic chemicals. DSBs are mainly repaired by homologous recombination (HR) and nonhomologous end joining (NHEJ). To repair DSBs, a large amount of DNA repair factors was observed to be concentrated at the end of DSBs in a specific spatiotemporal manner to form a repair center. Recently, this repair center was characterized as a condensate derived from liquid-liquid phase separation (LLPS) of key DSBs repair factors. LLPS has been found to be the mechanism of membraneless organelles formation and plays key roles in a variety of biological processes. In this review, the recent advances and mechanisms of LLPS in the formation of DSBs repair-related condensates are summarized.

Fig. 1. Principles of LLPS.

A Biomolecular condensates exhibit liquid-like characteristics, including the capability of FRAP, fusion and fission events, which are influenced by concentration, salt, temperature, and pH. B LLPS of biomolecules are driven by multivalent binding interaction (left), modular domains (middle), and intrinsically disordered regions (right). C The regulators of LLPS include RNA, posttranslational modifications, and ATP.

Fig. 2. Functions and mechanisms of condensates in DSBs repair.

A dilncRNAs induced 53BP1 condensates recruit and activate p53; AHNAK reduces the LLPS potency of 53BP1 by inhibiting 53BP1 oligomerization. B PAR accelerates FUS phase separation at DSBs site, which recruits Ku70/80, NBS1, SFPQ, 53BP1, and other repair factors; poly(ADP-ribose) glycohydrolase PARG is a suppressor of FUS condensation. C The interaction between MDC1 and pre-rRNA increases the multi-valency for MDC1 phase separation, resulting in MDC1 condensation at DSBs site and the recruitment of BRCA1, TopBP1; RNA Polymerase I inhibitor suppresses MDC1 condensation by diminishing pre-rRNA synthesis. D PAR-induced DDX3X condensation is essential for DDX3X accumulation at DSBs site. E Yeast RAD52 formed liquid-like condensates to cluster γ-H2A.X foci. F NONO condensates recruit ribosomal protein P0 (RPLP0), nuclear EGFR (nEGFR), and DNA-PK to enhance the DSB-induced activation and phosphorylation of DNA-PK. G MRNIP condensates recruit and concentrate MRN complex to DSB site to accelerate DSB sensing and end resection. H Histone methyltransferase SUVR2 in Medicago truncatula undergoes LLPS at DSBs site; it interacts with MtRAD51 and drives its phase separation, which enhances the stability of MtRAD51 proteins to facilitate error-free homologous recombination repair.