Phase separation in DNA double-strand break response

Abstract

DNA double-strand break (DSB) is the most dangerous type of DNA damage, which may lead to cell death or oncogenic mutations. Homologous recombination (HR) and nonhomologous end-joining (NHEJ) are two typical DSB repair mechanisms. Recently, many studies have revealed that liquid-liquid phase separation (LLPS) plays a pivotal role in DSB repair and response. Through LLPS, the crucial biomolecules are quickly recruited to damaged sites with a high concentration to ensure DNA repair is conducted quickly and efficiently, which facilitates DSB repair factors activating downstream proteins or transmitting signals. In addition, the dysregulation of the DSB repair factor's phase separation has been reported to promote the development of a variety of diseases. This review not only provides a comprehensive overview of the emerging roles of LLPS in the repair of DSB but also sheds light on the regulatory patterns of phase separation in relation to the DNA damage response (DDR).

Keywords: DNA damage response (DDR); DNA double-strand break (DSB); condensates; homologous recombination (HR); liquid-liquid phase separation (LLPS); nonhomologous end-joining (NHEJ).

Figure 1.

DNA repair factors LLPS involved in HR and NHEJ processes. HR occurs in cell S and G2 phases. (a) MRNIP droplets rapidly migrate to the sites of DNA damage, leading to the activation of downstream proteins and facilitating the autophosphorylation of ATM. MRE11-mediated resection leads to the formation of single-stranded DNA (ssDNA) tails. RPAs bind to the tails to protect them. BRCA2 assists RAD51 in displacing RPA. RAD51-ssDNA invades the homologous sequence, leading to synthesis of the DNA strands. (b) In this process, the assistance of PAR facilitates the essential role of FUS phase separation in the efficient assembly of DNA repair complexes and is necessary for recruiting DDR factors to DNA damage sites. (c) RAD52 droplets collaborate with various types of nuclear filaments to facilitate the formation of DNA repair centers. NHEJ is active throughout the cell cycle. Ku70/80s first quickly recognize DSB sites and bind them to promote DNA-PK formation. (d) NONO enhances DNA-PK phosphorylation at T2609 in response to DNA damage by generating high-concentration droplets. (e) 53BP1 has the ability to form condensates and subsequently recruit downstream factors such as RIF1, PTIP, and the shieldin complex.