CiRS-7 Enhances the Liquid-liquid Phase Separation of miRISC and Promotes DNA Damage Repair.

Noncoding RNAs have been found to play important roles in DNA damage repair, whereas the participation of circRNA remains undisclosed. Here, we characterized ciRS-7, a circRNA containing over 70 putative miR-7-binding sites, as an enhancer of miRISC condensation and DNA repair. Both in vivo and in vitro experiments confirmed the condensation of TNRC6B and AGO2, two core protein components of human miRISC. Moreover, overexpressing ciRS-7 largely increased the condensate number of TNRC6B and AGO2 in cells, while silencing ciRS-7 reduced it. Additionally, miR-7 overexpression also promoted miRISC condensation. Consistent with the previous report that AGO2 participated in RAD51-mediated DNA damage repair, the overexpression of ciRS-7 significantly promoted irradiation-induced DNA damage repair by enhancing RAD51 recruitment. Our results uncover a new role of circRNA in liquid-liquid phase separation and provide new insight into the regulatory mechanism of ciRS-7 on miRISC function and DNA repair.

RAP80 phase separation at DNA double-strand break promotes BRCA1 recruitment.

RAP80 has been characterized as a component of the BRCA1-A complex and is responsible for the recruitment of BRCA1 to DNA double-strand breaks (DSBs). However, we and others found that the recruitment of RAP80 and BRCA1 were not absolutely temporally synchronized, indicating that other mechanisms, apart from physical interaction, might be implicated. Recently, liquid-liquid phase separation (LLPS) has been characterized as a novel mechanism for the organization of key signaling molecules to drive their particular cellular functions. Here, we characterized that RAP80 LLPS at DSB was required for RAP80-mediated BRCA1 recruitment. Both cellular and in vitro experiments showed that RAP80 phase separated at DSB, which was ascribed to a highly disordered region (IDR) at its N-terminal. Meanwhile, the Lys63-linked poly-ubiquitin chains that quickly formed after DSBs occur, strongly enhanced RAP80 phase separation and were responsible for the induction of RAP80 condensation at the DSB site. Most importantly, abolishing the condensation of RAP80 significantly suppressed the formation of BRCA1 foci, encovering a pivotal role of RAP80 condensates in BRCA1 recruitment and radiosensitivity. Together, our study disclosed a new mechanism underlying RAP80-mediated BRCA1 recruitment, which provided new insight into the role of phase separation in DSB repair.

The effect of recombinant human epidermal growth factor on radiation dermatitis in rectal and anal cancer patients: a self-controlled study.

BACKGROUND: Our previous study reported that recombinant human epidermal growth factor (rhEGF)-triggered EGFR internalization promoted radioresistance. Here, we aimed to evaluate the effect of rhEGF on the skin protection of rectal and anal cancer patients receiving radiotherapy. METHODS: One hundred and ninety-three rectal and anal cancer patients who received radiotherapy were prospectively enrolled from January 2019 to December 2020. To perform self-controlled study, the left and right pelvic skin area (separated by midline) were randomly assigned to the rhEGF and control side. The association between radiation dermatitis and factors including rhEGF, the dose of radiotherapy and tumor distance from anal edge were analyzed. RESULTS: Among 193 enrolled patients, 41 patients (21.2%) did not develop radiation dermatitis, and 152 patients (78.8%) suffered radiation dermatitis on at least one side of pelvic skin at the end of radiotherapy. For the effect on radiation dermatitis grade, rhEGF had improved effect on 6 (4.0%) patients, detrimental effect on 2 (1.3%) patients, and no effect on 144 (94.7%) patients. Whereas for the effect on radiation dermatitis area, rhEGF showed improved effect on the radiation dermatitis area of 46 (30.2%) patients, detrimental effect on 15 (9.9%) patients, and no effect on 91 (59.9%) patients. The radiation dermatitis area of rhEGF side was significantly smaller than that of control side (P = 0.0007). CONCLUSIONS: rhEGF is a skin protective reagent for rectal and anal cancer patients receiving radiotherapy. TRIAL REGISTRATION: Chinese Clinical Trial Registry identifier: ChiCTR1900020842; Date of registration: 20/01/2019.

DNA damage-induced paraspeckle formation enhances DNA repair and tumor radioresistance by recruiting ribosomal protein P0.

Paraspeckles are mammal-specific membraneless nuclear bodies that participate in various biological processes. NONO, a central paraspeckle component, has been shown to play pivotal roles in DNA double-strand breaks (DSB) repair, whereas its underlying mechanism needs to be further disclosed. Here, using co-immunoprecipitation and mass spectrum, we identified ribosomal protein P0 (RPLP0) as a DSB-induced NONO-binding protein; RPLP0 binds to the RRM1 and RRM2 domains of NONO. Similar to NONO, RPLP0 enhances non-homologous end joining-mediated DSB repair, which was ascribed to a ribosome-independent manner. Interestingly, paraspeckles were induced as early as 15 min after irradiation; it further recruited nuclear RPLP0 to enhance its interaction with NONO. Radiation-induced NONO/RPLP0 complex subsequently anchored at the damaged DNA and increased the autophosphorylation of DNA-PK at Thr2609, thereby enhancing DSB repair. Consistently, in vivo and in vitro experiments showed that depletion of NONO sensitizes tumor cells to radiation. For patients with locally advanced rectal cancer, NONO expression was remarkably increased in tumor tissues and correlated with a poor response to radiochemotherapy. Our findings suggest a pivotal role of radiation-induced paraspeckles in DNA repair and tumor radioresistance, and provide a new insight into the ribosome-independent function of ribosomal proteins.