The 53BP1-RIF1 pathway antagonizes resection of DNA broken ends and confers PARP inhibitor sensitivity on BRCA1-mutated tumors. However, it is unclear how this pathway suppresses initiation of resection. Here, we identify ASF1 as a partner of RIF1 via an interacting manner similar to its interactions with histone chaperones CAF-1 and HIRA. ASF1 is recruited to distal chromatin flanking DNA breaks by 53BP1-RIF1 and promotes non-homologous end joining (NHEJ) using its histone chaperone activity. Epistasis analysis shows that ASF1 acts in the same NHEJ pathway as RIF1, but via a parallel pathway with the shieldin complex, which suppresses resection after initiation. Moreover, defects in end resection and homologous recombination (HR) in BRCA1-deficient cells are largely suppressed by ASF1 deficiency. Mechanistically, ASF1 compacts adjacent chromatin by heterochromatinization to protect broken DNA ends from BRCA1-mediated resection. Taken together, our findings identify a RIF1-ASF1 histone chaperone complex that promotes changes in high-order chromatin structure to stimulate the NHEJ pathway for DSB repair.
Bibliographical noteFunding Information:
We thank Weidong Wang for his advice and revisions to the manuscript. We thank the Analytical Instrumentation Center in Peking University, the Imaging Core and Mass-spectrum Core at the National Center for Protein Sciences at Peking University for imaging and mass-spectrum analysis. U2OS-265 cells were a gift from Daniel Durocher under a permission of Roger A. Greenberg. This work was supported in part by Beijing Outstanding Young Scientist Program (BJJWZYJH01201910001005) to Q.L., the National Key Research and Development Program of China (2021YFA0909304) to D.X., and the National Natural Science Foundation of China (31870807 and 32071285 to R.G., and 82002991 to S.F.).
© 2022, The Author(s).