Multisubunit protein assemblies offer integrated functionalities for efficient cell signal transduction control. One example of such protein assemblies, the BRCA1-A macromolecular complex, couples ubiquitin recognition and metabolism and promotes cellular responses to DNA damage. Specifically, the BRCA1-A complex not only recognizes Lys 63 -linked ubiquitin (K63-Ub) adducts at the damaged chromatin but is endowed with K63-Ub deubiquitylase (DUB) activity. To explore how the BRCA1-A DUB activity contributes to its function at DNA double strand breaks (DSBs), we used RNAi and genome editing approaches to target BRCC36, the protein subunit that confers the BRCA1-A complex its DUB activity. Intriguingly, we found that the K63-Ub DUB activity, although dispensable for maintaining the integrity of the macromolecular protein assembly, is important in enforcing the accumulation of the BRCA1-A complex onto DSBs. Inactivating BRCC36 DUB attenuated BRCA1-A functions at DSBs and led to unrestrained DSB end resection and hyperactive DNA repair. Together, our findings uncover a pivotal role of BRCC36 DUB in limiting DSB processing and repair and illustrate how cells may physically couple ubiquitin recognition and metabolizing activities for fine tuning of DNA repair processes.
Active hydrolysis of ubiquitin polymers by deubiquitylases (DUBs)2 has emerged as important biochemical processes that underlie diverse signal transduction pathways, including cell responses to DNA damage (1). To date, around 94 human DUBs have been identified and are classified into five families: ubiquitin C-terminal hydrolases, ubiquitin-specific proteases, ovarian tumor proteases, Josephins, and JAB1/MPN/MOV4 metalloproteases. Notably, the JAB1/MPN/MOV4 metalloprotease family members are zinc-dependent metalloproteases, and the other families are cysteine proteases (1).BRCC36, originally reported as the BRCA1/BRCA2-containing complex subunit 36 (2), is endowed with DUB activity for lysine 63-linked ubiquitin polymers (K63-Ub). BRCC36 DUB relies on its zinc-dependent JAB1/MPN/MOV4 metalloprotease domain (3) and its interaction with Abraxas/KIAA0157 (3-5). Although BRCC36 forms distinct nuclear and cytoplasmic complexes (5, 6) and plays pleiotropic roles during cell proliferation, the K63-Ub DUB is arguably best known for its strong links with the breast and ovarian susceptible gene product BRCA1 in DNA damage responses (DDRs). Indeed, BRCC36 resides within the BRCA1-A macromolecular protein complex, which comprises the ubiquitin-binding protein RAP80, BRCC45/BRE, Abraxas/CCDC98, Merit40/NBA1, and BRCA1. The BRCA1-A complex is targeted to chromatin domains surrounding DNA double strand breaks (DSBs) by the ubiquitin-binding protein RAP80, which preferentially binds to K63-Ub adducts generated by the ubiquitin-conjugating enzyme UBC13 (3, 7-12). Abraxas plays a major scaffolding role to support the integrity of the BRCA1-A assembly and directly anchors the tumor suppressor BRCA1 via a phosphorylation-dependent interaction (13-15). Indeed, BRCA1, via it...