期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2015
卷号：112
期号：11
页码：E1210-E1219
DOI：10.1073/pnas.1418335112
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：SignificanceDNA damage response is essential to preserve genomic stability. Here we report a previously unknown function for the baculovirus inhibitor of apoptosis protein repeat (BIR)-containing ubiquitin-conjugating enzyme (BRUCE) and ubiquitin-specific peptidase 8 (USP8) as activators of DNA damage response. They drive recruitment of the breast cancer susceptibility gene C terminus-repeat inhibitor of human telomerase reverse transcriptase expression (BRIT1) to DNA breaks by promoting BRIT1 deubiquitination. In contrast to the established regulation of repair foci formation by ubiquitination, our data demonstrate deubiquitination as a previously unrecognized critical step in promoting foci formation. Furthermore, we define a pathway by which BRUCE and USP8 activate BRIT1-switch/sucrose nonfermentable (SWI-SNF)-mediated chromatin relaxation to maximize cell responsiveness to DNA damage. Thus, BRUCE represents a novel component in safeguarding genomic stability and a promising therapeutic target in diseases of genomic instability such as cancer. The DNA damage response (DDR) is crucial for genomic integrity. BRIT1 (breast cancer susceptibility gene C terminus-repeat inhibitor of human telomerase repeat transcriptase expression), a tumor suppressor and early DDR factor, is recruited to DNA double-strand breaks (DSBs) by phosphorylated H2A histone family, member X ({gamma}-H2AX), where it promotes chromatin relaxation by recruiting the switch/sucrose nonfermentable (SWI-SNF) chromatin remodeler to facilitate DDR. However, regulation of BRIT1 recruitment is not fully understood. The baculovirus IAP repeat (BIR)-containing ubiquitin-conjugating enzyme (BRUCE) is an inhibitor of apoptosis protein (IAP). Here, we report a non-IAP function of BRUCE in the regulation of the BRIT1-SWI-SNF DSB-response pathway and genomic stability. We demonstrate that BRIT1 is K63 ubiquitinated in unstimulated cells and that deubiquitination of BRIT1 is a prerequisite for its recruitment to DSB sites by {gamma}-H2AX. We show mechanistically that BRUCE acts as a scaffold, bridging the ubiquitin-specific peptidase 8 (USP8) and BRIT1 in a complex to coordinate USP8-catalyzed deubiquitination of BRIT1. Loss of BRUCE or USP8 impairs BRIT1 deubiquitination, BRIT1 binding with {gamma}-H2AX, the formation of BRIT1 DNA damage foci, and chromatin relaxation. Moreover, BRUCE-depleted cells display reduced homologous recombination repair, and BRUCE-mutant mice exhibit repair defects and genomic instability. These findings identify BRUCE and USP8 as two hitherto uncharacterized critical DDR regulators and uncover a deubiquitination regulation of BRIT1 assembly at damaged chromatin for efficient DDR and genomic stability.
关键词：inhibitor of apoptosis ; DNA DSB repair ; BRUCE ; BRIT1
