The Roles of Cullin RING Ligases and the Anaphase Promoting Complex/Cyclosome in the Regulation of DNA Double Strand Break Repair

Abstract

Historically, genome maintenance has been viewed as the largely independent activities of (1) ubiquitin ligases driving unidirectional cell cycle progression and, (2) the activity of cellular checkpoints that monitor DNA integrity and DNA replication. It is well established that the DNA damage response (DDR) checkpoint machinery promotes the activation of repair mechanisms in addition to opening a window for repair. Emerging evidence demonstrates an integrated network of the central cell cycle driving E3 ubiquitin ligases and the checkpoint machinery, as well as deubiquitinating enzymes, which intermittently cooperate and antagonize one another to define windows of checkpoint and repair activities to optimize genome stability and cellular health. A growing number of components of the ubiquitin machinery are involved in the DDR. Herein, we focus on the regulation of cell cycle checkpoints and the DNA repair mechanisms for double strand breaks (DSBs) by the coordinated activities of Cullin RING ligases (CRLs) and the anaphase promoting complex/cyclosome (APC/C). Cdh1 activity upon replication stress and during recovery from APC/C Cdh1 activation during the G2 DDR. In G2 APC/C Cdh1 targets Plk1 for degradation, while USP28 prevents it from targeting Claspin. USP28 also stabilizes 53BP1 after DNA damage as well, possibly from APC/C Cdh1 (represented by, “ ? ” ). Chk1 activation requires Claspin function, which is protected from SCF β TrCP -mediated degradation by USP29 and USP7. USP20 stabilizes both Claspin and Rad17 to promote Chk1 activity, possibly from APC/C Cdh1 ( “ ? ” ) as they are both substrates of the ligases. ATR and Chk1 prevent checkpoint recovery by inhibiting the Plk1 activators Aurora and Bora. Irreversible checkpoint activation is prevented by the degradation of active Chk1 by SCF Fbx6 . USP7 prevents the complete destabilization of Chk1. The inset shows a potential feedback loop between ATR-Chk1 and the Fanconi pathway. FANCM promotes Chk1 activation (indirectly via ATR). Chk1 promotes FANCM-promoted FANCD2 monoubiquitination. In turn, FANCD2-Ub promotes the CRL4 Cdt2 -mediated degradation of Chk1. USP1 deubiquitinates FANCD2, stabilizing Chk1. The negative feedback loop favors silencing of Chk1 due to the inactivation of USP1 upon DNA damage.