Abstract
Cell cycle progression in mammals is modulated by two ubiquitin ligase complexes, CRL4 and SCF, which facilitate degradation of chromatin substrates involved in the regulation of DNA replication. One member of the CRL4 complex, the WD-40 containing protein RepID (DCAF14/PHIP), selectively binds and activates a group of replication origins. Here we show that RepID recruits the CRL4 complex to chromatin prior to DNA synthesis, thus playing a crucial architectural role in the proper licensing of chromosomes for replication. In the absence of RepID, cells rely on the alternative ubiquitin ligase, SKP2-containing SCF, to progress through the cell cycle. RepID depletion markedly increases cellular sensitivity to SKP2 inhibitors, which triggered massive genome re-replication. Both RepID and SKP2 interact with distinct, non-overlapping groups of replication origins, suggesting that selective interactions of replication origins with specific CRL components execute the DNA replication program and maintain genomic stability by preventing re-initiation of DNA replication.
Highlights
Cell cycle progression in mammals is modulated by two ubiquitin ligase complexes, CRL4 and SCF, which facilitate degradation of chromatin substrates involved in the regulation of DNA replication
CRL4-mediated ubiquitination of the licensing complex member CDT1 requires a DDB1/ CUL4-associated factor (DCAF), CDT213,33, which interacts with CUL4 and DDB1 to facilitate the degradation of CDT1 in a CDC48/p97-dependent pathway[34,35]
CDT1 is required for origin licensing and mitosis[50,51], and SET8 degradation is essential for proper S-phase progression and prevention of G2/M checkpoint activation, spontaneous DNA damage and rereplication[20,52,53]
Summary
Cell cycle progression in mammals is modulated by two ubiquitin ligase complexes, CRL4 and SCF, which facilitate degradation of chromatin substrates involved in the regulation of DNA replication. High CDK activity prevents the assembly of new complexes after the initial pre-RCs dissociate from replicated chromatin[2]. Cullin-RING E3 ubiquitin ligases (CRLs) mediate ubiquitination of proteins required for cell cycle control and DNA replication and play key roles in the regulatory interactions that maintain genomic stability[11,12]. CDT1, a licensing factor in preRC, is targeted by CRL4 (DDB1-CUL4-RBX1 Cullin-RING ubiquitin Ligase 4) during the transition between the G1 and S phases of the cell cycle, and by CRL1 (SKP1-CUL1-F-box, or SCF) during S and G2 phase[13,14,15,16]. DCAFs often recognize substrates that contain PCNA (proliferating cell nuclear antigen)-binding motifs (PIP boxes), but CUL4 is detected on chromatin during the G1 phase of the cell cycle[36], suggesting that it can be recruited to chromatin without PCNA
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