Proteasome-dependent degradation of replisome components regulates faithful DNA replication

Abstract

The replication machinery, or the replisome, collides with a variety of obstacles during the normal process of DNA replication. In addition to damaged template DNA, numerous chromosome regions are considered to be difficult to replicate owing to the presence of DNA secondary structures and DNA-binding proteins. Under these conditions, the replication fork stalls, generating replication stress. Stalled forks are prone to collapse, posing serious threats to genomic integrity. It is generally thought that the replication checkpoint functions to stabilize the replisome and replication fork structure upon replication stress. This is important in order to allow DNA replication to resume once the problem is solved. However, our recent studies demonstrated that some replisome components undergo proteasome-dependent degradation during DNA replication in the fission yeast Schizosaccharomyces pombe. Our investigation has revealed the involvement of the SCFPof3 (Skp1-Cullin/Cdc53-F-box) ubiquitin ligase in replisome regulation. We also demonstrated that forced accumulation of the replisome components leads to abnormal DNA replication upon replication stress. Here we review these findings and present additional data indicating the importance of replisome degradation for DNA replication. Our studies suggest that cells activate an alternative pathway to degrade replisome components in order to preserve genomic integrity.

SIRT1 Deacetylates TopBP1 and Modulates Intra-S-Phase Checkpoint and DNA Replication Origin Firing

“…In both cases, activation of TopBP1 enhances ATR-dependent phosphorylation events in response to replication stress, leading to activation of the intra-S-phase checkpoint. The impact of SIRT1 on the intra-S-phase checkpoint might be much more profound, as our data also indicate that SIRT1 interacts with CHK1, which is phosphorylated and activated by ATR, MRE11A and NBS1, which are ATM targets 3 - 5 , 47 , and p53, which is an upstream regulator of both the ATM and ATR signaling pathways 1 , 48 , 49 . All these proteins are implicated in the intra-S-phase cell cycle checkpoint 3 - 5 , 11 - 13 .…”

“…The progression of cells through the cell cycle is precisely regulated by multiple checkpoints at different transition phases of the cycle 1 - 5 . Upon DNA damage, the intra-S-phase checkpoint is activated to ensure the accuracy of DNA replication by suppressing late replication origin activation to allow the DNA damage repair machinery to repair DNA 3 - 5 .…”

“…The progression of cells through the cell cycle is precisely regulated by multiple checkpoints at different transition phases of the cycle 1 - 5 . Upon DNA damage, the intra-S-phase checkpoint is activated to ensure the accuracy of DNA replication by suppressing late replication origin activation to allow the DNA damage repair machinery to repair DNA 3 - 5 . Activation of the intra-S-phase checkpoint is largely mediated by upstream sensor kinases ATM (ataxia-mutated) and ATR (ataxia-telangiectasia and rad3-related), which are recruited to DNA double strand break or defective replication forks, respectively, where they phosphorylate downstream effector proteins.…”

Protein Degradation Pathways Regulate the Functions of Helicases in the DNA Damage Response and Maintenance of Genomic Stability

“…Regulation of proteins implicated in the DNA damage response or replication via their degradation is not unprecedented. For example, in yeast, proteasome degradation of replisome proteins regulates genomic stability [ 17 ]. However, much less is known about the intricacy of genome maintenance pathways and how they are regulated by proteasome degradation in higher eukaryotes.…”

Regulation of Unperturbed DNA Replication by Ubiquitylation

“…However, the level of Pol2 in the cells is constant due to continuous Pol2 translation. The authors suggested that this degradation mechanism could serve to “refresh” Pol2 enzymes during S-phase: provide newly synthesised Pol2 enzyme to be reloaded onto the leading strand [ 75 , 76 ].…”