SCFβTrCP-Mediated Degradation of Claspin Regulates Recovery from the DNA Replication Checkpoint Response

SummaryDuring replicative stress, Claspin mediates the phosphorylation and consequent activation of Chk1 by ATR. We found that during recovery from the DNA replication checkpoint response, Claspin is degraded in a βTrCP-dependent manner. In vivo, Claspin is phosphorylated in a canonical DSGxxS degron sequence, which is typical of βTrCP substrates. Phosphorylation of Claspin is mediated by Plk1 and is essential for binding to βTrCP. In vitro ubiquitylation of Claspin requires βTrCP, Plk1, and an intact DSGxxS degron. Significantly, expression of a stable Claspin mutant unable to bind βTrCP prolongs the activation of Chk1, thereby attenuating the recovery from the DNA replication stress response and significantly delaying entry into mitosis. Thus, the SCFβTrCP-dependent degradation of Claspin is necessary for the efficient and timely termination of the DNA replication checkpoint. Importantly, in response to DNA damage in G2, Claspin proteolysis is inhibited to allow the prompt reestablishment of the checkpoint.