Impaired protein translation inhibits DNA replication by a Claspin-Chk1-Rif1 pathway

DNA synthesis inhibition after global translational attenuation via the Unfolded Protein Response requires checkpoint adaptor protein Claspin and activation of checkpoint effector kinase Chk1. Here we show that DNA synthesis is also suppressed and Chk1 activated when ribosomal translation is inhibited by multiple, mechanistically distinct, protein synthesis inhibitors. Inhibition of DNA synthesis is rapid, reversible and not accompanied by detectable DNA damage. Our proteomic and functional characterisation shows that the kinases CK1-alpha and Cdc7 are necessary for transmission of the DNA replication-inhibitory signal in this process, likely by phosphorylating Claspin. Activation of Chk1 during protein synthesis inhibition also requires checkpoint proteins ATR and TopBP1, although activation occurs in the absence of multiple conventional markers of genotoxic stress signalling. We identified the replication and chromatin regulator Rif1 as a component of the DNA replication-inhibitory mechanism, whereas phosphatase PP1, a known functional partner of Rif1, was not required to suppress DNA replication during protein synthesis inhibition. Additionally, protein synthesis inhibition did not alter the phosphorylation of MCM2, a known target of Rif1/PP1, suggesting that Rif1 regulates DNA replication independently of MCM2-7 complex control. These findings elucidate a Claspin-Chk1-Rif1 pathway that links the fundamental processes of protein translation and DNA replication. Characterisation of the response to protein synthesis inhibition identifies a Claspin/Chk1/Rif1 pathway that couples translational attenuation to suppression of DNA replication.