CHK1 and SPRTN promote replication fork progression by removing DPCs. a Ectopic expression of CHK1-wt or of SPRTN-wt promotes replication fork progression over FA-induced DPCs in HEK293 cells. Upper panel shows the strategy for DNA fiber assay. Lower graph plots the quantification of IdU tract length. >100 DNA fibers were analysed per condition and experiment. Mean ± 25–75 percentile range (box) ± 10–90 percentile range (whiskers), n = 3 experiments, two-tailed Student's t-test. b, c Overexpression of CHK1-wt, but not of CHK1-S345A, reduces the amount of DPCs in HeLa-ΔSPRTN cells. DNA protein crosslink extracts were visualised by silver staining (b). ds-DNA blot is shown as a loading control. The immunoblots for Flag, SPRTN and actin were prepared from whole cell lysates. Data are representative immunoblots (b) and quantification of CHK1 on chromatin fraction normalised to histone H2B (c). Mean ± SEM; n = 3 experimental replicates, two-tailed Student's t-test. d Model for the SPRTN-CHK1 cross-activation loop. During steady-state DNA replication, SPRTN evicts CHK1 from replicative chromatin and stimulates CHK1 activity. In turn, CHK1 phosphorylates SPRTN on C-terminal serines. CHK1 activity enhances the recruitment of SPRTN to chromatin and its activity towards DPC proteolysis. This steady-state SPRTN-CHK1 cross-activation loop enables normal physiological replication fork velocity, inhibits unscheduled replication origins firing, stabilises replication forks and removes DPCs to safeguard genome stability. Source data for (a–c) are provided as a Source Data file
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