Chk1 regulates the density of active replication origins during the vertebrate S phase

Abstract

The checkpoint kinase 1 (Chk1) preserves genome integrity when replication is performed on damaged templates. Recently, Chk1 has also been implicated in regulating different aspects of unperturbed S phase. Using mammalian and avian cells with compromised Chk1 activity, we show that an increase in active replicons compensates for inefficient DNA polymerisation. In the absence of damage, loss of Chk1 activity correlates with the frequent stalling and, possibly, collapse of active forks and activation of adjacent, previously suppressed, origins. In human cells, super-activation of replication origins is restricted to preexisting replication factories. In avian cells, in contrast, Chk1 deletion also correlates with the super-activation of replication factories and loss of temporal continuity in the replication programme. The same phenotype is induced in wild-type avian cells when Chk1 or ATM/ATR is inhibited. These observations show that Chk1 regulates replication origin activation and contributes to S-phase progression in somatic vertebrate cells.

p53 and p16INK4A independent induction of senescence by chromatin-dependent alteration of S-phase progression

“…3e). Furthermore, we did not observe modifications in the distribution of the classified replication figures 13 in curcumin-treated cells ( Supplementary Fig. S5), suggesting that the increased S-phase length might not be due to replicative stress, even though we measured a doubling of S-phase length.…”

DNA-damage response, survival and differentiation in vitro of a human neural stem cell line in relation to ATM expression

“…Chk1, along with its upstream kinase ATR, constitutes an S-phase checkpoint that in unperturbed cells regulates the replication origin activation and contributes to S-phase progression. 36,37 Unprogrammed initiation of DNA synthesis in terminally differentiated neurons concomitant with the constitutive downregulation of Chk1 could thus contribute to aberrant replicative structures, fork collapse and ultimately cell death.…”

Defining replication origin efficiency using DNA fiber assays

“…These include overexpression of translesion DNA polymerases (Pillaire et al 2007), the depletion of CHK1 (Maya-Mendoza et al 2007), BLM (Rao et al 2007), HR proteins (Daboussi et al 2008), and topoisomerase I (Tuduri et al 2009) and exposure to HU (Ge et al 2007;Ibarra et al 2008). Importantly, the latter studies also revealed that dormant origins are dispensable for normal growth but are essential for viability under replication stress (Ge et al 2007;Ibarra et al 2008).…”