MYBL2 and ATM suppress replication stress in pluripotent stem cells

Abstract

Replication stress, a major cause of genome instability in cycling cells, is mainly prevented by the ATR-dependent replication stress response pathway in somatic cells. However, the replication stress response pathway in embryonic stem cells (ESCs) may be different due to alterations in cell cycle phase length. The transcription factor MYBL2, which is implicated in cell cycle regulation, is expressed a hundred to a thousand-fold more in ESCs compared with somatic cells. Here we show that MYBL2 activates ATM and suppresses replication stress in ESCs. Consequently, loss of MYBL2 or inhibition of ATM or Mre11 in ESCs results in replication fork slowing, increased fork stalling and elevated origin firing. Additionally, we demonstrate that inhibition of CDC7 activity rescues replication stress induced by MYBL2 loss and ATM inhibition, suggesting that uncontrolled new origin firing may underlie the replication stress phenotype resulting from loss/inhibition of MYBL2 and ATM. Overall, our study proposes that in addition to ATR, a MYBL2-MRN-ATM replication stress response pathway functions in ESCs to control DNA replication initiation and prevent genome instability.

Replication stress tolerance and management differs between naïve and primed pluripotent cells

“…What is unique in naïve pluripotent cells is the ease in which cultures activate Atm and slide into replication catastrophe when faced with a replication challenge. Considering this finding, it is not surprising that Atm was recently observed to play a prominent role in the replication stress response of naïve mESC cultures (Blakemore et al, 2021). In agreement, Atr deletion is lethal after E4.5, during a later developmental window than blastocyst-derived mESCs, and consistent with a less prominent role for Atr during naïve pluripotency (de Klein et al, 2000).…”

“…This includes H2ax phosphorylation and remodelled replication forks protected by Rad51 (Ahuja et al, 2016). Atr is implicated in somatic replication fork remodelling and protection (Berti et al, 2020), and inhibiting Atr reduces replication rates (Blakemore et al, 2021) and partially supresses spontaneous γ-H2ax (Ahuja et al, 2016) in mESC cultures. Additionally, we observe Atr-dependent Chek1 phosphorylation in HU treated mESCs.…”

Beyond the Double-Strand Breaks: The Role of DNA Repair Proteins in Cancer Stem-Cell Regulation

“…Consequently, loss of MYBL2 or inhibition of ATM in ESCs leads to replication fork slowing, increased replication fork stalling, and increased origin firing. This finding suggests that in addition to ATR-mediated DDR, a MYBL2-MRN-ATM replication stress response pathway in ESCs could be used to control DNA replication initiation and genome stability [ 51 ]. In addition, immunotherapeutic approaches would be promising to pursue, as a direct effect of ATR activity on programmed cell death 1 ligand (PD-L1) expression and stability has been observed since ATR inhibition results in down-regulation of PD-L1 protein levels [ 52 , 53 ].…”

Characterising replisome disassembly in human cells

“…However, it is known that embryonic cell cycles and DNA replication are regulated somewhat differently than in somatic cells. For example, the stabilisation of CDT1 during DNA replication is not enough to induce re-replication in Xenopus laevis egg extract (14), as it is in human somatic cells (15); whilst origin firing is regulated by both ATM and ATR in embryonic stem cells, but mainly by ATR in somatic cells (16). Moreover, embryonic systems are known to maintain fast cell cycles with non-existent or short gap phases, with reduced regulation of cell cycle phase transition and accumulation of high levels of replication factors to sustain this fast proliferation rate.…”