Stochastic Endogenous Replication Stress Causes ATR-Triggered Fluctuations in CDK2 Activity that Dynamically Adjust Global DNA Synthesis Rates

Leighton H Daigh,Tobias Meyer,Karlene A Cimprich,Chad Liu,Mingyu Chung

doi:10.1016/j.cels.2018.05.011

Abstract

SUMMARYFaithful DNA replication is challenged by stalling of replication forks during S phase. Replication stress is further increased in cancer cells or in response to genotoxic insults. Using live single-cell image analysis, we found that CDK2 activity fluctuates throughout an unperturbed S phase. We show that CDK2 fluctuations result from transient ATR signals triggered by stochastic replication stress events. In turn, fluctuating endogenous CDK2 activity causes corresponding decreases and increases in DNA synthesis rates, linking changes in stochastic replication stress to fluctuating global DNA replication rates throughout S phase. Moreover, cells that reenter the cell cycle after mitogen stimulation have increased CDK2 fluctuations and prolonged S phase resulting from increased replication stress-induced CDK2 suppression. Thus, our study reveals a dynamic control principle for DNA replication whereby CDK2 activity is suppressed and fluctuates throughout S phase to continually adjust global DNA synthesis rates in response to recurring stochastic replication stress events.

Highlights

Cells must survey and maintain genomic integrity to ensure proper cellular function and faithful duplication and distribution of DNA to daughter cells
We have previously shown that CDK2 activity can be monitored in individual cells by measuring the subcellular localization of a fragment of DNA helicase B tagged with the fluorescent protein mVenus (DHB-Ven) (Spencer et al, 2013)
Nuclear export signal (NES), nuclear localization signal (NLS), and serine residues phosphorylated by CDK2 are indicated

Summary

Introduction

Cells must survey and maintain genomic integrity to ensure proper cellular function and faithful duplication and distribution of DNA to daughter cells. Genomic integrity is constantly challenged by endogenous and exogenous threats. This is especially true during S phase, when stalling of DNA replication forks places the genome at increased risk for DNA damage and ensuing mutations. Replication stress and DNA damage during S phase are driving forces in the development of cancer and aging, possibly due to the effects of replication stress and subsequent mutations on tissue stem cells as they re-enter the cell cycle from quiescence (Magdalou et al, 2014). Stochastic damage events that occur during DNA replication have been proposed to be the predominant source of cancer-causing mutations (Tomasetti et al, 2017; Tomasetti and Vogelstein, 2015). Understanding DNA damage and replication stress signaling in unperturbed cells is of fundamental importance to understanding the origin of cancer-causing mutations (Gaillard et al, 2015)

Methods

Results

Discussion

Conclusion