DNA damage checkpoint dynamics drive cell cycle phase transitions

Abstract

DNA damage checkpoints are cellular mechanisms that protect the integrity of the genome during cell cycle progression. In response to genotoxic stress, these checkpoints halt cell cycle progression until the damage is repaired, allowing cells enough time to recover from damage before resuming normal proliferation. Here, we investigate the temporal dynamics of DNA damage checkpoints in individual proliferating cells by observing cell cycle phase transitions following acute DNA damage. We find that in gap phases (G1 and G2), DNA damage triggers an abrupt halt to cell cycle progression in which the duration of arrest correlates with the severity of damage. However, cells that have already progressed beyond a proposed "commitment point" within a given cell cycle phase readily transition to the next phase, revealing a relaxation of checkpoint stringency during later stages of certain cell cycle phases. In contrast to G1 and G2, cell cycle progression in S phase is significantly less sensitive to DNA damage. Instead of exhibiting a complete halt, we find that increasing DNA damage doses leads to decreased rates of S-phase progression followed by arrest in the subsequent G2. Moreover, these phase-specific differences in DNA damage checkpoint dynamics are associated with corresponding differences in the proportions of irreversibly arrested cells. Thus, the precise timing of DNA damage determines the sensitivity, rate of cell cycle progression, and functional outcomes for damaged cells. These findings should inform our understanding of cell fate decisions after treatment with common cancer therapeutics such as genotoxins or spindle poisons, which often target cells in a specific cell cycle phase.Recent live-imaging studies in single cells have shed light on some of the underlying parameters that confer differential sensitivity to endogenous DNA damage. For example, cell-to-cell variation in p21 levels leads to differences in checkpoint stringency (i.e., the robustness of cell cycle arrest in response to DNA damage) 11,12 .However, the underlying parameters that result in differential responses within a cell cycle phase and in response to exogenous DNA damage are generally unknown. Knowledge of these collective dynamical behaviors-which we refer to as DNA damage checkpoint dynamics-is necessary for understanding the relationship between the DNA damage response and functional cellular outcomes such as permanent cell cycle arrest. From a translational perspective, understanding DNA damage checkpoint dynamics could help explain the variability in cellular responses to many chemotherapeutic drugs, which act mainly by inducing DNA damage and interfering with cancer cell proliferation.Among the various forms of DNA damage, DNA double strand breaks (DSBs) are one of the most harmful types of lesions 13,14 . DSBs can give rise to chromosome rearrangements and deletions that can subsequently lead to cancer. The functional effects of DSBs can vary depending on the cell cycle phase in which the damage was incurred. For example, it ha...

A peculiar cell cycle arrest at g2/m stage during the stationary phase of growth in the wine yeast Hanseniaspora vineae.

“…There are two key events that punctuate the cell cycle progression: DNA replication, when nuclear genome is duplicated - which defines S (synthesis) phase -, and mitosis (M phase), defined as the period in which chromosomes are condensed, sorted and then equally distributed to daughter cell ( Hustedt and Durocher, 2017 ). During DNA replication, genotoxic stresses (such as DNA damage and incomplete replication) activate the checkpoints pathways, which prevents cell cycle progression until the damage are repair ( Chao et al., 2017 ). These checkpoints have the role of checking if the replication have been properly accomplished, and there are no physical impediments for chromosomes to be replicated or repaired prior to nuclear division ( Hartwell and Weinert, 1989 ; Russell, 1998 ).…”

Rucaparib Treatment Alters p53 Oscillations in Single Cells to Enhance DNA-Double-Strand-Break-Induced Cell Cycle Arrest

“…Although not explored in this study, the increased variability upon BRCA1 or BRCA2 knockdown may result from the cell cycle dependence of homologous recombination, which occurs only in S and G2 phase after replication of DNA. Singlecell studies of cell cycle regulation in response to DSBs have shown that the timing of DNA damage has pronounced effects on cell fate determination (Chao et al, 2017). As such, cells in different cell cycle phases may generate distinct p53 dynamics in response to the same genotoxic stress.…”

Excessive E2F Transcription in Single Cancer Cells Precludes Transient Cell-Cycle Exit after DNA Damage

“…Next, we investigated if uncontrolled E2F-dependent transcription during S phase also results in an altered response to exogenous DNA damage. We treated cells with the radiomimetic drug neocarzinostatin (NCS), which causes double-stranded DNA breaks (DSBs) irrespective of cell-cycle phase (Chao et al, 2017). Furthermore, NCS is highly unstable, which allows cells to recover without the need to wash the drug away during live-cell imaging experiments.…”