ATM/Wip1 activities at chromatin control Plk1 re‐activation to determine G2 checkpoint duration

After DNA damage, the cell cycle is arrested to avoid propagation of mutations. Arrest in G2 phase is initiated by ATM‐/ATR‐dependent signaling that inhibits mitosis‐promoting kinases such as Plk1. At the same time, Plk1 can counteract ATR‐dependent signaling and is required for eventual resumption of the cell cycle. However, what determines when Plk1 activity can resume remains unclear. Here, we use FRET‐based reporters to show that a global spread of ATM activity on chromatin and phosphorylation of ATM targets including KAP1 control Plk1 re‐activation. These phosphorylations are rapidly counteracted by the chromatin‐bound phosphatase Wip1, allowing cell cycle restart despite persistent ATM activity present at DNA lesions. Combining experimental data and mathematical modeling, we propose a model for how the minimal duration of cell cycle arrest is controlled. Our model shows how cell cycle restart can occur before completion of DNA repair and suggests a mechanism for checkpoint adaptation in human cells. Synopsis A FRET‐based sensor for ATM/ATR kinase signaling, which blocks cell cycle‐promoting kinases upon DNA damage, reveals that the minimal duration of damage‐induced G2 arrest is controlled by pan‐nuclear ATM activity on chromatin, rather than by the presence of ATM activity at DNA damage foci. The FRET‐based probe ATKAR visualizes ATM and ATR activity in live cells. DNA damage‐induced spread of ATM activity across chromatin prevents Plk1 activation. ATM activity is counteracted by the chromatin‐bound phosphatase Wip1. Plk1 re‐activation can be initiated despite the presence of active ATM at DDR foci. Graphical Abstract The minimal duration of a DNA damage‐induced G2 phase arrest is controlled by pan‐nuclear ATM activity on chromatin, and not by the presence of ATM activity at DNA damage foci.