c-Abl Phosphorylates Plk1 in Facilitating DNA Damage-Induced G2/M Checkpoint Release with a Trade-off of Micronuclei Formation

Abstract

DNA double-strand breaks (DSBs) pose a critical threat to cellular proliferation and genomic integrity. Upon genotoxic stress, the DNA damage response (DDR) rapidly activates repair pathways and halts cell cycle progression through checkpoint activation. Previously, we demonstrated that DDR-activated c-Abl tyrosine kinase (ABL1) attenuates error-prone late-phase DSB repair. However, the broader functional implications of c-Abl in DDR regulation, and the fate of any residual unrepaired DNA fragments remained poorly understood. Here, we show that c-Abl regulates G2/M checkpoint release by targeting Polo-like kinase1 (Plk1). Depletion or inhibition of c-Abl resulted in increased G2-M accumulation and impaired checkpoint exit. We identified Y217 as a c-Abl phosphorylation site on Plk1, important for Plk1-mediated Claspin destabilization, a key step in G2/M checkpoint release. CRISPR-mediated introduction of the phopsho-silencing Plk1 Y217F mutation or the phospho-mimicking Y217E mutation into cells resulted in impaired and enhanced G2/M checkpoint release, respectively. Intriguingly, c-Abl-mediated G2/M checkpoint release correlated with elevated DNA damage-induced micronuclei (MNi) formation. Depletion or inhibition of c-Abl reduced MNi formation, whereas induction of c-Abl expression increased it, implicating c-Abl as an active effector in both processes. We propose a trade-off model whereby, following the rapid initial repair phase, c-Abl shifts cellular priorities from prolonged, potentially error-prone DSB repair toward cell cycle resumption, thereby promoting G2-M checkpoint exit and DDR deactivation at the cost of increased MNi formation. Our findings describe a novel regulatory DDR axis involving c-Abl and Plk1 and provide mechanistic insights into how DDR termination is orchestrated.