Cell-cycle-dependent regulation of DNA end resection by PLK1 and PLK3 without CtIP level modulation

DNA double-strand breaks (DSBs) are highly cytotoxic lesions repaired primarily by homologous recombination (HR) and non-homologous end joining (NHEJ), with alternative end joining (alt-EJ) and single-strand annealing (SSA) functioning as backup. Repair pathway choice is governed by DNA end resection, suppressing NHEJ and committing repair to homology-based processes. Using pharmacological inhibition and protein depletion approaches in irradiated human cells, we show that PLK1 alone controls resection in S-phase-irradiated cells, while PLK1 and PLK3 act redundantly in G₂-phase-irradiated cells. This cell-cycle-dependent regulation operates through a mechanism distinct from SCF^SKP2-APC/C^CDH1-mediated CtIP level modulation. These findings establish PLK1 and PLK3 as cell-cycle-dependent regulators of DSB repair pathway choice, advancing our understanding of how cell-cycle progression is coupled to repair decisions through differential PLK activity.