ATM-activated Chk1-Cdc25C-Cdk1 pathway (ATM-Chk1-Cdc25C-Cdk1)

The ATM-activated Chk1-Cdc25C-Cdk1 pathway is a critical signaling cascade within the DNA damage response (DDR) that orchestrates cell cycle arrest at the G2/M phase transition. Upon detecting double-strand breaks, Ataxia-telangiectasia mutated (ATM) kinase is activated and phosphorylates transducer kinases, including Checkpoint kinase 1 (Chk1). Activated Chk1 subsequently phosphorylates the phosphatase Cdc25C at Ser216, which results in its cytoplasmic sequestration or degradation, preventing it from dephosphorylating and activating Cyclin-dependent kinase 1 (Cdk1). Because active Cdk1 is required for entry into mitosis, this signaling axis maintains Cdk1 in an inactive state, effectively halting the cell cycle to allow for DNA repair. In the context of oncology, this pathway is frequently exploited as a therapeutic target, particularly in tumors with p53 deficiencies that lack a functional G1 checkpoint and are thus highly dependent on the G2/M checkpoint for survival after genomic stress. Pharmaceutical agents such as ATM inhibitors and Chk1 inhibitors are designed to disrupt this arrest, sensitizing cancer cells to DNA-damaging therapies like ionizing radiation or chemotherapy by inducing mitotic catastrophe. While promising, the therapeutic use of pathway inhibitors faces challenges regarding systemic toxicity, as these components are also essential for maintaining the genomic integrity of normal proliferating cells.

Other names

ATM-Chk1 signaling axisG2/M DNA damage checkpoint pathwayATM-dependent G2/M arrest pathwayDNA damage response G2/M pathway

Small molecule inhibitors target specific enzymes within the cascade (e.g., ATM, Chk1, or Cdk1) to abrogate the G2/M checkpoint, thereby forcing cells with damaged DNA into premature and lethal mitosis (mitotic catastrophe).