Checkpoint Kinase 2 (Chk2)

Checkpoint Kinase 2 (Chk2, CHEK2) operates downstream of ATM in the DNA double-strand break response. ATM phosphorylates Chk2, promoting its dimerization and activation, after which the kinase phosphorylates p53, BRCA1, PPM1D and CDC25A to halt the cycle, support repair or trigger apoptosis. Bi-allelic loss is rare in tumors, but heterozygous truncating CHEK2 variants, especially the founder allele 1100delC, raise breast cancer risk several-fold and define a moderate-penetrance cancer predisposition syndrome. Chk2 is thus both a checkpoint kinase and a well-established human cancer susceptibility gene.