DNA Damage-Induced Activation of p53 by the Checkpoint Kinase Chk2

TLDR

Chk2 is a DNA damage–responsive kinase that can regulate cell cycle arrest. Chk2-deficient mouse cells were created by gene targeting, and Chk2 directly phosphorylates p53 at serine 20 to block Mdm2 binding. Chk2−/− cells fail to arrest in G2 after γ‑irradiation, resist DNA‑damage–induced apoptosis, show impaired p53 stabilization and p21 induction, and reintroducing Chk2 restores p53‑dependent transcription, demonstrating that Chk2 phosphorylation of p53 at Ser20 stabilizes the protein by preventing ubiquitination.

Abstract

Chk2 is a protein kinase that is activated in response to DNA damage and may regulate cell cycle arrest. We generated Chk2-deficient mouse cells by gene targeting. Chk2 −/− embryonic stem cells failed to maintain γ-irradiation–induced arrest in the G 2 phase of the cell cycle. Chk2 −/− thymocytes were resistant to DNA damage–induced apoptosis. Chk2 −/− cells were defective for p53 stabilization and for induction of p53-dependent transcripts such as p21 in response to γ irradiation. Reintroduction of the Chk2 gene restored p53-dependent transcription in response to γ irradiation. Chk2 directly phosphorylated p53 on serine 20, which is known to interfere with Mdm2 binding. This provides a mechanism for increased stability of p53 by prevention of ubiquitination in response to DNA damage.