Src Family Kinases Promote Silencing of ATR-Chk1 Signaling in Termination of DNA Damage Checkpoint

Background: Once DNA repair is completed, the DNA damage checkpoint is terminated, and the cell cycle is resumed. Results: Src inhibition induced a delay in G(2) checkpoint recovery and persistent ATR-Chk1 activation. Conclusion: Src inhibits ATR signaling to promote recovery from G(2) checkpoint arrest. Significance: Src sends a termination signal between the completion of DNA repair and the initiation of checkpoint termination. The DNA damage checkpoint arrests cell cycle progression to allow time for repair. Once DNA repair is completed, checkpoint signaling is terminated. Currently little is known about the mechanism by which checkpoint signaling is terminated, and the disappearance of DNA lesions is considered to induce the end of checkpoint signaling; however, here we show that the termination of checkpoint signaling is an active process promoted by Src family tyrosine kinases. Inhibition of Src activity delays recovery from the G(2) phase DNA damage checkpoint following DNA repair. Src activity is required for the termination of checkpoint signaling, and inhibition of Src activity induces persistent activation of ataxia telangiectasia mutated (ATM)- and Rad3-related (ATR) and Chk1 kinases. Src-dependent nuclear protein tyrosine phosphorylation and v-Src expression suppress the ATR-mediated Chk1 and Rad17 phosphorylation induced by DNA double strand breaks or DNA replication stress. Thus, Src family kinases promote checkpoint recovery through termination of ATR- and Chk1-dependent G(2) DNA damage checkpoint. These results suggest a model according to which Src family kinases send a termination signal between the completion of DNA repair and the initiation of checkpoint termination.