The PP2A phosphatase counteracts the function of the 9-1-1 axis in checkpoint activation.

DNA damage elicits a checkpoint response depending on the Mec1/ATR kinase, which detects the presence of single-stranded DNA and activates the effector kinase Rad53/CHK2. In Saccharomyces cerevisiae , one of the signaling circuits leading to Rad53 activation involves the evolutionarily conserved 9-1-1 complex, which acts as a platform for the binding of Dpb11 and Rad9 (referred to as the 9-1-1 axis) to generate a protein complex that allows Mec1 activation. By examining the effects of both loss-of-function and hypermorphic mutations, here, we show that the Cdc55 and Tpd3 subunits of the PP2A phosphatase counteract activation of the 9-1-1 axis. The lack of this inhibitory function results in DNA-damage sensitivity, sustained checkpoint-mediated cell-cycle arrest, and impaired resection of DNA double-strand breaks. This PP2A anti-checkpoint role depends on the capacity of Cdc55 to interact with Ddc1 and to counteract Ddc1-Dpb11 complex formation by preventing Dpb11 recognition of Ddc1 phosphorylated on Thr602. [Display omitted] • The PP2A phosphatase negatively regulates the 9-1-1 checkpoint axis • The lack of this function impairs checkpoint recovery and double-strand break resection • The Cdc55 PP2A subunit interacts with Ddc1 • Cdc55 counteracts Ddc1-Dpb11 interaction by preventing Ddc1 Thr602 phosphorylation Casari et al. show that the PP2A phosphatase dampens checkpoint signaling by the 9-1-1 axis. This anti-checkpoint function depends on the ability of the Cdc55 PP2A subunit to counteract Ddc1-Dpb11 complex formation by preventing Dpb11 recognition of Ddc1 phosphorylated on Thr602. [ABSTRACT FROM AUTHOR]