TORC2 Signaling Pathway Guarantees Genome Stability in the Face of DNA Strand Breaks

•An inhibitor of yeast TORC1 and TORC2 is identified and characterized•TORC2, but not TORC1, inhibition accentuates DNA damage induced by Zeocin•The Ypk1/Ypk2 pathway downstream of TORC2 is implicated in this synergism•Altered actin polymerization leads to massive chromosome fragmentation on Zeocin

SummaryA chemicogenetic screen was performed in budding yeast mutants that have a weakened replication stress response. This identified an inhibitor of target of rapamycin (TOR) complexes 1 and 2 that selectively enhances the sensitivity of sgs1Δ cells to hydroxyurea and camptothecin. More importantly, the inhibitor has strong synthetic lethality in combination with either the break-inducing antibiotic Zeocin or ionizing radiation, independent of the strain background. Lethality correlates with a rapid fragmentation of chromosomes that occurs only when TORC2, but not TORC1, is repressed. Genetic inhibition of Tor2 kinase, or its downstream effector kinases Ypk1/Ypk2, conferred similar synergistic effects in the presence of Zeocin. Given that Ypk1/Ypk2 controls the actin cytoskeleton, we tested the effects of actin modulators latrunculin A and jasplakinolide. These phenocopy TORC2 inhibition on Zeocin, although modulation of calcineurin-sensitive transcription does not. These results implicate TORC2-mediated actin filament regulation in the survival of low levels of DNA damage.