Chk1 loss creates replication barriers that compromise survival independently of origin firing levels

NICOLÁS L. CALZETTA; RÉMY BÉTOUS; SIMONE SABBIONEDA; SOFÍA M. LOUREIRO; MARIE-JEANNE PILLAIRE; SÉBASTIEN HOFFMANN; MARINA A. GONZÁLEZ BESTEIRO; MARTÍN HABIF; ANTONIO MAFFIA; VANESA GOTTIFREDI

EMBO JOURNAL

NATURE PUBLISHING GROUP

Lugar: Londres; Año: 2019 vol. 38 p. 1 - 16

0261-4189

The effectiveness of Checkpoint kinase 1 (Chk1) inhibitors at killing cancer cells is considered to be fully dependent on their effect on DNA replication initiation. Chk1 inhibition boosts origin firing, presumably limiting the availability of nucleotides and in turn provoking the slow-down and subsequent collapse of forks, thus decreasing cell viability. Here we show that slow fork progression in Chk1-inhibited cells is not an indirect effect of excess new origin firing. Instead, fork slow-down results from the accumulation of replication barriers, whose bypass is impeded by CDK-dependent phosphorylation of the specialized DNA polymerase eta (Pol). Also in contrast to the linear model, the accumulation of DNA damage in Chk1-deficient cells depends on origin density but is largely independent of fork speed. Notwithstanding this, origindysregulation contributes only mildly to the poor proliferation rates of Chk1-depleted cells. Moreover, elimination of replication barriers by down-regulation of helicase components, but not their bypass by Pol, improves cell survival. Our results thus shed light on the molecular basis of the sensitivity of tumors to Chk1 inhibition.