A new role of CDKs in the control of replication fork progression by Checkpoint Kinase 1

MARINA GONZÀLEZ BESTEIRO; MARTIN HABIF; SABRINA MANSILLA; MARIA BELEN VALLERGA; MARIA BELEN FEDERICO; VANESA GOTTIFREDI

Mar del Plata

Congreso; SAIB - 51st Annual Meeting Argentine Society for Biochemistry and Molecular Biology; 2015

The encounter of replication forks with DNA lesions activate Checkpoint Kinase 1 (Chk1), which stabilizes forks and inhibits replication origin firing. While the mechanisms that underlie Chk1-dependent inhibition of origin firing have been elucidated, the downstream effectors of Chk1 that control replication fork progression remain largely unexplored. We observed that roscovitine, a CDK (cyclin-dependent kinase) inhibitor, alleviates the exacerbated origin firing and impaired fork progression phenotypes caused by Chk1 depletion. Others have proposed that roscovitine restores the progression of active forks by reducing origin firing, thereby making the nucleotide pool available for DNA elongation. However, we provide evidence that this is not the case since the reduction in origin firing back to wild-type levels in Chk1-depleted cells (by means other than roscovitine) does not translate into normal DNA elongation rates.Reinforcing the notion of a direct role of CDKs in fork progression, we show that such roscovitine-induced elongation of DNA in Chk1-deficient cells requires Pol, an alternative polymerase that copies damaged DNA. Indeed, the DNA elongation defect caused by Chk1 depletion is rescued by forcing Polto replication forks. In conclusion, our study suggests that Chk1 signals via CDKs not only to inhibit origin firing but also to promote Poldependent fork stabilization.