The DNA repair endonuclease Mus81 facilitates fast DNA replication in the absence of exogenous damage.

Haiqing Fu,Liang Huang,Mirit I Aladjem,Tsutomu Shimura,Marie Regairaz,Yves Pommier,Yang You,Chi-Mei Lin,Michael Ryan,Ryangguk Kim,Melvenia M Martin

doi:10.1038/ncomms7746

Abstract

The Mus81 endonuclease resolves recombination intermediates and mediates cellular responses to exogenous replicative stress. Here, we show that Mus81 also regulates the rate of DNA replication during normal growth by promoting replication fork progression while reducing the frequency of replication initiation events. In the absence of Mus81 endonuclease activity, DNA synthesis is slowed and replication initiation events are more frequent. In addition, Mus81 deficient cells fail to recover from exposure to low doses of replication inhibitors and cell viability is dependent on the XPF endonuclease. Despite an increase in replication initiation frequency, cells lacking Mus81 use the same pool of replication origins as Mus81-expressing cells. Therefore, decelerated DNA replication in Mus81 deficient cells does not initiate from cryptic or latent origins not used during normal growth. These results indicate that Mus81 plays a key role in determining the rate of DNA replication without activating a novel group of replication origins.

Highlights

The Mus[81] endonuclease resolves recombination intermediates and mediates cellular responses to exogenous replicative stress
According to the terminology proposed by Mechali[6], potential replication origins are defined as ‘flexible origins’ if they are activated at various frequencies during normal cell proliferation, or as ‘dormant origins’ if they are not utilized during normal growth and are only activated under distinct metabolic conditions or following cell cycle perturbations
To determine whether Mus[81] affects replication under normal conditions, we measured replication fork progression and replication initiation frequency in HCT116 cells lacking Mus[81] (Mus81-deficient cells or Mus[81] À / À )[30,31]

Summary

Introduction

The Mus[81] endonuclease resolves recombination intermediates and mediates cellular responses to exogenous replicative stress. We have previously shown[29,30] that exposures to low, non-toxic doses of replication inhibitors slow the pace of DNA synthesis and activate a specialized signalling pathway including the cancer-predisposing Bloom syndrome, RecQ helicase-like (BLM); Mus[81] endonuclease homologue (S. cerevisiae) (Mus81); and the ataxia telangiectasia and Rad3-related (ATR) kinase. Activation of this pathway initially results in DNA breaks, which are rapidly repaired by the non-homologous end-joining pathway. Loss of Mus[81] increases initiation frequency from flexible replication origins that are utilized in both Mus81-proficient and deficient cells, but does not activate novel dormant replication origins

Methods

Results

Conclusion