The drinking water contaminant dibromoacetonitrile delays G1-S transition and suppresses Chk1 activation at broken replication forks

Thomas Caspari,Nathalie Fenner,Chris Freeman,James Dyer,Christian Dunn

doi:10.1038/s41598-017-13033-8

Thomas Caspari, Nathalie Fenner + Show 3 more

Open Access

https://doi.org/10.1038/s41598-017-13033-8

Copy DOI

Journal: Scientific Reports	Publication Date: Oct 6, 2017
Citations: 3	License type: open-access

Affiliation: Bangor University

Abstract

Chlorination of drinking water protects humans from water-born pathogens, but it also produces low concentrations of dibromoacetonitrile (DBAN), a common disinfectant by-product found in many water supply systems. DBAN is not mutagenic but causes DNA breaks and elevates sister chromatid exchange in mammalian cells. The WHO issued guidelines for DBAN after it was linked with cancer of the liver and stomach in rodents. How this haloacetonitrile promotes malignant cell transformation is unknown. Using fission yeast as a model, we report here that DBAN delays G1-S transition. DBAN does not hinder ongoing DNA replication, but specifically blocks the serine 345 phosphorylation of the DNA damage checkpoint kinase Chk1 by Rad3 (ATR) at broken replication forks. DBAN is particularly damaging for cells with defects in the lagging-strand DNA polymerase delta. This sensitivity can be explained by the dependency of pol delta mutants on Chk1 activation for survival. We conclude that DBAN targets a process or protein that acts at the start of S phase and is required for Chk1 phosphorylation. Taken together, DBAN may precipitate cancer by perturbing S phase and by blocking the Chk1-dependent response to replication fork damage.

Highlights

Dibromoacetonitrile (DBAN) is generated at low nanomolar concentrations when bromide reacts with nitrogenous organic matter during the chlorination of drinking water[1]
Since a second cycle G2 arrest is typical for drugs like hydroxyurea (HU) or camptothecin (CPT) that interfere with DNA replication, we concluded that DBAN and DCAN perturb S phase thereby triggering the G2 delay (Fig. 1G)
Since H2AX is phosphorylated during unperturbed S phase[31], this drop may be caused by depleting the pool of S phase cells due to the G2 arrest

Summary

Introduction

Dibromoacetonitrile (DBAN) is generated at low nanomolar concentrations when bromide reacts with nitrogenous organic matter during the chlorination of drinking water[1]. Monobromoacetontrile (BAN) was shown to induce endoreplication in Chinese hamster ovary cells by blocking mitosis[18]. While these findings indicate a potential health risk, it is still unclear how DBAN precipitates cancer. Using the model organism fission yeast (Schizosaccharomyces pombe), we report here that DBAN delays G1-S transition and blocks the activation of the DNA damage checkpoint kinase Chk[1] at broken DNA replication forks. The collision of replication forks with immobilised topoisomerase 1, which can be trapped on the DNA by camptothecin (CPT), triggers the phosphorylation of the DNA damage checkpoint kinase Chk[1] at serine 345 by Rad[326]. Activation of Cds[1] and Chk[1] both block the cell cycle activator Cdc[2] (CDK1) thereby initiating a transient G2-M arrest[27]

Methods

Results

Conclusion