Activation of Checkpoint Kinase Chk1 by Reactive Oxygen Species Resulting from Disruption of wat1/pop3 in Schizosaccharomyces pombe

Abstract

<p class="first" id="d2163450e147">DNA double-strand breaks are critical lesions that can lead to chromosomal aberrations and genomic instability. In response to DNA damage, Chk1, a serine/threonine kinase, is responsible for cell cycle arrest to prevent damaged cells from progressing through the cell cycle. Here, we report that the disruption of <i>wat1</i>, a WD repeat-containing protein, leads to the phosphorylation of Chk1. The double-deletion of <i>chk1</i> and <i>wat1</i> had a grave effect on the survival of fission yeast cells, and the spontaneous recombination rate was also high upon double-deletion of <i>wat1</i> and <i>chk1</i>, as compared to the single-mutant. In the absence of <i>wat1</i>, the cells exhibited a high level of nuclear fragmentation that resulted in the accumulation of Rad22 yellow fluorescent protein foci. Furthermore, we show that <i>wat1</i> is required for the regulation of the oxidative stress response. We observed elevated levels of reactive oxygen species (ROS) generation in <i>wat1</i>-null mutant that led to a high degree of propidium iodide staining at nonpermissive temperature. Based on the results presented here, we hypothesize that ROS production in <i>wat1</i>-null mutant cells generates DNA fragmentation that could trigger a checkpoint response and that, in the absence of checkpoint kinase Chk1, the cells exhibit severe growth defects leading to a synthetic lethal phenotype. </p>