Nitric oxide signaling and its role in oxidative stress response in Schizosaccharomyces pombe

In examining NO signaling in the fission yeast Schizosaccharomyces pombe, we found that the putative NO dioxygenase SPAC869.02c (named Yhb1) and the S-nitrosoglutathione reductase Fmd2 cooperatively reduced intracellular NO levels as NO-detoxification enzymes. Although both protein levels were increased with exogenous NO, their expression patterns were different during growth phases. While expression of Yhb1 in the log phase was abrogated by treatment with an NO synthase inhibitor, induction of Fmd2 in the stationary phase was correlated with elevated mitochondrial respiratory chain (MRC) activity and reactive oxygen species (ROS) generation. Moreover, NO was localized in the mitochondria specifically in the stationary phase, suggesting that there are at least two distinctive types of NO signaling in S. pombe cells. For mitochondrial NO signaling, pretreatment with an NO donor effectively rescued the cell viability by repressing generation of ROS under oxidative stress. DNA microarray analysis revealed that exogenous NO contributes to tolerance to hydrogen peroxide (H2O2) stress by (i) inhibition of Fe3+ to Fe2+conversion, (ii) upregulation of the H2O2-detoxifying enzymes, and (iii) downregulation of the MRC genes. Therefore, NO is suggested to play a pivotal role in the negative feedback system to regulate ROS levels under oxidative stress in S. pombe cells. We examined the effects of DETA NONOate treatment on gene expression of log-phase Scizosaccharomyces pombe cells by using Affymetrix Yeast Genome 2.0 Array. Total RNA samples were extracred from untreated cells (DetaNONOate 0) and cells treated with 0.5 mM DETA NONOate for 2 h (DetaNONOate 0.5) and were subjected for this DNA microarray analysis.