Distinct roles for glutathione S-transferases in the oxidative stress response in Schizosaccharomyces pombe

We have identified three genes, gst1(+), gst2(+), and gst3(+), encoding theta-class glutathione S-transferases (GSTs) in Schizosaccharomyces pombe. The gst1(+) and gst2(+) genes encode closely related proteins (79% identical). Our analysis suggests that Gst1, Gst2, and Gst3 all have GST activity with the substrate 1-chloro-2,4-dinitrobenzene and that Gst3 has glutathione peroxidase activity. Although Gst1 and Gst2 have no detectable peroxidase activity, all three gst genes are required for normal cellular resistance to peroxides. In contrast, each mutant is more resistant to diamide than wild-type cells. The gst1Delta, gst2Delta, and gst3Delta mutants are also more sensitive to fluconazole, suggesting that GSTs may be involved in anti-fungal drug detoxification. Both gst2(+) and gst3(+) mRNA levels increase in stationary phase, and all three gst genes are induced by hydrogen peroxide. Indeed, gst1(+), gst2(+), and gst3(+) are regulated by the stress-activated protein kinase Sty1. The Gst1 and Gst2 proteins are distributed throughout the cell and can form homodimers and Gst1-Gst2 heterodimers. In contrast, Gst3 is excluded from the nucleus and forms homodimers but not complexes with either Gst1 or Gst2. Collectively, our data suggest that GSTs have separate and overlapping roles in oxidative stress and drug responses in fission yeast.