The oxidative stress response mediated via Pos9/Skn7 is negatively regulated by the Ras/PKA pathway in Saccharomyces cerevisiae.

Exposure of Saccharomyces cerevisiae to elevated concentrations of hydrogen peroxide induces transcription of several genes involved in the oxidative stress response. Two major transcription factors are involved in this induction, Pos9/Skn7 and Yap1. Fusions of either Yap1 or Pos9/Skn7 with the Gal4 DNA binding domain are active as transcription factors. Gal4-Yap1-dependent reporter gene activity is only weakly regulated by oxidative stress. In contrast, fusion of the Gal4 DNA binding domain to the Pos9/Skn7 protein results in a transcription factor that is independent of the YAP1 gene and is strictly regulated by oxidative stress, indicating that a signaling cascade impinges on the Pos9/Skn7 protein. We have observed that the Ras/PKA (cAMP-dependent protein kinase A) pathway affects this signaling. When PKA activity was low (in the presence of multicopy PDE2 or a cyr1(D822-->A) mutation) maximum reporter gene activity was observed even in the absence of oxidative stress. In contrast, high PKA activity (in strains mutant for either pde2 or bcy1, or expressing the dominant active Ras2Val19) resulted in a complete loss of activation following oxidative stress. The transcription of Pos9/Skn7 target genes was also affected in Ras/PKA pathway mutants. Furthermore, we demonstrated that activated Pos9/Skn7 is necessary for Yap1-dependent reporter gene induction.