Mutations in WSC genes for putative stress receptors result in sensitivity to multiple stress conditions and impairment of Rlm1-dependent gene expression in Saccharomyces cerevisiae

Abstract

Intracellular signaling by mitogen-activated protein (MAP) kinase cascades plays an essential role in the cellular response to environmental stress. In the yeast Saccharomyces cerevisiae, the PKC1-regulated, stress-activated MAP kinase pathway, the MPK1 cascade, is activated by heat and by a decrease in osmolarity. The genes WSC1, WSC2 and WSC3 encode putative receptors that maintain cell wall integrity under conditions of heat stress. Genetic studies place the function of the WSC genes upstream of the MPK1 kinase cascade. To further define the role of the WSC family in the stress response we determined whether: (1) the wsc Δ mutants are sensitive to other environmental stress conditions, in addition to heat shock; (2) expression from four transcriptional control elements, known to be activated by stress, is impaired in wsc Δ mutants; and (3) Wsc4, a Wsc homolog, has functions that overlap with those of the other Wsc family members. We report here that deletion of WSC and PKC1 causes hypersensitivity to ethanol, hydrogen peroxide and DNA-damaging drugs. In wsc Δ mutants expression of β-galactosidase from the AP-1 response element (ARE), the heat shock response element (HSE) or the stress response element (STRE) is not reduced. In contrast, expression of a reporter gene placed under the control of the Rlm1 (transcription factor)-dependent response element is significantly reduced in wsc Δ mutants. This suggests that the lysis defect of wscΔ mutants is at least in part caused by a defect in transcriptional regulation by Rlm1. Phenotypic analysis of the effect of deleting WSC4 in a wsc1 Δ mutant show that, unlike WSC2 or WSC3, deletion of WSC4 does not exacerbate the lysis defect of a wsc1 Δ strain. In contrast, deletion of WSC4 enhances the sensitivity of the wsc1 Δ mutant to heat shock, ethanol, and a DNA-damaging drug, suggesting that WSC4 plays a role in the response to environmental stress but that its function may differ from those of the other WSC family members.