Activation and Regulation of the Spc1 Stress-Activated Protein Kinase in Schizosaccharomyces pombe

Abstract

Spc1, an osmotic-stress-stimulated mitogen-activated protein kinase (MAPK) homolog in the fission yeast Schizosaccharomyces pombe, is required for the induction of mitosis and survival in high-osmolarity conditions. Spc1, also known as Sty1, is activated by Wis1 MAPK kinase and inhibited by Pyp1 tyrosine phosphatase. Spc1 is most closely related to Saccharomyces cerevisiae Hog1 and mammalian p38 kinases. Whereas Hog1 is specifically responsive to osmotic stress, we report here that Spc1 is activated by multiple forms of stress, including high temperature and oxidative stress. In this regard Spc1 is more similar to mammalian p38. Activation of Spc1 is crucial for survival of various forms of stress. Spc1 regulates expression of genes encoding stress-related proteins such as glycerol-3-phosphate dehydrogenase (gpd1 ؉ ) and trehalose-6-phosphate synthase (tps1 ؉ ). Spc1 also promotes expression of pyp2 ؉ , which encodes a tyrosine phosphatase postulated as a negative regulator of Spc1. This proposal is supported by the finding that Spc1 associates with Pyp2 in vivo and that the amount of Spc1 tyrosine phosphorylation is lower in a Pyp2-overproducing strain than in the wild type. Moreover, the level of stress-stimulated gpd1 ؉ expression is higher in ⌬pyp2 mutants than in the wild type. These findings demonstrate that Spc1 promotes expression of genes involved in stress survival and that Spc1-regulated transcription of one of these genes, pyp2 ؉ , serves to attenuate Spc1 activity. This mechanism of regulation may be commonly employed to modulate MAPK signal transduction pathways in eukaryotic species.Eukaryotic cells have highly effective mechanisms of adapting to environmental changes which cause physiological stress. In several cases it is clear that exposure to environmental insults, such as high temperature, high osmolarity, genotoxic agents, or hydroxyl radicals, leads to stimulation of kinases that phosphorylate transcription factors and thereby modulate gene expression (21). Spc1, a mitogen-activated protein kinase (MAPK) homolog in the fission yeast Schizosaccharomyces pombe, is an example of a stress-stimulated kinase (23, 36). Spc1, also known as Sty1 (23), is activated following exposure to highosmolarity media or growth in suboptimal nutrient conditions. Like all MAPK homologs, Spc1 is activated by a MAPK kinase homolog, in this case Wis1 (40), which phosphorylates threonine 171 and tyrosine 173 of Spc1 (36). The activating tyrosine phosphorylation is convenient for analytical studies because it is easily monitored by immunoblotting with antiphosphotyrosine antibodies. The level of Spc1 tyrosine phosphorylation increases in response to osmotic stress, and this phosphorylation is dependent on Wis1 in vivo (23, 36).The spc1 ϩ gene was first discovered in a genetic screen that identified mutations of five loci that rescued lethal phenotypes caused by loss of protein phosphatase 2C activity (37). Our interest in the stress response arose from the discovery that spc1 Ϫ and wis1 Ϫ (spc2 Ϫ ) mutants grow to a ...

Trehalose synthesis is important for the acquisition of thermotolerance in Schizosaccharomyces pombe

“…If cAPK has a similar role in S. pombe, pka1 mutants would be expected to have high constitutive levels of hsps, including also Tps1 (Blá zquez et al, 1994;Degols et al, 1996). In accordance with this assumption, it has recently been reported that the level of tps1 þ mRNA in an unconditioned pka1 mutant is about threefold higher than in the corresponding control strain (Ferná ndez et al, 1997).…”

Role of the RNA-binding Protein Nrd1 and Pmk1 Mitogen-activated Protein Kinase in the Regulation of Myosin mRNA Stability in Fission Yeast

“…Notably, the deletion of Pmk1 MAPK, which regulates cell integrity (Toda et al, 1996;Sugiura et al, 1999Sugiura et al, , 2003, suppressed the temperature sensitivity of the cdc4-8 mutant cells ( Figure 6A, cdc4-8⌬pmk1). In contrast, the deletion of Spk1 MAPK, which regulates meiosis (Gotoh et al, 1993;Figure 6A, cdc4-8⌬spk1), or the deletion of Spc1/Sty1 MAPK, a homologue of p38 in fission yeast (Millar et al, 1995;Degols et al, 1996), did not suppress the temperature-sensitive growth of cdc4-8 mutant cells ( Figure 6A, cdc4-8⌬spc1). Thus, the deletion of Pmk1 specifically suppressed the temperature-sensitive phenotype of the cdc4-8 mutants, suggesting that the Pmk1 MAPK may phosphorylate Nrd1, thus controlling the function of Nrd1.…”

Two Protein-tyrosine Phosphatases Inactivate the Osmotic Stress Response Pathway in Yeast by Targeting the Mitogen-activated Protein Kinase, Hog1

“…MAPK pathway-induced expression of protein phosphatases is likely to be a general mechanism of adaptation. Expression of MSG5, a gene encoding a dual specificity phosphatase in S. cerevisiae, is induced by activation of the pheromone response pathway, and pyp2 ϩ , a gene encoding a PTP in S. pombe, is induced by an osmotic stress response pathway (15,19,20). Strains lacking pyp1 ϩ or pyp2 ϩ show a decreased rate of Sty1/Spc1-Tyr(P) dephosphorylation (19 -21).…”