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- Asp, Eva, 1970
(author)
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Downstream functions of the Sty1 MAPK pathway in S. pombe
- 2007
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Doctoral thesis (other academic/artistic)abstract
- MAP kinase pathways are involved in the response to environmental changes in eukaryotic cells regulating transcriptional and translational events. In S. pombe, the major stress activated MAP kinase, Sty1, is activated by a vast number of stresses hereby regulating the transcriptional response through its downstream target, transcription factor Atf1. We identified two MAPK activated kinases, Mkp1 and Mkp2, both found to interact with Sty1 in exponentially growing cells. Phosphorylation of Mkp1 is Sty1-dependent and this modification disappears upon nitrogen starvation. Overexpression of mkp1+ leads to severely elongated cells and a delay in mating and sporulation whereas mkp1- cells showed an enhanced rate of mating and entry into meiosis. Both kinases are cytoplasmatic, with a distinct sublocalization of Mkp2 to septa in actively dividing cells. The MAP kinase Sty1 is required for the translational adaptation after oxidative, hyperosmotic stress and after nitrogen starvation. The transcription factor Atf1 contributes to the recovery of translation after hyperosmotic stress, but not oxidative or nutrient stress. We found Sty1 to interact with translation factors eIF3a and eEF2. The Sty1-eEF2 interaction reaches a maximum shortly after nitrogen withdrawal and thereafter decreases. The Sty1-eIF3a interaction decreases after oxidative, hyperosmotic stress and upon nitrogen withdrawal. The eIF3a protein disappears upon nitrogen starvation at the time of polysomal re-initiation. The protein levels of eIF3a are reduced in sty1- cells. In a whole genome mRNA stability analysis, we find that there is a strong trend for mRNAs that are transcriptionally upregulated to also become stabilized after oxidative stress. This early, temporary change in stability of functional subgroups of mRNAs is largely Sty1-dependent. Transcripts involved in ribosome biogenesis and assembly have a stability defect in sty1- cells.
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| 2. |
- Asp, Eva, 1970, et al.
(author)
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Fission yeast mitogen-activated protein kinase Sty1 interacts with translation factors
- 2008
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In: Eukaryot. Cell. ; 7, s. 328-338
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Journal article (peer-reviewed)abstract
- Signaling by stress-activated mitogen-activated protein kinase (MAPK) pathways influences translation efficiency in mammalian cells and budding yeast. We have investigated the stress-activated MAPK from fission yeast, Sty1, and its downstream protein kinase, Mkp1/Srk1, for physically associated proteins using tandem affinity purification tagging. We find Sty1, but not Mkp1, to bind to the translation elongation factor eukaryotic elongation factor 2 (eEF2) and the translation initiation factor eukaryotic initiation factor 3a (eIF3a). The Sty1-eIF3a interaction is weakened under oxidative or hyperosmotic stress, whereas the Sty1-eEF2 interaction is stable. Nitrogen deprivation causes a transient strengthening of both the Sty1-eEF2 and the Sty1-Mkp1 interactions, overlapping with the time of maximal Sty1 activation. Analysis of polysome profiles from cells under oxidative stress, or after hyperosmotic shock or nitrogen deprivation, shows that translation in sty1 mutant cells recovers considerably less efficiently than that in the wild type. Cells lacking the Sty1-regulated transcription factor Atf1 are deficient in maintaining and recovering translational activity after hyperosmotic shock but not during oxidative stress or nitrogen starvation. In cells lacking Sty1, eIF3a levels are decreased, and phosphorylation of eIF3a is reduced. Taken together, our data point to a central role in translational adaptation for the stress-activated MAPK pathway in fission yeast similar to that in other investigated eukaryotes, with the exception that fission yeast MAPK-activated protein kinases seem not to be directly involved in this process.
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| 3. |
- Asp, Eva, 1970, et al.
(author)
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Mkp1 and Mkp2, two MAPKAP-kinase homologues in Schizosaccharomyces pombe, interact with the MAP kinase Sty1
- 2003
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In: Molecular Genetics and Genomics. - 1617-4615 .- 1617-4623. ; 268, s. 585-597
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Journal article (peer-reviewed)abstract
- Mkp1 ( MAPKAP kinase Schizosaccharomyces pombe 1) and Mkp2 are two members from fission yeast of the sub-class of putative MAPK-activated protein kinases in yeasts, the other known members being Rck1 and Rck2 from Saccharomyces cerevisiae. The Mkp1 protein is readily co-immunoprecipitated with Sty1 from S. pombe extracts; Mkp2 shows a weaker interaction with Sty1. In mkp1 mutants, conjugation and meiosis proceed more readily and rapidly than in wild-type cells, in analogy to what was previously found for S. cerevisiae rck1 mutants. Conversely, overexpression of mkp1(+) delays meiosis. Mkp1 is phosphorylated in vivo in a sty1(+)-dependent manner; this modification is removed when cells are starved for nitrogen, a condition that is conducive to entry into stationary phase and meiosis. Overexpression of mkp1(+), like a sty1 mutation, also causes vegetative cells to elongate. The level of Mkp1 phosphorylation drops as cells enter mitosis. We have localised Mkp1 to the cytoplasm, excluded from the nucleus, in vegetative cells. The Mkp1 protein accumulates in zygotic asci and is concentrated within spores. The mkp2(+) gene has no noticeable impact on meiosis. Mkp2 is excluded from the nucleus in vegetative cells, and is concentrated at the septa of dividing cells. Mkp2 does not accumulate in meiotic cells.
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