Heat stress activates fission yeast Spc1/StyI MAPK by a MEKK-independent mechanism.
Fission yeast Spc1/StyI MAPK is activated by many environmental insults including high osmolarity, oxidative stress, and heat shock. Spc1/StyI is activated by Wis1, a MAPK kinase (MEK), which is itself activated by Wik1/Wak1/Wis4, a MEK kinase (MEKK). Spc1/StyI is inactivated by the tyrosine phosphatases Pyp1 and Pyp2. Inhibition of Pyp1 ... was recently reported to play a crucial role in the oxidative stress and heat shock responses. These conclusions were based on three findings: 1) osmotic, oxidative, and heat stresses activate Spc1/StyI in wis4 cells; 2) oxidative stress and heat shock activate Spc1/StyI in cells that express Wis1AA, in which MEKK consensus phosphorylation sites were replaced with alanine; and 3) Spc1/StyI is maximally activated in Deltapyp1 cells. Contrary to these findings, we report: 1) Spc1/StyI activation by osmotic stress is greatly reduced in wis4 cells; 2) wis1-AA and Deltawis1 cells have identical phenotypes; and 3) all forms of stress activate Spc1/StyI in Deltapyp1 cells. We also report that heat shock, but not osmotic or oxidative stress, activate Spc1 in wis1-DD cells, which express Wis1 protein that has the MEKK consensus phosphorylation sites replaced with aspartic acid. Thus osmotic and oxidative stress activate Spc1/StyI by a MEKK-dependent process, whereas heat shock activates Spc1/StyI by a novel mechanism that does not require MEKK activation or Pyp1 inhibition.
Mesh Terms:
Binding Sites, Calcium-Calmodulin-Dependent Protein Kinases, Cell Cycle Proteins, Conserved Sequence, Enzyme Activation, Heat-Shock Response, MAP Kinase Kinase Kinases, Mitogen-Activated Protein Kinases, Osmotic Pressure, Oxidative Stress, Phosphorylation, Protein Tyrosine Phosphatases, Protein-Serine-Threonine Kinases, Schizosaccharomyces, Schizosaccharomyces pombe Proteins, Serine, Signal Transduction, Threonine
Binding Sites, Calcium-Calmodulin-Dependent Protein Kinases, Cell Cycle Proteins, Conserved Sequence, Enzyme Activation, Heat-Shock Response, MAP Kinase Kinase Kinases, Mitogen-Activated Protein Kinases, Osmotic Pressure, Oxidative Stress, Phosphorylation, Protein Tyrosine Phosphatases, Protein-Serine-Threonine Kinases, Schizosaccharomyces, Schizosaccharomyces pombe Proteins, Serine, Signal Transduction, Threonine
Mol. Biol. Cell
Date: Jun. 01, 1998
PubMed ID: 9614178
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