Shiozaki K, Shiozaki M, Russell P
Departments of Molecular Biology and Cell Biology, The Scripps Research Institute, La Jolla, California 92037, USA.
Mol Biol Cell. 1998 Jun;9(6):1339-49. doi: 10.1091/mbc.9.6.1339.
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.
裂殖酵母Spc1/StyI丝裂原活化蛋白激酶（MAPK）可被多种环境刺激激活，包括高渗透压、氧化应激和热休克。Spc1/StyI由MAPK激酶（MEK）Wis1激活，而Wis1本身则由MEK激酶（MEKK）Wik1/Wak1/Wis4激活。Spc1/StyI可被酪氨酸磷酸酶Pyp1和Pyp2失活。最近有报道称，抑制Pyp1在氧化应激和热休克反应中起关键作用。这些结论基于三项发现：1）渗透压、氧化和热应激在wis4细胞中激活Spc1/StyI；2）氧化应激和热休克在表达Wis1AA的细胞中激活Spc1/StyI，其中MEKK共有磷酸化位点被丙氨酸取代；3）Spc1/StyI在Deltapyp1细胞中被最大程度激活。与这些发现相反，我们报道：1）wis4细胞中渗透压应激对Spc1/StyI的激活作用大大降低；2）wis1-AA和Deltawis1细胞具有相同的表型；3）所有形式的应激在Deltapyp1细胞中激活Spc1/StyI。我们还报道，热休克而非渗透压或氧化应激在wis1-DD细胞中激活Spc1，wis1-DD细胞表达的Wis1蛋白中MEKK共有磷酸化位点被天冬氨酸取代。因此，渗透压和氧化应激通过MEKK依赖的过程激活Spc1/StyI，而热休克通过一种不需要MEKK激活或Pyp1抑制的新机制激活Spc1/StyI。
