Matsuda S, Kawasaki H, Moriguchi T, Gotoh Y, Nishida E
Department of Genetics and Molecular Biology, Kyoto University, Japan.
J Biol Chem. 1995 May 26;270(21):12781-6. doi: 10.1074/jbc.270.21.12781.
Osmotic shock induces a variety of biochemical and physiological responses in vertebrate cells. By analyzing extracts obtained from rat 3Y1 fibroblastic cells exposed to hyper-osmolar media, we have found that mitogen-activated protein kinases (MAPKs) and stress-activated protein kinases (SAPKs, also known as JNKs) are both activated in response to osmotic shock. MAPKK1 (MEK1) was also activated markedly. Furthermore, Raf-1 and MEKK were activated strikingly by the osmotic shock. Activation of Raf-1 and MEKK in response to osmotic shock was detected also in PC12 cells, in which MEKK activation by the osmotic shock was much stronger than that by epidermal growth factor. Activation of SAPKs in PC12 cells by the osmotic shock was also more marked than that by epidermal growth factor. The activated MEKK phosphorylated not only MAPKKs but also XMEK2, which is distantly related to MAPKK. Recombinant wild-type XMEK2, but not kinase-negative XMEK2, was able to phosphorylate and activate recombinant SAPK alpha in vitro. In addition, this activity of XMEK2 was activated by the activated MEKK. These results suggest that the MAPK cascade consisting of Raf-1, MAPKK, and MAPK and the SAPK cascade consisting of MEKK, XMEK2, and SAPK are both activated in response to osmotic shock. Finally, it was found that XMEK2 is a good substrate for SAPK.
渗透休克可在脊椎动物细胞中引发多种生化和生理反应。通过分析从暴露于高渗培养基的大鼠3Y1成纤维细胞中获得的提取物，我们发现丝裂原活化蛋白激酶（MAPK）和应激激活蛋白激酶（SAPK，也称为JNK）在渗透休克反应中均被激活。MAPKK1（MEK1）也被显著激活。此外，Raf-1和MEKK在渗透休克作用下被显著激活。在PC12细胞中也检测到Raf-1和MEKK在渗透休克反应中的激活，其中渗透休克对MEKK的激活作用比对表皮生长因子的激活作用强得多。渗透休克对PC12细胞中SAPK的激活作用也比表皮生长因子更显著。激活的MEKK不仅能磷酸化MAPKK，还能磷酸化与MAPKK关系较远的XMEK2。重组野生型XMEK2，而非激酶阴性的XMEK2，能够在体外磷酸化并激活重组SAPKα。此外，XMEK2的这种活性被激活的MEKK激活。这些结果表明，由Raf-1、MAPKK和MAPK组成的MAPK级联反应以及由MEKK、XMEK2和SAPK组成的SAPK级联反应在渗透休克反应中均被激活。最后，发现XMEK2是SAPK的良好底物。
