Blank J L, Gerwins P, Elliott E M, Sather S, Johnson G L
Division of Basic Sciences, National Jewish Center for Immunology and Respiratory Medicine, Denver, Colorado 80206, USA.
J Biol Chem. 1996 Mar 8;271(10):5361-8. doi: 10.1074/jbc.271.10.5361.
Mitogen-activated protein/ERK kinase kinases (MEKKs) phosphorylate and activate protein kinases which in turn phosphorylate and activate the p42/44 mitogen-activated protein kinase (MAPK), c-Jun/stress-activated protein kinases (JNKs), and p38/Hog1 kinase. We have isolated the cDNAs for two novel mammalian MEKKs (MEKK 2 and 3). MEKK 2 and 3 encode proteins of 69.7 and 71 kDa, respectively. The kinase domains encoded in the COOH-terminal moiety are 94% conserved; the NH2-terminal moieties are approximately 65% homologous, suggesting this region may encode sequences conferring differential regulation of the two kinases. Expression of MEKK 2 or 3 in HEK293 cells results in activation of p42/44MAPK and JNK but not of p38/Hog1 kinase. Immunoprecipitated MEKK 2 phosphorylated the MAP kinase kinases, MEK 1, and JNK kinase. Titration of MEKK 2 and 3 expression in transfection assays indicated that MEKK 2 preferentially activated JNK while MEKK 3 preferentially activated p42/44MAPK. These findings define a family of MEKK proteins capable of regulating sequential protein kinase pathways involving MAPK members.
丝裂原活化蛋白/细胞外信号调节激酶激酶（MEKKs）可磷酸化并激活蛋白激酶，而这些蛋白激酶反过来又会磷酸化并激活p42/44丝裂原活化蛋白激酶（MAPK）、c-Jun/应激激活蛋白激酶（JNKs）以及p38/Hog1激酶。我们已经分离出了两种新型哺乳动物MEKKs（MEKK 2和MEKK 3）的cDNA。MEKK 2和MEKK 3分别编码69.7 kDa和71 kDa的蛋白质。COOH末端部分编码的激酶结构域有94%的保守性；NH2末端部分约有65%的同源性，这表明该区域可能编码赋予这两种激酶不同调节作用的序列。在HEK293细胞中表达MEKK 2或MEKK 3会导致p42/44MAPK和JNK的激活，但不会导致p38/Hog1激酶的激活。免疫沉淀的MEKK 2可磷酸化MAP激酶激酶、MEK 1和JNK激酶。转染实验中对MEKK 2和MEKK 3表达的滴定表明，MEKK 2优先激活JNK，而MEKK 3优先激活p42/44MAPK。这些发现定义了一个MEKK蛋白家族，该家族能够调节涉及MAPK成员的连续蛋白激酶途径。
