Huang W, Erikson R L
Department of Cellular and Developmental Biology, Harvard University, Cambridge, MA 02138.
Proc Natl Acad Sci U S A. 1994 Sep 13;91(19):8960-3. doi: 10.1073/pnas.91.19.8960.
A variety of extracellular signals lead to the phosphorylation and activation of mitogen-activated protein kinases (MAP kinases). An activator of MAP kinases, Mek1, phosphorylates MAP kinases at threonine and tyrosine residues and is itself phosphorylated at serine-218 and -222 by the protooncogene product Raf-1. By introducing negatively charged residues that may mimic the effect of phosphorylation at positions 218 and 222, we have activated the capacity of Mek1 to phosphorylate MAP kinase by > 100-fold. The most effective activation by a single substitution resulted from the introduction of aspartate at position 218, whereas the introduction of either aspartate or glutamate at position 222 was ineffective. Expression of the activated Mek1 phosphorylation-site mutants in COS-7 cells led to the activation of MAP kinase in the cells and resulted in an increase in the mass of the transfected COS-7 cell population, suggesting an important role of Mek1 in the transduction of mitogenic signals.
多种细胞外信号可导致丝裂原活化蛋白激酶（MAP激酶）的磷酸化和激活。MAP激酶的激活剂Mek1在苏氨酸和酪氨酸残基处磷酸化MAP激酶，其自身在丝氨酸218和222处被原癌基因产物Raf-1磷酸化。通过引入可能模拟218和222位磷酸化作用的带负电荷残基，我们已将Mek1磷酸化MAP激酶的能力激活了100倍以上。单个取代产生的最有效激活是在218位引入天冬氨酸，而在222位引入天冬氨酸或谷氨酸均无效。在COS-7细胞中表达活化的Mek1磷酸化位点突变体导致细胞中MAP激酶的激活，并导致转染的COS-7细胞群体数量增加，提示Mek1在有丝分裂信号转导中起重要作用。
