Shapiro P S, Ahn N G
Department of Chemistry and Biochemistry, University of Colorado, Boulder 80309, USA.
J Biol Chem. 1998 Jan 16;273(3):1788-93. doi: 10.1074/jbc.273.3.1788.
Inactivation of growth factor-regulated mitogen-activated protein (MAP) kinases (ERK1 and ERK2) has been proposed to occur in part through dephosphorylation by the dual specificity MAP kinase phosphatase-1 (MKP-1), an immediate early gene that is induced by mitogenic signaling. In this study, we examined the effect of MKP-1 on signaling components upstream of ERK1 and ERK2. Coexpression of MKK1 or MKK2 with MKP-1 resulted in 7-10-fold activation of mitogen-activated protein kinase kinase (MKK), which required the presence of regulatory serine phosphorylation sites. Endogenous MKK1 and MKK2 were also activated upon MKP-1 expression. Raf-1, a direct regulator of MKK1 and MKK2, was activated under these conditions, and a synergistic activation of MKK was observed upon coexpression of Raf-1 and MKP-1. This effect did not appear to involve synthesis of autocrine growth factors or the inhibition of basal extracellular signal-regulated kinase (ERK) activity but was inhibited by a dominant negative Ras mutant, indicating that MKP-1 enhances Ras-dependent activation of Raf-1 in a cell autonomous manner. This study demonstrates positive feedback regulation of Raf-1 and MKK by the MKP-1 immediate early gene and a potential mechanism for activating Raf-1/MKK signaling pathways alternative to those involving ERK.
生长因子调节的丝裂原活化蛋白（MAP）激酶（ERK1和ERK2）的失活被认为部分是通过双特异性MAP激酶磷酸酶-1（MKP-1）去磷酸化而发生的，MKP-1是一种由促有丝分裂信号诱导的即刻早期基因。在本研究中，我们检测了MKP-1对ERK1和ERK2上游信号成分的影响。MKK1或MKK2与MKP-1共表达导致丝裂原活化蛋白激酶激酶（MKK）激活7至10倍，这需要调节性丝氨酸磷酸化位点的存在。内源性MKK1和MKK2在MKP-1表达时也被激活。MKK1和MKK2的直接调节因子Raf-1在这些条件下被激活，并且在Raf-1和MKP-1共表达时观察到MKK的协同激活。这种效应似乎不涉及自分泌生长因子的合成或基础细胞外信号调节激酶（ERK）活性的抑制，但被显性负性Ras突变体抑制，表明MKP-1以细胞自主方式增强Raf-1的Ras依赖性激活。本研究证明了MKP-1即刻早期基因对Raf-1和MKK的正反馈调节以及激活Raf-1/MKK信号通路的潜在机制，该机制不同于涉及ERK的信号通路。
