Raf and fibroblast growth factor phosphorylate Elk1 and activate the serum response element of the immediate early gene pip92 by mitogen-activated protein kinase-independent as well as -dependent signaling pathways
Raf and fibroblast growth factor phosphorylate Elk1 and activate the serum response element of the immediate early gene pip92 by mitogen-activated protein kinase-independent as well as -dependent signaling pathways
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DOI：
10.1128/mcb.18.4.2272
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发表时间：
1998-04-01
影响因子：
5.3
通讯作者：
Rosner, MR
中科院分区：
文献类型：
--
作者：
Chung, KC;Gomes, I;Rosner, MR
以往的研究表明，有丝分裂原活化蛋白（MAP）激酶（MEK）的非依赖性信号通路所需要的激活的naf或成纤维细胞衍生的生长因子（FGF）的大鼠海马神经元H19-7细胞的分化。我们现在证明，Raf和FGF类似地诱导延长转录和翻译的立即早期基因pip 92在没有激活的MAP激酶（MAPKs）ERK 1和ERK 2。为了确定这种情况发生的机制并鉴定RaF激活的信号通路，我们研究了FGF和雌二醇激活的Raf-1-雌激素受体融合蛋白对pip 92启动子的诱导作用（Delta Raf-1：ER）在H19-7细胞中，pip 92启动子的缺失分析表明，通过MAPK非依赖性途径的激活主要发生在含有血清反应元件（SRE）的区域内，通过使用异源胸苷激酶启动子对SRE的进一步分析表明，Ets和CARG样位点都是必需的。Elk 1，其中hinds的Ets网站，磷酸化在体外和体内的MAPK非依赖性途径，和磷酸化的Elk 1-GAL 4融合蛋白通过这一途径是足够的反式激活。最后，通过凝胶过滤分离至少两种Elk 1激酶，并且通过凝胶内激酶测定分析揭示了至少三种新的Raf-activated Elk 1激酶。这些结果表明，FGF和Raf都激活MAPK非依赖性激酶，其刺激Elk 1磷酸化和立即早期基因转录。
Previous studies have shown that a mitogen activated protein (MAP) kinase (MEK)-independent signaling pathway is required by activated naf or fibroblast derived growth factor (FGF) for the differentiation of rat hippocampal neuronal H19-7 cells. We now demonstrate that both Raf and FGF similarly induce prolonged transcription and translation of the immediate early gene pip92 in the absence of activation of the MAP kinases (MAPKs) ERK1 and ERK2. To determine the mechanism by which this occurs and to identify mover RaF-activated signaling pathways, we investigated the induction of the pip92 promoter by both FGF and an estradiol-activated Raf-1-estrogen receptor fusion protein (Delta Raf-1:ER) in H19-7 cells, Deletion analysis of the pip92 promotes indicated that activation by the MAPK-independent pathway occurs primarily within the region containing a serum response element (SRE), Further analysis of the SRE by using a heterologous thymidine kinase promoter showed that both an Ets and CArG-like site are required. Elk1, which hinds to the Ets site, was phosphorylated both in vitro and in vivo by the MAPK-independent pathway; and phosphorylation of an Elk1-GAL4 fusion protein by this pathway was sufficient for transactivation. Finally, at least two Elk1 kinases were fractionated by gel filtration, and analysis by an in-gel kinase assay revealed at least three novel Raf-activated Elk1 kinases. These results indicate that both FGF and Raf activate MAPK-independent kinases that ran stimulate Elk1 phosphorylation and immediate early gene transcription.