Modulation of Smad2-mediated signaling by extracellular signal-regulated kinase
Modulation of Smad2-mediated signaling by extracellular signal-regulated kinase
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DOI：
10.1074/jbc.m204597200
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发表时间：
2002-11-01
影响因子：
4.8
通讯作者：
Mathews, LS
中科院分区：
文献类型：
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作者：
Funaba, M;Zimmerman, CM;Mathews, LS
转化生长因子-β和丝裂原活化蛋白激酶通路的组成部分在控制细胞生长和分化方面相互作用。我们发现，激活素/转化生长因子-β信号的介体Smad2被激活的细胞外信号调节激酶1(ERK1)磷酸化，增加了Smad2蛋白的数量，导致转录活性增强。表皮生长因子增加了COS7细胞中Smad2的磷酸化，并通过共转染组分活性MEK1增强了水貂肺上皮细胞系L17中Smad2依赖的转录。此外，缺乏ERK位点的Smad2突变体可导致转录减少，而模拟ERK磷酸化的突变体则可刺激转录。转染组活性MEK1后，Smad2蛋白的量增加，而与ERK磷酸酶HVH2共转染后，Smad2蛋白的量减少。Smad2蛋白水平的升高是因为半衰期增加，并导致与Smad4形成的络合物增加。Smad2上ERK依赖的磷酸化位点位于Thr(8)，该位点与钙调蛋白结合区重叠。我们发现钙调蛋白通过ERK1抑制Smad2的磷酸化，而过度表达钙调蛋白或用离子霉素刺激钙调蛋白活性，会降低Smad2的水平。这些发现表明，ERK通路通过磷酸化Smad2来正向调节Smad2信号，而钙调素对Smad2信号的负调节部分是通过抑制这种磷酸化来实现的。
Components of the transforming growth factor-beta and mitogen-activated protein kinase pathways interact in controlling cell growth and differentiation. We show that phosphorylation of Smad2, a mediator of the activin/transforming growth factor-beta signal, by activated extracellular signal-regulated kinase 1 (ERK1) increases the amount of Smad2 protein and leads to enhanced transcriptional activity. Epidermal growth factor increased phosphorylation of Smad2 in COS7 cells, and Smad2-dependent transcription in a mink lung epithelial cell line, L17, was enhanced by co-transfection of a constitutively active MEK1. In addition, transfection of Smad2 mutants lacking ERK sites resulted in reduced transcription, whereas mutants that mimicked ERK phosphorylation stimulated transcription. The amount of Smad2 protein was increased by transfection with a constitutively active MEK1 and reduced by co-transfection with the ERK phosphatase, HVH2. The elevation of Smad2 protein levels was because of increased half-life and resulted in increased complex formation with Smad4. A site of ERK-dependent phosphorylation on Smad2 was located to Thr(8), a site that overlaps with the calmodulin binding region. We show that calmodulin inhibits Smad2 phosphorylation by ERK1, and overexpressing calmodulin, or stimulating calmodulin activity with ionomycin, reduces Smad2 levels. These findings suggest that the ERK pathway positively regulates Smad2 signaling by phosphorylating Smad2 and that negative regulation of Smad2 signaling by calmodulin is achieved in part by inhibiting this phosphorylation.