Wu Weidong, Jaspers Ilona, Zhang Wenli, Graves Lee M, Samet James M
Center for Environmental Medicine and Lung Biology, University of North Carolina, Chapel Hill 27599, USA.
Am J Physiol Lung Cell Mol Physiol. 2002 May;282(5):L1040-8. doi: 10.1152/ajplung.00390.2001.
We showed previously that epithelial growth factor (EGF) receptor (EGFR) signaling is triggered by metallic compounds associated with ambient air particles. Specifically, we demonstrated that As, Zn, and V activated the EGFR tyrosine kinase and the downstream kinases MEK1/2 and ERK1/2. In this study, we examined the role of Ras in EGFR signaling and the nuclear factor-kappaB (NF-kappaB) activation pathway and the possible interaction between these two signaling pathways in a human airway epithelial cell line (BEAS-2B) exposed to As, V, or Zn ions. Each metal significantly increased Ras activity, and this effect was inhibited by the EGFR tyrosine kinase activity inhibitor PD-153035. Adenoviral-mediated overexpression of a dominant-negative mutant form of Ras(N17) significantly blocked MEK1/2 or ERK1/2 phosphorylation in As-, Zn-, or V-exposed BEAS-2B cells but caused little inhibition of V-, Zn- or EGF-induced EGFR tyrosine phosphorylation. This confirmed Ras as an important intermediate effector in EGFR signaling. Interestingly, V, but not As, Zn, or EGF, induced IkappaBalpha serine phosphorylation, IkappaBalpha breakdown, and NF-kappaB DNA binding. Moreover, PD-153035 and overexpression of Ras(N17) each significantly blocked V-induced IkappaBalpha breakdown and NF-kappaB activation, while inhibition of MEK activity with PD-98059 failed to do so. In summary, exposure to As, Zn, and V initiated EGFR signaling and Ras-dependent activation of MEK1/2 and ERK1/2, but only V induced Ras-dependent NF-kappaB nuclear translocation. EGFR signaling appears to cross talk with NF-kappaB signaling at the level of Ras, but additional signals appear necessary for NF-kappaB activation. Together, these data suggest that, in V-treated BEAS-2B cells, Ras-dependent signaling is essential, but not sufficient, for activation of NF-kappaB.
我们之前表明，上皮生长因子（EGF）受体（EGFR）信号传导是由与环境空气颗粒物相关的金属化合物触发的。具体而言，我们证明了砷（As）、锌（Zn）和钒（V）激活了EGFR酪氨酸激酶以及下游激酶MEK1/2和ERK1/2。在本研究中，我们检测了Ras在EGFR信号传导和核因子-κB（NF-κB）激活途径中的作用，以及在暴露于As、V或Zn离子的人气道上皮细胞系（BEAS-2B）中这两条信号传导途径之间可能存在的相互作用。每种金属均显著增加Ras活性，且这种效应被EGFR酪氨酸激酶活性抑制剂PD-153035所抑制。腺病毒介导的显性负性突变形式的Ras（N17）过表达显著阻断了暴露于As、Zn或V的BEAS-2B细胞中MEK1/2或ERK1/2的磷酸化，但对V、Zn或EGF诱导的EGFR酪氨酸磷酸化几乎没有抑制作用。这证实了Ras是EGFR信号传导中的一个重要中间效应器。有趣的是，V而非As、Zn或EGF诱导了IκBα丝氨酸磷酸化、IκBα降解以及NF-κB与DNA结合。此外，PD-153035和Ras（N17）的过表达均显著阻断了V诱导的IκBα降解和NF-κB激活，而用PD-98059抑制MEK活性则未能做到这一点。总之，暴露于As、Zn和V启动了EGFR信号传导以及MEK1/2和ERK1/2的Ras依赖性激活，但只有V诱导了Ras依赖性NF-κB核转位。EGFR信号传导似乎在Ras水平与NF-κB信号传导相互作用，但NF-κB激活似乎还需要其他信号。这些数据共同表明，在V处理的BEAS-2B细胞中，Ras依赖性信号传导对于NF-κB激活是必不可少的，但并不充分。
