Activation of the EGF receptor signaling pathway in human airway epithelial cells exposed to metals

We have previously shown that exposure to combustion-derived metals rapidly (within 20 min) activated mitogen-activated protein kinases (MAPK), includ ing extracellular signal-regulated kinase (ERK), in the human bronchial epi thelial cell line BEAS. To study the mechanisms responsible for metal-induc ed activation of ERK, we examined the effect of noncytotoxic exposures to A s, Cu, V, or Zn on the kinases upstream of ERK in the epidermal growth fact or (EGF) receptor signaling pathway. Western blotting using phospho-specifi c ERK1/2 antibody demonstrated the selective MEK1/2 inhibitor PD-98059 bloc ked metal-induced phosphorylation of ERK1/2. Meanwhile, Western blotting us ing a phospho-specific MEK1/2 antibody showed that these metals induce a ra pid phosphorylation of MEK1/2. Kinase activity assays confirmed the activat ion of MEK1/2 by metal treatment. Immunoprecipitation studies demonstrated that As, Cu, V, or Zn induces EGF receptor phosphorylation. Furthermore, th e EGF receptor-specific tyrosine kinase inhibitor (PD-153035) significantly blocked the phosphorylation of MEK1/2 initiated by metals. Interestingly, we observed low levels of Raf-l activity that were not increased by metal e xposure in these cells through kinase activity assay. Finally, transfection assays showed that MEK1/2 inhibition could inhibit traits-activation of El k1, a transcription factor in the ERK pathway, in BEAS cells exposed to met als. Together, these data demonstrate that As, Cu, V, and Zn can activate t he EGF receptor signaling pathway in BEAS cells and suggest that this mecha nism may be involved in pulmonary responses to metal inhalation.