Persistent localization of activated extracellular signal-regulated kinases (ERK1/2) is epithelial cell-specific in an inhalation model of asbestosis.

Asbestos fibers up-regulate the extracellular signal-regulated kinase (ERK1/2) pathway in mesothelial and pulmonary epithelial cells in vitro, but the cell-type expression patterns and intracellular localization of activated, ie, phosphorylated, ERK in the lung after inhalation of asbestos are unclear. C57/BL6 mice were exposed to 7-mg/m(3) air of crocidolite asbestos for 5 and 30 days, the times required for the development of epithelial cell hyperplasia and fibrotic lesions, respectively. Exposure to asbestos caused striking increases in both unphosphorylated and phosphorylated ERK (p-ERK), which were most marked at 30 days and co-localized in bronchiolar and alveolar epithelial cells using an antibody to cytokeratin. Alveolar macrophages, detected with an anti-macrophage antibody, did not express p-ERK. p-ERK was localized at the apical cell surface of bronchiolar and alveolar type II epithelial cells exposed to asbestos fibers, and was most marked in areas of epithelial hyperplasia in association with fibrotic lesions. Because translocation of p-ERK to the nucleus is associated with activation of early response genes and transcription factors, laser scanning cytometry was used to determine the kinetics of activation and nuclear translocation of p-ERK in an alveolar type II epithelial cell line in vitro after exposure to asbestos or the ERK stimuli, epidermal growth factor, or H(2)O(2). Results showed that cytoplasmic to nuclear translocation of p-ERK occurred in a protracted manner in cells exposed to asbestos. The immunolocalization of p-ERK at the membrane surface, a site of initial exposure to asbestos fibers, and the chronic activation of p-ERK in epithelial cells at sites of fibrogenesis are consistent with the concept that epithelial cell signaling through the ERK pathway contributes to remodeling of the lung during the development of pulmonary fibrosis.

A mutant epidermal growth factor receptor targeted to lung epithelium inhibits asbestos-induced proliferation and proto-oncogene expression.

Asbestos is a ubiquitous naturally occurring fiber causing multiple cancers and fibroproliferativedisease. The mechanisms of epithelial cell hyperplasia, a hallmark of the initiation of lung cancers by asbestos, have been unclear. We demonstrate here that mice expressing a dominant-negative mutant epidermal growth factor receptor (EGFR) under the control of the human lung surfactant protein-C promoter exhibit decreased pulmonary epithelial cell proliferation without alterations in asbestos-induced inflammation. In contrast to transgene-negative littermates, inhalation of asbestos by mice expressing the mutant EGFR does not result in early and elevated expression of early response proto-oncogenes (fos/jun or activator protein 1 family members). Additionally, quantitative reverse transcriptase-PCR analysis for levels of c-jun and c-fos in bronchiolar epithelium isolated by laser capture microdissection demonstrates increases in expression of these genes in asbestos-exposed epithelial cells. Results show that the EGFR mediates both asbestos-induced proto-oncogene expression and epithelial cell proliferation, providing a rationale for modification of its phosphorylation in preventive and therapeutic approaches to lung cancers and mesothelioma.