Cell-specific activation profile of extracellular signal-regulated kinase 1/2, Jun N-terminal kinase, and p38 mitogen-activated protein kinases in asthmatic airways

Background: Many airway cells manifest signs of chronic activation in asthma. The mechanism of this chronic activation is unknown. Objectives: We sought to study the activation of the mitogen-activated protein kinase (MAPK) signaling pathway in airway cells. Methods: Endobronchial biopsy specimens from patients with severe and mild asthma (n = 17 in each group) and healthy, control subjects (n = 15) were analyzed for the phosphorylated MAPKs extracellular signal-regulated kinase (ERK) 1/2, p38, and Jun N-terminal kinase (JNK) and their downstream effectors by means of immunofluorescence staining. Airway epithelial activation of ERK1/2 and p38 was studied by using Western blotting. Epithelial function was studied by means of real-time PCR, ELISA, and the thymidine incorporation assay. Results: We detected strong phospho-ERK1/2 staining in airway epithelium and smooth muscle cells in biopsy specimens from asthmatic patients. Fluorescent areas per image, as well as mean fluorescence intensity, were significantly (P <.0001) different among the 3 study groups (patients with severe asthma, patients with mild asthma, and healthy control subjects). Patients with severe asthma also demonstrated strong phospho-p38 staining, mostly in epithelial cells, which was significantly different from that in patients with mild asthma (P =.0001) and healthy control subjects (P =.02). Phospho-JNK primarily stained airway smooth muscle cells. Healthy subjects showed the highest intensity of phospho-JNK staining compared with that seen in patients with severe (P =.004) and mild asthma (P =.003). Inhibition of ERKI/2 and p38 in primary airway epithelial cells blocked their proliferation and expression of select, but not all, chemokines. Conclusions: Significant phosphorylation of ERK1/2 and p38 and their correlation with disease severity suggests that the