Tyrosine kinase dependent mechanisms underlying airway inflammation in asthma

Hamilton, Lynnsey M (2003) Tyrosine kinase dependent mechanisms underlying airway inflammation in asthma. University of Southampton, Doctoral Thesis.

Record type: Thesis (Doctoral)

Abstract

Tyrosine phosphorylation in the bronchial epithelium in severe asthma was significantly greater than either normal controls or mild asthma, a change that was unaffected by the addition of corticosteroids. Tyrosine phosphorylation was significantly decreased in mild asthma when compared with normal controls and severe asthmatics. Treatment of bronchial epithelial cells with hydrogen peroxide (H₂O₂) TNFα or EGF led to changes in tyrosine phosphorylation of several proteins including the EGF receptor. As a functional readout, IL-8 release was measured and shown to be increased in EGF, TNFα or H₂O₂ treated cells, which could be suppressed with addition of the selective EGFR tyrosine kinase inhibitor, tyrphostin AG1478, but was unaffected by the corticosteroid, dexamethasone. Activation of NFκB by EGF was demonstrated using co-transfection studies with an IκBα reporter construct and a dominant negative EGFR construct. Microarrays identified the presence of 46 genes that were induced by TNFα in an EGFR dependent manner including inflammatory mediators, growth factors and lipid mediators. Expression of some of these genes were validated using qPCR. These data suggest that the activity of protein tyrosine kinases is increased in severe asthma and that components of the disease are unresponsive to corticosteroids. IL-8 release from bronchial epithelial cells is stimulated through EGFR dependent mechanism(s) that may involved NFκB. This may contribute to neutrophilic inflammation characteristic of severe asthma, and may reflect the enhanced responses caused by persistent inflammation and epithelial damage and repair.

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