Marked phenotypic changes of the bronchial epithelium characterize asthma, including thickening of the epithelial layer, mucous cell hyperplasia, and mucous hyper-secretion. Resolution of asthma, thus, necessitates activation of mechanisms that facilitate the re-emergence of a quiescent bronchial cell phenotype. Our work indicates that this process involves bronchial cell apoptosis. In this application, we propose to identify the signals that mediate this process with an emphasis on the role of Fas signaling. to do this we will employ an adoptive transfer model of airway inflammation and hyper-responsiveness to aero-allergens that we established in our laboratory. By performing adoptive transfers of activated T cells into mutant mice, the role of key molecules, such as Fas, in mediating events (i.e., apoptosis) in the epithelium will be examined. Our data also suggest that apoptosis of bronchial cells causes release of immunomodulatory substances such as IL-16 and tumor growth factor (TGF)-beta, which we speculate, further enhances asthma resolution. to explore this further, we plan to identify the role of caspases in mediating expression of these substances and will employ cytokine gene arrays to determine alterations in expression of other cytokines. In the second part of this application, we will examine the molecular mechanisms that control internal localization and cell surface transport of Fas. The foundation for these studies rests on collected observations indicating that Fas is normally sequestered in an internal vesicular compartment of airway cells, and is mobilized to the cell surface by specific signals, as exemplified by interferon-gamma, (IFN-gamma), thereby facilitating apoptosis. Our preliminary work suggests that IFN-gamma mediated transport involves an inducible tyrosine phosphorylation of the Fas protein. Using a variety of strategies in airway cell lines, including cell fractionation analysis, confocal microscopy, immunoprecipitations (IP) of metabolically labeled cells, coupled IP-Westerns, and cDNA expression analyses of truncated and mutated Fas constructs, we propose to further characterize and extend these findings. Overall, we believe these studies have significant implications for understanding basic biological processes that mediate resolution of airway cell activation in asthma.
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