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Title: cAMP-Mediated Responses in Human Airway Smooth Muscle Cells and Epithelial Cells: Roles for PKA?
Author: Kaur, Manminder
ISNI:       0000 0001 3595 6326
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2008
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p2-Adrenoceptor agonists are a mainstay in asthma therapy and act via adenylyl cyclase to increase intraceJlular cyclic adenosine-3 ,5 -monophosphate (cAMP). Upon binding ofcAMP to the regulatory subunits of protein kinase A (PKA), there is dissociation of the catalytic subunits. These may then phosphorylate downstream target proteins to playa key role in the regulation of airway smooth muscle relaxation and increased ciliary beat frequency in epithelial cells. PKA also regulates the release of inflammatory mediators in both human airway smo~h muscle (HASM) and epithelial cells. In HASM cells, p2-adrenoceptor agonists and cAMP-elevating agents repressed interleukin (IL)-Ip-induced granulocyte/macrophage colony stimulating factor (GM-CSF), intercellular adhesion molecule (ICAM)-l and IL-8 release, but had no effect on IL-6 release, suggesting that cAMP can differentially regulate cytokine release. The role of PKA in cAMP-mediated repression was investigated by over expressing PIGa, a highly selective inhibitor of PKA, which was introduced to cells by an adenoviral expression system. The effect of cAMP modulation on IL-Ip-stimulated GM~ CSF, ICAM-I, IL-8 and IL-6 expression was also investigated in bronchial airway epithelial BEAS2B cells. In BEAS-2B cells harbouring a 2 x GRE reporter, long-and short-acting Pradrenoceptor agonists as well as cAMP-elevating agents enhanced glucocorticoid (dexamethasone, budesonide and ,' fluticasone)-induced GRE-dependent transcription in a PKA-dependent manner. The effect of P2- adrenoceptor agonists and glucocorticoids was examined on nine previously identified glucocorticoidinducible genes using real-time peR. This analysis d.emonstrated that four of these genes (MKP-I, RGS2, p57kip2 and METIX) were additively or synergistically up-regulated in the presence of a cAMP elevating agent and a glucocorticoid in combination. Pathways mediating this synergistic effect were also investigated. These findings show that cAMP enhances the transactivation ability of glucocorticoids acting via the glucocorticoid receptor. This effect is steroid sparing and also produces levels of glucocorticoid-dependent transcription that cannot be achieved by glucocorticoid alone. Genes such as p57lcip2 and RGS2 provide proof of concept and may help explain the enhanced therapeutic effect seen clinically with long-acting Pradrenoceptor agonist/inhaled corticosteroid combination therapies such as AdvairllJ and Symbicort���®.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available