REGULATION OF BETA-AGONIST-MEDIATED AND PROSTAGLANDIN-E(2)-MEDIATED ADENYLYL-CYCLASE ACTIVITY IN HUMAN AIRWAY EPITHELIAL-CELLS

Despite the importance of beta(2)-adrenergic receptor (beta(2)AR) stimulation in mediating airway epithelial cell function, little is known regarding its regulation in airway epithelium. Perturbations of the airway environment associated with disease states, including the management of bronchomotor tone with beta-agonists, expose airways to putative regulators of beta(2)AR signal transduction. In this communication, we describe the desensitization of beta(2)AR signal transduction in the human airway epithelial cell line BEAS-2B. Examination of both beta-agonist- and prostaglandin E(2) (PGE(2))-mediated cAMP generation in BEAS-2B cells reveals both agonist-specific (homologous) and non-agonist-specific (heterologous) desensitization of these G protein-coupled receptor pathways. Short-term homologous desensitization of beta(2)AR-mediated cAMP generation was characterized by an similar to 60% loss of maximal responsiveness to isoproterenol (ISO) when cells were pretreated 30 min with 10 mu M ISO. A reduced sensitivity to ISO was also evidenced by an similar to 4-fold increase in the EC(50) for ISO stimulation of adenylyl cyclase (AC). Short-term heterologous desensitization was characterized by an increase in EC(50) (similar to 2- to 3-fold) with no change in maximal responsiveness to ISO in cells pretreated with either forskolin or PGE(2). Qualitatively similar findings characterized short-term homologous and heterologous desensitization of PGE(2)-mediated AC activity. Short-term agonist-specific desensitization of the beta(2)AR was associated with, but not dependent upon, rapid beta(2)AR sequestration. Long-term pretreatment of cells with 10 nM ISO and 1 mu M PGE(2) eliminated AC responsiveness to subsequent ISO and PGE(2) stimulation, respectively. Exposure of BEAS-2B cells to ISO for 24 h resulted in an similar to 70% loss of beta(2)ARs, whereas chronic forskolin or PGE(2) pretreatment had no effect on beta(2)AR number. Long-term pretreatment of cells designed to elicit heterologous desensitization was associated with reductions in maximal responsiveness to ISO and PGE(2) that appear to be related to a loss in inherent AC activity. These findings hold strong implications regarding the effect of beta(2)AR desensitization on epithelial cell function and the role of beta-agonists in the management of airway disease.