A2 adenosine receptors regulate CFTR through PKA and PLA2

Abstract

We investigated adenosine (Ado) activation of the cystic fibrosis transmembrane conductance regulator (CFTR) in vitro and in vivo. A_2B Ado receptors were identified in Calu-3, IB-3-1, COS-7, and primary human airway cells. Ado elevated cAMP in Calu-3, IB-3-1, and COS-7 cells and activated protein kinase A-dependent halide efflux in Calu-3 cells. Ado promoted arachidonic acid release from Calu-3 cells, and phospholipase A₂(PLA₂) inhibition blocked Ado-activated halide efflux in Calu-3 and COS-7 cells expressing CFTR. Forskolin- and β₂-adrenergic receptor-stimulated efflux were not affected by the same treatment. Cytoplasmic PLA₂(cPLA₂) was identified in Calu-3, IB-3-1, and COS-7 cells, but cPLA₂ inhibition did not affect Ado-stimulated cAMP concentrations. In cftr(+) and cftr(−/−) mice, Ado stimulated nasal Cl⁻ secretion that was CFTR dependent and sensitive to A₂ receptor and PLA₂ blockade. In COS-7 cells transiently expressing ΔF508 CFTR, Ado activated halide efflux. Ado also activated G551D CFTR-dependent halide efflux when combined with arachidonic acid and phosphodiesterase inhibition. In conclusion, PLA₂ and protein kinase A both contribute to A₂ receptor activation of CFTR, and components of this signaling pathway can augment wild-type and mutant CFTR activity.