Expression of functional β2-adrenergic receptors in the lung epithelial cell lines 16HBE14o-, Calu-3 and A549

Adrenergic drugs acting through the beta(2)-adrenoceptor (beta(2)-AR) adenylate cyclase (AC) signal transduction system elicit a variety of responses within the mammalian airway epithelium; however, its composition of multiple phenotypically differentiated cell types complicates the understanding of the regulation cascades within this tissue. The present study evaluates beta(2)-AR mRNA level, number, subtype and the cyclic adenosine-3',5'-monophosphate (cyclic AMP) response to isoproterenol (iso) in the human airway epithelial cell lines 16HBE14o(-), Calu-3 and A549, using reverse transcriptase polymerase chain reaction (RT-PCR), radioligand binding studies, [H-3]-radioimmunoassay and immunocytochemical staining. After 4-5 days in culture, all three cell types produced beta(2)-AR mRNA and protein at a magnitude of gene expression levels Calu-3 greater than or equal to 16HBE14o(-) > A549, whereas control cells Cos-1 and Caco-2 were negative. The beta(2)-AR adenylate cyclase system was highly expressed and functional in the human air-way epithelia] cells Calu-3 and 16HBE14o(-). The mean beta(2)-AR density (B-max), equilibrium dissociation constant (K-D), and the percentage of beta-AR subtypes assessed by radioligand binding were approximately 9908 +/- 1127 and 6423 +/- 895 binding sites/cell, 32 +/- 2.7 pM and 25 +/- 1.1 pM, and approximately 100% in Calu-3 and 16HBE14o(-) cells, respectively. However, in the alveolar cell type A549 the cell surface beta(2)-AR was virtually undetectable by (-)-[I-121]-iodocyanopindolol (ICYP) binding. Stimulation of cultured cells with (-)-isoproterenol enhanced the basal cyclic AMP accumulation only in Calu-3 and 16HBE14o- cells, which was blocked by the beta(2)-selective antagonist ICI 118,551, but not by the beta(1)-selective antagonist CGP 20712A, confirming functional coupling of the beta(2)-AR to adenylate cyclase in these cells. Immunocytochemical staining localised the receptor on the cell membrane and the cytoplasm in Calu-3 and 16HBE14o(-) cells, while it was confined to the cytoplasm only in A549 cells. In conclusion, the beta(2)-AR expression and its functional coupling to adenylyl cyclase was very high in the human airway epithelial cells Calu-3 and 16HBE14o(-), but not in A549, suggesting that the cell lines Calu-3 and 16HBE14o(-) present suitable models to study function and regulation of the beta-adrenoceptor signalling in the respiratory system. (C) 2004 Elsevier B.V. All rights reserved.