Identification in human airways smooth muscle cells of the prostanoid receptor and signalling pathway through which PGE2 inhibits the release of GM-CSF

1 The prostanoid receptor(s) on human airways smooth muscle (HASM) cells that mediates the inhibitory effect of PGE(2) on interleukin (IL)-1beta-induced granulocyte/macrophage colony-stimulating factor (GM-CSF) release has been classified. 2 IL-1beta evoked the release of GM-CSF from HASM cells, which was suppressed by PGE(2), 16,16-dimethyl PGE(2) (nonselective), misoprostol (EP2/EP3-selective), ONO-AE1-259 and butaprost (both EP2-selective) with pIC(50) values of 8.61, 7.13, 5.64, 8.79 and 5.43, respectively. EP-receptor agonists that have selectivity for the EP1- (17-phenyl-omega-trinor PGE(2)) and EP3-receptor (sulprostone) subtypes as well as cicaprost (IP-selective), PGD(2), PGF(2alpha) and U-46619 (TP-selective) were poorly active or inactive at concentrations up to 10 muM. 3 AH 6809, a drug that can be used to selectively block EP2-receptors in HASM cells, antagonised the inhibitory effect of PGE(2), 16,16-dimethyl PGE(2) and ONO-AE1-259 with apparent pA(2) values of 5.85, 6.09 and 6.1 respectively. In contrast, the EP4-receptor antagonists, AH 23848B and L-161,982, failed to displace to the right the concentration - response curves that described the inhibition of GMCSF release evoked by PGE(2) and ONO-AE1-259. 4 Inhibition of GM-CSF release by PGE(2) and 8-Br-cAMP was abolished in cells infected with an adenovirus vector encoding an inhibitor protein of cAMP-dependent protein kinase (PKA) but not by H-89, a purported small molecule inhibitor of PKA. 5 We conclude that prostanoid receptors of the EP2-subtype mediate the inhibitory effect of PGE(2) on GM-CSF release from HASM cells by recruiting a PKA-dependent pathway. In addition, the data illustrate that caution should be exercised when using H-89 in studies designed to assess the role of PKA in biological processes.