Airway smooth muscle prostaglandin-EP1 receptors directly modulate β2-adrenergic receptors within a unique heterodimeric complex

Multiple and paradoxical effects of airway smooth muscle (ASM) 7-transmembrane-spanning receptors activated during asthma, or by treatment with bronchodilators such as beta(2)-adrenergic receptor (PAR) agonists, indicate extensive receptor crosstalk. We examined the signaling of the prostanoid-EP1 receptor, since its endogenous agonist prostaglandin E-2 is abundant in the airway, but its functional implications are poorly defined. Activation of EP1 failed to elicit ASM contraction in mouse trachea via this G(alpha q)-coupled receptor. However, EP1 activation markedly reduced the bronchodilatory function Of PAR agonist, but not forskolin, indicating an early pathway interaction. Activation of EP1 reduced PAR-stimulated cAMP in ASM but did not promote or augment PAR phosphorylation or alter PAR trafficking. Bioluminescence resonant energy transfer showed EP1 and beta(2)AR formed heterodimers, which were further modified by EP1 agonist. In cell membrane [S-35]GTP gamma S binding studies, the presence of the EP1 component of the dimer uncoupled PAR from Gus, an effect accentuated by EP1 agonist activation. Thus alone, EP1 does not appear to have a significant direct effect on airway tone but acts as a modulator of the PAR, altering Gus coupling via steric interactions imposed by the EP1:beta(2)AR heterodimeric signaling complex and ultimately affecting PAR-mediated bronchial relaxation. This mechanism may contribute to beta-agonist resistance found in asthma.