Airway smooth muscle prostaglandin-EP1 receptors directly modulate  2-adrenergic receptors within a unique heterodimeric complex

Abstract

Multiple and paradoxical effects of airway smooth muscle (ASM) 7-transmembrane-spanning receptors activated during asthma, or by treatment with bronchodilators such as β 2 -adrenergic receptor (β 2 AR) agonists, indicate extensive receptor crosstalk. We examined the signaling of the prostanoid-EP 1 receptor, since its endogenous agonist prostaglandin E 2 is abundant in the airway, but its functional implications are poorly defined. Activation of EP 1 failed to elicit ASM contraction in mouse trachea via this G αq -coupled receptor. However, EP 1 activation markedly reduced the bronchodilatory function of β 2 AR agonist, but not forskolin, indicating an early pathway interaction. Activation of EP 1 reduced β 2 AR-stimulated cAMP in ASM but did not promote or augment β 2 AR phosphorylation or alter β 2 AR trafficking. Bioluminescence resonant energy transfer showed EP 1 and β 2 AR formed heterodimers, which were further modified by EP 1 agonist. In cell membrane [ 35 S]GTPγS binding studies, the presence of the EP 1 component of the dimer uncoupled β 2 AR from G αs , an effect accentuated by EP 1 agonist activation. Thus alone, EP 1 does not appear to have a significant direct effect on airway tone but acts as a modulator of the β 2 AR, altering G αs coupling via steric interactions imposed by the EP 1 :β 2 AR heterodimeric signaling complex and ultimately affecting β 2 AR-mediated bronchial relaxation. This mechanism may contribute to β-agonist resistance found in asthma. IntroductionThe 7-transmembrane-spanning (7-TM-spanning) receptors represent the largest signaling family in the genome. We estimate that the lung expresses 25-50 7-TM receptors in airway epithelial cells, airway smooth muscle (ASM), pulmonary vasculature, alveolar walls, and resident immune cells (1). In regard to asthma, several 7-TM receptors play established roles in bronchoconstriction (e.g., M 3 -muscarinic receptor) and bronchodilation (e.g., β 2 -adrenergic receptor [β 2 AR]). Despite identification of the endogenous ligands and receptor localization, there are a number of 7-TM receptors expressed in the airway whose functions are unknown, or appear to function paradoxically, based on recombinantly expressed receptors in model cell systems. This lack of understanding of receptor function has impeded our ability to ascertain the role of these ligands (some of which are markedly increased in asthma) in the relaxation/contraction of ASM; thus the mechanistic basis of bronchial hyperreactivity and bronchoconstriction in asthma remains only partially understood. In many cases the basis for incomplete mechanistic information can be attributed to the nature of recombinant expression systems, which may not take

Chemokine (C-X-C Motif) Receptor 4 and Atypical Chemokine Receptor 3 Regulate Vascular α1-Adrenergic Receptor Function

“…Regulation of GPCR function is complex and cross-talk between GPCR-signaling pathways, whereby activation of one receptor system positively or negatively affects the signaling of another signaling receptor system in the same cell, is a wellrecognized principle that permits fine tuning of GPCR functions (56)(57)(58)(59)(60)(61). Receptor cross-talk has been attributed to various molecular mechanisms, such as interactions between intracellular signal transduction pathways, receptor transactivation or receptor hetero-oligomerization (56)(57)(58)(59)(60)(61)(62)(63). The formation of homoand/or heteromers between GPCRs is known to be important for many aspects of GPCR function (64).…”

Heteromerization of chemokine (C-X-C motif) receptor 4 with α1A/B-adrenergic receptors controls α1-adrenergic receptor function

“…Receptor crosstalk can be attributed to a variety of molecular mechanisms, including receptor hetero-oligomerization (14)(15)(16)(17)(18)(19)(20)(21)(22)(23). The formation of homoand/or hetero-oligomeric complexes among GPCRs is thought to be important for many aspects of GPCR function (22)(23)(24).…”

GPR17 is a negative regulator of the cysteinyl leukotriene 1 receptor response to leukotriene D 4

“…In addition, 1321N1 cell clones stably expressing mouse GPR17 did not respond to 100 M of UDP-glucose. Since heterodimerization of G protein-coupled receptors modulates expression and/or function either negatively (36,37) or positively (38,39) in various transfectants, we considered the possibility that GPR17 may associate with CysLT 1 R to control its calcium signaling function. Here we show that GPR17 may function as a negative regulator for the CysLT 1 R response to LTD 4 not only in cotransfection of transformed cells but also constitutively in primary cells in which its knockdown resulted in increased membrane expression and LTD 4 -mediated function of CysLT 1 R. We provide physiologic evidence for this regulatory role of GPR17 by demonstrating that the vascular leak following IgEdependent, mast cell-mediated passive cutaneous anaphylaxis (PCA) is significantly increased in GPR17-deficient mice and that this response is blocked by administration of a CysLT 1 R antagonist.…”