D-type prostanoid receptor enhances the signaling of chemoattractant receptor-homologous molecule expressed on TH2 cells

Background: Prostaglandin (PG) D-2 is substantially involved in allergic responses and signals through the 7 transmembrane-spanning/G protein-coupled receptors, chemoattractant receptor-homologous molecule expressed on T(H)2 cells (CRTH2), and D-type prostanoid (DP) receptor. Objective: Although the proinflammatory function of CRTH2 is well recognized and CRTH2 is hence considered an important emerging pharmacotherapeutic target, the role of the DP receptor in mediating the biological effects of PGD(2) in patients with allergic inflammation has remained unclear. Methods: The cross-talk of CRTH2 and DP receptors was investigated by using both a recombinant HEK293 cell model and human eosinophils in Ca2+ mobilization assays, coimmunoprecipitation, Western blotting, radioligand binding, and immunofluorescence. Results: We show that CRTH2 and DP receptors modulate one another's signaling properties and form CRTH2/DP heteromers without altering their ligand-binding capacities. We find that the DP receptor amplifies the CRTH2-induced Ca2+ release from intracellular stores and coincidentally forfeits its own signaling potency. Moreover, desensitization or pharmacologic blockade of the DP receptor hinders CRTH2-mediated signal transduction. However, CRTH2 internalization occurs independently of the DP receptor. In cells that express both receptors, pharmacologic blockade of G(aq/11) proteins abolishes the Ca2+ response to both CRTH2 and DP agonists, whereas inhibition of G(alpha i) proteins selectively attenuates the CRTH2-mediated response but not the DP signal. Conclusion: Our data demonstrate the capacity of DP receptors to amplify the biological response to CRTH2 activation. Therefore the CRTH2/DP heteromer might not only represent a functional signaling unit for PGD(2) but also a potential target for the development of heteromer-directed therapies to treat allergic diseases. (J Allergy Clin Immunol 2012;129:492-500.)