The C-terminal domain of the human EP4 receptor confers agonist-induced receptor desensitization in a receptor hybrid with the rat EP3beta receptor.

Prostaglandin E2 receptors (EPR), which belong to the family of heterotrimeric G protein-coupled ectoreceptors with seven transmembrane domains, can be classified into four subtypes according to their ligand binding and G protein coupling specificity. Of these, EP3betaR is coupled to Gi, whereas EP4R is coupled to Gs. EP4R, in contrast to EP3betaR, shows agonist-induced desensitization. The C-terminal domain and the third intracellular loop of these receptors have been implicated in G protein coupling specificity and desensitization. Here, receptor hybrids consisting of the main portion of rat EP3betaR and either the C-terminal domain or the third intracellular loop of human EP4R were used to study the contribution of the respective receptor domains to G protein coupling and desensitization. Neither the EP4R C-terminal domain nor the EP4R third intracellular loop alone was sufficient to change the coupling specificity of the rEP3hEP4 receptor hybrids from Gi to Gs or to confer additional Gs coupling. However, the EP4R C-terminal domain but not the third intracellular loop was necessary and sufficient to mediate rapid agonist-induced, second messenger-independent desensitization in the Gi-coupled hybrid receptors.