Molecular cloning and characterization of chicken prostaglandin E receptor subtypes 2 and 4 (EP2 and EP4)

Prostaglandin E2 (PGE2) is an important chemical mediator responsible for regulation of many vital physiological processes. Four receptor subtypes have been identified to mediate its biological actions. Among these subtypes, prostaglandin E receptor subtypes 2 and 4 (EP2 and EP4), both coupled to cAMP-protein kinase A (cAMP-PKA) signaling pathway, are proposed to play crucial roles under both physiological and pathological conditions. Though both receptors were extensively studied in mammals, little is known about their functionality and expression in non-mammalian species including chicken. In present study, the full-length cDNAs for chicken EP2 and EP4 receptors were first cloned from adult chicken ovary and testis, respectively. Chicken EP2 is 356 amino acids in length and shows high amino acid identity to that of human (61%), mouse (63%), and rat (61%). On the other hand, the full-length cDNA of EP4 gene encodes a precursor of 475 amino acids with a high degree of amino acid identity to that of mammals, including human (87%), mouse (86%), rat (84%), dog (85%), and cattle (83%), and a comparatively lower sequence identity to zebrafish (52%). RT-PCR assays revealed that EP2 mRNA was expressed in all tissues examined including the oviduct, while EP4 expression was detected only in a few tissues. Using the pGL3-CRE-luciferase reporter system, we also demonstrated that PGE2 could induce luciferase activity in DF-1 cells expressing EP2 and EP4 in dose-dependent manners (EC50: <1 nM), confirming that both receptors could be activated by PGE2 and functionally coupled to the cAMP-PKA signaling pathway. Together, our study establishes a molecular basis to understand the physiological roles of PGE2 in target tissues of chicken.