Cloning and expression of three isoforms of the human EP3 prostanoid receptor

Abstract

Functional cDNA clones coding for three isoforms of the human prostaglandin E receptor EP₃ subtype have been isolated from kidney and uterus cDNA libraries. The three isoforms, designated hEP_3‐I, hEP_3‐II and hEP_3‐III, have open reading frames corresponding to 390, 388 and 365 amino acids, respectively. They differ only in the length and amino acid composition of their carboxy‐terminal regions, beginning at position 360. The human EP₃ receptor has seven predicted transmembrane spanning domains and therefore belongs to the G‐protein‐coupled receptor family. The rank order of potency for prostaglandins and related analogs in competition for [³H]PGE₂ specific binding to membranes prepared from transfected COS cells was comparable for all three isoforms, and as predicted for the EP₃ receptor, with PGE₂ = PGE₁ > PGF_2α = iloprost > PGD₂ ⪢ U46619. In addition, the EP₃‐selective agonist MB28767 was a potent competing ligand with an IC₅₀ value of 0.3 nM, whereas the EP₁‐selective antagonist AH6909 gave IC₅₀ values of 2–7 μM and the EP₂‐selective agonist butaprost was inactive. In summary, we have cloned three isoforms of the human EP, receptor having comparable ligand binding properties.