Cloning and expression of three isoforms of the human EP 3 prostanoid receptor

Abstract

Functional cDNA clones coding for three isoforms of the human prostaglandin E receptor EP 3 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 EP 3 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]PGE 2 specific binding to membranes prepared from transfected COS cells was comparable for all three isoforms, and as predicted for the EP 3 receptor, with PGE 2 = PGE 1 > PGF 2α = iloprost > PGD 2 ⪢ U46619. In addition, the EP 3-selective agonist MB28767 was a potent competing ligand with an IC 50 value of 0.3 nM, whereas the EP 1-selective antagonist AH6909 gave IC 50 values of 2–7 μM and the EP 2-selective agonist butaprost was inactive. In summary, we have cloned three isoforms of the human EP, receptor having comparable ligand binding properties.