Ligand binding specificities of the eight types and subtypes of the mouse prostanoid receptors expressed in Chinese hamster ovary cells

Abstract

Eight types and subtypes of the mouse prostanoid receptor, the prostaglandin D (DP) receptor, the prostaglandin F (FP) receptor, the prostaglandin I (IP) receptor, the thromboxane A (TP) receptor and the EP 1, EP 2, EP 3 and EP 4 subtypes of the prostaglandin E receptor, were stably expressed in Chinese hamster ovary cells. Their ligand binding characteristics were examined with thirty two prostanoids and their analogues by determining the Ki values from the displacement curves of radioligand binding to the respective receptors. The DP, IP and TP receptors showed high ligand binding specificity and only bound their own putative ligands with high affinity such as PGD 2, BW245C and BW868C for DP, cicaprost, iloprost and isocabacyclin for IP, and S‐145, I‐BOP and GR 32191 for TP. The FP receptor bound PGF 2α and fluprostenol with Ki values of 3–4 n M. In addition, PGD 2, 17‐phenyl‐PGE 2, STA 2, I‐BOP, PGE 2 and M&B̀‐28767 bound to this receptor with Ki values less than 100 n M. The EP 1 receptor bound 17‐phenyl‐PGE 2, sulprostone and iloprost in addition to PGE 2 and PGE 1, with Ki values of 14–36 n M. 16,16‐dimethyl‐PGE 2 and two putative EP 1 antagonists, AH6809 and SC‐19220, did not show any significant binding to this receptor. M&B‐28767, a putative EP 3 agonist, and misoprostol, a putative EP 2/EP 3 agonist, also bound to this receptor with Ki values of 120 n M. The EP 2 and EP 4 receptors showed similar binding profiles. They bound 16,16‐dimethyl PGE 2 and 11‐deoxy‐PGE 1 in addition to PGE 2 and PGE 1. The two receptors were discriminated by butaprost, AH‐13205 and AH‐6809 that bound to the EP 2 receptor but not to the EP 4 receptor, and by 1‐OH‐PGE 1 that bound to the EP 4 but not to the EP 2 receptor. The EP 3 receptor showed the broadest binding profile, and bound sulprostone, M&B‐28767, GR63799X, 11‐deoxy‐PGE 1, 16,16‐dimethyl‐PGE 2 and 17‐phenyl‐PGE 2, in addition to PGE 2 and PGE 1, with Ki values of 0.6–3.7 n M. In addition, three IP ligands, iloprost, carbacyclin and isocarbacyclin, and one TP ligand, STA 2, bound to this receptor with Ki values comparable to the Ki values of these compounds for the IP and TP receptors, respectively. 8‐Epi‐PGF 2α showed only weak binding to the IP, TP, FP, EP 2 and EP 3 receptor at 10 μ M concentration. British Journal of Pharmacology (1997) 122, 217–224; doi:10.1038/sj.bjp.0701367