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We previously cloned a cDNA for a mouse PGE receptor positively coupled to adenylate cyclase from mouse mastocytoma cells, and reported it as EP2 subtype of PGE receptor [Honda, A., Sugimoto, Y., Namba, T., Watabe, A., Irie, A., Negishi, M., Narumiya, S. and Ichikawa, A. (1993) J. Biol. Chem. 268, 7759–7762]. However, it is not sensitive to one of the EP2 agonists, butaprost. Recently another subtype of PGE receptor coupled to adenylate cyclase has been identified pharmacologically and named EP4. These findings have led us to examine whether the cloned receptor is the EP4 subtype. AH23848B, a selective EP4 antagonist, not only displaced the [3H]PGE2 binding to the cloned receptor but antagonized the PGE2-stimulated cAMP formation in the receptor. In contrast, EP2 specific agonists, butaprost and 19(R)OH-PGE2 neither bound to the receptor nor stimulated the cAMP formation. These results suggest that this receptor previously reported as ‘EP2’ subtype is identical to the pharmacologically defined EP4 subtype and not of EP2 subtype.

A functional cDNA for the human prostacyclin receptor was isolated from a cDNA library of CMK cells, a human megakaryocytic leukaemia cell line. The cDNA encodes a protein consisting of 386 amino acid residues with seven putative transmembrane domains and a deduced molecular weight of 40,956. [3H]Iloprost specifically bound to the membrane of CHO cells stably expressing the cDNA with a Kd of 3.3 nM. This binding was displaced by unlabelled prostanoids in the order of iloprost = cicaprost ⪢ carbacyclin ⪢ prostaglandin E1 (PGE1) > STA2. PGE2, PGD2 and PGF2α did not inhibit it. Iloprost in a concentration-dependent manner increased the cAMP level and generated inositol trisphosphate in these cells, indicating that this human receptor can couple to multiple signal transduction pathways.