Profile of prostaglandin E1 and E2 binding to four subtype prostaglandin E receptors

Prostaglandin E 1 (PGE 1 ) and E 2 (PGE 2 ) are ligands for prostaglandin E 2 receptor (EP) family, which are designated as EP 1 , EP 2 , EP 3 and EP 4 . Interestingly, PGE 2 mediates inflammation whereas PGE 1 is acting as an anti‐inflammatory factor. However the molecular basis of their opposite actions on the EP receptors is poorly understood. In this study, the PGE 1 and PGE 2 binding affinity and signaling on the human recombinant EPs expressed in the live HEK293 stable cell lines were determined by [ 3 H]PGE 2 binding and the calcium and cyclic AMP signaling, respectively. The Kd of [ 3 H]PGE 2 binding to the EP 1 , EP 2 , EP 3 & EP 4 was 0.35 nM, 0.45 nM, 0.021 nM, and 0.047 nM, respectively. PGE 2 showed higher affinity or preference for EP 3 and EP 4 as compared to that of EP 1 and EP 2 . The IC50 thus calculated from [ 3 H]PGE 2 displacement experiments using cold PGE 1 and PGE 2 for the EPs is, EP 1 ( PGE 1 0.1mM, PGE 2 5μM), EP 2 ( PGE 1 1μM, PGE 2 1μM), EP 3 ( PGE 1 1μM,PGE 2 100 nM) and EP 4 ( PGE 1 1μM, PGE 2 100nM). PGE 1 showed a higher calcium signal in EP 1 as compared to that of PGE 2 . In addition, there was a one log concentration difference between PGE 2 and PGE 1 for generation of calcium signal in EP 4 . The calcium signal indicated that the EP 1 is the likely dominant receptor in terms of signaling in tissues that co express the EPs. This study provides a molecular basis to understand the biological functions of PGE 1 and PGE 2 through their binding and signaling properties.