PGE1 and E3 show lower efficacies than E2 to β-catenin-mediated activity as biased ligands of EP4 prostanoid receptors.

The 2-series of prostaglandin E (PGE2 ) is regarded as a pro-cancer prostanoid, whereas the 1-series (PGE1 ) and the 3-series (PGE3 ) are considered to act as anti-cancer prostanoids. In the present study, we provide possible reasons why PGE1 and PGE3 , but not PGE2 , exert anti-cancer effects by focusing on each diverged E-type prostanoid (EP)4 receptor-mediated signaling pathway. PGE1 , PGE2 and PGE3 function as full agonists in terms of Gαs - and Gαi -protein-mediated signaling. However, PGE1 and PGE3 function as partial agonists of T-cell factor (TCF)/β-catenin (β-cat)-mediated activity, the well-known cancer-related signaling pathway. Furthermore, pretreatment with PGE1 or PGE3 almost completely reduces PGE2 -induced TCF/β-cat activity. These results provide a plausible reason why PGE1 and PGE3 function as anti-cancer prostanoids as a result of novel biased activity for EP4 receptors.