Prostaglandins are bioactive lipids involved in many physiological and pathophysiological conditions, such as pain, atherosclerosis, type II diabetes, and parturition. Prostaglandin E2 (PGE2) activates four G protein-coupled receptors (GPCRs), named the PGE2 types 1-4 receptors (EP1-4), to elicit the intracellular signaling responsible for their physiological actions. There are more than twelve EP3 isoforms in humans that differ only by the sequence of their C-termini. However, the signaling mechanisms engaged by the various isoforms have never been clearly defined. In this study, we used a recently described BRET-based biosensor technology to define the signaling profiles for each of the human isoforms on a selection of signaling pathways using the agonists, PGE2 and sulprostone, and the purportedly EP3-specific antagonist L798106. We found that L798106 is a biased agonist of the Gαz pathway for some human EP3 isoforms, an effect that is not detected in the close ortholog mouse EP3 isoform α. We also found that the presence of a threonine residue at position 107 in the binding site of human EP3, which is a serine in most other species including mice, is important for L798106-mediated Gαz efficacy. Given the reported importance of EP3-Gαz signaling on the potential therapeutic efficacy of EP3 and since many preclinical studies for these mechanisms have been performed in rodents, this finding demonstrates the importance of determining a detailed signaling profile of ligands for different species and receptor isoforms, which constitutes an important step to better understand the therapeutic potential of the EP3.
Keywords: Biased agonists; Bioluminescence resonance energy transfer (BRET); EP3 receptor isoforms; Heterotrimeric Gα(z) protein; L798106; Signaling profile.
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