LPA3: Pharmacodynamic differences between lysophosphatidic acid and oleoyl-methoxy glycerophosphothionate. Biased agonism, two sites.

Lysophosphatidic acid (LPA) and oleoyl-methoxy glycerophosphothionate (OMPT) increased LPA 3 phosphorylation; OMPT being considerably more potent than LPA. OMPT was also more potent than LPA to activate ERK 1/2. In contrast, to increase intracellular calcium OMPT was less effective than LPA. LPA-induced LPA 3 -β-arrestin 2 interaction was fast and robust, whereas that induced by OMPT was only detected at 60 min of incubation. LPA- and OMPT-induced receptor internalization was fast but that of OMPT was more marked. LPA-induced internalization was blocked by Pitstop 2, whereas OMPT-induced receptor internalization was partially inhibited by Pitstop 2 and Filipin and entirely by the combination of both. The data again indicate differences in the actions of these agonists. When LPA-stimulated cells were rechallenged with 1 µM LPA, hardly any response was detected, i.e., a “refractory” state was induced. However, if OMPT was used as the second stimulus, a conspicuous and robust response was observed. These data again suggest the possibility that two binding sites for these agonists might exist in the LPA 3 receptor, one showing a very high affinity for OMPT and another, likely shared by LPA and OMPT (structural analogs) with lower affinity. One sentence summary OMPT, oleoyl-methoxy glycerophosphothionate, a biased agonits interacting with an additional binding site in LPA 3 receptors.