Protean Agonism at the Dopamine D₂ Receptor: (S)-3-(3-Hydroxyphenyl)-N-propylpiperidine Is an Agonist for Activation of G_o1 but an Antagonist/Inverse Agonist for G_i1,G_i2, and G_i3

Abstract

A range of ligands displayed agonism at the long isoform of the human dopamine D 2 receptor, whether using receptor-G protein fusions or membranes of cells in which pertussis toxinresistant mutants of individual G␣ i -family G proteins could be expressed in an inducible fashion. Varying degrees of efficacy were observed for individual ligands as monitored by their capacity to load [35 S]GTP␥S onto each of G␣ i1 , G␣ i2 , G␣ i3 , and G␣ o1 . By contrast, (S)-(Ϫ)-3-(3-hydroxyphenyl)-N-propylpiperidine was a partial agonist when G␣ o1 was the target G protein but an antagonist/inverse agonist at G␣ i1 , G␣ i2 , and G␣ i3 . In ligand binding assays, dopamine identified both high-and lowaffinity states at each of the dopamine D 2 receptor-G protein fusion proteins, and the high-affinity state was eliminated by guanine nucleotide. (S)-(Ϫ)-3-(3-Hydroxyphenyl)-N-propylpiperidine bound to an apparent single state of the constructs in which the D 2 receptor was fused to G␣ i1 , G␣ i2 , or G␣ i3 . However, it bound to distinct high-and low-affinity states of the D 2 receptor-G␣ o1 fusion, with the high-affinity state being eliminated by guanine nucleotide. Likewise, although dopamine identified guanine nucleotide-sensitive high-affinity states of the D 2 receptor when expression of pertussis toxin-resistant forms of each of G␣ i1 , G␣ i2 , G␣ i3 , and G␣ o1 was induced, (S)-(Ϫ)-3-(3-hydroxyphenyl)-N-propylpiperidine identified a high-affinity site only in the presence of G␣ o1 . p-Tyramine displayed a protean ligand profile similar to that of (S)-(Ϫ)-3-(3-hydroxyphenyl)-N-propylpiperidine but with lower potency. These results demonstrate (S)-(Ϫ)-3-(3-hydroxyphenyl)-N-propylpiperidine to be a protean agonist at the D 2 receptor and may explain in vivo actions of this ligand.A large number of G protein-coupled receptors (GPCRs) are able to generate a variety of intracellular signals, and for those with a rich pharmacology of synthetic small-molecule ligands, it has often been possible to observe differential pharmacology for individual end points (Perez and Karnik, 2005). This has resulted in an appreciation that different ligands may stabilize distinct conformational states of GPCRs (Kenakin, 2001;Perez and Karnik, 2005) and in an expansion of the simple "active" or "inactive" "two-state" model (Leff, 1996) of GPCR function into "three-state" models (Leff et al., 1997) and subsequent chemical and physical considerations of GPCRs that allow the potential for an essentially unlimited number of states (Milligan and IJzerman, 2000;Vauquelin and Van Liefde, 2005). Although GPCRs are defined by their capacity to activate heterotrimeric G proteins, a number of ligand-induced signals seem not to require G protein interactions (Wei et al., 2003;Gesty-Palmer et al., 2006). In the case of the ␤ 2 -adrenoceptor, for example, such separation of signal transduction has resulted in the identification of ligands that can be defined as inverse agonists for their effects on adenylyl cyclase activity but as agonists for their capacity...

Functional Selective Oxytocin-derived Agonists Discriminate between Individual G Protein Family Subtypes

“…These findings together indicate that ligands can discriminate different G i family members at a single GPCR. G i /G o -biased activity has been reported previously (47,48), but, to the best of our knowledge, this is the first clear example of ligands biased toward a single G i family member.…”

Discovery and Characterization of a G Protein–Biased Agonist That Inhibits β-Arrestin Recruitment to the D2 Dopamine Receptor

“…Although the mechanisms underlying functional selectivity are not known, a leading hypothesis is that GPCRs can adopt multiple functionally "active" conformational states that are either stabilized or induced by these selective ligands (Kobilka and Deupi, 2007;Wess et al, 2008). Although relatively few biased ligands have been described for the D2R Mottola et al, 2002;Gay et al, 2004;Lane et al, 2007Lane et al, , 2008, existing examples strongly support the concept of the D2R being able to adopt multiple signalingbiased confirmations. Recently, a structural basis for functional selectivity of several GPCRs has been proposed (Liu et al, 2012;Dror et al, 2013;Kruse et al, 2013;Wacker et al, 2013;Abdul-Ridha et al, 2014) suggesting that rational design of functionally selective compounds may be possible.…”

Histidine 6.55 Is a Major Determinant of Ligand-Biased Signaling in Dopamine D2LReceptor

“…It is well established that, similar to other 7TM receptors, D 2 has the ability to differentially process ligand-based signals to produce a partial activation of cellular signaling pathways in response to some ligands (Burris et al, 2002;Gay et al, 2004;Lane et al, 2007;Urban et al, 2007;Klewe et al, 2008;Masri et al, 2008). Aripiprazole, a 1,4-disubstituted phenylpiperazine, is the first D 2 /D 3 dopamine receptor drug that acts as a partial agonist and has been approved for the treatment of psychiatric disorders (Burris et al, 2002).…”