Agonist-Specific Coupling of a ClonedDrosophila melanogasterD1-Like Dopamine Receptor to Multiple Second Messenger Pathways by Synthetic Agonists

Abstract

The mechanism of coupling of a cloned Drosophila D1-like dopamine receptor, DopR99B, to multiple second messenger systems when expressed in Xenopus oocytes is described. The receptor is coupled directly to the generation of a rapid, transient intracellular Ca 2ϩ signal, monitored as changes in inward current mediated by the oocyte endogenous Ca 2ϩ -activated chloride channel, by a pertussis toxin-insensitive G-proteincoupled pathway. The more prolonged receptor-mediated changes in adenylyl cyclase activity are generated by an independent G-protein-coupled pathway that is pertussis toxinsensitive but calcium-independent, and G ␤␥ -subunits appear to be involved in the transduction of this response. This is the first evidence for the direct coupling of a cloned D1-like dopamine receptor both to the activation of adenylyl cyclase and to the initiation of an intracellular Ca 2ϩ signal. The pharmacological profile of both second messenger effects is identical for a range of naturally occurring catecholamine ligands (dopamine Ͼ norepinephrine Ͼ epinephrine) and for the blockade of dopamine responses by a range of synthetic antagonists. However, the pharmacological profiles of the two second messenger responses differ for a range of synthetic agonists. Thus, the receptor exhibits agonist-specific coupling to second messenger systems for synthetic agonists. This feature could provide a useful tool in the genetic analysis of the roles of the multiple second messenger pathways activated by this receptor, given the likely involvement of dopamine in the processes of learning and memory in the insect nervous system.

Rapid, Nongenomic Responses to Ecdysteroids and Catecholamines Mediated by a NovelDrosophilaG-Protein-Coupled Receptor

“…Both the PI3K pathway (Scheid and Woodgate, 2001) and catecholamines (Pendelton et al, 1997) are known to have important roles in the control of Drosophila development, and, in addition, the activation of the MAPK pathway is an important regulator of cellular differentiation in Drosophila (Bier, 1998). A wide range of other Drosophila GPCRs, including the OA/TYR receptor (Robb et al, 1994), the DopR99B D 1 -like DA receptor (Reale et al, 1997), and the short neuropeptide F receptor , have also been shown to exhibit various forms of agonist-specific coupling, as have several vertebrate adrenergic and neuropeptide GPCRs (Spengler et al, 1993;Airriess et al, 1997). It remains to be determined whether both DA and the ecdysteroids can signal or modulate each other's actions through DmDopEcR in vivo.…”

“…Sense cRNA was prepared from the DmDopEcR clone in pcDNA3 and from the DopR99Bclone in pBluescript II SK(Ϫ) using the mCAP RNA capping kit (Stratagene, La Jolla, CA). Xenopus oocytes were prepared, as described previously (Reale et al, 1997), and injected with 50 ng of receptor sense cRNA. Injected oocytes were incubated at 19°C for 2-5 d before recording; uninjected oocytes were processed in parallel as controls.…”

“…Injected oocytes were incubated at 19°C for 2-5 d before recording; uninjected oocytes were processed in parallel as controls. Recordings were made as described previously (Reale et al, 1997).…”

“…2 D). Third, the ecdysteroids had no effect on the OA-mediated inhibition of cAMP production observed in CHO cells stably expressing the Drosophila OA/tyramine (TYR) receptor (Robb et al, 1994) (data not shown) or on the DA-mediated stimulation of cAMP levels in CHO cells transiently expressing the DopR99B (DAMB) DA D 1 -like receptor (Reale et al, 1997) (data not shown). In addition, the ecdysteroids did not inhibit the DA-mediated, Ca 2ϩ -dependent activation of the endogenous inward chloride currents in Xenopus oocytes expressing the DopR99B receptor (Reale et al, 1997) (data not shown).…”

Biased agonism: a novel paradigm in G protein-coupled receptor signaling observed in acquired hypocalciuric hypercalcemia [Review]

“…This suggests that agonist activation of multiple signaling mechanisms is not uniform but is in fact often biased toward some but not all signaling pathways, and that agonist-selective states can produce biased agonism [15]. The findings of subsequent studies have supported this concept including ligand specific conformational changes of the β2-adrenergic receptor [16,17], different types of agonists that induce selective coupling to a distinct second messenger pathway via the Drosophila D1-like dopamine receptor expressed in Xenopus oocytes [18], and receptor ligand specific dominancy between PLC-mediated inositol phosphate (IP) accumulation and PLA2-mediated arachidonic one G protein.…”