Regulation of Dopamine D1 Receptor Signaling at the Golgi Apparatus by a Low Affinity Dopamine Transporter

G protein-coupled receptors (GPCRs) are the largest family of membrane receptors expressed in humans. It has been traditionally thought that GPCRs can only signal on the plasma membrane, where receptors are activated upon binding of external cues. However, recent work has demonstrated that, in several cases, subcellularly-localized GPCRs are also activated upon the presence of external cues resulting in downstream signaling pathways. Whether subcellular activation of GPCRs is limited to subsets of GPCRs or is a general aspect of GPCR signaling is not known. Additionally, establishing GPCR signaling from subcellular compartments is the first step in unraveling the physiological consequences of compartmentalized signaling for each GPCR family member. Here, using novel nanobody-based biosensors, we demonstrate that dopamine D1 receptor (D1DR), the primary mediator of dopaminergic signaling in the brain and kidney, is activated at both the plasma membrane and the Golgi apparatus upon the presence of its ligand. Interestingly, we found that activation of the Golgi pools of D1DRs is dependent on Organic Cation Transporter 2 (OCT2), a low affinity dopamine transporter, providing an explanation for how dopamine, a membrane impermeant ligand, accesses subcellular pools of D1DR. We also show that Golgi-localized D1DRs regulate local cAMP production and mediate protein kinase A activation at the Golgi membranes. Together, our data suggest that spatially compartmentalized signaling hubs are previously unappreciated regulatory aspects of D1DR signaling. Our data also provide further evidence for the role of transporters in regulating subcellular GPCR activity.