UCSF

Compartmentalized G protein-coupled receptor (GPCR) signaling has been increasingly proven to play a large role in regulating distinct cellular responses. The idea that GPCRs could signal from endosomes was already a relatively novel concept a mere two decades ago. However, early evidence showed that internalization of some GPCRs led to sustained activity rather than an abolishment of signaling. Still, this secondary phase of GPCR signaling was implicated in activation sourced from the cell surface. The concept of distinct signaling hubs originating from other membrane-bound organelles was truly novel. The discovery that the beta 1 adrenergic receptor, an important GPCR in regulating heart contractility and relaxation responses, could signal from the Golgi apparatus begged the question of whether other similar GPCRs could signal from subcellular organelles. Here, I uncover that D1 dopamine receptor (D1DR) can signal from multiple signaling hubs, identify the mechanism in which dopamine accesses intracellular membrane compartments, and speculate on the potential implications of this novel work. First, I use a biosensor tool to visualize compartmentalized D1DR signaling using live-cell confocal fluorescence microscopy. I identified that organic cation transporter 2 (OCT2), a low-affinity high-capacity transporter of several neurotransmitters such as dopamine, facilitated dopamine transport intracellularly to access the Golgi pool of receptor. I also observed compartmentalized dopaminergic signaling in physiologically relevant cell types, including in key dopaminergic neurons and in kidney cells. Finally, I show that GPCR signals originating from distinct subcellular signaling hubs leads to distinct modulations of the downstream signaling cascades, indicating that receptor signaling from the Golgi could be regulating transcriptional responses. Put together, this work identifies a novel pathway of dopaminergic signaling and suggests that discrete signaling hubs within the cell distinctly regulate vital cellular responses.