Endocytosis Promotes Rapid Dopaminergic Signaling

Abstract

SUMMARY D1 dopamine receptors are primary mediators of dopaminergic signaling in the CNS. These receptors internalize rapidly following agonist-induced activation but the functional significance of this process is unknown. We investigated D1 receptor endocytosis and signaling in HEK 293 cells and cultured striatal neurons using real-time fluorescence imaging and cAMP biosensor technology. Agonist-induced activation of D1 receptors promoted endocytosis of receptors with a time course overlapping that of acute cAMP accumulation. Inhibiting receptor endocytosis blunted acute D1 receptor-mediated signaling in both dissociated cells and striatal slice preparations. While endocytic inhibition markedly attenuated acute cAMP accumulation, inhibiting the subsequent recycling of receptors had no effect. Further, D1 receptors localized in close proximity to endomembrane-associated trimeric G protein and adenylyl cyclase immediately after endocytosis. Together, these results suggest a previously unanticipated role of endocytosis, and the early endocytic pathway, in supporting rapid dopaminergic neurotransmission.

Noncanonical Control of Vasopressin Receptor Type 2 Signaling by Retromer and Arrestin

“…Retromer co-localized with V2R after internalization and formed a complex with it; titrating retromer expression by transgene overexpression or by siRNA knockdown showed that retromer has an antagonistic effect on cAMP generation by V2R. Together with recent work on ␤-arrestins and the PTHR (6,9,10,53), this work supports a new noncanonical model of GPCR signaling, wherein ␤-arrestins augment rather than attenuate hormone actions and in which desensitization is instead mediated by the retromer sorting complex on early endosomes.…”

Noncanonical GPCR signaling arising from a PTH receptor–arrestin–Gβγ complex

“…Sustained cAMP and G S signaling by receptor internalization in early endosomes was originally reported in 2009 for two distinct GPCRs, the thyroid-stimulating hormone receptor (TSHR) (35) and PTHR (2), and recently expanded to the dopamine D1 receptor (D1R) (36). Endosomal G-protein signaling appears to be an alternative pathway not only for G S -but also for inhibitory G protein (Gi)-coupled receptors, as demonstrated for the sphingosine-1-phosphate receptor (37).…”

Spatial and Temporal Aspects of Signaling by G-Protein–Coupled Receptors

“…These specific downstream effects appear to include selective changes in gene expression, demonstrated for b-adrenergic receptors, and the control of thyroid hormone secretion in the case of the thyroid-stimulating hormone receptors (Calebiro et al, 2010;Tsvetanova et al, 2015). However, signaling from internal sites may also affect processes at the cell surface, as shown for dopamine D 1 -receptor-dependent neuronal excitability (Kotowski et al, 2011).…”