AGAP1/AP-3-dependent endocytic recycling of M5 muscarinic receptors promotes dopamine release

Of the five mammalian muscarinic acetylcholine (ACh) receptors, M-5 is the only subtype expressed in midbrain dopaminergic neurons, where it functions to potentiate dopamine release. We have identified a direct physical interaction between M-5 and the AP-3 adaptor complex regulator AGAP1. This interaction was specific with regard to muscarinic receptor (MR) and AGAP subtypes, and mediated the binding of AP-3 to M-5. Interaction with AGAP1 and activity of AP-3 were required for the endocytic recycling of M-5 in neurons, the lack of which resulted in the downregulation of cell surface receptor density after sustained receptor stimulation. The elimination of AP-3 or abrogation of AGAP1-M-5 interaction in vivo decreased the magnitude of presynaptic M-5-mediated dopamine release potentiation in the striatum. Our study argues for the presence of a previously unknown receptor-recycling pathway that may underlie mechanisms of G-protein-coupled receptor (GPCR) homeostasis. These results also suggest a novel therapeutic target for the treatment of dopaminergic dysfunction. The EMBO Journal (2010) 29, 2813-2826. doi:10.1038/emboj.2010.154; Published online 27 July 2010