Sensory Neuron-Specific Mas-Related Gene-X1 Receptors Resist Agonist-Promoted Endocytosis

Abstract

Human sensory neuron-specific mas-related gene X1 receptors (hMrgX1s) belong to the superfamily of G protein-coupled receptors (GPCRs), bind cleavage products of pro-enkephalin with high affinity, and have been suggested to participate in pain sensation. Murine or rat MrgC receptors exhibit high similarities with hMrgX1 in terms of expression pattern, sequence homology, and binding profile. Therefore, rodents have been used as an in vivo model to explore the physiological functions and pharmacodynamics of the hMrgX1. Agonist-promoted receptor endocytosis significantly affects the pharmacodynamics of a GPCR but is not yet investigated for hMrgX1. Therefore, we analyzed the effects of prolonged agonist exposure on cell surface protein levels of hMrgX1 and murine or rat MrgC in human embryonic kidney 293, Cos, F11, and ND-C cells. We observed that hMrgX1 are resistant and both MrgC are prone to agonist-promoted receptor endocytosis. In Cos cells, coexpression of ␤-arrestins strongly enhanced endocytosis of murine MrgC but did not alter cell surface expression of hMrgX1 receptors. These data define the hMrgX1 as one of the few members within the superfamily of GPCRs whose signaling is not regulated by agonist-promoted endocytosis and reveal species-specific differences in the regulation of Mrg receptor signaling. Given the importance of receptor endocytosis for the pharmacodynamics of a given ligand, our results may have a strong impact on the development of future drugs that suppose to control pain in humans but were tested in rodents.

Human Sensory Neuron-specific Mas-related G Protein-coupled Receptors-X1 Sensitize and Directly Activate Transient Receptor Potential Cation Channel V1 via Distinct Signaling Pathways

“…Regarding the MRGPR-X1 subtype, one rodent receptor activated by BAM8 -22 was identified in mice and rats (MRGPR-C) (1, 2). However, apart from common high affinity binding to BAM8 -22, rodent MRGPR-C and human MRGPR-X1 exhibit fundamental differences in their affinity to other endogenous peptides, as previously reported (4,52,53). Furthermore, in contrast to rodent MRGPR-C, human MRGPR-X1 resist ␤-arrestin-dependent, agonist-promoted endocytosis (4), not only affecting signal duration but also directing GPCR-promoted signaling toward distinct signaling pathways (54).…”

“…Recently, Mas-related G protein-coupled receptors-X1 (MRGPR-X1) 2 have been shown to be exclusively expressed in primary sensory neurons and to be activated by bovine adrenal medulla peptide-8-22 (BAM8 -22) originating from proteolytic cleavage of pro-enkephalin by pro-hormone convertases (1,2). Several studies reported activation of the G q pathway by MRGPR-X1 in overexpression systems (1,(3)(4)(5), and a recent study revealed increased pain sensation in 15 healthy volunteers after BAM8 -22 application (6). In contrast, overexpression of MRGPR-X1 in rat dorsal root ganglia (DRG) neurons resulted in BAM8 -22-mediated inhibition of voltage-gated calcium currents and activation of M-type potassium channels via G i/o proteins believed to blunt pain perception (7).…”

GABAB receptor promotes its own surface expression by recruiting a Rap1-dependent signaling cascade

“…How the surface expression of these receptors is downregulated in an activity-dependent manner has been very well characterized (Calebiro et al, 2010;Premont and Gainetdinov, 2007;Shenoy and Lefkowitz, 2011). However, some other GPCRs such as GABA B receptor remain relatively stable at the cell surface even after prolonged agonist treatment (Benke, 2010;Chu et al, 1997;Nantel et al, 1993;Schreff et al, 2000;Solinski et al, 2010). GABA is the primary inhibitory neurotransmitter in the mammalian CNS.…”

PMX-53 as a Dual CD88 Antagonist and an Agonist for Mas-Related Gene 2 (MrgX2) in Human Mast Cells

“…Furthermore, phosphorylation-deficient mutants of CD88 are resistant to desensitization (Pollok-Kopp et al, 2007). Solinski et al (2010) showed that MrgX1 is one of the few GPCRs that does not associate with ␤-arrestin and is resistant to agonist-induced receptor internalization. Thus, the possibility that MrgX2 receptor is also resistant to agonist-induced phosphorylation, ␤-arrestin recruitment, and desensitization remains to be determined.…”