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

Sensory neuron-specific Mas-related G protein-coupled receptors-X1 (MRGPR-X1) are primate-specific proteins that are exclusively expressed in primary sensory neurons and provoke pain in humans. Hence, MRGPR-X1 represent promising targets for future pain therapy, but signaling pathways activated by MRGPR-X1 are poorly understood. The transient receptor potential cation channel V1 (TRPV1) is also expressed in primary sensory neurons and detects painful stimuli such as protons and heat. G_q-promoted signaling has been shown to sensitize TRPV1 via protein kinase C (PKC)-dependent phosphorylation. In addition, recent studies suggested TRPV1 activation via a G_q-mediated mechanism involving diacylglycerol (DAG) or phosphatidylinositol-4,5-bisphosphate (PIP₂). However, it is not clear if DAG-promoted TRPV1 activation occurs independently from classic TRPV1 activation modes induced by heat and protons. Herein, we analyzed putative functional interactions between MRGPR-X1 and TRPV1 in a previously reported F11 cell line stably over-expressing MRGPR-X1. First, we found that MRGPR-X1 sensitized TRPV1 to heat and protons in a PKC-dependent manner. Second, we observed direct MRGPR-X1-mediated TRPV1 activation independent of MRGPR-X1-induced Ca²⁺-release and PKC activity or other TRPV1 affecting enzymes such as lipoxygenase, extracellular signal-regulated kinases-1/2, sarcoma, or phosphoinositide 3-kinase. Investigating several TRPV1 mutants, we observed that removal of the TRPV1 binding site for DAG and of the putative PIP₂ sensor decreased MRGPR-X1-induced TRPV1 activation by 71 and 43%, respectively. Therefore, we demonstrate dual functional interactions between MRGPR-X1 and TRPV1, resulting in PKC-dependent TRPV1 sensitization and DAG/PIP₂-mediated activation. The molecular discrimination between TRPV1 sensitization and activation may help improve the specificity of current pain therapies.