NMBR

NMBR is a Gq-coupled receptor for neuromedin B (NMB) that signals through phospholipase Cβ to mobilize intracellular Ca2+, governing sensory itch transmission, cell proliferation, and innate antiviral responses (PMID:34919054, PMID:41257985). Upon agonist binding it undergoes homologous desensitization through internalization and down-regulation, with surface recovery and resensitization depending on recycling from an intracellular compartment rather than new protein synthesis (PMID:8163469). In the spinal cord, NMBR mediates histaminergic itch and engages in cross-inhibitory signaling with GRPR, with GRPR+ neurons acting downstream of NMBR+ neurons to integrate NMB-encoded itch information; NMB signals exclusively through NMBR while GRP can act through both receptors (PMID:25209280). NMBR-encoded histaminergic itch is amplified when BNP-bound NPRC, co-expressed with NMBR, facilitates the receptor's Gq–PLCβ–Ca2+ signaling (PMID:34919054). Beyond sensory neurons, NMB-NMBR-driven PLCβ1 activation and ER Ca2+ release promote MAM formation through the IRE1α–IP3R–VDAC1 axis to enhance mitochondrial Ca2+ uptake, respiration, and cell-cycle progression (PMID:41257985), and NMBR activation amplifies RIG-I/TRIM25/STAT1 antiviral signaling while suppressing the deubiquitinase CYLD to restrict influenza replication (PMID:41242095). NMBR signaling additionally modulates serotonergic activity in the dorsal raphe and influences stress-related behavior (PMID:12031854).

1. 1994 High

   Established that NMBR is a desensitizing GPCR whose signaling capacity is restored not by new receptor synthesis but by recycling of internalized receptor back to the cell surface, defining the basis of its resensitization.

   Evidence Radioligand binding, inositol phosphate and Ca2+ assays with monensin/cycloheximide dissection in glioblastoma and transfected fibroblast cells

   PMID:8163469

   Open questions at the time

   • Identity of the recycling compartment and trafficking machinery not defined
   • No mapping of receptor residues controlling internalization
2. 2002 Medium

   Linked NMBR signaling to central neuromodulation by showing its loss alters serotonergic tone in the dorsal raphe and downstream behavior, extending NMBR function beyond peripheral signaling.

   Evidence Nmbr knockout mice with behavioral assays, p-CPA 5-HT depletion, immunohistochemistry, RT-PCR and HPLC for 5-HT and 5-HT1A

   PMID:12031854

   Open questions at the time

   • Pathway placement is indirect
   • No direct circuit-level connection between NMBR neurons and raphe serotonergic cells
   • Sex-specific effects unexplained
3. 2002 Low

   Implicated NMBR in stress resilience by showing receptor-null mice fail to recover behavior after acute restraint stress.

   Evidence Nmbr knockout mice subjected to restraint stress with maternal behavior scoring

   PMID:12231437

   Open questions at the time

   • Single behavioral knockout study with no molecular mechanism
   • No identification of relevant neural substrate
   • Not independently confirmed
4. 2014 High

   Resolved how NMBR and GRPR partition itch modalities, establishing cross-inhibitory signaling and a NMBR→GRPR neuronal hierarchy that maintains histaminergic itch.

   Evidence Single and double Nmbr/Grpr knockout mice with intradermal pruritogen challenge and scratching quantification

   PMID:25209280

   Open questions at the time

   • Molecular basis of receptor cross-inhibition unknown
   • Mechanism of ligand selectivity (NMB vs GRP) not defined
5. 2021 High

   Identified BNP-NPRC as a heterologous facilitator of NMBR signaling, showing co-expressed NPRC amplifies NMB-encoded histaminergic itch through NMBR's Gq–PLCβ–Ca2+ pathway.

   Evidence Npr3 knockout mice, pruritogen behavioral assays, Ca2+ imaging in co-transfected HEK293 cells and dorsal horn neurons, immunofluorescence co-localization

   PMID:34919054

   Open questions at the time

   • Physical mode of NMBR-NPRC functional coupling not resolved
   • How NPRC, a clearance receptor, transduces a Gq signal unexplained
6. 2025 Medium

   Defined a peripheral proliferative role for NMBR, linking PLCβ1-driven ER Ca2+ release to MAM-mediated mitochondrial Ca2+ uptake and cell-cycle entry in granulosa cells.

   Evidence Exogenous NMB and NMBR antagonist in goat granulosa cells with cell-cycle flow cytometry, Western blot of MAM axis proteins, Ca2+ imaging, mitochondrial function assays

   PMID:41257985

   Open questions at the time

   • Single lab, no receptor mutagenesis or structural validation
   • Generalizability beyond granulosa cells untested
   • Direct demonstration of receptor-IRE1α coupling absent
7. 2025 Medium

   Placed NMBR in innate antiviral immunity, showing it amplifies RIG-I/TRIM25/STAT1 signaling and suppresses CYLD to restrict influenza replication.

   Evidence NMBR overexpression/knockdown in A549 cells and mouse lung infection, IFN-β reporters, ubiquitination assays, STAT1 phosphorylation and ISG15 Western blot, viral replication measurement

   PMID:41242095

   Open questions at the time

   • Single lab, not independently replicated
   • Mechanism linking NMBR Gq signaling to TRIM25/CYLD regulation unclear
   • Whether endogenous NMB ligand drives this in vivo unknown

• How NMBR's single Gq-PLCβ-Ca2+ signaling module is differentially routed to produce distinct outcomes across sensory neurons, proliferating cells, and immune cells remains unresolved.
• No structural model of NMBR or its ligand-receptor interface in the corpus
• Mechanism of context-specific downstream coupling unknown
• Cross-talk partners (GRPR, NPRC) lack defined physical interaction data