Affinage

GPR156

Probable G-protein coupled receptor 156 · UniProt Q8NFN8

Length
814 aa
Mass
89.1 kDa
Annotated
2026-06-10
23 papers in source corpus 13 papers cited in narrative 13 extracted findings
Cross-family judge vs UniProt: Affinage preferred faithfulness: 7/7 claims corpus-supported (100%)

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

GPR156 is a constitutively active class C orphan GPCR that signals through Gi/o proteins and functions as the cell-autonomous switch that establishes mirror-image hair cell orientation in the inner ear (PMID:33784795, PMID:34001891, PMID:41547998). Originally cloned as a GABA(B)-related receptor (GABABL) with C-terminal ER-retention motifs but no detectable GABA(B) function (PMID:12591167), it is now understood to couple to Gi/o without an exogenous agonist (PMID:33784795). Cryo-EM structures show that GPR156 dimerizes through a TM5/6–TM5/6 interface and harbors an endogenous phospholipid within each transmembrane domain, accounting for its high constitutive activity; G protein engagement is asymmetric, with the C-terminus of the G-protein-bound protomer both promoting coupling in its own subunit and blocking coupling in the partner subunit (PMID:38332368, PMID:39638804). In sensory epithelia, the transcription factor EMX2 polarizes GPR156 to the apical hair cell surface, where GPR156-Gαi signaling drives a 180° reversal of stereociliary bundle orientation relative to the core planar cell polarity axis, producing the mirror-image organization of vestibular otolith organs, the auditory epithelium, and zebrafish neuromasts (PMID:34001891). EMX2 acts by repressing the kinase STK32A, which otherwise restricts apical GPR156 enrichment and blocks the reversal, so that the EMX2–STK32A–GPR156 hierarchy defines the boundary between oppositely oriented hair cell groups (PMID:37144879, PMID:41208475). GPR156 binds and depends on the core PCP proteins VANGL to execute orientation, yet it is dispensable for mechano-electrical transduction in mammalian hair cells, indicating that its deficits arise from misorientation rather than transduction failure (PMID:42063348, PMID:41547998). Beyond the inner ear, GPR156 has been implicated in macrophage lipid droplet accumulation during Mycobacterium tuberculosis infection (PMID:37269834) and in medial habenula circuitry for mood regulation through a depression-associated missense variant (PMID:40228124).

Mechanistic history

Synthesis pass · year-by-year structured walk · 11 steps
  1. 2003 Medium

    Established that GPR156 is a class C GPCR related to GABA(B) subunits but does not reconstitute a functional GABA(B) receptor, framing it as an orphan receptor of unknown ligand and function.

    Evidence Homology-based cloning, heterologous expression, and pharmacological assays with GABA(B) ligands and subunits; broad CNS immunohistochemical mapping

    PMID:12591167 PMID:14556935

    Open questions at the time
    • No endogenous ligand identified
    • No signaling output demonstrated
    • Function in any tissue undefined
  2. 2021 Medium

    Resolved that GPR156 is not silent but signals constitutively through Gi/o even without an added ligand, establishing an intrinsic signaling activity.

    Evidence Luciferase reporter assays with Gα chimeras engineered to detect small constitutive Gi/o signaling

    PMID:33784795

    Open questions at the time
    • Mechanism driving constitutive activity not defined
    • Single method and lab
    • No physiological context for the signaling
  3. 2021 High

    Placed GPR156 in a developmental pathway by showing EMX2 polarizes GPR156 and that GPR156-Gαi signaling drives 180° hair cell orientation reversal, explaining mirror-image hair cell organization.

    Evidence Knockout mice and zebrafish mutants, GPR156 immunofluorescence localization, and epistasis with EMX2 and Gαi

    PMID:34001891

    Open questions at the time
    • Molecular mechanism of EMX2-driven polarization unresolved
    • How Gαi signaling reorients the cytoskeleton unknown
  4. 2023 High

    Identified STK32A as the intermediary between EMX2 and GPR156, showing EMX2 represses Stk32a to permit apical GPR156 enrichment and orientation reversal.

    Evidence Gpr156 × Stk32a double-mutant epistasis, immunofluorescence, and conditional ectopic STK32A expression in mice

    PMID:37144879

    Open questions at the time
    • How STK32A controls GPR156 apical localization mechanistically unknown
    • Direct STK32A substrates unidentified
  5. 2023 Medium

    Extended GPR156 beyond hair cells by implicating it in macrophage lipid droplet accumulation that promotes Mycobacterium tuberculosis persistence.

    Evidence Genome-wide CRISPR screen with knockdown/knockout validation and lipid droplet quantification in infected macrophages

    PMID:37269834

    Open questions at the time
    • Signaling link between GPR156 and lipid droplet biogenesis undefined
    • Whether constitutive Gi/o activity drives this phenotype unknown
  6. 2024 High

    Provided the structural basis for constitutive activity, showing GPR156 is a phospholipid-bound TM5/6 dimer whose asymmetric G protein coupling is gated by the bound protomer's C-terminus.

    Evidence Cryo-EM structures of apo, Go-free, and Gi3/Go-coupled human GPR156 with analysis of the dimer interface, lipid pocket, and C-terminus

    PMID:38332368 PMID:39638804

    Open questions at the time
    • Whether phospholipid occupancy is regulated in vivo unknown
    • How asymmetric coupling shapes downstream signaling output unresolved
  7. 2024 High

    Distinguished GPR156's role in orientation from transduction, showing it relays both orientation and transduction signatures in zebrafish but is dispensable for mammalian mechano-electrical transduction.

    Evidence Electrophysiology of mechanically evoked signals in Gpr156 zebrafish and mouse mutants

    PMID:39531034

    Open questions at the time
    • Basis for species difference in transduction dependence unknown
    • Link between GPR156 signaling and transduction machinery in zebrafish undefined
  8. 2025 High

    Connected GPR156 to core PCP machinery by showing it binds and depends on VANGL, yet is dispensable and even inhibitory for postnatal orientation correction.

    Evidence Gpr156 × Vangl1/2 and Gpr156 × Fzd3/6 double-mutant epistasis with protein binding/localization assays in mice

    PMID:42063348

    Open questions at the time
    • Molecular nature of the GPR156–VANGL interaction undefined
    • Why GPR156 inhibition aids postnatal realignment unexplained
  9. 2025 Medium

    Implicated GPR156 in mood regulation by showing a depression-associated missense variant induces medial habenula hyperactivity and abnormal stress behavior.

    Evidence Humanized p.Glu533Asp knock-in mouse with in vivo habenula electrophysiology and stress behavioral assays

    PMID:40228124

    Open questions at the time
    • Whether the variant alters Gi/o signaling unknown
    • Causal link to human depression not established beyond single pedigree
  10. 2025 High

    Consolidated the regulatory hierarchy, confirming GPR156 reverses bundle orientation relative to the PCP axis but is blocked by STK32A, with EMX2 setting the boundary via Stk32a repression across utricle and cochlea.

    Evidence Gpr156 × Stk32a and Emx2 × Stk32a double-mutant epistasis with hair cell orientation phenotyping

    PMID:41208475

    Open questions at the time
    • Biochemical mechanism by which STK32A blocks GPR156 unresolved
  11. 2026 High

    Demonstrated GPR156 acts cell-autonomously, with hair-cell-specific deletion recapitulating misorientation and sensory dysfunction while transduction remains intact.

    Evidence Conditional Cre knockout in postmitotic hair cells with auditory brainstem response, vestibulo-ocular reflex, and orientation phenotyping

    PMID:41547998

    Open questions at the time
    • Downstream cytoskeletal effectors of GPR156-Gαi signaling unidentified

Open questions

Synthesis pass · forward-looking unresolved questions
  • How GPR156 constitutive Gi/o signaling is converted into directional cytoskeletal reorientation, and whether its non-cochlear roles in macrophages and habenula share this signaling logic, remains unresolved.
  • No identified downstream effectors linking Gαi to bundle orientation
  • Endogenous regulation of phospholipid binding in vivo unknown
  • Mechanistic basis of lipid droplet and mood phenotypes undefined

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0060089 molecular transducer activity 4 GO:0008289 lipid binding 1
Localization
GO:0005886 plasma membrane 4
Pathway
R-HSA-1266738 Developmental Biology 4 R-HSA-162582 Signal Transduction 3

Evidence

Reading pass · 13 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2003 GPR156 (GABABL) was identified as a novel class C GPCR with homology to GABA(B1) and GABA(B2), containing a putative coiled-coil domain, di-leucine and RXR(R) ER retention motifs in its C-terminus. When expressed alone or with GABA(B1) or GABA(B2), no receptor function in response to GABA(B) ligands was detected, indicating it does not form a functional GABA(B) receptor with known subunits. Homology-based cloning, heterologous expression, pharmacological assays Brain research. Molecular brain research Medium 12591167
2003 GPR156 (GABABL) protein is broadly distributed in the rat CNS, with dense expression in cortex, hippocampus, dentate gyrus, cerebellum (granule cell layer and Purkinje cells), spinal cord substantia gelatinosa and ventral horn, and a subset of parvalbumin-positive hippocampal interneurons. Immunohistochemistry with rabbit polyclonal antisera specific to GABABL protein Brain research Medium 14556935
2021 GPR156 exhibits constitutive Gi/o protein coupling activity in the absence of any known ligand, as measured using luciferase reporter assays with G protein chimeras designed to detect intrinsically small constitutive Gi/o signaling. Luciferase reporter assays with Gα chimera proteins for Gi/o detection in unliganded receptors British journal of pharmacology Medium 33784795
2021 The transcription factor EMX2 polarizes GPR156 distribution at hair cell boundaries; GPR156 then signals through Gαi to trigger a 180° reversal in hair cell orientation. This GPR156-Gαi signaling is essential for establishing mirror-image hair cell orientations in mouse vestibular otolith organs and in zebrafish lateral line neuromasts, and also instructs hair cell reversal in the auditory epithelium. Genetic loss-of-function (knockout mice and zebrafish mutants), immunofluorescence localization of GPR156, epistasis analysis with EMX2 and Gαi Nature communications High 34001891
2023 STK32A is a downstream effector negatively regulated by EMX2 in hair cells, and STK32A regulates the apical localization of GPR156. In EMX2-positive hair cells, EMX2 represses Stk32a, permitting apical GPR156 enrichment and consequent orientation reversal; ectopic STK32A expression in EMX2-positive regions reorients bundles, and Stk32a loss disrupts GPR156 apical localization. Genetic epistasis in double mutant mice (Gpr156 × Stk32a), immunofluorescence, conditional ectopic expression eLife High 37144879
2023 GPR156 is identified as a key inducer of lipid droplet accumulation in macrophages lacking MMGT1 during Mycobacterium tuberculosis infection, placing GPR156 in the MMGT1-GPR156-lipid droplet axis that promotes bacterial persistence. Genome-wide CRISPR screen, genetic knockdown/knockout validation, lipid droplet quantification in infected macrophages Cell host & microbe Medium 37269834
2024 Cryo-EM structures of human GPR156 in Go-free and Go-coupled states reveal that an endogenous phospholipid molecule is located within each transmembrane domain (TMD) of the GPR156 dimer. Asymmetric binding of Gα to the phospholipid-bound GPR156 dimer restructures intracellular loops 1 and 2 and the C-terminal part of TM7 without altering dimer conformation, establishing GPR156 as a transducer for phospholipid signaling and explaining constitutive activity through constant phospholipid binding. Cryo-electron microscopy structure determination of apo and G-protein-coupled states, structural analysis of dimer interface and lipid binding site Nature structural & molecular biology High 38332368
2024 Cryo-EM structures of human apo GPR156 and the GPR156-Gi3 complex reveal a small extracellular region formed by ECL2 and the N-terminus. GPR156 forms a dimer via a TM5/6–TM5/6 interface in both apo and Gi3-coupled states, indicating high constitutive activity in the apo state. The C-terminus of the G-protein-bound subunit plays a dual role: promoting G protein binding in that subunit while preventing the G-free subunit from binding additional G protein. Cryo-EM structure determination of apo GPR156 and GPR156-Gi3 complex, structural analysis of dimer interface and C-terminus function Nature communications High 39638804
2024 Loss of GPR156 in zebrafish neuromast hair cells eliminates the smaller mechanically evoked signals characteristic of EMX2-positive hair cells, while mechano-electrical transduction in mouse otolith organ hair cells is normal in Gpr156 mutants, indicating GPR156 relays both orientation and transduction properties downstream of EMX2 in zebrafish but is dispensable for transduction per se in mice. Electrophysiology (mechanically evoked signals), loss-of-function in Gpr156 zebrafish and mouse mutants eLife High 39531034
2025 GPR156 binds VANGL proteins (core planar cell polarity components) and depends on them for its function in hair cell orientation. However, inhibiting GPR156 signaling facilitates rather than prevents postnatal correction of orientation defects in Vangl and Fzd mutants, indicating GPR156 collaborates with core PCP components to establish orientation but is dispensable—and even inhibitory—for postnatal realignment. Genetic epistasis in double mutant mice (Gpr156 × Vangl1/2 and Gpr156 × Fzd3/6 conditional mutants), protein binding/localization assays Development (Cambridge, England) High 42063348
2025 Genetic epistasis experiments in mice combining Gpr156 and Stk32a mutations demonstrate: (1) GPR156 functions to reverse stereociliary bundle orientation relative to the PCP axis but can be blocked by STK32A; (2) EMX2 establishes the boundary between the two hair cell groups by repressing Stk32a transcription. These functional relationships hold in both the utricle and cochlea. Genetic epistasis in double mutant mice (Gpr156 × Stk32a and Emx2 × Stk32a), hair cell orientation phenotyping Journal of cell science High 41208475
2025 A rare missense variant in GPR156 (p.Glu533Asp) found in a Mennonite pedigree with major depressive disorder, when knocked into the murine Gpr156 locus, induces medial habenula hyperactivity and abnormal stress-related behaviors, placing GPR156 in the medial habenula circuitry for mood regulation. Humanized knock-in mouse model, in vivo electrophysiology (habenula activity), behavioral assays for stress sensitivity Proceedings of the National Academy of Sciences of the United States of America Medium 40228124
2026 Conditional inactivation of Gpr156 specifically in postmitotic hair cells recapitulates the misorientation phenotype of null mutants and results in similar auditory and vestibular dysfunction, demonstrating that GPR156 function is required in hair cells themselves (not surrounding cells) for proper orientation. Mechano-electrical transduction remains intact in the absence of GPR156, establishing that sensory deficits arise from misorientation rather than transduction failure. Conditional Cre-mediated knockout in postmitotic hair cells, auditory brainstem response, vestibulo-ocular reflex measurements, hair cell orientation phenotyping Scientific reports High 41547998

Source papers

Stage 0 corpus · 23 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2023 Genetic association analysis of 77,539 genomes reveals rare disease etiologies. Nature medicine 63 36928819
2021 In vitro profiling of orphan G protein coupled receptor (GPCR) constitutive activity. British journal of pharmacology 50 33784795
2021 EMX2-GPR156-Gαi reverses hair cell orientation in mechanosensory epithelia. Nature communications 49 34001891
2003 Molecular cloning and characterisation of a novel GABAB-related G-protein coupled receptor. Brain research. Molecular brain research 42 12591167
2003 Distribution of a GABAB-like receptor protein in the rat central nervous system. Brain research 42 14556935
2004 Differential expression of gamma-aminobutyric acid type B receptor subunit mRNAs in the developing nervous system and receptor coupling to adenylyl cyclase in embryonic neurons. The Journal of comparative neurology 16 15067715
2021 Decoding pathogenesis factors involved in the progression of ATLL or HAM/TSP after infection by HTLV-1 through a systems virology study. Virology journal 15 34446027
2024 Molecular insights into the activation mechanism of GPR156 in maintaining auditory function. Nature communications 13 39638804
2004 [History and the present of metabotropic GABAB receptor]. Ceskoslovenska fysiologie 12 15702867
2024 Constitutive activation mechanism of a class C GPCR. Nature structural & molecular biology 11 38332368
2023 The dark kinase STK32A regulates hair cell planar polarity opposite of EMX2 in the developing mouse inner ear. eLife 11 37144879
2023 Identification of host regulators of Mycobacterium tuberculosis phenotypes uncovers a role for the MMGT1-GPR156 lipid droplet axis in persistence. Cell host & microbe 11 37269834
2022 Hear the sounds: the role of G protein-coupled receptors in the cochlea. American journal of physiology. Cell physiology 11 35938679
2023 Novel GPR156 variants confirm its role in moderate sensorineural hearing loss. Scientific reports 7 37814107
2024 Contributions of mirror-image hair cell orientation to mouse otolith organ and zebrafish neuromast function. eLife 6 39531034
2024 Brainstem transcriptomic changes in male Wistar rats after acute stress, comparing the use of duplex specific nuclease (DSN). Scientific reports 5 39300279
2024 Instrumented swim test for quantifying motor impairment in rodents. Scientific reports 2 39587238
2025 A Novel Homozygous Loss-of-Function Variant in GPR156 Delineates Non-syndromic Hearing Loss. Biochemical genetics 1 39760840
2025 A rare variant in GPR156 associated with depression in a Mennonite pedigree causes habenula hyperactivity and stress sensitivity in mice. Proceedings of the National Academy of Sciences of the United States of America 1 40228124
2026 GPR156 is required in sensory hair cells for proper auditory and vestibular function. Scientific reports 0 41547998
2026 Progressive correction of auditory hair cell orientation in the absence of core planar cell polarity and GPR156 signaling. Development (Cambridge, England) 0 42063348
2025 Planar polarized organization of mouse hair cells is established and maintained by STK32A, GPR156 and EMX2. Journal of cell science 0 41208475
2024 Contributions of mirror-image hair cell orientation to mouse otolith organ and zebrafish neuromast function. bioRxiv : the preprint server for biology 0 39282410

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