GABBR1

GABBR1 is the obligatory subunit 1 of the metabotropic GABA-B receptor, which heterodimerizes with GABBR2 to form a functional class C GPCR whose loss produces spontaneous epileptiform activity, hyperalgesia, impaired memory, and premature death [PMID:bio_10.1101_2025.01.23.634473]. De novo missense variants stratify the receptor's functional anatomy: substitutions in transmembrane domain 3 (p.Gly673Asp) abolish surface expression and signaling, variants near the orthosteric site (p.Glu368Asp) reduce GABA potency and efficacy, and others selectively lower efficacy or raise constitutive activity, with these loss- and gain-of-function alterations causing neurodevelopmental delay, epilepsy, autism spectrum disorder, intellectual disability, and ADHD (PMID:36103875, PMID:41803176). Beyond the nervous system, GABBR1 is required for hematopoietic stem/progenitor cell proliferation, reconstitution capacity, and B-cell differentiation, and agonist stimulation of human cord-blood HSPCs enhances long-term engraftment (PMID:32881992). GABBR1 is repressed post-transcriptionally through direct binding of microRNAs to its 3'UTR—miR-7b acting downstream of an angiotensin II/AT1R/HoxD10 axis to drive sympathoexcitation in heart failure (PMID:26699387), and miR-17-92 cluster members (miR-106a/b, miR-20a/b, miR-17) to promote colorectal cancer proliferation and invasion (PMID:27230463). GABBR1 can also heterodimerize with the non-GABBR2 class C GPCR CaSR to alter its signaling [PMID:bio_10.1101_2025.01.23.634473].

1. 2001 Medium

   Established the molecular identity and CNS-predominant expression of the murine receptor, providing the gene structure and splice variants needed to study GABBR1 function.

   Evidence cDNA cloning, sequence analysis, and radiation hybrid mapping of mouse Gabbr1

   PMID:11306808

   Open questions at the time

   • Did not establish a functional receptor assay
   • No partner subunit or signaling readout defined
2. 2015 High

   Answered how GABBR1 is post-transcriptionally controlled in disease by showing direct miR-7b targeting of its 3'UTR within an Ang II/AT1R/HoxD10 cascade drives sympathoexcitation in heart failure.

   Evidence Luciferase reporter with 3'UTR mutagenesis plus in vivo PVN infusion and AT1R/HoxD10 manipulation in a CHF rat model

   PMID:26699387

   Open questions at the time

   • Mechanism is upstream regulation, not receptor signaling per se
   • Does not address GABBR1's downstream effectors in PVN neurons
3. 2016 Medium

   Showed GABBR1 acts as a functional tumor suppressor in colorectal cancer, repressed by direct miR-17-92 cluster binding to its 3'UTR.

   Evidence Luciferase reporter, western blotting, and proliferation/invasion rescue in HCT116 and HT-29 cells

   PMID:27230463

   Open questions at the time

   • Single lab
   • Downstream signaling linking GABBR1 to proliferation/invasion not defined
4. 2021 High

   Defined a non-neural role for GABBR1 by demonstrating it is required for hematopoietic stem/progenitor cell proliferation and engraftment, with agonist stimulation enhancing human HSPC function.

   Evidence Constitutive Gabbr1 knockout mice, competitive transplantation, and ex vivo agonist/antagonist treatment of human cord-blood HSPCs followed by xenotransplantation

   PMID:32881992

   Open questions at the time

   • Intracellular signaling pathway in HSPCs not resolved
   • Whether GABBR2 heterodimerization is required in HSPCs untested
5. 2022 High

   Mapped the functional consequences of de novo missense variants onto receptor anatomy, distinguishing trafficking-dead, orthosteric, and efficacy-reducing mutations as a mechanistic basis for neurodevelopmental disorders.

   Evidence In vitro functional characterization of four variants in HEK293 cells with potency, efficacy, and surface-expression readouts

   PMID:36103875

   Open questions at the time

   • No in vivo modeling of the variants
   • Patient genotype-phenotype correlation limited
6. 2024 Low

   Linked GABBR1 to inflammatory signaling by correlating its expression with p38 MAPK in arthritic joints and showing both decline with glucocorticoid treatment.

   Evidence Collagen-induced arthritis mouse model with IHC, western blot, and dexamethasone treatment of mononuclear cells

   PMID:38836679

   Open questions at the time

   • No direct mechanistic link between GABBR1 and p38 MAPK
   • Correlative expression only, single method
7. 2025 Medium

   Confirmed obligatory GABBR1/GABBR2 heterodimerization through matched knockout phenotypes and revealed GABBR1 can heterodimerize with CaSR to modulate its signaling.

   Evidence Global and conditional knockout mice plus in vitro heterodimerization studies in HEK and breast cancer cells (preprint)

   PMID:bio_10.1101_2025.01.23.634473

   Open questions at the time

   • Preprint, not peer-reviewed
   • Functional consequences of CaSR heterodimer in vivo undefined
8. 2025 Low

   Proposed a hepatic metabolic role via a GABBR1/miR-19b-3p/WNT2B axis alleviating insulin resistance and liver injury.

   Evidence GABBR1 and miR-19b-3p overexpression/knockdown in AML12 cells and a diabetic mouse model

   PMID:40999757

   Open questions at the time

   • No direct binding validation of the miR-19b-3p/WNT2B regulation
   • Single lab, indirect pathway evidence
9. 2026 High

   Broadened the variant spectrum to include gain-of-function (increased constitutive activity) alongside loss-of-function, expanding the disorder phenotypes to autism, intellectual disability, and ADHD.

   Evidence In vitro functional characterization of seven de novo GABBR1/GABBR2 variants with constitutive activity, potency, efficacy, and surface-expression assays

   PMID:41803176

   Open questions at the time

   • No in vivo correlate of constitutive-activity variants
   • Mechanism distinguishing gain- vs loss-of-function clinical outcomes unclear
10. 2026 Medium

    Identified valerate as a biased ligand that upregulates GABBR1 to drive a GABBR1→CXCL13 axis promoting anti-tumor CD8+ T-cell immunity in lung cancer.

    Evidence In vitro/in vivo assays, scRNA-seq, GABBR1 overexpression/knockdown, and CXCL13 measurement in NSCLC models

    PMID:42157924

    Open questions at the time

    • Direct molecular coupling of GABBR1 to CXCL13 transcription not resolved
    • Single lab

• The intracellular effector pathways linking GABBR1 activation to its diverse cellular phenotypes (HSPC proliferation, hepatic metabolism, tumor immunity) remain undefined.
• No unified downstream signaling mechanism across non-neural contexts
• Role of GABBR2 vs alternative heterodimer partners in each context untested