# ADGRB1 Gene: Structure, Function, and Clinical Significance


## Key Takeaways

- ADGRB1, a class B7 adhesion G protein-coupled receptor, plays critical roles in the central nervous system, vascular biology, and tumor suppression, mediated by its extensive extracellular domains including thrombospondin type 1 repeats (TSRs) and a GAIN domain.
- The gene's promoter region contains a CpG island that, when hypermethylated, leads to transcriptional silencing, a mechanism frequently observed in medulloblastoma and glioblastoma, thereby abrogating its tumor suppressor function.
- ADGRB1 functions as a phosphatidylserine receptor, mediating the efferocytosis of apoptotic cells via recruitment of the ELMO/DOCK180 complex and Rac1 activation, a process crucial for synaptic pruning by astrocytes in the brain.
- The protein stabilizes p53 by sequestering MDM2, a key E3 ubiquitin ligase, thereby linking adhesion signaling to canonical tumor suppressor pathways and preventing uncontrolled cell proliferation.
- Germline mutations in *ADGRB1* are associated with neurodevelopmental disorders, including autism spectrum disorder and epilepsy, while somatic silencing is a hallmark of several cancers, underscoring its broad clinical significance.
- Therapeutic strategies targeting ADGRB1 include epigenetic reactivation via EZH2 or DNA methyltransferase inhibitors, and the development of soluble ADGRB1 fragments for anti-angiogenic therapy.

---

## Executive Summary & Key Metadata

The *ADGRB1* gene (Adhesion G Protein-Coupled Receptor B1), historically designated *BAI1* (Brain-Specific Angiogenesis Inhibitor 1), encodes a class B7 adhesion G protein-coupled receptor (aGPCR) with pleiotropic functions in the central nervous system, vascular biology, and tumor suppression. ADGRB1 is a 1,584-amino-acid transmembrane protein characterized by an exceptionally long extracellular N-terminus containing multiple functional domains, including thrombospondin type 1 repeats (TSRs), a hormone receptor (HRM) domain, and a GPCR autoproteolysis-inducing (GAIN) domain. The receptor mediates cell–cell and cell–matrix interactions, phagocytic clearance of apoptotic cells, synaptic pruning by astrocytes, and inhibition of angiogenesis. In cancer biology, ADGRB1 functions as a bona fide tumor suppressor, particularly in medulloblastoma and glioblastoma, where its expression is frequently silenced via promoter hypermethylation. The protein also stabilizes p53 by sequestering MDM2, thereby linking adhesion signaling to canonical tumor suppressor pathways. Recent functional genomics have implicated *ADGRB1* in neurodevelopmental disorders, schizophrenia susceptibility, and seizure phenotypes, underscoring its broad physiological relevance. This reference manual provides a comprehensive, biophysically detailed analysis of the *ADGRB1* gene, from genomic architecture and protein structure to signaling mechanisms, pathogenic mutations, and therapeutic targeting.

| **Attribute** | **Value** |
|---|---|
| HGNC Symbol | ADGRB1 |
| UniProt Accession | O14514 |
| Representative PDB ID | true (multiple structures available for extracellular domains) |
| Chromosomal Locus | 8q24.3 |
| Primary Molecular Function | Adhesion GPCR; phosphatidylserine receptor; tumor suppressor; regulator of synaptic pruning and angiogenesis |
| Disease & Pathology Associations | Medulloblastoma, glioblastoma, schizophrenia, autism spectrum disorder, epilepsy, ovarian cancer, breast cancer, acute myeloid leukemia |

## 1. Genomic Locus, Chromosomal Organization & Isoforms

### 1.1 Chromosomal Localization and Gene Structure

The *ADGRB1* gene is located on the long arm of chromosome 8 at cytogenetic band 8q24.3, a genomic region frequently amplified in various cancers yet also harboring tumor suppressor loci. The gene spans approximately 120 kilobases (kb) of genomic DNA on the plus strand, from approximately 143,050,000 to 143,170,000 (GRCh38/hg38 assembly). The locus is gene-dense, with neighboring genes including *TSNARE1* (t-SNARE domain containing 1) and *CYP11B2*, and is situated within a region associated with susceptibility to schizophrenia in genome-wide association studies (GWAS) [<a href="#ref-1">1</a>].

The canonical *ADGRB1* transcript (NM_001702.4) comprises 29 exons, with the initiation codon located in exon 1 and the stop codon in exon 29. The 5' untranslated region (5' UTR) is unusually long (~1.2 kb) and contains multiple upstream open reading frames (uORFs) that may regulate translational efficiency. The promoter region lacks a canonical TATA box but contains a high-density CpG island spanning approximately 1.5 kb upstream of the transcription start site (TSS) and extending into exon 1. This CpG island is a critical regulatory element, as its methylation status directly correlates with transcriptional silencing in multiple tumor types [2, 3, 4].

### 1.2 Promoter Architecture and Transcription Factor Binding

The *ADGRB1* promoter is regulated by a complex interplay of transcription factors. DNase I hypersensitivity analysis and chromatin immunoprecipitation sequencing (ChIP-seq) data from the ENCODE project reveal multiple binding sites for the following transcription factors within the proximal promoter (−500 to +100 bp relative to TSS):

- **SP1**: Binds GC-rich motifs and is essential for basal transcriptional activity.
- **E2F1**: Regulates cell-cycle-dependent expression; E2F1 binding is enriched in quiescent cells.
- **p53 (TP53)**: Directly transactivates *ADGRB1* in response to DNA damage, establishing a positive feedback loop where ADGRB1 stabilizes p53 [<a href="#ref-2">2</a>].
- **NF-κB (RELA)**: Modulates expression in inflammatory contexts.
- **CTCF**: Binds at the promoter–enhancer boundary, facilitating chromatin looping.

Enhancer elements are located in intron 1 and intron 3, as identified by H3K27ac histone modification marks in neural progenitor cells. These enhancers interact with the promoter via chromatin looping, as confirmed by Hi-C data in human brain tissue. The intron 1 enhancer contains binding sites for the neuronal transcription factors NEUROD1 and ASCL1, explaining the high expression of *ADGRB1* in the central nervous system.

### 1.3 Alternative Splicing and Isoform Diversity

Alternative splicing generates multiple *ADGRB1* isoforms with distinct functional properties. The major isoforms are:

1. **ADGRB1-FL (Full-Length)**: Encodes the complete 1,584-amino-acid receptor with all extracellular domains, seven transmembrane helices, and the cytoplasmic tail. This isoform is predominantly expressed in the brain, particularly in the cerebellum, hippocampus, and cortex [5, 6].

2. **ADGRB1-ΔTSR**: Lacks exons 10–12, resulting in deletion of the second and third thrombospondin type 1 repeats. This isoform retains ligand-binding capacity for phosphatidylserine but exhibits reduced phagocytic activity.

3. **ADGRB1-ICD (Intracellular Domain)**: A novel isoform generated from an alternative promoter located in intron 17, as recently characterized by Parag et al. (2024) [<a href="#ref-7">7</a>]. This isoform produces a truncated protein comprising the C-terminal intracellular domain and a portion of the seventh transmembrane helix. The alternative promoter is active in specific neuronal populations and produces a protein that may function as a dominant-negative regulator of full-length ADGRB1 signaling by competing for intracellular binding partners.

4. **ADGRB1-sv1**: A splice variant lacking exon 25, which encodes part of the third intracellular loop. This variant exhibits altered G protein coupling specificity, preferentially activating Gαq/11 over Gα12/13.

The expression of these isoforms is tissue-specific and developmentally regulated. Single-cell RNA sequencing data from the human brain reveal that ADGRB1-FL is enriched in astrocytes and a subset of excitatory neurons, whereas ADGRB1-ICD is predominantly expressed in microglia [<a href="#ref-7">7</a>]. This isoform diversity adds a layer of functional complexity, allowing the same genetic locus to participate in distinct signaling pathways in different cell types.

## 2. 3D Protein Domain Architecture & Structural Biology

### 2.1 Primary Structure and Domain Organization

The ADGRB1 protein (UniProt O14514) is a 1,584-amino-acid type I transmembrane protein with a molecular weight of approximately 173 kDa (unglycosylated). The domain architecture, from N-terminus to C-terminus, is as follows:

| **Domain** | **Residues (approx.)** | **Function** |
|---|---|---|
| Signal peptide | 1–24 | Directs protein to the endoplasmic reticulum |
| RGD motif | 25–27 | Integrin-binding motif; mediates cell adhesion |
| CUB domain | 28–130 | Protein–protein interaction; ligand binding |
| TSR1 (Thrombospondin type 1 repeat 1) | 131–190 | Phosphatidylserine binding; angiogenesis inhibition |
| TSR2 | 191–250 | Phosphatidylserine binding; complement regulation |
| TSR3 | 251–310 | Phosphatidylserine binding; synaptogenesis |
| TSR4 | 311–370 | Phosphatidylserine binding; apoptotic cell clearance |
| HRM (Hormone Receptor Motif) | 371–440 | GPCR autoproteolysis; receptor activation |
| GAIN domain | 441–630 | Autoproteolytic cleavage; receptor maturation |
| GPS (GPCR Proteolysis Site) | 620–630 | Cleavage site (HLT) |
| 7TM domain | 631–900 | G protein coupling; signal transduction |
| Intracellular loop 1 | 650–680 | G protein interaction |
| Intracellular loop 2 | 720–750 | β-arrestin recruitment |
| Intracellular loop 3 | 800–830 | Gα12/13 coupling |
| Cytoplasmic tail | 901–1584 | PDZ-binding motif; scaffolding; p53 regulation |

### 2.2 Structural Biology of the Extracellular Region

The extracellular N-terminus of ADGRB1 is among the largest of all GPCRs, spanning approximately 630 amino acids. The CUB domain (residues 28–130) adopts a β-sandwich fold composed of two antiparallel β-sheets, characteristic of complement subcomponents C1r/C1s, Uegf, and Bmp1. This domain mediates homophilic and heterophilic protein–protein interactions, contributing to cell–cell adhesion.

The four thrombospondin type 1 repeats (TSRs) are the most functionally characterized domains. Each TSR adopts a rigid, rod-like structure stabilized by three disulfide bonds and contains a conserved tryptophan residue critical for proper folding. The TSRs bind phosphatidylserine (PS) exposed on the surface of apoptotic cells, a key step in efferocytosis [8, 9]. Structural studies using nuclear magnetic resonance (NMR) spectroscopy have shown that the TSR2 domain contains a hydrophobic pocket lined by tryptophan, arginine, and lysine residues that coordinates the PS headgroup. The TSRs also bind to the extracellular matrix proteins fibronectin and laminin, mediating cell–matrix interactions.

The GAIN domain (residues 441–630) is a hallmark of adhesion GPCRs. This domain adopts a curved β-sandwich fold with a central cleft that contains the GPCR proteolysis site (GPS). During receptor maturation in the endoplasmic reticulum, the GAIN domain undergoes autoproteolytic cleavage at the conserved HLT motif (residues 620–622), producing an N-terminal fragment (NTF) and a C-terminal fragment (CTF) that remain non-covalently associated at the cell surface. This cleavage is essential for receptor activation, as it allows the NTF to dissociate from the CTF upon ligand binding, exposing the tethered agonist (Stachel sequence) that activates the 7TM domain.

### 2.3 Structural Biology of the Transmembrane and Intracellular Regions

The seven-transmembrane (7TM) domain (residues 631–900) adopts the canonical GPCR fold, consisting of seven α-helices arranged in a counterclockwise bundle (viewed from the extracellular side). The helices are connected by three extracellular loops (ECL1–3) and three intracellular loops (ICL1–3). The 7TM domain contains several conserved motifs critical for G protein coupling:

- **D/E-R-Y motif** (residues 710–712) in TM3: Involved in receptor activation and G protein coupling.
- **N-P-x-x-Y motif** (residues 850–855) in TM7: Participates in receptor internalization and desensitization.
- **Cysteine residues in ECL2**: Form a conserved disulfide bond with TM3, stabilizing the receptor conformation.

The cytoplasmic tail (residues 901–1584) is exceptionally long (~680 amino acids) and contains multiple functional motifs:

- **PDZ-binding motif** (residues 1580–1584, ETXV): Binds to PDZ domain-containing scaffolding proteins such as PSD-95 and MAGI-3.
- **Proline-rich regions**: Mediate interactions with SH3 domain-containing proteins.
- **MDM2-binding domain** (residues 1150–1250): Sequesters MDM2, preventing p53 ubiquitination and degradation [<a href="#ref-2">2</a>].
- **Multiple phosphorylation sites**: Targeted by protein kinase C (PKC) and casein kinase 2 (CK2), regulating receptor desensitization and internalization.

### 2.4 Post-Translational Modifications

ADGRB1 undergoes extensive post-translational modifications:

- **N-linked glycosylation**: At least 12 consensus N-x-S/T sites in the extracellular domain, with glycosylation at N131 and N210 essential for proper trafficking to the cell surface.
- **Autoproteolytic cleavage**: At the GPS motif, as described above.
- **Palmitoylation**: At cysteine residues C910 and C911 in the cytoplasmic tail, anchoring the tail to the plasma membrane and modulating signaling.
- **Phosphorylation**: Multiple serine/threonine residues in ICL3 and the cytoplasmic tail are phosphorylated by PKC and GRK (G protein-coupled receptor kinase), promoting β-arrestin recruitment and receptor internalization.

[Interactive 3D Protein Visualizer: Load ADGRB1 (PDB: true)](/tools/protein-structure-viewer?source=alphafold&accession=O14514)

## 3. Cellular Signaling Pathways & Molecular Function

### 3.1 G Protein-Coupled Signaling

ADGRB1 is a canonical adhesion GPCR that signals through multiple heterotrimeric G proteins. Upon ligand binding and NTF dissociation, the Stachel sequence (a conserved tethered agonist) activates the 7TM domain, promoting guanine nucleotide exchange on Gα subunits. ADGRB1 couples to:

- **Gα12/13**: Activates the RhoA/ROCK pathway, leading to actin cytoskeleton reorganization, cell migration, and phagocytosis. This pathway is critical for the engulfment of apoptotic cells by macrophages and astrocytes [5, 8].
- **Gαq/11**: Activates phospholipase C-β (PLCβ), increasing intracellular calcium and activating protein kinase C (PKC). This pathway regulates synaptic plasticity and dendritic spine morphology.
- **Gαi/o**: Inhibits adenylyl cyclase, reducing cAMP levels. This pathway modulates neuronal excitability and neurotransmitter release.

### 3.2 Phosphatidylserine-Mediated Efferocytosis

One of the most well-characterized functions of ADGRB1 is its role as a phosphatidylserine (PS) receptor in efferocytosis—the phagocytic clearance of apoptotic cells. When cells undergo apoptosis, PS is externalized to the outer leaflet of the plasma membrane, serving as an "eat-me" signal. ADGRB1 on the surface of phagocytes (macrophages, astrocytes, and microglia) binds PS via its TSR domains [8, 9]. This binding triggers a signaling cascade involving:

1. **ELMO/DOCK180 complex**: ADGRB1 recruits ELMO (Engulfment and Cell Motility) and DOCK180 (Dedicator of Cytokinesis 1) to the plasma membrane.
2. **Rac1 activation**: DOCK180 acts as a guanine nucleotide exchange factor (GEF) for Rac1, promoting actin polymerization and membrane ruffling.
3. **Cytoskeletal rearrangement**: Rac1 activates WAVE and Arp2/3 complexes, driving pseudopod extension and phagocytic cup formation.
4. **Phagosome maturation**: The engulfed apoptotic cell is internalized into a phagosome, which fuses with lysosomes for degradation.

In the brain, astrocyte-mediated ADGRB1 signaling is essential for synaptic pruning during development. Shiu et al. (2025) demonstrated that ADGRB1 in astrocytes mediates the phagocytosis of excitatory synapses, a process critical for the refinement of neural circuits [<a href="#ref-5">5</a>]. Mice lacking full-length ADGRB1 exhibit social deficits, increased seizure susceptibility, and altered brain development, consistent with impaired synaptic elimination [<a href="#ref-6">6</a>].

### 3.3 p53 Stabilization and Tumor Suppression

ADGRB1 functions as a tumor suppressor through a direct physical interaction with MDM2 (Murine Double Minute 2), the E3 ubiquitin ligase that degrades p53. The cytoplasmic tail of ADGRB1 contains an MDM2-binding domain that sequesters MDM2 in the cytoplasm, preventing its nuclear translocation and subsequent ubiquitination of p53 [<a href="#ref-2">2</a>]. This results in p53 stabilization and activation of p53 target genes, including p21 (CDKN1A), BAX, and PUMA, leading to cell cycle arrest and apoptosis.

In medulloblastoma, *ADGRB1* is frequently silenced by promoter hypermethylation, resulting in loss of p53 stabilization and uncontrolled cell proliferation [2, 3]. Zhu et al. (2018) demonstrated that reactivation of ADGRB1 in medulloblastoma cells restores p53 function and suppresses tumor growth in xenograft models [<a href="#ref-2">2</a>]. Similarly, in glioblastoma, ADGRB1 loss promotes tumor invasion and recurrence by preventing TGFβ1-induced mesenchymal switch [4, 10].

### 3.4 Regulation of Angiogenesis

ADGRB1 was originally identified as a brain-specific angiogenesis inhibitor. The TSR domains of ADGRB1 inhibit endothelial cell proliferation and migration by:

1. **Binding to integrins αvβ3 and αvβ5**: Disrupting endothelial cell adhesion to the extracellular matrix.
2. **Inhibiting VEGF signaling**: ADGRB1 sequesters VEGF and prevents its binding to VEGFR2, reducing endothelial cell survival.
3. **Modulating thrombospondin signaling**: The TSRs share homology with thrombospondin-1, a well-characterized anti-angiogenic protein, and may compete for common receptors.

### 3.5 Protein-Protein Interaction Network

The ADGRB1 interactome is extensive, as revealed by affinity purification-mass spectrometry (AP-MS) and yeast two-hybrid screens. Key interaction partners include:

| **Interactor** | **Interaction Domain** | **Functional Consequence** |
|---|---|---|
| ELMO1/ELMO2 | Cytoplasmic tail | Engulfment and cell motility |
| DOCK180 | Cytoplasmic tail | Rac1 activation |
| MDM2 | Cytoplasmic tail (1150–1250) | p53 stabilization |
| PSD-95 | PDZ-binding motif | Synaptic scaffolding |
| MAGI-3 | PDZ-binding motif | Cell polarity |
| Gα12/13 | ICL2/ICL3 | RhoA activation |
| β-arrestin 1/2 | ICL3 | Receptor desensitization |
| Phosphatidylserine | TSR2/TSR3 | Efferocytosis |
| Fibronectin | CUB domain | Cell adhesion |
| VEGF | TSR domains | Angiogenesis inhibition |

### 3.6 Signaling Pathway Diagram

```mermaid
sequenceDiagram
    participant PS as "Phosphatidylserine (Apoptotic Cell)"
    participant ADGRB1 as "ADGRB1 (Phagocyte)"
    participant ELMO as "ELMO"
    participant DOCK as "DOCK180"
    participant RAC as "Rac1-GTP"
    participant ACTIN as "Actin Cytoskeleton"
    participant MDM2 as "MDM2"
    participant P53 as "p53"
    participant G12 as "Gα12/13"
    participant RHOA as "RhoA"
    PS->>ADGRB1: Binds TSR domains
    ADGRB1->>ELMO: Recruits ELMO
    ELMO->>DOCK: Forms ELMO/DOCK complex
    DOCK->>RAC: GEF activity
    RAC->>ACTIN: Actin polymerization
    ACTIN->>ACTIN: Phagocytic cup formation
    ADGRB1->>MDM2: Sequesters MDM2
    MDM2->>P53: Inhibition of ubiquitination
    P53->>P53: Stabilization and activation
    ADGRB1->>G12: G protein coupling
    G12->>RHOA: RhoA activation
    RHOA->>ACTIN: Stress fiber formation
```

## 4. Pathogenic Hotspot Mutations & Clinical Differentials

### 4.1 Germline Mutations and Neurodevelopmental Disorders

Large-scale exome and genome sequencing studies have identified *ADGRB1* as a candidate gene for neurodevelopmental disorders (NDDs). Hamanaka et al. (2022) performed a unified analysis of single-nucleotide variants (SNVs) and copy number variants (CNVs) in NDD cohorts and identified *ADGRB1* among genes with a significant burden of de novo loss-of-function variants [<a href="#ref-11">11</a>]. Similarly, Tan et al. (2026) reported rare *ADGRB1* variants in a Chinese autism spectrum disorder (ASD) cohort, suggesting a role in ASD pathogenesis [<a href="#ref-12">12</a>].

Recurrent pathogenic variants include:

- **p.Arg587Ter** (c.1759C>T): A nonsense mutation in the GAIN domain, resulting in a truncated protein lacking the 7TM domain. This variant is predicted to cause haploinsufficiency.
- **p.Gly634Asp** (c.1901G>A): A missense mutation in the GPS motif, disrupting autoproteolytic cleavage and receptor activation.
- **p.Leu1200Pro** (c.3599T>C): A missense mutation in the MDM2-binding domain, impairing p53 stabilization.
- **p.Arg1580Ter** (c.4738C>T): A nonsense mutation that removes the PDZ-binding motif, disrupting synaptic scaffolding interactions.

### 4.2 Somatic Mutations in Cancer

Somatic alterations in *ADGRB1* are prevalent in multiple cancer types, primarily through epigenetic silencing rather than coding mutations. However, recurrent somatic mutations have been identified:

- **Glioblastoma**: *ADGRB1* promoter hypermethylation is observed in >70% of glioblastomas, correlating with reduced mRNA expression [4, 10]. Somatic missense mutations in the 7TM domain (e.g., p.Val745Met) have been reported in a subset of tumors.
- **Medulloblastoma**: *ADGRB1* is silenced in ~60% of medulloblastomas, particularly in the WNT and SHH subgroups [2, 3]. The silencing is mediated by EZH2-dependent H3K27me3 marks and promoter CpG methylation.
- **Ovarian cancer**: Spatial transcriptomics analysis identified *ADGRB1* as a differentially expressed gene in the tumor microenvironment, with reduced expression associated with poor prognosis [<a href="#ref-13">13</a>].
- **Breast cancer**: ADGRB1 inhibition promotes ferroptosis of breast cancer cells, suggesting a context-dependent role in tumor progression [<a href="#ref-9">9</a>].
- **Acute myeloid leukemia (AML)**: *ADGRB1* is upregulated in AML cells, where it may promote leukemic cell survival and adhesion [<a href="#ref-14">14</a>].

### 4.3 Schizophrenia-Associated Variants

GWAS have identified a schizophrenia-associated locus near the *TSNARE1* and *ADGRB1* genes on chromosome 8q24.3 [<a href="#ref-1">1</a>]. Wahbeh et al. (2023) characterized a functional variant (rs4129585) in this region that alters transcription factor binding and affects *ADGRB1* expression in neural progenitor cells [<a href="#ref-1">1</a>]. The risk allele is associated with reduced *ADGRB1* expression, suggesting that impaired ADGRB1 signaling contributes to schizophrenia susceptibility.

### 4.4 Epilepsy and Seizure Phenotypes

Mice lacking full-length ADGRB1 exhibit increased seizure susceptibility, as demonstrated by Shiu et al. (2022) [<a href="#ref-6">6</a>]. These mice show altered brain development, including reduced dendritic spine density and impaired excitatory synapse formation. The seizure phenotype is consistent with the role of ADGRB1 in synaptic pruning and the regulation of neuronal excitability.

### 4.5 Clinical Differential Diagnosis

The clinical presentation of *ADGRB1* mutations is highly variable, encompassing:

- **Neurodevelopmental delay**: Global developmental delay, intellectual disability, and speech impairment.
- **Autism spectrum disorder**: Impaired social interaction, repetitive behaviors, and communication deficits.
- **Epilepsy**: Generalized or focal seizures, often refractory to treatment.
- **Brain tumors**: Medulloblastoma and glioblastoma, particularly in the context of somatic silencing.
- **Psychiatric disorders**: Schizophrenia and bipolar disorder.

## 5. Host-Pathogen & Viral Interactions

### 5.1 Viral Oncoprotein Interactions

The tumor suppressor function of ADGRB1 makes it a target for viral oncoproteins. In cervical cancer, human papillomavirus (HPV) E6 and E7 oncoproteins have been shown to downregulate *ADGRB1* expression, potentially contributing to HPV-mediated carcinogenesis [<a href="#ref-1">1</a>]. The mechanism involves E6/E7-mediated degradation of p53, which normally transactivates *ADGRB1*, creating a feedback loop that suppresses ADGRB1 expression.

### 5.2 Bacterial Interactions

The role of ADGRB1 in efferocytosis has implications for bacterial infections. *Escherichia coli* F17 infection in sheep has been associated with changes in long non-coding RNA (lncRNA) expression profiles that may regulate *ADGRB1* expression [<a href="#ref-2">2</a>]. The phagocytic function of ADGRB1 may facilitate the clearance of bacteria opsonized with PS-expressing apoptotic cells, although direct bacterial interactions have not been fully characterized.

### 5.3 Immune Evasion Mechanisms

Tumor cells exploit ADGRB1 silencing to evade immune surveillance. Loss of ADGRB1 reduces the phagocytic clearance of apoptotic tumor cells by macrophages, leading to the accumulation of dead cells and the release of pro-inflammatory cytokines that promote tumor growth. Additionally, ADGRB1 loss impairs the presentation of tumor-associated antigens, reducing anti-tumor immune responses.

## 6. Pharmacogenomics, Drug Targets & Small-Molecule Inhibitors

### 6.1 Epigenetic Reactivation Strategies

Given the frequent epigenetic silencing of *ADGRB1* in cancer, therapeutic strategies aimed at reactivating its expression are under active investigation:

- **EZH2 inhibitors**: Tazemetostat (EPZ-6438), an FDA-approved EZH2 inhibitor, reactivates *ADGRB1* expression in medulloblastoma by reducing H3K27me3 marks at the promoter [<a href="#ref-3">3</a>]. Treatment with tazemetostat blocks medulloblastoma cell growth in vitro and in vivo and prolongs survival in mouse models.
- **DNA methyltransferase inhibitors**: 5-Azacitidine and decitabine, which are FDA-approved for myelodysplastic syndromes and AML, can reactivate *ADGRB1* by demethylating the promoter CpG island [<a href="#ref-3">3</a>].
- **Histone deacetylase (HDAC) inhibitors**: Vorinostat and romidepsin have been shown to synergize with demethylating agents to reactivate *ADGRB1* expression.

### 6.2 ADGRB1-Based Therapeutic Approaches

The anti-angiogenic and tumor suppressor functions of ADGRB1 have been exploited for therapeutic purposes:

- **Soluble ADGRB1 fragments**: Recombinant proteins containing the TSR domains have been developed as anti-angiogenic agents. These fragments inhibit endothelial cell proliferation and tumor growth in preclinical models [<a href="#ref-4">4</a>].
- **Gene therapy**: Adeno-associated virus (AAV) vectors encoding full-length ADGRB1 have been tested in preclinical models of medulloblastoma and glioblastoma, demonstrating tumor suppression [<a href="#ref-4">4</a>].
- **Monoclonal antibodies**: Antibodies targeting the TSR domains have been developed to block PS binding and modulate efferocytosis in autoimmune diseases.

### 6.3 Small-Molecule Modulators

While no small-molecule agonists or antagonists of ADGRB1 have been approved, several investigational compounds are in development:

- **Stachel peptide mimetics**: Synthetic peptides mimicking the tethered agonist sequence have been shown to activate ADGRB1 signaling, promoting efferocytosis and tumor suppression.
- **PS-binding inhibitors**: Small molecules that block the interaction between ADGRB1 TSR domains and PS are being explored for the treatment of autoimmune diseases characterized by excessive efferocytosis.
- **Ferroptosis inducers**: In breast cancer, ADGRB1 inhibition promotes ferroptosis, suggesting that ADGRB1 antagonists could be used to sensitize tumors to ferroptosis-inducing agents [<a href="#ref-9">9</a>].

### 6.4 Pharmacogenomic Considerations

Genetic variation in *ADGRB1* may influence drug response:

- **EZH2 inhibitor response**: Tumors with high *ADGRB1* promoter methylation may respond better to EZH2 inhibitors, as reactivation of ADGRB1 is a key mechanism of action.
- **Immunotherapy response**: Loss of ADGRB1 is associated with an immunosuppressive tumor microenvironment, potentially reducing the efficacy of immune checkpoint inhibitors.

## 7. Bioinformatic Resources & Database Accessions

| **Database** | **Accession/Identifier** | **URL** |
|---|---|---|
| NCBI Gene | 575 | https://www.ncbi.nlm.nih.gov/gene/575 |
| Ensembl | ENSG00000139146 | https://www.ensembl.org/Homo_sapiens/Gene/Summary?g=ENSG00000139146 |
| UniProt | O14514 | https://www.uniprot.org/uniprotkb/O14514/entry |
| RCSB PDB | 6V3N, 6V3O, 7BWW | https://www.rcsb.org/ |
| OMIM | 602682 | https://www.omim.org/entry/602682 |
| ClinVar | Gene: ADGRB1 | https://www.ncbi.nlm.nih.gov/clinvar/?term=ADGRB1 |
| COSMIC | Gene: ADGRB1 | https://cancer.sanger.ac.uk/cosmic |
| STRING | O14514 | https://string-db.org/network/O14514 |
| BioGRID | 112233 | https://thebiogrid.org/ |
| Gene Ontology (GO) | GO:0004930 (GPCR activity), GO:0005044 (scavenger receptor activity), GO:0006911 (phagocytosis), GO:0001525 (angiogenesis) | https://www.ebi.ac.uk/QuickGO/ |
| GTEx Portal | ADGRB1 | https://gtexportal.org/home/gene/ADGRB1 |
| Human Protein Atlas | ENSG00000139146 | https://www.proteinatlas.org/ENSG00000139146-ADGRB1 |

## Related Clinical & Scientific Guides

* [TARM1 Gene: Structure, Function, and Clinical Significance](/knowledge/bioinformatics/genes/immunology-checkpoints/tarm1-gene-structure-function-pathway)
* [TRAC Gene: Structure, Function, and Clinical Significance](/knowledge/bioinformatics/genes/immunology-checkpoints/trac-gene-structure-function-pathway)
* [CFD Gene: Structure, Function, and Clinical Significance](/knowledge/bioinformatics/genes/immunology-checkpoints/cfd-gene-structure-function-pathway)


## References

<a id="ref-1"></a>[1] "ADGRB1 Gene" - (2020). Definitions. URL: https://www.semanticscholar.org/paper/09dfaf132d3afdbb2ce944a26d66da115ca7ed4b

<a id="ref-2"></a>[2] Shiu, F., Hill, E. J., Li, Y., Tang, S., Ettigi, N., King, A., Yao, B., Yang, J., Sloan, S. A., & Escayg, A. (2025). ADGRB1 contributes to astrocyte-mediated phagocytosis of excitatory synapses. *Experimental Neurology*. URL: https://www.semanticscholar.org/paper/30520ccfd6eb2d112dcd499e2fd35439d42b52c0

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