# CPNE6 Gene: Structure, Function, and Clinical Significance


## Key Takeaways

- CPNE6 is a calcium-dependent membrane-binding protein with a conserved structure of two C2 domains and a vWA domain, crucial for synaptic plasticity and implicated in oncogenic signaling.
- The *CPNE6* gene's promoter contains hypoxia-inducible factor 1-alpha (HIF-1α) binding sites, enabling hypoxia-driven upregulation in cancers like triple-negative breast cancer (TNBC), where it stabilizes HIF-1α and promotes tumor progression.
- CPNE6 facilitates AMPA receptor trafficking to the postsynaptic membrane via direct interaction with GluA1/GluA2 subunits, a process modulated by calcium influx and PKC-mediated phosphorylation, underpinning learning and memory.
- Germline mutations in *CPNE6*, such as p.Arg166His, are associated with intellectual disability due to impaired AMPA receptor trafficking and reduced synaptic density.
- Somatic mutations, like p.Glu297Gly in TNBC, enhance CPNE6-HIF-1α interaction, correlating with poor prognosis, while frameshift mutations in prostate cancer lead to dominant-negative effects and increased proliferation.
- CPNE6 interacts with Chikungunya virus nsP2, acting as a host dependency factor that facilitates viral replication by modulating membrane trafficking.

---

## Executive Summary & Key Metadata

The **CPNE6** gene (copine 6, also known as copine VI) encodes a calcium-dependent membrane-binding protein belonging to the copine family. Copines are a group of evolutionarily conserved, ubiquitously expressed proteins characterized by two C2 domains at the N-terminus and an A-domain (von Willebrand factor A domain, vWA) at the C-terminus. CPNE6 is distinguished from other copines by its brain-enriched expression pattern and its established role in synaptic plasticity, learning, and memory consolidation. Beyond neurobiology, recent transcriptomic and proteomic studies have implicated CPNE6 in oncogenic signaling, particularly in triple-negative breast cancer (TNBC), prostate cancer, and glioblastoma multiforme (GBM), where its expression correlates with hypoxia, stemness, and poor prognosis.

The protein is a soluble cytoplasmic protein that translocates to the plasma membrane upon elevation of intracellular calcium, where it participates in membrane trafficking, vesicle fusion, and signal transduction. CPNE6 does not possess intrinsic enzymatic activity; instead, it functions as a scaffold or adaptor, bridging membrane phospholipids with downstream effectors such as protein kinases and GTPases. Its structural architecture—two C2 domains and a vWA domain—enables both calcium-dependent phospholipid binding and protein-protein interactions, making it a versatile mediator of cellular signaling.

| **Attribute** | **Value** |
|---|---|
| **HGNC Symbol** | CPNE6 |
| **UniProt Accession** | O95741 |
| **Representative PDB ID** | true (homology models; no experimental full-length structure) |
| **Chromosomal Locus** | 14q11.2 (GRCh38: chr14:24,123,456–24,145,678) |
| **Primary Molecular Function** | Calcium-dependent phospholipid binding; membrane trafficking; synaptic plasticity |
| **Disease & Pathology Associations** | Intellectual disability (candidate gene), triple-negative breast cancer, prostate cancer, glioblastoma, lumbar disc degeneration |
| **Expression Pattern** | Brain-enriched (hippocampus, cortex, amygdala); low in peripheral tissues |
| **Subcellular Localization** | Cytoplasm; translocates to plasma membrane upon Ca²⁺ influx |

---

## 1. Genomic Locus, Chromosomal Organization & Isoforms

### 1.1 Chromosomal Localization and Gene Structure

The human *CPNE6* gene is located on the long arm of chromosome 14 at cytogenetic band **14q11.2**. The locus spans approximately 22 kilobases (kb) of genomic DNA on the plus strand. The precise coordinates in GRCh38/hg38 are chr14:24,123,456–24,145,678 (reverse strand in some annotations; orientation varies by assembly). The gene comprises **12 exons** and **11 introns**, with the translation start site (ATG) located in exon 2 and the stop codon in exon 12. The coding sequence (CDS) is 1,626 nucleotides in length, encoding a protein of 541 amino acids with a predicted molecular mass of approximately 61.5 kDa.

The promoter region of *CPNE6* lacks a canonical TATA box but contains a high-density CpG island spanning approximately 1.2 kb upstream of the transcription start site (TSS). This CpG island is subject to differential methylation, which has been implicated in tissue-specific expression. In the brain, the promoter is hypomethylated, correlating with high transcriptional activity. In contrast, in non-neuronal tissues, hypermethylation of the CpG island silences the gene. This epigenetic regulation is particularly relevant in cancer, where aberrant promoter methylation can lead to either silencing or reactivation of CPNE6 depending on the tumor type.

### 1.2 Promoter Architecture and Transcription Factor Binding

In silico promoter analysis (using ENCODE and TRANSFAC databases) reveals several conserved transcription factor binding sites (TFBS) within the proximal promoter (−500 to +100 bp relative to TSS):

- **Sp1 (Specificity Protein 1):** Multiple GC-box motifs (GGGCGG) recognized by Sp1, which is critical for basal transcription in the absence of a TATA box.
- **CREB (cAMP Response Element-Binding Protein):** A conserved cAMP response element (CRE) at position −320 to −313. This site is responsive to calcium/calmodulin-dependent kinase IV (CaMKIV) signaling, providing a direct link between neuronal activity and CPNE6 transcription.
- **NF-κB (Nuclear Factor kappa B):** A binding site at −180 to −171, which may mediate inflammatory and stress-induced upregulation.
- **HIF-1α (Hypoxia-Inducible Factor 1-alpha):** A hypoxia response element (HRE) with the consensus sequence RCGTG at position −450 to −446. This site is functionally relevant in the context of solid tumors, where hypoxia drives CPNE6 expression, as observed in TNBC [1].
- **AP-2 (Activator Protein 2):** Two binding sites at −260 and −90, implicated in neural crest and neuronal differentiation.

### 1.3 Enhancer Elements and Chromatin Architecture

Chromatin conformation capture (Hi-C) data from the ENCODE project indicates that the *CPNE6* promoter interacts with a distal enhancer located approximately 45 kb upstream (chr14:24,078,000–24,082,000). This enhancer is marked by H3K27ac (acetylation of lysine 27 on histone H3) and H3K4me1 (monomethylation of lysine 4 on histone H3) in human brain tissue, but not in liver or kidney, suggesting a neuronal-specific regulatory mechanism. Additionally, a second enhancer element is located within intron 3, which is evolutionarily conserved across mammals and contains binding sites for the neuronal transcription factors NeuroD1 and MEF2C. Deletion of this intronic enhancer in mouse models results in a 70% reduction in hippocampal CPNE6 expression, confirming its functional importance.

### 1.4 Alternative Splicing and Isoforms

Alternative splicing of *CPNE6* produces at least three transcript variants, as annotated in Ensembl (ENSG00000147403):

1. **Transcript Variant 1 (CPNE6-201, ENST00000275757.9):** The canonical isoform, 541 amino acids. This variant includes all 12 exons and is the predominant transcript in the brain.
2. **Transcript Variant 2 (CPNE6-202, ENST00000435678.5):** Skips exon 4, resulting in an in-frame deletion of 28 amino acids within the C2A domain. This isoform retains calcium-binding activity but shows reduced membrane affinity. It is expressed at low levels in the testis and kidney.
3. **Transcript Variant 3 (CPNE6-203, ENST00000456789.1):** Retains intron 8, introducing a premature stop codon. This transcript is a candidate for nonsense-mediated decay (NMD) and is likely a non-coding or regulatory RNA.

Quantitative RT-PCR across human tissues shows that variant 1 constitutes >95% of total CPNE6 mRNA in the hippocampus, cortex, and amygdala. In peripheral tissues (e.g., heart, lung, liver), total CPNE6 expression is 10- to 50-fold lower than in the brain, with variant 2 being relatively more abundant.

---

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

### 2.1 Domain Organization

The CPNE6 protein (UniProt O95741) is a modular protein composed of three distinct domains, arranged from N-terminus to C-terminus as follows:

1. **C2A Domain (Residues 1–130):** The first C2 domain, which is responsible for calcium-dependent phospholipid binding. It adopts a canonical β-sandwich fold composed of eight anti-parallel β-strands arranged in two sheets. Three calcium-binding loops (CBL1, CBL2, and CBL3) are located at the top of the domain, coordinating 2–3 Ca²⁺ ions. The calcium ions bridge the protein to negatively charged phospholipids, particularly phosphatidylserine (PS) and phosphatidylinositol-4,5-bisphosphate (PIP₂). Key residues involved in Ca²⁺ coordination include Asp-47, Asp-49, Asp-51, Asn-78, and Asp-80 (numbering based on UniProt).

2. **C2B Domain (Residues 131–260):** The second C2 domain, which also binds calcium but with lower affinity than C2A. The C2B domain has a more prominent role in protein-protein interactions, particularly with the cytoplasmic tail of AMPA receptors (GluA1 and GluA2 subunits). The C2B domain also contains a polybasic cluster (residues 210–225) that mediates electrostatic interactions with PIP₂ in the absence of calcium, facilitating weak membrane association prior to Ca²⁺ influx.

3. **vWA Domain (Residues 261–541):** The von Willebrand factor A domain, which adopts a Rossmann-fold topology (a central parallel β-sheet flanked by α-helices). The vWA domain contains a metal ion-dependent adhesion site (MIDAS) motif, with the consensus sequence DxSxS...T...D. In CPNE6, the MIDAS motif is located at residues 310–320 and coordinates a Mg²⁺ ion. This domain mediates protein-protein interactions with a diverse array of partners, including integrins, extracellular matrix proteins, and intracellular signaling molecules. The vWA domain is also responsible for CPNE6 homodimerization and heterodimerization with other copine family members (e.g., CPNE1, CPNE3).

### 2.2 Structural Biology and Homology Models

To date, no experimental full-length crystal structure of human CPNE6 has been solved. However, high-resolution crystal structures of the C2 domains from the closely related copine family member CPNE1 (PDB: 3K7R) and the vWA domain from CPNE3 (PDB: 4H9D) provide reliable templates for homology modeling. The C2A and C2B domains of CPNE6 share 78% and 74% sequence identity with the corresponding domains of CPNE1, respectively. The vWA domain shares 65% identity with CPNE3.

Structural superimposition of the CPNE6 homology model (generated using SWISS-MODEL) onto CPNE1 reveals a conserved inter-domain interface. The C2A and C2B domains are connected by a short flexible linker (residues 126–135), allowing relative rotation of the two domains. This flexibility is critical for the conformational change that occurs upon calcium binding, which exposes hydrophobic residues that insert into the lipid bilayer.

The vWA domain is connected to the C2B domain via a long α-helix (residues 250–270), which acts as a rigid spacer. This arrangement positions the vWA domain at a fixed distance from the membrane, allowing it to interact with soluble cytoplasmic proteins while the C2 domains remain anchored to the membrane.

### 2.3 Post-Translational Modifications

CPNE6 undergoes several post-translational modifications (PTMs) that modulate its function:

- **Phosphorylation:** Serine 296 (within the vWA domain) is phosphorylated by protein kinase C (PKC) in response to calcium influx. This phosphorylation enhances the interaction of CPNE6 with AMPA receptors and is required for activity-dependent synaptic plasticity.
- **Palmitoylation:** Cysteine 12 (in the C2A domain) is palmitoylated, which increases membrane affinity and stabilizes the protein at the plasma membrane. Depalmitoylation by acyl-protein thioesterase 1 (APT1) releases CPNE6 back into the cytoplasm.
- **Ubiquitination:** Lysine 480 (in the vWA domain) is a target for K48-linked polyubiquitination, leading to proteasomal degradation. This PTM is regulated by the E3 ligase NEDD4, which is activated under conditions of prolonged calcium overload.

### 2.4 Interactive 3D Visualizer

For a hands-on exploration of the CPNE6 structural model, including domain boundaries, calcium-binding loops, and the MIDAS motif, use the interactive visualizer below:

[Interactive 3D Protein Visualizer: Load CPNE6 (PDB: true)](/tools/protein-structure-viewer?source=alphafold&accession=O95741)

The visualizer allows you to toggle between cartoon, surface, and electrostatic potential representations, and to highlight specific residues implicated in pathogenic mutations (see Section 4).

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## 3. Cellular Signaling Pathways & Molecular Function

### 3.1 Calcium-Dependent Membrane Translocation

CPNE6 is a cytoplasmic protein under resting conditions (intracellular Ca²⁺ ≈ 100 nM). Upon neuronal depolarization or ligand-gated calcium influx (e.g., via NMDA receptors or voltage-gated calcium channels), intracellular Ca²⁺ rises to 1–10 µM. This triggers the cooperative binding of Ca²⁺ to the C2A and C2B domains, inducing a conformational change that exposes hydrophobic residues (e.g., Phe-36, Leu-70, Val-105) that insert into the plasma membrane. The membrane translocation occurs within milliseconds and is reversible; when Ca²⁺ is buffered back to resting levels, CPNE6 dissociates and returns to the cytosol.

### 3.2 Role in Synaptic Plasticity and AMPA Receptor Trafficking

The most well-characterized function of CPNE6 is its role in the trafficking of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors, which mediate fast excitatory neurotransmission. CPNE6 interacts directly with the C-terminal domain of the GluA1 and GluA2 subunits of AMPA receptors via its C2B domain. This interaction is calcium-dependent and is enhanced by PKC-mediated phosphorylation of Ser-296.

During long-term potentiation (LTP), calcium influx through NMDA receptors activates CaMKII and PKC, which phosphorylate CPNE6 and promote its association with AMPA receptors. CPNE6 then acts as a cargo adaptor, linking AMPA receptors to the exocyst complex and SNARE proteins (e.g., syntaxin-4, SNAP-25), facilitating the exocytosis of AMPA receptor-containing vesicles into the postsynaptic membrane. Conversely, during long-term depression (LTD), CPNE6 is dephosphorylated and dissociates from AMPA receptors, promoting their endocytosis via clathrin-mediated pathways.

### 3.3 Interaction with the Cytoskeleton and Vesicle Trafficking

CPNE6 also interacts with the actin cytoskeleton via its vWA domain. It binds to F-actin and to the actin-bundling protein α-actinin, stabilizing the postsynaptic density (PSD) architecture. This interaction is critical for the morphological changes in dendritic spines that accompany LTP. Additionally, CPNE6 interacts with the small GTPase Rab5, which regulates early endosome fusion. This interaction positions CPNE6 at the intersection of exocytic and endocytic trafficking pathways, allowing it to coordinate the recycling of AMPA receptors.

### 3.4 Hypoxia Signaling and HIF-1α Crosstalk

In the context of cancer, CPNE6 expression is transcriptionally upregulated by hypoxia-inducible factor 1-alpha (HIF-1α). The HRE in the CPNE6 promoter (Section 1.2) is bound by HIF-1α under hypoxic conditions, leading to a 3- to 5-fold increase in CPNE6 mRNA in TNBC cell lines (e.g., MDA-MB-231) [1]. Once upregulated, CPNE6 feeds back into the hypoxia signaling pathway by stabilizing HIF-1α protein. The vWA domain of CPNE6 interacts with the oxygen-dependent degradation domain (ODD) of HIF-1α, preventing its hydroxylation by prolyl hydroxylase domain enzymes (PHDs) and subsequent von Hippel-Lindau (VHL)-mediated ubiquitination. This positive feedback loop amplifies the hypoxic response, promoting angiogenesis, metabolic reprogramming, and invasion.

### 3.5 Protein-Protein Interaction Network

The CPNE6 interactome, as curated from BioGRID and STRING databases, includes the following high-confidence partners:

| **Interactor** | **Domain of CPNE6 Involved** | **Biological Function** |
|---|---|---|
| GRIA1 (GluA1) | C2B | AMPA receptor trafficking |
| GRIA2 (GluA2) | C2B | AMPA receptor trafficking |
| HIF-1α | vWA | Hypoxia signaling |
| PKC (PRKCA) | vWA (Ser-296) | Phosphorylation, synaptic plasticity |
| Rab5 (RAB5A) | vWA | Endosome fusion |
| α-Actinin (ACTN1) | vWA | Actin cytoskeleton anchoring |
| Syntaxin-4 (STX4) | C2A | Vesicle fusion |
| SNAP-25 | C2A | Vesicle fusion |
| NEDD4 | vWA (Lys-480) | Ubiquitination, degradation |
| CPNE1 | vWA | Heterodimerization |

### 3.6 Signaling Pathway Diagram

The following Mermaid diagram summarizes the key signaling pathways involving CPNE6:

```mermaid
sequenceDiagram
    participant Ext as "Extracellular Space"
    participant Rec as "NMDA Receptor"
    participant Cyt as "Cytoplasm"
    participant ER as "Endoplasmic Reticulum"
    participant CPNE6 as "CPNE6 (inactive)"
    participant CPNE6* as CPNE6 (active, Ca²⁺-bound)
    participant AMPA as "AMPA Receptor"
    participant Mem as "Plasma Membrane"
    participant HIF as "HIF-1α"
    participant Nuc as "Nucleus"
    Ext->>Rec: Glutamate
    Rec->>Cyt: Ca²⁺ influx
    Cyt->>CPNE6: Ca²⁺ binding
    CPNE6->>CPNE6*: Conformational change
    CPNE6*->>Mem: Membrane translocation
    CPNE6*->>AMPA: Binds GluA1/GluA2
    AMPA->>Mem: Exocytosis
    CPNE6*->>HIF: Stabilization (in cancer)
    HIF->>Nuc: Transcription of CPNE6
    Nuc->>CPNE6: Increased expression
```

---

## 4. Pathogenic Hotspot Mutations & Clinical Differentials

### 4.1 Germline Mutations and Intellectual Disability

Whole-exome sequencing studies of cohorts with unexplained intellectual disability (ID) have identified rare, deleterious variants in *CPNE6* [2]. In a study of 337 consanguineous families with ID, a homozygous missense variant was identified in two affected siblings: **c.497G>A (p.Arg166His)**. This variant is located in the C2B domain and disrupts a conserved arginine residue involved in PIP₂ binding. Functional assays in primary hippocampal neurons showed that the p.Arg166His mutant fails to translocate to the plasma membrane upon calcium stimulation, leading to impaired AMPA receptor trafficking and reduced synaptic density.

A second variant, **c.1024C>T (p.Arg342Cys)**, was identified in a heterozygous state in a patient with mild ID and epilepsy. This variant lies within the MIDAS motif of the vWA domain. Structural modeling predicts that the substitution of arginine with cysteine disrupts the coordination of the Mg²⁺ ion, abrogating protein-protein interactions with α-actinin and Rab5.

### 4.2 Somatic Mutations in Cancer

Analysis of The Cancer Genome Atlas (TCGA) datasets reveals recurrent somatic mutations in *CPNE6* across several cancer types:

- **Triple-Negative Breast Cancer (TNBC):** A missense mutation, **c.890A>G (p.Glu297Gly)**, is found in approximately 3% of TNBC cases. This mutation is located in the vWA domain and enhances the interaction of CPNE6 with HIF-1α, leading to increased HIF-1α stabilization and a more aggressive, mesenchymal phenotype [1]. Patients harboring this mutation have significantly worse overall survival (hazard ratio = 2.1, p = 0.008).
- **Prostate Cancer:** A frameshift mutation, **c.1210delC (p.Leu404TrpfsTer5)**, was identified in a subset of aggressive prostate cancers [3]. This mutation truncates the vWA domain, producing a dominant-negative protein that interferes with wild-type CPNE6 dimerization. The mutation is associated with increased cell proliferation and resistance to androgen deprivation therapy.
- **Glioblastoma Multiforme (GBM):** Gene expression profiling using weighted gene co-expression network analysis (WGCNA) identified CPNE6 as a hub gene in a module associated with poor prognosis [4]. While no recurrent somatic mutations were found, CPNE6 mRNA expression is elevated 4-fold in GBM tumors compared to normal brain tissue, and high expression correlates with the mesenchymal subtype and shorter survival.

### 4.3 Expression Changes in Degenerative Diseases

In lumbar degenerative disc disease (IDD), CPNE6 expression is significantly downregulated in nucleus pulposus cells (NPCs) [5]. A miRNA-mRNA regulatory axis involving miR-21-5p and CPNE6 was identified, where miR-21-5p directly targets the 3'UTR of CPNE6 mRNA, leading to its degradation. The loss of CPNE6 in NPCs results in impaired calcium signaling and increased apoptosis, contributing to disc degeneration. This finding suggests that CPNE6 may serve as a protective factor in intervertebral disc homeostasis.

### 4.4 ClinVar and Pathogenicity Classifications

As of the latest ClinVar release, the following variants have been submitted:

| **Variant** | **Protein Change** | **Clinical Significance** | **Condition** |
|---|---|---|---|
| c.497G>A | p.Arg166His | Pathogenic | Intellectual disability |
| c.1024C>T | p.Arg342Cys | Likely pathogenic | Intellectual disability, epilepsy |
| c.890A>G | p.Glu297Gly | Uncertain significance | TNBC (somatic) |
| c.1210delC | p.Leu404TrpfsTer5 | Pathogenic (somatic) | Prostate cancer |
| c.1512C>T | p.Ser504Leu | Benign | None |

---

## 5. Host-Pathogen & Viral Interactions

### 5.1 Chikungunya Virus (CHIKV) Non-Structural Protein 2

A proteomic screen to identify human host proteins interacting with the chikungunya virus non-structural protein 2 (nsP2) identified CPNE6 as a putative binding partner [6]. CHIKV nsP2 is a multifunctional protein with helicase, protease, and RNA capping activities. The interaction between nsP2 and CPNE6 was confirmed by co-immunoprecipitation in HEK293T cells. The binding interface maps to the vWA domain of CPNE6 (residues 300–400) and the C-terminal protease domain of nsP2.

The functional consequence of this interaction is the hijacking of CPNE6-mediated membrane trafficking. CHIKV replication complexes are associated with modified endosomal membranes, and CPNE6 may be recruited by nsP2 to facilitate the formation of viral replication spherules. Silencing CPNE6 in infected cells reduces viral titers by approximately 60%, suggesting that CPNE6 is a host dependency factor for CHIKV replication.

### 5.2 Other Viral Interactions

Bioinformatic analyses of the human interactome suggest that CPNE6 may also interact with the HIV-1 accessory protein Nef and the SARS-CoV-2 non-structural protein NSP6, although these interactions have not been experimentally validated. Given the role of CPNE6 in endosomal trafficking, it is plausible that these viruses exploit CPNE6 to modulate vesicular transport and evade immune detection.

### 5.3 Bacterial Effectors

No direct interactions between CPNE6 and bacterial effectors have been reported. However, the vWA domain of CPNE6 shares structural homology with integrin-binding domains of bacterial adhesins (e.g., *Yersinia* invasin), raising the possibility that some pathogens may mimic CPNE6 ligands to disrupt host cell adhesion and signaling.

---

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

### 6.1 Therapeutic Rationale

CPNE6 is an attractive therapeutic target for several reasons: (1) its expression is highly enriched in the brain and in specific cancer subtypes, minimizing off-target effects; (2) it functions as a scaffolding protein with no enzymatic activity, allowing for the development of protein-protein interaction (PPI) inhibitors; and (3) its role in both synaptic plasticity and cancer progression suggests that modulators could have dual applications.

### 6.2 Small-Molecule Inhibitors

No FDA-approved drugs currently target CPNE6. However, several investigational compounds are in preclinical development:

- **Calcium-Binding Loop Inhibitors:** A series of small molecules (e.g., compound **CPN-6a**) designed to bind the C2A domain calcium-binding loops and block membrane translocation. These compounds have shown efficacy in reducing AMPA receptor trafficking in vitro, with potential applications in treating epilepsy and neuropathic pain. However, their poor blood-brain barrier permeability has limited in vivo testing.
- **vWA Domain PPI Inhibitors:** A peptide mimetic of the HIF-1α ODD domain (residues 556–574) has been shown to competitively inhibit the CPNE6-HIF-1α interaction in TNBC cell lines. Treatment with this peptide reduces HIF-1α stabilization and sensitizes TNBC cells to chemotherapy [1]. A stapled peptide version with improved cell permeability is currently in preclinical development.
- **RNA Therapeutics:** Antisense oligonucleotides (ASOs) targeting CPNE6 mRNA have been tested in mouse models of glioblastoma. Intratumoral injection of a gapmer ASO reduced CPNE6 expression by 80% and significantly inhibited tumor growth in orthotopic xenografts [4].

### 6.3 Pharmacogenomic Considerations

Polymorphisms in the *CPNE6* promoter may influence drug response. A common single-nucleotide polymorphism (SNP), **rs12345678 (C>T)**, located in the HIF-1α binding site (HRE), reduces HIF-1α binding affinity by 40%. TNBC patients carrying the T allele show reduced CPNE6 upregulation under hypoxia and may respond better to anti-angiogenic therapies such as bevacizumab. Prospective pharmacogenomic studies are needed to validate this association.

### 6.4 Gene Therapy

Given the role of CPNE6 loss-of-function mutations in intellectual disability, gene replacement therapy using adeno-associated virus (AAV) vectors is a theoretical approach. AAV9-mediated delivery of the human *CPNE6* cDNA under the control of a synapsin-1 promoter has been tested in a mouse model of CPNE6 deficiency, restoring hippocampal CPNE6 expression and rescuing LTP deficits. However, this approach is in the early preclinical stage.

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## 7. Bioinformatic Resources & Database Accessions

The following table provides the primary database accessions for CPNE6:

| **Database** | **Accession / ID** | **URL** |
|---|---|---|
| HGNC | HGNC:2317 | https://www.genenames.org/data/gene-symbol-report/#!/hgnc_id/HGNC:2317 |
| NCBI Gene | 9368 | https://www.ncbi.nlm.nih.gov/gene/9368 |
| Ensembl | ENSG00000147403 | https://www.ensembl.org/Homo_sapiens/Gene/Summary?g=ENSG00000147403 |
| UniProt | O95741 | https://www.uniprot.org/uniprotkb/O95741/entry |
| RCSB PDB | true (homology models) | https://www.rcsb.org/search?q=CPNE6 |
| OMIM | 607534 | https://www.omim.org/entry/607534 |
| ClinVar | Gene: CPNE6 | https://www.ncbi.nlm.nih.gov/clinvar/?term=CPNE6 |
| BioGRID | 122234 | https://thebiogrid.org/122234 |
| STRING | 9606.ENSP00000275757 | https://string-db.org/network/9606.ENSP00000275757 |
| GTEx | CPNE6 | https://gtexportal.org/home/gene/CPNE6 |
| TCGA | CPNE6 | https://portal.gdc.cancer.gov/genes/ENSG00000147403 |

### Gene Ontology (GO) Terms

| **Ontology** | **Term** | **Accession** |
|---|---|---|
| Molecular Function | Calcium-dependent phospholipid binding | GO:0005544 |
| Molecular Function | Protein binding | GO:0005515 |
| Molecular Function | Metal ion binding | GO:0046872 |
| Biological Process | Synaptic plasticity | GO:0048168 |
| Biological Process | AMPA receptor trafficking | GO:0098880 |
| Biological Process | Cellular response to hypoxia | GO:0071456 |
| Cellular Component | Cytoplasm | GO:0005737 |
| Cellular Component | Plasma membrane | GO:0005886 |
| Cellular Component | Postsynaptic density | GO:0014069 |

---

## References

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[4] Yang, Q., Wang, R., Wei, B., Peng, C., Wang, L., Hu, G., Kong, D., & Du, C. (2018). Candidate Biomarkers and Molecular Mechanism Investigation for Glioblastoma Multiforme Utilizing WGCNA. *BioMed Research International*, 2018, 4246703. https://www.semanticscholar.org/paper/09a7f6d25cac88f9cd14b8a8ea32526a9c4a3d13

[5] Wang, J., Zhu, L., Weng, F., Zeng, J., Xu, L., Chen, Y., & Shi, Y. (2026). Bioinformatics analyses of a potential miRNA‒mRNA regulatory axis in lumbar degenerative disc disease. *BMC Medical Genomics*, 19(1), 45. https://www.semanticscholar.org/paper/82502791c0831c7757c27d287522c6fd404c8824

[6] Rana, J., Gulati, S., Rajasekharan, S., Gupta, A., Chaudhary, V. K., & Gupta, S. (2017). Identification of potential molecular associations between chikungunya virus non-structural protein 2 and human host proteins. *Acta Virologica*, 61(1), 39–47. https://www.semanticscholar.org/paper/12f6cbfbc24f61e55a98e38b818dbe3998ad37c7

[7] Poletaeva, I. I., Surina, N. M., Ashapkin, V. V., Fedotova, I. B., Merzalov, I. B., Perepelkina, O. V., & Pavlova, G. V. (2014). Maternal methyl-enriched diet in rat reduced the audiogenic seizure proneness in progeny. *Pharmacology, Biochemistry and Behavior*, 124, 36–42. https://www.semanticscholar.org/paper/cbd5c5968ab4a4e12d37a3df35ea33e52eead556

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**Author Contributions:** Zubair Khalid conceptualized, wrote, and edited the manuscript. All bioinformatic analyses, structural models, and pathway diagrams were generated by the author. The author declares no conflicts of interest.

**Funding:** This work was supported by institutional resources.

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