UBQLN4 Gene

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UBQLN4 Gene

<table class="infobox infobox-gene">
<tr>
<th class="infobox-header" colspan="2">UBQLN4 — Ubiquilin 4</th>
</tr>
<tr> [@vcpubiquilin2018]
<td class="label">Symbol</td> [@neuronal2019]
<td>UBQLN4</td> [@proteasome2017]
</tr> [@autophagy2020]
<tr> [@vcp2018]
<td class="label">Full Name</td> [@ubqln2020]
<td>Ubiquilin 4</td> [@ubqln2020a]
</tr> [@nuclear2021]
<tr> [@tdp2019]
<td class="label">Chromosome</td> [@recessive2018]
<td>Xq24</td>
</tr>
<tr>
<td class="label">NCBI Gene</td>
<td><a href="https://www.ncbi.nlm.nih.gov/gene/94160" target="_blank">94160</a></td>
</tr>
<tr>
<td class="label">Ensembl</td>
<td><a href="https://ensembl.org/Homo_sapiens/Gene/Summary?g=ENSG00000163527" target="_blank">ENSG00000163527</a></td>
</tr>
<tr>
<td class="label">OMIM</td>
<td><a href="https://omim.org/entry/300368" target="_blank">300368</a></td>
</tr>
<tr>
<td class="label">UniProt</td>
<td><a href="https://www.uniprot.org/uniprot/Q9Y5X5" target="_blank">Q9Y5X5</a></td>
</tr>
<tr>
<td class="label">Diseases</td>
<td>[ALS](/diseases/als), FTD</td>
</tr>
<tr>
<td class="label">Expression</td>
<td>Motor cortex, Hippocampus, Cerebellum</td>
</tr>
<tr>
<th class="infobox-subheader" colspan="2">Key Mutations</th>
</tr>
<tr>
<td colspan="2" style="font-size:0.85em">P497S, T187fs, R198X</td>
</tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">1 edges</a></td>
</tr>
</table>

...

UBQLN4 Gene

UBQLN4 — Ubiquilin 4

Introduction

UBQLN4 (Ubiquilin 4) is a gene located on chromosome Xq24 that encodes a member of the ubiquilin family of proteins involved in protein quality control and degradation pathways. Mutations in UBQLN4 have been increasingly recognized as important contributors to neurodegenerative diseases, particularly amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). This gene encodes a protein that plays critical roles in targeting misfolded proteins for proteasomal and autophagic degradation, making it essential for maintaining neuronal proteostasis.

The ubiquilin family (UBQLN1, UBQLN2, UBQLN3, UBQLN4, and UBQLNL in humans) shares a common architecture featuring an N-terminal ubiquitin-like (Ubl) domain and a C-terminal ubiquitin-associated (UBA) domain, connected by a variable middle region containing multiple stiff-chain (STI) motifs. UBQLN4, also known as UBIN or GIDE, is particularly enriched in the brain and has been implicated in both autosomal dominant and recessive forms of neurodegeneration[1].

Overview

UBQLN4 is a 624-amino acid protein that serves as a molecular adaptor linking ubiquitinated proteins to the proteasome and autophagy machinery. The gene is catalogued as NCBI Gene ID 94160 and OMIM 300368. UBQLN4 is expressed throughout the brain with high expression in motor cortex, hippocampus, and cerebellum — regions prominently affected in ALS and FTD[2]. The protein localizes to the cytoplasm and nucleus, where it participates in various protein quality control pathways. Dysfunction of UBQLN4 leads to accumulation of ubiquitinated protein aggregates, a hallmark pathology observed in most neurodegenerative diseases.

Protein Structure and Domains

The UBQLN4 protein contains several functionally important domains:

N-Terminal Ubiquitin-Like (Ubl) Domain (aa 1-70)

The N-terminal Ubl domain adopts a β-grasp fold similar to ubiquitin and is involved in binding to proteasome subunits. This domain facilitates the delivery of ubiquitinated substrates to the 26S proteasome for degradation. The Ubl domain also interacts with autophagy receptors, enabling selective autophagy pathways[3].

STI1 Domains (aa 150-550)

The middle region of UBQLN4 contains multiple STI1 (Stress-Induced Phosphoprotein 1) repeat motifs. These coiled-coil domains mediate protein-protein interactions and are crucial for forming homomeric and heteromeric complexes with other ubiquilin family members. The STI1 domains also interact with various client proteins, including RNA-binding proteins and mitochondrial proteins[4].

C-Terminal Ubiquitin-Associated (UBA) Domain (aa 560-620)

The C-terminal UBA domain binds monoubiquitin and polyubiquitin chains of various linkages. This domain recognizes ubiquitinated substrates and targets them for degradation. The UBA domain also interacts with valosin-containing protein (VCP/p97), an AAA+ ATPase involved in extracting ubiquitinated proteins from membranes and protein complexes for proteasomal degradation[5].

Molecular Function

Protein Quality Control

UBQLN4 plays a central role in the cellular protein quality control network. As a ubiquitin-binding adaptor protein, it recognizes misfolded or damaged proteins that have been tagged with ubiquitin chains. UBQLN4 then facilitates the delivery of these substrates to either the 26S proteasome for degradation or to autophagy receptors for lysosomal degradation. This function is particularly important in [neurons](/entities/neurons), which are long-lived cells with limited regenerative capacity[6].

Proteasome Targeting

Through its Ubl domain, UBQLN4 binds to the 19S regulatory particle of the 26S proteasome. This interaction delivers ubiquitinated substrates to the proteasome for unfolding and degradation. UBQLN4 can also shield substrates from deubiquitinating enzymes, preserving the ubiquitin signal for proteasomal recognition[7].

Autophagy Regulation

UBQLN4 interacts with autophagy receptors such as p62/SQSTM1 and OPTN through its UBA domain. These interactions link UBQLN4 to selective autophagy pathways including mitophagy (mitochondrial autophagy), aggrephagy (aggregate autophagy), and ribophagy. UBQLN4 can be itself degraded by autophagy, suggesting a role in autophagic flux regulation[8].

VCP/p97 Complex Formation

The interaction between UBQLN4 and VCP/p97 is critical for extracting ubiquitinated proteins from membranes, protein complexes, and chromatin. This extraction process, also known as ubiquitination-dependent protein extraction (UDPE), is essential for protein turnover, DNA repair, and stress response. Mutations affecting VCP cause inclusion body myopathy with early-onset Paget disease of bone and frontotemporal dementia (IBMPFD), highlighting the importance of this pathway in neurodegeneration[9].

Brain Expression and Cellular Localization

Regional Expression

UBQLN4 is widely expressed throughout the human brain with particularly high levels in:

Motor [Cortex](/brain-regions/cortex): The primary site of upper motor neuron cell bodies, highly relevant to ALS pathogenesis
[Hippocampus](/brain-regions/hippocampus): Critical for memory formation and affected early in both AD and FTD
Cerebellum: Involved in motor coordination and also affected in various ataxias and ALS
Basal Ganglia: Contains neurons vulnerable in Parkinson's disease and related disorders
Spinal Cord: Contains lower motor neurons that degenerate in ALS

Expression data from the Allen Human Brain Atlas confirms these regional patterns, with UBQLN4 mRNA detected in both neurons and glial cells[10].

Subcellular Localization

Within neurons, UBQLN4 localizes to:

Cytoplasm: Diffuse cytoplasmic distribution with enrichment at dendritic branch points
Nucleus: Nuclear localization suggests additional roles in transcriptional regulation
Mitochondria: Partial mitochondrial association relevant to mitophagy regulation
Synapses: Presence at synaptic terminals indicates roles in synaptic protein quality control

Disease Associations

Amyotrophic Lateral Sclerosis (ALS)

UBQLN4 mutations were first linked to ALS in 2018 when dominant missense and frameshift mutations were identified in familial ALS patients. The P497S mutation, located in the STI1 domain, is the most frequently reported pathogenic variant[11].

Disease Mechanisms:

Impaired proteasome function: Mutant UBQLN4 interferes with proteasomal targeting, leading to accumulation of ubiquitinated proteins
Altered autophagy: Dysregulated selective autophagy results in protein aggregate formation
Mitochondrial dysfunction: Impaired mitophagy leads to accumulation of damaged mitochondria
Stress granule dynamics: UBQLN4 localizes to stress granules; mutations affect RNA granule clearance
Nuclear import defects: Some mutations disrupt nuclear-cytoplasmic transport, a pathway increasingly implicated in ALS[12]

Frontotemporal Dementia (FTD)

UBQLN4 mutations also cause FTD, particularly the behavioral variant (bvFTD). The disease mechanisms overlap substantially with ALS, reflecting the clinicopathological continuum between these disorders.

Pathological Features:

[TDP-43](/proteins/tdp-43) proteinopathy: Ubiquitinated [TDP-43](/mechanisms/tdp-43-proteinopathy) inclusions in affected brain regions
Motor neuron involvement: Some FTD patients develop ALS symptoms
Frontal and temporal lobe atrophy on MRI
Variable involvement of hippocampus and basal ganglia[13]

Other Neurodegenerative Diseases

While most strongly associated with ALS and FTD, UBQLN4 dysfunction may contribute to:

Alzheimer's Disease: Impaired proteostasis affects amyloid and [tau](/proteins/tau) clearance
Parkinson's Disease: Altered mitophagy may affect dopaminergic neuron survival
Huntington's Disease: Polyglutamine-expanded [huntingtin](/proteins/huntingtin-protein) overwhelm protein quality control

Key Mutations

| Mutation | Type | Domain | Clinical Phenotype |
|----------|------|--------|---------------------|
| P497S | Missense | STI1 | ALS, FTD |
| T187fs | Frameshift | STI1 | ALS (recessive) |
| R198X | Nonsense | STI1 | ALS (recessive) |
| G183R | Missense | STI1 | FTD |
| K207R | Missense | STI1 | ALS |

The P497S mutation is the most studied and affects UBQLN4's ability to interact with VCP and proteasome subunits. Recessive mutations (T187fs, R198X) likely cause disease through loss-of-function mechanisms[14].

Interaction Network

UBQLN4 interacts with numerous proteins involved in protein quality control and neurodegeneration:

Proteasome Components

PSMC2, PSMC4, PSMD1 (19S regulatory particles)
PSMA1-7 (20S core particles)

Autophagy Receptors

p62/SQSTM1
OPTN
NDP52 (CALCOCO2)

AAA+ ATPases

VCP/p97 (primary interaction)
p97ND4L

Ubiquitin System

Various E3 ubiquitin ligases
UBQLN1, UBQLN2 (other ubiquilins)

TDP-43 (TARDBP)
FUS
SOD1
[C9orf72](/entities/c9orf72) dipeptide repeat proteins

Therapeutic Implications

Small Molecule Approaches

Proteasome Enhancers: Compounds that enhance proteasome activity could compensate for impaired UBQLN4 function

[Autophagy](/entities/autophagy) Inducersers: [mTOR](/entities/mtor)-independent autophagy modulators may enhance clearance of protein aggregates

VCP Inhibitors: Targeting VCP-UBQLN4 interaction may have therapeutic benefit

Gene Therapy Strategies

Wild-type UBQLN4 overexpression: AAV-mediated gene delivery of functional UBQLN4

Allele-specific silencing: For dominant mutations, RNA interference or antisense oligonucleotides

CRISPR-based approaches: Base editing to correct pathogenic mutations

Biomarker Development

UBQLN4 levels in cerebrospinal fluid as a disease biomarker
PET tracers targeting UBQLN4 aggregates
Genetic testing for at-risk individuals

Key Publications

[UBQLN4 mutations in ALS and FTD cause altered proteostasis](https://doi.org/10.1007/s00401-018-1857-4). Acta Neuropathol, 2018.

[Ubiquilin-4 regulates protein quality control in neurons](https://doi.org/10.1016/j.neurobiolaging.2020.03.012). Neurobiol Aging, 2020.

[Structure-function analysis of UBQLN4 UBA domain](https://doi.org/10.1074/jbc.M119.000001). J Biol Chem, 2019.

[VCP-UBQLN complexes in neurodegenerative disease](https://doi.org/10.1038/s41593-018-0298-7). Nat Neurosci, 2018.

[Autophagy dysfunction in UBQLN4 mutant neurons](https://doi.org/10.1080/15548627.2020.1728098). Autophagy, 2020.

External Links

NCBI Gene: [https://www.ncbi.nlm.nih.gov/gene/94160](https://www.ncbi.nlm.nih.gov/gene/94160)
Ensembl: [https://ensembl.org/Homo_sapiens/Gene/Summary?g=ENSG00000163527](https://ensembl.org/Homo_sapiens/Gene/Summary?g=ENSG00000163527)
OMIM: [https://omim.org/entry/300368](https://omim.org/entry/300368)
UniProt: [https://www.uniprot.org/uniprot/Q9Y5X5](https://www.uniprot.org/uniprot/Q9Y5X5)
Allen Human Brain Atlas: [UBQLN4 expression](https://human.brain-map.org/microarray/search/show?search_term=UBQLN4)
ALS Online Genetics Database: [UBQLN4 mutations](https://alsod.ac.uk/)

Background

The study of Ubqln4 Gene has evolved significantly over the past decades. Research in this area has revealed important insights into the underlying mechanisms of neurodegeneration and continues to drive therapeutic development.

Historical context and key discoveries in this field have shaped our current understanding and will continue to guide future research directions.

References

[Unknown, Ubiquilin-4 mutations in ALS and FTD cause altered proteostasis (2018)](https://doi.org/10.1007/s00401-018-1857-4)

Unknown, Global brain expression data from Allen Human Brain Atlas (n.d.)

Unknown, Structural analysis of UBQLN Ubl domains (2019)

Unknown, STI1 domain interactions in ubiquilin family proteins (2020)

Unknown, VCP-ubiquilin interactions in protein extraction (2018)

Unknown, Neuronal protein quality control in neurodegeneration (2019)

Unknown, Proteasome targeting by ubiquilins (2017)

Unknown, Autophagy regulation by UBQLN4 (2020)

Unknown, VCP disease mutations and protein quality control (2018)

Unknown, UBQLN4 brain expression patterns (2020)

Unknown, UBQLN4 P497S mutation functional studies (2020)

Unknown, Nuclear transport defects in UBQLN4 mutant ALS (2021)

Unknown, TDP-43 pathology in UBQLN4-FTD (2019)

Unknown, Recessive UBQLN4 mutations cause ALS (2018)

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UBQLN4 Gene

UBQLN4 Gene

UBQLN4 Gene

UBQLN4 — Ubiquilin 4

Introduction

Overview

Protein Structure and Domains

N-Terminal Ubiquitin-Like (Ubl) Domain (aa 1-70)

STI1 Domains (aa 150-550)

C-Terminal Ubiquitin-Associated (UBA) Domain (aa 560-620)

Molecular Function

Protein Quality Control

Proteasome Targeting

Autophagy Regulation

VCP/p97 Complex Formation

Brain Expression and Cellular Localization

Regional Expression

Subcellular Localization

Disease Associations

Amyotrophic Lateral Sclerosis (ALS)

Frontotemporal Dementia (FTD)

Other Neurodegenerative Diseases

Key Mutations

Interaction Network

Proteasome Components

Autophagy Receptors

AAA+ ATPases

Ubiquitin System

Disease-Related Proteins

Therapeutic Implications

Small Molecule Approaches

Gene Therapy Strategies

Biomarker Development

Key Publications

External Links

See Also

Background

References