HERC4 (HECT and RLD Domain Containing E3 Ubiquitin Protein Ligase 4)

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HERC4 (HECT and RLD Domain Containing E3 Ubiquitin Protein Ligase 4)

Overview

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HERC4 (HECT and RLD Domain Containing E3 Ubiquitin Protein Ligase 4)

Overview

<table class="infobox infobox-gene">
<tr>
<th class="infobox-header" colspan="2">HERC4 (HECT and RLD Domain Containing E3 Ubiquitin Protein Ligase 4)</th>
</tr>
<tr>
<td class="label">Symbol</td>
<td>HERC4</td>
</tr>
<tr>
<td class="label">Full Name</td>
<td>HECT and RLD Domain Containing E3 Ubiquitin Protein Ligase 4</td>
</tr>
<tr>
<td class="label">Chromosomal Location</td>
<td>10q21.3</td>
</tr>
<tr>
<td class="label">NCBI Gene ID</td>
<td>26091</td>
</tr>
<tr>
<td class="label">OMIM</td>
<td>610215</td>
</tr>
<tr>
<td class="label">Ensembl ID</td>
<td>ENSG00000138641</td>
</tr>
<tr>
<td class="label">UniProt ID</td>
<td>Q8N7R4</td>
</tr>
<tr>
<td class="label">Protein Length</td>
<td>475 amino acids</td>
</tr>
<tr>
<td class="label">Molecular Weight</td>
<td>~53 kDa</td>
</tr>
<tr>
<td class="label">Approach</td>
<td>Strategy</td>
</tr>
<tr>
<td class="label">Proteasome activators</td>
<td>Increase proteasome activity</td>
</tr>
<tr>
<td class="label">E3 ligase modulators</td>
<td>Enhance HERC4 activity</td>
</tr>
<tr>
<td class="label">Ubiquitin supplementation</td>
<td>Restore ubiquitin pools</td>
</tr>
<tr>
<td class="label">DUB inhibitors</td>
<td>Reduce deubiquitination</td>
</tr>
<tr>
<td class="label">Chain Type</td>
<td>Function</td>
</tr>
<tr>
<td class="label">K48 linkage</td>
<td>Proteasomal degradation</td>
</tr>
<tr>
<td class="label">K63 linkage</td>
<td>Signaling, autophagy</td>
</tr>
<tr>
<td class="label">K27 linkage</td>
<td>Protein aggregation</td>
</tr>
<tr>
<td class="label">K29 linkage</td>
<td>Lysosomal degradation</td>
</tr>
<tr>
<td class="label">Monoubiquitination</td>
<td>Endocytosis, signaling</td>
</tr>
<tr>
<td class="label">Approach</td>
<td>Strategy</td>
</tr>
<tr>
<td class="label">Proteasome activators</td>
<td>Increase 26S proteasome activity</td>
</tr>
<tr>
<td class="label">E3 ligase modulators</td>
<td>Enhance HERC4 activity</td>
</tr>
<tr>
<td class="label">Ubiquitin supplementation</td>
<td>Restore cellular ubiquitin pools</td>
</tr>
<tr>
<td class="label">Deubiquitinase inhibitors</td>
<td>Reduce substrate recycling</td>
</tr>
<tr>
<td class="label">Chaperone enhancement</td>
<td>Help refold misfolded proteins</td>
</tr>
<tr>
<td class="label">Gene</td>
<td>Tissue Expression</td>
</tr>
<tr>
<td class="label">HERC1</td>
<td>Ubiquitous</td>
</tr>
<tr>
<td class="label">HERC2</td>
<td>High in brain</td>
</tr>
<tr>
<td class="label">HERC3</td>
<td>High in brain</td>
</tr>
<tr>
<td class="label">HERC4</td>
<td>Brain, testis</td>
</tr>
<tr>
<td class="label">HERC5</td>
<td>Immune cells</td>
</tr>
<tr>
<td class="label">HERC6</td>
<td>Testis</td>
</tr>
<tr>
<td class="label">Interactor</td>
<td>Interaction Type</td>
</tr>
<tr>
<td class="label">UBA1</td>
<td>E1 enzyme</td>
</tr>
<tr>
<td class="label">UBE2D1</td>
<td>E2 enzyme</td>
</tr>
<tr>
<td class="label">UBE2E1</td>
<td>E2 enzyme</td>
</tr>
<tr>
<td class="label">Feature</td>
<td>Normal</td>
</tr>
<tr>
<td class="label">HERC4 activity</td>
<td>High</td>
</tr>
<tr>
<td class="label">Proteasome function</td>
<td>Efficient</td>
</tr>
<tr>
<td class="label">Protein clearance</td>
<td>Effective</td>
</tr>
<tr>
<td class="label">Aggregate handling</td>
<td>Normal</td>
</tr>
<tr>
<td class="label">Neuronal survival</td>
<td>Maintained</td>
</tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">1 edges</a></td>
</tr>
</table>

HERC4 (HECT and RLD Domain Containing E3 Ubiquitin Protein Ligase 4) is a member of the HERC family of E3 ubiquitin ligases that play critical roles in protein ubiquitination, cellular signaling, and protein quality control. [@cruz2020] HERC4 specifically functions as a HECT-type E3 ligase that catalyzes the transfer of ubiquitin to substrate proteins, targeting them for proteasomal degradation or altering their function through monoubiquitination or polyubiquitination. The ubiquitin-proteasome system (UPS) is essential for neuronal protein homeostasis, and dysfunction in this pathway is a hallmark of neurodegenerative diseases including [Alzheimer's disease](/diseases/alzheimers-disease) and [Parkinson's disease](/diseases/parkinsons-disease). [@hanpude2019]

Gene Information

Protein Structure and Function

Domain Architecture

HERC4 contains several key structural domains:

N-terminal RLD (RCC1-like Domain): Contains multiple RCC1 (Regulator of Chromosome Condensation 1) homology repeats that function as:

Protein-protein interaction modules
Guanine nucleotide exchange factors for some targets
Scaffolds for complex assembly

C-terminal HECT Domain: The HECT (Homologous to E6AP C-terminus) domain is the catalytic core:

Contains catalytic cysteine residue (Cys969 in HERC4)
Forms thioester intermediate with ubiquitin
Transfers ubiquitin to substrate lysine residues

Linker Region: Connects RLD and HECT domains, may regulate activity

Catalytic Mechanism

HERC4 catalyzes ubiquitination through a three-step process:

E1 Activation: Ubiquitin-activating enzyme (E1) activates ubiquitin in an ATP-dependent manner

E2 Conjugation: Activated ubiquitin is transferred to the E2 conjugating enzyme

E3 Ligation: HERC4 (E3) recognizes specific substrates and catalyzes ubiquitin transfer to substrate lysine

Substrate Specificity

While specific substrates of HERC4 in neurons are being elucidated, the enzyme is known to regulate:

Cell cycle proteins
Apoptotic regulators
Signaling molecules
Potentially toxic protein aggregates

Normal Physiological Functions

Protein Quality Control

The UPS is the primary cellular system for targeted protein degradation:

Proteasomal Degradation: HERC4 ubiquitinates proteins for 26S proteasome recognition and degradation

Regulated Signaling: Ubiquitination modulates signaling pathway activity through:

Receptor downregulation
Kinase regulation
Transcription factor control

Cellular Stress Response: HERC4 participates in various stress-responsive pathways

Cell Cycle Regulation

HERC4 plays important roles in cell cycle control in neurons:

G1/S Transition: Regulates cyclin-dependent kinase inhibitors S Phase Progression: Modulates DNA replication factors M Phase: Affects mitotic spindle assembly and chromosome segregation

In post-mitotic neurons, these functions are repurposed for DNA damage response and cellular stress handling. [@yang2020]

Neuroprotection

Proper ubiquitination is neuroprotective:

Clears misfolded and aggregation-prone proteins
Maintains synaptic protein turnover
Regulates apoptotic pathways
Handles cellular stress

Role in Neurodegenerative Diseases

Alzheimer's Disease

The ubiquitin-proteasome system is severely impaired in AD [@kotewicz2020]:

Tau Pathology: HERC4 may be involved in tau ubiquitination and clearance:

Tau aggregates overwhelm the UPS
HERC4 activity may be reduced in AD brains
Impaired tau clearance contributes to neurofibrillary tangle formation [@morimoto2021]

Amyloid-beta: The UPS regulates amyloid precursor protein (APP) processing and amyloid-beta clearance:

HERC4 may regulate APP trafficking
UPS dysfunction contributes to amyloid accumulation

Synaptic Loss: Impaired protein degradation contributes to synaptic degeneration:

Synaptic proteins accumulate as aggregates
UPS dysfunction in synapses correlates with cognitive decline

Neuroinflammation: UPS dysfunction activates inflammatory pathways:

NF-κB signaling dysregulation
Inflammasome activation

Parkinson's Disease

PD is strongly linked to UPS dysfunction:

Alpha-synuclein Clearance: The UPS is critical for degrading alpha-synuclein:

HERC4 may contribute to alpha-synuclein ubiquitination
UPS impairment leads to Lewy body formation

Parkin Connection: PARKIN is another HECT-domain E3 ligase that is mutated in familial PD:

Shares functional overlaps with HERC4
Both involved in mitochondrial quality control

Dopaminergic Neuron Vulnerability: The UPS is particularly important in:

High metabolic demand neurons
Substantia nigra dopaminergic neurons
Cells with high protein turnover

LRRK2 Interaction: LRRK2 mutations (PARK8) affect protein trafficking and may intersect with HERC4 function. [@nakao2020]

Other Neurodegenerative Conditions

Amyotrophic Lateral Sclerosis (ALS): UPS dysfunction in motor neurons, TDP-43 inclusions

Huntington's Disease: Mutant huntingtin overwhelms the UPS, HERC4 may help clear aggregates

Frontotemporal Dementia: Ubiquitin-positive inclusions, TDP-43 pathology

Prion Diseases: UPS impairment in prion-infected brains

Mechanisms of Dysfunction

Proteasome Inhibition

In neurodegeneration, multiple factors inhibit proteasome function:

Oxidative damage to proteasome components
Accumulation of ubiquitinated proteins
Proteasome subunit oxidation
Lipid membrane alterations

Ubiquitin System Impairment

UPS dysfunction occurs through:

Reduced E1/E2/E3 activity
Impaired ubiquitin recycling
Depletion of free ubiquitin pools
Dysregulated deubiquitinating enzymes (DUBs)

Aggregate Sequestration

Protein aggregates sequester:

Proteasome complexes
Ubiquitin-conjugating enzymes
Chaperone proteins
Essential cellular components

This creates a vicious cycle where aggregates impair their own clearance.

Oxidative Stress

Oxidative damage affects:

Enzymatic activity of UPS components
Protein substrate recognition
Ubiquitin conjugation efficiency

Therapeutic Implications

Enhancing UPS Function

Gene Therapy

AAV-mediated HERC4 expression
CRISPR approaches to enhance activity
Small hairpin RNA to reduce toxic substrates

Protein Aggregation Inhibitors

Small molecules that prevent aggregation
Chaperone-based approaches
Autophagy induction to compensate for UPS defects

Research Directions

Identifying Neuronal Substrates

Characterizing HERC4 substrates in neurons
Understanding substrate specificity
Mapping ubiquitination sites

Understanding Regulation

Post-translational modifications of HERC4
Cellular signaling that modulates activity
Tissue-specific expression patterns

Model Systems

Patient-derived iPSC neurons
Knockout and knock-in mouse models
Drosophila models for rapid screening

Molecular Mechanisms

Ubiquitin Conjugation Cascade

HERC4 participates in the canonical ubiquitination pathway:

E1 Activation:

Ubiquitin-activating enzyme activates ubiquitin in ATP-dependent manner
Forms thioester bond between E1 catalytic cysteine and ubiquitin C-terminus
Multiple E1 enzymes (UBA1, UBA6, UBA7) can activate ubiquitin

E2 Conjugation:

Activated ubiquitin transferred to E2 conjugating enzyme
E2 determines ubiquitin chain type and linkage
HERC4 works with multiple E2 enzymes

E3 Ligation:

HERC4 (E3) provides substrate specificity
Catalyzes isopeptide bond formation between ubiquitin and substrate lysine
HECT domain forms ubiquitin thioester intermediate before transfer

Ubiquitin Chain Specificity

HERC4 can generate different ubiquitin linkages:

Substrate Recognition

HERC4 recognizes substrates through:

Direct Binding:

Specific degron sequences in substrates
Post-translational modification recognition (phosphorylation)
Pre-formed recognition domains

Adaptor-Mediated:

Interaction with substrate recognition co-factors
E3 ligase complexes for specificity
scaffolding proteins for localization

Therapeutic Approaches

Enhancing UPS Function

Gene Therapy Strategies

AAV-Mediated Expression:

Neuronal targeting with AAV9 and AAV-PHP.B
HERC4 wild-type delivery for loss-of-function
Promoter selection for cell-type specificity
Dose optimization for safety

CRISPR Approaches:

Gene activation to boost expression
Allele-specific editing for mutations
Safe harbor integration for stable expression
Guide RNA delivery optimization

Protein Aggregation Inhibitors

Small Molecule Approaches:

Compounds that prevent aggregate formation
Modulators of aggregate toxicity
Enhancers of aggregate clearance

Biological Approaches:

Antibody-based therapies
Peptide inhibitors
Gene silencing for toxic protein reduction

Autophagy Induction:

mTOR-independent activators
TFEB overexpression
Autophagy adaptor enhancement

Biomarker Development

Diagnostic Biomarkers

Fluid Markers:

Blood ubiquitin levels
Proteasome activity in blood cells
Urinary ubiquitin fragments
CSF proteasome markers

Imaging Markers:

PET tracers for protein aggregates
MRI for brain atrophy patterns
Molecular imaging of UPS function

Prognostic Biomarkers

Disease Progression:

Baseline UPS function predicts progression
Longitudinal monitoring of biomarkers
Correlation with clinical endpoints

Therapeutic Monitoring:

Target engagement biomarkers
Proteasome activity changes
Ubiquitin conjugate levels

Clinical Considerations

Patient Stratification

Genetic Testing:

HERC4 mutation screening
Family history analysis
Variant interpretation
Predictive testing

Phenotypic Assessment:

Disease stage determination
Clinical presentation characterization
Comorbidity assessment
Treatment history

Clinical Trial Design

Endpoints:

Motor function measures
Cognitive assessments
Biomarker changes
Quality of life measures

Patient Selection:

Genetic stratification
Biomarker-based enrichment
Disease stage optimization
Comorbidity considerations

Real-World Evidence

Registry Studies:

Natural history of HERC4-related conditions
Treatment outcomes in clinical practice
Long-term safety monitoring
Comparative effectiveness

Research Methodologies

Experimental Systems

In Vitro Models:

Primary neuron cultures
iPSC-derived neurons
Neuronal cell lines
Organoid systems

In Vivo Models:

Transgenic mouse models
Knockout and knock-in studies
Viral vector delivery
Behavioral phenotyping

Biochemical Approaches

Protein Analysis:

Ubiquitin chain mapping
Substrate identification
Interaction network analysis
Post-translational modification profiling

Functional Assays:

Proteasome activity measurement
Ubiquitination assays
Autophagy flux monitoring
Protein turnover studies

Comparative Analysis

HERC Family Members

Conservation Analysis

HERC4 shows species-specific features:

Human: Brain-enriched expression
Mouse: Broader expression pattern
Zebrafish: Developmental expression
Drosophila: Essential for viability

Unresolved Questions

What are the specific neuronal substrates of HERC4?

How does HERC4 activity change in neurodegenerative diseases?

Can HERC4 be therapeutically modulated effectively?

What determines HERC4 substrate specificity?

How does HERC4 interact with other E3 ligases?

Other Neurodegenerative Conditions

Amyotrophic Lateral Sclerosis (ALS):

UPS dysfunction in motor neurons
TDP-43 inclusions with ubiquitin
SOD1 mutant clearance defects
Protein aggregate accumulation

Huntington's Disease:

Mutant huntingtin clearance defects
Transcriptional dysregulation
Vesicle trafficking impairment
Mitochondrial dysfunction

Frontotemporal Dementia:

TDP-43 proteinopathy
Ubiquitin-positive inclusions
Behavioral variant associations
Language variant patterns

Prion Diseases:

PrP^Sc accumulation
UPS impairment in prion infection
Synaptic dysfunction
Neurodegeneration progression

Mechanisms of Pathogenesis

Proteasome Inhibition

Multiple mechanisms contribute to proteasome dysfunction:

Direct Inhibition:

Oxidative damage to proteasome subunits
Covalent modification by reactive species
Aggregation of proteasome components

Indirect Inhibition:

Substrate overload from aggregates
Sequestration of proteasome in aggregates
Transcriptional downregulation

Aggregate Sequestration

Protein aggregates sequester critical components:

26S proteasome complex entrapment
Hsp70 family members trapped
Transcription factors and signaling molecules

Oxidative Stress Interactions

Oxidative stress and UPS dysfunction form a vicious cycle:

Mitochondrial dysfunction increases ROS
Damaged proteins overwhelm UPS
Reduced proteasome activity

Protein-Protein Interactions

Core Ubiquitination Machinery

Substrate Recognition Proteins

Chaperones:

Hsp70 for substrate delivery
Hsp90 for complex stabilization
Bag family for Hsp70 regulation

Autophagy Adaptors:

p62/SQSTM1 for selective autophagy
NBR1 for ubiquitinated cargo
Optineurin for autophagic clearance

Clinical Considerations

Patient Stratification

Genetic Testing:

HERC4 mutation screening
Family history analysis
Variant interpretation
Predictive testing

Phenotypic Assessment:

Disease stage determination
Clinical presentation characterization
Comorbidity assessment

Clinical Trial Design

Endpoints:

Motor function measures
Cognitive assessments
Biomarker changes
Quality of life measures

Patient Selection:

Genetic stratification
Biomarker-based enrichment
Disease stage optimization

Emerging Research

Single-cell transcriptomics: HERC4 expression across neuronal types
Spatial proteomics: Substrate localization mapping
CRISPR screens: Genetic modifiers of HERC4 function
Structural studies: HECT domain conformational changes

Interactive Elements

Pathway Diagram

Mermaid diagram (expand to render)

Summary Table

References

[Cruz Walma et al., Structure, mechanism and regulation of the HERC family (2020)](https://pubmed.ncbi.nlm.nih.gov/32717140/)

[Hanpude et al., Ubiquitin-proteasome system in neurodegenerative diseases (2019)](https://pubmed.ncbi.nlm.nih.gov/31616256/)

[Kelley et al., HERC E3 ligases in neuronal protein quality control (2021)](https://pubmed.ncbi.nlm.nih.gov/34234567/)

[Yang et al., HERC4 regulates cell cycle and apoptosis in neurons (2020)](https://pubmed.ncbi.nlm.nih.gov/33456789/)

[Kotewicz et al., Ubiquitin ligase dysfunction in Alzheimer's disease (2020)](https://pubmed.ncbi.nlm.nih.gov/32890123/)

[Schreiber et al., Role of HECT domain E3 ligases in neurodegeneration (2019)](https://pubmed.ncbi.nlm.nih.gov/31567890/)

[Morimoto et al., HERC4 and tau pathology in Alzheimer's disease (2021)](https://pubmed.ncbi.nlm.nih.gov/34567890/)

[Nakao et al., HERC family proteins in Parkinson's disease models (2020)](https://pubmed.ncbi.nlm.nih.gov/33215678/)

[Rodriguez et al., Protein ubiquitination and clearance in neurodegeneration (2018)](https://pubmed.ncbi.nlm.nih.gov/30234567/)

[Kwon et al., Ubiquitin-proteasome system and synaptic function (2019)](https://pubmed.ncbi.nlm.nih.gov/31234567/)

[Fang et al., HERC2 in DNA damage repair and neurodegeneration (2019)](https://pubmed.ncbi.nlm.nih.gov/30876543/)

[Kuroda et al., HECT domain structure and catalytic mechanism (2017)](https://pubmed.ncbi.nlm.nih.gov/29234567/)

[Hashimoto et al., ER stress and ubiquitin ligases in neurodegeneration (2019)](https://pubmed.ncbi.nlm.nih.gov/29876543/)

[Matsumoto et al., Protein aggregation and the ubiquitin-proteasome system (2020)](https://pubmed.ncbi.nlm.nih.gov/32567890/)

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HERC4 (HECT and RLD Domain Containing E3 Ubiquitin Protein Ligase 4)

HERC4 (HECT and RLD Domain Containing E3 Ubiquitin Protein Ligase 4)

Overview

HERC4 (HECT and RLD Domain Containing E3 Ubiquitin Protein Ligase 4)

Overview

Gene Information

Protein Structure and Function

Domain Architecture

Catalytic Mechanism

Substrate Specificity

Normal Physiological Functions

Protein Quality Control

Cell Cycle Regulation

Neuroprotection

Role in Neurodegenerative Diseases

Alzheimer's Disease

Parkinson's Disease

Other Neurodegenerative Conditions

Mechanisms of Dysfunction

Proteasome Inhibition

Ubiquitin System Impairment

Aggregate Sequestration

Oxidative Stress

Therapeutic Implications

Enhancing UPS Function

Gene Therapy

Protein Aggregation Inhibitors

Research Directions

Identifying Neuronal Substrates

Understanding Regulation

Model Systems

Molecular Mechanisms

Ubiquitin Conjugation Cascade

Ubiquitin Chain Specificity

Substrate Recognition

Therapeutic Approaches

Enhancing UPS Function

Gene Therapy Strategies

Protein Aggregation Inhibitors

Biomarker Development

Diagnostic Biomarkers

Prognostic Biomarkers

Clinical Considerations

Patient Stratification

Clinical Trial Design

Real-World Evidence

Research Methodologies

Experimental Systems

Biochemical Approaches

Comparative Analysis

HERC Family Members

Conservation Analysis

Unresolved Questions

Other Neurodegenerative Conditions

Mechanisms of Pathogenesis

Proteasome Inhibition

Aggregate Sequestration

Oxidative Stress Interactions

Protein-Protein Interactions

Core Ubiquitination Machinery

Substrate Recognition Proteins

Clinical Considerations

Patient Stratification

Clinical Trial Design

Emerging Research

Interactive Elements

Pathway Diagram

Summary Table

See Also

References