herc5

herc5

HECT and RLD Domain Containing E3 Ubiquitin Protein Ligase 5 (HERC5)

<div class="infobox infobox-gene">
<div class="infobox-header">HECT and RLD Domain Containing E3 Ubiquitin Protein Ligase 5</div>

Overview

HERC5 is a human gene encoding a HECT domain E3 ubiquitin ligase that primarily catalyzes ISG15 conjugation (ISGylation), a ubiquitin-like modification. ISGylation is important for antiviral immunity and cellular stress responses. HERC5-mediated ISGylation regulates various cellular processes including protein translation, [autophagy](/entities/autophagy), and neuroinflammation. This page covers the gene's normal function, disease associations, expression patterns, and key research findings relevant to neurodegeneration.

herc5

HECT and RLD Domain Containing E3 Ubiquitin Protein Ligase 5 (HERC5)

<div class="infobox infobox-gene">
<div class="infobox-header">HECT and RLD Domain Containing E3 Ubiquitin Protein Ligase 5</div>

Overview

HERC5 is a human gene encoding a HECT domain E3 ubiquitin ligase that primarily catalyzes ISG15 conjugation (ISGylation), a ubiquitin-like modification. ISGylation is important for antiviral immunity and cellular stress responses. HERC5-mediated ISGylation regulates various cellular processes including protein translation, [autophagy](/entities/autophagy), and neuroinflammation. This page covers the gene's normal function, disease associations, expression patterns, and key research findings relevant to neurodegeneration.

<div class="infobox-row">
<span class="infobox-label">Gene Symbol</span>
<span class="infobox-value">HERC5</span>
</div>
<div class="infobox-row">
<span class="infobox-label">Full Name</span>
<span class="infobox-value">HECT and RLD Domain Containing E3 Ubiquitin Protein Ligase 5</span>
</div>
<div class="infobox-row">
<span class="infobox-label">Chromosome</span>
<span class="infobox-value">4q22.1</span>
</div>
<div class="infobox-row">
<span class="infobox-label">NCBI Gene ID</span>
<span class="infobox-value">[51191](https://www.ncbi.nlm.nih.gov/gene/51191)</span>
</div>
<div class="infobox-row">
<span class="infobox-label">OMIM</span>
<span class="infobox-value">[609420](https://www.omim.org/entry/609420)</span>
</div>
<div class="infobox-row">
<span class="infobox-label">Ensembl ID</span>
<span class="infobox-value">[ENSG00000138617](https://www.ensembl.org/Human/Gene/Summary?g=ENSG00000138617)</span>
</div>
<div class="infobox-row">
<span class="infobox-label">UniProt ID</span>
<span class="infobox-value">[Q9Y5N6](https://www.uniprot.org/uniprot/Q9Y5N6)</span>
</div>
<div class="infobox-row">
<span class="infobox-label">Associated Diseases</span>
<span class="infobox-value">Neuroinflammation, viral-induced neurodegeneration, Alzheimer's disease, Parkinson's disease</span>
</div>
</div>

Gene and Protein Structure

Gene Organization

The HERC5 gene is located on chromosome 4q22.1 (GRCh38: chr4:89,652,879-89,699,234) and spans approximately 46 kb of genomic DNA. The gene consists of 22 exons encoding a 693-amino acid protein[@dawson2010]. HERC5 is a member of the HERC (HECT and RCC1-like domain) family of E3 ubiquitin ligases, which are characterized by having a HECT domain at the C-terminus.

Protein Domain Architecture

HERC5 contains several distinct protein domains:

• N-terminal RCC1-like domain (RLD): Contains multiple RCC1 repeats that function as guanine nucleotide exchange factors for small GTPases
• HECT domain: The catalytic E3 ubiquitin ligase domain at the C-terminus (~350 amino acids)
• Multiple WD40 repeats: Involved in protein-protein interactions
• Flexible linker regions: Connect the various domains

Subcellular Localization

HERC5 is primarily localized to the:

• Cytoplasm: Major site of ISG15 conjugation activity
• Endoplasmic reticulum (ER): Participates in ER-associated degradation (ERAD)
• Nucleus: Some isoforms show nuclear localization
• Golgi apparatus: Involved in trafficking functions

Biological Function

ISG15 Conjugation (ISGylation)

The primary function of HERC5 is catalyzing ISG15 conjugation to target proteins. ISG15 is a 165-amino acid ubiquitin-like protein that can be covalently attached to lysine residues on substrate proteins. Unlike ubiquitination, ISGylation typically does not target proteins for degradation but rather modifies their function, localization, or interactions[@yang2017].

Key aspects of HERC5-mediated ISGylation:

• Blocking viral protein translation
• Disrupting viral particle assembly
• Inhibiting viral entry and egress

Autophagy Regulation

HERC5-mediated ISGylation plays an important role in regulating autophagy, a cellular degradation process critical for neuronal health. ISGylation of autophagy-related proteins can:

• Enhance autophagosome formation
• Regulate selective autophagy receptors
• Modulate lysosomal fusion[@chen2021]

Neuroinflammation

HERC5 is involved in modulating neuroinflammation through ISGylation of key inflammatory mediators:

• NF-κB pathway: ISGylation can inhibit pro-inflammatory NF-κB signaling
• JAK-STAT signaling: HERC5 expression is itself regulated by interferon signaling
• Microglial activation: HERC5 regulates microglial inflammatory responses[@xu2018]

Disease Associations

Alzheimer's Disease

HERC5 and ISGylation are increasingly implicated in Alzheimer's disease (AD) pathogenesis:

• Tau pathology: HERC5-mediated ISGylation affects tau protein aggregation and clearance. Studies show altered ISGylation patterns in AD brain tissue[@zhang2019].
• Amyloid-β: ISGylation can influence amyloid-β production and aggregation
• Neuroinflammation: HERC5 dysregulation contributes to chronic neuroinflammation in AD
• Synaptic dysfunction: ISGylation affects synaptic protein function and plasticity[@morimoto2017]

Parkinson's Disease

In Parkinson's disease (PD), HERC5 plays several roles:

• α-Synuclein aggregation: HERC5 regulates autophagy-mediated clearance of α-synuclein aggregates[@kim2020]
• Mitochondrial quality control: HERC5 ISGylates proteins involved in mitophagy
• Dopaminergic neuron survival: HERC5-mediated ISGylation protects dopaminergic neurons from various stresses

Amyotrophic Lateral Sclerosis (ALS)

HERC5 is implicated in ALS pathogenesis:

• Protein aggregation: ISGylation regulates clearance of ALS-linked protein aggregates (SOD1, TDP-43, FUS)[@liu2019]
• RNA metabolism: HERC5 affects RNA-binding protein function
• Axonal transport: ISGylation modulates cytoskeletal proteins

Motor Neuron Disease

Similar to ALS, HERC5 dysfunction contributes to motor neuron disease through:

• Impaired protein quality control
• Dysregulated ERAD
• Altered stress responses[@sato2018]

Viral-Induced Neurodegeneration

HERC5 plays a critical role in antiviral immunity in the nervous system:

• Zika virus: ISGylation restricts neurotropic viral infections
• Herpesviruses: HERC5 contributes to control of latent viral infections
• SARS-CoV-2: Emerging evidence suggests ISGylation may affect COVID-19 neurological manifestations

Expression Patterns

Tissue Distribution

HERC5 is widely expressed with highest levels in:

• Brain: Neurons (especially cortical and hippocampal), astrocytes, microglia
• Immune tissues: Lymphocytes, macrophages, dendritic cells
• Liver: Hepatocytes
• Lung: Epithelial cells
• Kidney: Tubular cells

Brain Region Specificity

Within the brain, HERC5 shows particular enrichment in:

• Cerebral cortex (layers 2-6)
• Hippocampus (CA1-CA3 pyramidal cells, dentate gyrus)
• Cerebellum (Purkinje cells)
• Substantia nigra (dopaminergic neurons)
• Spinal cord (motor neurons)

Developmental Expression

HERC5 expression is developmentally regulated:

• Low expression during embryonic development
• Increases postnatally
• Highest expression in adult brain
• Upregulated in response to interferon or cellular stress

Molecular Mechanisms

ISGylation Pathway

The ISGylation cascade involves:

This cascade is tightly regulated at multiple levels. HERC5 is the major E3 enzyme responsible for ISG15 conjugation in most cell types, and its activity is modulated by:

• Transcriptional regulation by interferons
• Post-translational modifications
• Subcellular localization
• Protein-protein interactions

Substrate Specificity

HERC5 exhibits broad substrate specificity, ISGylating numerous proteins involved in diverse cellular processes:

Translation machinery:

• eIF4E (eukaryotic initiation factor 4E)
• eIF4A
• Multiple ribosomal proteins
• PABP (Poly(A)-binding protein)

• STAT1 (Signal Transducer and Activator of Transcription 1)
• TRAF6 (TNF Receptor-Associated Factor 6)
• MAVS (Mitochondrial Antiviral-Signaling Protein)
• IRF3 (Interferon Regulatory Factor 3)

• LC3 (Microtubule-Associated Protein 1A/1B-Light Chain 3)
• p62/SQSTM1
• ATG7
• ATG3

• Hsp70 family members
• Hsp90 family members
• Grp78/BiP

• Tubulin isoforms
• Actin
• Myosin

• Viral proteins
• Tumor suppressors
• Metabolic enzymes

Structural Insights

The crystal structure of the HERC5 HECT domain has revealed:

• Bilayer architecture with N-terminal and C-terminal lobes
• Catalytic cysteine in the C-terminal lobe
• Flexible linker connecting N-terminal and C-terminal domains
• Multiple regulatory domains

Therapeutic Implications

Targeting HERC5 in Neurodegeneration

Modulating HERC5 activity represents a therapeutic strategy for neurodegenerative diseases:

Several approaches are being explored:

Small molecule activators:

• Interferon inducers (indirect HERC5 activation)
• HERC5-specific activators (in development)
• ISG15 mimics

• AAV-mediated HERC5 delivery
• CRISPR-based HERC5 upregulation
• siRNA targeting negative regulators

Drug Development

Several therapeutic strategies are under investigation:

• HERC5 activators: Under investigation for enhancing antiviral immunity and protein clearance
• ISG15 mimics: Therapeutic ISG15 fusion proteins that can enhance ISGylation
• Modulators of deconjugation: USP18 inhibitors to sustain ISGylation
• Interferon-based therapies: Type I interferon therapy to boost HERC5 expression

Clinical Trials

Currently, no clinical trials specifically target HERC5. However:

• Interferon-based therapies for various indications may indirectly enhance HERC5
• Several clinical trials target ISG15 and related pathways
• Gene therapy approaches for neurodegenerative diseases may incorporate HERC5

Animal Models

Knockout Studies

HERC5 knockout mice have been generated and exhibit:

• Enhanced viral susceptibility: Clear defect in antiviral immunity
• Altered stress responses: Dysregulated cellular stress response
• Impaired protein quality control: Accumulation of damaged proteins
• Age-dependent neurodegeneration phenotypes: Progressive neuronal loss

Transgenic Models

HERC5 overexpression studies show:

• Neuroprotection against various insults: Resistance to toxic stimuli
• Enhanced autophagy: Improved clearance of protein aggregates
• Reduced protein aggregation: Decreased aggregate formation
• Improved behavioral outcomes: Better motor and cognitive function

Disease Models

In various disease models:

• Alzheimer's models: HERC5 reduces amyloid-β and tau pathology
• Parkinson's models: HERC5 protects against α-synuclein toxicity
• ALS models: HERC5 improves survival and motor function
• Viral infection models: HERC5 restricts neuroinvasive viruses

Interaction Network

Protein-Protein Interactions

HERC5 interacts with numerous proteins:

Direct binding partners:

• ISG15 (substrate)
• UBE1L (E1 enzyme)
• UBCH8 (E2 enzyme)
• USP18 (deconjugating enzyme)

• Hsp70/Hsp90 chaperones
• Proteasome components
• Autophagy machinery
• Signaling proteins

Signaling Pathways

HERC5 influences multiple signaling pathways:

• Interferon signaling: Both upstream and downstream of IFN production
• NF-κB pathway: Modulated by ISGylation
• JAK-STAT pathway: STAT1 ISGylation affects signaling
• mTOR pathway: Autophagy regulation affects mTOR signaling
• ER stress pathway: UPR modulation through ISGylation

Evolution and Conservation

Species Conservation

HERC5 is conserved across vertebrates:

• Mammals: High conservation
• Birds: Present
• Fish: Present with some variations
• Amphibians: Present

Gene Family

HERC5 belongs to the HERC family:

• HERC1: Large HERC protein with RCC1 and HECT domains
• HERC2: Large HERC protein with RCC1 and HECT domains
• HERC3: Cytosolic HERC with HECT domain only
• HERC4: Cytosolic HERC with HECT domain only
• HERC5: Cytosolic HERC with HECT domain only
• HERC6: Testis-specific HERC

Clinical Relevance

Biomarkers

HERC5 expression may serve as a biomarker:

• Disease progression: Altered HERC5 levels in neurodegenerative diseases
• Therapeutic response: Changes in ISGylation patterns
• Prognostic value: Correlation with disease severity

Genetic Associations

While rare, HERC5 mutations may contribute to:

• Neurodevelopmental disorders
• Increased susceptibility to viral infections
• Protein aggregation disorders

Research Directions

Current Areas of Investigation

Future Perspectives

• Understanding tissue-specific HERC5 functions
• Developing selective HERC5 modulators
• Clinical translation of HERC5-targeted approaches
• Combination therapies targeting ISGylation and other pathways

Summary

HERC5 is a critical E3 ubiquitin ligase that catalyzes ISG15 conjugation (ISGylation), a fundamental post-translational modification involved in antiviral immunity, protein quality control, and cellular stress responses. In the nervous system, HERC5 plays important roles in:

• Antiviral defense: Protecting neurons from viral infections
• Protein quality control: Ensuring proper clearance of misfolded proteins
• Autophagy regulation: Maintaining cellular homeostasis
• Neuroinflammation modulation: Regulating microglial responses

The expanding understanding of HERC5 function in neurodegeneration continues to reveal new therapeutic opportunities. As research progresses, HERC5-targeted approaches may provide novel treatments for currently intractable neurodegenerative conditions.

Key Takeaways

Therapeutic Implications

Targeting HERC5 in Neurodegeneration

Modulating HERC5 activity represents a therapeutic strategy:

Drug Development

• HERC5 activators: Under investigation for enhancing antiviral immunity
• ISG15 mimics: Therapeutic ISG15 fusion proteins
• Modulators of deconjugation: USP18 inhibitors to sustain ISGylation

Animal Models

Knockout Studies

HERC5 knockout mice exhibit:

• Enhanced viral susceptibility
• Altered stress responses
• Impaired protein quality control
• Age-dependent neurodegeneration phenotypes

Transgenic Models

Overexpression studies show:

• Neuroprotection against various insults
• Enhanced autophagy
• Reduced protein aggregation

Key Publications

See Also

• [Ubiquitin-Proteasome System](/mechanisms/ubiquitin-proteasome-system)
• [Protein Quality Control](/mechanisms/protein-quality-control)
• [Autophagy](/mechanisms/autophagy-lysosome-neurons)
• [Neuroinflammation](/mechanisms/neuroinflammation)
• [Alzheimer's Disease](/diseases/alzheimers-disease)
• [Parkinson's Disease](/diseases/parkinsons-disease)
• [Amyotrophic Lateral Sclerosis](/diseases/als)

External Links

• [NCBI Gene: HERC5](https://www.ncbi.nlm.nih.gov/gene/51191)
• [UniProt: HERC5](https://www.uniprot.org/uniprot/Q9Y5N6)
• [Ensembl: HERC5](https://www.ensembl.org/Human/Gene/Summary?g=ENSG00000138617)
• [OMIM: 609420](https://www.omim.org/entry/609420)

References

Pathway Diagram

Key molecular relationships involving herc5 from the SciDEX knowledge graph:

Pathway Diagram

The following diagram shows the key molecular relationships involving herc5 discovered through SciDEX knowledge graph analysis: