VCP (Valosin-Containing Protein)

VCP (Valosin-Containing Protein)

Introduction

<table class="infobox infobox-protein">
<tr>
<th class="infobox-header" colspan="2">VCP (Valosin-Containing Protein)</th>
</tr>
<tr>
<td class="label">Cofactor</td>
<td>Function</td>
</tr>
<tr>
<td class="label">UFD1-NPL4</td>
<td>Substrate recognition</td>
</tr>
<tr>
<td class="label">p47</td>
<td>Membrane fusion</td>
</tr>
<tr>
<td class="label">UBXD1/UBXD8</td>
<td>Ubiquitin chain binding</td>
</tr>
<tr>
<td class="label">Ataxin-3</td>
<td>Deubiquitination</td>
</tr>
<tr>
<td class="label">p37</td>
<td>Membrane trafficking</td>
</tr>
<tr>
<td class="label">Mutation</td>
<td>Location</td>
</tr>
<tr>
<td class="label">R155H/C</td>
<td>N-domain</td>
</tr>
<tr>
<td class="label">R191Q</td>
<td>N-domain</td>
</tr>
<tr>
<td class="label">A232E</td>
<td>N-domain</td>
</tr>
<tr>
<td class="label">G97E</td>
<td>N-domain</td>
</tr>
<tr>
<td class="label">P137L</td>
<td>N-domain</td>
</tr>
<tr>
<td class="label">Associated Diseases</td>
<td><a href="/wiki/als" style="color:#ef9a9a">Als</a>, <a href="/wiki/alzheimer" style="color:#ef9a9a">Alzheimer</a>, <a href="/wiki/amyotrophic-lateral-sclerosis" style="color:#ef9a9a">Amyotrophic Lateral Sclerosis</a>, <a href="/wiki/dementia" style="color:#ef9a9a">Dementia</a>, <a href="/wiki/frontotemporal-dementia" style="color:#ef9a9a">Frontotemporal Dementia</a></td>
</tr>
<tr>
<td class="label">KG Connections</td>
<td><

VCP (Valosin-Containing Protein)

Introduction

<table class="infobox infobox-protein">
<tr>
<th class="infobox-header" colspan="2">VCP (Valosin-Containing Protein)</th>
</tr>
<tr>
<td class="label">Cofactor</td>
<td>Function</td>
</tr>
<tr>
<td class="label">UFD1-NPL4</td>
<td>Substrate recognition</td>
</tr>
<tr>
<td class="label">p47</td>
<td>Membrane fusion</td>
</tr>
<tr>
<td class="label">UBXD1/UBXD8</td>
<td>Ubiquitin chain binding</td>
</tr>
<tr>
<td class="label">Ataxin-3</td>
<td>Deubiquitination</td>
</tr>
<tr>
<td class="label">p37</td>
<td>Membrane trafficking</td>
</tr>
<tr>
<td class="label">Mutation</td>
<td>Location</td>
</tr>
<tr>
<td class="label">R155H/C</td>
<td>N-domain</td>
</tr>
<tr>
<td class="label">R191Q</td>
<td>N-domain</td>
</tr>
<tr>
<td class="label">A232E</td>
<td>N-domain</td>
</tr>
<tr>
<td class="label">G97E</td>
<td>N-domain</td>
</tr>
<tr>
<td class="label">P137L</td>
<td>N-domain</td>
</tr>
<tr>
<td class="label">Associated Diseases</td>
<td><a href="/wiki/als" style="color:#ef9a9a">Als</a>, <a href="/wiki/alzheimer" style="color:#ef9a9a">Alzheimer</a>, <a href="/wiki/amyotrophic-lateral-sclerosis" style="color:#ef9a9a">Amyotrophic Lateral Sclerosis</a>, <a href="/wiki/dementia" style="color:#ef9a9a">Dementia</a>, <a href="/wiki/frontotemporal-dementia" style="color:#ef9a9a">Frontotemporal Dementia</a></td>
</tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">153 edges</a></td>
</tr>
</table>

Valosin-Containing Protein (VCP), also known as p97 in mammals or CDC48 in yeast, is a highly conserved AAA+ (ATPase Associated with various cellular Activities) adenosine triphosphatase that plays central roles in protein quality control, ER-associated degradation (ERAD), autophagy, chromatin dynamics, and DNA repair. VCP forms a hexameric ring complex that uses ATP hydrolysis to extract ubiquitinated substrates from membranes or protein complexes, making it essential for cellular homeostasis[@zhao2020].

Pathogenic mutations in the VCP gene cause a multisystem disorder termed inclusion body myopathy with early-onset Paget disease of bone (PDB) and frontotemporal dementia (IBMPFD), now more broadly termed VCP disease. This condition is characterized by progressive muscle weakness (inclusion body myopathy), bone deformities (Paget disease), and progressive dementia (FTD). Additionally, VCP mutations are found in approximately 1-2% of familial amyotrophic lateral sclerosis (ALS) cases and are implicated in the pathogenesis of sporadic ALS and FTD[@ji2021].

Molecular Structure and Mechanism

Domain Architecture

VCP is a 97 kDa protein composed of an N-terminal (N) domain followed by two ATPase domains (D1 and D2) and a C-terminal (C) domain:

• N-terminal domain (1-200 aa): Contains the N/D1 linker and mediates cofactor binding. The N-domain itself adopts a double-psi beta barrel fold that interacts with various cofactors including UFD1-NPL4, p47, and UBXD proteins.
• D1 ATPase domain (200-400 aa): The first ATPase domain responsible for hexamer assembly. This domain forms the core of the ring structure and contributes to ATP-dependent conformational changes.
• D2 ATPase domain (400-760 aa): The major ATPase activity resides here, responsible for the bulk of mechanical work performed by VCP. The D2 domain undergoes dramatic conformational changes during the ATP hydrolysis cycle.
• C-terminal domain (760-806 aa): Provides regulatory functions and serves as a binding platform for additional interactors.

Hexameric Assembly

VCP assembles as a homo-hexamer, forming a barrel-like structure with central pore. Each monomer contributes to the overall complex, and the six ATPase sites coordinate their activities. This architecture allows VCP to translocate substrates through its central channel, using the energy from ATP hydrolysis to "pull" or "extract" proteins from complexes or membranes.

Conformational Cycle

VCP undergoes dramatic ATP-dependent conformational changes:

This cycle can be repeated multiple times, allowing VCP to process numerous substrates.

Cofactor Interactions

VCP recruits specific cofactors that determine its substrate specificity and cellular function:

The pathogenic mutations in VCP predominantly affect cofactor binding, particularly to UFD1-NPL4, disrupting the protein's normal function in substrate extraction.

Normal Cellular Functions

Protein Quality Control

VCP is central to cellular protein quality control systems:

ER-Associated Degradation (ERAD): VCP, in complex with UFD1-NPL4, extracts misfolded proteins from the endoplasmic reticulum lumen or membrane for delivery to the proteasome. This process is essential for maintaining ER homeostasis and preventing accumulation of toxic protein aggregates[@zhao2020].

Ubiquitin-Proteasome System: VCP delivers polyubiquitinated substrates to the 26S proteasome, functioning as a "segregase" that separates substrates from their binding partners before proteasomal degradation.

Mitochondrial Quality Control: VCP participates in mitochondrial protein turnover, extracting damaged proteins from the mitochondrial outer membrane for degradation.

Autophagy Regulation

VCP plays multiple roles in autophagy:

Autophagosome Maturation: VCP is required for autophagosome-lysosome fusion. Loss of VCP function leads to accumulation of immature autophagic vacuoles.

Selective Autophagy: VCP participates in selective autophagy pathways, including the clearance of protein aggregates (aggrephagy) and damaged organelles (mitophagy, ribophagy).

Stress Granule Dynamics: VCP regulates stress granule assembly and disassembly. Mutations in VCP cause abnormal stress granule persistence, leading to toxic RNA granule accumulation[@buchan2013].

DNA Repair and Genome Stability

VCP participates in several DNA repair pathways[@kopp2019]:

• Nucleotide Excision Repair (NER): VCP verifies DNA damage and helps remove damaged oligonucleotides
• Homologous Recombination: Facilitates fork regression and repair of double-strand breaks
• Chromatin Remodeling: Regulates histone dynamics and chromatin assembly

Membrane Dynamics

• Nuclear Envelope Reassembly: Essential for proper nuclear envelope reformation after mitosis
• Golgi Apparatus Reconstruction: Required for Golgi stack reformation after fragmentation
• Endosomal Sorting: Coordinates trafficking through the endosomal system

VCP Disease: Clinical and Molecular Features

Disease Spectrum

VCP mutations cause a spectrum of disorders:

Pathogenic Mutations

Over 50 pathogenic VCP mutations have been identified, predominantly in the N-domain:

These mutations cause disease through a combination of:

• Loss of function: Impaired protein quality control
• Gain of toxic function: Altered substrate specificity
• Aggregation: Formation of VCP-positive inclusions

Pathogenesis Mechanisms

TDP-43 Pathology

A hallmark of VCP disease is TDP-43 proteinopathy. Pathological TDP-43 inclusions are found in:

• Muscle fibers (rimmed vacuoles)
• Neurons of frontal cortex and hippocampus
• Motor neurons (in ALS cases)
• Astrocytes and oligodendrocytes

Phenotype-Genotype Correlations

Different mutations show variable penetrance and phenotype expression:

• R155H: High penetrance for myopathy, variable FTD/ALS
• A232E: Severe early-onset disease with prominent ALS features
• R191Q: Myopathy predominant, later-onset cognitive changes

Therapeutic Approaches

Small Molecule Strategies

VCP Inhibitors: Specific inhibitors that reduce toxic gain-of-function are being developed. However, complete inhibition is toxic, necessitating careful dosing[@davidson2020].

Autophagy Enhancers: Compounds that compensate for impaired autophagic clearance:

• Rapamycin (mTOR inhibitor)
• Trehalose (autophagy inducer)

Protein Aggregation Inhibitors: Agents that prevent TDP-43 and other protein aggregation.

Gene-Based Therapies

Antisense Oligonucleotides (ASOs): Targeting mutant VCP transcripts for degradation. ASOs can selectively reduce mutant protein while preserving wild-type expression.

Gene Replacement: AAV-delivered wild-type VCP. Currently in preclinical development.

CRISPR Editing: Potential for directly correcting pathogenic mutations. Challenges include delivery to muscle and CNS.

Biomarkers

• Neurofilament light chain (NfL): Blood and CSF marker of neuroaxonal injury
• Creatine kinase (CK): Elevated in myopathy
• Bone-specific alkaline phosphatase: Marker of Paget disease activity

Clinical Management

Multidisciplinary care includes:

• Physical therapy for myopathy
• Bisphosphonates for Paget disease
• Symptomatic treatment for FTD/ALS
• Genetic counseling for families

Research Directions

Unanswered Questions

Model Systems

• Yeast: Cdc48 mutants reveal conserved mechanisms
• Drosophila: VCP models show neurodegeneration
• Mouse: Transgenic and knock-in models recapitulate disease
• Induced neurons: Patient-derived iPSCs differentiate into neurons and muscle

Clinical Trials

Currently no approved disease-modifying therapies for VCP disease. Clinical trials for related disorders (ALS, FTD) may inform therapeutic development for VCP-associated disease.

See Also

• [VCP Gene](/genes/vcp)
• [Amyotrophic Lateral Sclerosis](/diseases/amyotrophic-lateral-sclerosis)
• [Frontotemporal Dementia](/diseases/frontotemporal-dementia)
• [Inclusion Body Myopathy](/diseases/inclusion-body-myo)
• [ER-Associated Degradation Pathway](/mechanisms/erad-pathway)
• [Autophagy Pathway](/mechanisms/autophagy-lysosome-neurodegeneration)
• [TDP-43 Proteinopathy](/mechanisms/tdp-43-proteinopathy)
• [Protein Quality Control Network](/mechanisms/protein-quality-control-network)
• [Stress Granules in Neurodegeneration](/mechanisms/stress-granules-neurodegeneration)

External Links

• [UniProt: VCP](https://www.uniprot.org/uniprot/P62162)
• [NCBI Gene: VCP](https://www.ncbi.nlm.nih.gov/gene/7415)
• [GeneCards: VCP](https://www.genecards.org/cgi-bin/carddisp.pl?gene=VCP)
• [OMIM: VCP Disease](https://www.omim.org/entry/167320)
• [PubMed VCP ALS FTD](https://pubmed.ncbi.nlm.nih.gov/?term=VCP+ALS+FTD)

References

Pathway Diagram

The following diagram shows the key molecular relationships involving VCP (Valosin-Containing Protein) discovered through SciDEX knowledge graph analysis: