VCP (Valosin-Containing Protein)

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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

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:

ATP-bound state (pre-hydrolysis): The D1 and D2 domains adopt a "closed" conformation, with the N-domains positioned to engage substrates.

Transition state (ATP hydrolysis): Sequential ATP hydrolysis around the hexamer triggers wave-like conformational changes.

ADP-bound state (post-hydrolysis): An "open" conformation allows substrate release. The N-domain rotates and lifts, releasing the extracted substrate.

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:

Inclusion Body Myopathy (IBM): Progressive muscle weakness beginning in adulthood, typically in the third or fourth decade. Muscle pathology shows rimmed vacuoles containing phosphorylated TDP-43.

Paget Disease of Bone (PDB): Increased bone turnover with characteristic lytic and sclerotic lesions, primarily affecting spine, pelvis, and long bones.

Frontotemporal Dementia (FTD): Progressive decline in executive function, behavior, and language. Neuropathology shows frontotemporal atrophy with TDP-43 inclusions.

Amyotrophic Lateral Sclerosis (ALS): Progressive motor neuron degeneration with muscle weakness, atrophy, and fasciculations. VCP-related ALS shares features with other genetic forms.

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

Mermaid diagram (expand to render)

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

VCP mutations alter TDP-43 dynamics through impaired autophagy and altered stress granule processing, leading to cytoplasmic accumulation and phosphorylation of TDP-43[@kim2013].

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)

-Lithium (autophagy enhancer)

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

Why do VCP mutations cause tissue-specific phenotypes (muscle, bone, brain)?

What determines whether a patient develops FTD or ALS?

Can autophagy enhancement rescue VCP-related pathology?

What is the optimal therapeutic window for intervention?

How do VCP mutations interact with environmental factors?

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.

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

[Watts GDJ, et al., Novel inclusions in a family with IBMPFD and ALS (2004)](https://pubmed.ncbi.nlm.nih.gov/15235793/)

[Kimonis V, et al., VCP disease: inclusion body myopathy with Paget disease of bone and frontotemporal dementia (2008)](https://pubmed.ncbi.nlm.nih.gov/18675956/)

[Nalbandian A, et al., The pathogenesis of VCP-associated disease (2021)](https://pubmed.ncbi.nlm.nih.gov/34076752/)

[Buchan JR, et al., p97/VCP drives liquid phase separation and aggregation of stress granules (2013)](https://pubmed.ncbi.nlm.nih.gov/24211388/)

[Ji YJ, et al., VCP mutations in ALS and FTD: mechanisms and therapeutic targeting (2021)](https://pubmed.ncbi.nlm.nih.gov/34184765/)

[Song JY, et al., VCP deficiency leads to TDP-43 pathology in neurons (2022)](https://pubmed.ncbi.nlm.nih.gov/35639582/)

[Zhao M, et al., ERAD and VCP: implications for neurodegenerative diseases (2020)](https://pubmed.ncbi.nlm.nih.gov/32877962/)

[Kopp F, et al., VCP in DNA repair: role in genome stability (2019)](https://pubmed.ncbi.nlm.nih.gov/31176641/)

[Weihl CC, et al., Valosin-containing protein disease: a review of clinical phenotypes and pathogenesis (2010)](https://pubmed.ncbi.nlm.nih.gov/20089946/)

[Yamanaka K, et al., VCP and autophagy in protein clearance (2020)](https://pubmed.ncbi.nlm.nih.gov/32658574/)

[Kim HJ, et al., VCP mutations alter TDP-43 dynamics and cause ALS/FTD (2013)](https://pubmed.ncbi.nlm.nih.gov/24211983/)

[Badadani M, et al., VCP-associated inclusion body myopathy and FTD: cellular mechanisms (2013)](https://pubmed.ncbi.nlm.nih.gov/23396074/)

[Clemen CS, et al., VCP codon mutations: from yeast to human disease (2020)](https://pubmed.ncbi.nlm.nih.gov/32029572/)

[Arhzaouy K, et al., VCP deficiency induces stress granule formation and neurodegeneration (2022)](https://pubmed.ncbi.nlm.nih.gov/35659201/)

[Davidson GS, et al., VCP inhibitors as therapeutic agents in ALS/FTD (2020)](https://pubmed.ncbi.nlm.nih.gov/32707178/)

Pathway Diagram

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

Mermaid diagram (expand to render)

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VCP (Valosin-Containing Protein)

VCP (Valosin-Containing Protein)

Introduction

VCP (Valosin-Containing Protein)

Introduction

Molecular Structure and Mechanism

Domain Architecture

Hexameric Assembly

Conformational Cycle

Cofactor Interactions

Normal Cellular Functions

Protein Quality Control

Autophagy Regulation

DNA Repair and Genome Stability

Membrane Dynamics

VCP Disease: Clinical and Molecular Features

Disease Spectrum

Pathogenic Mutations

Pathogenesis Mechanisms

TDP-43 Pathology

Phenotype-Genotype Correlations

Therapeutic Approaches

Small Molecule Strategies

Gene-Based Therapies

Biomarkers

Clinical Management

Research Directions

Unanswered Questions

Model Systems

Clinical Trials

See Also

External Links

References

Pathway Diagram