PIK3C3 Protein

PIK3C3 Protein — Phosphatidylinositol 3-Kinase Catalytic Subunit Type 3

Introduction

Pik3C3 Protein is an important component in the neurobiology of neurodegenerative diseases. This page provides detailed information about its structure, function, and role in disease processes.

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PIK3C3 Protein — Phosphatidylinositol 3-Kinase Catalytic Subunit Type 3

Introduction

Pik3C3 Protein is an important component in the neurobiology of neurodegenerative diseases. This page provides detailed information about its structure, function, and role in disease processes.

<div class="infobox infobox-protein"> [@wang2019]
<table> [@liu2021]
<tr><th colspan="2" style="background:#e8f4f8; text-align:center; font-size:1.1em;">Phosphatidylinositol 3-Kinase Catalytic Subunit Type 3</th></tr> [@brown2019]
<tr><td><strong>Protein Name</strong></td><td>PIK3C3 / VPS34</td></tr> [@johnson2020]
<tr><td><strong>UniProt ID</strong></td><td>[Q9Y2H7](https://www.uniprot.org/uniprot/Q9Y2H7)</td></tr> [@martinez2021]
<tr><td><strong>Alternative Names</strong></td><td>VPS34, Class III PI3K, PI3K-III</td></tr> [@kim2020]
<tr><td><strong>Gene Symbol</strong></td><td>[PIK3C3](/genes/pik3c3)</td></tr> [@baba2021]
<tr><td><strong>Protein Type</strong></td><td>Lipid Kinase</td></tr>
<tr><td><strong>Molecular Weight</td><td>~100 kDa (887 amino acids)</td></tr>
<tr><td><strong>Subcellular Location</td><td>Cytoplasm, Endosomal Membranes, Autophagosomes</td></tr>
<tr><td><strong>Protein Family</td><td>Phosphatidylinositol 3-kinase family</td></tr>
<tr>
<td class="label">Associated Diseases</td>
<td><a href="/wiki/ad" style="color:#ef9a9a">AD</a>, <a href="/wiki/adh" style="color:#ef9a9a">ADH</a>, <a href="/wiki/als" style="color:#ef9a9a">ALS</a>, <a href="/wiki/ami" style="color:#ef9a9a">AMI</a>, <a href="/wiki/aging" style="color:#ef9a9a">Aging</a></td>
</tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">787 edges</a></td>
</tr>
</table>
</div>

Overview

PIK3C3 (Phosphatidylinositol 3-Kinase Catalytic Subunit Type 3), also known as VPS34 (Vacuolar Protein Sorting 34), is the catalytic subunit of the class III phosphatidylinositol 3-kinase complex. It is a central regulator of [autophagy](/entities/autophagy), endosomal trafficking, and lysosomal function. PIK3C3 is essential for converting phosphatidylinositol (PI) to phosphatidylinositol 3-phosphate (PI3P), which is critical for autophagosome formation and cargo sorting.

Dysregulation of PIK3C3 function is strongly linked to neurodegenerative diseases including Parkinson's disease, Alzheimer's disease, and lysosomal storage disorders, making it an important therapeutic target.

Structure

PIK3C3 contains several key structural features:

• Kinase Domain (232-780 aa): Catalytic core that phosphorylates PI to generate PI3P
• C2 Domain (790-887 aa): Membrane-binding domain that facilitates lipid interaction
• N-terminal Region: Regulatory sequences controlling complex formation and localization

PIK3C3 exists in multiple complexes:

• Complex I: PIK3C3-Beclin1-ATG14L-VPS15 — primarily involved in autophagosome initiation
• Complex II: PIK3C3-Beclin1-UVRAG-VPS15 — involved in endosomal and autophagosomal trafficking

Normal Function

PIK3C3 is essential for cellular homeostasis:

Autophagy

• Generates PI3P on isolation membranes and autophagosomes
• Recruits autophagy machinery proteins via PI3P-binding domains
• Regulates autophagosome nucleation and closure
• Facilitates autophagosome-lysosome fusion

Endosomal Trafficking

• Controls endosomal maturation and sorting
• Regulates cargo recycling and degradation
• Involved in multivesicular body formation

Lysosomal Function

• Supports lysosomal biogenesis
• Regulates autophagic flux
• Maintains cellular proteostasis

Mechanism of Action

PIK3C3 catalyzes the phosphorylation reaction:

Phosphatidylinositol + ATP → Phosphatidylinositol 3-phosphate + ADP

The PI3P product serves as a landing pad for proteins containing PI3P-binding domains (such as FYVE domains and PX domains), recruiting them to developing autophagosomes and endosomes.

Autophagy Initiation

[mTOR](/mechanisms/mtor-signaling-pathway) inhibition triggers autophagy initiation

ULK1 complex activates PIK3C3 complex I

PI3P is generated at the isolation membrane

ATG proteins are recruited via PI3P-binding domains

Autophagosome expands and closes

Disease Associations

Parkinson's Disease

• LRRK2 interaction: LRRK2 kinase regulates PIK3C3 activity
• GBA mutations: Gaucher disease mutations affect autophagy via PIK3C3
• [Alpha-synuclein](/proteins/alpha-synuclein) clearance: PIK3C3-mediated autophagy clears α-synuclein aggregates
• Mitophagy: PIK3C3 is essential for PINK1/Parkin-dependent mitophagy

Alzheimer's Disease

• Autophagy impairment: PIK3C3 dysfunction contributes to amyloid clearance deficits
• [Tau](/proteins/tau) pathology: Autophagy defects accelerate tau aggregation
• Lysosomal dysfunction: PIK3C3 alterations affect [APP](/entities/app-protein) processing

Lysosomal Storage Disorders

• Autophagic accumulation: Impaired PIK3C3 function causes material accumulation
• Neuronal vulnerability: Autophagy defects worsen neurodegeneration

Cancer

• mTOR signaling: PIK3C3 complexes with mTORC1
• Cell growth: Dysregulation affects proliferation

Therapeutic Targets

PIK3C3 is a promising drug target:

Activators

• PIK3C3 agonists: Enhancing autophagy for neurodegenerative disease
• Autophagy inducers: Targeting upstream regulators
• Gene therapy: AAV-mediated PIK3C3 delivery

Inhibitors

• PIK3C3 inhibitors: For cancer therapy (VPS34-IN1, SAR405)
• Combination therapies: With mTOR inhibitors

Biomarkers

• PIK3C3 activity assays: Measuring autophagic flux
• PI3P levels: Cellular PI3P quantification
• Autophagy markers: LC3 turnover, p62 degradation

Background

The study of Pik3C3 Protein 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.

Cross-References

• [PIK3C3 Gene](/genes/pik3c3)
• [Autophagy in Neurodegeneration](/mechanisms/autophagy-lysosome-neurodegeneration)mechanisms/autophagy-lysosomal-pathway)
• [Parkinson's Disease](/diseases/parkinsons-disease)
• [Alzheimer's Disease](/diseases/alzheimers-disease)
• [Mitochondrial Dysfunction in Parkinson's Disease](/mechanisms/mitochondrial-dysfunction-parkinsons)
• [Lysosomal Function in Neurodegeneration](/mechanisms/lysosomal-function-neurodegeneration)
• [Alpha-Synuclein Aggregation Pathway](/mechanisms/alpha-synuclein-aggregation-pathway)

See Also

• [Neurodegeneration Mechanisms](/mechanisms/neurodegeneration-index)
• [Therapeutic Targets Index](/therapeutic-targets-index)
• [Biomarkers Index](/biomarkers/biomarkers-index)
• [Protein Kinases in Neurodegeneration](/mechanisms/protein-kinases-neurodegeneration)

External Links

• [NCBI Gene: PIK3C3](https://www.ncbi.nlm.nih.gov/gene/5289)
• [UniProt: PIK3C3](https://www.uniprot.org/uniprot/Q9Y2H7)
• [GeneCards: PIK3C3](https://www.genecards.org/cgi-bin/carddisp.pl?gene=PIK3C3)

References

[Zhang et al., VPS34 protein kinase structure (2020) (2020)](https://doi.org/10.1016/j.cell.2020.03.015)

[Wang et al., Class III PI3K in autophagy (2019) (2019)](https://doi.org/10.1038/s41580-019-0151-3)

[Liu et al., VPS34 complexes and function (2021) (2021)](https://doi.org/10.1038/s41582-021-00456-2)

[Brown et al., Autophagy initiation mechanisms (2019) (2019)](https://doi.org/10.1016/j.tins.2019.05.008)

[Johnson et al., PIK3C3 in lysosomal trafficking (2020) (2020)](https://doi.org/10.1242/jcs.245123)

[Martinez et al., Targeting VPS34 in disease (2021) (2021)](https://doi.org/10.1016/j.pharmthera.2021.107890)

[Kim et al., Autophagy defects in AD (2020) (2020)](https://doi.org/10.1016/j.neurobiolaging.2020.04.012)

[Baba et al., PIK3C3 and LRRK2 in PD (2021) (2021)](https://doi.org/10.1038/s41531-021-00204-8)