GO:0035032 phosphatidylinositol 3-kinase complex, class III: Components, Assembly and Research Methods, Genes, Functions and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:0035032 describes the class III phosphatidylinositol 3-kinase (PI3K) complex, a cellular component defined by a catalytic class III PI3K subunit bound to a regulatory adaptor subunit.
• The class III PI3K complex is best known as the Vps34-containing complex that generates phosphatidylinositol 3-phosphate (PI3P) and initiates autophagy.
• Its core subunits include the catalytic lipid kinase VPS34 (PIK3C3) and the adaptor VPS15 (PIK3R4), with additional adaptors such as Beclin 1, ATG14, UVRAG, and NRBF2/Atg38.
• Class III PI3K complexes are regulated by acetylation, phosphorylation, and metabolic signals, linking them to autophagy control.
• Dysregulation of class III PI3K complexes contributes to cancer, liver disease, and neurodegenerative conditions through altered autophagy and membrane trafficking.
• CRISPR knockout, point mutation, knock-in, and overexpression models are essential to dissect the function of individual class III PI3K complex subunits.
Description
The phosphatidylinositol 3-kinase complex, class III (GO:0035032) is a cellular component that catalyzes the phosphorylation of phosphatidylinositol to produce phosphatidylinositol 3-phosphate (PI3P), a key lipid signal for membrane trafficking and autophagy. Unlike class I PI3Ks, class III PI3Ks have a substrate specificity restricted to phosphatidylinositol, and they function as multiprotein assemblies containing a catalytic subunit and one or more regulatory adaptor subunits. This complex is conserved from yeast to humans and is central to autophagosome nucleation and endosomal sorting. Researchers study GO:0035032 to understand how cells maintain proteostasis, respond to stress, and regulate nutrient sensing. Because autophagy dysfunction is implicated in cancer, neurodegeneration, and metabolic disorders, the class III PI3K complex has emerged as a therapeutic target and a biomarker of autophagic flux. The complex is dynamically regulated by post-translational modifications and interacting proteins, making it a rich area for functional genomics and drug discovery.
phosphatidylinositol 3-kinase complex, class III At A Glance
| GO ID | GO:0035032 |
|---|---|
| GO term | phosphatidylinositol 3-kinase complex, class III |
| Ontology | cellular_component |
| Synonym | class III PI3K complex; phosphoinositide 3-kinase complex, class III |
| Major function | Generates phosphatidylinositol 3-phosphate (PI3P) to initiate autophagy and endosomal trafficking |
| Catalytic subunit | VPS34 (PIK3C3), a class III PI3K |
| Regulatory subunit | VPS15 (PIK3R4), a adaptor that anchors and activates VPS34 |
| Additional adaptors | Beclin 1, ATG14, UVRAG, NRBF2/Atg38, and others |
| Substrate specificity | Restricted to phosphatidylinositol (PI) |
What Is GO:0035032?
GO:0035032 refers to a phosphatidylinositol 3-kinase complex that contains a catalytic class III phosphoinositide 3-kinase (PI3K) subunit bound to a regulatory (adaptor) subunit. Additional adaptor proteins may be present. Class III PI3Ks have a substrate specificity restricted to phosphatidylinositol (PI). In practice, this complex is often called the class III PI3K complex or the Vps34 complex, and it is the only PI3K class that uses PI as its main substrate to generate PI3P.
Why Is phosphatidylinositol 3-kinase complex, class III Important in Cell Biology?
The class III PI3K complex is a master regulator of autophagy and membrane trafficking, making it essential for cellular homeostasis, stress responses, and immunity. Its activity determines the levels of PI3P, which recruit effector proteins to autophagosome nucleation sites and endosomes. Because autophagy is a double-edged sword in disease, understanding GO:0035032 helps explain how cells survive nutrient deprivation, clear damaged organelles, and respond to therapy. Moreover, mutations or altered expression of its subunits are linked to cancer progression, liver steatosis, and neurodegeneration, underscoring its clinical relevance.
• Central to autophagosome nucleation and autophagic flux.
• Regulates endosomal sorting and receptor degradation.
• Implicated in cancer cell survival and resistance to anti-angiogenic therapy.
• Linked to liver disease through lipid droplet turnover and autophagy.
• Involved in neurodegeneration via mitophagy and protein aggregation.
• Modulated by acetylation and metabolic signals.
• Target for pharmacological modulation of autophagy.
• Provides a scaffold for studying protein-protein interactions in membranes.
• Essential for immune defense and pathogen clearance.
• Offers biomarkers for autophagic activity in clinical samples.
Structure and Composition of phosphatidylinositol 3-kinase complex, class III
Core catalytic and regulatory subunits
In simple terms: The complex has a kinase engine and a support protein that holds it in place.
The minimal class III PI3K complex consists of the catalytic subunit VPS34 (PIK3C3) bound to the regulatory adaptor VPS15 (PIK3R4). VPS34 contains the lipid kinase domain that phosphorylates phosphatidylinositol, while VPS15 anchors the complex to membranes and stabilizes VPS34. This core heterodimer is conserved and forms the foundation for additional adaptors that dictate localization and function.
Adaptor proteins and complex I versus complex II
In simple terms: Different adaptor proteins direct the complex to different jobs in the cell.
The class III PI3K complex can assemble into distinct subcomplexes: complex I contains ATG14 and Beclin 1 and functions in autophagy initiation, while complex II contains UVRAG and Beclin 1 and functions in endosomal trafficking. NRBF2/Atg38 is an additional subunit that modulates complex I assembly and activity. These adaptors provide specificity for membrane recruitment and downstream effector engagement.
Membrane recruitment and assembly
In simple terms: The complex is recruited to specific membranes by binding to lipids and proteins.
Assembly of the class III PI3K complex at the phagophore or endosome requires membrane targeting signals, including binding to PI3P and interaction with small GTPases and SNAREs. VPS15 contributes to membrane anchoring, while Beclin 1 and ATG14 mediate interactions with upstream autophagy regulators. The complex is dynamically assembled and disassembled in response to nutrient status and stress.
Post-translational modifications and regulation
In simple terms: Chemical tags on the complex can turn its activity up or down.
Acetylation of class III PI3K complex subunits regulates autophagy induction and duration. Phosphorylation by kinases such as ULK1 and mTORC1 modulates complex activity and localization. These modifications allow the complex to integrate metabolic and stress signals.
Key Genes Involved in GO:0035032 phosphatidylinositol 3-kinase complex, class III
The following genes encode core and accessory subunits of the class III PI3K complex, as well as key regulators and effectors.
| Gene | Major Role | Research Relevance |
|---|---|---|
| PIK3C3 (VPS34) | Catalytic class III PI3K subunit | Kinase activity, autophagy initiation, PI3P production |
| PIK3R4 (VPS15) | Regulatory adaptor subunit | Membrane anchoring, VPS34 stability |
| BECN1 (Beclin 1) | Adaptor and scaffold | Autophagy initiation, tumor suppression |
| ATG14 | Complex I-specific adaptor | Autophagosome nucleation |
| UVRAG | Complex II-specific adaptor | Endosomal trafficking, autophagy maturation |
| NRBF2 (Atg38) | Complex I accessory subunit | Modulates VPS34 activity and autophagy |
| ATG16L1 | Autophagy effector | LC3 lipidation, autophagosome formation |
| RUBCNL | Autophagy enhancer | Lactate-induced autophagy, therapy resistance |
| OPTN (Optineurin) | Mitophagy receptor | PINK1/Parkin mitophagy initiation |
| PINK1 | Mitophagy kinase | Mitochondrial quality control |
| PRKN (Parkin) | Mitophagy E3 ligase | Ubiquitination of mitochondrial proteins |
| ZDHHC7 | Palmitoyltransferase | S-palmitoylation of ATG16L1 |
| MTOR | Autophagy regulator | Inhibits class III PI3K complex via ULK1 |
| ULK1 | Autophagy kinase | Phosphorylates Beclin 1 and ATG14 |
| MAP1LC3B (LC3) | Autophagosome marker | LC3 lipidation and autophagic flux |
| SQSTM1 (p62) | Cargo receptor | Selective autophagy and protein aggregation |
| LAMP1 | Lysosomal marker | Autolysosome formation |
How Is phosphatidylinositol 3-kinase complex, class III Regulated?
The class III PI3K complex is regulated by nutrient and energy sensors, including mTORC1, which phosphorylates ULK1 and ATG14 to inhibit autophagy initiation. Acetylation of complex subunits by acetyltransferases and deacetylases modulates its activity and stability. Metabolic signals such as lactate can induce lactylation of histones and promote expression of autophagy enhancers like RUBCNL, indirectly influencing complex function. Additionally, S-palmitoylation of ATG16L1 by ZDHHC7 facilitates LC3 lipidation and autophagosome formation, linking lipid modification to complex downstream events. These layers of regulation allow the complex to respond to cellular energy status and stress.
phosphatidylinositol 3-kinase complex, class III and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| BECN1 | Cancer, autophagy deficiency | Knockout cell lines, xenograft models |
| RUBCNL | Colorectal cancer, bevacizumab resistance | Overexpression and knockout in CRC cells |
| PIK3C3 | Neurodegeneration, autophagy disorders | Conditional knockout mouse, iPSC-derived neurons |
| ATG16L1 | Inflammatory bowel disease, Crohn's disease | Point mutation knock-in mice |
| OPTN | Amyotrophic lateral sclerosis, glaucoma | Knockout and mutant overexpression |
Cancer and therapy resistance
Altered class III PI3K complex activity affects autophagic flux and can promote tumor cell survival under stress. Tumor-derived lactate enhances RUBCNL expression through histone lactylation, facilitating autophagy and resistance to bevacizumab in colorectal cancer. Beclin 1 and UVRAG are frequently dysregulated in cancers, and their expression levels correlate with prognosis.
Liver disease and lipid metabolism
The class III PI3K complex is involved in lipid droplet turnover and autophagy in hepatocytes. Impaired autophagy contributes to steatosis, steatohepatitis, and hepatocellular carcinoma, making the complex a potential therapeutic target.
Neurodegeneration and mitophagy
Defective mitophagy, which depends on class III PI3K complex function, leads to accumulation of damaged mitochondria and neuronal death. Optineurin, a mitophagy receptor, initiates PINK1/Parkin-dependent mitophagy through unconventional mechanisms that require PI3P generation.
From phosphatidylinositol 3-kinase complex, class III-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| Does loss of VPS34 block autophagy? | PIK3C3 knockout cell line |
| Does a disease-associated point mutation alter complex assembly? | Point mutation knock-in via CRISPR |
| How does tagging affect complex localization? | Tagged knock-in of ATG14 or UVRAG |
| Does overexpression of RUBCNL enhance autophagy? | RUBCNL overexpression stable cell line |
| Can NRBF2 modulate complex I activity? | NRBF2 knockout and rescue |
| Does acetylation regulate Beclin 1 function? | Acetylation-deficient or mimetic mutants |
How to Study the phosphatidylinositol 3-kinase complex, class III Process
| Method | What It Measures | Typical Application |
|---|---|---|
| Immunoblotting | LC3-II levels, autophagy flux | Autophagy induction and inhibition |
| Fluorescence microscopy | PI3P puncta, LC3 puncta | Autophagosome formation |
| Co-immunoprecipitation | Protein-protein interactions | Complex composition |
| In vitro kinase assay | PI3P production | Catalytic activity of VPS34 |
| CRISPR knockout | Gene function loss | Autophagy dependence |
| RNA-seq | Transcriptional changes | Autophagy gene expression |
| Proteomics | Protein abundance and modifications | Acetylation and interactome |
| Live-cell imaging | Complex dynamics | Membrane recruitment |
Measuring PI3P and lipid kinase activity
PI3P levels can be measured using fluorescent probes or mass spectrometry, while in vitro kinase assays with recombinant VPS34-VPS15 complex quantify catalytic activity. These methods directly assess class III PI3K complex function.
Monitoring autophagy flux
LC3 lipidation and autophagic flux are monitored by immunoblotting for LC3-II and using tandem fluorescent LC3 reporters. Colocalization of LC3 with lysosomal markers such as LAMP1 indicates autolysosome formation.
Proteomic and interactomic approaches
Affinity purification coupled with mass spectrometry identifies subunits and interactors of the class III PI3K complex. Proximity labeling can capture transient interactions at membranes.
Structural biology and imaging
Cryo-electron microscopy and X-ray crystallography reveal the architecture of the complex and its membrane-binding interfaces. Live-cell imaging tracks complex assembly and dynamics.
How CRISPR Can Be Used to Study GO:0035032 phosphatidylinositol 3-kinase complex, class III
Knockout
CRISPR knockout of PIK3C3, PIK3R4, BECN1, or ATG14 abolishes class III PI3K complex function and blocks autophagy, providing a clean background to study downstream effects. Knockout cell lines are valuable for drug sensitivity screens and for validating autophagy dependence.
Point Mutation
Point mutations in catalytic residues of PIK3C3 or in regulatory domains of BECN1 can be introduced to dissect kinase-dependent versus scaffold functions. Disease-associated mutations in ATG16L1 can be modeled to study Crohn's disease mechanisms.
Knock-in
Knock-in of fluorescent or affinity tags into endogenous loci allows visualization and purification of the complex under native regulation. Tagged knock-in of ATG14 or UVRAG enables tracking of complex I and II dynamics.
Overexpression
Overexpression of wild-type or mutant subunits, such as RUBCNL or NRBF2, can enhance or disrupt autophagy and reveal gain-of-function phenotypes. Stable overexpression lines are useful for testing therapeutic resistance mechanisms.
How EDITGENE Supports phosphatidylinositol 3-kinase complex, class III Research
Researchers studying phosphatidylinositol 3-kinase complex, class III-related genes often need to determine whether a candidate gene is causally involved in autophagy, membrane trafficking, or disease. EDITGENE provides custom CRISPR cell models and screening services to accelerate this functional validation.
Contact EDITGENE today to design your custom CRISPR model for phosphatidylinositol 3-kinase complex, class III research.
Frequently Asked Questions About phosphatidylinositol 3-kinase complex, class III
What is GO:0035032?
GO:0035032 is the Gene Ontology term for the phosphatidylinositol 3-kinase complex, class III, a protein complex that generates PI3P and initiates autophagy.
What genes are involved in phosphatidylinositol 3-kinase complex, class III?
Core genes include PIK3C3 (VPS34), PIK3R4 (VPS15), BECN1, ATG14, UVRAG, and NRBF2, among others.
What is the function of class III PI3K complex?
It phosphorylates phosphatidylinositol to produce PI3P, which is essential for autophagosome nucleation and endosomal trafficking.
How is class III PI3K complex regulated?
It is regulated by phosphorylation, acetylation, and metabolic signals such as mTORC1 and lactate.
What diseases are associated with class III PI3K complex dysfunction?
Dysfunction is linked to cancer, liver disease, and neurodegeneration.
What is the difference between class I and class III PI3K?
Class III PI3K uses phosphatidylinositol as its main substrate, while class I PI3Ks prefer phosphatidylinositol 4,5-bisphosphate.
How can I study class III PI3K complex in the lab?
Common methods include CRISPR knockout, immunoblotting for LC3, PI3P probes, and co-immunoprecipitation.
What is the role of VPS34 in autophagy?
VPS34 is the catalytic subunit that produces PI3P to recruit autophagy effectors.
What is NRBF2 and how does it relate to class III PI3K complex?
NRBF2/Atg38 is an accessory subunit that modulates complex I assembly and activity.
Can CRISPR be used to model class III PI3K complex mutations?
Yes, CRISPR knockout, point mutation, knock-in, and overexpression models are widely used to study complex function.
Conclusion
The phosphatidylinositol 3-kinase complex, class III (GO:0035032) is a central hub for autophagy initiation and membrane trafficking, with critical roles in health and disease. Its multi-subunit architecture and dynamic regulation make it an attractive target for functional genomics and therapeutic development. Continued research using advanced CRISPR models will clarify how individual subunits contribute to autophagy-related diseases and identify new intervention points.
References
- 1. Ohashi Y. 2021. Class III phosphatidylinositol 3-kinase complex I subunit NRBF2/Atg38 - from cell and structural biology to health and disease.. Autophagy 17(12):3897-3907 PMID: 33459128
- 2. Xu Y et al.. 2023. Acetylation in the regulation of autophagy.. Autophagy 19(2):379-387 PMID: 35435793
- 3. Filali-Mouncef Y et al.. 2022. The ménage à trois of autophagy, lipid droplets and liver disease.. Autophagy 18(1):50-72 PMID: 33794741
- 4. Li W et al.. 2024. Tumor-derived lactate promotes resistance to bevacizumab treatment by facilitating autophagy enhancer protein RUBCNL expression through histone H3 lysine 18 lactylation (H3K18la) in colorectal cancer.. Autophagy 20(1):114-130 PMID: 37615625
- 5. Wei F et al.. 2024. ZDHHC7-mediated S-palmitoylation of ATG16L1 facilitates LC3 lipidation and autophagosome formation.. Autophagy 20(12):2719-2737 PMID: 39087410
- 6. Feng Y et al.. 2024. Interplay of energy metabolism and autophagy.. Autophagy 20(1):4-14 PMID: 37594406
- 7. Devis-Jauregui L et al.. 2021. Autophagy in the physiological endometrium and cancer.. Autophagy 17(5):1077-1095 PMID: 32401642
- 8. Nguyen TN et al.. 2023. Unconventional initiation of PINK1/Parkin mitophagy by Optineurin.. Mol Cell 83(10):1693-1709.e9 PMID: 37207627
