GO:0005943 phosphatidylinositol 3-kinase complex, class IA: Components, Assembly and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:0005943 describes the class IA phosphatidylinositol 3-kinase (PI3K) complex, a heterodimer of a catalytic p110 subunit (e.g., PIK3CA, PIK3CB, PIK3CD) and an SH2-containing regulatory subunit (e.g., PIK3R1/p85alpha).
• The complex is recruited to activated tyrosine kinase receptors and phosphorylates phosphatidylinositol-4-phosphate (PI4P) to generate phosphatidylinositol-3,4,5-trisphosphate (PIP3), a key second messenger.
• Class IA PI3K signaling controls diverse cellular processes including autophagy, insulin secretion, immune evasion, and cell survival.
• Dysregulation of class IA PI3K is implicated in cancers such as non-small cell lung cancer, bladder cancer, and uterine cancer.
• The complex is a major drug target; understanding its assembly and regulation is essential for developing isoform-selective inhibitors.
• CRISPR-based models (knockout, point mutation, knock-in) enable precise dissection of class IA PI3K subunit functions in health and disease.
Description
The phosphatidylinositol 3-kinase complex, class IA (GO:0005943) is a cellular component defined by the Gene Ontology as a class I PI3K complex that possesses 1-phosphatidylinositol-4-phosphate 3-kinase activity. It comprises a catalytic class IA phosphoinositide 3-kinase (PI3K) subunit and an associated SH2 domain-containing regulatory subunit, often called p85 proteins. This complex is a central node in tyrosine kinase signaling, linking activated receptors to downstream effectors such as Akt. Researchers study GO:0005943 because its activity is frequently altered in cancer, metabolic disorders, and immune diseases, making it a prime target for therapeutic intervention.
phosphatidylinositol 3-kinase complex, class IA At A Glance
| GO ID | GO:0005943 |
|---|---|
| GO term | phosphatidylinositol 3-kinase complex, class IA |
| Ontology | cellular_component |
| Synonym | class IA PI3K complex; phosphoinositide 3-kinase complex, class IA; 1-phosphatidylinositol-4-phosphate 3-kinase, class IA complex |
| Major function | Phosphorylates phosphatidylinositol-4-phosphate to generate phosphatidylinositol-3,4,5-trisphosphate, a key signaling lipid |
| Catalytic subunit | Class IA PI3K catalytic subunits (e.g., p110alpha, p110beta, p110delta) |
| Regulatory subunit | SH2 domain-containing regulatory subunits (e.g., p85alpha, p85beta, p55gamma) |
| Associated activity | 1-phosphatidylinositol-4-phosphate 3-kinase activity |
| Pathways | Tyrosine kinase signaling, Akt/mTOR pathway, autophagy, insulin secretion |
What Is GO:0005943?
GO:0005943 refers to the class IA phosphatidylinositol 3-kinase complex, a heterodimeric enzyme composed of a catalytic p110 subunit and a regulatory p85 subunit. The complex catalyzes the phosphorylation of phosphatidylinositol-4-phosphate to produce phosphatidylinositol-3,4,5-trisphosphate, a lipid second messenger that recruits and activates downstream signaling proteins. Through its SH2-containing regulatory subunit, the complex interacts with activated tyrosine kinase receptors or adaptor proteins, thereby integrating extracellular signals into intracellular responses.
Why Is phosphatidylinositol 3-kinase complex, class IA Important in Cell Biology?
The class IA PI3K complex is a master regulator of cell growth, survival, metabolism, and motility. Its dysregulation is a hallmark of many cancers, where mutations in PIK3CA or loss of PTEN lead to constitutive PIP3 production and oncogenic signaling. Beyond cancer, class IA PI3K signaling is critical for normal physiology, including insulin secretion in pancreatic beta cells and immune cell function. Understanding the assembly, regulation, and downstream effects of GO:0005943 is therefore essential for both basic biology and translational medicine.
• Central mediator of tyrosine kinase receptor signaling to Akt and mTOR.
• Frequently mutated or amplified in human cancers, including non-small cell lung cancer and bladder cancer.
• Regulates autophagy, with p110beta as a positive regulator.
• Controls insulin secretion in pancreatic beta cells.
• Involved in immune evasion by downregulating MHC-I in bladder cancer.
• Target of approved and investigational PI3K inhibitors.
• Modulated by G-protein subunits such as Galpha16.
• Interacts with MHC class II-derived peptides, suggesting immunomodulatory roles.
• Activated by tamoxifen in uterine cancer, highlighting context-dependent regulation.
• Essential for understanding resistance mechanisms to targeted therapies.
Structure and Composition of phosphatidylinositol 3-kinase complex, class IA
Catalytic p110 Subunit
In simple terms: The p110 subunit is the enzyme that does the actual work of adding a phosphate group to a lipid.
The catalytic subunit of class IA PI3K, known as p110, exists in several isoforms (p110alpha, p110beta, p110delta) encoded by PIK3CA, PIK3CB, and PIK3CD, respectively. It contains a kinase domain that phosphorylates phosphatidylinositol-4-phosphate at the 3-position to generate PIP3. The p110 subunit is unstable in the absence of a regulatory subunit and requires heterodimerization for proper folding and activity.
Regulatory p85 Subunit
In simple terms: The p85 subunit acts like a handle that attaches the enzyme to activated receptors and keeps it stable.
The regulatory subunit, typically p85alpha (PIK3R1), contains SH2 domains that bind to phosphotyrosine motifs on activated receptors or adaptor proteins. This interaction recruits the complex to the membrane and relieves inhibitory contacts, activating the catalytic subunit. Multiple regulatory isoforms exist (p85alpha, p85beta, p55gamma), contributing to signaling diversity.
Heterodimer Assembly
In simple terms: The two subunits must come together to form a functional enzyme.
The class IA PI3K complex is an obligate heterodimer. The inter-subunit interaction involves the N-terminal region of p85 and the adaptor-binding domain of p110. This interaction stabilizes both subunits and maintains the enzyme in a low-activity state until recruited to the membrane.
Membrane Recruitment
In simple terms: The complex moves to the cell membrane where its substrate is located.
Upon growth factor stimulation, receptor tyrosine kinases autophosphorylate and create docking sites for the SH2 domains of p85. This recruitment brings the catalytic subunit into proximity with its lipid substrate, phosphatidylinositol-4-phosphate, in the plasma membrane.
Interaction with G Proteins
In simple terms: Other signaling proteins can also influence the complex.
Galpha16, a heterotrimeric G protein subunit, has been shown to interact with class IA PI3K and inhibit Akt signaling, demonstrating that the complex integrates signals beyond receptor tyrosine kinases.
Key Genes Involved in GO:0005943 phosphatidylinositol 3-kinase complex, class IA
The following genes encode subunits and regulators of the class IA PI3K complex, as well as related signaling components.
| Gene | Major Role | Research Relevance |
|---|---|---|
| PIK3CA | Encodes p110alpha catalytic subunit | Frequently mutated in cancers; target for isoform-selective inhibitors |
| PIK3CB | Encodes p110beta catalytic subunit | Regulates autophagy and insulin secretion |
| PIK3CD | Encodes p110delta catalytic subunit | Primarily expressed in leukocytes; role in immune signaling |
| PIK3R1 | Encodes p85alpha regulatory subunit | Mutations cause immune dysregulation and cancer predisposition |
| PIK3R2 | Encodes p85beta regulatory subunit | Less studied; may modulate PI3K signaling |
| PIK3R3 | Encodes p55gamma regulatory subunit | Tissue-specific regulatory roles |
| PTEN | Lipid phosphatase that opposes PI3K | Tumor suppressor; loss activates PI3K/Akt |
| AKT1 | Downstream effector of PIP3 | Mediates survival and growth signals |
| MTOR | Kinase downstream of PI3K/Akt | Central regulator of cell growth |
| GNA16 | Galpha16 subunit | Interacts with class IA PI3K to inhibit Akt |
| G3BP1 | RNA-binding protein | Promotes immune evasion via PI3K/Akt in bladder cancer |
| SLU7 | Splicing factor | Cooperates with G3BP1 to downregulate MHC-I via PI3K/Akt |
| HLA-DR | MHC class II protein | Peptides interact with class IA PI3K |
| INS | Insulin | Secreted by pancreatic beta cells; regulated by PI3K |
| EGFR | Receptor tyrosine kinase | Activates class IA PI3K in cancers |
| ERBB2 | Receptor tyrosine kinase | Heterodimerizes with EGFR to activate PI3K |
| IGF1R | Receptor tyrosine kinase | Activates PI3K in metabolic tissues |
| IRS1 | Insulin receptor substrate | Adaptor that recruits PI3K to insulin receptor |
How Is phosphatidylinositol 3-kinase complex, class IA Regulated?
The class IA PI3K complex is tightly regulated by multiple mechanisms. Inter-subunit interactions between p110 and p85 maintain low basal activity; binding of p85 SH2 domains to phosphotyrosine motifs on activated receptors relieves this inhibition and promotes membrane recruitment. Additionally, Galpha16 can interact with class IA PI3K and inhibit Akt signaling, providing an additional layer of regulation. The complex is also subject to feedback regulation by downstream effectors such as mTOR and S6K, which can phosphorylate IRS1 and dampen PI3K activation. In uterine cancer, tamoxifen has been shown to induce PI3K activation, illustrating context-dependent regulation.
phosphatidylinositol 3-kinase complex, class IA and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| PIK3CA | Non-small cell lung cancer, bladder cancer | Knockout or point mutation in cancer cell lines |
| PIK3CB | Autophagy regulation, insulin secretion | Beta-cell specific knockout |
| PIK3R1 | Immune dysregulation, cancer predisposition | Knock-in of patient mutations |
| PTEN | Tumor suppressor loss in cancers | PTEN knockout with PI3K inhibition |
| G3BP1/SLU7 | Immune evasion in bladder cancer | Knockdown or knockout in bladder cancer models |
Class IA PI3K in Cancer
Dysregulation of class IA PI3K signaling is a common feature of many cancers. Activating mutations in PIK3CA or loss of PTEN lead to constitutive PIP3 production, driving uncontrolled cell proliferation and survival. In non-small cell lung cancer, class IA PI3K signaling promotes tumor growth and resistance to therapy. In bladder cancer, G3BP1 and SLU7 jointly promote immune evasion by downregulating MHC-I via PI3K/Akt activation. Tamoxifen treatment in uterine cancer can induce PI3K activation, potentially contributing to resistance.
Metabolic Disorders
Class IA PI3K in pancreatic beta cells controls insulin secretion through multiple mechanisms, linking the complex to glucose homeostasis and diabetes. Dysregulation of this pathway can impair insulin secretion and contribute to type 2 diabetes pathogenesis.
Immune Regulation
The class IA PI3K complex is involved in immune cell signaling and immune evasion. In bladder cancer, its activation downstream of G3BP1 and SLU7 reduces MHC-I presentation, helping tumor cells escape immune detection. Additionally, MHC class II-derived peptides can directly interact with class IA PI3K, resulting in dose-dependent stimulatory effects, suggesting a role in immune modulation.
From phosphatidylinositol 3-kinase complex, class IA-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| Does PIK3CA mutation drive tumor growth? | Point mutation knock-in in cancer cell lines |
| What is the role of p110beta in autophagy? | PIK3CB knockout in cell lines |
| How does p85alpha regulate insulin secretion? | Beta-cell specific PIK3R1 knockout |
| Can class IA PI3K be targeted to enhance immunotherapy? | Knockout of PIK3CA in combination with immune checkpoint blockade |
| What is the effect of Galpha16 on PI3K signaling? | Overexpression of GNA16 in cell lines |
| How do MHC class II peptides modulate PI3K? | Peptide treatment in PI3K-expressing cells |
How to Study the phosphatidylinositol 3-kinase complex, class IA Process
| Method | What It Measures | Typical Application |
|---|---|---|
| CRISPR knockout | Loss of protein function | Determine subunit-specific roles |
| Phosphoproteomics | Changes in phosphorylation | Pathway activation profiling |
| Lipid biosensors | PIP3 levels in live cells | Real-time PI3K activity |
| Co-immunoprecipitation | Protein-protein interactions | Validate heterodimer assembly |
| RNA-seq | Transcriptional changes | Downstream gene expression |
| Western blot | Protein expression and phosphorylation | Akt activation status |
| Cell proliferation assay | Cell growth | Effect of PI3K inhibitors |
| Immune evasion assays | MHC-I surface levels | Tumor immune escape |
CRISPR-Cas9 Knockout
CRISPR-Cas9 knockout of individual class IA PI3K subunits (e.g., PIK3CA, PIK3CB, PIK3R1) allows researchers to dissect their specific roles in signaling and disease. For example, knockout of PIK3CB has been used to demonstrate its positive role in autophagy.
Phosphoproteomics
Mass spectrometry-based phosphoproteomics can quantify changes in downstream phosphorylation events (e.g., Akt, S6K) upon modulation of class IA PI3K activity, providing a global view of pathway output.
Lipidomics
Measurement of PIP3 levels by lipidomics or biosensors (e.g., GFP-AktPH) directly assesses class IA PI3K activity in live cells or tissues.
Co-immunoprecipitation
Co-immunoprecipitation followed by western blotting can confirm the assembly of p110-p85 heterodimers and interactions with other proteins such as Galpha16.
How CRISPR Can Be Used to Study GO:0005943 phosphatidylinositol 3-kinase complex, class IA
Knockout
CRISPR knockout of PIK3CA, PIK3CB, or PIK3R1 is used to study loss-of-function phenotypes. For example, PIK3CB knockout reduces autophagy, confirming its positive regulatory role. Knockout of PIK3CA in cancer cell lines can reduce Akt phosphorylation and inhibit proliferation.
Point Mutation
Point mutation knock-in models, such as the common PIK3CA H1047R or E545K mutations, recapitulate oncogenic activation and are valuable for testing targeted inhibitors.
Knock-in
Knock-in of tagged versions of p110 or p85 (e.g., GFP or HA tags) allows for live-cell imaging and proteomic analysis of the complex.
Overexpression
Overexpression of wild-type or mutant class IA PI3K subunits in cell lines can drive constitutive pathway activation and is used to model gain-of-function states.
How EDITGENE Supports phosphatidylinositol 3-kinase complex, class IA Research
Researchers studying phosphatidylinositol 3-kinase complex, class IA-related genes often need to determine whether a candidate gene is causally involved in pathway regulation, disease progression, or drug response. Precise genetic models are essential to move from correlation to causation.
Contact EDITGENE today to design your custom CRISPR model for phosphatidylinositol 3-kinase complex, class IA research.
Frequently Asked Questions About phosphatidylinositol 3-kinase complex, class IA
What is GO:0005943?
GO:0005943 is the Gene Ontology term for the phosphatidylinositol 3-kinase complex, class IA, a heterodimeric enzyme that phosphorylates phosphatidylinositol-4-phosphate to generate PIP3.
What genes are involved in phosphatidylinositol 3-kinase complex, class IA?
Key genes include PIK3CA, PIK3CB, PIK3CD (catalytic subunits) and PIK3R1, PIK3R2, PIK3R3 (regulatory subunits).
What is the function of class IA PI3K?
It transduces signals from tyrosine kinase receptors to downstream effectors like Akt, regulating cell growth, survival, and metabolism.
How is class IA PI3K activated?
It is recruited to activated receptors via SH2 domains of the p85 regulatory subunit, which relieves inhibition of the p110 catalytic subunit.
What diseases are associated with class IA PI3K mutations?
Mutations are linked to cancers such as non-small cell lung cancer, bladder cancer, and uterine cancer, as well as metabolic disorders.
What is the role of p110beta in autophagy?
p110beta is a positive regulator of autophagy, as shown by knockout studies.
How does class IA PI3K affect insulin secretion?
In pancreatic beta cells, class IA PI3K controls insulin secretion through multiple mechanisms.
Can class IA PI3K be targeted for cancer therapy?
Yes, several PI3K inhibitors are in clinical use or trials, but isoform selectivity and resistance remain challenges.
What is the difference between class IA and class IB PI3K?
Class IA PI3K is activated by tyrosine kinase receptors via p85, while class IB is activated by G-protein-coupled receptors.
How can CRISPR help study class IA PI3K?
CRISPR knockout, point mutation, and knock-in models allow precise manipulation of PI3K genes to study their roles in signaling and disease.
Conclusion
The phosphatidylinositol 3-kinase complex, class IA (GO:0005943) is a pivotal signaling hub that integrates extracellular cues into diverse cellular responses. Its dysregulation underlies numerous diseases, particularly cancer and metabolic disorders. Continued research using advanced CRISPR models and multi-omics approaches will further illuminate its biology and therapeutic potential.
References
- 1. Zheng X et al.. 2024. G3BP1 and SLU7 Jointly Promote Immune Evasion by Downregulating MHC-I via PI3K/Akt Activation in Bladder Cancer.. Adv Sci (Weinh) 11(7):e2305922 PMID: 38084438
- 2. Kübler K et al.. 2025. Tamoxifen induces PI3K activation in uterine cancer.. Nat Genet 57(9):2192-2202 PMID: 40846762
- 3. Dou Z et al.. 2010. The class IA phosphatidylinositol 3-kinase p110-beta subunit is a positive regulator of autophagy.. J Cell Biol 191(4):827-43 PMID: 21059846
- 4. Backer JM. 2010. The regulation of class IA PI 3-kinases by inter-subunit interactions.. Curr Top Microbiol Immunol 346:87-114 PMID: 20544340
- 5. Yeung WW et al.. 2010. Galpha16 interacts with Class IA phosphatidylinositol 3-kinases and inhibits Akt signaling.. Cell Signal 22(9):1379-87 PMID: 20471473
- 6. Kaneko K et al.. 2010. Class IA phosphatidylinositol 3-kinase in pancreatic β cells controls insulin secretion by multiple mechanisms.. Cell Metab 12(6):619-32 PMID: 21109194
- 7. Solomon B et al.. 2009. Class IA phosphatidylinositol 3-kinase signaling in non-small cell lung cancer.. J Thorac Oncol 4(7):787-91 PMID: 19550242
- 8. Foukas LC et al.. 2004. Direct interaction of major histocompatibility complex class II-derived peptides with class Ia phosphoinositide 3-kinase results in dose-dependent stimulatory effects.. J Biol Chem 279(9):7505-11 PMID: 14660637
