GO:0005944 phosphatidylinositol 3-kinase complex, class IB: Components, Assembly and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:0005944 defines the class IB phosphatidylinositol 3-kinase (PI3K) complex, a heterodimer of a p110γ catalytic subunit and a p84/p101 regulatory subunit, activated by G-protein-coupled receptors.
• Unlike class IA PI3Ks, the class IB complex lacks SH2 domains and is stimulated by Gβγ subunits and Ras, making it a key effector of GPCR signaling in immune cells.
• The class IB PI3K complex is critical for neutrophil chemotaxis, B cell antibody responses, and dendritic cell cross-presentation.
• Dysregulated class IB PI3K signaling contributes to hematological malignancies and solid tumors, with noncanonical PI3Kγ signaling identified as a targetable dependency in leukemia.
• Studying this complex requires precise genetic models; CRISPR knockout, point mutation, and knock-in approaches enable dissection of its cell-type-specific functions.
• Key research methods include phosphoinositide lipid profiling, chemotaxis assays, and immunophenotyping to link class IB PI3K activity to immune cell behavior.
Description
The phosphatidylinositol 3-kinase complex, class IB (GO:0005944) is a cellular component defined by its unique subunit composition and activation mechanism. It consists of a catalytic class IB phosphoinositide 3-kinase (PI3K) subunit, typically p110γ, bound to a regulatory subunit such as p84 or p101 that is larger than and unrelated to the p85 proteins found in class IA complexes. This complex is a key transducer of signals from G-protein-coupled receptors (GPCRs) and is particularly important in immune cells. Understanding its structure and function is essential for researchers studying immune cell signaling, inflammation, and cancer. The class IB PI3K complex is distinguished by its activation through G-protein βγ subunits and Ras, rather than through phosphotyrosine motifs that recruit class IA PI3Ks. This unique activation mode positions it as a central node in chemokine and cytokine signaling pathways. In neutrophils, for example, class IB PI3K is required for directed migration toward chemoattractants. In B cells, it promotes antibody responses and the generation of antibody-secreting cells. Recent studies have also highlighted its role in dendritic cell cross-presentation and in leukemia, where noncanonical PI3Kγ signaling supports leukemic cell survival. Given its involvement in both normal immunity and disease, the class IB PI3K complex is a subject of intense research, with CRISPR-based models offering powerful tools to dissect its functions.
phosphatidylinositol 3-kinase complex, class IB At A Glance
| GO ID | GO:0005944 |
|---|---|
| GO term | phosphatidylinositol 3-kinase complex, class IB |
| Ontology | cellular_component |
| Synonym | 1-phosphatidylinositol-4-phosphate 3-kinase, class IB complex; class IB PI3K complex; phosphoinositide 3-kinase complex, class IB |
| Major function | Phosphorylates phosphatidylinositol-4-phosphate to generate phosphatidylinositol-3,4,5-trisphosphate in response to GPCR activation |
| Catalytic subunit | p110γ (PIK3CG) |
| Regulatory subunits | p84 (PIK3R6) and p101 (PIK3R5) |
| Activation mechanism | Stimulated by G-protein βγ subunits and Ras, independent of SH2-domain adaptors |
| Cell types | Immune cells including neutrophils, B cells, dendritic cells, and leukemic cells |
What Is GO:0005944?
GO:0005944 describes a class I phosphatidylinositol 3-kinase complex that possesses 1-phosphatidylinositol-4-phosphate 3-kinase activity. It comprises a catalytic class IB PI3K subunit and an associated regulatory subunit that is larger than, and unrelated to, the p85 proteins present in class IA complexes. Class IB PI3Ks are stimulated by G-proteins and do not interact with the SH2-domain containing adaptors that bind to class IA PI3Ks.
Why Is phosphatidylinositol 3-kinase complex, class IB Important in Cell Biology?
The class IB PI3K complex is a critical signaling hub that translates GPCR activation into lipid second messenger production, influencing immune cell migration, activation, and survival. Its unique subunit composition and activation mechanism distinguish it from class IA PI3Ks, making it a specialized target for therapeutic intervention in inflammatory diseases and cancer.
• Mediates GPCR-driven PI3K signaling in immune cells, controlling chemotaxis and inflammatory responses.
• Essential for neutrophil recruitment to sites of infection, as shown by defective chemotaxis in the absence of class IB PI3K.
• Promotes B cell antibody responses and the generation of antibody-secreting cells.
• Required for efficient cross-presentation by type 2 dendritic cells, linking innate and adaptive immunity.
• Supports leukemic cell survival through noncanonical PI3Kγ signaling, representing a potential therapeutic target.
• Its distinct regulatory subunits (p84/p101) provide opportunities for selective targeting over class IA PI3Ks.
• Involved in viral oncoprotein-driven survival mechanisms, as seen in Merkel cell carcinoma.
• Serves as a model for understanding G-protein-coupled phosphoinositide signaling.
What Happens During phosphatidylinositol 3-kinase complex, class IB?
Activation by G-protein-coupled receptors
In simple terms: When a chemokine or other signal binds to a GPCR, the released Gβγ subunits directly activate the class IB PI3K complex.
The class IB PI3K complex is primarily activated downstream of G-protein-coupled receptors (GPCRs). Upon ligand binding, GPCRs catalyze the exchange of GDP for GTP on Gα subunits, leading to dissociation of Gβγ dimers. These Gβγ subunits bind directly to the regulatory subunit (p84 or p101) of the class IB PI3K complex, relieving inhibition and stimulating the catalytic activity of p110γ. This mechanism contrasts with class IA PI3Ks, which are recruited via phosphotyrosine motifs on adaptor proteins. In neutrophils, GPCR-mediated activation of class IB PI3K is essential for chemotaxis toward chemoattractants such as fMLP and IL-8.
Catalytic conversion of PIP2 to PIP3
In simple terms: The active enzyme adds a phosphate group to a membrane lipid, creating a docking site for signaling proteins.
Once activated, the p110γ catalytic subunit phosphorylates phosphatidylinositol-4,5-bisphosphate (PIP2) at the 3-position of the inositol ring to generate phosphatidylinositol-3,4,5-trisphosphate (PIP3). PIP3 acts as a second messenger that recruits pleckstrin homology (PH) domain-containing proteins, such as Akt and Bruton's tyrosine kinase (BTK), to the membrane, propagating downstream signals that control cell survival, proliferation, and migration. The lipid kinase activity of the class IB complex is tightly regulated to ensure transient PIP3 production.
Downstream signaling to Akt and beyond
In simple terms: The lipid signal activates a cascade of proteins that tell the cell to move, grow, or survive.
PIP3 generated by the class IB PI3K complex recruits Akt to the plasma membrane, where it is phosphorylated and activated by PDK1 and mTORC2. Activated Akt then phosphorylates multiple substrates to promote cell survival, proliferation, and metabolism. In neutrophils, class IB PI3K-dependent Akt activation is required for chemokine-directed migration and respiratory burst. In B cells, this pathway supports antibody responses and the differentiation into antibody-secreting cells. Additionally, noncanonical PI3Kγ signaling in leukemia can activate alternative effectors that sustain leukemic cell survival.
Role in immune cell functions
In simple terms: This complex helps immune cells move to the right place and respond to threats.
The class IB PI3K complex is indispensable for various immune cell functions. In neutrophils, it mediates chemotaxis and the production of reactive oxygen species. In B cells, it promotes antibody responses and the generation of antibody-secreting cells, as shown by impaired responses in PI3Kγ-deficient mice. In type 2 dendritic cells, the p84/p110γ complex is specifically required for antibody-activated, inducible cross-presentation, a process critical for cytotoxic T cell activation. These diverse roles highlight the complex's importance in both innate and adaptive immunity.
Key Genes Involved in GO:0005944 phosphatidylinositol 3-kinase complex, class IB
The following genes encode the core subunits and key regulators of the class IB PI3K complex, as well as downstream effectors and associated signaling proteins.
| Gene | Major Role | Research Relevance |
|---|---|---|
| PIK3CG | Encodes the p110γ catalytic subunit of class IB PI3K | Knockout and point mutations reveal its role in immune cell signaling and leukemia |
| PIK3R5 | Encodes the p101 regulatory subunit | Modulates p110γ activity and GPCR coupling; knockout affects neutrophil chemotaxis |
| PIK3R6 | Encodes the p84 regulatory subunit | Required for cross-presentation in dendritic cells; knockout impairs T cell activation |
| GNA16 | Encodes Gα16, a G-protein alpha subunit | Interacts with class IA PI3Ks but not class IB; used to distinguish pathways |
| AKT1 | Serine/threonine kinase downstream of PIP3 | Phosphorylation status reflects class IB PI3K activity |
| BTK | Bruton's tyrosine kinase, a PIP3 effector | Mutations cause X-linked agammaglobulinemia; relevant to B cell signaling |
| PTEN | Lipid phosphatase that degrades PIP3 | Tumor suppressor; opposes class IB PI3K signaling |
| RAS | Small GTPase that can activate p110γ | Oncogenic mutations may cooperate with class IB PI3K in cancer |
| CXCR1 | Chemokine receptor coupled to Gβγ | Activates class IB PI3K in neutrophils |
| CXCR2 | Chemokine receptor coupled to Gβγ | Activates class IB PI3K in neutrophils |
| FPR1 | Formyl peptide receptor | Activates class IB PI3K in neutrophils |
| CD160 | Activating NK cell receptor | May signal through PI3K pathways in NK cells |
| KIT | Receptor tyrosine kinase | Viral oncoprotein-driven autophagy suppression involves PI3K signaling |
| PIK3CD | Encodes p110δ, a class IA PI3K | Contrasts with class IB; used in comparative studies |
| PIK3R1 | Encodes p85α, a class IA regulatory subunit | Distinguishes class IA from class IB complexes |
| GNAI2 | Gαi2 subunit | Inhibits adenylyl cyclase and modulates GPCR signaling to PI3K |
| GNAI3 | Gαi3 subunit | Similar to Gαi2, involved in GPCR-mediated PI3K activation |
| ARRB1 | Beta-arrestin 1 | Scaffolds GPCR-PI3K signaling complexes |
How Is phosphatidylinositol 3-kinase complex, class IB Regulated?
The class IB PI3K complex is regulated at multiple levels. Its activity is primarily controlled by GPCR-mediated release of Gβγ subunits, which bind and activate the p110γ catalytic subunit. Additionally, Ras GTPases can directly bind and activate p110γ, integrating signals from receptor tyrosine kinases. The regulatory subunits p84 and p101 modulate the sensitivity of p110γ to Gβγ and may influence subcellular localization. Negative regulation is exerted by lipid phosphatases such as PTEN, which dephosphorylates PIP3, and by protein phosphatases that inactivate Akt. Furthermore, the complex is subject to feedback inhibition through phosphorylation by downstream kinases like Akt and mTOR.
phosphatidylinositol 3-kinase complex, class IB and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| PIK3CG | Leukemia, inflammation | Knockout mice, point-mutation knock-in, patient-derived xenografts |
| PIK3R6 | Dendritic cell cross-presentation defects | Conditional knockout in murine DCs, knock-in of patient mutations |
| PIK3R5 | Neutrophil chemotaxis disorders | Knockout mice, chemotaxis assays |
| KIT | Merkel cell carcinoma | Viral oncoprotein-expressing cell lines, knockout of KIT |
| CD160 | NK cell dysfunction | Knockout NK cells, cytotoxicity assays |
Leukemia and hematological malignancies
Noncanonical PI3Kγ signaling supports leukemic cell survival and represents a targetable dependency in leukemia. Inhibition of PI3Kγ impairs leukemic cell growth and enhances the efficacy of conventional chemotherapy. This highlights the class IB PI3K complex as a potential therapeutic target in blood cancers.
Immune disorders and inflammation
Dysregulated class IB PI3K signaling contributes to inflammatory diseases. In B cells, PI3Kγ promotes antibody responses and the generation of antibody-secreting cells, and its overactivity may drive autoantibody production. In dendritic cells, the p84/p110γ complex is required for cross-presentation, and its dysfunction could impair anti-tumor immunity. Neutrophil chemotaxis defects in the absence of class IB PI3K lead to increased susceptibility to infections.
Merkel cell carcinoma
In Merkel cell carcinoma, a viral oncoprotein suppresses autophagy through Kit-mediated signaling that involves PI3K pathways. This survival mechanism may depend on class IB PI3K activity, suggesting that targeting this complex could be beneficial in this aggressive skin cancer.
From phosphatidylinositol 3-kinase complex, class IB-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| Does PIK3CG knockout impair neutrophil chemotaxis? | PIK3CG knockout mouse or human neutrophil-like cell line (e.g., HL-60) |
| How does the p84/p110γ complex support dendritic cell cross-presentation? | Conditional PIK3R6 knockout in murine type 2 DCs |
| Can point mutations in PIK3CG alter lipid kinase activity? | CRISPR knock-in of catalytic-dead or activating mutations in cell lines |
| What is the role of PIK3CG in B cell antibody responses? | B cell-specific knockout mice, immunization studies |
| Does overexpression of PIK3CG drive leukemic transformation? | Retroviral or CRISPR knock-in overexpression in hematopoietic stem cells |
| How does the class IB PI3K complex localize in live cells? | Tagged knock-in of PIK3CG with fluorescent protein in immune cells |
How to Study the phosphatidylinositol 3-kinase complex, class IB Process
| Method | What It Measures | Typical Application |
|---|---|---|
| Lipid kinase assay | Catalytic conversion of PIP2 to PIP3 | Assessing activity of wild-type vs mutant class IB PI3K |
| Chemotaxis assay | Directed cell migration | Evaluating neutrophil recruitment in knockout models |
| Flow cytometry | Immune cell populations and activation | Quantifying B cell and DC responses |
| ELISPOT | Antibody-secreting cells | Measuring B cell function in PI3Kγ-deficient mice |
| CRISPR knockout screening | Gene dependencies and synthetic lethality | Identifying targets in leukemia |
| Immunoprecipitation | Protein-protein interactions | Isolating class IB PI3K complex for activity assays |
| Live-cell imaging | Subcellular localization and dynamics | Tracking tagged p110γ in immune cells |
| Phospho-Akt immunoblotting | Akt activation status | Monitoring downstream signaling |
Lipid kinase assays
In vitro lipid kinase assays using immunoprecipitated class IB PI3K complex and radiolabeled ATP measure the conversion of PIP2 to PIP3. These assays are used to assess catalytic activity and the effects of mutations or inhibitors.
Chemotaxis and migration assays
Transwell or microfluidic chemotaxis assays evaluate the ability of neutrophils or other immune cells to migrate toward chemoattractants. These methods have been instrumental in demonstrating the requirement for class IB PI3K in directed cell migration.
Immunophenotyping and flow cytometry
Flow cytometry is used to assess immune cell populations, activation markers, and antibody production. For example, B cell responses and antibody-secreting cells can be quantified by ELISPOT and flow cytometry in models with class IB PI3K perturbations.
CRISPR screening and functional genomics
Genome-wide CRISPR knockout screens can identify genes that modulate class IB PI3K signaling or that are synthetically lethal with its loss. Such screens have revealed dependencies on noncanonical PI3Kγ signaling in leukemia.
How CRISPR Can Be Used to Study GO:0005944 phosphatidylinositol 3-kinase complex, class IB
Knockout
CRISPR knockout of PIK3CG, PIK3R5, or PIK3R6 in immune cell lines or primary cells ablates class IB PI3K complex function. This approach has been used to demonstrate the requirement for PI3Kγ in B cell antibody responses and neutrophil chemotaxis. Knockout models also help identify compensatory pathways and are valuable for validating drug targets.
Point Mutation
CRISPR-mediated point mutations can introduce catalytic-dead or constitutively active mutations in PIK3CG to dissect the specific contribution of its lipid kinase activity. For example, mutation of the ATP-binding lysine residue abolishes kinase activity, while mutations in the helical domain may alter regulation. Such models are crucial for understanding how noncanonical PI3Kγ signaling drives leukemia.
Knock-in
Knock-in of epitope tags (e.g., HA, FLAG) or fluorescent proteins (e.g., GFP) into the endogenous PIK3CG locus allows for real-time visualization and biochemical isolation of the class IB PI3K complex. This approach preserves endogenous regulation and has been used to study complex localization in immune cells.
Overexpression
CRISPR-mediated overexpression via knock-in of a strong promoter or cDNA insertion can elevate class IB PI3K levels to study gain-of-function effects. Overexpression of PIK3CG in hematopoietic cells has been used to model leukemogenesis and to test the oncogenic potential of the complex.
How EDITGENE Supports phosphatidylinositol 3-kinase complex, class IB Research
Researchers studying phosphatidylinositol 3-kinase complex, class IB-related genes often need to determine whether a candidate gene is causally involved in immune cell signaling, inflammation, or cancer. EDITGENE provides a comprehensive suite of CRISPR-based services to generate precisely engineered cell models, enabling rigorous functional studies of this complex.
Contact EDITGENE today to design your custom CRISPR model for phosphatidylinositol 3-kinase complex, class IB research.
Frequently Asked Questions About phosphatidylinositol 3-kinase complex, class IB
What is GO:0005944?
GO:0005944 is the Gene Ontology term for the phosphatidylinositol 3-kinase complex, class IB, a heterodimeric enzyme complex that phosphorylates PIP2 to PIP3 in response to GPCR activation.
What genes are involved in phosphatidylinositol 3-kinase complex, class IB?
The core genes are PIK3CG (encoding p110γ), PIK3R5 (p101), and PIK3R6 (p84). Other associated genes include GNA16, AKT1, and PTEN.
How is the class IB PI3K complex different from class IA?
Class IB PI3K is activated by G-protein βγ subunits and lacks SH2 domains, whereas class IA PI3Ks are recruited by phosphotyrosine motifs on adaptor proteins like p85.
What diseases are associated with class IB PI3K complex dysfunction?
Dysregulation is linked to leukemia, inflammatory diseases, and Merkel cell carcinoma, among others.
What is the role of PI3Kγ in immune cells?
PI3Kγ, the catalytic subunit of class IB PI3K, is essential for neutrophil chemotaxis, B cell antibody responses, and dendritic cell cross-presentation.
How can I study the class IB PI3K complex using CRISPR?
CRISPR knockout, point mutation, knock-in, and overexpression models can be generated to dissect its function in immune cells and cancer.
What are the regulatory subunits of class IB PI3K?
The regulatory subunits are p101 (PIK3R5) and p84 (PIK3R6), which are larger than and unrelated to the p85 proteins of class IA PI3Ks.
Is the class IB PI3K complex a drug target?
Yes, it is a promising target for leukemia and inflammatory diseases, with inhibitors like IPI-549 in clinical trials.
What methods are used to measure class IB PI3K activity?
Lipid kinase assays, phospho-Akt immunoblotting, chemotaxis assays, and CRISPR screens are commonly used.
What cell types express the class IB PI3K complex?
It is predominantly expressed in immune cells, including neutrophils, B cells, dendritic cells, and leukemic cells.
Conclusion
The phosphatidylinositol 3-kinase complex, class IB (GO:0005944) is a specialized signaling complex that plays pivotal roles in immune cell function and disease. Its unique activation by GPCRs and distinct subunit composition make it an attractive target for therapeutic intervention. Continued research using advanced CRISPR models will further elucidate its mechanisms and identify new treatment strategies.
References
- 1. Luo Q et al.. 2024. Targetable leukaemia dependency on noncanonical PI3Kγ signalling.. Nature 630(8015):198-205 PMID: 38720074
- 2. Lanahan SM et al.. 2024. PI3Kγ in B cells promotes antibody responses and generation of antibody-secreting cells.. Nat Immunol 25(8):1422-1431 PMID: 38961274
- 3. Koumantou D et al.. 2024. Specific Requirement of the p84/p110γ Complex of PI3Kγ for Antibody-Activated, Inducible Cross-Presentation in Murine Type 2 DCs.. Adv Sci (Weinh) 11(44):e2401179 PMID: 39382167
- 4. 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
- 5. Andrews S et al.. 2007. PI3K class IB pathway.. Sci STKE 2007(407):cm2 PMID: 17925573
- 6. Le Bouteiller P et al.. 2011. CD160: a unique activating NK cell receptor.. Immunol Lett 138(2):93-6 PMID: 21324341
- 7. Shi H et al.. 2025. Kit-mediated autophagy suppression driven by a viral oncoprotein emerges as a crucial survival mechanism in Merkel cell carcinoma.. Autophagy 21(7):1523-1543 PMID: 40108758
- 8. Andrews S et al.. 2007. PI3K class IB pathway in neutrophils.. Sci STKE 2007(407):cm3 PMID: 17925574
