PIK3CB encodes the catalytic subunit beta (p110β) of phosphatidylinositol 3-kinase (PI3K), a key enzyme in the PI3K/AKT signaling pathway. PI3K catalyzes the phosphorylation of phosphatidylinositol (4,5)-bisphosphate (PIP2) to generate phosphatidylinositol (3,4,5)-trisphosphate (PIP3), a critical second messenger that activates AKT (also known as PKB) and downstream signaling cascades. [@franke2007]
PIK3CB is a class IA PI3K catalytic subunit that plays essential roles in:
- Signal transduction in response to growth factors, neurotrophins, and cytokines
- Neuronal survival through AKT-mediated anti-apoptotic pathways
- Synaptic plasticity controlling learning and memory
- mTOR signaling regulating protein synthesis and autophagy
- Cell migration and cytoskeletal reorganization
The PIK3CB isoform has distinct functions from other class I PI3K catalytic subunits (p110α, p110γ, p110δ) and is particularly important in neuronal function and neurodegenerative diseases. [@yang2014]
| Property |
Value |
Reference |
| Gene Symbol |
PIK3CB |
|
| Full Name |
Phosphatidylinositol-4,5-bisphosphate 3-kinase Catalytic Subunit Beta |
|
| Alternative Names |
PI3Kβ, p110β |
|
| Chromosomal Location |
22q13.33 |
|
| NCBI Gene ID |
5293 |
|
| Ensembl ID |
ENSG00000077150 |
|
| UniProt ID |
Q14184 |
|
PIK3CB (p110β) is a ~1048 amino acid protein composed of several functional domains:
¶ N-Terminal Domains
- Adapter-Binding Domain (ABD): Mediates interaction with regulatory subunits (p85)
- C2 Domain: Binds to lipid membranes and is involved in substrate positioning
- Helical Domain: Provides structural framework for catalytic activity
- Kinase Domain: The catalytic core that transfers phosphate groups from ATP to PIP2
- p85 Interaction Interface: The N-terminal SH2 domain (nSH2) and inter-SH2 (iSH2) domain of p85 regulatory subunit bind to p110β, regulating its activity
- Phosphorylation Sites: Multiple tyrosine and serine/threonine phosphorylation sites regulate activity
The p110β isoform has unique functions compared to p110α:
- GPCR coupling: More efficiently coupled to G-protein coupled receptors
- RTK signaling: Can be activated by receptor tyrosine kinases independently of p85
- Cell type specificity: Higher expression in certain tissues including brain
The PI3K/AKT pathway is a major signaling cascade in neurons:
- Receptor Activation: Growth factors (e.g., BDNF, NGF), insulin, or cytokines bind to their cognate receptors
- PI3K Activation: Activated receptors recruit PI3K (p85/p110 complex) to the membrane
- PIP3 Generation: PIK3CB catalyzes PIP2 → PIP3 conversion
- AKT Recruitment: PH domain of AKT binds PIP3 at the membrane
- AKT Activation: PDK1 and mTORC2 phosphorylate and activate AKT
- Downstream Effects: AKT phosphorylates numerous targets affecting survival, growth, and plasticity
Neuronal Survival
- AKT phosphorylates and inhibits pro-apoptotic proteins (Bad, Caspase-9)
- Activates NF-κB transcription factor promoting survival genes
- Inhibits GSK-3β, reducing tau hyperphosphorylation [@song2012]
Synaptic Plasticity
- Modulates NMDA receptor trafficking and function
- Regulates AMPA receptor insertion at synapses
- Controls local protein synthesis at dendritic spines [@hu2019]
Dendritic Development
- Regulates cytoskeletal dynamics through Rac1, Cdc42
- Controls dendritic branching and spine morphogenesis
- Influences axonal guidance and growth
Autophagy Regulation
- mTOR activation by AKT inhibits autophagy
- PI3K/AKT/mTOR pathway balances protein synthesis and degradation
- Dysregulation contributes to protein aggregate accumulation in neurodegeneration
- Neurons: High expression in cortex, hippocampus, basal ganglia
- Astrocytes: Modulates metabolic support and neuroinflammation
- Microglia: Regulates inflammatory responses
- Oligodendrocytes: Controls myelination and survival
| Brain Region |
Expression Level |
Function |
| Cerebral Cortex |
High |
Synaptic plasticity, learning |
| Hippocampus |
High |
Memory formation, neuronal survival |
| Basal Ganglia |
Moderate |
Motor control, dopaminergic signaling |
| Cerebellum |
Moderate |
Motor learning |
| Brainstem |
Low-Moderate |
Autonomic functions |
PIK3CB is widely expressed throughout the CNS and PNS, with particularly important roles in dopaminergic neurons of the substantia nigra.
PIK3CB is significantly implicated in AD pathogenesis:
-
Amyloid-beta effects: Aβ reduces PI3K/AKT signaling, contributing to neuronal death. [@barlow2006] Amyloid deposition disrupts the normal PI3K cascade, creating a vicious cycle of neurodegeneration.
-
Tau phosphorylation: AKT regulates GSK-3β activity, which in turn controls tau hyperphosphorylation. Impaired PI3K/AKT signaling leads to excessive tau pathology. [@song2012]
-
Synaptic dysfunction: PI3K/AKT is crucial for synaptic plasticity and memory formation. Reduced signaling contributes to cognitive decline. [@hu2019]
-
Neuronal survival: The neuroprotective effects of PI3K/AKT are compromised in AD, making neurons more vulnerable to apoptotic stimuli. [@cao2009]
-
Therapeutic implications: Enhancing PI3K/AKT signaling is considered a potential therapeutic strategy for AD. [@kumar2018]
-
Dopaminergic neuron survival: PI3K/AKT signaling is critical for survival of dopaminergic neurons in the substantia nigra. Alterations in this pathway contribute to PD pathogenesis.
-
GWAS associations: Genetic variants near PIK3CB have been implicated in PD risk in genome-wide association studies.
-
Neuroprotection: PI3K activators have shown promise in protecting dopaminergic neurons in preclinical models.
-
α-Synuclein pathology: PI3K/AKT signaling may be affected by α-synuclein aggregation, though the relationship is complex.
-
Motor neuron survival: PI3K/AKT pathway is important for motor neuron survival. Dysregulation occurs in both familial and sporadic ALS.
-
Growth factor signaling: Impaired signaling in response to neurotrophic factors (BDNF, GDNF) contributes to motor neuron degeneration.
-
mTOR dysregulation: Altered mTOR signaling affects autophagy, potentially leading to accumulation of toxic protein aggregates.
-
Energy metabolism: PI3K/AKT regulates cellular energy metabolism, which is perturbed in ALS.
- Stroke/ischemia: PI3K/AKT mediates neuroprotective effects of preconditioning and growth factors
- Traumatic brain injury: Enhanced PI3K signaling promotes recovery
- Epilepsy: Altered PI3K signaling affects neuronal excitability
- Intellectual disability: PI3K signaling crucial for neurodevelopment
While not the focus of NeuroWiki, PIK3CB has important roles in cancer:
- PTEN-deficient cancers: When PTEN (negative regulator of PI3K) is lost, cancers become dependent on PIK3CB. [@hollander2011]
- Glioblastoma: PIK3CB promotes survival of glioblastoma cells. [@winkler2017]
- Resistance to therapy: PIK3CB can confer resistance to PI3Kα inhibitors. [@jia2016]
graph TD
A["Growth Factors (BDNF, NGF)"] --> B["RTK/GPCR"]
B --> C["PI3K Regulatory (p85)"]
C --> D["PIK3CB (p110β)"]
D --> E["PIP2"]
E --> F["PIP3"]
F --> G["AKT/PKB"]
G --> H1["mTORC1 (Protein Synthesis)"]
G --> H2["GSK-3β (Tau Phosphorylation)"]
G --> H3["Bad (Apoptosis)"]
G --> H4["NF-κB (Survival Genes)"]
H1 --> I1["Autophagy Inhibition"]
H1 --> I2["Synaptic Plasticity"]
H2 --> I3["Tau Pathology"]
H3 --> I4["Neuronal Survival"]
J["Aβ Plaques"] -->|"Inhibit"| K["PI3K/AKT"]
K -->|"Reduce"| G
G -->|"Reduce"| I4
style A fill:#f3e5f5
style F fill:#9f9
style J fill:#ffcdd2
style I4 fill:#ffcdd2
PIK3CB is a therapeutic target in multiple contexts:
| Agent |
Type |
Status |
Notes |
| AZD8186 |
PIK3CB inhibitor |
Preclinical/Phase I |
Cancer trials, neurological potential |
| GSK2636771 |
PIK3CB inhibitor |
Phase I/II |
Cancer applications |
| PF-04691502 |
Dual PI3K/mTOR |
Research |
CNS penetration issues |
- Blood-brain barrier: Achieving sufficient brain penetration remains challenging
- Isoform selectivity: Developing selective PIK3CB inhibitors vs. other isoforms
- Dose optimization: Balancing efficacy with metabolic side effects
- Timing: Optimal intervention point in disease progression
- Combination therapy: Synergy with other AD/PD therapeutics
- PI3K activators: Small molecules that enhance PI3K/AKT signaling
- AKT agonists: Direct AKT activators bypassing PI3K
- mTOR modulators: Adjusting the downstream balance between synthesis and autophagy
- Neurotrophic factors: BDNF or GDNF mimetics that activate PI3K
- Isoform-specific functions: Understanding distinct roles of p110β vs. other class I PI3Ks in neurons
- GPCR coupling: PIK3CB's role in mediating neurotransmitter effects
- Subcellular localization: PI3K signaling microdomains in neurons
- Optogenetics: Light-controlled PI3K signaling probes
- Biomarkers: PIP3/AKT pathway activity markers in CSF
- What are the precise molecular mechanisms by which PIK3CB loss contributes to neurodegeneration?
- Can selective PIK3CB modulation provide neuroprotection without cancer risk?
- What is the optimal timing for intervention in AD/PD progression?
- How do different neuronal cell types depend on PIK3CB signaling?
- Song et al., PI3K/Akt signaling in Alzheimer's disease (2012)
- Franke, PI3K/Akt: getting it right matters (2007)
- Brachmann et al., Phosphoinositide 3-kinase signaling in neuronal development (2005)
- Barlow et al., PI3K in Alzheimer's disease amyloid metabolism (2006)
- Cao et al., PI3K/Akt signaling in neuroprotection and neuronal death (2009)
- Yang et al., Class I PI3K isoforms in neuronal development (2014)
- Miller et al., Phosphoinositide 3-kinase in brain disease (2011)
- Friessel et al., PIK3CB promotes oesophageal cancer proliferation (2024)
- Lee et al., PI3K beta in cancer biology and therapy (2022)
- Jia et al., PIK3CB confers resistance to PI3K inhibition (2016)
- Hollander et al., PTEN-deficient cancers depend on PIK3CB (2011)
- Winkler et al., PI3Kβ is required for glioblastoma cell survival (2017)
- Thornton et al., The role of PI3Kβ in neuronal signaling (2016)
- Hu et al., PI3K/AKT pathway in synaptic plasticity and memory (2019)
- Kumar et al., Targeting PI3K signaling in Alzheimer's disease (2018)