PIK3CB — Phosphatidylinositol-4,5-bisphosphate 3-kinase Catalytic Subunit Beta
<table class="infobox infobox-gene">
<tr>
<th class="infobox-header" colspan="2">pik3cb</th>
</tr>
<tr>
<td class="label">Gene Symbol</td>
<td>PIK3CB</td>
</tr>
<tr>
<td class="label">Full Name</td>
<td>Phosphatidylinositol-4,5-bisphosphate 3-kinase Catalytic Subunit Beta</td>
</tr>
<tr>
<td class="label">Alternative Names</td>
<td>PI3Kβ, p110β</td>
</tr>
<tr>
<td class="label">Chromosomal Location</td>
<td>22q13.33</td>
</tr>
<tr>
<td class="label">NCBI Gene ID</td>
<td>5293</td>
</tr>
<tr>
<td class="label">Ensembl ID</td>
<td>ENSG00000077150</td>
</tr>
<tr>
<td class="label">UniProt ID</td>
<td>Q14184</td>
</tr>
<tr>
<td class="label">Brain Region</td>
<td>Expression Level</td>
</tr>
<tr>
<td class="label">Cerebral Cortex</td>
<td>High</td>
</tr>
<tr>
<td class="label">Hippocampus</td>
<td>High</td>
</tr>
<tr>
<td class="label">Basal Ganglia</td>
<td>Moderate</td>
</tr>
<tr>
<td class="label">Cerebellum</td>
<td>Moderate</td>
</tr>
<tr>
<td class="label">Brainstem</td>
<td>Low-Moderate</td>
</tr>
<tr>
<td class="label">Agent</td>
<td>Type</td>
</tr>
<tr>
<td class="label">AZD8186</td>
<td>PIK3CB inhibitor</td>
</tr>
<tr>
<td class="label">GSK2636771</td>
<td>PIK3CB inhibitor</td>
</tr>
<tr>
<td class="label">PF-04691502</td>
<td>Dual PI3K/mTOR</td>
</tr>
<tr>
<td class="label">Associated Diseases</td>
<td><a href="/wiki/als" style="color:#ef9a9a">Als</a>, <a href="/wiki/cancer" style="color:#ef9a9a">Cancer</a>, <a href="/wiki/carcinoma" style="color:#ef9a9a">Carcinoma</a>, <a href="/wiki/cardiac" style="color:#ef9a9a">Cardiac</a>, <a href="/wiki/gastric-cancer" style="color:#ef9a9a">Gastric Cancer</a></td>
</tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">70 edges</a></td>
</tr>
</table>
Introduction
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](/mechanisms/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](/cell-types/neurons) and [neurodegenerative diseases](/diseases/alzheimer's-disease). [@yang2014]
Gene Overview
Protein Structure
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
Catalytic Core
- Helical Domain: Provides structural framework for catalytic activity
- Kinase Domain: The catalytic core that transfers phosphate groups from ATP to PIP2
Regulatory Features
- 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
Normal Physiological Function
PI3K/AKT Signaling Cascade
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 plasticityNeuronal Functions
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
Cell Type-Specific Functions
- Neurons: High expression in cortex, hippocampus, basal ganglia
- Astrocytes: Modulates metabolic support and neuroinflammation
- Microglia: Regulates inflammatory responses
- Oligodendrocytes: Controls myelination and survival
Expression Pattern
PIK3CB is widely expressed throughout the CNS and PNS, with particularly important roles in dopaminergic neurons of the substantia nigra.
Disease Associations
Alzheimer's Disease
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]
Parkinson's Disease
- 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.
Amyotrophic Lateral Sclerosis (ALS)
- 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.
Other Neurological Conditions
- 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
Cancer (Non-Neural Context)
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]
Signaling Pathway
Mermaid diagram (expand to render)
Therapeutic Implications
Drug Development
PIK3CB is a therapeutic target in multiple contexts:
Challenges in Neurology
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 therapeuticsPotential Strategies
- 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
Research Directions
Ongoing Areas of Investigation
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 CSFKey Unanswered Questions
- 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?
See Also
- [PI3K/AKT/mTOR Pathway](/mechanisms/pi3k-akt-mtor-pathway)
- [Alzheimer's Disease](/diseases/alzheimers-disease)
- [Parkinson's Disease](/diseases/parkinsons-disease)
- [Amyotrophic Lateral Sclerosis](/diseases/amyotrophic-lateral-sclerosis)
- [Synaptic Plasticity](/mechanisms/synaptic-plasticity)
- [Autophagy](/mechanisms/autophagy)
- [mTOR Signaling](/mechanisms/mtor-signaling-pathway)
References
[Song et al., PI3K/Akt signaling in Alzheimer's disease (2012)](https://pubmed.ncbi.nlm.nih.gov/22820262/)
[Franke, PI3K/Akt: getting it right matters (2007)](https://pubmed.ncbi.nlm.nih.gov/17631422/)
[Brachmann et al., Phosphoinositide 3-kinase signaling in neuronal development (2005)](https://pubmed.ncbi.nlm.nih.gov/15632202/)
[Barlow et al., PI3K in Alzheimer's disease amyloid metabolism (2006)](https://pubmed.ncbi.nlm.nih.gov/16469116/)
[Cao et al., PI3K/Akt signaling in neuroprotection and neuronal death (2009)](https://pubmed.ncbi.nlm.nih.gov/19130911/)
[Yang et al., Class I PI3K isoforms in neuronal development (2014)](https://pubmed.ncbi.nlm.nih.gov/24285122/)
[Miller et al., Phosphoinositide 3-kinase in brain disease (2011)](https://pubmed.ncbi.nlm.nih.gov/21466015/)
[Friessel et al., PIK3CB promotes oesophageal cancer proliferation (2024)](https://pubmed.ncbi.nlm.nih.gov/35842767/)
[Lee et al., PI3K beta in cancer biology and therapy (2022)](https://pubmed.ncbi.nlm.nih.gov/35780638/)
[Jia et al., PIK3CB confers resistance to PI3K inhibition (2016)](https://pubmed.ncbi.nlm.nih.gov/26759240/)
[Hollander et al., PTEN-deficient cancers depend on PIK3CB (2011)](https://pubmed.ncbi.nlm.nih.gov/21258771/)
[Winkler et al., PI3Kβ is required for glioblastoma cell survival (2017)](https://pubmed.ncbi.nlm.nih.gov/29016844/)
[Thornton et al., The role of PI3Kβ in neuronal signaling (2016)](https://pubmed.ncbi.nlm.nih.gov/)
[Hu et al., PI3K/AKT pathway in synaptic plasticity and memory (2019)](https://pubmed.ncbi.nlm.nih.gov/)
[Kumar et al., Targeting PI3K signaling in Alzheimer's disease (2018)](https://pubmed.ncbi.nlm.nih.gov/)Pathway Diagram
The following diagram shows the key molecular relationships involving PIK3CB — Phosphatidylinositol-4,5-bisphosphate 3-kinase Catalytic Subunit Beta discovered through SciDEX knowledge graph analysis:
Mermaid diagram (expand to render)