PP2A Protein (Protein Phosphatase 2A)

PP2A Protein — Protein Phosphatase 2A (PP2A)

Introduction

Protein Phosphatase 2A (PP2A) is a major serine/threonine phosphatase that accounts for the majority of cellular phosphatase activity in eukaryotes. Encoded by the [PPP2CA](/genes/ppp2ca) gene (catalytic subunit), PP2A is a heterotrimeric enzyme consisting of a catalytic C subunit, a structural A subunit, and a regulatory B subunit. This combination creates a diverse family of holoenzymes with distinct substrate specificities and cellular functions [1](https://pubmed.ncbi.nlm.nih.gov/10828776/). In the nervous system, PP2A plays critical roles in synaptic plasticity, neuronal signaling, and tau phosphorylation regulation. Importantly, PP2A activity is significantly reduced in [Alzheimer's Disease](/diseases/alzheimers-disease) and other neurodegenerative disorders, contributing to the hyperphosphorylation of [tau](/proteins/tau) and other pathological features [2](https://pubmed.ncbi.nlm.nih.gov/10828773/).

PP2A Protein — Protein Phosphatase 2A (PP2A)

Introduction

Protein Phosphatase 2A (PP2A) is a major serine/threonine phosphatase that accounts for the majority of cellular phosphatase activity in eukaryotes. Encoded by the [PPP2CA](/genes/ppp2ca) gene (catalytic subunit), PP2A is a heterotrimeric enzyme consisting of a catalytic C subunit, a structural A subunit, and a regulatory B subunit. This combination creates a diverse family of holoenzymes with distinct substrate specificities and cellular functions [1](https://pubmed.ncbi.nlm.nih.gov/10828776/). In the nervous system, PP2A plays critical roles in synaptic plasticity, neuronal signaling, and tau phosphorylation regulation. Importantly, PP2A activity is significantly reduced in [Alzheimer's Disease](/diseases/alzheimers-disease) and other neurodegenerative disorders, contributing to the hyperphosphorylation of [tau](/proteins/tau) and other pathological features [2](https://pubmed.ncbi.nlm.nih.gov/10828773/).

<div class="infobox infobox-protein">
<table>
<tr><th colspan="2" style="background:#e8f4f8; text-align:center; font-size:1.1em;">PP2A Protein</th></tr>
<tr><td><strong>Protein Name</strong></td><td>Protein Phosphatase 2A (PP2A)</td></tr>
<tr><td><strong>Gene</strong></td><td>[PPP2CA](/genes/ppp2ca)</td></tr>
<tr><td><strong>UniProt ID</strong></td><td>[P67775](https://www.uniprot.org/uniprot/P67775)</td></tr>
<tr><td><strong>PDB ID</strong></td><td>2IAE, 3DW8, 4X7W, 5O8L, 6N8U</td></tr>
<tr><td><strong>Molecular Weight</strong></td><td>~36 kDa (catalytic subunit)</td></tr>
<tr><td><strong>Subcellular Localization</strong></td><td>Cytoplasm, nucleus, synapses</td></tr>
<tr><td><strong>Protein Family</strong></td><td>Ser/Thr Phosphatase family</td></tr>
<tr><td><strong>Tissue Expression</strong></td><td>Ubiquitous, high in brain</td></tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">1 edges</a></td>
</tr>
</table>
</div>

Structure

Catalytic Subunit (PP2Ac)

• Metal-binding motif: Two metal ions (typically Fe²⁺ and Zn²⁺) coordinated by conserved residues in the active site
• Active site pocket: Contains the signature motif GDYGHG (residues 124-129)
• C-terminal tail: Contains a mobile region involved in regulatory interactions

Structural Subunit (PPP2R1A/PPP2R1B)

• Contains 15 tandem HEAT repeats
• Provides binding sites for both C and B subunits
• Mediates interactions with other regulatory proteins

Regulatory Subunit (B Subunit)

• B (PPP2R2A): Neuronal isoform, enriched in brain
• B' (PPP2R5 family): Various isoforms with distinct tissue distributions
• B'' (PPP2R3 family): Calcium-binding subunits

Holoenzyme Assembly

This combinatorial assembly creates over 60 different PP2A holoenzymes with distinct functions [3](https://pubmed.ncbi.nlm.nih.gov/8621523/).

Normal Function in the Nervous System

Tau Dephosphorylation

• Dephosphorylates tau at over 30 serine/threonine sites
• Maintains tau in a functional, hypophosphorylated state
• Critical for microtubule stability and axonal transport [4](https://pubmed.ncbi.nlm.nih.gov/10828773/)

Synaptic Plasticity

• Long-term potentiation (LTP): PP2A activity modulates LTP induction and maintenance
• Long-term depression (LTD): Required for certain forms of LTD
• AMPA receptor trafficking: Regulates receptor internalization and recycling
• NMDA receptor signaling: Modulates receptor function and downstream signaling [5](https://pubmed.ncbi.nlm.nih.gov/21930975/)

Signal Transduction

• AKT/PKB: Negative regulator of cell survival pathways
• MAPK/ERK: Modulates growth factor signaling
• mTOR: Regulates translation and growth pathways
• GSK-3β: Counteracts tau kinase activity

Gene Expression

• Dephosphorylates CREB, affecting memory-related gene expression
• Modulates NF-κB signaling and inflammatory responses
• Regulates RNA polymerase II activity

Role in Alzheimer's Disease

PP2A dysfunction is a central event in AD pathogenesis:

Reduced PP2A Activity

Consequences of PP2A Dysfunction

Tau Hyperphosphorylation
Reduced PP2A activity leads to tau hyperphosphorylation:

• Neurofibrillary tangle formation
• Microtubule disruption
• Axonal transport defects [7](https://pubmed.ncbi.nlm.nih.gov/18203161/)

• Impaired LTP/LTD
• Reduced spine density
• Memory deficits

• Lower PP2A promotes amyloidogenic path
• May increase Aβ production

• Microglial activation
• Cytokine production
• Chronic inflammation

Evidence from Human Studies

• PP2A activity reduced by 30-50% in AD brains
• PP2A mRNA and protein levels altered
• Genetic variants in PPP2CA associated with AD risk [8](https://pubmed.ncbi.nlm.nih.gov/23455149/)

Role in Parkinson's Disease

PP2A is also implicated in PD pathogenesis:

Alpha-Synuclein Phosphorylation

• Phosphorylated Ser129 is a major pathological modification
• PP2A can dephosphorylate this site
• Reduced PP2A may contribute to pathological phosphorylation [9](https://pubmed.ncbi.nlm.nih.gov/18687675/)

Mitochondrial Function

• Modulates mitophagy pathways
• Affects mitochondrial dynamics
• Contributes to dopaminergic neuron vulnerability

Neuroprotection

• Reduces dopaminergic neuron death
• Improves behavioral outcomes
• May reduce alpha-synuclein toxicity [10](https://pubmed.ncbi.nlm.nih.gov/2680833/)

Role in Other Neurodegenerative Diseases

Huntington's Disease

• PP2A activity reduced in HD models
• Contributes to mutant huntingtin toxicity
• Targeting PP2A may be therapeutic [11](https://pubmed.ncbi.nlm.nih.gov/22846657/)

Amyotrophic Lateral Sclerosis

• Altered PP2A in motor neurons
• May contribute to protein aggregation
• Related to sporadic and familial ALS

Multiple Sclerosis

• PP2A regulates myelin gene expression
• Involved in oligodendrocyte function
• Potential therapeutic target

Therapeutic Targeting

PP2A Activators

| Compound | Status | Mechanism |
|----------|--------|-----------|
| Sodium selenate | Clinical trials | Direct PP2A activation |
| AVP-923 | Preclinical | Combination therapy |
| Novel small molecules | Preclinical | Direct activators |

Sodium Selenate

• Increases PP2A activity in the brain
• Reduces tau phosphorylation in models
• Currently in clinical trials for AD [12](https://pubmed.ncbi.nlm.nih.gov/3197834/)

Challenges and Considerations

Interaction Network

Direct Protein Partners

| Partner Protein | Interaction Type | Functional Consequence |
|-----------------|-----------------|------------------------|
| Tau | Dephosphorylation | Microtubule stability |
| Alpha-synuclein | Dephosphorylation | Aggregation control |
| AKT | Dephosphorylation | Cell survival regulation |
| GSK-3β | Regulation | Tau kinase activity |
| NMDA Receptor | Dephosphorylation | Synaptic signaling |

Signaling Pathways

Clinical Trials

Several clinical trials are investigating PP2A-targeting approaches:

• Sodium selenate in AD: Phase II completed; showed reduced tau pathology
• Sodium selenate in TBI: Phase I/II trial
• Novel activators: Preclinical development

Key Publications

See Also

• [PPP2CA Gene](/genes/ppp2ca)
• [Tau Protein](/proteins/tau)
• [Alpha-Synuclein](/proteins/alpha-synuclein)
• [Alzheimer's Disease](/diseases/alzheimers-disease)
• [Parkinson's Disease](/diseases/parkinsons-disease)
• [Tau Phosphorylation Pathway](/mechanisms/tau-phosphorylation)
• [Synaptic Plasticity](/mechanisms/synaptic-plasticity)

References