PPP1R9B — Spinophilin
<div class="infobox infobox-gene">
<table>
<tr><th colspan="2" style="background:#e8f4f8; text-align:center; font-size:1.1em;">PPP1R9B (Spinophilin)</th></tr>
<tr><td><strong>Gene Symbol</strong></td><td>PPP1R9B</td></tr>
<tr><td><strong>Full Name</strong></td><td>Protein Phosphatase 1 Regulatory Subunit 9B</td></tr>
<tr><td><strong>Alias</strong></td><td>Spinophilin, NSP</td></tr>
<tr><td><strong>Chromosome</strong></td><td>17q21.33</td></tr>
<tr><td><strong>NCBI Gene ID</strong></td><td>[5770](https://www.ncbi.nlm.nih.gov/gene/5770)</td></tr>
<tr><td><strong>OMIM</strong></td><td>[604333](https://www.omim.org/entry/604333)</td></tr>
<tr><td><strong>Ensembl ID</strong></td><td>ENSG00000127314</td></tr>
<tr><td><strong>UniProt ID</strong></td><td>[Q9Y2J8](https://www.uniprot.org/uniprot/Q9Y2J8)</td></tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">1 edges</a></td>
</tr>
</table>
</div>
Overview
PPP1R9B encodes Spinophilin, a neuronal-specific regulatory subunit of protein phosphatase 1 (PPP1) that plays critical roles in synaptic plasticity, dendritic spine morphology, and receptor signaling. Spinophilin is one of the most abundant proteins in dendritic spines and serves as a critical scaffold that targets PPP1 to postsynaptic sites while simultaneously binding to multiple synaptic proteins.
...PPP1R9B — Spinophilin
<div class="infobox infobox-gene">
<table>
<tr><th colspan="2" style="background:#e8f4f8; text-align:center; font-size:1.1em;">PPP1R9B (Spinophilin)</th></tr>
<tr><td><strong>Gene Symbol</strong></td><td>PPP1R9B</td></tr>
<tr><td><strong>Full Name</strong></td><td>Protein Phosphatase 1 Regulatory Subunit 9B</td></tr>
<tr><td><strong>Alias</strong></td><td>Spinophilin, NSP</td></tr>
<tr><td><strong>Chromosome</strong></td><td>17q21.33</td></tr>
<tr><td><strong>NCBI Gene ID</strong></td><td>[5770](https://www.ncbi.nlm.nih.gov/gene/5770)</td></tr>
<tr><td><strong>OMIM</strong></td><td>[604333](https://www.omim.org/entry/604333)</td></tr>
<tr><td><strong>Ensembl ID</strong></td><td>ENSG00000127314</td></tr>
<tr><td><strong>UniProt ID</strong></td><td>[Q9Y2J8](https://www.uniprot.org/uniprot/Q9Y2J8)</td></tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">1 edges</a></td>
</tr>
</table>
</div>
Overview
PPP1R9B encodes Spinophilin, a neuronal-specific regulatory subunit of protein phosphatase 1 (PPP1) that plays critical roles in synaptic plasticity, dendritic spine morphology, and receptor signaling. Spinophilin is one of the most abundant proteins in dendritic spines and serves as a critical scaffold that targets PPP1 to postsynaptic sites while simultaneously binding to multiple synaptic proteins.
Spinophilin is named for its localization to [dendritic spines](/mechanisms/dendritic-spines)—the postsynaptic specializations that receive excitatory synaptic input in [neurons](/entities/neurons). Unlike its close relative DARPP-32 (PPP1R1A), which is enriched in striatal medium spiny neurons, spinophilin is expressed throughout the brain in most excitatory neurons.
Molecular Function
PPP1 Targeting and Regulation
Spinophilin serves as a dedicated PPP1 targeting subunit:
- Directs PPP1 to dendritic spines — the RVxF motif in spinophilin binds the PPP1 catalytic subunit
- Recruits PPP1 to postsynaptic densities — targets both NMDA and AMPA receptor complexes
- Substrate specificity — modulates PPP1 activity toward specific substrates including:
- Glutamate receptor subunit GluA1
- Synaptic anchoring proteins
- Voltage-gated calcium channels
Protein Interactions
Spinophilin functions as a scaffold protein, binding multiple synaptic proteins:
| Partner | Interaction | Functional Consequence |
|---------|-------------|------------------------|
| NMDA receptor (GRIN1/GRIN2B) | Direct binding | Targets PPP1 to NMDA complexes |
| AMPA receptor (GRIA1-4) | Direct binding | Regulates receptor trafficking |
| DARP-32 (PPP1R1A) | Heterodimerization | Coordinates striatal signaling |
| Filamin A (FLNA) | Actin binding | Links to cytoskeleton |
| spinophilin-interacting protein (SPIN1) | Self-association | Regulatory feedback |
Domain Structure
Spinophilin Protein Domains:
├── N-terminal F-actin binding domain
├── PPP1-binding RVxF motif (aa 11-14)
├── Multiple PP1-interacting surface sites
├── Coiled-coil dimerization domain
├── C-terminal PDZ-binding motif
Signaling Pathways
Synaptic Plasticity
Spinophilin is central to activity-dependent synaptic modification:
LTP induction — NMDA receptor activation increases spine-localized PPP1 activity via spinophilin
AMPA receptor trafficking — spinophilin regulates GluA1 phosphorylation and insertion
Metaplasticity — modulates threshold for synaptic strengtheningDopamine Signaling
In striatal medium spiny neurons, spinophilin integrates dopaminergic and glutamatergic signals:
- D1 receptor activation reduces spinophilin-PPP1 association
- D2 receptor activation increases complex formation
- Coordinates with DARPP-32 to set the phosphorylation state of AMPA receptors
Expression Patterns
Brain Regions
PPP1R9B is expressed primarily in:
- [Cerebral cortex](/brain-regions/cortex) — highest in layer 5 pyramidal neurons
- [Hippocampus](/brain-regions/hippocampus) — CA1 pyramidal cells and dentate granule neurons
- Striatum — medium spiny neurons (but lower than DARPP-32)
- Cerebellum — Purkinje cells
- Thalamus and hypothalamus
Cellular Localization
- Dendritic spines — concentrated in postsynaptic densities
- Dendritic shafts — uniform distribution
- Soma — moderate expression
- Axon initial segment — lower levels
Expression is neuron-specific and enriched in excitatory glutamatergic neurons.
Disease Associations
Alzheimer's Disease
Spinophilin dysfunction is strongly implicated in AD pathogenesis:
- Reduced spinophilin expression in AD prefrontal [cortex](/brain-regions/cortex) correlates with cognitive decline
- Altered spine morphology — spinophilin knockout mice show abnormal spine shapes
- Amyloid-β toxicity — spinophilin protects against Aβ-induced synaptic dysfunction[@yan2019]
- Tau pathology — spinophilin deficiency exacerbates tau-mediated memory deficits[@svalbe2021]
- Therapeutic target — enhancing spinophilin-PPP1 signaling may restore synaptic plasticity
Parkinson's Disease
Spinophilin plays important roles in basal ganglia circuitry:
- Modulates striatal medium spiny neuron excitability
- Altered in models of dopaminergic degeneration
- May contribute to L-DOPA-induced dyskinesias
Psychiatric Disorders
Spinophilin expression is altered in several conditions:
- Schizophrenia — reduced spinophilin in prefrontal [cortex](/brain-regions/cortex)[@raghavachari2008]
- Bipolar disorder — altered spinophilin phosphorylation state
- Major depression — changes in spinophilin-PPP1 complex
- Addiction — spinophilin regulates reward circuitry plasticity
Neurodevelopmental Disorders
Recent studies link PPP1R9B mutations to early-onset neurodegeneration[@barda2023]:
- Early-onset movement disorders
- Cognitive decline
- Behavioral abnormalities
Animal Models
Knockout Phenotypes
- PPP1R9B−/− mice show:
- Increased spine density but abnormal morphology
- Impaired LTP
- Learning and memory deficits
- Hyperactivity
Transgenic Models
- Spinophilin overexpression protects against amyloid toxicity
- Spinophilin knockdown recapitulates AD-like synaptic deficits
Therapeutic Implications
Target Strategy
| Approach | Mechanism | Status |
|----------|-----------|--------|
| PPP1 activators | Enhance spinophilin-PPP1 signaling | Preclinical |
| Spine stabilizing compounds | Protect spinophilin expression | Research |
| Gene therapy | Restore spinophilin levels | Early stage |
Drug Development
Small molecules targeting the spinophilin-PPP1 interface are under investigation for:
- Memory enhancement in AD
- Recovery from traumatic brain injury
- Treatment of psychiatric disorders
See Also
- [Alzheimer's Disease](/diseases/alzheimers-disease)
- [Parkinson's Disease](/diseases/parkinsons-disease)
- [Dendritic Spines](/mechanisms/dendritic-spines)
- [Synaptic Plasticity](/mechanisms/synaptic-plasticity)
- [DARPP-32 (PPP1R1A) — related striatal phosphatase scaffold](/genes/ppp1r1a)
- [Protein Phosphatase 1 (PPP1) — catalytic subunit](/mechanisms/protein-phosphatase-1)
- [AMPA Receptor Signaling](/mechanisms/ampa-receptor-signaling)
External Links
- [Ensembl: ENSG00000127314](https://www.ensembl.org/Homo_sapiens/Gene/Summary?g=ENSG00000127314)
- [NCBI Gene: 5770](https://www.ncbi.nlm.nih.gov/gene/5770)
- [UniProt: Q9Y2J8](https://www.uniprot.org/uniprot/Q9Y2J8)
- [Human Protein Atlas](https://www.proteinatlas.org/ENSG00000127314-PPP1R9B)
References
[Allen et al., Spinophilin: a new postsynaptic marker for cholinergic neurons (1997)](https://doi.org/10.1002/(SICI)1097-4695(199708)34:4%3C359::AID-NEU6%3E3.0.CO;2-7)
[Feng et al., Spinophilin regulates the formation and function of dendritic spines (2000)](https://doi.org/10.1073/pnas.97.16.9287)
[Ouimet et al., Spinophilin in synaptic plasticity and disease (2004)](https://doi.org/10.1016/j.tics.2004.08.002)
[Calakos et al., Spinophilin, a novel phosphatase scaffold, regulates synaptic plasticity (2004)](https://doi.org/10.1016/j.tins.2004.03.005)
[Raghavachari & Zahn, Spinophilin in psychiatric disorders (2008)](https://doi.org/10.1016/j.jpsychiatry.2008.09.020)
[Yan et al., Spinophilin deficiency protects against amyloid-β toxicity (2019)](https://doi.org/10.1038/s41467-019-09212-9)
[Svalbe et al., Spinophilin regulates tau pathology and memory deficits (2021)](https://doi.org/10.1093/brain/awab045)
[Barda et al., PPP1R9B mutations associated with early-onset neurodegeneration (2023)](https://doi.org/10.1093/brain/awad123)