HDAC5 Protein

HDAC5 Protein

Histone Deacetylase 5

<div class="infobox infobox-protein">
<table>
<tr><th colspan="2" style="background:#e8f4f8; text-align:center; font-size:1.1em;">HDAC5 Protein</th></tr>
<tr><td><strong>Protein Name</strong></td><td>Histone Deacetylase 5</td></tr>
<tr><td><strong>Gene</strong></td><td>[HDAC5](/genes/hdac5)</td></tr>
<tr><td><strong>UniProt ID</strong></td><td>[Q9UQL6](https://www.uniprot.org/uniprot/Q9UQL6)</td></tr>
<tr><td><strong>PDB Structures</strong></td><td>2VQM, 5A2U, 5VX9</td></tr>
<tr><td><strong>Protein Length</strong></td><td>1122 amino acids</td></tr>
<tr><td><strong>Molecular Weight</strong></td><td>~112 kDa</td></tr>
<tr><td><strong>Protein Class</strong></td><td>Class IIa Histone Deacetylase</td></tr>
<tr><td><strong>Subcellular Localization</strong></td><td>Nucleus/Cytoplasm (signal-dependent shuttling)</td></tr>
<tr><td><strong>Expression</strong></td><td>Brain (high), heart, skeletal muscle</td></tr>
<tr><td><strong>Chromosomal Location</strong></td><td>18q21.1</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/tumor" style="color:#ef9a9a">Tumor</a></td>
</tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">39 edges</a></td>
</tr>
</table>
</div>

Overview

HDAC5 Protein

Histone Deacetylase 5

<div class="infobox infobox-protein">
<table>
<tr><th colspan="2" style="background:#e8f4f8; text-align:center; font-size:1.1em;">HDAC5 Protein</th></tr>
<tr><td><strong>Protein Name</strong></td><td>Histone Deacetylase 5</td></tr>
<tr><td><strong>Gene</strong></td><td>[HDAC5](/genes/hdac5)</td></tr>
<tr><td><strong>UniProt ID</strong></td><td>[Q9UQL6](https://www.uniprot.org/uniprot/Q9UQL6)</td></tr>
<tr><td><strong>PDB Structures</strong></td><td>2VQM, 5A2U, 5VX9</td></tr>
<tr><td><strong>Protein Length</strong></td><td>1122 amino acids</td></tr>
<tr><td><strong>Molecular Weight</strong></td><td>~112 kDa</td></tr>
<tr><td><strong>Protein Class</strong></td><td>Class IIa Histone Deacetylase</td></tr>
<tr><td><strong>Subcellular Localization</strong></td><td>Nucleus/Cytoplasm (signal-dependent shuttling)</td></tr>
<tr><td><strong>Expression</strong></td><td>Brain (high), heart, skeletal muscle</td></tr>
<tr><td><strong>Chromosomal Location</strong></td><td>18q21.1</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/tumor" style="color:#ef9a9a">Tumor</a></td>
</tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">39 edges</a></td>
</tr>
</table>
</div>

Overview

HDAC5 (Histone Deacetylase 5) is a Class IIa histone deacetylase that functions as a signal-dependent transcriptional regulator[@haberland2009]. HDAC5 contains 1122 amino acids (~112 kDa) and shuttles dynamically between the nucleus and cytoplasm in response to cellular signals, allowing it to regulate both transcriptional programs and cytoplasmic signaling pathways. In the brain, HDAC5 plays critical roles in synaptic plasticity, memory formation, neuronal survival, and stress responses. Dysregulation of HDAC5 has been implicated in Alzheimer's disease, Parkinson's disease, and Huntington's disease, making it an attractive therapeutic target[@hu2022].

Protein Structure

Domain Architecture

HDAC5 contains three major structural domains[@yang2003][@kirlic2020]:

N-terminal Regulatory Domain (aa 1-421):

• Contains binding sites for transcription factors ([MEF2](/entities/mef2), [REST](/entities/rest))
• Interacts with 14-3-3 chaperone proteins
• Multiple phosphorylation sites for signal-dependent regulation
• Docking site for kinases (CaMK, PKD, PKA)
• CRM1-dependent nuclear export signal

• Zinc-dependent deacetylase active site
• Class IIa HDACs have lower catalytic activity than Class I enzymes
• Requires association with HDAC3 for full repression activity
• Contains structural features that accommodate Class IIa-specific substrates

• Additional phosphorylation regulatory sites
• NLS (nuclear localization signal) sequences
• HDAC3-binding interface
• Dimerization capability

Post-Translational Modifications

HDAC5 is extensively regulated by post-translational modifications that control its localization and activity[@mckinsey2000][@grozinger2000]:

| Modification | Site | Kinase/Enzyme | Effect |
|-------------|------|---------------|--------|
| Phosphorylation | Ser259 | CaMK, AMPK | Creates 14-3-3 binding site, promotes nuclear export |
| Phosphorylation | Ser498 | CaMK, AMPK | Creates 14-3-3 binding site, promotes nuclear export |
| Phosphorylation | Ser310 | PKD | Regulates nuclear-cytoplasmic shuttling |
| Phosphorylation | Ser275 | PKA | Modulates subcellular localization |
| Acetylation | Lys559 | p300/CBP | Alters HDAC5 transcriptional repressive activity |
| SUMOylation | Lys899 | SUMO E3 ligases | Modulates protein interactions |
| Ubiquitination | Multiple | E3 ligases | Proteasomal degradation |

3D Structure

Crystal structures of the HDAC4/5 catalytic domain (PDB: 2VQM) reveal[@kirlic2020]:

• Rossmann-fold catalytic core with zinc ion at the active site
• Class IIa characteristic shallow, elongated binding pocket
• Two coordinated water molecules at the active site explaining reduced deacetylase activity
• Conformational flexibility important for substrate recognition

Molecular Function

Catalytic Activity

HDAC5 catalyzes the removal of acetyl groups from lysine residues, though with different substrate specificity than Class I HDACs[@haberland2009]:

Histone substrates:

• H3K9, H3K14, H4K5 (weak deacetylation activity)
• Histone deacetylation promotes chromatin compaction and transcriptional repression

• Transcription factors ([p53](/proteins/p53-protein), MEF2, [NF-κB](/entities/nf-kb))
• Signaling proteins (14-3-3 proteins, kinases)
• Cytoskeletal proteins (actin, tubulin)

Signal-Dependent Nuclear-Cytoplasmic Shuttling

HDAC5 is a paradigmatic signal-regulated deacetylase[@mckinsey2000]:

Nucleus-to-Cytoplasm transport:

• CaMK-dependent phosphorylation of Ser259/498
• 14-3-3 protein binding to phosphorylated HDAC5
• CRM1-mediated nuclear export
• Results in relief of transcriptional repression

• Protein phosphatases (PP1, PP2A) dephosphorylate HDAC5
• 14-3-3 release allows nuclear re-entry
• NLS-mediated nuclear import
• Restores transcriptional repression at target genes

• Elevated intracellular calcium activates CaMK
• Synaptic activity triggers HDAC5 nuclear export
• Activity-dependent gene expression changes
• Links environmental signals to chromatin state

Transcriptional Repression

HDAC5 represses gene transcription through multiple mechanisms[@graff2013]:

1. Direct chromatin modification:

• Histone deacetylation at target gene promoters
• Recruitment of additional repressive modifiers
• Creation of transcriptionally silent chromatin

• MEF2 binding and repression
• REST complex recruitment
• NF-κB inhibition
• p53 modulation

• HDAC3/NCoR/SMRT complexes
• Sin3A co-repressor complexes
• NuRD complexes

Role in Neurodegeneration

Alzheimer's Disease

HDAC5 alterations contribute to AD pathogenesis through multiple mechanisms[@volakakis2016][@marathe2018]:

Transcriptional dysregulation:

• Altered HDAC5 nuclear/cytoplasmic ratio in AD patient brains
• Reduced expression of memory-related genes (BDNF, Arc, c-Fos)
• Contributes to synaptic plasticity deficits

• [Aβ](/proteins/amyloid-beta) oligomers alter HDAC5 phosphorylation and localization
• Aβ-induced calcium dysregulation affects HDAC5 nuclear shuttling
• Promotes HDAC5 nuclear export in affected neurons

• HDAC5 interacts with tau phosphorylation through GSK3β and [CDK5](/proteins/cdk5)
• Tau pathology is associated with altered HDAC5 distribution
• Bidirectional relationship between tau and HDAC5 dysregulation

• HDAC inhibitors show cognitive enhancement in AD models
• HDAC5-selective modulators represent a promising approach
• Brain penetration remains a challenge for clinical development

Parkinson's Disease

In Parkinson's disease[@hu2022]:

Dopaminergic neuron vulnerability:

• HDAC5 affects survival of [substantia nigra](/brain-regions/substantia-nigra) dopaminergic neurons
• Altered HDAC5 localization in PD models
• Contributes to transcriptional dysfunction

• [α-Synuclein](/proteins/alpha-synuclein) aggregates induce HDAC5 nuclear export
• Nuclear HDAC5 redistribution in α-synuclein overexpressing cells
• May contribute to transcriptional dysregulation in PD

• HDAC5 modulators show neuroprotective effects in PD models
• May enhance expression of neuroprotective genes
• Therapeutic targeting under active investigation

Huntington's Disease

HDAC5 is a compelling therapeutic target in Huntington's disease[@bardai2019][@thomas2008]:

Mutant huntingtin effects:

• Mutant [huntingtin](/proteins/huntingtin-protein) alters HDAC5 localization and function
• HDAC5 mislocalization contributes to transcriptional dysfunction
• Mutant HTT sequesters HDAC4/5 in the cytoplasm

• HDAC inhibitor 4b improves phenotypes in HD mouse models
• HDAC5 reduction or inhibition reduces mutant HTT toxicity
• Restores expression of brain-derived neurotrophic factor (BDNF)
• Corrects HDAC5-regulated gene expression programs

• Restoring neuronal survival pathways
• Reducing mutant HTT-induced transcriptional repression
• Modulating astrocyte and microglial function

Therapeutic Targeting

HDAC Inhibitors

Pan-HDAC inhibitors have shown therapeutic potential in neurodegeneration models[@thomas2008]:

| Drug | HDAC Selectivity | Status | Neurological Use |
|------|-----------------|--------|-----------------|
| Vorinostat (SAHA) | Pan-HDAC | Approved (CTCL) | Preclinical in AD/PD/HD |
| Entinostat (MS-275) | HDAC1/2/3 | Clinical trials | AD/HD models |
| Romidepsin | Pan-HDAC | Approved (CTCL) | Preclinical |
| Trichostatin A | Class I/II | Research only | Proof-of-concept |
| PCI-34051 | HDAC8 | Preclinical | HDAC5 indirectly affected |

Class IIa-Selective Approaches

Class IIa HDAC-selective compounds offer potential advantages[@kirlic2020]:

Development status:

• Few selective HDAC4/5 inhibitors exist
• TP-138 studied in oncology
• New scaffolds being explored for CNS applications
• Natural products (e.g., garcinol) show Class IIa activity

• Reduced Class I-mediated toxicity
• More specific gene regulation
• Better therapeutic window for chronic CNS diseases

• Achieving brain penetration
• Selectivity over Class I HDACs
• Understanding optimal mechanism (inhibition vs. modulation)

Interactions and Pathways

Key Protein Interactions

HDAC5 interacts with numerous proteins to execute its functions[@sando2012][@chawla2003]:

| Partner | Interaction Domain | Functional Consequence |
|---------|-------------------|----------------------|
| [MEF2A/C](/genes/mef2c) | N-terminal (aa 1-200) | Transcriptional repression of MEF2 targets |
| [REST](/entities/rest) | N-terminal | Neuronal gene repression |
| [NF-κB](/entities/nf-kb) (p65) | N-terminal | Inflammatory gene suppression |
| HDAC3 | Catalytic domain (aa 500-680) | Corepressor complex formation |
| NCoR/SMRT | N-terminal | Transcriptional repression complex |
| 14-3-3 proteins | C-terminal (phospho-Ser259/498) | Cytoplasmic retention |
| CaMK | Cytoplasmic | Phosphorylation and nuclear export |
| PKD | Cytoplasmic | Phosphorylation and nuclear export |
| CRM1 | C-terminal | Nuclear export |

Key Signaling Pathways

MEF2 Pathway:

• HDAC5 represses MEF2-dependent transcription of synaptic genes
• MEF2 regulates neuronal survival, differentiation, and plasticity
• MEF2-HDAC5 balance critical for memory formation

• Cross-talk with CREB-mediated transcription
• Affects BDNF and activity-regulated genes
• Activity-dependent regulation of plasticity genes

• HDAC5 inhibits NF-κB transcriptional activity
• Suppresses inflammatory gene expression
• Anti-inflammatory potential in neurodegeneration

• HDAC5 represses p38 MAPK signaling through MAPK14 targeting[@marathe2018]
• Affects cellular stress responses
• Modulates neuroinflammatory pathways

Expression and Localization

Brain Regional Expression

HDAC5 shows specific patterns of expression in the brain[@broide2007]:

High expression regions:

• Cerebral cortex (particularly layer 5 pyramidal neurons)
• [Hippocampus](/brain-regions/hippocampus): CA1-CA3 pyramidal cells, dentate gyrus granule cells
• Basal ganglia: Striatum (medium spiny neurons), globus pallidus
• Cerebellum: Purkinje cells
• Amygdala

• Both neuronal and glial cell expression
• Nuclear localization in resting neurons
• Activity-dependent nuclear-cytoplasmic shuttling
• Cell type-specific patterns

Animal Models

Knockout and Knockdown Models

HDAC5 global knockout:

• Viable with no major developmental abnormalities
• Enhanced memory formation and synaptic plasticity
• Altered cardiac development (mild)
• Increased anxiety-like behavior in some contexts

• Enhanced learning and memory in contextual fear conditioning
• Increased dendritic spine density
• Altered synaptic gene expression
• Enhanced hippocampal synaptic plasticity

Disease Model Studies

AD models (APP/PS1, 3xTg-AD):

• HDAC5 changes correlate with cognitive deficits
• Response to HDAC inhibitor treatment
• Altered nuclear/cytoplasmic distribution

• HDAC5 alterations in dopaminergic neurons
• Neuroprotective effects of HDAC5 modulation
• Role in alpha-synuclein toxicity response

• Mutant HTT alters HDAC5 localization
• HDAC5 modulation improves disease phenotypes
• Restores BDNF expression in striatum

See Also

• [HDAC5 Gene](/genes/hdac5) — Gene page with genomic information
• [HDAC4 Protein](/proteins/hdac4-protein) — Related Class IIa HDAC
• [HDAC Enzymes](/entities/hdac-enzymes) — HDAC family overview
• [Alzheimer's Disease](/diseases/alzheimers-disease) — AD disease page
• [Parkinson's Disease](/diseases/parkinsons-disease) — PD disease page
• [Huntington's Disease](/diseases/huntington-disease) — HD disease page
• [HDAC Inhibitors](/therapeutics/hdac-inhibitors) — Therapeutic agents
• [Epigenetics in Neurodegeneration](/mechanisms/epigenetics-neurodegeneration) — Epigenetic mechanisms

References