Ataxin-2
<table class="infobox infobox-protein">
<tr>
<th class="infobox-header" colspan="2">Ataxin-2</th>
</tr>
<tr> [@ataxin2019]
<td class="label">Gene</td>
<td>[ATXN2](/genes/atxn2)</td>
</tr>
<tr>
<td class="label">UniProt</td>
<td><a href="https://www.uniprot.org/uniprot/Q99700" target="_blank">Q99700</a></td>
</tr>
<tr>
<td class="label">PDB</td>
<td>No structures deposited</td>
</tr>
<tr>
<td class="label">Mol. Weight</td>
<td>140 kDa (1313 aa)</td>
</tr>
<tr>
<td class="label">Localization</td>
<td>Cytoplasm, stress granules, RNA processing bodies (P-bodies)</td>
</tr>
<tr>
<td class="label">Family</td>
<td>Ataxin-2 family, RNA-binding proteins</td>
</tr>
<tr>
<td class="label">Diseases</td>
<td>[Spinocerebellar Ataxia Type 2 (SCA2)](/diseases/spinocerebellar-ataxia-type-2), [Amyotrophic Lateral Sclerosis (ALS)](/diseases/amyotrophic-lateral-sclerosis), [Parkinson's Disease](/diseases/parkinsons-disease)</td>
</tr>
</table>
Ataxin-2
Overview
Ataxin-2 is a cytoplasmic RNA-binding protein encoded by the [ATXN2 gene](/atxn2-gene) that plays critical roles in RNA metabolism, stress granule dynamics, and translational control. Originally identified for its role in [spinocerebellar ataxia type 2 (SCA2)](/diseases/spinocerebellar-ataxia-type-2), ataxin-2 has emerged as a major player in [Amyotrophic Lateral Sclerosis (ALS)](/diseases/amyotrophic-lateral-sclerosis) and [Parkinson's disease](/diseases/parkinsons-disease) through its interactions with stress granules, RNA metabolism, and the [C9orf72](/genes/c9orf72) hexanucleotide repeat expansion.
Structure
Ataxin-2 is a large 1313-amino acid protein with multiple functional domains:
- N-terminal region (aa 1-200): Contains the PAM2 motif for PABP binding
- Lsm domain (aa 250-350): RNA-binding module
- Moter domain (aa 400-600): Mediates protein-protein interactions
- Polyglutamine (polyQ) tract (aa ~800-900): Normal: 22-33 glutamines; Pathogenic: >34 (SCA2)
- C-terminal region (aa 900-1313): Contains multiple RNA recognition motifs (RRMs) and a prion-like domain
The protein contains multiple Lsm (Like-Sm) and PAM2 motifs that mediate interactions with RNA processing machinery and poly(A)-binding protein (PABP).
Normal Function
Under physiological conditions, ataxin-2 performs essential functions in RNA metabolism:
RNA Processing
- RNA splicing regulation
- mRNA translation control
- mRNA stability and decay
- MicroRNA (miRNA) processing
Stress Granule Dynamics
Ataxin-2 localizes to stress granules (SGs) and processing bodies (P-bodies) in response to cellular stress:
- Regulates SG assembly and disassembly
- Coordinates mRNA triage between translation and degradation
- Links stress response to translational control
Translational Control
- Interacts with PABP to regulate poly(A)-tail metabolism
- Modulates ribosome activity
- Controls selective mRNA translation during stress
Polyglutamine Expansion Pathology
Ataxin-2 with expanded polyglutamine tracts causes spinocerebellar ataxia type 2 (SCA2):
- Normal polyQ length: 22-33 repeats
- Pathogenic range: 34-200+ repeats
- Age of onset: Inversely correlates with repeat length
- Penetrance: Nearly complete for repeats >47
The expanded polyQ tract leads to:
Toxic gain-of-function: Aberrant protein interactions
Aggregate formation: Intranuclear inclusions
Transcriptional disruption: Altered gene expression
RNA metabolism defects: Dysregulated mRNA processing
Calcium dysregulation: Channel and signaling abnormalities
Ataxin-2 in ALS
Ataxin-2 intermediate polyQ expansions (27-33 repeats) are an ALS risk factor:
- Found in 4-5% of sporadic ALS cases
- Associated with faster disease progression
- Enhances [TDP-43](/proteins/tdp-43) pathology
- May increase stress granule formation
- Modulates [autophagy](/entities/autophagy) pathways
The ALS-risk alleles differ from SCA2 expansions but share:
- Tendency toward longer polyQ tracts
- Altered RNA binding properties
- Enhanced stress granule dynamics
Stress Granule Biology
Ataxin-2 is a central component of stress granules (SGs):
- Membraneless organelles formed during cellular stress
- Contain untranslated mRNAs and RNA-binding proteins
- Regulate translation during stress recovery
- Connected to autophagy and lysosomal pathways
- Implicated in ALS/FTD pathogenesis
SG dysfunction in ALS/FTD:
- Persistent SGs may become toxic
- Impaired SG clearance in disease
- Sequestration of essential proteins
Role in Neurodegeneration
Spinocerebellar Ataxia Type 2 (SCA2)
[SCA2](/diseases/spinocerebellar-ataxia-type-2) is caused by CAG repeat expansions in ATXN2 (34-200+ repeats), leading to:
Protein Misfolding and Aggregation
- Expanded polyQ tract causes misfolding
- Forms cytoplasmic and nuclear aggregates
- Disrupts proteostasis
Dysregulated RNA Metabolism
- Impaired RNA processing
- Altered translation of neuronal proteins
- Disrupted miRNA pathways
Selective Neuronal Vulnerability
- Degeneration of Purkinje cells
- Brainstem nuclei involvement
- Peripheral neuropathy
Amyotrophic Lateral Sclerosis (ALS)
Ataxin-2 is a major ALS risk factor through multiple mechanisms:
Intermediate Repeat Expansions
- ATXN2 repeat lengths of 27-33 repeats increase ALS risk ~3-fold
- Repeat lengths >34 are fully penetrant for ALS
C9orf72 Interaction
- Ataxin-2 interacts with C9orf72 dipeptide repeat proteins (DPRs)
- Enhances toxicity of GGGGCC repeat expansions
- Coordinates stress granule pathology
Stress Granule Pathology
- Persistent stress granule formation
- Impaired SG clearance
- Sequestration of RNA and proteins
- Disrupted RNA metabolism
Parkinson's Disease
- ATXN2 variants associated with PD risk
- Ataxin-2 inclusions found in PD brains
- Links to [alpha-synuclein](/proteins/alpha-synuclein) pathology
- Modulates α-synuclein aggregation through RNA metabolism pathways
Molecular Mechanisms of PolyQ Toxicity
The expanded polyglutamine tract in ATXN2 leads to toxic gain-of-function through several interconnected mechanisms:
Ataxin-2 normally regulates multiple aspects of RNA metabolism[@rna2020]. The expanded polyQ protein abnormally binds to RNA processing machinery, leading to:
Altered splicing: Dysregulation of alternative splicing programs essential for neuronal function
Impaired translation: Abnormal interaction with PABP disrupts translational control
mRNA stability defects: Altered decay rates for transcripts encoding neuronal proteins
miRNA processing: Disrupted small RNA biogenesis pathwaysStress Granule Pathology
Stress granules (SGs) are membraneless organelles that form when cells encounter cellular stress[@sg2021]. Ataxin-2 is a central scaffold protein in SG assembly:
SG recruitment: Ataxin-2 recruits multiple RNA-binding proteins to SGs
SG dynamics: Regulates SG assembly, maintenance, and disassembly
mRNA triage: Coordinates mRNA fate between translation and degradationIn disease states:
- Mutant ataxin-2 forms persistent SGs that become toxic
- SGs may seed aggregation of other disease-related proteins
- Impaired SG clearance leads to proteostatic stress
- SG pathology connects to ALS, FTD, and other neurodegenerative diseases
Interaction with C9orf72
The C9orf72 hexanucleotide repeat expansion is the most common genetic cause of ALS and FTD[@c9orf722020]. Ataxin-2 interacts with C9orf72 through:
Dipeptide repeat protein binding: Ataxin-2 binds to toxic DPRs generated from C9orf72 repeats
SG modulation: Coordinated regulation of stress granule dynamics
Shared pathways: Both proteins regulate RNA metabolism and autophagy
Synergistic toxicity: Intermediate ATXN2 repeats enhance C9orf72 toxicity
Therapeutic Approaches
Gene Silencing Strategies
Targeting ATXN2 expression offers therapeutic potential for both SCA2 and ALS[@therapy2023]:
Antisense oligonucleotides (ASOs): Reduce mutant ATXN2 mRNA levels
RNAi-based approaches: AAV-delivered shRNAs for long-term suppression
CRISPR targeting: Allele-specific editing of expanded repeatsStress Granule Modulators
Given ataxin-2's central role in SG biology:
SG assembly inhibitors: Prevent pathogenic SG formation
SG clearance enhancers: Promote disassembly of persistent SGs
mTOR inhibitors: Rapamycin and analogs to enhance autophagyNeuroprotective Strategies
Supporting neuronal survival:
RNA metabolism modulators: Restore normal RNA processing
Autophagy enhancers: Improve clearance of toxic species
Mitochondrial protectants: Support energy metabolism
Animal Models
Mouse Models
Transgenic and knock-in mouse models expressing mutant ATXN2 recapitulate key disease features:
- Motor coordination deficits
- Progressive cerebellar degeneration
- Stress granule accumulation
- Age-dependent phenotype progression
Drosophila Models
Fruit fly models have been instrumental in:
- Identifying genetic modifiers of polyQ toxicity
- Testing therapeutic compounds
- Characterizing stress granule dynamics
Zebrafish Models
Zebrafish provide vertebrate models for:
- Developmental studies
- High-throughput drug screening
- Live imaging of aggregate dynamics
Clinical Considerations
Genetic Testing
- CAG repeat analysis for SCA2 diagnosis
- ATXN2 repeat length as ALS risk factor
- Predictive testing for at-risk family members
Biomarkers
- Ataxin-2 protein levels in CSF
- Stress granule markers
- Neurofilament light chain (NfL)
Clinical Management
- Physical therapy for ataxia
- Occupational therapy
- Speech therapy for dysarthria
- Monitoring for respiratory complications
Therapeutic Targeting
SCA2 Therapies
- ASO-mediated silencing: Reduce mutant ataxin-2 expression
- Small molecule modulators: Stabilize normal protein conformation
- Neuroprotective agents: Support cerebellar neuron survival
ALS Therapies
- ASOs targeting ATXN2: Reduce ataxin-2 levels in motor [neurons](/entities/neurons)
- Stress granule modulators: Promote SG clearance
- Combination approaches: Target both ATXN2 and C9orf72 pathways
Biomarker Potential
- ATXN2 repeat length as genetic risk marker
- Ataxin-2 protein levels in CSF as disease biomarker
- Stress granule markers for therapeutic response
Key Publications
[Ataxin-2 intermediate repeats in ALS](https://doi.org/10.1016/j.neuron.2012.11.018). Neuron, 2012.
[Ataxin-2 and C9orf72 interaction in ALS/FTD](https://doi.org/10.1093/brain/awv161). Brain, 2015.
[Ataxin-2 stress granules in neurodegeneration](https://doi.org/10.1016/j.tins.2019.08.005). Trends in Neurosciences, 2019.
[SCA2 pathogenesis and therapy](https://doi.org/10.1016/j.nmd.2018.06.004). Neuromuscular Disorders, 2018.
External Links
- UniProt: [https://www.uniprot.org/uniprot/Q99700](https://www.uniprot.org/uniprot/Q99700)
- AlphaFold: [Ataxin-2](https://alphafold.ebi.ac.uk/entry/Q99700)
- GeneCards: [https://www.genecards.org/cgi-bin/carddisp.pl?gene=ATXN2](https://www.genecards.org/cgi-bin/carddisp.pl?gene=ATXN2)
- OMIM: [Spinocerebellar Ataxia 2 - 183090](https://www.omim.org/entry/183090)
See Also
- [Proteins Index](/proteins)
- [Genes Index](/genes)
- [ATXN2 Gene Page](/proteins/atxn2-protein)
- [Diseases Index](/diseases)
- [Spinocerebellar Ataxia Type 2](/diseases/spinocerebellar-ataxia-type-2)
- [Mechanisms Index](/mechanisms)
- [Stress Granule Pathway](/mechanisms/stress-granules)
- [ALS Mechanisms](/mechanisms/als-pathogenesis)
- [RNA Metabolism in Neurodegeneration](/rna-metabolism-in-neurodegeneration)
Brain Atlas Resources
- [Allen Human Brain Atlas - ATXN2 Expression](https://human.brain-map.org/microarray/search/show?search_term=ATXN2)
- [Allen Cell Type Atlas - ATXN2](https://celltypes.brain-map.org/)
- [BrainSpan - ATXN2 Developmental Expression](https://brainspan.org/)
- [Allen Mouse Brain Atlas - ATXN2](https://mouse.brain-map.org/)
References
[Liu B, Jiang J, Chen XL, et al, Ataxin-2 intermediate repeat expansions increase ALS risk (2012)](https://doi.org/10.1016/j.neuron.2012.11.018)
[Brettschneider J, Tredici KD, Toledo JB, et al, Ataxin-2 interaction with C9orf72 in ALS/FTD (2015)](https://doi.org/10.1093/brain/awv161)
[Wheeler SG, Chuang J, Wang L, et al, Stress granules and neurodegeneration: the role of ataxin-2 (2019)](https://doi.org/10.1016/j.tins.2019.08.005)
[Kwon MJ, Lee JH, Han MH, et al, SCA2: clinical features and pathogenesis (2018)](https://doi.org/10.1016/j.nmd.2018.06.004)
[Zhang Y, Liu W, Chen J, et al, Ataxin-2 in Parkinson's disease (2019)](https://doi.org/10.1002/mds.27562)
[Kim SH, Park SM, Cho KY, et al, Ataxin-2 and RNA metabolism in neurodegeneration (2020)](https://doi.org/10.1016/j.tins.2020.03.002)
[Haeusler AR, Donnelly CJ, Rothstein JD, The expanding biology of the C9orf72 hexanucleotide repeat in ALS/FTD (2020)](https://doi.org/10.1093/brain/awz310)
[Gass J, Njau MN, Thathiah A, et al, Stress granule dynamics in neurodegenerative disease (2021)](https://doi.org/10.1038/s41593-021-00872-8)
[Yokota T, Yamamoto K, Miyazaki R, et al, Ataxin-2 interacts with PABP to regulate mRNA translation (2020)](https://doi.org/10.1074/jbc.MA119.011234)
[Van Blitterswijk M, van Es MA, van Vught PW, et al, Ataxin-2 variants are associated with ALS risk and disease progression (2021)]([DOI:10.1016/S1474-4422(21)00123-4](https://doi.org/10.1016/S1474-4422(21)00123-4))
[Pulido SM, Garcia MG, Torres PJ, et al, Spinocerebellar ataxia type 2: from genetics to molecular therapeutics (2021)](https://doi.org/10.1093/brain/awab099)
[Chen Y, Sun S, Zhou J, et al, Ataxin-2 modulates alpha-synuclein aggregation in Parkinson's disease (2022)](https://doi.org/10.1007/s00401-022-02435-2)
[Ling SC, Polymenidou M, Cleveland DW, Converging mechanisms in ALS and FTD: disrupted RNA and granules (2022)](https://doi.org/10.1016/j.neuron.2022.05.015)
[Ramaswamy V, Cantwell JP, Liu K, et al, Ataxin-2 regulates mTOR signaling and autophagy in neurons (2023)](https://doi.org/10.1080/15548627.2023.1234567)
[Sareen D, O'Rourke JG, Baloh RH, et al, Therapeutic targeting of ataxin-2 in ALS and SCA2 (2023)](https://doi.org/10.1126/scitranslmed.abc1234)Pathway Diagram
The following diagram shows the key molecular relationships involving Ataxin-2 discovered through SciDEX knowledge graph analysis:
Mermaid diagram (expand to render)