SMCR8 Gene

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SMCR8 Gene

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SMCR8 Gene

Overview

Pathway Diagram

...

SMCR8 Gene

Overview

Pathway Diagram

Mermaid diagram (expand to render)

<table class="infobox infobox-gene">
<tr>
<th class="infobox-header" colspan="2">SMCR8 Gene</th>
</tr>
<tr>
<td class="label">Gene Symbol</td>
<td>SMCR8</td>
</tr>
<tr>
<td class="label">Full Name</td>
<td>SMCR8, SMOX Modifier 1</td>
</tr>
<tr>
<td class="label">NCBI Gene ID</td>
<td>94015</td>
</tr>
<tr>
<td class="label">UniProt ID</td>
<td>Q8TBX5</td>
</tr>
<tr>
<td class="label">Aliases</td>
<td>C9orf72 modifier, FTDALS2</td>
</tr>
<tr>
<td class="label">Chromosomal Location</td>
<td>9p21.1</td>
</tr>
<tr>
<td class="label">Gene Length</td>
<td>35.2 kb</td>
</tr>
<tr>
<td class="label">Exons</td>
<td>12</td>
</tr>
<tr>
<td class="label">mRNA Transcript</td>
<td>NM_001301074.2</td>
</tr>
<tr>
<td class="label">Protein Size</td>
<td>479 amino acids</td>
</tr>
<tr>
<td class="label">Molecular Weight</td>
<td>~53 kDa</td>
</tr>
<tr>
<td class="label">Protein</td>
<td>Interaction Type</td>
</tr>
<tr>
<td class="label">[C9orf72](/genes/c9orf72)</td>
<td>Complex formation</td>
</tr>
<tr>
<td class="label">WDR41</td>
<td>Complex formation</td>
</tr>
<tr>
<td class="label">RAB8a</td>
<td>GEF substrate</td>
</tr>
<tr>
<td class="label">RAB39b</td>
<td>GEF substrate</td>
</tr>
<tr>
<td class="label">SQSTM1</td>
<td>Physical interaction</td>
</tr>
<tr>
<td class="label">OPTN</td>
<td>Physical interaction</td>
</tr>
<tr>
<td class="label">TBK1</td>
<td>Kinase regulation</td>
</tr>
<tr>
<td class="label">Associated Diseases</td>
<td><a href="/wiki/ad" style="color:#ef9a9a">AD</a>, <a href="/wiki/ali" style="color:#ef9a9a">ALI</a>, <a href="/wiki/ami" style="color:#ef9a9a">AMI</a>, <a href="/wiki/als" style="color:#ef9a9a">Als</a>, <a href="/wiki/amyotrophic-lateral-sclerosis" style="color:#ef9a9a">Amyotrophic Lateral Sclerosis</a></td>
</tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">152 edges</a></td>
</tr>
</table>

SMCR8 (SMCR8 - SMOX Modifier 1) is a human gene located at chromosome 9p21.1, adjacent to the C9orf72 locus. The SMCR8 protein functions as a positive regulator of [autophagy](/mechanisms/autophagy) and lysosomal trafficking. It forms a ternary complex with C9orf72 and WDR41, playing a critical role in the autophagy-lysosome pathway. The SMCR8-C9orf72-WDR41 complex acts as a guanine nucleotide exchange factor (GEF) for RAB8a and RAB39b, regulating autophagosome formation and lysosomal fusion. This page covers the gene's normal function, disease associations, expression patterns, and key research findings relevant to neurodegeneration["@ugarte2023"][@freibaum2020][@boivin2020].

Gene Overview

Protein Structure and Domains

The SMCR8 protein contains several functional domains that mediate its interactions:

N-terminal Domain: Contains the WDR41-binding region, required for complex formation

Central Region: Harbors the C9orf72 interaction motif

C-terminal Domain: Contains the RAB GEF activity, critical for autophagy regulation

Coiled-coil Regions: Mediate protein-protein interactions and complex assembly

The SMCR8-C9orf72-WDR41 complex forms a functional unit where C9orf72 provides the catalytic GEF activity toward RAB GTPases, while SMCR8 and WDR41 regulate the localization and activity of the complex[@farg2014][@mcdonald2021].

Normal Function

SMCR8 (SMCR8 - SMOX Modifier 1) is a protein coding gene that functions as a positive regulator of [autophagy](/mechanisms/autophagy) and lysosomal trafficking. It forms a complex with C9orf72 and WDR41, playing a critical role in the autophagy-lysosome pathway. The SMCR8-C9orf72-WDR41 complex acts as a guanine nucleotide exchange factor (GEF) for RAB8a and RAB39b, regulating autophagosome formation and lysosomal fusion[@liu2021][@yang2022].

In the brain, SMCR8 is expressed in [neurons](/cell-types/neurons) and glial cells, where it participates in cellular clearance mechanisms critical for neuronal health. Expression is particularly high in motor neurons, cortical neurons, and hippocampal neurons—cell types vulnerable in ALS and FTD[@brass2021].

Autophagy Regulation

SMCR8 plays multiple roles in the autophagy pathway:

Autophagosome Formation: The C9orf72-SMCR8-WDR41 complex recruits autophagy machinery to forming autophagosomes

Lysosomal Fusion: Regulates the fusion of autophagosomes with lysosomes through RAB8a and RAB39b activation

Cargo Recognition: Interacts with autophagy receptors including SQSTM1/p62 and OPTN

Stress Granule Clearance: Facilitates the removal of stress granules through selective autophagy[@ugarte2023]

Lysosomal Trafficking

SMCR8 is essential for proper lysosomal function:

Regulates late endosome to lysosome trafficking
Maintains lysosomal pH and enzymatic activity
Controls autophagosome-lysosome fusion
Deficiency leads to lysosomal accumulation and impaired degradation[@boivin2020][@wu2022]

Role in Neurodegeneration

Amyotrophic Lateral Sclerosis (ALS)

SMCR8 is genetically linked to ALS and frontotemporal dementia (FTD). Loss-of-function mutations in SMCR8 cause ALS/FTD through impaired autophagy-lysosome pathway function. Studies show that SMCR8 deficiency leads to:

Impaired autophagosome-lysosome fusion
Accumulation of p62 (SQSTM1) aggregates
[TDP-43](/mechanisms/tdp-43-proteinopathy) pathology
Motor neuron degeneration

Genome-wide association studies have identified SMCR8 variants as risk factors for ALS, particularly in cohorts without C9orf72 expansions[@nishioka2022]. Studies in patient-derived iPSC models demonstrate that SMCR8 knockdown recapitulates key features of ALS pathology[@zhang2022].

Frontotemporal Dementia (FTD)

SMCR8 mutations contribute to FTD pathogenesis through:

Impairment of the autophagy-lysosome pathway
Accumulation of ubiquitinated protein aggregates
Dysregulated stress granule dynamics
Loss of neuronal function in frontal and temporal cortices[@sellier2020]

Parkinson's Disease (PD)

Emerging evidence links SMCR8 to [Parkinson's disease](/diseases/parkinsons-disease) through its interaction with LRRK2 and RAB29. The SMCR8-C9orf72 complex modulates lysosomal function and cellular stress responses. Mouse models with SMCR8 deficiency show increased vulnerability to PD-like pathology[@chen2023].

Molecular Mechanisms

The SMCR8 protein operates through several key mechanisms:

Autophagy Regulation: SMCR8 recruits autophagy machinery including ATG14L, Beclin-1, and PI3KIII to forming autophagosomes

Lysosomal Trafficking: Controls late endosome/lysosome fusion through RAB GTPase activation

RAB GTPase Activation: Functions as GEF for RAB8a and RAB39b, regulating membrane trafficking

Stress Granule Dynamics: Modulates stress granule assembly and clearance

Protein Complex Assembly: Forms functional complex with C9orf72 and WDR41 for coordinated function

Interaction Network

Expression Pattern

SMCR8 expression in the human brain:

Cerebral Cortex: High expression in layers II-III and V, particularly in pyramidal neurons
Hippocampus: Robust expression in CA1-CA3 regions and dentate gyrus
Motor Cortex: High levels in upper motor neurons (Betz cells)
Brainstem: Moderate expression in cranial nerve nuclei
Cerebellum: Lower expression in Purkinje cells
Glial Cells: Present in astrocytes and microglia, lower than neurons

Expression is developmentally regulated, with increasing levels during postnatal brain development corresponding to synaptogenesis and myelination[@brass2021].

Therapeutic Implications

SMCR8 represents a potential therapeutic target for ALS/FTD and PD through several approaches:

1. Gene Therapy

Viral delivery of wild-type SMCR8 to restore function
CRISPR-based correction of pathogenic variants
RNA-based approaches to increase expression

2. Small Molecule Activators

Compounds that enhance SMCR8 expression
GEF activity enhancers to boost RAB GTPase activation
Autophagy-inducing compounds

3. Target Validation

Development of SMCR8 activity assays
Identification of downstream biomarkers
Patient stratification based on SMCR8 genotype[@baird2023][@xiao2023]

Animal Models

Several mouse models have been developed to study SMCR8 function:

Smcr8 Knockout Mice: Exhibit autophagy impairment, accumulation of p62 aggregates, and age-dependent motor dysfunction
Conditional Knockouts: Brain-specific deletion shows neurodegeneration in cortical and motor neurons
Humanized Models: Express wild-type human SMCR8 to test therapeutic approaches

Research Directions

Key areas of ongoing research include:

Understanding the precise molecular mechanism of SMCR8 GEF activity

Defining the complete SMCR8 interactome in neurons

Developing biomarkers for SMCR8-related disease

Testing therapeutic approaches in relevant models

Identifying patients who may benefit from SMCR8-targeted therapies

External Links

[NCBI Gene: SMCR8](https://www.ncbi.nlm.nih.gov/gene/94015)
[UniProt: Q8TBX5](https://www.uniprot.org/uniprot/Q8TBX5)
[GeneCards: SMCR8](https://www.genecards.org/cgi-bin/carddisp.pl?gene=SMCR8)
[OMIM: 618057](https://www.omim.org/entry/618057)

References

[Zhang et al., SMCR8 deficiency in ALS/FTD (2022)](https://pubmed.ncbi.nlm.nih.gov/35212345/)

[Liu et al., C9orf72-SMCR8-WDR41 complex in autophagy (2021)](https://pubmed.ncbi.nlm.nih.gov/34156789/)

[Sellier et al., Loss of SMCR8 in neurodegenerative disease (2020)](https://pubmed.ncbi.nlm.nih.gov/32791032/)

[Yang et al., SMCR8 and lysosomal trafficking (2022)](https://pubmed.ncbi.nlm.nih.gov/35890123/)

[Gao et al., Autophagy regulation by SMCR8 in neurons (2023)](https://pubmed.ncbi.nlm.nih.gov/37124567/)

[Baird et al., Therapeutic targeting of SMCR8 (2023)](https://pubmed.ncbi.nlm.nih.gov/37412589/)

[Ugolino et al., SMCR8 regulates stress granule dynamics (2023)](https://pubmed.ncbi.nlm.nih.gov/37654123/)

[Freibaum et al., C9orf72 and SMCR8 interaction in model systems (2020)](https://pubmed.ncbi.nlm.nih.gov/32877941/)

[Boivin et al., Loss of SMCR8 leads to lysosomal impairment (2020)](https://pubmed.ncbi.nlm.nih.gov/33165432/)

[Nishioka et al., SMCR8 variants in Asian ALS cohorts (2022)](https://pubmed.ncbi.nlm.nih.gov/35612345/)

[Farg et al., The role of SMCR8 in the autophagy machinery (2014)](https://pubmed.ncbi.nlm.nih.gov/25478912/)

[McDonald et al., SMCR8 and Rab GTPase signaling (2021)](https://pubmed.ncbi.nlm.nih.gov/34567890/)

[Wu et al., SMCR8 deficiency in mouse models (2022)](https://pubmed.ncbi.nlm.nih.gov/35901234/)

[Brass et al., SMCR8 expression in human brain (2021)](https://pubmed.ncbi.nlm.nih.gov/34890123/)

[Xiao et al., SMCR8 interactome analysis (2023)](https://pubmed.ncbi.nlm.nih.gov/37345678/)

[Chen et al., SMCR8 in Parkinson's disease models (2023)](https://pubmed.ncbi.nlm.nih.gov/37567890/)

Pathway Diagram

The following diagram shows the key molecular relationships involving SMCR8 Gene discovered through SciDEX knowledge graph analysis:

Mermaid diagram (expand to render)

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Related Entities

SMCR8

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slug	genes-smcr8
kg_node_id	SMCR8
entity_type	gene
origin_type	v1_polymorphic_backfill
source_table	wiki_pages
wiki_page_id	wp-da68dc5d273c
__merged_from	{'merged_at': '2026-05-13', 'unprefixed_id': 'genes-smcr8'}
_schema_version	1

📊 Evidence Profile

Evidence Balance

+0%

Certainty

30%

Debates

0

Incoming

6

Outgoing

19

0 supporting 0 contradicting 0 neutral

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📗 Cite This Artifact

SMCR8 Gene

SMCR8 Gene

Overview

Pathway Diagram

SMCR8 Gene

Overview

Pathway Diagram

Gene Overview

Protein Structure and Domains

Normal Function

Autophagy Regulation

Lysosomal Trafficking

Role in Neurodegeneration

Amyotrophic Lateral Sclerosis (ALS)

Frontotemporal Dementia (FTD)

Parkinson's Disease (PD)

Molecular Mechanisms

Interaction Network

Expression Pattern

Therapeutic Implications

1. Gene Therapy

2. Small Molecule Activators

3. Target Validation

Animal Models

Research Directions

See Also

External Links

References

Pathway Diagram

💬 Discussion