UNC-5A Protein

UNC-5A Protein

Introduction

Unc 5A Protein is an important component in the neurobiology of neurodegenerative diseases. This page provides detailed information about its structure, function, and role in disease processes.

--- [@finger2002]
title: UNC-5A Protein [@williams2014]
description: Mediates netrin-1 induced repulsion. Contains death domain that triggers [apoptosis](/entities/apoptosis) in absence of netrin. [@mehlen2011]
--- [@liu2019]

<div class="infobox infobox-protein"> [@yam2020]
<table>
<tr><th colspan="2" class="infobox-header">UNC-5A Protein</th></tr>
<tr><td class="label">Protein Name</td><td>UNC-5A (Unc-5 Homolog A)</td></tr>
<tr><td class="label">Gene</td><td><a href="/genes/UNC5A">UNC5A</a></td></tr>
<tr><td class="label">UniProt ID</td><td><a href="https://www.uniprot.org/uniprot/Q8IZJ3">Q8IZJ3</a></td></tr>
<tr><td class="label">PDB ID</td><td>4J2V</td></tr>
<tr><td class="label">Molecular Weight</td><td>~130 kDa (946 amino acids)</td></tr>
<tr><td class="label">Subcellular Localization</td><td>Plasma membrane, cytoplasmic</td></tr>
<tr><td class="label">Protein Family</td><td>UNC-5 family, Netrin receptors</td></tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">1 edges</a></td>
</tr>
</table>
</div>

Overview

UNC-5A Protein

Introduction

Unc 5A Protein is an important component in the neurobiology of neurodegenerative diseases. This page provides detailed information about its structure, function, and role in disease processes.

--- [@finger2002]
title: UNC-5A Protein [@williams2014]
description: Mediates netrin-1 induced repulsion. Contains death domain that triggers [apoptosis](/entities/apoptosis) in absence of netrin. [@mehlen2011]
--- [@liu2019]

<div class="infobox infobox-protein"> [@yam2020]
<table>
<tr><th colspan="2" class="infobox-header">UNC-5A Protein</th></tr>
<tr><td class="label">Protein Name</td><td>UNC-5A (Unc-5 Homolog A)</td></tr>
<tr><td class="label">Gene</td><td><a href="/genes/UNC5A">UNC5A</a></td></tr>
<tr><td class="label">UniProt ID</td><td><a href="https://www.uniprot.org/uniprot/Q8IZJ3">Q8IZJ3</a></td></tr>
<tr><td class="label">PDB ID</td><td>4J2V</td></tr>
<tr><td class="label">Molecular Weight</td><td>~130 kDa (946 amino acids)</td></tr>
<tr><td class="label">Subcellular Localization</td><td>Plasma membrane, cytoplasmic</td></tr>
<tr><td class="label">Protein Family</td><td>UNC-5 family, Netrin receptors</td></tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">1 edges</a></td>
</tr>
</table>
</div>

Overview

UNC-5A (also known as UNC5A or Unc-5 Homolog A) is a cell surface receptor belonging to the UNC-5 family of netrin receptors. It plays a critical role in axon guidance and neuronal migration during development, mediating the repulsive effects of netrin ligands. UNC-5A is essential for proper neuronal circuit formation and has been implicated in various neurological disorders.

The UNC-5 family includes four members in mammals (UNC5A, UNC5B, UNC5C, and UNC5D), each with distinct expression patterns and functional specializations. UNC5A is primarily expressed in the nervous system, with highest levels in the brain and spinal cord.

Structure

UNC5A possesses a complex multi-domain architecture:

Extracellular Domain

• Immunoglobulin-like (Ig) domain: Mediates ligand binding
• Type I thrombospondin domain (TSR): Involved in interactions with netrins
• Zinc-dependent metalloprotease-like domain: May process or interact with ligands
• Phosphatidylinositol phospholipase C (PI-PLC) homology domain: Regulatory functions

Transmembrane Domain

• Single-pass transmembrane helix
• Connects extracellular and intracellular signaling domains

Intracellular Domain

• Death domain (DD): Triggers apoptosis in the absence of netrin
• ZU5 domain: Scaffold for protein interactions
• C-terminal proline-rich region: Binds SH3 domain-containing proteins

Function

UNC5A mediates several critical functions in the nervous system:

Axon Guidance

UNC5A is a major receptor for netrin-1 and netrin-2, mediating:

• Axon repulsion: Directs axonal growth cones away from netrin sources
• Midline crossing: Prevents axons from recrossing the midline
• Circuit assembly: Guides formation of specific neural connections
• Dendritic patterning: Regulates dendritic arbor morphology

Cell Migration

During development, UNC5A regulates:

• Neuronal migration from ventricular zones
• Axon tract formation
• Cell positioning in the developing brain

Apoptosis Regulation

The UNC5A death domain plays a dual role:

• Netrin-bound state: Blocks death domain signaling, promoting survival
• Unbound state: Triggers apoptosis through caspase activation

Mechanism of Action

UNC5A signals through multiple pathways depending on its ligand binding state:

Netrin-bound Signaling

When bound to netrin-1 or netrin-2:

• DCC engagement: UNC5A can form complexes with DCC (Deleted in Colorectal Cancer) to convert repulsive signals into attractive ones
• Src family kinases: Activate downstream signaling
• PI3K/Akt pathway: Promotes survival and cytoskeletal reorganization
• MAPK/ERK pathway: Supports neuronal growth

Death Domain Signaling

In the absence of netrin:

• Caspase recruitment: Death domain recruits and activates caspases-8 and -3
• Apoptosis execution: Leads to neuronal cell death
• Cellular dismantling: Characteristic apoptotic morphology

Alternative Signaling

UNC5A also engages:

• Rho GTPases: Regulation of cytoskeletal dynamics
• FAK: Focal adhesion kinase signaling
• FAK: Integrin-mediated adhesion modulation

Role in Neurodegenerative Diseases

Alzheimer's Disease

UNC5A has been implicated in [Alzheimer's disease](/diseases/alzheimers-disease) pathogenesis:

• [Amyloid-beta](/proteins/amyloid-beta) effects: Aβ may alter UNC5A signaling
• Axon guidance disruption: Aβ-induced changes in netrin signaling could contribute to circuit dysfunction
• Synaptic plasticity: UNC5A may affect learning and memory through circuit modification

Parkinson's Disease

In [Parkinson's disease](/diseases/parkinsons-disease):

• Dopaminergic neuron development: UNC5A guides development of substantia nigra neurons
• Potential neuroprotection: Netrin-1/UNC5A signaling may protect dopaminergic neurons
• Axonal maintenance: UNC5A may help maintain axonal integrity

Amyotrophic Lateral Sclerosis

[ALS](/diseases/amyotrophic-lateral-sclerosis) research suggests:

• Motor neuron guidance defects may involve UNC5A
• Axon guidance molecules are increasingly recognized in ALS pathogenesis

Developmental Disorders

• Callosal agenesis: UNC5A mutations may contribute to corpus callosum defects
• Neurodevelopmental disorders: Altered netrin-UNC5A signaling affects brain wiring
• Autism spectrum disorders: Potential links through circuit formation genes

Therapeutic Implications

UNC5A represents a potential therapeutic target:

Neurodegeneration

• Neuroprotective strategies: Enhancing netrin-1/UNC5A signaling may protect neurons
• Death domain blockers: Small molecules preventing UNC5A-mediated apoptosis
• Combination approaches: UNC5A modulators with other neurotrophic factors

Brain Repair

• Axon regeneration: Modulating UNC5A could promote axonal growth after injury
• Circuit reconstruction: Guiding appropriate reinnervation
• Stem cell therapy: Directing migration of transplanted neurons

Cancer

• Tumor suppression: UNC5A acts as a dependence receptor in cancer
• Metastasis: UNC5A loss may promote cancer cell migration

Interactions and Network

UNC5A interacts with multiple proteins:

• [Netrin-1](/entities/netrin-1): Primary ligand
• [Netrin-2](/proteins/NTN2-Protein): Secondary ligand
• DCC: Co-receptor for netrin signaling
• [DCC Protein](/proteins/dcc-protein): Deleted in Colorectal Cancer
• Caspase-8: Death domain signaling
• Caspase-3: Apoptosis execution
• Src family kinases: Downstream signaling
• Rho GTPases: Cytoskeletal regulation

Research Directions

Current research focuses on:

See Also

• [UNC5B Protein](/proteins/UNC5B-Protein) - UNC5B receptor
• [UNC5C Protein](/proteins/unc5c-protein) - UNC5C receptor
• [Netrin-1](/entities/netrin-1) - Primary ligand
• [DCC Protein](/proteins/dcc-protein) - DCC netrin receptor
• [Axon Guidance Pathway](/mechanisms/axon-guidance)

External Links

• [UniProt Q8IZJ3](https://www.uniprot.org/uniprot/Q8IZJ3)
• [PDB 4J2V](https://www.rcsb.org/structure/4J2V)
• [Human UNC5A Gene](https://www.genecards.org/cgi-bin/carddisp.pl?gene=UNC5A)

Background

The study of Unc 5A Protein has evolved significantly over the past decades. Research in this area has revealed important insights into the underlying mechanisms of neurodegeneration and continues to drive therapeutic development.

Historical context and key discoveries in this field have shaped our current understanding and will continue to guide future research directions.

Brain Atlas Resources

• [Allen Human Brain Atlas](https://human.brain-map.org/) — protein expression data
• [Allen Cell Type Atlas](https://celltypes.brain-map.org/) — cell type specific expression
• [BrainSpan Atlas](https://brainspan.org/) — developmental transcriptome
• [Allen Mouse Brain Atlas](https://mouse.brain-map.org/) — mouse brain expression

References