RAD50 Gene

RAD50 Gene

<table class="infobox infobox-gene">
<tr>
<th class="infobox-header" colspan="2">rad50</th>
</tr>
<tr>
<td class="label">Gene Symbol</td>
<td>RAD50</td>
</tr>
<tr>
<td class="label">Full Name</td>
<td>DNA Repair Protein RAD50</td>
</tr>
<tr>
<td class="label">Chromosomal Location</td>
<td>5q23.2</td>
</tr>
<tr>
<td class="label">NCBI Gene ID</td>
<td>10111</td>
</tr>
<tr>
<td class="label">Ensembl ID</td>
<td>ENSG00000113522</td>
</tr>
<tr>
<td class="label">UniProt ID</td>
<td>Q9XQB3</td>
</tr>
<tr>
<td class="label">OMIM</td>
<td>604040</td>
</tr>
<tr>
<td class="label">Gene Type</td>
<td>Protein coding</td>
</tr>
<tr>
<td class="label">Aliases</td>
<td>RAD50 homolog, SMC5/6 complex subunit</td>
</tr>
<tr>
<td class="label">Protein Name</td>
<td>DNA Repair Protein RAD50</td>
</tr>
<tr>
<td class="label">Molecular Weight</td>
<td>~180 kDa (1586 amino acids)</td>
</tr>
<tr>
<td class="label">Subcellular Localization</td>
<td>Nucleus (chromatin-associated)</td>
</tr>
<tr>
<td class="label">Protein Family</td>
<td>SMC family (Structural Maintenance of Chromosomes)</td>
</tr>
<tr>
<td class="label">Structure</td>
<td>Coiled-coil domains with central hinge</td>
</tr>
<tr>
<td class="label">Associated Diseases</td>
<td><a href="/wiki/aging" style="color:#ef9a9a">Aging</a></td>
</tr>
<tr>
<td class="label">KG Connections<

RAD50 Gene

<table class="infobox infobox-gene">
<tr>
<th class="infobox-header" colspan="2">rad50</th>
</tr>
<tr>
<td class="label">Gene Symbol</td>
<td>RAD50</td>
</tr>
<tr>
<td class="label">Full Name</td>
<td>DNA Repair Protein RAD50</td>
</tr>
<tr>
<td class="label">Chromosomal Location</td>
<td>5q23.2</td>
</tr>
<tr>
<td class="label">NCBI Gene ID</td>
<td>10111</td>
</tr>
<tr>
<td class="label">Ensembl ID</td>
<td>ENSG00000113522</td>
</tr>
<tr>
<td class="label">UniProt ID</td>
<td>Q9XQB3</td>
</tr>
<tr>
<td class="label">OMIM</td>
<td>604040</td>
</tr>
<tr>
<td class="label">Gene Type</td>
<td>Protein coding</td>
</tr>
<tr>
<td class="label">Aliases</td>
<td>RAD50 homolog, SMC5/6 complex subunit</td>
</tr>
<tr>
<td class="label">Protein Name</td>
<td>DNA Repair Protein RAD50</td>
</tr>
<tr>
<td class="label">Molecular Weight</td>
<td>~180 kDa (1586 amino acids)</td>
</tr>
<tr>
<td class="label">Subcellular Localization</td>
<td>Nucleus (chromatin-associated)</td>
</tr>
<tr>
<td class="label">Protein Family</td>
<td>SMC family (Structural Maintenance of Chromosomes)</td>
</tr>
<tr>
<td class="label">Structure</td>
<td>Coiled-coil domains with central hinge</td>
</tr>
<tr>
<td class="label">Associated Diseases</td>
<td><a href="/wiki/aging" style="color:#ef9a9a">Aging</a></td>
</tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">4 edges</a></td>
</tr>
</table>

Introduction

RAD50 encodes a crucial DNA repair protein that serves as the structural scaffold of the MRN complex (MRE11-RAD50-NBS1), which is essential for recognizing and repairing DNA double-strand breaks (DSBs). As a member of the Structural Maintenance of Chromosomes (SMC) family, RAD50 functions as a molecular hinge that bridges DNA ends and facilitates the recruitment of downstream repair factors including ATM kinase. Beyond its fundamental role in DNA repair, RAD50 has been implicated in neurodegenerative diseases including Alzheimer's disease (AD), Parkinson's disease (PD), and ataxia-telangiectasia-like disorder, where defective DNA repair contributes to neuronal death. The protein's functions in telomere maintenance, cell cycle regulation, and genomic stability make it a critical factor in neuronal survival and aging. [@hopfner2002][@deJager2001]

Gene Information

Protein Overview

Structural Features

RAD50 possesses a distinctive structure optimized for DNA binding and protein scaffolding:

• N-terminal ATPase Domain: Contains Walker A (P-loop) and Walker B motifs that bind and hydrolyze ATP, regulating complex assembly and disassembly
• Coiled-Coil Domains: Long alpha-helical regions that mediate protein dimerization and interactions with other repair factors
• Zinc Hook Domain: A unique zinc-binding motif at the apex of the coiled-coils that forms a dimeric interface, literally "hooking" two RAD50 proteins together to bridge DNA ends
• C-terminal MRE11-binding Domain: Interacts with MRE11 nuclease to form the MRN complex
• DNA-binding Interface: Positively charged regions that contact DNA substrates

Isoforms

• RAD50-001: Full-length isoform (1586 amino acids), predominant form
• RAD50-002: Alternative splice variant with truncated ATPase domain
• RAD50-003: Minor isoform with distinct tissue distribution

Normal Biological Function

DNA Double-Strand Break Repair

RAD50 is the central scaffolding component of the MRN complex, which initiates the cellular response to DNA double-strand breaks:

DNA End Recognition: The MRN complex rapidly localizes to DSB sites, with RAD50's coiled-coil domains facilitating dimerization and DNA end bridging.

DNA End Bridging: RAD50's zinc hook and coiled-coils bring distant DNA ends together, creating a platform for subsequent repair reactions. This bridging function is essential for both canonical and alternative end-joining pathways.

ATM Activation: The MRN complex directly activates ATM kinase, which phosphorylates downstream targets including CHK2, p53, and H2AX. RAD50 is required for stable ATM recruitment to damage sites.

End Processing: Working with MRE11's nuclease activity, RAD50 facilitates DNA end resection—a critical step for homologous recombination repair.

Homologous Recombination: RAD50 supports HR by creating and maintaining DNA end accessibility for RAD51 filament formation.

MRN Complex Formation

RAD50 forms a stable heterotrimeric complex with MRE11 and NBS1:

• MRE11: Nuclease with both endonuclease and exonuclease activities
• RAD50: Structural scaffold and ATP-dependent regulator
• NBS1: Adaptor protein that recruits downstream effectors (including ATM)

Cellular Functions

Cell Cycle Regulation: RAD50 contributes to cell cycle checkpoints that prevent progression with unrepaired DNA:

• G1/S checkpoint activation
• Intra-S phase checkpoint maintenance
• G2/M checkpoint enforcement

• Telomere end processing
• Prevention of telomere fusion events
• TERT-independent telomere elongation mechanisms

• Initiation of meiotic DSBs
• Homologous chromosome pairing
• Crossover formation

• Chromosomal translocations
• Gene amplifications
• Aneuploidy

Expression Patterns

Brain Region Expression

• Hippocampus: High expression in dentate gyrus and CA regions
• Cortex: Moderate expression throughout cortical layers
• Cerebellum: Purkinje cells and granule cells
• Substantia nigra: Dopaminergic neurons
• Spinal cord: Motor neurons

Cellular Expression

• Neurons: High expression in post-mitotic neurons
• Neural progenitor cells: Cell cycle-dependent expression
• Astrocytes: Lower expression than neurons
• Oligodendrocytes: Moderate expression

Regulation

• Cell cycle regulation: Expression peaks in S and G2 phases
• DNA damage induction: Transcriptional upregulation following DSBs
• Post-translational modifications: Phosphorylation by ATM/ATR, SUMOylation, acetylation
• Subcellular localization: Chromatin association increases upon DNA damage

Disease Associations

Alzheimer's Disease

RAD50 and the MRN complex have been implicated in Alzheimer's disease pathogenesis:

DNA Repair Deficits: neurons show reduced RAD50 expression and impaired MRN complex function in AD brain tissue. This deficit may contribute to the accumulation of DNA damage observed in AD neurons.

Genomic Instability: AD neurons exhibit increased chromosomal aberrations, consistent with defective RAD50-mediated DSB repair.

Amyloid Toxicity: Amyloid-beta can interfere with RAD50 function, creating a vicious cycle where amyloid deposition impairs DNA repair, leading to more amyloid-producing events.

Tau Pathology: Tau pathology is associated with impaired DNA damage responses, potentially through effects on MRN complex recruitment.

Therapeutic Implications: Enhancing RAD50 function or MRN complex activity could potentially protect neurons from DNA damage-induced death in AD. [@scharrer2019]

Parkinson's Disease

Connections between RAD50 and Parkinson's disease include:

Dopaminergic Neuron Vulnerability: The substantia nigra may have particularly high DNA repair requirements due to oxidative stress, making RAD50 deficits especially damaging.

Mitochondrial DNA Damage: RAD50 may participate in repair of mitochondrial DNA damage, and impaired function could contribute to PD-related mitochondrial dysfunction.

Alpha-Synuclein Interaction: Evidence suggests alpha-synuclein may interfere with nuclear DNA repair processes, potentially affecting RAD50 function.

PARP Activation: DNA damage in PD triggers excessive PARP activation, which may deplete NAD+ and ATP, indirectly affecting RAD50-mediated repair.

Ataxia-Telangiectasia-Like Disorder (ATLD)

RAD50 deficiency causes a rare autosomal recessive disorder:

Clinical Features:

• Cerebellar ataxia
• Microcephaly
• Growth retardation
• Immunodeficiency
• Cancer predisposition
• Radiation sensitivity

Cancer Predisposition

RAD50 mutations increase cancer risk:

• Lymphoid malignancies: Increased risk of T-cell and B-cell lymphomas
• Solid tumors: Breast, colorectal, and other cancers
• Mechanism: Impaired DNA repair leads to genomic instability

Molecular Mechanisms

Signaling Pathways

RAD50 participates in several key pathways:

Protein Interactions

RAD50 interacts with numerous proteins:

• MRE11: Core complex formation
• NBS1: Downstream signaling
• ATM: Activation and recruitment
• CTIP: DNA end resection
• RAD51: Homologous recombination
• BRCA1: DNA repair coordination
• 53BP1: Pathway choice in DSB repair

Post-Translational Modifications

• Phosphorylation: ATM phosphorylates RAD50 at S635 and other sites upon DNA damage
• SUMOylation: Modulates protein-protein interactions
• Acetylation: Affects DNA binding and complex formation
• Ubiquitination: Controls protein stability

Therapeutic Implications

Drug Development

Targeting RAD50 pathways:

• MRN complex enhancers: Small molecules that stabilize MRN at damage sites
• ATM activators: Compounds that enhance ATM activation by MRN
• Synthetic lethality: PARP inhibitors effective in RAD50-deficient cancers

Biomarker Potential

• DNA damage markers: RAD50 foci formation as indicator
• Therapeutic response: MRN complex function predicts response to DNA-damaging agents
• Cancer prognosis: RAD50 expression in tumors

Research Directions

Emerging Areas

• Single-molecule studies: Understanding RAD50 dynamics at the molecular level
• CRISPR screening: Identifying synthetic lethal partners
• Neurological models: iPSC-derived neurons to study RAD50 function
• Structural biology: Cryo-EM studies of the MRN complex

Unresolved Questions

• Cell-type-specific functions of RAD50 in the brain
• Mechanisms of neuronal vulnerability to RAD50 loss
• Therapeutic targeting of the MRN complex
• Relationship between RAD50 and tau pathology

Summary

RAD50 encodes a critical DNA repair protein that serves as the structural backbone of the MRN complex, essential for recognizing and repairing DNA double-strand breaks. The protein's unique zinc hook structure enables DNA end bridging, while its ATPase activity regulates complex assembly. Beyond DNA repair, RAD50 maintains telomere integrity, enforces cell cycle checkpoints, and ensures genomic stability. In neurodegenerative diseases including AD and PD, RAD50 dysfunction contributes to neuronal death through accumulated DNA damage. The protein represents both a potential therapeutic target and a biomarker for DNA damage-related pathology in neurodegeneration.

References