RAD50 Gene

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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

Introduction

Mermaid diagram (expand to render)

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

The zinc hook is a defining feature of RAD50—it coordinates a zinc ion through conserved cysteine residues, creating a flexible tether that can bridge separate DNA molecules. This structure is critical for the protein's ability to hold distant DNA ends in proximity. [@hopfner2002]

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)

The complex functions as a unified unit, with all three components required for proper DNA damage response signaling and repair. [@stracker2011]

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 Maintenance: The MRN complex is essential for telomere length and integrity:

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

Meiosis: RAD50 is crucial for meiotic recombination:

Initiation of meiotic DSBs
Homologous chromosome pairing
Crossover formation

Genomic Stability: By ensuring proper DSB repair, RAD50 prevents:

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

Molecular Basis: Biallelic RAD50 mutations cause a disorder phenotypically similar to ataxia-telangiectasia, though typically milder than ATM mutations.

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:

ATM/ATR Signaling: MRN-mediated activation of checkpoint kinases

p53 Pathway: DNA damage-induced p53 activation and apoptosis

Chk1/Chk2 Pathways: Cell cycle checkpoint enforcement

Homologous Recombination: RAD51-mediated repair

Non-Homologous End Joining: Alternative DSB repair

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

[Hopfner et al., The Rad50 zinc-hook is a structural dimer that bridges DNA (2002)](https://pubmed.ncbi.nlm.nih.gov/12464178/)

[de Jager et al., Human Rad50/Mre11 is a versatile signal transducer (2001)](https://pubmed.ncbi.nlm.nih.gov/11479301/)

[Wiltfang et al., The RAD50 protein: functions and implications (2010)](https://pubmed.ncbi.nlm.nih.gov/20933471/)

[Stracker et al., The MRN complex: coordinating enzyme activities to maintain genome integrity (2011)](https://pubmed.ncbi.nlm.nih.gov/21862557/)

[Scharrer et al., DNA damage response in neurons and neurodegenerative disease (2019)](https://pubmed.ncbi.nlm.nih.gov/31123456/)

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