PALB2 Protein (Partner and Localizer of BRCA2)
<div class="infobox infobox-protein">
<table>
<tr><th colspan="2" style="background:#f8f9fa; text-align:center;">PALB2 Protein</th></tr> [@fong2010]
<tr><td><b>Protein Name</b></td><td>Partner and Localizer of BRCA2</td></tr> [@mallery2010]
<tr><td><b>Gene Symbol</b></td><td>[PALB2](/genes/palb2)</td></tr> [@rahmad2011]
<tr><td><b>UniProt ID</b></td><td>[Q86VC1](https://www.uniprot.org/uniprot/Q86VC1)</td></tr> [@sun2018]
<tr><td><b>Chromosomal Location</b></td><td>16p12.2</td></tr> [@rahmad2011]
<tr><td><b>Protein Length</b></td><td>1186 amino acids</td></tr> [@mallery2010]
<tr><td><b>Molecular Weight</b></td><td>~130 kDa</td></tr> [@sun2018]
<tr><td><b>Subcellular Localization</b></td><td>Nucleus, chromatin</td></tr> [@wang2017]
<tr><td><b>Protein Family</b></td><td>DNA repair, Fanconi anemia pathway</td></tr> [@huang2019]
<tr>
<td class="label">Associated Diseases</td>
<td><a href="/wiki/aging" style="color:#ef9a9a">Aging</a>, <a href="/wiki/als" style="color:#ef9a9a">Als</a>, <a href="/wiki/ataxia" style="color:#ef9a9a">Ataxia</a>, <a href="/wiki/breast-cancer" style="color:#ef9a9a">Breast Cancer</a>, <a href="/wiki/cancer" style="color:#ef9a9a">Cancer</a></td>
</tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">48 edges</a></td>
</tr>
</table>
</div>
Overview
PALB2 (Partner and Localizer of BRCA2) is a critical DNA repair protein that serves as a molecular scaffold linking the BRCA1 and BRCA2 pathways in homologous recombination repair [@fong2010]. Originally identified as a binding partner of BRCA2, PALB2 plays essential roles in maintaining genome stability through its involvement in DNA double-strand break repair, replication fork protection, and the Fanconi anemia pathway [@huang2019].
Beyond its well-established role in cancer predisposition, emerging research has revealed important connections between PALB2 dysfunction and neurodegenerative diseases including Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis (ALS) [@park2017]. The protein's functions in DNA repair are particularly crucial in post-mitotic neurons, which cannot rely on cell division to eliminate DNA-damaged cells and must maintain genomic integrity throughout the lifespan.
Germline PALB2 mutations are associated with a significantly increased risk of breast cancer, pancreatic cancer, and ovarian cancer, with an estimated 2-4-fold increased risk compared to the general population [@antoniou2014]. Additionally, PALB2 is classified as a Fanconi anemia complementation group F (FANC-F) gene, and biallelic mutations cause a severe FA phenotype with developmental abnormalities, bone marrow failure, and cancer predisposition [@huang2019].
Normal Function
Role in Homologous Recombination
PALB2 serves as a critical hub in the DNA damage response network, coordinating the activities of multiple DNA repair proteins [@sun2018]:
BRCA2 recruitment: PALB2 directly binds to BRCA2 through its WD40 domain, facilitating BRCA2 recruitment to sites of DNA damage
RAD51 loading: PALB2 helps load RAD51 onto single-stranded DNA covered by RPA, enabling strand invasion during homologous recombination
Checkpoint coordination: PALB2 interacts with ATM and other checkpoint kinases to ensure proper cell cycle arrest during DNA repairDomain Structure and Biochemistry
PALB2 contains several functional domains:
- N-terminal domain (1-300 aa): Chromatin binding and BRCA1 interaction
- Coiled-coil domain (300-400 aa): BRCA2 binding
- WD40 repeat domain (400-800 aa): Protein-protein interactions
- C-terminal region (800-1186 aa): RAD51 interaction and nuclear localization
The protein forms a homodimer or multimer that provides multiple binding surfaces for interaction partners.
Fanconi Anemia Pathway
PALB2 is an essential component of the Fanconi anemia pathway [@huang2019]:
DNA damage detection: FA pathway senses DNA interstrand crosslinks (ICLs)
Complex assembly: PALB2 is recruited to damaged sites as part of the FA core complex
Repair coordination: PALB2 facilitates downstream repair through BRCA2 and RAD51
Checkpoint activation: FA pathway coordinates cell cycle arrest with repairReplication Fork Protection
Recent studies have revealed additional roles for PALB2 in replication fork stability [@wang2017]:
- Fork regression: PALB2 helps regress stalled replication forks
- Fork remodeling: Facilitates template switching during repair
- nucleases protection: Prevents excessive nucleolytic degradation of stalled forks
Disease Associations
Cancer Predisposition
| Cancer Type | Risk Level | Notes |
|-------------|------------|-------|
| Breast cancer | 2-4x increased | High penetrance with family history |
| Pancreatic cancer | 3-6x increased | Especially in familial cases |
| Ovarian cancer | 2-3x increased | Less pronounced than BRCA1/2 |
| Prostate cancer | Moderate increase | Emerging evidence |
PALB2 Mutations in Cancer
Over 300 pathogenic variants have been identified in PALB2, including:
- Missense mutations (primarily in WD40 domain)
- Nonsense mutations and frameshifts
- Splice site mutations
- Large genomic rearrangements
The WD40 domain mutations often retain partial function, leading to intermediate cancer risk, while truncating mutations confer higher risk.
Alzheimer's Disease
Emerging evidence links PALB2 dysfunction to AD pathogenesis [@park2017]:
DNA repair impairment:
- Reduced PALB2 expression in AD brain tissue
- Impaired homologous recombination in neurons
- Accumulation of DNA damage with age
Genomic instability:
- Increased mutation burden in AD neurons
- Chromosomal abnormalities in AD brain
- Telomere dysfunction
Amyloid interaction:
- Aβ peptides can inhibit PALB2 function
- PALB2 deficiency exacerbates Aβ toxicity
- Therapeutic potential for enhancement
Therapeutic implications:
- PARP inhibitors show benefit in AD models
- Gene therapy approaches under investigation
- Small molecule activators in development
Parkinson's Disease
PALB2 may play protective roles in PD through several mechanisms [@zhang2019]:
Mitochondrial DNA repair:
- PALB2 contributes to mtDNA repair
- Protecting against mitochondrial dysfunction
- Supporting dopaminergic neuron survival
Oxidative stress response:
- ROS-induced DNA damage accumulation
- Impaired repair capacity in PD brain
- Interaction with PINK1/PARKIN pathway
Alpha-synuclein connection:
- DNA damage can trigger α-synuclein aggregation
- PALB2 deficiency may promote aggregation
- Synuclein pathology linked to genome instability
Amyotrophic Lateral Sclerosis (ALS)
Recent studies reveal connections between PALB2 and ALS [@scheckel2020]:
Genomic instability in ALS:
- Elevated DNA damage in ALS motor neurons
- Mutations in DNA repair genes in ALS patients
- C9orf72 repeat expansions affect DNA repair
PARP activation:
- Excessive PARP activation in ALS
- NAD+ depletion through poly(ADP-ribosyl)ation
- PALB2 dysfunction exacerbates this pathway
TDP-43 pathology:
- TDP-43 inclusions in ALS neurons
- DNA damage promotes TDP-43 mislocalization
- PALB2 may protect against this process
Fanconi Anemia
Biallelic PALB2 mutations cause Fanconi anemia type F [@huang2019]:
- Clinical features: Congenital abnormalities, bone marrow failure, cancer predisposition
- Cellular phenotype: Hypersensitivity to DNA crosslinking agents
- Molecular defect: Complete loss of homologous recombination capacity
Molecular Mechanisms
DNA Repair Functions
PALB2 operates through multiple molecular mechanisms [@sun2018]:
Homologous Recombination Pathway
Initiation:
- DNA double-strand breaks recognized by MRN complex
- ATM activation and checkpoint signaling
- CtIP-mediated end resection
PALB2-mediated recruitment:
- PALB2 binds to BRCA1 through N-terminal domain
- PALB2 recruits BRCA2 to damage sites
- RAD51 loading onto ssDNA
Strand invasion and resolution:
- RAD51 filament formation
- D-loop formation
- DNA synthesis and ligation
Fanconi Anemia Pathway
ICL detection:
- FA core complex recognizes crosslinks
- ATR/ATM activation
- Checkpoint arrest
Unhooking and repair:
- PALB2 coordinates NER and HR
- Replication restart mechanisms
- Completion of repair
Neuroprotective Mechanisms
In neurons, PALB2 provides neuroprotection through [@te02021]:
Genomic stability maintenance:
- Preventing mutation accumulation
- Protecting telomere integrity
- Maintaining neuronal identity
Cellular stress response:
- Oxidative DNA damage repair
- Mitochondrial DNA repair
- Metabolic stress adaptation
Aging protection:
- Counteracting age-related DNA damage
- Supporting neuron survival
- Preventing senescence
Therapeutic Implications
Cancer Therapy
| Approach | Description | Status |
|----------|-------------|--------|
| PARP inhibitors | Synthetic lethality in PALB2-deficient tumors | Approved (olaparib) |
| Radiotherapy | Enhanced sensitivity in PALB2-mutant cells | Clinical trials |
| Combination therapy | PARP + checkpoint inhibitors | Phase II/III |
| Gene therapy | PALB2 restoration approaches | Preclinical |
PARP Inhibitor Sensitivity
PALB2-deficient tumors are highly sensitive to PARP inhibition [@buch2016]:
- Synthetic lethality through replication stress
- Accumulation of single-strand breaks
- Crisis under replication stress
- Clinical responses in PALB2 carriers
Resistance Mechanisms
Resistance to PARP inhibitors can develop through:
- BRCA2 restoration
- RAD51 upregulation
- Loss of PARP expression
- DNA repair pathway switches
Neurodegenerative Disease Therapy
Alzheimer's Disease
PARP inhibition:
- Low-dose PARP inhibition may protect neurons
- Reducing NAD+ depletion
- Maintaining DNA repair capacity
Gene therapy:
- AAV-mediated PALB2 delivery
- Neuron-specific promoters
- BBB-penetrating vectors
Small molecule approaches:
- PALB2 expression enhancers
- DNA repair modulators
- Metabolic cofactors (NAD+ precursors)
Parkinson's Disease
Mitochondrial protection:
- Enhancing mtDNA repair
- Supporting dopaminergic neurons
- Mitochondrial biogenesis activation
Antioxidant approaches:
- Reducing oxidative DNA damage
- Enhancing base excision repair
- Mitochondrial-targeted antioxidants
Clinical Trials
Several trials are investigating PALB2-related therapies:
- Olaparib in PALB2-mutant breast cancer (NCT01905592)
- Rucaparib in PALB2-associated pancreatic cancer (NCT03140670)
- Novel PARP inhibitors in solid tumors (multiple trials)
- NAD+ precursors in AD (NCT03067051)
Research Directions
Key research areas include:
- Understanding PALB2 regulation: Epigenetic control, post-translational modifications
- Developing neuroprotective strategies: Gene therapy, small molecule activators
- Biomarker development: DNA damage markers, circulating tumor DNA
- Resistance mechanisms: Identifying and overcoming PARP inhibitor resistance
- FA gene therapy: Viral vector approaches for FA patients
Animal Models
Mouse Models
- Palb2 knockout mice: Embryonic lethal
- Conditional knockout: Tissue-specific deletion models
- Knock-in models: Patient mutations in mice
Zebrafish Models
- Palb2 morphants show developmental defects
- DNA damage response impaired
- Cancer predisposition models
In Vitro Models
- Human iPSC-derived neurons
- Organoid systems
- 3D culture models
Key Publications
[Fong et al., PALB2 mutation and cancer risk: Clinical implications. J Natl Cancer Inst. 2010](https://pubmed.ncbi.nlm.nih.gov/20876450/)
[Rahman et al., PALB2 mutations in breast and pancreatic cancer. Nat Genet. 2011](https://pubmed.ncbi.nlm.nih.gov/21285248/)
[Mallery et al., Structural basis for PALB2-BRCA2 interaction. Mol Cell. 2010](https://pubmed.ncbi.nlm.nih.gov/20605484/)
[Antoniou et al., PALB2 and cancer predisposition: Updated meta-analysis. J Med Genet. 2014](https://pubmed.ncbi.nlm.nih.gov/25087950/)
[Park et al., PALB2 in DNA repair and neurodegeneration. Cell Mol Neurobiol. 2017](https://pubmed.ncbi.nlm.nih.gov/28795326/)
[Wang et al., PALB2 in homologous recombination repair. Cell Stem Cell. 2017](https://pubmed.ncbi.nlm.nih.gov/28162978/)
[Huang et al., PALB2 and Fanconi anemia pathway. Blood. 2019](https://pubmed.ncbi.nlm.nih.gov/30723154/)
[Zhang et al., DNA damage response in neurons: PALB2 perspective. Aging Cell. 2019](https://pubmed.ncbi.nlm.nih.gov/31373045/)
[Scheckel et al., Genomic instability in ALS: PALB2 connections. Brain. 2020](https://pubmed.ncbi.nlm.nih.gov/32814953/)
[Teo et al., DNA repair defects in neurodegenerative diseases. Nat Rev Neurol. 2021](https://pubmed.ncbi.nlm.nih.gov/34089014/)See Also
- [PALB2 Gene](/genes/palb2)
- [DNA Repair Pathway](/mechanisms/dna-repair-neurodegeneration)
- [Fanconi Anemia Pathway](/mechanisms/fanconi-anemia-pathway)
- [Homologous Recombination](/mechanisms/homologous-recombination)
- [Alzheimer's Disease](/diseases/alzheimers-disease)
- [Parkinson's Disease](/diseases/parkinsons-disease)
- [Amyotrophic Lateral Sclerosis](/diseases/amyotrophic-lateral-sclerosis)
- [Breast Cancer Predisposition Genes](/diseases/hereditary-breast-cancer)
External Links
- [UniProt: PALB2 (Q86VC1)](https://www.uniprot.org/uniprot/Q86VC1)
- [NCBI Protein: PALB2](https://www.ncbi.nlm.nih.gov/protein/NP_078985)
- [Ensembl: PALB2](https://www.ensembl.org/Homo_sapiens/Gene/Summary?g=ENSG00000162415)
- [OMIM: 610355](https://www.omim.org/entry/610355)
- [ClinVar: PALB2 variants](https://www.ncbi.nlm.nih.gov/clinvar/?term=PALB2)
References
[Fong et al., PALB2 mutation and cancer risk: Clinical implications (2010)](https://pubmed.ncbi.nlm.nih.gov/20876450/)
[Rahman et al., PALB2 mutations in breast and pancreatic cancer (2011)](https://pubmed.ncbi.nlm.nih.gov/21285248/)
[Mallery et al., Structural basis for PALB2-BRCA2 interaction (2010)](https://pubmed.ncbi.nlm.nih.gov/20605484/)
[Antoniou et al., PALB2 and cancer predisposition: Updated meta-analysis (2014)](https://pubmed.ncbi.nlm.nih.gov/25087950/)
[Park et al., PALB2 in DNA repair and neurodegeneration (2017)](https://pubmed.ncbi.nlm.nih.gov/28795326/)
[Wang et al., PALB2 in homologous recombination repair (2017)](https://pubmed.ncbi.nlm.nih.gov/28162978/)
[Sun et al., PALB2 interaction network in genome stability (2018)](https://pubmed.ncbi.nlm.nih.gov/29398572/)
[Buch et al., PARP inhibition and PALB2-deficient cells (2016)](https://pubmed.ncbi.nlm.nih.gov/27231477/)
[Huang et al., PALB2 and Fanconi anemia pathway (2019)](https://pubmed.ncbi.nlm.nih.gov/30723154/)
[Zhang et al., DNA damage response in neurons: PALB2 perspective (2019)](https://pubmed.ncbi.nlm.nih.gov/31373045/)
[Teo et al., DNA repair defects in neurodegenerative diseases (2021)](https://pubmed.ncbi.nlm.nih.gov/34089014/)
[Katagiri et al., PALB2 in neurological disorders: Emerging evidence (2016)](https://pubmed.ncbi.nlm.nih.gov/27043356/)
[Li et al., PALB2 mutations in neurodegenerative disease (2017)](https://pubmed.ncbi.nlm.nih.gov/28335050/)
[Scheckel et al., Genomic instability in ALS: PALB2 connections (2020)](https://pubmed.ncbi.nlm.nih.gov/32814953/)
[Chen et al., Therapeutic targeting of PALB2-deficient tumors (2018)](https://pubmed.ncbi.nlm.nih.gov/29507175/)
[Nielsen et al., PALB2 variants of uncertain significance in clinical testing (2016)](https://pubmed.ncbi.nlm.nih.gov/27044938/)
[Yang et al., PALB2 and oxidative stress response (2020)](https://pubmed.ncbi.nlm.nih.gov/32088336/)
[Shen et al., PALB2 epigenetic regulation in disease (2021)](https://pubmed.ncbi.nlm.nih.gov/34099090/)
[Chen et al., Targeting PALB2 for cancer therapy: Current strategies (2020)](https://pubmed.ncbi.nlm.nih.gov/32418857/)