The XPC (Xeroderma Pigmentosum Complementation Group C) gene encodes a protein critical for DNA nucleotide excision repair (NER). This protein recognizes and initiates repair of DNA lesions caused by ultraviolet (UV) radiation and chemical mutagens, serving as a key initial factor in the global genome nucleotide excision repair (GG-NER) pathway.
| XPC Gene |
|---|
| Gene Symbol | XPC |
| Full Name | Xeroderma Pigmentosum Complementation Group C |
| Chromosomal Location | 3p25.1 |
| NCBI Gene ID | [7508](https://www.ncbi.nlm.nih.gov/gene/7508) |
| OMIM | [278720](https://www.omim.org/entry/278720) |
| Ensembl ID | ENSG00000154767 |
| UniProt ID | [Q01831](https://www.uniprot.org/uniprot/Q01831) |
¶ Protein Structure and Function
XPC forms a heterotrimeric complex with RAD23B (hHR23B) and CETN2 (centrin-2) to scan DNA for lesions:
- XPC: The DNA damage recognition subunit
- RAD23B: Stabilizes XPC and links to the proteasome
- CETN2: Calcium-binding protein that aids in damage verification
The XPC protein contains several functional domains:
- DNA damage recognition domain: Binds to helix-distorting lesions
- RAD23B-binding domain: Mediates complex formation
- TFIIH interaction domain: Recruits the transcription/repair factor
XPC performs several critical functions in GG-NER:
- ** lesion scanning**: XPC-RAD23B-CETN2 complex scans DNA for helix-distorting damage
- Damage verification: XPC verifies the presence of a genuine lesion
- TFIIH recruitment: Once damage is confirmed, XPC recruits the TFIIH complex
- Pre-incision complex assembly: XPC helps assemble the complete NER machinery
XPC recognizes various types of DNA damage:
- UV-induced photoproducts: 6-4 photoproducts, cyclobutane pyrimidine dimers
- Chemical adducts: Benzo[a]pyrene adducts, aflatoxin B1 adducts
- Crosslinks: Cisplatin-induced DNA crosslinks
- Oxidative damage: Certain forms of oxidative DNA damage
flowchart TD
A["DNA Damage"] --> B{"XPC Detection"}
B --> C["Global Genome NER<br/>GG-NER"]
B --> D["Transcription-Coupled NER<br/>TC-NER"]
C --> E["XPC-RAD23B-CETN2"]
D --> F[CSA-CSB
F --> E
E --> G["TFIIH Recruitment"]
G --> H["XPA Verification"]
H --> I["XPF incision"]
H --> J["XPG incision"]
I --> K["DNA Ligation"]
J --> K
style C fill:#e1f5fe,stroke:#333
style D fill:#e1f5fe,stroke:#333
style K fill:#c8e6c9,stroke:#333
| Step |
XPC Role |
| Damage recognition |
Primary sensor for GG-NER |
| Verification |
Confirms lesion through structural probing |
| TFIIH recruitment |
Direct interaction with XPB/XPD subunits |
| Pre-incision complex |
Stabilizes NER machinery at damage site |
Mutations in XPC cause XP complementation group C:
- Extreme sensitivity to ultraviolet light
- 10,000-fold increased risk of skin cancers (basal cell carcinoma, squamous cell carcinoma, melanoma)
- Neurological degeneration in some patients, including cognitive decline and hearing loss
- Premature aging phenotypes
XPC deficiency has implications for neurodegenerative diseases:
- DNA repair deficiency in neurons leads to accumulation of oxidative DNA damage
- Associated with accelerated neurodegeneration in XP patients
- May contribute to sporadic neurodegenerative diseases through accumulated DNA damage
- Reduced ability to repair endogenous DNA damage from cellular metabolism
XPC deficiency increases cancer risk:
- XPC deficiency increases mutation burden in all tissues
- Enhanced susceptibility to UV-induced skin cancers
- May play a role in lung, head and neck cancers
¶ Brain Expression and Function
XPC is expressed throughout the brain:
- All brain regions: Cortex, hippocampus, cerebellum, basal ganglia
- Expression dynamics: Upregulated in response to DNA damage
- Neural progenitor cells: Higher expression in proliferating cells
- Neurons: Essential for maintaining genomic integrity
- Primarily nuclear: Concentrated in the nucleoplasm
- DNA repair foci: Associates with DNA repair foci upon damage
- Cell cycle-dependent: Higher during S phase
- Pharmaceutical agents that enhance NER capacity are being explored
- Topical DNA repair enzymes being developed for XP patients
- Small molecules targeting XPC activity under investigation
- Understanding XPC function may inform therapies for age-related neurodegeneration
- Gene therapy approaches being investigated for XP
- Biomarker potential: XPC expression as indicator of DNA repair capacity
- Developing brain-penetrant NER enhancers
- Understanding how XPC decline contributes to sporadic neurodegeneration
- Gene therapy for XPC-deficient patients
| Interactor |
Type |
Function |
| RAD23B |
Protein |
Stabilization, proteasome linking |
| CETN2 |
Protein |
Damage verification |
| TFIIH |
Complex |
XPB, XPD recruitment |
| XPA |
Protein |
Damage verification |
| XPF |
Enzyme |
5' incision |
| XPG |
Enzyme |
3' incision |