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Increased UV resistance in xeroderma pigmentosum group A cells after transformation with a human genomic DNA clone
1Center in Molecular Toxicology, Vanderbilt University School of Medicine, Nashville, TN 37232.
Abstract:
Xeroderma pigmentosum (XP) is an autosomal recessive disease in which the major clinical manifestation is a 2,000-fold enhanced probability of developing sunlight-induced skin tumors, and the molecular basis for the disease is a defective DNA excision repair system. To clone the gene defective in XP complementation group A (XP-A), cDNA clones were isolated by a competition hybridization strategy in which the corresponding mRNAs were more abundant in cells of the obligately heterozygous parents relative to cells of the homozygous proband affected with the disease. In this report, a human genomic DNA clone that contains this cDNA was transformed into two independent homozygous XP-A cell lines, and these transformants displayed partial restoration of resistance to the killing effects of UV irradiation. The abundance of mRNA corresponding to this cDNA appears to correlate well with the observed UV cell survival. The results of unscheduled DNA synthesis after UV exposure indicate that the transformed cells are repair proficient relative to that of the control XP-A cells. However, using this same genomic DNA, transformation of an XP-F cell line did not confer any enhancement of UV survival or promote unscheduled DNA synthesis after UV exposure.
Insights
Researchers identified a gene crucial for DNA repair in Xeroderma pigmentosum group A (XP-A). Restoring this gene partially corrected UV sensitivity and DNA repair defects in XP-A cells, advancing understanding of this rare genetic disorder.
Area of Science:
- Molecular Biology
- Genetics
- Dermatology
Background:
- Xeroderma pigmentosum (XP) is an autosomal recessive disorder.
- XP is characterized by a defective DNA excision repair system.
- XP patients have a significantly increased risk of skin tumors due to UV exposure.
Purpose of the Study:
- To clone the gene responsible for XP complementation group A (XP-A).
- To investigate the functional restoration of DNA repair mechanisms in XP-A cells.
Main Methods:
- cDNA clones were isolated using a competition hybridization strategy.
- Human genomic DNA containing the identified cDNA was transformed into XP-A cell lines.
- UV irradiation survival assays and unscheduled DNA synthesis were performed.
Main Results:
- Transformed XP-A cells showed partial restoration of resistance to UV irradiation.
- mRNA abundance correlated with UV cell survival.
- Transformed XP-F cells did not exhibit enhanced UV survival or DNA repair.
Conclusions:
- The cloned gene is defective in XP-A and plays a role in DNA repair.
- The findings contribute to understanding the molecular basis of XP-A.
- The study highlights the specificity of the identified gene for XP-A.