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G2 phase repair of X-ray-induced chromosomal DNA damage in trichothiodystrophy cells
K K Sanford1, R Parshad, F M Price
1Laboratory of Cellular and Molecular Biology, National Cancer Institute, Bethesda, MD 20892.
Abstract:
The repair of X-ray-induced DNA damage during G2 cell-cycle phase has been examined in lines of skin fibroblasts from three patients with trichothiodystrophy (TTD), one with apparently normal and two with defective nucleotide excision repair (NER). These responses are compared with those of five lines from clinically normal controls, lines from xeroderma pigmentosum (XP), Cockayne syndrome (CS), Down syndrome (DS), and ataxia telangiectasia (AT) patients. Chromosomal DNA repair was measured as the chromatid aberration frequency (CAF) or total number of chromatid breaks and long gaps per 100 metaphase cells, determined 0.5-1.5 h after X-irradiation (53 rad). Chromatid breaks and gaps (as defined herein) represent unrepaired DNA strand breaks. Only one of the TTD lines, TTD 1BR, showed an abnormally high CAF. This line was shown subsequently to be of a different complementation group, representing a new nucleotide excision repair gene. An abnormally high CAF was also observed, as reported previously, in XP-C, AT and DS but not in CS skin fibroblasts. In addition, cell lines were examined for DNA incision activity by an indirect method in which chromatid aberrations were enumerated with or without ara-C, an inhibitor of repair synthesis, added after X-irradiation. All TTD lines had abnormally low incision activity.
Insights
Trichothiodystrophy (TTD) patients exhibit defective DNA repair. Two TTD cell lines showed low DNA incision activity, indicating a novel nucleotide excision repair defect in one patient.
Area of Science:
- Genetics
- Molecular Biology
- Cell Biology
Background:
- Trichothiodystrophy (TTD) is a rare genetic disorder.
- DNA repair mechanisms are crucial for maintaining genomic stability.
- Defects in DNA repair are linked to various genetic syndromes.
Purpose of the Study:
- To investigate the DNA repair capacity in skin fibroblasts from TTD patients.
- To identify potential defects in nucleotide excision repair (NER) in TTD.
- To compare DNA repair responses in TTD with other genetic disorder cell lines.
Main Methods:
- X-ray irradiation of skin fibroblast cell lines.
- Measurement of chromatid aberration frequency (CAF) as an indicator of DNA repair.
- Assessment of DNA incision activity using an indirect method with ara-C.
Main Results:
- One TTD cell line (TTD 1BR) exhibited an abnormally high CAF, suggesting a defect in DNA repair.
- This TTD line represented a new complementation group, indicating a novel NER gene.
- All TTD lines displayed abnormally low DNA incision activity, irrespective of CAF results.
Conclusions:
- TTD patients can present with defective DNA repair, specifically impacting NER.
- A novel NER gene defect was identified in one TTD patient.
- Reduced DNA incision activity is a common feature in TTD fibroblasts.