Chromatid damage after G2 phase x-irradiation of cells from cancer-prone individuals implicates deficiency in DNA repair.

Abstract

Ten lines. of. skin fibroblasts from individuals with genetic disorders predisposing to a high risk of cancer were compared with nine lines from normal adult-donors with respect to chromatid damage after x-irradiation [25, 50, and 100 rad (0.25 0.50, and 1 gray)] during G2 phase. The 10 cell lines represented five genetic disorders: Bloom syndrome, familial polyposis, Fanconi anemia, Gardner syndrome, and xeroderma.pigmentosum, complementation groups A(XP-A), C(XP-C), E(XP-E), and variant (XP-Va).. The incidence of chromatid breaks in all cancer-prone lines except XP-E and XP-A was significantly higher. than in the normal lines; The incidence of chromatid gaps in all cancer-prone lines except XP-A and XP-Va was significantly higher than in the normal lines. Because each chromatid apparently contains a-single continuous DNA double strand, chromatid breaks and gaps represent unrepaired DNA strand breaks arising directly or indirectly during excision repair of x-ray-inducedDNA damage. These cytogenetic data together with results-from use of the DNA repair.inhibitor arabinofuranosyl cytosine (cytosine arabinoside) suggest that cells from all of these cancer-prone individuals are deficient in some step of DNA repair, predominantly excision repair operative during the G2-prophase period of the cell cycle.-It appears that these DNA repair. deficiencies are associated with a genetic predisposition to a high risk of cancer.A number of inherited human disorders, including ataxia telangiectasia, Gardner syndrome (GS), familial polyposis (FP), Fanconi anemia (FA), Bloom syndrome (BS), and xeroderma pigmentosum (XP), predispose the individual to a high risk of cancer. Cells from these individuals are useful for elucidating mechanisms of carcinogenesis. A deficiency in the repair of UV-induced DNA damage was described in 1968 (1) in cells from XP individuals with a high incidence of skin cancer. Subsequently, studies on ataxia telangiectasia and FA cells provided some evidence that these cells may be defective in repair of DNA damage produced by ionizing radiation or DNA crosslinking agents (2-9). However, numerous attempts with biochemical methods have failed to reveal a DNA repair deficiency(ies) in all of these genetic disorders. When exposed to ionizing radiation during the G2 phase of the cell cycle, skin fibroblasts from ataxia telangiectasia and FA individuals show a high incidence of chromatid breaks or gaps at metaphase compared.with cells from normal individuals (3,8,9). Because. each chromatid apparently contains a single continuous DNA double strand, chromatid breaks and gaps represent unrepaired DNA strand breaks (3,[8][9][10][11][12][13][14][15][16][17]. These strand breaks could arise directly or indirectly during excision repair of the DNA damage produced by ionizing radiation (9, 13, 16). In view of this interpretation of cytogenetic results, cells from at least two of the.genetic disorders, ataxia telangiectasia and FA, appear to have a DNA repair defect operative during G2-prophase.The present stud...

Multiplexed DNA repair assays for multiple lesions and multiple doses via transcription inhibition and transcriptional mutagenesis

“…Lymphoblastoid WT None GM15510 (8) Lymphoblastoid WT None GM15213 (9) Lymphoblastoid WT None GM15221 (10) Lymphoblastoid WT None GM15227 (11) Lymphoblastoid WT None GM15385 (12) Lymphoblastoid WT None GM15590 (13) Lymphoblastoid WT None GM15038 (14) Lymphoblastoid WT None GM15056 (15) Lymphoblastoid WT None GM15072 (16) Lymphoblastoid WT None GM15144 (17) Lymphoblastoid WT None GM15216 (18) Lymphoblastoid WT None GM15226 (19) Lymphoblastoid WT None GM15242 (20) Lymphoblastoid WT None GM15268 (21) Lymphoblastoid WT None GM15324 (22) Lymphoblastoid WT None GM15386 (23) Lymphoblastoid WT None GM15061 (24) Lymphoblastoid WT None…”

“…More direct measurements of DRC in vitro using cell lysates have overcome some of this complexity by integrating these factors into a single readout (17)(18)(19)(20); however, these methods require separate assays for measurements in more than one repair pathway, and may not be representative of DRC in cells. Measuring the consequences of DNA repair in intact cells by monitoring sister chromatid exchanges, chromosome aberrations, or DNA strand breaks by comet assays also integrates complexity into a single readout, but it requires labor-intensive analyses that make it refractory to implementation in a clinical setting (21)(22)(23). Although recently developed high-throughput comet assays provide an excellent alternative, they are limited to DNA damage that leads to, or can be converted to, DNA strand breaks (24).…”

Influence of polymorphisms at loci encoding DNA repair proteins on cancer susceptibility and G2chromosomal radiosensitivity

“…Unrepaired damage is seen at the subsequent metaphase as chromatid gaps and breaks. The assay was originally developed in fibroblasts as a possible measure of cancer predisposition [Parshad et al, 1983;Sanford et al, 1989] and subsequently adapted for lymphocytes [Scott et al, 1996]. Enhanced G 2 chromosomal radiosensitivity has been detected in several welldefined cancer susceptibility syndromes, most notably ataxia telangiectasia [Parshad and Sanford, 2001].…”

Bleomycin-induced chromosomal damage in tuberous sclerosis

“…It is likely that chromosomal sensitivity to mutagens plays an important role in carcinogenesis of organs and tissues that have direct contact with the external environment, such as respiratory, digestive, and integumentary systems (Hsu et al, 1989). Furthermore, a similar increase in number of chromosomal aberrations was also found in some heritable cancer-prone conditions after X-irradiation or BLM treatment in vitro (Parshad et al, 1983;Sanford et al, 1987;Vorechovsky et al, 1989b). It appears that this increased chromosomal damage results from deficient mechanisms of DNA repair (Gantt et al, 1987).…”