Investigation of G2-phase chromosomal radiosensitivity in hereditary non-polyposis colorectal cancer cells.
OBJECTIVE
To investigate whether cells from hereditary nonpolyposis colorectal cancer (HNPCC) patients, a genetic condition characterized by constitutional mutations in DNA mismatch repair genes and associated with predisposition to colorectal carcinoma (CRC), could present a higher G2 chromosomal radiosensitivity. It is generally hypothesized that cancer predisposition in HNPCC is associated with the loss of the wild-type allele in somatic cells, resulting in defective DNA mismatch repair but, to date, no data on G2 radiosensitivity have been reported for HNPCC.


METHODS
Lymphoblastoid cell lines derived from six HNPCC patients heterozygous for MLH1, one HNPCC patient carrying a mutant MSH2 allele and three healthy controls were treated with 50 cGy of X-rays and sampled at various harvesting times, monitoring cell-cycle progression by 5-bromo-2-deoxyuridine (BrdUrd) incorporation in order to analyse chromosomal damage in the homogeneous G2 population.


RESULTS
There were no differences between lymphoblasts derived from patients in the frequency of G2 chromosomal aberrations induced by X-rays when compared with control cell lines. However, despite the absence of G2 radiosensitivity in HNPCC cells, lymphoblasts from patients heterozygous for MLH1 mutations showed a higher induction of chromatid exchanges.


CONCLUSIONS
The observed possible incorrect rejoining of double-strand breaks in MLH1 heterozygotes would be an additional and important factor contributing to loss of heterozygosity in HNPCC patients.
Franchitto
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Laboratorio di Citogenetica Molecolare e Mutagenesi - DABAC, Università degli Studi della Tuscia, Via S. Camillo de Lellis, I-01100 Viterbo, Italy.
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De Santis
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Palitti
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D048868:Adaptor Proteins, Signal Transducing; D000483:Alleles; D020137:Base Pair Mismatch; D001973:Bromodeoxyuridine / Q000378:metabolism; D002352:Carrier Proteins; D002875:Chromosomes / Q000528:radiation effects*; D003123:Colorectal Neoplasms, Hereditary Nonpolyposis / Q000235:genetics* / Q000532:radiotherapy*; D004260:DNA Repair; D004268:DNA-Binding Proteins; D016195:G2 Phase / Q000528:radiation effects*; D020022:Genetic Predisposition to Disease; D006579:Heterozygote; D006801:Humans; D019656:Loss of Heterozygosity; D000070957:MutL Protein Homolog 1; D051718:MutS Homolog 2 Protein; D009154:Mutation; D009363:Neoplasm Proteins / Q000235:genetics; D009687:Nuclear Proteins; D011518:Proto-Oncogene Proteins / Q000235:genetics; D013997:Time Factors; D014407:Tumor Cells, Cultured; D014965:X-Rays
D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; D004268:DNA-Binding Proteins; C501486:MLH1 protein, human; D009363:Neoplasm Proteins; D009687:Nuclear Proteins; D011518:Proto-Oncogene Proteins; C497172:MSH2 protein, human; D000070957:MutL Protein Homolog 1; D051718:MutS Homolog 2 Protein; D001973:Bromodeoxyuridine