Homology-directed dna repair, mitomycin-c resistance, and chromosome stability is restored with correction of a Brca1 mutation.
Chromosomal breaks occur spontaneously as a result of normal DNA metabolism and after exposure to DNA-damaging agents. A major pathway involved in chromosomal double-strand break repair is homologous recombination. In this pathway, a DNA sequence with similarity to a damaged chromosome directs the repair of the damage. The protein products of the hereditary breast cancer susceptibility genes, BRCA1 and BRCA2, interact with the Rad51 protein, a central component of homologous repair pathways. We have recently shown that this interaction is significant by demonstrating that Brca1- and BRCA2-deficient cells are defective in homology-directed chromosomal break repair. We confirm that Brca1-deficient embryonic stem (ES) cells are defective in gene targeting and homology-directed repair of an I-Sce I-induced chromosome break. The phenotypic paradigm that defines homology-directed repair mutants is extended to these Brca1-deficient cells by the demonstration of 100-fold sensitivity to the interstrand cross-linking agent mitomycin-C and spontaneous chromosome instability. Interestingly, although chromosome aberrations were evident, aneuploidy was not observed. Repair phenotypes are partially restored by expression of a Brca1 transgene, whereas correction of one mutated Brca1 allele through gene targeting fully restores mitomycin-C resistance and chromosome stability. We conclude that the inability to properly repair strand breaks by homology-directed repair gives rise to defects in chromosome maintenance that promote genetic instability and, it is likely, tumorigenesis.
Moynahan
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ME
Department of Medicine, Memorial Sloan-Kettering Cancer Center, New York, New York 10021, USA.
Cui
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Jasin
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M
D000818:Animals; D002460:Cell Line; D019457:Chromosome Breakage; D003432:Cross-Linking Reagents / Q000494:pharmacology*; D004249:DNA Damage; D004260:DNA Repair / Q000235:genetics*; D019008:Drug Resistance, Neoplasm / Q000235:genetics; D015870:Gene Expression; D019398:Genes, BRCA1 / Q000235:genetics*; D005816:Genetic Complementation Test; D051379:Mice; D016685:Mitomycin / Q000494:pharmacology*; D009154:Mutation; D010641:Phenotype; D013234:Stem Cells / Q000502:physiology; D014162:Transfection; D019076:Transgenes
D003432:Cross-Linking Reagents; D016685:Mitomycin