Double-strand breaks, genomic integrity, and cancer
Memorial Sloan-Kettering Cancer Center, New York, NY, United States
AIM: Tumorigenesis results from multiple genetic and epigenetic alterations in growth control genes, but is usually suppressed by a variety of DNA repair pathways which prevent the accumulation of mutations. Our goal is to understand repair of a potentially mutagenic lesion, the DNA double-strand break (DSB), which can give rise to deletions, translocations, loss of heterozygosity (LOH), and other genomic alterations. Specific and recurrent translocations occur in some leukemias, lymphomas, and sarcomas, although most tumors of epithelial origin carry a variety of genomic rearrangements. METHODS: We have employed the use of a rare-cutting endonuclease to introduce DSBs at predetermined locations in the the mammalian genome. RESULTS: DSBs are repaired in mammalian cells by three pathways: homologous recombination (HR), nonhomologous end-joining (NHEJ), and single-strand annealing (SSA). We have examined inter-homolog and inter-heterolog DSB repair events in mammalian cells. In HR events involving either homologous or heterologous chromosomes, we find that crossover events that would lead to LOH or translocations, respectively, are extremely rare. By contrast to HR, we find that NHEJ and SSA readily give rise to translocations. The SSA events were designed to occur within an Alu element that is involved in genomic rearrangements at the ALL1 gene in some leukemias. This system will allow us to examine parameters affecting Alu-Alu recombination, which has been implicated in several human diseases. CONCLUSIONS: HR is for the most part a particularly genome-protective repair pathway but other pathways of DSB repair are more likely to genome altering. We are currently dissecting the roles of various protein components in these pathways, including BRCA2 and BRCA1.
Paper presented at the International Symposium on Predictive Oncology and Intervention Strategies; Nice, France; February 7 - 10, 2004; in oral session 796 (Genetic instability).