XRCC3 is required for chromosome stability in human cells
Department of Human Genetics, Research Institute for Radiation Biology and Medicine, Hiroshima University, Hiroshima Japan
AIM: XRCC3 is known as a RAD51 paralog which is required for the homologous recombinational repair of damaged DNA. A single C-to-T nucleotide change at codon 241 (Thr241Met) has been identified in the XRCC3 gene. The T241M variant has been associated with an increased cancer risk. We tried to explore a role for the gene in human somatic cells. METHODS: We generated XRCC3-deficient cells from a human colon cancer cell line by gene targeting. RESULTS: The XRCC3 mutant cells showed 2-fold sensitivity to interstrand cross-linking agents. Frequency of sister chromatid exchange was reduced mildly in the mutant cells. However, the frequency of targeting integration was not affected. The observed phenotypes were complemented by expression of the wild-type and variant XRCC3 genes. The relationship between DNA repair and endoreduplication, a process that gives rise to cells with extra copies of genomic DNA without cytokinesis, is not well understood. We show that XRCC3-deficient cells underwent endoreduplication at high rate with intact checkpoints. Expression of the transfected wild-type XRCC3 cDNA completely restored this phenotype, while expression of the variant did not restore the increased endoreduplication. CONCLUSIONS: These findings suggest that the XRCC3 gene is required for chromosome stability via recombinational repair and replication initiation in human cells.
Paper presented at the International Symposium on Predictive Oncology and Intervention Strategies; Nice, France; February 7 - 10, 2004; in poster session 796 (Genetic instability).