FANCONI-ANEMIA CELLS HAVE A NORMAL GENE STRUCTURE FOR TOPOISOMERASE-I

Cells from Fanconi anemia (FA) patients have defective DNA repair and are hypersensitive to DNA crosslinking agents such as mitomycin C (MMC ). We examined the possibility that topoisomerase I is involved in the DNA crosslink repair system and is deficient in FA group A cells. FA cells and control cells were exposed to MMC with or without camptothec in (CPT), a topoisomerase I inhibitor. The cells did not show any incr eased sensitivity to killing by MMC with CPT, suggesting that the topo isomerase I is not involved in MMC-damaged DNA repair. However, FA cel ls showed increased sensitivity to CPT in comparison to control cells, raising the possibility of altered topoisomerase I in FA cells. There fore, a mutation analysis was performed on topoisomerase I cDNA from F A cells by using chemical cleavage mismatch scanning and nucleotide se quencing. No mutation was detected from GM1309, a group A FA cell line . A base transition (C to T) at position 241, causing an amino acid ch ange (His to Tyr), was found in GM2061, a FA cell line of unknown comp lementation group. However, allele-specific oligonucleotide hybridizat ion analysis showed that this is a gene polymorphism. We conclude that FA cells have normal gene structure for topoisomerase I.