Mutation at the Catalytic Site of Topoisomerase I in CEM/C2, a Human Leukemia Cell Line Resistant to Camptothecin

摘要: We developed previously a resistant cell line, CEM/C2, from the human leukemia line CCRF-CEM by stepwise selection in camptothecin. This is 974-fold more to camptothecin than parental cells. Resistance only partially explained 2-fold reductions topoisomerase I protein and mRNA levels. further investigated biochemical molecular features of line. Sequence analyses top1 cDNA CEM/C2 identified mutations corresponding two amino acid substitutions, Met370Thr Asn722Ser. Asn722Ser next catalytic Tyr723 region highly conserved among type eukaryotic DNA topoisomerases. Recombinant with substitution was found be catalytically active These results indicate that resistance due mutation strongly suggest asparagine immediately flanking tyrosine important for action.