A combination of genetic suppressor elements produces resistance to drugs inhibiting DNA replication

Many anticancer drugs inhibit DNA replication. To investigate the mechanism of permanent growth inhibition after transient arrest of DNA replication, we selected genetic suppressor elements (GSEs) conferring resistance to rep lication inhibitor Aphidicolin. Starting from a retroviral expression libra ry carrying normalized fragments of human cell cDNA, we isolated four GSEs which, when introduced as a combination, produced resistance to Aphidicolin , doxorubicin and hydroxyurea in HT1080 fibrosarcoma cells. The four GSEs w ere derived from ORFX bromodomain protein gene, WIZ zinc finger protein gen e, the gene for subunit 3 of cytochrome c oxidase, and the gene correspondi ng to an EST with no known function. A cell line carrying all four GSEs sho wed a weaker induction of the senescence-like phenotype after treatment wit h Aphidicolin or doxorubicin; the resistance of this cell line was not asso ciated with decreased doxorubicin accumulation. These results indicate that combined effects of GSEs derived from these four genes increase cellular r esistance to replication-inhibiting drugs, possibly by inhibiting drug-indu ced senescence.