title: A Ham1p-dependent mechanism and modulation of the pyrimidine biosynthetic pathway can both confer resistance to 5-fluorouracil in yeast.
abstract: 5-Fluorouracil (5-FU) is an anticancer drug and pyrimidine analogue. A problem in 5-FU therapy is acquired resistance to the drug. To find out more about the mechanisms of resistance, we screened a plasmid library in yeast for genes that confer 5-FU resistance when overexpressed. We cloned five genes: CPA1, CPA2, HMS1, HAM1 and YJL055W. CPA1 and CPA2 encode a carbamoyl phosphate synthase involved in arginine biosynthesis and HMS1 a helix-loop-helix transcription factor. Our results suggest that CPA1, CPA2, and HMS1 confer 5-FU resistance by stimulating pyrimidine biosynthesis. Thus, they are unable to confer 5-FU resistance in a ura2 mutant, and inhibit the uptake and incorporation into RNA of both uracil and 5-FU. In contrast, HAM1 and YJL055W confer 5-FU resistance in a ura2 mutant, and selectively inhibit incorporation into RNA of 5-FU but not uracil. HAM1 is the strongest resistance gene, but it partially depends on YJL055W for its function. This suggests that HAM1 and YJL055W function together in mediating resistance to 5-FU. Ham1p encodes an inosine triphosphate pyrophosphatase that has been implicated in resistance to purine analogues. Our results suggest that Ham1p could have a broader specificity that includes 5-FUTP and other pyrimidine analogoue triphosphates.
authors.affiliation: Department of Microbiology, Swedish University of Agricultural Sciences, Uppsala, Sweden.
authors.forename: Mattias
authors.initials: M
authors.lastname: Carlsson
authors.forename: Marie
authors.initials: M
authors.lastname: Gustavsson
authors.forename: Guo-Zhen
authors.initials: GZ
authors.lastname: Hu
authors.forename: Eva
authors.initials: E
authors.lastname: Murén
authors.forename: Hans
authors.initials: H
authors.lastname: Ronne
mesh_terms: D001221:Aspartate Carbamoyltransferase / Q000235:genetics / Q000378:metabolism; D002223:Carbamoyl-Phosphate Synthase (Glutamine-Hydrolyzing) / Q000235:genetics / Q000378:metabolism; D005472:Fluorouracil / Q000494:pharmacology*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism*; D015003:Yeasts / Q000187:drug effects* / Q000378:metabolism*
chemical_list: D029701:Saccharomyces cerevisiae Proteins; C110837:URA2 protein, S cerevisiae; C531894:YJL055w protein, S cerevisiae; D001221:Aspartate Carbamoyltransferase; C403521:CPA1 protein, S cerevisiae; D002223:Carbamoyl-Phosphate Synthase (Glutamine-Hydrolyzing); D005472:Fluorouracil