5-Formyluracil and its nucleoside derivatives confer toxicity and mutagenicity to mammalian cells by interfering with normal RNA and DNA metabolism.
Oxidation of the methyl group of thymine yields 5-(hydroxymethyl)uracil (5-hmU) and 5-formyluracil (5-foU) as major products. Whereas 5-hmU appears to have normal base pairing properties, the biological effects of 5-foU are rather poorly characterised. Here, we show that the colony forming ability of Chinese hamster fibroblast (CHF) cells is greatly reduced by addition of 5-foU, 5-formyluridine (5-foUrd) and 5-formyl-2'-deoxyuridine (5-fodUrd) to the growth medium. There are no toxic effects of 5-fodUrd on cells defective in thymidine kinase or thymidylate synthetase, suggesting that the toxicity may be caused by 5-fodUrd phosphorylation and subsequent inhibition of thymidylate synthetase. Whereas 5-fodUrd was the most effective 5-foU derivative causing cell growth inhibition, the corresponding ribonucleoside 5-foUrd was more effective in inhibiting [3H]uridine incorporation in non-dividing rat nerve cells in culture, suggesting that 5-foUrd exerts its toxicity through interference with RNA rather than DNA synthesis. Addition of 5-foU and 5-fodUrd was also found to promote mutagenicity at the hypoxanthine-guanine phosphoribosyltransferase (HPRT) locus of CHF cells; 5-fodUrd being three orders of magnitude more potent than 5-foU. In contrast, neither 5-hmU nor 5-(hydroxymethyl)-2'-deoxyuridine induced HPRT mutations. The mutation induction indicates that 5-foU will be incorporated into DNA and has base pairing properties different from that of thymine. These results suggest that 5-foU residues, originating from incorporation of oxidised bases, nucleosides or nucleotides or by oxidation of DNA, may contribute significantly to the damaging effects of oxygen radical species in mammalian cells.
Department of Molecular Biology, Institute of Medical Microbiology, University of Oslo, The National Hospital, 0027, Oslo, Norway.
A
A
Klungland
R
R
Paulsen
V
V
Rolseth
Y
Y
Yamada
Y
Y
Ueno
P
P
Wiik
A
A
Matsuda
E
E
Seeberg
S
S
Bjelland
D000818:Animals; D002455:Cell Division / Q000187:drug effects; D006224:Cricetinae; D004247:DNA / Q000378:metabolism*; D003857:Deoxyuridine / Q000031:analogs & derivatives* / Q000633:toxicity*; D005347:Fibroblasts / Q000187:drug effects / Q000378:metabolism; D051379:Mice; D009153:Mutagens / Q000633:toxicity*; D009474:Neurons / Q000187:drug effects / Q000378:metabolism; D012313:RNA / Q000378:metabolism*; D051381:Rats; D014407:Tumor Cells, Cultured; D014498:Uracil / Q000031:analogs & derivatives* / Q000633:toxicity*; D014529:Uridine / Q000031:analogs & derivatives* / Q000633:toxicity*
D009153:Mutagens; C007777:5-formyluracil; C012983:5-formyluridine; C061519:5-formyl-2'-deoxyuridine; D014498:Uracil; D012313:RNA; D004247:DNA; D003857:Deoxyuridine; D014529:Uridine