Role of nucleotide excision repair in processing of O4-alkylthymines in human cells.
O4-Alkylthymines have been implicated as potential carcinogenic DNA lesions. We have studied the effects of O4-methylthymine, O4-ethylthymine, and O4-n-propylthymine in a model system in which a single lesion was located at a defined position on a SV40-based shuttle vector and have found large differences in the effects of these lesions in repair-proficient and nucleotide excision repair-deficient cells. In repair-competent human HeLa cells, normal fibroblasts, and XP-A (2OS) revertant cells, all 3 residues were highly mutagenic; a mutation frequency of approximately 20% was found for both O4-methylthymine and O4-ethylthymine, whereas that of O4-n-propylthymine was approximately 12%. These frequencies were independent of the activity of the O6-alkylguanine DNA alkyltransferase. All three O4-alkylthymines induced T-->C transitions exclusively. In nucleotide excision repair-deficient XP-A cells, however, these lesions were not mutagenic but strongly inhibited plasmid replication (> 90%). These results indicate that O4-alkylthymines are efficiently recognized by the nucleotide excision repair system and cause a complete cessation of plasmid replication if this system is deficient. Nevertheless, proficiency in the nucleotide excision repair pathway correlates with a high frequency of mutation induction by these lesions.
Klein
J C
JC
Division of Molecular Carcinogenesis, The Netherlands Cancer Institute, Amsterdam.
Bleeker
M J
MJ
Roelen
H C
HC
Rafferty
J A
JA
Margison
G P
GP
Brugghe
H F
HF
van den Elst
H
H
van der Marel
G A
GA
van Boom
J H
JH
Kriek
E
E
D019883:Alkyl and Aryl Transferases; D001483:Base Sequence; D004260:DNA Repair; D004261:DNA Replication; D005347:Fibroblasts / Q000166:cytology; D006367:HeLa Cells; D006801:Humans; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010957:Plasmids / Q000235:genetics; D013539:Simian virus 40 / Q000235:genetics; D013941:Thymine / Q000031:analogs & derivatives* / Q000378:metabolism; D014162:Transfection; D014166:Transferases / Q000378:metabolism; D014983:Xeroderma Pigmentosum / Q000235:genetics / Q000378:metabolism
C040384:4-ethylthymine; C089944:O-4-propylthymine; C021223:O-4-methylthymine; D014166:Transferases; D019883:Alkyl and Aryl Transferases; C050956:DNA alkyltransferase; D013941:Thymine