Alkylpurine-DNA-N-glycosylase knockout mice show increased susceptibility to induction of mutations by methyl methanesulfonate.
Alkylpurine-DNA-N-glycosylase (APNG) null mice have been generated by homologous recombination in embryonic stem cells. The null status of the animals was confirmed at the mRNA level by reverse transcription-PCR and by the inability of cell extracts of tissues from the knockout (ko) animals to release 3-methyladenine (3-meA) or 7-methylguanine (7-meG) from 3H-methylated calf thymus DNA in vitro. Following treatment with DNA-methylating agents, increased persistence of 7-meG was found in liver sections of APNG ko mice in comparison with wild-type (wt) mice, demonstrating an in vivo phenotype for the APNG null animals. Unlike other null mutants of the base excision repair pathway, the APNG ko mice exhibit a very mild phenotype, show no outward abnormalities, are fertile, and have an apparently normal life span. Neither a difference in the number of leukocytes in peripheral blood nor a difference in the number of bone marrow polychromatic erythrocytes was found when ko and wt mice were exposed to methylating or chloroethylating agents. These agents also showed similar growth-inhibitory effects in primary embryonic fibroblasts isolated from ko and wt mice. However, treatment with methyl methanesulfonate resulted in three- to fourfold more hprt mutations in splenic T lymphocytes from APNG ko mice than in those from wt mice. These mutations were predominantly single-base-pair changes; in the ko mice, they consisted primarily of AT-->TA and GC-->TA transversions, which most likely are caused by 3-meA and 3- or 7-meG, respectively. These results clearly show an important role for APNG in attenuating the mutagenic effects of N-alkylpurines in vivo.
Elder
R H
RH
CRC Section of Genome Damage and Repair, Paterson Institute for Cancer Research, Christie Hospital (NHS) Trust, Manchester M20 4BX, United Kingdom. RElder@picr.man.ac.uk
Jansen
J G
JG
Weeks
R J
RJ
Willington
M A
MA
Deans
B
B
Watson
A J
AJ
Mynett
K J
KJ
Bailey
J A
JA
Cooper
D P
DP
Rafferty
J A
JA
Heeran
M C
MC
Wijnhoven
S W
SW
van Zeeland
A A
AA
Margison
G P
GP
D000818:Animals; D001854:Bone Marrow Cells / Q000187:drug effects; D002478:Cells, Cultured; D045647:DNA Glycosylases; D003606:Dacarbazine / Q000031:analogs & derivatives / Q000494:pharmacology; D004912:Erythrocytes / Q000187:drug effects; D005038:Ethylnitrosourea / Q000031:analogs & derivatives / Q000494:pharmacology; D005260:Female; D005347:Fibroblasts / Q000187:drug effects; D006147:Guanine / Q000031:analogs & derivatives / Q000378:metabolism; D007041:Hypoxanthine Phosphoribosyltransferase / Q000235:genetics*; D007958:Leukocyte Count / Q000187:drug effects; D008099:Liver / Q000378:metabolism; D008297:Male; D008741:Methyl Methanesulfonate / Q000633:toxicity*; D051379:Mice; D008810:Mice, Inbred C57BL; D008811:Mice, Inbred DBA; D018345:Mice, Knockout; D009153:Mutagens / Q000633:toxicity*; D009154:Mutation; D009699:N-Glycosyl Hydrolases / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D000077204:Temozolomide
D009153:Mutagens; C017139:1-(2-chloroethyl)-1-nitrosourea; D006147:Guanine; C008450:7-methylguanine; D003606:Dacarbazine; C008449:O-(6)-methylguanine; D008741:Methyl Methanesulfonate; D007041:Hypoxanthine Phosphoribosyltransferase; C021565:3-methyladenine-DNA glycosylase; C037081:7-methylguanine DNA glycosylase; D045647:DNA Glycosylases; D009699:N-Glycosyl Hydrolases; C076131:DNA-3-methyladenine glycosidase II; D005038:Ethylnitrosourea; D000077204:Temozolomide