Overexpression of human DNA repair protein N-methylpurine-DNA glycosylase results in the increased removal of N-methylpurines in DNA without a concomitant increase in resistance to alkylating agents in Chinese hamster ovary cells.
N-Alkylpurines induced in DNA by simple monofunctional alkylating agents are known to be cytotoxic and possibly indirectly mutagenic. These adducts are removed by the ubiquitous N-methylpurine-DNA glycosylase (MPG) in a multistep repair pathway. Chinese hamster ovary (CHO) cell clones expressing 2- to 16-fold enhanced levels of MPG activity were isolated from cells stably transfected with human MPG cDNA expression plasmids. The in vivo removal of 3-methyladenine and 7-methylguanine from some of these lines was analyzed and was observed to reflect their MPG levels. These cell lines did not develop increased resistance, as compared to the control, in regards to cytotoxic, mutagenic and sister chromatid exchange inducing effects of the alkylating agents that induce 3-alkyladenine and 7-alkylguanine as the major alkyl adducts in DNA. These results suggest that the MPG activity is not limiting in the multi-step repair pathway of N-alkylpurines in CHO cells.
Ibeanu
G
G
Biology Division, Oak Ridge National Laboratory, TN 37831.
Hartenstein
B
B
Dunn
W C
WC
Chang
L Y
LY
Hofmann
E
E
Coquerelle
T
T
Mitra
S
S
Kaina
B
B
D000477:Alkylating Agents / Q000494:pharmacology*; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D016466:CHO Cells; D006224:Cricetinae; D004247:DNA / Q000187:drug effects / Q000378:metabolism*; D045647:DNA Glycosylases; D004260:DNA Repair; D004351:Drug Resistance; D006801:Humans; D008745:Methylation; D008969:Molecular Sequence Data; D009154:Mutation; D009699:N-Glycosyl Hydrolases / Q000235:genetics / Q000378:metabolism*; D010957:Plasmids; D011687:Purines / Q000378:metabolism*; D012854:Sister Chromatid Exchange; D013866:Thioguanine / Q000378:metabolism; D014162:Transfection
D000477:Alkylating Agents; D011687:Purines; D004247:DNA; D045647:DNA Glycosylases; D009699:N-Glycosyl Hydrolases; C076131:DNA-3-methyladenine glycosidase II; D013866:Thioguanine