Adaptive increase of O6-methylguanine-acceptor protein in HeLa cells following N-methyl-N'-nitro-N-nitrosoguanidine treatment.
We have assayed in extracts of HeLa cells the amount of acceptor protein that removes O6-methylguanine adducts from alkylated DNA. Cells were treated with single or multiple nontoxic doses of N-methyl-N'-nitrosoguanidine (MNNG) and the extracts were analyzed up to 32 h after the last exposure. The acceptor activity assayed immediately (1 h) after single exposures decreases linearly with dose indicating that the acceptor protein is used up by endogenous O6-methylguanine adducts in a stoichiometric reaction. Multiple exposures, assayed 8-24 h after the last exposure, increase the amount of acceptor protein in a dose dependent fashion followed by a decrease above a cumulative dose of 100 ng/ml. Under conditions of maximum induction, there are about 300,000 acceptor protein sites per cell, approximately 3 fold above the constitutive level. Both in adapted and unadapted cells the methyl group from O6-methylguanine adducts in the alkylated DNA is transferred to cysteine residues of the acceptor protein(s).
D001665:Binding Sites; D006147:Guanine / Q000031:analogs & derivatives* / Q000378:metabolism; D006367:HeLa Cells / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D008769:Methylnitronitrosoguanidine / Q000494:pharmacology*; D011485:Protein Binding
D008769:Methylnitronitrosoguanidine; D006147:Guanine; C008449:O-(6)-methylguanine