TY - JOUR
T1 - Inhibition of DNA methyltransferases in vitro by benzo[a]pyrene diol epoxide-modified substrates
AU - Wojciechowski, M. F.
AU - Meehan, T.
N1 - Copyright:
Copyright 2004 Elsevier B.V., All rights reserved.
PY - 1984
Y1 - 1984
N2 - Covalent adducts formed from the ultimate carcinogen 7β,8α-dihydroxy-9α,10α-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene inhibit the enzyme-catalyzed transfer of methyl groups from S-adenosylmethionine to cytosine residues in DNA. Two DNA methyltransferase enzymes, isolated from the bacterium Haemophilus and mouse spleen nuclei, were tested for their ability to methylate carcinogen-modified substrates in vitro. These model enzymes possess the known methylation activities found in mammalian cells, de novo, and maintenance methylation of CpG-containing nucleotide sequences. The in vitro alkylation of DNA substrates by the carcinogen effectively decreases the methyltransferase reaction of both enzymes in a manner that is directly dependent upon the level of covalent modification of the DNA. Inhibition of de novo methylation activity can be detected at very low levels of carcinogen modification, 1 hydrocaron residue per 20,000-40,000 nucleotides. Adduct levels in this range are capable of initiating transformation. Both enzymes are inactivated by direct reaction with the carcinogen in the absence of DNA. We also find that carcinogen adducts are capable of inhibiting DNA methylation at CpG sites removed from the primary lesion. These results support the proposal that carcinogen-induced DNA damage can cause alterations in methylation patterns that may eventually lead to heritable changes in gene expression.
AB - Covalent adducts formed from the ultimate carcinogen 7β,8α-dihydroxy-9α,10α-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene inhibit the enzyme-catalyzed transfer of methyl groups from S-adenosylmethionine to cytosine residues in DNA. Two DNA methyltransferase enzymes, isolated from the bacterium Haemophilus and mouse spleen nuclei, were tested for their ability to methylate carcinogen-modified substrates in vitro. These model enzymes possess the known methylation activities found in mammalian cells, de novo, and maintenance methylation of CpG-containing nucleotide sequences. The in vitro alkylation of DNA substrates by the carcinogen effectively decreases the methyltransferase reaction of both enzymes in a manner that is directly dependent upon the level of covalent modification of the DNA. Inhibition of de novo methylation activity can be detected at very low levels of carcinogen modification, 1 hydrocaron residue per 20,000-40,000 nucleotides. Adduct levels in this range are capable of initiating transformation. Both enzymes are inactivated by direct reaction with the carcinogen in the absence of DNA. We also find that carcinogen adducts are capable of inhibiting DNA methylation at CpG sites removed from the primary lesion. These results support the proposal that carcinogen-induced DNA damage can cause alterations in methylation patterns that may eventually lead to heritable changes in gene expression.
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M3 - Article
C2 - 6430903
AN - SCOPUS:0021176199
SN - 0021-9258
VL - 259
SP - 9711
EP - 9716
JO - Journal of Biological Chemistry
JF - Journal of Biological Chemistry
IS - 15
ER -