title: Impact of benzo[a]pyrene-2'-deoxyguanosine lesions on methylation of DNA by SssI and HhaI DNA methyltransferases.
abstract: DNA damage caused by the binding of the tumorigen 7R,8S-diol 9S,10R-epoxide (B[a]PDE), a metabolite of bezo[a]pyrene, to guanine in CpG dinucleotide sequences could affect DNA methylation and, thus, represent a potential epigenetic mechanism of chemical carcinogenesis. In this work, we investigated the impact of stereoisomeric (+)- and (-)-trans-anti-B[a]P-N(2)-dG adducts (B(+) and B(-)) on DNA methylation by prokaryotic DNA methyltransferases M.SssI and M.HhaI. These two methyltransferases recognize CpG and GCGC sequences, respectively, and transfer a methyl group to the C5 atom of cytosine (C). A series of 18-mer unmethylated or hemimethylated oligodeoxynucleotide duplexes containing trans-anti-B[a]P-N(2)-dG adducts was generated. The B(+) or B(-) residues were introduced either 5' or 3' adjacent or opposite to the target 2'-deoxycytidines. The B[a]PDE lesions practically produced no effect on M.SssI binding to DNA but reduced M.HhaI binding by 1-2 orders of magnitude. In most cases, the benzo[a]pyrenyl residues decreased the methylation efficiency of hemimethylated and unmethylated DNA by M.SssI and M.HhaI. An absence of the methylation of hemimethylated duplexes was observed when either the (+)- or the (-)-trans-anti-B[a]P-N(2)-dG adduct was positioned 5' to the target dC. The effects observed may be related to the minor groove conformation of the bulky benzo[a]pyrenyl residue and to a perturbation of the normal contacts of the methyltransferase catalytic loop with the B[a]PDE-modified DNA. Our results indicate that a trans-anti-B[a]P-N(2)-dG lesion flanking a target dC in the CpG dinucleotide sequence on its 5'-side has a greater adverse impact on methylation than the same lesion when it is 3' adjacent or opposite to the target dC.
authors: Chemistry Department, Moscow State University, Moscow, 119992, Russia.
authors: Oksana M
authors: OM
authors: Subach
authors: Vladimir B
authors: VB
authors: Baskunov
authors: Maria V
authors: MV
authors: Darii
authors: Diana V
authors: DV
authors: Maltseva
authors: Dmitrii A
authors: DA
authors: Alexandrov
authors: Olga V
authors: OV
authors: Kirsanova
authors: Alexander
authors: A
authors: Kolbanovskiy
authors: Marina
authors: M
authors: Kolbanovskiy
authors: Francis
authors: F
authors: Johnson
authors: Radha
authors: R
authors: Bonala
authors: Nicholas E
authors: NE
authors: Geacintov
authors: Elizaveta S
authors: ES
authors: Gromova