5-Azacytidine induced methyltransferase-DNA adducts block DNA replication in vivo.

Journal Article (Journal Article)

5-Azacytidine (aza-C) and its derivatives are cytidine analogues used for leukemia chemotherapy. The primary effect of aza-C is the prohibition of cytosine methylation, which results in covalent methyltransferase-DNA (MTase-DNA) adducts at cytosine methylation sites. These adducts have been suggested to cause chromosomal rearrangements and contribute to cytotoxicity, but the detailed mechanisms have not been elucidated. We used two-dimensional agarose gel electrophoresis and electron microscopy to analyze plasmid pBR322 replication dynamics in Escherichia coli cells grown in the presence of aza-C. Two-dimensional gel analysis revealed the accumulation of specific bubble and Y molecules, dependent on overproduction of the cytosine MTase EcoRII (M.EcoRII) and treatment with aza-C. Furthermore, a point mutation that eliminates a particular EcoRII methylation site resulted in disappearance of the corresponding bubble and Y molecules. These results imply that aza-C-induced MTase-DNA adducts block DNA replication in vivo. RecA-dependent X structures were also observed after aza-C treatment. These molecules may be generated from blocked forks by recombinational repair and/or replication fork regression. In addition, electron microscopy analysis revealed both bubbles and rolling circles (RC) after aza-C treatment. These results suggest that replication can switch from theta to RC mode after a replication fork is stalled by an MTase-DNA adduct. The simplest model for the conversion of theta to RC mode is that the blocked replication fork is cleaved by a branch-specific endonuclease. Such replication-dependent DNA breaks may represent an important pathway that contributes to genome rearrangement and/or cytotoxicity.

Full Text

Duke Authors

Cited Authors

  • Kuo, HK; Griffith, JD; Kreuzer, KN

Published Date

  • September 1, 2007

Published In

Volume / Issue

  • 67 / 17

Start / End Page

  • 8248 - 8254

PubMed ID

  • 17804739

International Standard Serial Number (ISSN)

  • 0008-5472

Digital Object Identifier (DOI)

  • 10.1158/0008-5472.CAN-07-1038


  • eng

Conference Location

  • United States