DNA Methylation

• Methylation of Cytosine --> change gene expression (naturally occurring modification)
• Steps:

  • After DNA replication --> Newly synthesized dsDNA have hemimethylated sites --> signal DNA methylases --> transfer methyl groups (CH3) from SAM --> to cytosine on newly synthesized strand
• Higher degree of methylation = Lower expression of gene (Inversely correlated)
• Some non-genotoxic carcinogens (e.g. Reactive oxygen species) --> interfere with Methyltransferase --> change DNA methylation profile & gene expression
• Normal tissue

  • Promoter of Tumor Suppressor genes = Hypomethylated = can be transcribed
  • Promotor of Oncogenes = Hypermethylated = cannot be transcribed
• Cancer tissue

  • Promoter of Tumor Suppressor genes = Hypermethylated = cannot be transcribed
  • Promotor of Oncogenes = Hypomethylated = can be transcribed