Figure 1: Simplified cartoon showing gene transcription by unmethylated promoter and gene silencing by the methylated promoter. In normal cells, promoter of some genes such as tumor suppressor protein, DNA repair proteins is unmethylated and accessible to binding to the transcription factors (TF) allowing transcription. But, in many cancers these genes are methylated by DNA methyltransferase 1 and therefore bound by the methyl-CpG binding proteins (MBD) and histone deacetylase (HDAC). Thus the methylated promoter is not accessible to binding to the transcription factors and inactive. In tumor tissues and biological fluids such as serum and urine, the methylated DNA is measured by various methods for the development of diagnostic and prognostic tools for the cancer. HAT indicates histone acetyltransferase; RNA pol II, RNA polymerase II; and HMT, histone methyltransferase.
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