Methylation of CpG dinucleotides is one of the major epigenetic processes involved in the regulation of gene expression. Catalyzed by DNA methyltransferases, hypermethylation of CpG islands in promoter regions is typically associated with gene silencing. DNA methylation plays an important role in normal differentiation, development, and maintenance of genomic stability, with aberrant CpG methylation being linked with a number of disease states. Three CpG islands within a 1.15- kb region characterize the chromatin landscape surrounding the transcriptional start site of the multidrug resistance 1 (MDR1) gene. We and others have demonstrated that hypermethylation of this region is correlated withMDR1gene silencing and the inability of chemotherapeutic agents to activateMDR1transcription. The bisulphite sequencing and cloning method allows a precise interpretation of the methylation status of each individual CpG dinucleotide in theMDR1region.
