Naperville Central High School, IL
Teacher: Nicholas DiGiovanni
Epigenetics is the study of changes in gene expression based on mechanisms other than changes in the genetic code itself. One such epigenetic mechanism is methylation
- the bonding of methyl groups to the 5’ location of cytosine bases in the DNA strand. This process keeps DNA tightly condensed silencing transcription through the inhibition of
transcription factor binding. The connection between methylation and oncogenesis arises from methyl groups bonded at CpG regulatory islands that can influence the expression of
many genes, including cancer-related genes such as oncogenes and tumor-suppressor genes.
. . . Whereas global hypomethylation seems to cause genomic instability and oncogene expression, local hypermethylation, which inhibits tumor-suppressor genes, also promotes
oncogenesis (Jones and Baylin, 2002). This is due to the hypermethylation of the CpG islands of said genes. A study conducted to analyze the extent of CpG island hypermethylation
in 98 preneoplastic tumors and cancers found that an average of 600 of the 45,000 CpG islands typically found in the human genome were hypermethylated (Costello et al., 2000). This
contrasts the normal human DNA sequence, which has around 10 hypermethylated CpG islands. This is due to the overrepresentation of DNA methyltransferase (DNMT), the enzyme that
catalyzes the methylation of DNA.