5-hydroxymethylcytosine marks regions with reduced mutation frequency in human DNA

Area of Science:

• Epigenetics and Cancer Genomics
• DNA Methylation and Mutation

Background:

• CpG dinucleotides are major cancer mutation hotspots, with C>T mutations linked to 5-methylcytosine (5mC).
• 5-hydroxymethylcytosine (5hmC), a 5mC derivative, is abundant in brain, but its role in mutagenesis is unclear.

Purpose of the Study:

• To investigate the impact of 5-hydroxymethylcytosine (5hmC) on C>T mutation rates at CpG sites.
• To compare the mutagenic effects of 5hmC and 5-methylcytosine (5mC) in different human tissues.

Main Methods:

• Analysis of mutation frequencies in relation to 5hmC and 5mC levels across various tissues.
• Correlation of tissue-specific 5hmC patterns with regional mutation rates in cancer genomes.

Main Results:

• 5hmC is associated with a significant decrease (up to 53%) in C>T mutations at CpG sites compared to 5mC.
• Tissue-specific 5hmC distributions correlate with lower CpG>T mutation frequencies in cancers from brain, kidney, and blood.

Conclusions:

• 5hmC has a protective role against C>T mutations at CpG sites, opposing the effect of 5mC.
• Differential cytosine modifications (5mC vs. 5hmC) influence cancer mutation landscapes in a cell-type-specific manner.