5-Hydroxymethylcytosine is a predominantly stable DNA modification

Area of Science:

• Epigenetics and DNA modifications
• Biochemistry of nucleic acids

Background:

• 5-Hydroxymethylcytosine (hmC) is an oxidation product of 5-methylcytosine in mammalian DNA.
• Reduced hmC levels are a hallmark of various cancers, necessitating a deeper understanding of its dynamics.

Purpose of the Study:

• To elucidate the dynamics and lifetime of hmC in DNA.
• To determine if hmC is a stable modification or a transient intermediate.

Main Methods:

• Stable isotope labeling of cytosine derivatives in mammalian cell DNA.
• Ultrasensitive tandem liquid-chromatography mass spectrometry.
• In vivo isotopic labeling of DNA in mouse tissues.

Main Results:

• The majority of hmC in DNA is a stable modification.
• hmC forms slowly over 30 hours post-DNA synthesis, unlike immediate DNA methylation.
• Global hmC levels correlate with cell proliferation in vivo.

Conclusions:

• hmC is a stable epigenetic mark with slow formation kinetics.
• Understanding hmC stability and formation is crucial for interpreting its role in health and disease, particularly in cancer.