Genome-wide hydroxymethylation tested using the HELP-GT assay shows redistribution in cancer

Nucleic Acids Res. 2013 Sep;41(16):e157. doi: 10.1093/nar/gkt601. Epub 2013 Jul 16.

Abstract

5-hydroxymethylcytosine (5-hmC) is a recently discovered epigenetic modification that is altered in cancers. Genome-wide assays for 5-hmC determination are needed as many of the techniques for 5-methylcytosine (5-mC) determination, including methyl-sensitive restriction digestion and bisulfite sequencing cannot distinguish between 5-mC and 5-hmC. Glycosylation of 5-hmC residues by beta-glucosyl transferase (β-GT) can make CCGG residues insensitive to digestion by MspI. Restriction digestion by HpaII, MspI or MspI after β-GT conversion, followed by adapter ligation, massive parallel sequencing and custom bioinformatic analysis allowed us determine distribution of 5-mC and 5-hmC at single base pair resolution at MspI restriction sites. The resulting HpaII tiny fragment Enrichment by Ligation-mediated PCR with β-GT (HELP-GT) assay identified 5-hmC loci that were validated at global level by liquid chromatography-mass spectrometry (LC-MS) and the locus-specific level by quantitative reverse transcriptase polymerase chain reaction of 5-hmC pull-down DNA. Hydroxymethylation at both promoter and intragenic locations correlated positively with gene expression. Analysis of pancreatic cancer samples revealed striking redistribution of 5-hmC sites in cancer cells and demonstrated enrichment of this modification at many oncogenic promoters such as GATA6. The HELP-GT assay allowed global determination of 5-hmC and 5-mC from low amounts of DNA and with the use of modest sequencing resources. Redistribution of 5-hmC seen in cancer highlights the importance of determination of this modification in conjugation with conventional methylome analysis.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • 5-Methylcytosine / analysis
  • Animals
  • Cell Line, Tumor
  • Cell Transformation, Neoplastic
  • Cytosine / analogs & derivatives*
  • Cytosine / analysis
  • Cytosine / metabolism
  • DNA, Neoplasm / chemistry*
  • Gene Expression
  • Genome, Human
  • Genomics / methods
  • Glycosyltransferases / metabolism
  • Humans
  • Mice
  • Pancreatic Neoplasms / genetics
  • Polymerase Chain Reaction

Substances

  • DNA, Neoplasm
  • 5-hydroxymethylcytosine
  • 5-Methylcytosine
  • Cytosine
  • Glycosyltransferases