Overexpression of TET dioxygenases in seminomas associates with low levels of DNA methylation and hydroxymethylation

Mol Carcinog. 2017 Aug;56(8):1837-1850. doi: 10.1002/mc.22638. Epub 2017 May 24.

Abstract

Germ cell tumors and particularly seminomas reflect the epigenomic features of their parental primordial germ cells (PGCs), including genomic DNA hypomethylation and expression of pluripotent cell markers. Because the DNA hypomethylation might be a result of TET dioxygenase activity, we examined expression of TET1-3 enzymes and the level of their product, 5-hydroxymethylcytosine (5hmC), in a panel of histologically characterized seminomas and non-seminomatous germ cell tumors. Expression of TET dioxygenase mRNAs was quantified by real-time PCR. TET1 expression and the level of 5hmC were examined immunohistochemically. Quantitative assessment of 5-methylcytosine (5mC) and 5hmC levels was done by the liquid chromatography-mass spectroscopy technique. We found highly increased expression of TET1 dioxygenase in most seminomas and strong TET1 staining in seminoma cells. Isocitrate dehydrogenase 1 and 2 mutations were not detected, suggesting the enzymatic activity of TET1. The levels of 5mC and 5hmC in seminomas were found decreased in comparison to non-seminomatous germ cell tumors and healthy testicular tissue. We propose that TET1 expression should be studied as a potential marker of seminomas and mixed germ cell tumors and we suggest that elevated expression of TET dioxygenase enzymes is associated with the maintenance of low DNA methylation levels in seminomas. This "anti-methylator" phenotype of seminomas is in contrast to the CpG island methylator phenotype (CIMP) observed in a fraction of tumors of various types.

Keywords: 5-hydroxymethylcytosine; 5-methylcytosine; TET1; germ cell tumor; seminoma.

MeSH terms

  • 5-Methylcytosine / analogs & derivatives
  • 5-Methylcytosine / analysis
  • Adult
  • DNA Methylation*
  • DNA-Binding Proteins / analysis
  • DNA-Binding Proteins / genetics*
  • Dioxygenases / analysis
  • Dioxygenases / genetics*
  • Gene Expression Regulation, Neoplastic
  • Humans
  • Male
  • Mixed Function Oxygenases / analysis
  • Mixed Function Oxygenases / genetics*
  • Proto-Oncogene Proteins / analysis
  • Proto-Oncogene Proteins / genetics*
  • Seminoma / genetics*
  • Seminoma / pathology
  • Testicular Neoplasms / genetics*
  • Testicular Neoplasms / pathology
  • Testis / metabolism
  • Testis / pathology*
  • Up-Regulation

Substances

  • DNA-Binding Proteins
  • Proto-Oncogene Proteins
  • 5-hydroxymethylcytosine
  • 5-Methylcytosine
  • Mixed Function Oxygenases
  • TET1 protein, human
  • TET3 protein, human
  • Dioxygenases
  • TET2 protein, human