Specific features of DNA methylome in Glioblastoma Multiforme


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Maria Eleftheriou1
1University of Nottingham

Abstract

Background

DNA methylation (5-methylcytosine, 5mC) is the major epigenetic modification involved in transcriptional regulation during the early stages of development in eukaryotes.  The patterns of 5mC are frequently altered in cancer. TET proteins can enzymatically oxidize 5mC producing 5-hydroxymethylcytosine (5hmC), 5-formylcytosine (5fC) and 5-carboxylcytosine (5caC). Although the exact biological roles of these oxidized forms of 5mC in cancer pathogenesis are still unknown, there are indications that they might contribute to malignant transformation. According to several reports, 5hmC levels are reduced in human tumours; however, the distribution of 5fC and 5caC in cancers is poorly studied. Although our previous studies showed that 5caC is surprisingly enriched in a proportion of breast cancers and pediatric brain tumors, the distribution and the biological role of this mark in glioblastoma multiforme (GBM) has not been systematically assessed.

Method

Here, using mass spectrometry and immunofluorescence, we examine the global levels of 5hmC and 5caC in four human GBM cell lines (LN18, LN228, U251 and U87MG). 

Results

We show that while the GBM cell lines exhibit low levels of 5hmC, they are, rather unexpectedly, characterized by relatively high immunochemistry and mass-spec detectable 5caC levels paralleled by the absence of 5fC. Remarkably, 5caC content in GBM does not correlate with 5hmC levels but corresponds to elevated levels of TET2 transcript in these cancers where its transient siRNA mediated knockdown leads to a dramatic decrease in 5caC levels.

Conclusion

Our data reveals the unique epigenetic signature of GBM contributing to potential development of novel approaches for diagnosis and therapy of these tumours.