MTSS1 is epigenetically regulated in glioma cells and inhibits glioma cell motility.

Epigenetic silencing by DNA methylation in brain tumors has been reported for many genes, however, their function on pathogenesis needs to be evaluated. We investigated the MTSS1 gene, identified as hypermethylated by differential methylation hybridization (DMH). Fifty-nine glioma tissue samples and seven glioma cell lines were examined for hypermethylation of the MTSS1 promotor, MTSS1 expression levels and gene dosage. GBM cell lines were treated with demethylating agents and interrogated for functional consequences of MTSS1 expression after transient transfection. Hypermethylation was significantly associated with IDH1/2 mutation. Comparative SNP analysis indicates higher incidence of loss of heterozygosity of MTSS1 in anaplastic astrocytomas and secondary glioblastomas as well as hypermethylation of the remaining allele. Reversal of promoter hypermethylation results in an increased MTSS1 expression. Cell motility was significantly inhibited by MTSS1 overexpression without influencing cell growth or apoptosis. Immunofluorescence analysis of MTSS1 in human astrocytes indicates co-localization with actin filaments. MTSS1 is down-regulated by DNA methylation in glioblastoma cell lines and is part of the G-CIMP phenotype in primary glioma tissues. Our data on normal astrocytes suggest a function of MTSS1 at focal contact structures with an impact on migratory capacity but no influence on apoptosis or cellular proliferation.

Nuclear exclusion of TET1 is associated with loss of 5-hydroxymethylcytosine in IDH1 wild-type gliomas.

The recent identification of isocitrate dehydrogenase 1 (IDH1) gene mutations in gliomas stimulated various studies to explore the molecular consequences and the clinical implications of such alterations. The Cancer Genome Atlas Research Network showed evidence for a CpG island methylator phenotype in glioblastomas that was associated with IDH1 mutations. These alterations were associated with the production of the oncometabolite, 2-hydroxyglutarate, that inhibits oxygenases [ie, ten-eleven translocation (TET) enzymes involved in the oxidation of 5-methylcytosine to 5-hydroxymethylcytosine (5hmC)]. We investigated 60 gliomas for 5hmC presence, 5-methylcytosine content, TET1 expression, and IDH1 mutation to gain insight into their relationships on a histological level. Of gliomas, 61% revealed no immunoreactivity for 5hmC, and no correlation was observed between IDH1 mutations and loss of 5hmC. Interestingly, expression of TET1 showed remarkable differences regarding overall protein levels and subcellular localization. We found a highly significant (P = 0.0007) correlation between IDH1 mutations and nuclear accumulation of TET1, but not with loss of 5hmC. Of 5hmC-negative gliomas, 70% showed either exclusive or dominant cytoplasmic expression, or no detectable TET1 protein (P = 0.0122). Our data suggest that the loss of 5hmC is a frequent event in gliomas, independent of IDH1 mutation, and may be influenced by the nuclear exclusion of TET1 from the nuclei of glioma cells.