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High-grade gliomas (HGGs) of childhood represent approximately 7% of pediatric brain tumors. They are highly invasive tumors and respond poorly to conventional treatments in contrast to pilocytic astrocytomas, which usually are well demarcated and frequently can be cured by surgery. The molecular events for this clinical relevant finding are only partially understood. In the current study, to identify aberrantly methylated genes that may be involved in the tumorigenesis of pediatric HGGs, we performed a microarray-based differential methylation hybridization approach and found frequent hypermethylation of the LHX9 (human Lim-homebox 9) gene encoding a transcription factor involved in brain development. Bisulfite genomic sequencing and combined bisulfite restriction analysis showed that HGGs were frequently methylated at two CpG-rich LHX9 regions in comparison to benign, nondiffuse pilocytic astrocytomas and normal brain tissues. The LHX9 hypermethylation was associated with reduced messenger RNA expression in pediatric HGG samples and corresponding cell lines. This epigenetic modification was reversible by pharmacological inhibition (5-aza-2'-deoxycytidine), and reexpression of LHX9 transcript was induced in pediatric glioma cell lines. Exogenous expression of LHX9 in glioma cell lines did not directly affect cell proliferation and apoptosis but specifically inhibited glioma cell migration and invasion in vitro, suggesting a possible implication of LHX9 in the migratory phenotype of HGGs. Our results demonstrate that the LHX9 gene is frequently silenced in pediatric malignant astrocytomas by hypermethylation and that this epigenetic alteration is involved in glioma cell migration and invasiveness.

Runx2 is a member of the Runx family of transcription factors (Runx1-3) with a restricted expression pattern. It has so far been detected predominantly in skeletal tissues where, inter alia, it regulates the expression of the beta-galactoside-specific lectin galectin-3. Here we show that, in contrast to Runx3, Runx1 and Runx2 are expressed in a variety of human glioma cells. Runx2 expression pattern in these cells correlated completely with that of galectin-3, but not with that of other galectins. A similar correlation in the expression pattern of galectin-3 and Runx2 transcripts was detected in distinct types of 70 primary neural tumors, such as glioblastoma multiforme, but not in others, such as gangliocytomas. In glioma cells, Runx2 is directly involved in the regulation of galectin-3 expression, as shown by RNAi and transcription factor binding assays demonstrating that Runx2 interacts with a Runx2-binding motif present in the human galectin-3 promoter. Knockdown of Runx2 was thus accompanied by a reduction of both galectin-3 mRNA and protein levels by at least 50%, dependent on the glial tumor cell line tested. Reverse transcriptase-polymerase chain reaction analyses, aimed at finding other potential target genes of Runx2 in glial tumor cells, revealed the presence of bone sialoprotein, osteocalcin, osteopontin, and osteoprotegerin. However, their expression patterns only partially overlap with that of Runx2. These data suggest a functional contribution of Runx-2-regulated galectin-3 expression to glial tumor malignancy.

Mutations of both the IDH1 and IDH2 (isocitratedehydrogenase enzyme 1 and 2) genes have recently been described in cases of human glioma. Since IDH1 mutations have been associated with better clinical outcome , they are suitable predictive markers for adult glioma patients. We have developed a pyrosequencing assay that allows both the sensitive and rapid detection of mutant IDH1 alleles in DNA extracted from formalin-fixed , paraffin-embedded tissues. PCR products that span exon 4 of IDH1 were used as a template for pyrosequencing. For validation , PCR products were additionally cloned and sequenced conventionally by Sanger sequencing. Sensitivity was measured by titration of wild-type and mutant sequences. PCR kinetic experiments were performed to investigate the influences of PCR cycle number on the accuracy of the assay. We found that a minimum of 5% of mutant IDH1 alleles can easily be detected with the pyrosequencing approach. So far, there are few data regarding IDH1 mutation status in high-grade gliomas of childhood. Therefore , we applied this assay to 47 pediatric high-grade glioma samples (age range 6 weeks to 23 years). Mutations were found in 5/14 astrocytoma III and in 6/33 glioblastomas. In conclusion , we have developed a pyrosequencing-based assay for the detection of mutations at the hotspot regions of IDH1 and provide proof for its applicability as a molecular diagnostic assay for clinical samples.

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