gms | German Medical Science

Objective: Deletions of chromosome 10 are among the most common genetic alterations in glioblastomas. They are found in up to 90% of the cases. Molecular analyses have revealed evidence for several distinct tumor suppressor gene loci at 10p, 10q23 and 10q24-qter, respectively. We were interested in the identification of novel tumor suppressor microRNAs located distal of the known glioblastoma- associated PTEN tumor suppressor gene on 10q23-qter.

Method: Therefore, we screened a series of astrocytic gliomas of different malignancy for the expression of 12 microRNAs located in the respective chromosomal region using real-time reverse-transcriptase-PCR.

Results: We identified three microRNAs (miR-107, miR-146b and miR-346) exhibiting a significant decrease in their expression levels in high grade astrocytic gliomas compared to their expression in normal brain tissue samples. Pyrosequencing of sodium bisulfite-modified DNA revealed hypermethylation of CpG islands located in the miR-346 genomic region in the majority of primary glioblastomas. Hypermethylation correlated inversely with the expression of this miRNA. Over-expression of precursors of each of the three miRNAs in glioma cells influenced cell proliferation and caspase-3/7-activity. Real-time PCR expression analysis, Western blotting and luciferase-reporter gene assays identified CDK6, EGFR, and BCL6 as targets regulated by miR-107, miR-146b or miR-346, respectively.

Conclusions: Taken together, we identified three putative glioma-suppressor candidate microRNAs that are frequently downregulated in high-grade astrocytic gliomas, regulate glioma-associated proto-oncogenes and thus likely play an important role in glioma pathogenesis.