Differential proteome analysis of human gliomas stratified for loss of heterozygosity on chromosomal arms 1p and 19q.

Combined deletion of chromosomal arms 1p and 19q is an independent prognostic marker in patients with oligodendroglial brain tumors, including oligodendrogliomas and oligoastrocytomas. However, the relevant genes in these chromosome arms and the molecular mechanisms underlying the prognostic significance of 1p/19q deletion are yet unknown. We used two-dimensional difference gel electrophoresis followed by mass spectrometry to perform a proteome-wide profiling of low-grade oligoastrocytomas stratified for the presence or absence of 1p/19q deletions. Thereby, we identified 22 different proteins showing differential expression in tumors with or without combined deletions of 1p and 19q. Four of the differentially expressed proteins, which are vimentin, villin 2 (ezrin), annexin A1, and glial fibrillary acidic protein, were selected for further analysis. Lower relative expression levels of these proteins in 1p/19q-deleted gliomas were confirmed at the protein level by Western blot analysis and immunohistochemistry. Furthermore, sequencing of sodium bisulfite-treated tumor DNA revealed more frequent methylation of 5'-CpG islands associated with the VIM and VIL2 genes in 1p/19q-deleted gliomas when compared with gliomas without these deletions. In summary, we confirm proteome-wide profiling as a powerful means to identify candidate biomarkers in gliomas. In addition, our data support the hypothesis that 1p/19q-deleted gliomas frequently show epigenetic down-regulation of multiple genes due to aberrant methylation of the 5'-CpG islands.