DNA methylation and allelic losses on chromosome arm 14q in oligodendroglial tumours

Cytogenetic and molecular genetic studies have shown frequent losses on the long arm of chromosome 14 in different types of human gliomas. Using differential methylation hybridization as a genome-wide screening approach to determine DNA methylation patterns in gliomas, we recently identified two DNA fragments in 14q23.1 (CGI-clone sharp396) and 14q32.12 (CGI-clone sharp519) that were differentially methylated between astrocytic gliomas and mixed oligoastrocytomas. To validate this observation, we examined these 14q32.12 locus for methylation in an extended series of 43 astrocytic and oligodendroglial gliomas. All tumours were additionally investigated for loss of heterozygosity (LOH). Microsatellite analysis showed LOH in seven of 28 (25%) oligodendroglial tumours and three of 15 (20%) astrocytic tumours. Seven tumours demonstrated LOH at all informative 14q loci whereas three tumours carried partial deletions defining a commonly deleted region at 14q22.3-q32.1 between the microsatellite markers D14S282 and D14S995. Methylation-specific PCR analysis of the 14q32.12 locus revealed hypermethylation in 12 of 43 gliomas (28%). Hypermethylation was restricted to tumours with oligodendroglial differentiation (12 of 28 tumours, 43%). However, none of the hypermethylated tumours demonstrated LOH on 14q and vice versa. In total, 19 of 28 oligodendroglial tumours (68%) showed either hypermethylation at the 14q32.12 locus or LOH at 14q22.3-q32.2. Taken together, our data lend further support for the location of one or more yet to be identified glioma-associated tumour suppressor gene(s) on 14q. In addition, the restriction of 14q32.12 methylation to oligodendroglial tumours suggests a role for epigenetic DNA modifications in these particular gliomas.