TP53 promoter methylation in human gliomas
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Methylation of the promoter region of tumor suppressor genes may be associated with transcriptional silencing and tumor progression. The 5′ region of the TP53 gene does not contain a CpG island, but a basal promoter region of 85 bp is essential for its full promoter activity. In the present study, we assessed whether TP53 promoter methylation is present in malignant glioma cells and whether this is associated with reduced TP53 expression. Methylation-specific PCR revealed TP53 promoter methylation in three (U87MG, LNT-229, T98G) out of six malignant glioma cell lines studied. Treatment with 5-aza-2’-deoxycytidine (5-aza-dC) led to up-regulated expression of TP53 mRNA and protein in U87MG and T98G cells, suggesting that promoter methylation is associated with reduced expression in some malignant glioma cells. We then assessed TP53 promoter methylation in primary tissue of low-grade gliomas, and observed TP53 promoter methylation in 29/48 (60%) low-grade astrocytomas, 11/18 (61%) oligoastrocytomas, and 31/42 (74%) oligodendrogliomas. Promoter methylation of the p14ARF gene, another gene involved in the TP53 pathway, was detected by methylation-specific PCR in 5/49 (10%) low-grade astrocytomas, 7/18 (39%) oligoastrocytomas, and 15/41 (37%) oligodendrogliomas. Our previous and present data show alterations of at least one of TP53 promoter methylation, p14ARF promoter methylation, and TP53 mutations in 43/49 (88%) of low-grade astrocytomas, 15/18 (83%) of oligoastrocytomas, and 35/42 (83%) oligodendrogliomas, suggesting that disruption of the TP53/p14ARF pathway is frequent in all histological types of low-grade glioma.