ABSTRACT
Reduced expression of TP53 by promoter methylation has been reported in several neoplasms. It remains unclear whether TP53 promoter methylation is associated with reduced transcriptional and protein expression in glioblastoma (GB). The aim of our work was to study the impact of TP53 methylation and mutations on TP53 mRNA level and protein expression in 42 molecularly characterized primary GB tumors. We also evaluate the impact of all molecular alterations on the overall patient survival. The frequency of TP53 promoter methylation was found in 21.4%. To the best of our knowledge, this is the first report showing such high frequency of TP53 promoter methylation in primary GB. There was no relation between TP53 promoter methylation and TP53 mRNA level (p=0.5722) and between TP53 promoter methylation and TP53 protein expression (p=0.2045). No significant associations were found between TP53 mRNA expression and mutation of TP53 gene (p=0.9076). However, significant association between TP53 mutation and TP53 protein expression was found (p=0.0016). Our data suggest that in primary GB TP53 promoter methylation does not play a role in silencing of TP53 transcriptional and protein expression and is probably regulated by other genetic and epigenetic mechanisms associated with genes involved in the TP53 pathway.
Subject(s)
DNA Methylation , Glioblastoma/genetics , Promoter Regions, Genetic/genetics , RNA, Messenger/metabolism , Tumor Suppressor Protein p53/genetics , Tumor Suppressor Protein p53/metabolism , Base Sequence , DNA Primers/genetics , Epigenesis, Genetic/genetics , ErbB Receptors/metabolism , Female , Humans , Immunohistochemistry , Male , Molecular Sequence Data , Mutation/genetics , Poland , Real-Time Polymerase Chain Reaction , Reverse Transcriptase Polymerase Chain Reaction , Sequence Analysis, DNA , Statistics, Nonparametric , Superoxide Dismutase/metabolism , Superoxide Dismutase-1ABSTRACT
O(6)-methylguanine DNA methyltransferase (MGMT) reduces cytotoxicity of therapeutic or environmental alkylating agents. MGMT promoter methylation has been associated with TP53 G: C to A:T transition mutations in various types of cancers, and with poor prognosis in patients who did not receive chemotherapy. Mutations of TP53 are more frequent in secondary than in primary glioblastoma, thus the expected MGMT promoter methylation was low in primary glioblastoma. Glioblastoma patients with MGMT promoter methylation showed better response to chemotherapy based on alkylating agents and longer survival than patients without MGMT methylation. We examined 32 primary glioblastomas, treated with radiotherapy and surgery, for TP53 mutation by direct sequencing and MGMT promoter methylation by methylation-specific PCR. MGMT promoter methylation and TP53 mutations were detected in 72% and 31% of primary glioblastoma, respectively. Although not statistically significant, the frequency of TP53 G:C to A:T mutations were higher in cases with (26%) than without (11%) MGMT promoter methylation (p=0.376). MGMT promoter methylation had no impact on patient survival. Our data indicate that MGMT promoter methylation occurs frequently in primary glioblastoma, but does not lead to G:C to A:T TP53 mutations, has no independent prognostic value and is not a predictive marker unless glioblastoma patients are treated with chemotherapy.
Subject(s)
Genes, p53/genetics , Glioblastoma/genetics , O(6)-Methylguanine-DNA Methyltransferase/genetics , Promoter Regions, Genetic , Tumor Suppressor Protein p53/genetics , Adult , Aged , Female , Gene Silencing , Glioblastoma/drug therapy , Glioblastoma/radiotherapy , Humans , Incidence , Male , Methylation , Middle Aged , Mutation , Young AdultABSTRACT
The aim of our study was to evaluate the frequencies of loss of heterozygosity (LOH) on chromosomes 1p, 10q, and 19q in gliomas and to correlate them with the histological diagnosis and with patient age and gender. We found deletions within chromosome 1p to be significantly associated with the histological subtype of glial tumor (P < 0.05); frequency of 1p deletions increased from astrocytoma (0%) through glioblastoma (31%) and oligoastrocytoma (57%) to oligodendroglioma (63%). In patients with 1p LOH, the odds for having astrocytoma or glioblastoma were approximately 10-fold and 4-fold lower, respectively, than oligodendroglioma. The odds for having oligoastrocytoma were similar to oligodendroglioma (OR = 1.3). The frequency of 10q LOH in patients with glioblastoma was significantly higher than in patients with oligodendroglioma (89% vs. 36%; P < 0.005). In patients with oligodendroglioma, most cases with LOH on chromosome 1p also had LOH 19q (90%), one case of 1p LOH also had a deletion on 10q. Statistical analyses revealed a significant association between deletions on 1p and 19q (P < 0.05). Our data provide evidence that use of molecular genetic analyses of chromosomes 1p, 19q, and 10q might improve the diagnosis of gliomas.
