RESUMEN
Gliomas are tumors of the central nervous system with a wide spectrum of different tumor types. They range from pilocytic astrocytoma, with a generally good prognosis, to the extremely aggressive malignant glioblastoma. In addition to these 2 types of contrasting neoplasms, several other subtypes can be distinguished, each characterized by specific phenotypic, as well as genotypic features. Recently, the epigenotype, as evident from differentially methylated DNA loci, has been proposed to be useful as a further criterion to distinguish between tumor types. In our study, we screened 139 tissue samples, including 33 pilocytic astrocytomas, 46 astrocytomas of different grades, 7 oligoastrocytomas, 10 oligodendrogliomas, 10 glioblastoma multiforme samples and 33 control tissues, for methylation at CpG islands of 15 different gene loci. We used the semiquantitative high throughput method MethyLight to analyze a gene panel comprising ARF, CDKN2B, RB1, APC, CDH1, ESR1, GSTP1, TGFBR2, THBS1, TIMP3, PTGS2, CTNNB1, CALCA, MYOD1 and HIC1. Seven of these loci showed tumor specific methylation changes. We found tissue as well as grade specific methylation profiles. Interestingly, pilocytic astrocytomas showed no evidence of CpG island hypermethylation, but were significantly hypomethylated, relative to control tissues, at MYOD1. Our results show that glioma subtypes have characteristic methylation profiles and, with the exception of pilocytic astrocytomas, show both locus specific hyper- as well as hypomethylation.
Asunto(s)
Neoplasias Encefálicas/diagnóstico , Neoplasias del Sistema Nervioso Central/diagnóstico , Glioma/diagnóstico , Metilación , Adolescente , Adulto , Anciano , Astrocitoma/diagnóstico , Astrocitoma/genética , Encéfalo/patología , Neoplasias Encefálicas/genética , Neoplasias del Sistema Nervioso Central/genética , Niño , Preescolar , Islas de CpG , Femenino , Glioblastoma/diagnóstico , Glioblastoma/genética , Glioma/genética , Humanos , Lactante , Masculino , Persona de Mediana Edad , Oligodendroglioma/diagnóstico , Oligodendroglioma/genética , Pronóstico , Sulfitos/farmacologíaRESUMEN
Tumorigenesis is characterized by alterations of methylation profiles including loss and gain of 5-methylcytosine. Recently, we identified a single CpG, which seemed to be consistently hypomethylated in pilocytic astrocytomas but not in other gliomas. To evaluate its applicability as a biomarker, we examined its methylation status in a large panel of gliomas (n = 97). Methylation-dependent DNA sequence variation may be considered a kind of single nucleotide polymorphism (methylSNP). MethylSNPs can be easily converted into common SNPs of the C/T type by sodium bisulfite treatment of the DNA and afterwards subjected to conventional SNP typing. We adapted SnaPshot trade mark and Pyrosequencing trade mark to determine the methylation of our test CpG in a quantitative manner. The adapted methods, called SNaPmeth and PyroMeth, respectively, gave nearly identical results, however data obtained with PyroMeth showed less scattering. Furthermore, the integrated software for allele frequency determination from Pyrosequencing could be used directly for data analysis while SnaPmeth data had to be exported and processed manually. Although data did not confirm our previous result of a preferential hypomethylation of the tested CpG in pilocytic astrocytomas, we consider quantitative methylSNP analysis by SNaPmeth or PyroMeth a favorable alternative to existing high-throughput methylation assays. It combines single CpG analysis with accurate quantitation and is amenable to high throughput.
