RESUMEN
Certain risk groups among tumors of the central nervous system (CNS) in children take an almost inevitably fatal course. The elucidation of molecular mechanisms offers hope for improved therapy. Aberrant methylation is common in malignant brain tumors of childhood and may have implications for stratification and therapy. Methylation of p16 (INK4A), p14 (ARF), TIMP3, CDH1, p15 (INK4B )and DAPK1 in medulloblastoma (MB) and ependymoma has been discussed controversially in the literature. DUTT1 and SOCS1 have not previously been analyzed. We examined methylation in MB, sPNET and ependymoma using methylation-specific PCR (MSP), quantitative Combined Bisulfite Restriction Analysis (COBRA) and direct and clone sequencing of bisulfite PCR products. We detected methylation of p16 (INK4A) (17/43), p14 (ARF) (11/42) and TIMP3 (9/44) in MB and others by MSP. CDH1 was not only methylated in MB (31/41), but also in normal controls. Evaluation of MSP results by quantitative COBRA and sequencing yielded methylation between the detection limits of COBRA (1%) and MSP (0.1%). Only p16 (INK4A )and TIMP3 were methylated consistently in medulloblastomas (p16 (INK4A ) 14%, TIMP3 11%) and p16 (INK4A) also in anaplastic ependymomas (1/4 tumors). Methylation ranged from 1-5%. Evaluation of methylation using MSP has thus to be supplemented by quantitative methods. Our analyses raise the issue of the functional significance of low level methylation, which may disturb the delicate growth factor equilibrium within the cell. Therapeutic and diagnostic implications urge into depth analyses of methylation as a mechanism, which might fill some of the gaps of our understanding of brain tumor origin.
Asunto(s)
Neoplasias Encefálicas/genética , Neoplasias Cerebelosas/genética , Metilación de ADN , Genes p16 , Meduloblastoma/genética , Tumores Neuroectodérmicos Primitivos/genética , Inhibidor Tisular de Metaloproteinasa-3/genética , Adolescente , Adulto , Anciano , Proteínas Reguladoras de la Apoptosis/genética , Proteínas Quinasas Dependientes de Calcio-Calmodulina/genética , Niño , Preescolar , Proteínas Quinasas Asociadas a Muerte Celular , Femenino , Silenciador del Gen , Humanos , Lactante , Masculino , Persona de Mediana Edad , Proteínas del Tejido Nervioso/genética , Receptores Inmunológicos/genética , Proteínas RoundaboutRESUMEN
Selenoprotein P (SePP) is central to selenium (Se) metabolism in the mammalian organism. Human SePP contains 10 Se atoms that are covalent constituents of the polypeptide chain incorporated as the rare amino acid selenocysteine (Sec). Since hepatocytes secrete SePP into plasma, SePP is commonly regarded as a Se transport protein, although SePP mRNA is expressed in many organs. Gene targeting of SePP in mice leads to neurological dysfunction resulting from Se deficiency and associated reduction of selenoenzyme activities in the brain. However, more recent data revealed that isolated hepatic SePP deficiency does not alter brain Se levels, suggesting a role for SePP locally expressed in the brain. Some of the best characterized and most abundant selenoenzymes, glutathione peroxidases, thioredoxin reductases, and methionine sulfoxide reductase B, play major roles in the cellular defense against reactive oxygen species. Therefore, it was hypothesized that reduced brain Se bioavailability may be involved in the pathogenesis of neurodegenerative disease and normal ageing. We present evidence that human CSF contains SePP and that the human brain expresses SePP mRNA. Moreover, SePP-like immunoreactivity localizes to neurons and ependymal cells and thus appears strategically situated for maintenance and control of Se-dependent anti-oxidative defense systems.