M. Josefa Bello

High-Resolution Analysis of Chromosome Arm 1p Alterations in Meningioma

Loss of heterozygosity (LOH) for loci on chromosome arm 1p is a relatively common event in human meningioma, and this anomaly has been proposed to be associated with the development of grade II or grade III forms (atypical and anaplastic meningiomas). Nevertheless, the limited data available do not allow the establishment of the frequency and the extent of the affected 1p regions. To determine the status of chromosome 1p in meningiomas, we have performed a comprehensive analysis of LOH on 1p in 100 meningiomas using a high density of 1p-marker loci. Allelic loss was found in 35% of tumors, most corresponding to nontypical meningiomas that also displayed losses for loci on chromosome 22. Although some tumors displayed complex rearrangements leading to distinct 1p deletions, the patterns of loss indicated two main target regions: 1p36 and 1p34-p32, which represent the most frequently involved regions, whereas 1p22 and 1p21.1-1p13 regions appeared deleted in some tumors. These results suggest that there may be several putative tumor suppressor genes on 1p, the inactivation of which may be important in the pathogenesis of meningiomas, as well as in other tumor types.

Genetic and epigenetic alteration of the NF2 gene in sporadic meningiomas

The role of the NF2 gene in the development of meningiomas has recently been documented; inactivating mutations plus allelic loss at 22q, the site of this gene (at 22q12), have been identified in both sporadic and neurofibromatosis type 2–associated tumors. Although epigenetic inactivation through aberrant CpG island methylation of the NF2 5′ flanking region has been documented in schwannoma (another NF2‐associated neoplasm), data on participation of this epigenetic modification in meningiomas are not yet widely available. Using methylation‐specific PCR (MSP) plus sequencing, we assessed the presence of aberrant promoter NF2 methylation in a series of 88 meningiomas (61 grade I, 24 grade II, and 3 grade III), in which the allelic constitution at 22q and the NF2 mutational status also were determined by RFLP/microsatellite and PCR‐SSCP analyses. Chromosome 22 allelic loss, NF2 gene mutation, and aberrant NF2 promoter methylation were detected in 49%, 24%, and 26% of cases, respectively. Aberrant NF2 methylation with loss of heterozygosity (LOH) at 22q was found in five cases, and aberrant methylation with NF2 mutation in another; LOH 22q and the mutation were found in 16 samples. The aberrant methylation of the NF2 gene also was the sole alteration in 15 samples, most of which were from grade I tumors. These results indicate that aberrant NF2 hypermethylation may participate in the development of a significant proportion of sporadic meningiomas, primarily those of grade I. ©2005 Wiley‐Liss, Inc.

Analysis of p73 gene in meningiomas with deletion at 1p

The p73 gene has been mapped to 1p36.33, a chromosome region that is frequently deleted in a wide variety of neoplasms including meningiomas. The protein encoded by p73 shows structural and functional similarities to p53 and may thus represent a candidate tumor suppressor gene. To determine whether p73 is involved in the development of meningiomas, we examined 30 meningioma samples with proven 1p deletion for mutations of p73. Sequence analysis of the entire coding region of the p73 gene revealed previously reported polymorphisms in eight cases. A tumor-specific missense mutation as a result of an A-to-G transition with an Asn204Ser change was found in one meningioma that nevertheless retained the normal allele. These results suggest that if p73 plays a role in meningioma carcinogenesis, it must be in a manner different from the Knudson two-hit model.

DNA methylation of multiple promoter-associated CpG islands in meningiomas: relationship with the allelic status at 1p and 22q

The purpose of this research was to examine the DNA methylation profile of meningiomas. Accordingly, we examined the DNA methylation status of ten tumor-related genes (RB1, p16INK4a, p73, MGMT, ER, DAPK, TIMP-3, p14ARF, THBS1, and Caspase-8) in 98 meningiomas (68 grade I; 27 grade II; and 3 grade III samples) using methylation-specific PCR and sequencing. The most frequently methylated genes were THBS1 (30%), TIMP-3 (24%), p16INK4a (17%), MGMT (16%), p73 (15%), ER (15%), and p14ARF (13%), whereas methylation was relatively rare in the other genes (<10%). Methylation occurred in at least one gene in 77.5% of the cases and in three or more genes in 25.5%. Methylation was tumor specific since it was absent in the controls: two non-neoplastic meningeal samples and two non-neoplastic brain samples. The frequency of aberrant gene methylation in grade I versus grade II–III tumors showed some differences for TIMP-3, THBS1, MGMT, p16INK4a and p73; these differences reached statistical significance for TIMP-3: 18% in grade I versus 40% in grade II–III (P<0.02). Our previous loss of heterozygosity studies provided the allelic constitution at 1p and 22q for 60 of the 98 meningiomas included in this report. The level of aberrant promoter methylation increased in tumors (30 samples) displaying 1p loss (either isolated or as concurrent deletion at 1p/22q; P=0.014). These meningiomas primarily accumulated the epigenetic changes of THBS1 (14/30; 47%; P<0.005), TIMP-3 (12/30; 40%; P<0.05), p73 (10/30; 26%; P<0.02) and p14ARF/p16INK4a(7/30 each one; 23%; not significant). Our findings indicate that aberrant DNA methylation of promoter-associated CpG islands in meningiomas contributes to the development of these tumors.

Aberrant CpG island methylation of multiple genes in ependymal tumors.

Aberrant methylation of promoter CpG islands in human genes represents an alternative mechanism for genetic inactivation, and contributes to the development of human tumors. Nevertheless, thus far, few reports have analyzed methylation in ependymomas. We determined the frequency of aberrant CpG island methylation of several tumor-associated genes: p16INK4a, RB1, MGMT, DAPK, TIMP3, THBS1, TP73, NF2 and Caspase 8 in a group of 27 ependymomas, consisting of 22 WHO grade II samples and five anaplastic WHO grade III tumors. The respective methylation indices (number of genes methylated/total genes analyzed) for both tumor groups was 0.195 and 0.198. Overall methylation rates greater than 20% were detected in MGMT, TIMP3, THBS1 and TP73. NF2 and Caspase 8 each presented hypermethylation in less than 10% of cases, and the cell-cycle regulators RB1/p16INK4a were hypermethylated in 4% and 18% of the samples, respectively, mostly affecting the low-grade forms. Our findings suggest that methylation commonly contributes to the inactivation of cancer-related genes in ependymomas.

Analysis of the NF2 gene in oligodendrogliomas and ependymomas

Allelic losses of chromosome 22 are commonly found in ependymomas and oligodendrogliomas, suggesting that at least one tumor suppressor gene on chromosome 22 must be inactivated during the multistep process of tumorigenesis in these glial tumors. The neurofibromatosis 2 gene (NF2) located at 22q12, is a candidate tumor suppressor gene potentially involved in the pathogenesis of gliomas. Because there have been only a few studies of the NF2 gene in glial tumors other than astrocytoma, we screened the entire 17 NF2 exons for mutations in a series of 47 nonastrocytic tumors, including 40 oligodendrogliomas and 7 ependymomas. Only one mutation was detected, a 59-base pair insertion in exon 3 from a spinal anaplastic ependymoma. These results concur with previous findings proposing preferential inactivation of the NF2 gene in a subgroup of ependymomas, and suggest that the NF2 gene is not the target of chromosome 22 aberrations in oligodendrogliomas.

CpG island methylation of tumor-related genes in three primary central nervous system lymphomas in immunocompetent patients

We have determined the promoter CpG island methylation status of O(6)-methylguanine-DNA methyltransferase (MGMT), glutathione-S-transferase P1 (GSTP1), death-associated protein kinase (DAPK), p14(ARF), thrombospondin-1 (THBS1), tissue inhibitor of metalloproteinase-3 gene (TIMP-3), p73, p16(INK4A), RB1, and TP53 genes in three primary central nervous system lymphomas (PCNSL). Five genes (GSTP1, DAPK, TIMP-3, p16(INK4A), and RB1) were hypermethylated in two samples, whereas MGMT, THBS1, and p73 were aberrantly methylated in only one sample. No case presented CpG island methylation for the p14(ARF) and TP53 genes. These findings concur with previous data suggesting a frequent inactivation of p16(INK4A) and very limited involvement of TP53 in PCNSL and also provide insights into the epigenetic molecular involvement of other tumor-related genes in this neoplasm.

Chromosomal abnormalities in pituitary adenomas.

Cytogenetic studies were conducted on 30 pituitary adenomas, using both direct and/or short-term in vitro culture methods. An apparently normal chromosome complement was found in 14 tumors; 5 adenomas were characterized by hyperdiploid or near-triploid modal chromosome numbers. Recurrent numerical deviations were identified in 12 samples, which primarily involved gains of chromosomes 4, 7, 8, 9, 12, and 20 by gains, and losses of chromosomes 10, 14, 19, and 22. Four adenomas were shown to have structural chromosome rearrangements with no apparent recurrent pattern of involvement.

Metástasis en el sistema nervioso central: biología molecular

Resumen Las metastasis en el sistema nervioso representan un importante y creciente problema en la practica clinica, siendo causa de gran mortalidad en los paises desarrollados. En este articulo revisamos los escasos datos existentes hasta el momento acerca de los mecanismos moleculares implicados en la patogenesis de las metastasis en el sistema nervioso, que incluyen diversas alteraciones geneticas, en genes supresores de tumores y oncogenes, asi como la alteracion del equilibrio epigenetico de la celula. Concluimos que en un futuro un mayor conocimiento de dichos mecanismos moleculares contribuiran a un mejor diagnostico, tratamiento y evolucion clinica de estos pacientes.