Mutation analysis of the p73 gene in nonastrocytic brain tumours

Homozygous deletion of TNFRSF4, TP73, PPAP2B and DPYD at 1p and PDCD5 at 19q identified by multiplex ligation-dependent probe amplification (MLPA) analysis in pediatric anaplastic glioma with questionable oligodendroglial component

Background

Pediatric oligodendrogliomas are rare and appear to show a different molecular profile from adult tumors. Some gliomas display allelic losses at 1p/19q in pediatric patients, although less frequently than in adult patients, but this is rare in tumors with an oligodendroglial component. The molecular basis of this genomic abnormality is unknown in pediatric gliomas, but it represents a relatively common finding in pediatric oligodendroglioma-like neoplasms with leptomeningeal dissemination.

Results

Multiplex ligation-dependent probe amplification (MLPA) analysis using SALSA P088-B1 for the analysis of the 1p/19q allelic constitution in a pediatric anaplastic (oligodendro)-glioma showed homozygous co-deletion for markers: TNFRSF4 (located at 1p36.33), TP73 (1p36.32), PPAP2B (1pter-p22.1), DPYD (1p21.3), and PDCD5 (19q13.12), and hemizygous deletion of BAX (19q13.3-q13.4). No sequence changes for R132 and R172 of the IDH1/2 genes were identified.

Conclusions

The molecular findings in this pediatric anaplastic glioma do not allow for a clearly definitive pathological diagnosis. However, the findings provide data on a number of 1p/19q genomic regions that, because of homozygotic deletion, might be the location of genes that are important for the development and clinical evolution of some malignant gliomas in children.

Role of p53 family members p73 and p63 in human hematological malignancies

p53, mutated in over half of human cancers and about 13% of all hematological malignancies, maintains genomic integrity and triggers cellular senescence and apoptosis of damaged cells. In contrast to p53, the homologs p73 and p63 play critical roles in development of the central nervous system and skin/limbs, respectively. Moreover, dependent on the context they can exert tumor suppressor activities that cooperate with p53. Unlike p53, p73 and p63 are rarely mutated in cancers. Instead, up-regulation of the anti-apoptotic dominant-negative ΔNp73 and ΔNp63 isoforms is the most frequent abnormality in solid cancers. In hematological malignancies the most frequent p73 defect is promoter methylation and loss of expression, associated with unfavorable clinical outcomes. This suggests an essential tumor suppressor role of p73 in blood cells, also supported by genetic mouse models. Many therapeutic approaches aiming to restore p73 activity are currently being investigated. In contrast, the most frequent p63 abnormality is protein overexpression, associated with higher disease grade and poorer prognosis. Surprisingly, although available data are still scarce, the emerging picture is up-regulation of transactivation-competent TAp63 isoforms, suggesting a tumor-promoting role in this context.

Genomic deletions at 1p and 14q are associated with an abnormal cDNA microarray gene expression pattern in meningiomas but not in schwannomas

The molecular pathology of meningiomas and shwannomas involve the inactivation of the NF2 gene to generate grade I tumors. Genomic losses at 1p and 14q are observed in both neoplasms, although more frequently in meningiomas. The inactivation of unidentified genes located in these regions appears associated with tumor progression in meningiomas, but no clues to its molecular/clinical meaning are available in schwannomas. Recent microarray gene expression studies have demonstrated the existence of molecular subgroups in both entities. In the present study, we correlated the presence of genomic deletions at 1p, 14q, and 22q with the expression patterns of 96 tumor-related genes obtained by cDNA low-density microarrays in a series of 65 tumors including 42 meningiomas and 23 schwannomas. Two expression pattern groups were identified by cDNA mycroarray analysis when compared to the expression pattern in normal control RNA in both meningiomas and schwannomas, each one with patterns similar and different from the normal control. Meningioma and schwannoma subgroups differed in the expression of 38 and 16 genes, respectively. Using MLPA and microsatellites, we identified genomic losses at 1p, 14q, and 22q at nonrandom frequencies (12.5-69%) in meningiomas and schwannomas. Losses at 22q were almost equally frequent in both molecular expression subgroups in both neoplasms. However, deletions at 1p and 14q accumulated in meningiomas with a gene expression pattern different from the normal pattern, whereas the inverse situation occurred in schwannomas. Those anomalies characterized the schwannomas with expression pattern similar to the normal control. These findings suggest that deletions at 1p and 14q enhance the development of an abnormal tumor-related gene expression pattern in meningiomas, but this fact is not corroborated in schwannomas.

Allelic status of 1p and 19q in oligodendrogliomas and glioblastomas: multiplex ligation-dependent probe amplification versus loss of heterozygosity

Identification of the 1p/19q allelic status in gliomas, primarily those with a major oligodendroglial component, has become an excellent molecular complement to tumor histology in order to identify those cases sensitive to chemotherapy. In addition to loss of heterozygosity (LOH), fluorescence in situ hybridization (FISH), or comparative genomic hybridization (CGH), multiplex ligation-dependent probe amplification (MLPA) has been shown to be an alternative methodology to identify deletions of those chromosome arms. We used MLPA to explore the 1p and 19q allelic constitution in a series of 76 gliomas: 41 tumors with a major oligodendroglial component, 34 glioblastomas, and one low-grade astrocytoma. We compared the MLPA findings of the oligodendroglial cases with those previously obtained using LOH in the same samples. Thirty-eight of 41 oligodendrogliomas displayed identical findings by both LOH and MLPA, and losses at either 1p and/or 19q were identified in 12 of 35 (34%) astrocytic tumors. These findings agree with data previously reported comparing MLPA versus FISH or CGH in gliomas and suggest that MLPA can be used in the identification of the 1p/19q allelic deletions on these brain neoplasms.

Overexpressed TP73 induces apoptosis in medulloblastoma

Background

Medulloblastoma is the most common malignant brain tumor of childhood. Children who relapse usually die of their disease, which reflects resistance to radiation and/or chemotherapy. Improvements in outcome require a better understanding of the molecular basis of medulloblastoma growth and treatment response. TP73 is a member of the TP53 tumor suppressor gene family that has been found to be overexpressed in a variety of tumors and mediates apoptotic responses to genotoxic stress. In this study, we assessed expression of TP73 RNA species in patient tumor specimens and in medulloblastoma cell lines, and manipulated expression of full-length TAp73 and amino-terminal truncated ΔNp73 to assess their effects on growth.

Methods

We analyzed medulloblastoma samples from thirty-four pediatric patients and the established medulloblastoma cell lines, Daoy and D283MED, for expression of TP73 RNA including the full-length transcript and the 5'-terminal variants that encode the ΔNp73 isoform, as well as TP53 RNA using quantitative real time-RTPCR. Protein expression of TAp73 and ΔNp73 was quantitated with immunoblotting methods. Clinical outcome was analyzed based on TP73 RNA and p53 protein expression. To determine effects of overexpression or knock-down of TAp73 and ΔNp73 on cell cycle and apoptosis, we analyzed transiently transfected medulloblastoma cell lines with flow cytometric and TUNEL methods.

Results

Patient medulloblastoma samples and cell lines expressed full-length and 5'-terminal variant TP73 RNA species in 100-fold excess compared to non-neoplastic brain controls. Western immunoblot analysis confirmed their elevated levels of TAp73 and amino-terminal truncated ΔNp73 proteins. Kaplan-Meier analysis revealed trends toward favorable overall and progression-free survival of patients whose tumors display TAp73 RNA overexpression. Overexpression of TAp73 or ΔNp73 induced apoptosis under basal growth conditions in vitro and sensitized them to cell death in response to chemotherapeutic agents.

Conclusion

These results indicate that primary medulloblastomas express significant levels of TP73 isoforms, and suggest that they can modulate the survival and genotoxic responsiveness of medulloblastomas cells.

The role of p73 in hematological malignancies

The P73 gene is a homologue of the P53 tumor suppressor. Owing to its structural similarity with p53, p73 was originally considered to have tumor suppressor function. However, the discovery of N-terminal truncated isoforms with oncogenic properties showed a 'two in one' structure of its product, p73 protein. The full-length variants are strong inducers of apoptosis, whereas the truncated isoforms inhibit proapoptotic activity of p53 and the full-length p73. Thus, p73 is involved in the regulation of cell cycle, cell death and development. Moreover, it plays a role in carcinogenesis and controls tumor sensitivity to treatment. p73 is commonly expressed in tumor cells in hematological malignancies. Overexpression of p73 protein and aberrant expression of its particular isoforms, with very low frequency of P73 hypermethylation or mutations, were found in malignant myeloproliferations, including acute myeloblastic leukemia. In contrast, hypermethylation and subsequent inactivation of the P73 gene are the most common findings in malignant lymphoproliferative disorders, especially acute lymphoblastic leukemia (ALL) and non-Hodgkin's lymphomas. Assessment of P73 methylation may provide important prognostic information, as was confirmed in patients with ALL. This review summarizes some aspects of p73 biology with particular reference to its possible pathogenetic role and prognostic significance in hematological malignancies.

p73 modulates HIV-1 Tat transcriptional and apoptotic activities in human astrocytes

HIV-1 Tat is a potent transcriptional activator of the viral promoter with the ability to modulate a number of cellular regulatory circuits including apoptosis. Tat exerts its effects through interaction with viral as well as cellular proteins. Here, we studied the influence of p73, a protein that is implicated in apoptosis and cell cycle control, on Tat apoptotic function in the central nervous system. We recently demonstrated the ability of Tat to associate with p73, and that this association modulates Tat transcriptional activity (Amini et al., Mol Cell Biol 2005; 18: 8126-8138). We demonstrated that p73 interferes with Tat-mediated apoptosis by preventing the up-regulation of Bax and down-regulation of Bcl-2 proteins in astrocytes. Thus, the interplay between Tat and p73 may affect Tat contribution to apoptotic events in the brain, limiting its involvement in the neuropathology often observed in the brains of HIV-1 patients.

p73 Interacts with human immunodeficiency virus type 1 Tat in astrocytic cells and prevents its acetylation on lysine 28

Human immunodeficiency virus type 1 (HIV-1) Tat is a potent transcriptional activator of the HIV-1 promoter and also has the ability to modulate a number of cellular regulatory circuits including apoptosis. Tat exerts its effects through interaction with viral as well as cellular proteins. Here, we studied the influence of p73, a protein that is implicated in apoptosis and cell cycle control, on Tat functions in the central nervous system. Protein interaction studies using immunoprecipitation followed by Western blot and glutathione S-transferase pull-down assays demonstrated the association of Tat with p73. Tat bound to the N-terminal region of p73 spanning amino acids 1 to 120, and this interaction required the cysteine-rich domain (amino acids 30 to 40) of Tat. Association of p73 with Tat prevented the acetylation of Tat on lysine 28 by PCAF. Functional studies including RNA interference showed that p73 inhibited Tat stimulation of the HIV-1 promoter. Furthermore, p73 prevented the interaction of Tat with cyclin T1 in vitro but not in vivo. These findings suggest possible new therapeutic approaches, using p73, for Tat-mediated AIDS pathogenesis.

No evidence of INI1hSNF5 (SMARCB1) and PARVG point mutations in oligodendroglial neoplasms

Allelic losses of chromosome 22 found in oligodendrogliomas suggest that at least one tumor suppressor gene on chromosome 22 is inactivated during the multistep process of tumorigenesis in this glial tumor. INI1hSNF5 (HUGO symbol: SMARCB1), located at 22q11, encodes a component of the ATP-dependent chromatin remodeling hSWI-SNF complex; it is a tumor suppressor gene that is mutated in several malignant tumors. The PARVG gene, located at 22q13, has been found to exhibit reduced expression in some cancer lines. Both genes are thus candidate tumor suppressors, potentially involved in the pathogenesis of gliomas. We performed mutation analyses of INI1hSNF5 and PARVG in a series of 40 oligodendrogliomas, but only sequence polymorphic variations were identified. Accordingly, INI1hSNF5 and PARVG do not seem to be the tumor suppressor genes involved in oligodendroglioma development and progression.

Comprehensive DNA copy number profiling of meningioma using a chromosome 1 tiling path microarray identifies novel candidate tumor suppressor loci

Meningiomas are common neoplasms of the meninges lining of the central nervous system. Deletions of 1p have been established as important for the initiation and/or progression of meningioma. The rationale of this array-CGH study was to characterize copy number imbalances of chromosome 1 in meningioma, using a full-coverage genomic microarray containing 2,118 distinct measurement points. In total, 82 meningiomas were analyzed, making this the most detailed analysis of chromosome 1 in a comprehensive series of tumors. We detected a broad range of aberrations, such as deletions and/or gains of various sizes. Deletions were the predominant finding and ranged from monosomy to a 3.5-Mb terminal 1p homozygous deletion. Although multiple aberrations were observed across chromosome 1, every meningioma in which imbalances were detected harbored 1p deletions. Tumor heterogeneity was also observed in three recurrent meningiomas, which most likely reflects a progressive loss of chromosomal segments at different stages of tumor development. The distribution of aberrations supports the existence of at least four candidate loci on chromosome 1, which are important for meningioma tumorigenesis. In one of these regions, our results already allow the analysis of a number of candidate genes. In a large series of cases, we observed an association between the presence of segmental duplications and deletion breakpoints, which suggests their role in the generation of these tumor-specific aberrations. As 1p is the site of the genome most frequently affected by tumor-specific aberrations, our results indicate loci of general importance for cancer development and progression.

Expression and clinical significance of TAp73α, p53, PCNA and apoptosis in hepatocellular carcinoma

AIM: To study the prognostic role of TAp73α, p53, proliferating cell nuclear antigen (PCNA) and apoptosis in patients with hepatocellular carcinoma (HCC) after surgical tumor ablation.

METHODS: Forty-seven human resected HCC tissues and 42 adjacent non-cancerous tissues were studied with 10 normal liver tissues as control group. TAp73α, p53, and PCNA were detected with Elivision immunohistochemistry. Terminal deoxynucleotidyl transferase (TdT)-mediated d-UTP-biotin nick-end labeling (TUNEL) method was used to detect the apoptosis cells. All clinical and pathological materials were analyzed by SPSS10.0 statistical package.

RESULTS: TAp73α overexpressed in HCC tissues (36.2%) when compared with adjacent non-cancerous tissues (2.38%, P<0.005) and normal liver tissues (0, P<0.01). Mutant type p53 (mt-p53) overexpressed in HCC tissues (38.3%) when contracted with adjacent non-cancerous tissues (16.7%, P<0.05) and normal liver tissues (0, P<0.01). Proliferation index (PI) level in HCC tissues was significantly higher than that in adjacent non-cancerous tissues (30.34%±4.46% vs 27.88%±5.89%, t, P = 0.028). Apoptosis index (AI) level in HCC tissues was higher than that in adjacent non-cancerous tissues (8.62%±2.28% vs 7.38%±2.61%, t, P = 0.019). Expression of TAp73α was associated with lymph node metastasis and mt-p53, with r = 0.407 and 0.265, respectively. Expression of mt-p53 was associated with Edmondson’s stage and AFP, with r = 0.295 and -0.357, respectively. In Kaplan-Meier univariant analysis, TAp73α, AFP, TNM stage, portal vein invasion, liver membrane invasion and HBsAg correlated with prognosis (log rank, P = 0.039, 0.012, 0.002, 0.000, 0.014, 0.007, respectively). Multivariant Cox regression analysis showed that TAp73α, AFP, TNM stage, portal vein invasion, liver membrane invasion and age were independent factors of prognosis.

CONCLUSION: These results suggest that TAp73α can be used as a prognostic indicator of patients with HCC undergoing surgical tumor ablation. AFP, TNM, portal vein invasion, liver membrane invasion and age also have a potency of predicting the prognosis of HCC.

Allelic Losses at 1p36 and 19q13 in Gliomas: Correlation with Histologic Classification, Definition of a 150-kb Minimal Deleted Region on 1p36, and Evaluation of CAMTA1 as a Candidate Tumor Suppressor Gene

Purpose: Allelic loss at 1p is seen in 70% to 85% of oligodendrogliomas (typically in association with 19q allelic loss) and 20-30% of astrocytomas. Because most 1p deletions in gliomas involve almost the entire chromosome arm, narrowing the region of the putative tumor suppressor gene has been difficult. To better define the histologic correlates of different patterns of 1p and 19q loss, we evaluated 1p/19q status in a large group of gliomas. This also allowed us to define a very small minimal deleted region (MDR) on 1p36.

Experimental Design: Among 205 consecutive cases of glioma studied for 1p loss of heterozygosity (LOH), 112 tumors were evaluated for both 1p and 19q LOH using at least three polymorphic markers on 1p and 19q each. The latter group included both low-grade tumors (oligodendroglioma, diffuse astrocytoma, and “oligoastrocytoma”) and high-grade tumors (anaplastic oligodendrogliomas, anaplastic astrocytomas, anaplastic oligoastrocytomas). Tumors with small segmental 1p losses (defined as LOH at some loci with retention of heterozygosity at other loci) were studied using a more extensive panel of markers to define the 1p MDR. The candidate gene was screened for mutations and its expression was studied by qualitative and quantitative reverse transcriptase-PCR and Northern blotting.

Results: Allelic losses on 1p and 19q, either separately or combined, were more common in classic oligodendrogliomas than in either astrocytomas or oligoastrocytomas (P &lt; 0.0001). Classic oligodendrogliomas showed 1p loss in 35 of 42 (83%) cases, 19q loss in 28 of 39 (72%), and these were combined in 27 of 39 (69%) cases. There was no significant difference in 1p/19q LOH status between low-grade and anaplastic oligodendrogliomas. In contrast, no astrocytomas and only 6 of 30 (20%) oligoastrocytic tumors had combined 1p/19q loss. Although rare, 1p deletions were more often segmental in astrocytomas (5 of 6, 83%) than in oligodendrogliomas (3 of 35, 9%; P = 0.006). Eleven tumors (6 oligodendrogliomas or having oligodendroglial components, 5 purely astrocytic) with small segmental 1p losses underwent further detailed LOH mapping. All informative tumors in the oligodendroglial group and 2 of 3 informative astrocytomas showed LOH at 1p36.23, with a 150-kb MDR located between D1S2694 and D1S2666, entirely within the CAMTA1 transcription factor gene. Mutation analysis of the exons encoding conserved regions of CAMTA1 showed no somatic mutations in 10 gliomas, including 6 cases with and 4 cases without 1p LOH. CAMTA1 is normally expressed predominantly in non-neoplastic adult brain tissue. Relative to the latter, the expression level of CAMTA1 was low in oligodendroglial tumors and was further halved in cases with 1p deletion compared with those without 1p deletion (Mann-Whitney, P = 0.03).

Conclusions: Our data confirm the strong association of combined 1p/19q loss with classic oligodendroglioma histology and identify a very small segment of 1p36 located within CAMTA1 that was deleted in all oligodendroglial tumors with 1p LOH. This MDR also overlaps the neuroblastoma 1p36 MDR. CAMTA1 shows no evidence of inactivation by somatic mutations but its expression is reduced by half in cases with 1p LOH, suggesting that the functional effects of CAMTA1 haploinsufficiency warrant further investigation.

Diagnostic clinical application of two-color fluorescence in situ hybridization that detects chromosome 1 and 17 alterations to direct touch smear and liquid-based thin-layer cytologic preparations of endometrial cancers

We performed two-color fluorescence in situ hybridization (FISH) on direct touch smears and liquid-based thin-layer (ThinPrep) cytological preparations of endometrial tumors to detect alterations of chromosome 1 and 17 that present with high incidence in endometrial cancers. The DNA probes used for two-color FISH analysis were a combination of the probes designed for 17cen (cCI 17-321) and 17p13.3 (D17S34), and a combination of the probes designed for 1q12 (D1Z1) and 1p36 (cCI1-5335). Numerical or structural alterations of chromosome 1 and/or 17 were detected in 95% (19 of 20 cases) of the direct touch smears obtained from endometrial cancer, while these alterations were also detected in 93% (12 of 13 cases) of samples obtained from grade 1 endometrioid adenocarcinoma cases, including three cases that could not be diagnosed as positive by conventional Papanicolaou cytopathologic staining. Using ThinPrep cytopathologic preparations, numerical or structural abnormalities were found in 26 (90%) and five (100%) cases, respectively, of samples obtained transcervically from 29 endometrial cancer and five atypical endometrial hyperplasia cases. Therefore, two-color FISH may be a useful diagnostic method for endometrial adenocarcinoma and premalignant lesions that demonstrate only slight cellular atypia in conventional cytopathologic preparations.

Identification of two contiguous minimally deleted regions on chromosome 1p36.31-p36.32 in oligodendroglial tumours

Loss of the short arm of chromosome 1 is a hallmark of oligodendroglial tumours (OTs). Deletion mapping studies in OTs have revealed multiple commonly deleted regions on chromosome 1p, suggesting that there are more than one tumour suppressor gene. To map critical deletion regions on 1p, a series of 25 OTs were examined for loss of heterozygosity (LOH) on 19 polymorphic markers across the 1p arm using microsatellite analysis. Our study revealed that 60% of tumours had LOH of all informative markers on 1p and identified one tumour showing LOH at telomeric markers only. Since this deletion region lies in one of the critical deletion intervals defined previously, we then screened another series of 27 OTs specifically at 1p36.3 for LOH using nine polymorphic markers. A total of 12% (six out of 52) of tumours were found to carry interstitial deletions. The allelic status and the deletion breakpoints in these tumours with interstitial deletion were further verified by fluorescent in situ hybridisation. The small overlapping intervals facilitated the delineation of two contiguous minimally deleted regions of 0.76 Mb, defined by D1S468 and D1S2845, and of 0.41 Mb, bound by D1S2893 and D1S1608, on 1p36.31–36.32. Based on current reference human genome sequence these deletion regions have been sequenced almost to entirety and contain eight annotated genes. TP73, DFFB and SHREW1 are the only known genes located in these deletion regions, while the others are uncharacterised novel genes. In conclusion, our study has narrowed down the critical tumour suppressor loci on 1p36.3, in which two minimally deleted regions are mapped, and markedly reduced the number of candidate genes to be screened for their involvement in OT development.

Molecular pathogenesis of oligodendroglial tumors

Based on their histopathological appearances, most diffusely infiltrative gliomas can be classified either as astrocytic tumors (As), pure oligodendroglial tumors (Os) or mixed oligoastrocytic tumors (OAs). The latter two may be grouped together as oligodendroglial tumors (OTs). The distinction between As and OTs is important because of the more favorable clinical behavior of OTs. Unfortunately, the histopathological delineation of OAs, Os and As can be difficult because of vague and subjective histopathological criteria. Over the last decade, the knowledge on the molecular genetic background of OTs has drastically increased. This review provides an overview of molecular genetic aberrations in OTs and discusses the pathobiological and clinical significance of these aberrations. In contrast to As, OTs frequently show frequent loss of heterozygosity on chromosome arms 1p and 19q. Since these aberrations are significantly correlated with clinically relevant parameters, such as prognosis and chemosensitivity, and given the difficulties in histopathological typing and grading of glial tumors, genetic testing should be included in routine glioma diagnostics. It is to be expected that the identification of the relevant tumor suppressor genes located on 1p and 19q will lead to more refined genetic tests for OTs. Furthermore, as microarray technology is rapidly increasing, it is likely that clinically relevant markers for OTs will be identified on other chromosomes and need to be included into routine glioma diagnostics as well.

Meningiomas may be a component tumor of multiple endocrine neoplasia type 1

PURPOSE

Recently, an increased incidence of some nonendocrine tumors are reported in patients with multiple endocrine neoplasia type 1 (MEN 1). There are rare reports of meningiomas and other central nervous system tumors in these patients, but it is unknown if they are more frequent or if allelic loss of the MEN1 gene is important in their pathogenesis. The aim of this study was to address these two latter questions.

EXPERIMENTAL DESIGN

Results from a prospective study of 74 MEN 1 patients with suspected/proven pancreatic endocrine tumors (PETs) were analyzed, as well as molecular studies performed on a resected meningioma. All patients had serial brain imaging studies (computed tomography, magnetic resonance imaging, and octreoscanning since 1994) and yearly studies evaluating MEN 1 involvement with a mean follow-up of 7.2 years. Results were compared with 185 patients with sporadic Zollinger-Ellison syndrome.

RESULTS

Six patients (8%) had meningiomas. Meningiomas were single and found late in the MEN 1 course (mean age = 51 years). Magnetic resonance imaging/computed tomography were more sensitive than octreoscanning. Their diagnosis averaged 18 years after the onset of hyperparathyroidism, 10-15 years after pituitary disease or PETs. Meningiomas were 11 times more frequent in patients with PETs with MEN 1 than without MEN 1 (P = 0.017). No clinical, laboratory, or MEN 1 feature distinguished patients with meningiomas. Meningiomas were asymptomatic and 60% showed no growth. A resected meningioma showed loss of heterozygosity at 11q13 and 1p, including at p73 and ARHI/NOEY2 locus, but not at the neurofibromatosis 2 gene locus.

CONCLUSIONS

These results show meningiomas are not an infrequent occurrence in MEN 1, and loss of the function of the MEN1 gene product plays a role in their pathogenesis in these patients.

Pathology and molecular genetics of oligodendroglial tumors

Oligodendroglial gliomas are second only to astrocytic gliomas in frequency. The lack of stringent diagnostic criteria cause high interobserver variation in regard to classification and grading of these tumors. Previous studies have described oligodendrogliomas with features that overlap with those of neurocytic tumors, thus further complicating diagnostic decisions. The increasing need for standardized diagnostic criteria in this subset of gliomas is emphasized by the benefit of adjuvant therapies in patients with anaplastic oligodendrogliomas. Characteristic chromosomal aberrations have been successfully determined for oligodendroglial tumors in recent years. In contrast to astrocytomas, however, no genes in the affected regions have been clearly linked to their pathogenesis. However, the molecular findings promise to be helpful for diagnostic and therapeutic decisions. This review compiles clinical, pathological, and molecular genetic findings on WHO grades II and III oligodendrogliomas and oligoastrocytomas.

Oligodendroglial tumors: refinement of candidate regions on chromosome arm 1p and correlation of 1p/19q status with survival

Loss of heterozygosity (LOH) on the chromosome arms 1p and 19q is frequent in oligodendroglial tumors and has been correlated with chemosensitivity and good prognosis in anaplastic oligodendrogliomas. The oligodendroglioma-associated tumor suppressor genes on 1p and 19q are as yet unknown. To narrow down candidate regions on 1p, we investigated oligodendroglial tumors from 89 patients for LOH at up to 30 polymorphic loci on 1p. In addition, all tumors were studied for LOH at 7 loci on 19q. Combined LOH on 1p and 19q was detected in 20 (83%) of 24 oligodendrogliomas, 15(63%) of 24 anaplastic oligodendrogliomas, 10 (56%) of 18 oligoastrocytomas, and 12 (52%) of 23 anaplastic oligoastrocytomas. Five tumors demonstrated partial deletions on 1p, which allowed to define 3 distinct candidate regions at 1p36.31-pter distal to D1S2633, 1p36.22-p36.31 between D1S489 and D1S2642, and 1p34.2-p36.1 between D1S2743 and D1S482, respectively. No partial deletions were detected on 19q. Combined LOH on 1p and 19q was associated with prolonged time to progression (TTP), longer overall survival (OS), and a higher 5-year survival rate. Depending on the presence or absence of combined LOH on 1p and 19q, patients with anaplastic oligodendroglial tumors treated with adjuvant radio- and/or chemotherapy showed a median TTP of 86 months versus 39 months, a median OS of 91 months versus 46 months, and a 5-year survival rate of 80% versus 36%, respectively. Similarly, LOH on 1p and 19q was associated with longer survival in patients with low-grade oligodendroglial tumors (TTP: 57 months versus 47 months; OS: 172 months versus 105 months; 5-year survival rate: 92% versus 70%). Thus, our results refine the location of putative oligodendroglioma suppressor genes on 1p and support the significance of LOH on 1p and 19q as a favorable prognostic marker.

Methylation status of TP73 in meningiomas

Deletions at 1p are frequent in meningioma and represent a genetic marker associated with the genesis of atypical WHO grade II forms. Previous mutational analysis of TP73, a structurally and functionally TP53 homologous gene located at 1p36.33, failed to demonstrate a significant rate of sequence variations linked to gene inactivation in meningiomas with 1p loss. As an alternative, TP73 may be inactivated through aberrant 5' CpG island methylation, a primary mechanism participating in the inactivation of tumor suppressor genes during tumorigenesis. We determined the methylation status of the TP73 gene in a series of 60 meningiomas (33 grade I, 24 grade II, and 3 grade III samples), including tumors with deletion at 1p (n=30) and with intact 1p (n=30). Aberrant methylation was detected in 10 cases (33%) with 1p deletion and in 3 tumors (10%) with retention of alleles at this chromosome arm. The distribution of the 13 cases of methylation according to malignancy grade was 7 grade I, 5 grade II, and 1 grade III tumor. Accordingly, although TP73 aberrant methylation was more frequent in meningiomas with 1p deletion (P<0.05), no association with the grade of malignancy could be established. These findings, together with the previously reported increased TP73 expression in malignant meningiomas suggest that opposing functions of this gene may characterize distinct subsets of tumors: suppressed or reduced expression as a result of CpG methylation in some grade I-grade II tumors, and enhanced expression in some more malignant forms.

A naturally occurring p73 mutation in a p73-p53 double-mutant lung cancer cell line encodes p73 alpha protein with a dominant-negative function

p73, a close homolog of p53 tumor suppressor, induces growth arrest and apoptosis. However, its role in cancers is controversial because of the rarity of p73 mutations, lack of tumors in p73-knockout mice, and the presence of multiple isotypes, among which Delta N isotypes inhibit the function of TA isotypes. We analyzed three naturally occurring p73 mutants found in lung cancer cell lines, NCI-H1155, DMS 92 and A427. NCI-H1155 is a cell line that has a p73 mutation [p73(G264W)] in the DNA-binding domain, as well as a p53 mutation [p53(R273H)], which is frequently found in human cancers and has a "gain-of-function" characteristic. p73 alpha(G264W) not only lacks transactivation activity itself, but also suppressed the transactivation activity of the wild-type p73 alpha in a dose-dependent manner, indicating that p73 alpha(G264W) is a dominant-negative mutant. p73 alpha(G264W) failed to suppress colony formation. We tested two other mutations, p73(Del418) in DMS 92 and p73(Del603) in A427. Both mutants retained similar levels of transactivation activity and suppression of colony formation to those of wild-type p73. The biological significance of these two mutations is unclear. In NCI-H1155 cells the coexistence of mutations that abrogate the normal functions of p73 and p53 may indicate that each mutation confers an additive growth advantage upon the cells.

Aberrant promoter methylation of multiple genes in oligodendrogliomas and ependymomas

Promoter hypermethylation represents a primary mechanism in the inactivation of tumor suppressor genes during tumorigenesis. To determine the frequency and timing of hypermethylation during carcinogenesis of nonastrocytic tumors, we analyzed promoter methylation status of 10 tumor-associated genes in a series of 41 oligodendrogliomas (22 World Health Organization [WHO] grade II; 13 WHO grade III; 6 WHO grade II-III oligoastrocytomas) and 7 WHO grade II-III ependymomas, as well as 2 nonneoplastic brain samples, by a methylation-specific polymerase chain reaction. Aberrant CpG island methylation was detected in 9 of 10 genes analyzed, and all but one sample displayed anomalies in at least one gene. The frequencies of hypermethylation for the 10 genes were as follows, in oligodendrogliomas and ependymomas, respectively: 80% and 28% for MGMT; 70% and 28% for GSTP1; 66% and 57% for DAPK; 44% and 28% for TP14(ARF); 39% and 0% for THBS1; 24% and 28% for TIMP3; 24% and 14% for TP73; 22% and 0% for TP16(INK4A); 3% and 14% for RB1; and 0% in both neoplasms for TP53. No methylation of these genes was detected in normal brain tissue samples. We conclude that a high frequency of aberrant methylation of the 5' CpG island of the MGMT, GSTP1, TP14(ARF), THBS1, TIMP3, and TP73 genes is observed in nonastrocytic neoplasms. This aberration seems to occur early in the carcinogenesis process (it is already present in the low-grade forms), although in some instances (DAPK, THBS1, and TP73) it appears also associated with the genesis of anaplastic forms.

Immunohistochemical analysis of p16INK4a, p14ARF, p18INK4c, p21CIP1, p27KIP1 and p73 expression in 271 meningiomas correlation with tumor grade and clinical outcome

Routine pathological examination cannot distinctively predict the clinical course of meningiomas because even histologically benign tumors may recur after gross total resection. Numerous efforts have been made for the evaluation of different immunohistochemical assays in meningioma prognosis. We investigated the prognostic significance of p16INK4a, p14ARF, p18INK4c, p21CIP1, p27KIP1 and p73 expression by immunohistochemical analysis of 271 meningiomas. All tumors were additionally stained for the proliferation markers Ki-67 and DNA topoisomerase II alpha (TopoIIalpha). Significant differences between the number of p16INK4a-, p18INK4c- and p21CIP1-positive cases were noted among the 3 grades of meningiomas. p16INK4a- and p21CIP-positive tumors were found to prevail among benign meningiomas, whereas p18INK4c immunostaining was closely associated to anaplastic meningiomas. The number of p16INK4a- and p21CIP-positive cases was significantly lower in the cohort of recurrent meningiomas. In contrast, p18INK4c-positive cases were clustered among recurrent meningiomas regardless of tumor grade. Immunoreactivity of p14ARF, p27KIP1 and p73 did not show any differences between meningiomas of various histology and clinical outcomes. Multivariate analysis revealed that only tumor grade and TopoIIalpha index are independent criteria for predicting meningioma recurrence. Thus, the immunohistochemical assessment of p16INK4a, p14ARF, p18INK4c, p21CIP1, p27KIP1 and p73 expression in meningiomas does not appear to provide prognostically useful information. Further studies are needed to identify more reliable prognostic markers and to address in more detail the role of cell cycle aberrations in these tumors.

Correlation between genetic alteration and long-term clinical outcome of patients with oligodendroglial tumors, with identification of a consistent region of deletion on chromosome arm 1p

BACKGROUND

In oligodendroglial tumors, allelic losses on chromosome arms 1p and 19q are not only diagnostic molecular markers but also statistically significant predictors of both chemosensitivity and longer recurrence-free survival. In the current study, the authors attempted to analyze 21 patients genetically and clinically, with special emphasis on the correlation between genetic alterations and long-term therapeutic results.

METHODS

The authors reviewed the clinical cases of 21 patients who had undergone surgery for oligodendroglial tumors (13 oligodendrogliomas, World Health Organization [WHO] Grade II; 3 anaplastic oligodendrogliomas, WHO Grade III; 3 oligoastrocytomas, WHO Grade II; and 2 anaplastic oligoastrocytomas, WHO Grade III). Genetic testing for 1p deletions was performed using fluorescence in situ hybridization, and testing for 1p, 17p, and 19q deletions was carried out by microsatellite analysis. Survival was analyzed with univariate and multivariate Cox regression models. In addition, a high-resolution deletion map of 1p, which led to the discovery of a new deleted region on 1p, was obtained.

RESULTS

Statistical analysis revealed that both loss of 1p and loss of 19q independently and significantly predicted overall survival. A high-resolution deletion map, which displayed unusually narrow deletions, revealed a new region of deletion between D1S513 and D1S458 (1p34.3-36.11).

CONCLUSIONS

One of the putative tumor suppressor loci exists more proximally than ever reported. Based on the observation that 1p and 19q deletions predicted survival, the authors suggest further use of diagnostic and prognostic genetic testing in the clinical setting.

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.

The expression of p73, p21 and MDM2 proteins in gliomas

p73 protein, a member of the p53 family protein, induce p21 and MDM2 transcription. In some carcinomas, the expression of p73 was higher in carcinoma than in normal tissue, and the overexpression was correlated to grade, stage or prognosis. However, either the expression of p73 protein or the relationship among p73, p21 and MDM2 proteins was not known well in glioma. In this study, we examined the expression of p73, p21 and MDM2 proteins immunohistochemically and analyzed the relationship among these three proteins in sixty surgical specimens of gliomas including 10 glioblastomas, 10 anaplastic astrocytomas, 6 diffuse astrocytomas, 8 pilocytic astrocytomas, 1 anaplastic ependymoma, 8 ependymomas, 9 anaplastic oligodendroglial tumors and 8 low grade oligodendroglial tumors. The p73 labelling index (LI)s and p21 LIs differed among the tumor types, but there was no difference in the MDM2 LIs among all of the tumor types. The mean p73 LI of ependymomas was significantly higher than in any other tumor type. The mean p2I LIs of ependymomas and pilocytic astrocytomas were significantly higher than in any other tumor type. There were no significant correlations among p73 LIs, p21 LIs, MDM2 LIs and MIB-1 LIs in all p73 immunopositive tumors. The present results suggest that p73 and p21 overexpression of ependymomas and p21 overexpression of pilocytic astrocytomas are one of the features of these tumors, and that p73 overexpression does not influence the expression manners of either p21 or MDM2 in gliomas.

Oligodendroglioma: toward molecular definitions in diagnostic neuro-oncology

Oligodendroglial tumors have attracted great interest in both basic and clinical neuro-oncology over the past decade. This interest is mainly due to the clinical observation that anaplastic oligodendrogliomas and anaplastic oligoastrocytomas, in contrast to the vast majority of anaplastic astrocytomas and glioblastomas, frequently respond favorably to chemotherapy. In addition, oligodendroglial tumors are associated with longer survival times than the diffuse astrocytic gliomas. These differences in response to therapy and in prognosis have been associated with distinct genetic aberrations, in particular the frequent loss of alleles on chromosome arms 1p and 19q in oligodendroglial tumors. In addition, other genetic changes have been reported as indicators of poor response to therapy and short survival, including homozygous deletion of the CDKN2A gene at 9p21, mutation of the PTEN gene at 10q23, and amplification of the EGFR gene at 7p12. In this review we summarize the current state of the art concerning the molecular genetics of oligodendroglial tumors. A particular focus is placed on the role of molecular genetic findings in the diagnostic and prognostic assessment of these neoplasms. As a result of the recent advances in the field, we propose that clinical decisions in the management of patients with oligodendroglial tumors should be based on the combined assessment of clinical and neuroimaging features, histological classification and grading, as well as molecular genetic characteristics.