Somatic mutations of WNT/wingless signaling pathway components in primitive neuroectodermal tumors

Role of Wnt inhibitory factor-1 and Wnt/wingless signaling in choroid plexus tumors

Little is known on pathways involved in the pathogenesis of choroid plexus tumors (CPTs). The finding of overexpression of Wnt inhibitory factor-1 (Wif-1) prompted us to investigate the functional role of Wif-1 as well as nuclear accumulation of beta-catenin in CPT. In Z310 neoplastic choroid plexus epithelial cells, silencing of Wif1 expression increased proliferative activity not associated with increased canonical Wnt signaling. Nuclear beta-catenin accumulation was also lacking in a series of 16 CPT. In conclusion, our data show that Wif-1 inhibits proliferation of neoplastic choroid plexus epithelial cells, but argue against a role of canonical Wnt/wingless signaling in CPT.

Genetic and protein changes of E-cadherin in meningiomas

PURPOSE

The molecular mechanisms and candidate genes involved in development of meningiomas still needs investigation and elucidation.

METHODS

In the present study 60 meningiomas were analyzed regarding changes of tumor suppressor gene E-cadherin (CDH1), a component of adherens junction and an indirect modulator of the wnt signaling. Gene instability was tested by polymerase chain reaction/loss of heterozygosity (LOH) method. Protein expression was analyzed by immunohistochemistry.

RESULTS

The results of our analysis showed altogether 32% of samples with LOH of the CDH1 gene. Interestingly, another type of genomic instability was detected; replication error-positive samples (RER+). Three out of 28 heterozygous samples were RER+ (11%). The instability is the result of impaired cellular mismatch repair. Fibrous and angiomatous cases showed higher percent of genetic changes, 67 and 75%, respectively. Immunostaining showed that overall 73% of samples had downregulation of E-cadherin expression. Intense downregulation of E-cadherin was noticed in tumors with grades II and III. Five out of nine samples with LOH were accompanied with the downregulation of E-cadherin protein expression (56%). One RER+ sample had lower expression of E-cadherin. We noticed that 36.4% of samples with lower E-cadherin expression had beta-catenin located in the nucleus. Also, 75% of samples with genomic instabilities had beta-catenin in the nucleus. Our findings demonstrated that there is significant association between the genetic changes of CDH1 and the nuclear localization of beta-catenin protein (chi(2) = 5.25, df = 1, P < 0.022). Beta-catenin was progressively upregulated from meningothelial to atypical, while 60% of anaplastic showed upregulation and nuclear localization of the protein.

CONCLUSIONS

Our results suggest that genetic instabilities of the E-cadherin gene have a role in meningioma development and progression. Detected microsatellite instability indicates that mismatch repair may also be targeted in meningioma.

Medulloblastoma

Medulloblastoma is the most common malignant brain tumor in children. Patients with medulloblastoma are stratified into ''standard'' and ''high'' risk categories based on age at diagnosis, degree of surgical resection, and disease spread. In children older than 3 years of age, the long-term survival can be achieved in approximately 85% of standard risk patients and 70% of high risk patients with a combination of chemotherapy and irradiation. Younger children, particularly infants, are at a significantly higher risk of side-effects of treatment. Despite tremendous progress in the field of molecular biology of medulloblastoma, much remains to be achieved in understanding the pathogenesis, critical pathways responsible for medulloblastoma, and molecular risk stratification, and in devising treatment strategies with even better survival and less long-term sequelae.

Mouse models of CNS embryonal tumors

Central nervous system (CNS) embryonal tumors are devastating cancers in children, consisting of medulloblastomas, CNS primitive neuroectodermal tumors, and atypical teratoid/rhabdoid tumors. One of the reasons that CNS embryonal tumors remain difficult to treat is their rarity, which makes conducting clinical trials for these tumors difficult. Recent advances of molecular biology have led us to identify molecular and genetic causality of brain tumors. Based on the genetic alterations found in humans, multiple models of human CNS embryonal tumors have been generated in genetically engineered mice. These mouse models are valuable tools for understanding brain tumor biology and discovering novel therapeutic targets and drugs. In this article, we review molecular and cytogenetic characteristics of human CNS embryonal tumors and corresponding mouse models that have been developed. These findings indicate that common genetic abnormalities are seen in variants of human CNS embryonal tumors, and multiple histological variants of these tumors can be generated from a single set of genetic abnormalities in mice. These data provide insight into the biology and classification of CNS embryonal tumors.

Amplification and overexpression of KIT, PDGFRA, and VEGFR2 in medulloblastomas and primitive neuroectodermal tumors

Medulloblastomas (MB) and primitive neuroectodermal tumors (PNET) are the most common malignant brain tumors in children. These two tumor types are histologically similar, but have different genetic backgrounds and clinical outcomes. Other brain tumors, such as gliomas, frequently have coamplification and overexpression of receptor tyrosine kinases KIT, platelet-derived growth factor receptor alpha (PDGFRA), and vascular endothelial growth factor receptor 2 (VEGFR2). We investigated protein expression and gene copy numbers of KIT, PDGFRA, and VEGFR2 in 41 MB and 11 PNET samples by immunohistochemistry (IHC) and chromogenic in situ hybridization (CISH). KIT and PDGFRA expression was detected in both MBs and PNETs, whereas VEGFR2 expression was weak in these tumors. KIT, PDGFRA, and VEGFR2 amplifications were all present in 4% of MBs/PNETs, and KIT amplification was associated with concurrent PDGFRA and VEGFR2 amplifications (P <or= 0.001). Most strikingly, increased gene copy number of PDGFRA was associated with poor overall survival (P = 0.027). We suggest that coamplification of PDGFRA or VEGFR2 with KIT may be clinically useful novel molecular markers in MBs and PNETs.

Wnt signaling in development and disease

The Wnt signaling pathway is one of the central morphogenic signaling pathways regulating early vertebrate development. In recent years, it has become clear that the Wnt pathway also regulates many aspects of nervous system development from the patterning stage through the regulation of neural plasticity. In this review, we first present an overview of the components of the Wnt signaling pathway and then go on to discuss the literature describing the multitude of roles of Wnts in nervous system. In the latter portion of the review, we turn to the ways that defects in Wnt signaling lead to neurologic disease.

CTNNB1 (beta-catenin) mutation is rare in brain tumours but involved as a sporadic event in a brain metastasis

BACKGROUND

The Wnt signaling pathway has been implicated in colon and other cancers. Nevertheless, few or no mutations of CTNNB1 (beta-catenin) have so far been described in brain cancer. We therefore examined the prevalence of constitutive activation of the Wnt signaling pathway in brain cancer specimens as well as cancer cell lines.

METHOD

We used polymerase chain reaction PCR and direct sequencing methods to investigate whether mutations in the CTNNB1 phosphorylation sites S33, S37, S41 and T45 were present in 68 brain tumours, including meningioma, astrocytoma, pituitary adenoma, neuroblastoma, metastasis to the brain, and cell lines.

FINDINGS

CTNNB1 gene mutations were not found in either the original brain tumour specimens or the cell lines. However, a missense mutation of CTNNB1 was identified at residue 33, TCT (Ser) --> TGT (Cys) in a patient with lung metastasis to brain. In addition, in vitro functional assay showed that the S33C mutant of beta-catenin did affect transcriptional activity in a TCF-4-luciferase reporter construct.

CONCLUSIONS

These results indicate that the mutation of exon 3 of the CTNNB1 gene in brain tumours may be a rare event and yet may be required for a small subset of human metastatic brain tumours.

An investigation of WNT pathway activation and association with survival in central nervous system primitive neuroectodermal tumours (CNS PNET)

Central nervous system primitive neuroectodermal tumours (CNS PNET) are high-grade, predominantly paediatric, brain tumours. Previously they have been grouped with medulloblastomas owing to their histological similarities. The WNT/β-catenin pathway has been implicated in many tumour types, including medulloblastoma. On pathway activation β-catenin (CTNNB1) translocates to the nucleus, where it induces transcription of target genes. It is commonly upregulated in tumours by mutations in the key pathway components APC and CTNNB1. WNT/β-catenin pathway status was investigated by immunohistochemical analysis of CTNNB1 and the pathway target cyclin D1 (CCND1) in 49 CNS PNETs and 46 medulloblastomas. The mutational status of APC and CTNNB1 (β-catenin) was investigated in 33 CNS PNETs and 22 medulloblastomas. CTNNB1 nuclear localisation was seen in 36% of CNS PNETs and 27% of medulloblastomas. A significant correlation was found between CTNNB1 nuclear localisation and CCND1 levels. Mutations in CTNNB1 were identified in 4% of CNS PNETs and 20% of medulloblastomas. No mutations were identified in APC. A potential link between the level of nuclear staining and a better prognosis was identified in the CNS PNETs, suggesting that the extent of pathway activation is linked to outcome. The results suggest that the WNT/β-catenin pathway plays an important role in the pathogenesis of CNS PNETs. However, activation is not caused by mutations in CTNNB1 or APC in the majority of CNS PNET cases.

Downregulation of Wnt2 and beta-catenin by siRNA suppresses malignant glioma cell growth

Increasing evidence suggests that aberrant activation of Wnt signaling is involved in tumor development and progression. Our earlier study on gene expression profile in human gliomas by microarray found that some members of Wnt family were overexpressed. To further investigate the involvement of Wnt signaling in gliomas, the expression of core components of Wnt signaling cascade in 45 astrocytic glioma specimens with different tumor grades was examined by reverse transcription-PCR and immunohistochemistry. Wnt2, Wnt5a, frizzled2 and beta-catenin were overexpressed in gliomas. Knockdown of Wnt2 and its key mediator beta-catenin in the canonical Wnt pathway by siRNA in human U251 glioma cells inhibited cell proliferation and invasive ability, and induced apoptotic cell death. Furthermore, treating the nude mice carrying established subcutaneous U251 gliomas with siRNA targeting Wnt2 and beta-catenin intratumorally also delayed the tumor growth. In both in vitro and in vivo studies, downregulation of Wnt2 and beta-catenin was associated with the decrease of PI3K/p-AKT expression, indicating the interplay between Wnt/beta-catenin and PI3K/AKT signaling cascades. In conclusion, the canonical Wnt pathway is of critical importance in the gliomagenesis and intervention of this pathway may provide a new therapeutic approach for malignant gliomas.

Integrated genomics identifies five medulloblastoma subtypes with distinct genetic profiles, pathway signatures and clinicopathological features

BACKGROUND

Medulloblastoma is the most common malignant brain tumor in children. Despite recent improvements in cure rates, prediction of disease outcome remains a major challenge and survivors suffer from serious therapy-related side-effects. Recent data showed that patients with WNT-activated tumors have a favorable prognosis, suggesting that these patients could be treated less intensively, thereby reducing the side-effects. This illustrates the potential benefits of a robust classification of medulloblastoma patients and a detailed knowledge of associated biological mechanisms.

METHODS AND FINDINGS

To get a better insight into the molecular biology of medulloblastoma we established mRNA expression profiles of 62 medulloblastomas and analyzed 52 of them also by comparative genomic hybridization (CGH) arrays. Five molecular subtypes were identified, characterized by WNT signaling (A; 9 cases), SHH signaling (B; 15 cases), expression of neuronal differentiation genes (C and D; 16 and 11 cases, respectively) or photoreceptor genes (D and E; both 11 cases). Mutations in beta-catenin were identified in all 9 type A tumors, but not in any other tumor. PTCH1 mutations were exclusively identified in type B tumors. CGH analysis identified several fully or partly subtype-specific chromosomal aberrations. Monosomy of chromosome 6 occurred only in type A tumors, loss of 9q mostly occurred in type B tumors, whereas chromosome 17 aberrations, most common in medulloblastoma, were strongly associated with type C or D tumors. Loss of the inactivated X-chromosome was highly specific for female cases of type C, D and E tumors. Gene expression levels faithfully reflected the chromosomal copy number changes. Clinicopathological features significantly different between the 5 subtypes included metastatic disease and age at diagnosis and histology. Metastatic disease at diagnosis was significantly associated with subtypes C and D and most strongly with subtype E. Patients below 3 yrs of age had type B, D, or E tumors. Type B included most desmoplastic cases. We validated and confirmed the molecular subtypes and their associated clinicopathological features with expression data from a second independent series of 46 medulloblastomas.

CONCLUSIONS

The new medulloblastoma classification presented in this study will greatly enhance the understanding of this heterogeneous disease. It will enable a better selection and evaluation of patients in clinical trials, and it will support the development of new molecular targeted therapies. Ultimately, our results may lead to more individualized therapies with improved cure rates and a better quality of life.

Biological background of pediatric medulloblastoma and ependymoma: a review from a translational research perspective

Survival rates of pediatric brain tumor patients have significantly improved over the years due to developments in diagnostic techniques, neurosurgery, chemotherapy, radiotherapy, and supportive care. However, brain tumors are still an important cause of cancer-related deaths in children. Prognosis is still highly dependent on clinical characteristics, such as the age of the patient, tumor type, stage, and localization, but increased knowledge about the genetic and biological features of these tumors is being obtained and might be useful to further improve outcome for these patients. It has become clear that the deregulation of signaling pathways essential in brain development, for example, sonic hedgehog (SHH), Wnt, and Notch pathways, plays an important role in pathogenesis and biological behavior, especially for medulloblastomas. More recently, data have become available about the cells of origin of brain tumors and the possible existence of brain tumor stem cells. Newly developed array-based techniques for studying gene expression, protein expression, copy number aberrations, and epigenetic events have led to the identification of other potentially important biological abnormalities in pediatric medulloblastomas and ependymomas.

The origins of medulloblastoma subtypes

Childhood tumors containing cells that are morphologically and functionally similar to normal progenitor cells provide fertile ground for investigating the links between development and cancer. In this respect, integrated studies of normal cerebellar development and the medulloblastoma, a malignant embryonal tumor of the cerebellum, have proven especially fruitful. Emerging evidence indicates that the different precursor cell populations that form the cerebellum and the cell signaling pathways that regulate its development likely represent distinct compartments from which the various subtypes of medulloblastoma arise. Definitive characterization of each medulloblastoma subtype will undoubtedly improve treatment of this disease and provide important insights to the origins of cancer.

Pathogenesis of medulloblastoma and current treatment outlook

Medulloblastoma is the most common malignant tumor of the cerebellum in children, with a tendency to metastasize via CSF pathway. Survival rate varies depending on several factors, but is rather favorable, with radiotherapy as the treatment of choice. Irradiation of the craniospinal axis results, however, in severe neuropsychological and psychosocial impairments pertaining to memory, attention, motor functioning, language, and visuospatial abilities. Precise mechanisms underlying the formation of medulloblastoma are still unclear, but implication of at least three signaling molecules is postulated: insulin-like growth factor-I, WNT, and Sonic hedgehog. Thanks to increasing knowledge on the cellular mechanisms contributing to tumor formation, it is possible to propose new therapies that could replace radiotherapy or allow decreasing irradiation doses. The current review presents recent developments in medulloblastoma pathophysiology research and proposed inhibitors that could constitute good candidates for further pharmacological research.

c-Myc and beta-catenin cooperate with loss of p53 to generate multiple members of the primitive neuroectodermal tumor family in mice

Primitive neuroectodermal tumors (PNETs) are a family of primary malignant brain tumors that include medulloblastomas. Although genetic models of a subset of medulloblastomas are documented over the past decade, the molecular basis of other subclasses of PNET remains unclear. As elevated c-Myc expression, activation of Wnt/beta-catenin signaling and dysfunction of p53 are seen in human PNETs, we investigated what role these abnormalities have in the formation of PNETs. Incorporating these abnormalities, we generated supratentorial PNET (sPNET) in mice using somatic cell gene transfer. We show that sPNETs arise from GFAP-expressing cells by forced c-Myc expression combined with p53 inactivation. beta-catenin activation promotes tumor progression and induces divergent differentiation. These c-Myc+beta-catenin-induced PNETs are histologically similar to large cell/anaplastic medulloblastomas and can occur in both cerebrum and cerebellum. Furthermore, we have obtained one PNET with marked epithelial differentiation having histological resemblance to choroid plexus carcinoma in this series. Our results in mice suggest that sPNET with varied differentiation and large cell/anaplastic medulloblastomas may be two tumor groups with similar genetic foundations. These data provide insights into the biology and classification of human PNETs and suggest that multiple tumor types or variants can be generated from a fixed set of genetic abnormalities.

Functional and molecular interactions between the HGF/c-Met pathway and c-Myc in large-cell medulloblastoma

The growth factor hepatocyte growth factor (HGF), also known as scatter factor, and its tyrosine kinase receptor c-Met play important roles in medulloblastoma malignancy. The transcription factor c-Myc is another contributor to the malignancy of these most common pediatric brain tumors. In the present study, we observed strong morphological similarities between medulloblastoma xenografts overexpressing HGF and medulloblastoma xenografts overexpressing c-Myc. We therefore hypothesized a biologically significant link between HGF/c-Met and c-Myc in medulloblastoma malignancy and studied the molecular and functional interactions between them. We found that HGF induces c-Myc mRNA and protein in established and primary medulloblastoma cells. HGF regulated c-Myc levels via transcriptional and post-transcriptional mechanisms as evidenced by HGF induction of c-Myc promoter activity and induction of c-Myc protein levels in the setting of inhibited transcription and translation. We also found that HGF induces cell cycle progression, cell proliferation, apoptosis and increase in cell size in a c-Myc-dependent manner. Activation of MAPK and PI3K, inhibition of GSK-3beta and translocation of beta-catenin to the nucleus as well as Tcf/Lef transcriptional activity were involved in mediating c-Myc induction by HGF. Induction of Cdk2 kinase activity was involved in mediating the cell cycle progression effects, and downregulation of Bcl-XL was involved in mediating the proapoptotic effects of HGF downstream of c-Myc. All molecules that mediated the effects of HGF on c-Myc expression, cell proliferation and apoptosis were expressed in human large-cell medulloblastoma tissues. We therefore established for the first time a functional cooperation between HGF/c-Met and c-Myc in human medulloblastoma and elucidated the molecular mechanisms of this cooperation. The findings provide a potential explanation for the high frequency of c-Myc overexpression in medulloblastoma and suggest a cooperative role for c-Met and c-Myc in large-cell anaplastic medulloblastoma formation.

Molecular pathogenesis of adult brain tumors and the role of stem cells

Primary brain tumors consist of neoplasms with varied molecular defects, morphologic phenotypes, and clinical outcomes. The genetic and signaling abnormalities involved in tumor initiation and progression of the most prevalent adult primary brain tumors, including gliomas, meningiomas, and medulloblastomas, are described in this article. The current understanding of the cell-of-origin of these neoplasms is reviewed, which suggests that the malignant phenotype is propelled by cells with stem-like qualities. A comprehensive understanding of the molecular basis of transformation and the cell-of-origin of these neoplasms will enable the formulation of more targeted treatment alternatives that could improve survival and quality of life.

Genetic alterations of E-cadherin and beta-catenin in germinoma and teratoma: report of two central nervous system cases

The genetic basis as well as mechanisms of development of germ cell tumors of the CNS are still unexplained. In the present article changes of Ecadherin (CDH1) and beta-catenin (CTNNB1) genes in two CNS germ cell tumors are reported. Both gene products are components of adherens junctions, but are also involved in the Wnt signaling pathway. A case of germinoma of the central nervous system and a case of spinal channel teratoma were tested for loss of heterozygosity (LOH) of E-cadherin gene by PCR amplification of tetranucleotide polymorphism (D16S752). Changes of beta-catenin were tested by heteroduplex method. Both germ cell tumors analyzed demonstrated LOH of the CDH1 gene. Analysis of exon 3 of the CTNNB1 gene showed additional band in the germinoma, suggesting that this sample harbors mutation in the beta-catenin gene. Immunostaining showed that LOHs in our samples were accompanied with the absence of E-cadherin protein. We also investigated E-cadherin expression in four other germinomas, of which three were negative and one was mildly positive. Our findings may contribute to better understanding of the genetic profile of germ cell tumors.

Meningiomas exhibit loss of heterozygosity of the APC gene

The molecular mechanisms and candidate genes involved in development of meningiomas still need investigation and elucidation. In the present study 33 meningiomas were analyzed regarding genetic changes of tumor suppressor gene Adenomatous polyposis coli (APC), a component of the wnt signaling. Gene instability was tested by polymerase chain reaction/loss of heterozygosity (LOH) using Restriction Fragment Length Polymorphism (RFLP) method. RFLP was performed by two genetic markers, Rsa I in APC's exon 11 and Msp I in its exon 15. The results of our analysis showed altogether 15 samples with LOH of the APC gene out of 32 heterozygous patients (47%). Seven patients had LOHs at both exons, while four LOHs were exclusive for exon 11 and four for exon 15. The changes were distributed according to pathohistological grade as follows: 46% of meningothelial meningioma showed LOH; 33% of fibrous; 75% of mixed (transitional); 75% of angiomatous, and one LOH was found in a single case of psammomatous meningioma. None of the LOHs were found in atypical and anaplastic cases. Immunostaining showed that samples with LOHs were accompanied with the absence of APC protein expression or presence of mutant APC proteins (chi(2 )= 13.81, df = 2, P < 0.001). We also showed that nuclear localization of beta-catenin correlates to APC genetic changes (chi(2 )= 21.96, df = 2, P < 0.0001). The results of this investigation suggest that genetic changes of APC gene play a role in meningioma formation.

Genetic changes of CDH1, APC, and CTNNB1 found in human brain tumors

This paper focuses on changes in E-cadherin (CDH1), adenomatous polyposis coli (APC), and beta-catenin (CTNNB1) in 50 tumors of the central nervous system. All gene products are components of adherens junctions, but are also involved in wnt signaling. The results of our analysis showed LOH of CDH1 gene in 31% of meningiomas examined (significant correlation; p=0.002). LOH was noted in a single case of germinoma, while other tumor types did not demonstrate any change in CDH1. Fourteen samples (29.2%) with changes in APC gene were observed. The changes were seen in 33.3% of glioblastomas and in 27% of meningiomas; LOH occurred in five informative astocytomas (20%) and in six informative neurinomas (17%). One oligoastrocytoma showed LOH at exon 11, and one medulloblastoma had allelic imbalance at both exons. Five samples (10%) showed heteroduplexes in exon 3 of beta-catenin. Potential mutations were confined to two meningiomas, one astrocytoma, one glioblastoma, and one germinoma. Our results suggest that genetic changes in wnt components are involved in brain tumor genesis. Changes in E-cadherin are involved in meningiomas, while changes in APC gene occur in different tumor types, with glioblastomas showing the highest percentage.

Mutations of the Wnt antagonist AXIN2 (Conductin) result in TCF-dependent transcription in medulloblastomas

Medulloblastomas (MBs) represent the most common malignant brain tumors in children. Most MBs develop sporadically in the cerebellum, but their incidence is highly elevated in patients with familial adenomatous polyposis coli. These patients carry germline mutations in the APC tumor suppressor gene. APC is part of a multiprotein complex involved in the Wnt signaling pathway that controls the stability of beta-catenin, the central effector in this cascade. Previous genetic studies in MBs have identified mutations in genes coding for beta-catenin and its partners, APC and AXIN1, which cause activation of Wnt signaling. The pathway is negatively controlled by the tumor suppressor AXIN2 (Conductin), a scaffold protein of this signaling complex. To investigate whether alterations in AXIN2 may also be involved in the pathogenesis of sporadic MBs, we performed a mutational screening of the AXIN2 gene in 116 MB biopsy samples and 11 MB cell lines using single-strand conformation polymorphism and sequencing analysis. One MB displayed a somatic, tumor-specific 2 bp insertion in exon 5, leading to carboxy-terminal truncation of the AXIN2 protein. This tumor biopsy showed nuclear accumulation of beta-catenin protein, indicating an activation of Wnt signaling. In 2 further MB biopsies, mutations were identified in exon 5 (Glu408Lys) and exon 8 (Ser738Phe) of the AXIN2 gene, which are due to predicted germline mutations and rare polymorphisms. mRNA expression analysis in 22 MBs revealed reduced expression of AXIN2 mRNA compared to 8 fetal cerebellar tissues. Promoter hypermethylation could be ruled out as a major cause for transcriptional silencing by bisulfite sequencing. To study the functional role of AXIN2 in MBs, wild-type AXIN2 was overexpressed in MB cell lines in which the Wnt signaling pathway was activated by Wnt-3a. In this assay, AXIN2 inhibited Wnt signaling demonstrated in luciferase reporter assays. In contrast, overexpression of mutated AXIN2 with a deleted C-terminal DIX-domain resulted in an activation of the Wnt signaling pathway. These findings indicate that mutations of AXIN2 can lead to an oncogenic activation of the Wnt pathway in MBs.

Intracellular distribution of beta-catenin in human medulloblastoma cell lines with different degree of neuronal differentiation

Gene mutations impairing the functions of the WNT signaling transduction pathway have been found in approximately 15% of human sporadic medulloblastomas. To understand the functional role of the WNT pathway in medulloblastoma, we have investigated the intracellular distribution of beta-catenin in a series of 17 human medulloblastomas to correlate such expression with neuronal differentiation and in cultured cell models following functional silencing of the APC gene by small-interference RNA (siRNA). Transient siRNA transfection resulted in a 50% reduction of the APC gene product levels in both DAOY and D283MED cell lines. In the former, less-differentiated cell line, beta-catenin levels remained unchanged or were slightly reduced, but beta-catenin translocated in the nucleus following APC gene siRNA silencing. In contrast, in the more differentiated D283MED cells, beta-catenin levels increased about twofold while mainly maintaining the cytoplasmic and cell membrane localization. Cytoplasmic/nuclear localization of beta-catenin was present in 12 of 17 cases of medulloblastoma with a prevalent distribution in the classic, 6/7 cases, and large cell/anaplastic variant, 4/4 cases. The nodular/desmoplastic lesions showed strongly positivity in the cell membrane mainly of intranodular cells with advanced neuronal differentiation. These observations support an important functional role of WNT/beta-catenin pathway in neuronal differentiation in medulloblastoma.

Dickkopf-1 is an epigenetically silenced candidate tumor suppressor gene in medulloblastoma

Medulloblastoma is a heterogeneous pediatric brain tumor with significant therapy-related morbidity, its five-year survival rates ranging from 30% to 70%. Improvement in diagnosis and therapy requires better understanding of medulloblastoma pathology. We used whole-genome microarray analysis to identify putative tumor suppressor genes silenced by epigenetic mechanisms in medulloblastoma. This analysis yielded 714 up-regulated genes in immortalized medulloblastoma cell line D283 on treatment with histone deacetylase (HDAC) inhibitor trichostatin A (TSA). Dickkopf-1 (DKK1), a Wnt antagonist, was found to be up-regulated on HDAC inhibition. We examined DKK1 expression in primary medulloblastoma cells and patient samples by reverse transcriptase PCR and found it to be significantly down-regulated relative to normal cerebellum. Transfection of a DKK1 gene construct into D283 cell lines suppressed medulloblastoma tumor growth in colony focus assays by 60% (P < 0.001). In addition, adenoviral vector-mediated expression of DKK1 in medulloblastoma cells increased apoptosis fourfold (P < 0.001). These data reveal that inappropriate histone modifications might deregulate DKK1 expression in medulloblastoma tumorigenesis and block its tumor-suppressive activity.

Stratification of medulloblastoma on the basis of histopathological grading

Medulloblastoma (WHO grade IV) is an embryonal tumour of the cerebellum and the most common malignant central nervous system tumour in children. Despite significant advances in treatment, 5-year survival rates are still less than 70%, suggesting the presence of subgroups with different response to radio/chemotherapy. In the present study, we re-evaluated a series of 347 medulloblastomas from the SIOP II clinical trial of the International Society of Paediatric Oncology to identify features predictive of clinical outcome. Relapse free survival for medulloblastomas with severe anaplasia [5-year rate: S(60)=49.5%], was significantly shorter than for tumours with moderate or mild anaplasia S(60)=65.4%; P=0.001). The difference between both groups was even larger when the presence or absence of extensive apoptosis was included (46.5 vs. 66.7%; P=0.0216). Other histological features including nodularity, necrosis, vascular proliferation and the presence of beta-catenin mutations (7% of cases) were not predictive for relapse free survival. These findings indicate that degree of anaplasia is the most significant histologic feature predictive of the survival of medulloblastoma patients.

The neurobiology of neurooncology

The histological classification of brain tumors currently is based on the morphological appearance and protein expression patterns that reflect specific cell types within the central nervous system. Recent studies have suggested that the cells of origin for brain tumors may persist in the fully formed tumors, and that these "cancer stem cells" might represent the relevant cellular targets for anticancer therapy. In this regard, insights into the developmental neurobiology of brain tumors has significant impact on our understanding of the molecular and cellular pathogenesis of these devastating cancers, as well as the development of new strategies for treating brain tumors.

Expression of Notch and Wnt pathway components and activation of Notch signaling in medulloblastomas from heterozygous patched mice

Hedgehog (Hh), Notch, and Wingless (Wnt) signaling control normal development of the cerebellum, and dysregulation of these signaling pathways are associated with medulloblastoma (MB). As an initial step in the study of the role of interacting signaling pathways in MB pathogenesis, we demonstrate the expression of several components of the Notch and Wnt signaling pathways, and activation of Notch signaling in MB from Ptch +/- mice that have elevated Hh signaling. We also show a marked downregulation in the expression of Notch2, Jagged1, Hes1, mSfrp1, and mFrz7 in cerebella of developing mice with reduced Hh signaling, suggesting that Hh signaling regulates the expression of these genes. Together with recent published data, these findings indicate that Hh signaling might synergize simultaneously with Notch and Wnt signaling in MB development by controlling Notch and Wnt pathway ligand, receptor and/or target gene expression.

Abnormal expression of REST/NRSF and Myc in neural stem/progenitor cells causes cerebellar tumors by blocking neuronal differentiation

Medulloblastoma, one of the most malignant brain tumors in children, is thought to arise from undifferentiated neural stem/progenitor cells (NSCs) present in the external granule layer of the cerebellum. However, the mechanism of tumorigenesis remains unknown for the majority of medulloblastomas. In this study, we found that many human medulloblastomas express significantly elevated levels of both myc oncogenes, regulators of neural progenitor proliferation, and REST/NRSF, a transcriptional repressor of neuronal differentiation genes. Previous studies have shown that neither c-Myc nor REST/NRSF alone could cause tumor formation. To determine whether c-Myc and REST/NRSF act together to cause medulloblastomas, we used a previously established cell line derived from external granule layer stem cells transduced with activated c-myc (NSC-M). These immortalized NSCs were able to differentiate into neurons in vitro. In contrast, when the cells were engineered to express a doxycycline-regulated REST/NRSF transgene (NSC-M-R), they no longer underwent terminal neuronal differentiation in vitro. When injected into intracranial locations in mice, the NSC-M cells did not form tumors either in the cerebellum or in the cerebral cortex. In contrast, the NSC-M-R cells did produce tumors in the cerebellum, the site of human medulloblastoma formation, but not when injected into the cerebral cortex. Furthermore, the NSC-M-R tumors were blocked from terminal neuronal differentiation. In addition, countering REST/NRSF function blocked the tumorigenic potential of NSC-M-R cells. To our knowledge, this is the first study in which abnormal expression of a sequence-specific DNA-binding transcriptional repressor has been shown to contribute directly to brain tumor formation. Our findings indicate that abnormal expression of REST/NRSF and Myc in NSCs causes cerebellum-specific tumors by blocking neuronal differentiation and thus maintaining the "stemness" of these cells. Furthermore, these results suggest that such a mechanism plays a role in the formation of human medulloblastoma.

Comprehensive genomic analysis of desmoplastic medulloblastomas: identification of novel amplified genes and separate evaluation of the different histological components

Desmoplastic medulloblastoma (DMB) is a malignant cerebellar tumour composed of two distinct tissue components, pale islands and desmoplastic areas. Previous studies revealed mutations in genes encoding members of the sonic hedgehog pathway, including PTCH, SMOH and SUFUH in DMBs. However, little is known about other genomic aberrations. We performed comparative genomic hybridization (CGH) analysis of 22 sporadic DMBs and identified chromosomal imbalances in 20 tumours (91%; mean, 4.9 imbalances/tumour). Recurrent chromosomal gains were found on chromosomes 3, 9 (six tumours each), 20, 22 (five tumours each), 2, 6, 7, 17 (four tumours each) and 1 (three tumours). Recurrent losses involved chromosomes X (eight tumours), Y (six of eleven tumours from male patients), 9, 12 (four tumours each), as well as 10, 13 and 17 (three tumours each). Four tumours demonstrated high-level amplifications involving sequences from 1p22, 5p15, 9p, 12p13, 13q33-q34 and 17q22-q24, respectively. Further analysis of the 9p and 17q22-q24 amplicons by array-based CGH (matrix-CGH) and candidate gene analyses revealed amplification of JMJD2C at 9p24 in one DMB and amplification of RPS6KB1, APPBP2, PPM1D and BCAS3 from 17q23 in three DMBs. Among the 17q23 genes, RPS6KB1 showed markedly elevated transcript levels as compared to normal cerebellum in five of six DMBs and four of five classic medulloblastomas investigated. Finally, CGH analysis of microdissected pale islands and desmoplastic areas showed common chromosomal imbalances in five of six informative tumours. In summary, we have identified several novel genetic alterations in DMBs and provide genetic evidence for a monoclonal origin of their different tissue components.

β-Catenin Status Predicts a Favorable Outcome in Childhood Medulloblastoma: The United Kingdom Children's Cancer Study Group Brain Tumour Committee

Purpose

Identifying pathobiological correlates of clinical behavior or therapeutic response currently represents a key challenge for medulloblastoma research. Nuclear accumulation of the β-catenin protein is associated with activation of the Wnt/Wg signaling pathway, and mutations affecting components of this pathway have been reported in approximately 15% of sporadic medulloblastomas. We tested the hypothesis that nuclear immunoreactivity for β-catenin is a prognostic marker in medulloblastoma, and assessed the relationship between nuclear β-catenin immunoreactivity and mutations of CTNNB1 and APC.

Patients and Methods

Medulloblastomas from children entered onto the International Society for Pediatric Oncology (SIOP)/United Kingdom Children's Cancer Study Group (UKCCSG) PNET3 trial (n = 109) were examined for β-catenin immunoreactivity, and where tissue was available, evidence of CTNNB1 and APC mutations. The results were correlated with clinicopathologic variables, principally outcome.

Results

Children with medulloblastomas that showed a nucleopositive β-catenin immunophenotype (27 of 109; 25%) had significantly better overall (OS) and event-free (EFS) survivals than children with tumors that showed either membranous/cytoplasmic β-catenin immunoreactivity or no immunoreactivity (P = .0015 and P = .0026, respectively). For β-catenin nucleopositive and nucleonegative medulloblastomas, 5-year OS was 92.3% (95% CI, 82% to 100%) versus 65.3% (95% CI, 54.8 to 75.7%), and 5-year EFS was 88.9% (95% CI, 77% to 100%) versus 59.5% (95% CI, 48.8 to 70.2%), respectively. Mutations in CTNNB1 were found exclusively among medulloblastomas that demonstrated nuclear β-catenin immunoreactivity, but no evidence of APC mutation was found in these cases. All children with β-catenin nucleopositive large cell/anaplastic medulloblastomas and β-catenin nucleopositive medulloblastomas presenting with metastatic disease are alive at least 5 years postdiagnosis.

Conclusion

Nuclear accumulation of β-catenin appears to be a marker of favorable outcome in medulloblastoma, and should be investigated further in large group-wide trials.

Molecular genetics of supratentorial primitive neuroectodermal tumors and pineoblastoma

The supratentorial primitive neuroectodermal tumors (PNETs) are a group of highly malignant lesions primarily affecting young children. Although these tumors are histologically indistinguishable from infratentorial medulloblastoma, they often respond poorly to medulloblastoma-specific therapy. Indeed, existing molecular genetic studies indicate that supratentorial PNETs have transcriptional and cytogenetic profiles that are different from those of medullo-blastomas, thus pointing to unique biological derivation for the supratentorial PNET. Due to the rarity of these tumors and disagreement about their histopathological diagnoses, very little is known about the molecular characteristics of the supratentorial PNET. Clearly, future concerted efforts to characterize the molecular features of these rare tumors will be necessary for development of more effective supratentorial PNET treatment protocols and appropriate disease models. In this article the authors review existing molecular genetic data derived from human and mouse studies, with the aim of providing some insight into the putative histogenesis of these rare tumors and the underlying transforming pathways that drive their development. Studies of the related but distinct pineoblastoma PNET are also reviewed.

Morphing into cancer: the role of developmental signaling pathways in brain tumor formation

Morphogens play a critical role in most aspects of development, including expansion and patterning of the central nervous system. Activating germline mutations in components of the Hedgehog and Wnt pathways have provided evidence for the important roles morphogens play in the genesis of brain tumors such as cerebellar medulloblastoma. In addition, aberrant expression of transforming growth factor-beta (TGF-beta) superfamily members has been demonstrated to contribute to progression of malignant gliomas. This review summarizes our current knowledge about the roles of morphogens in central nervous system tumorigenesis.

Two Sides of the Same Coin: Wnt Signaling in Neurodegeneration and Neuro-Oncology

Wnts function through the activation of at least three intracellular signal transduction pathways, of which the canonical β-catenin mediated pathway is the best understood. Aberrant canonical Wnt signaling has been involved in both neurodegeneration and cancer. An impairment of Wnt signals appears to be associated with aspects of neurodegenerative pathologies while overactivation of Wnt signaling is a common theme in several types of human tumors. Therefore, although therapeutic approaches aimed at modulating Wnt signaling in neurodegenerative and hyperproliferative diseases might impinge on the same molecular mechanisms, different pharmacological outcomes are required. Here we review recent developments on the understanding of the role of Wnt signaling in Alzheimer's disease and CNS tumors, and identify possible avenues for therapeutic intervention within a complex and multi-faceted signaling pathway.

Correlation of gamma-catenin expression with good prognosis in medulloblastomas

OBJECT

Medulloblastoma is a malignant cerebellar tumor of childhood and is difficult to cure due to frequent cerebrospinal fluid dissemination. Amplification of the c-myc gene (4%) and messenger (mRNA) overexpression (50%) are known to be adverse prognostic indicators. Because mRNA overexpression cannot be explained by gene amplification alone, mechanisms other than gene amplification are postulated. Molecules on the Wnt signal pathway in primary tumors were examined.

METHODS

Immunohistochemical and cytogenetic examinations of beta- and gamma-catenin, c-myc, N-myc, and cyclin D1 in 24 primary medulloblastomas were conducted, and their clinical relevance was evaluated. Cytoplasmic/membranous staining of beta- and gamma-catenin was detected in 19 (79%) and nine (37%) cases, respectively, and nuclear expression of cyclin D1 and c-myc was detected in six (25%) and 21 (83%) cases, respectively. The expression levels of gamma-catenin in Western blot analysis and immunohistochemistry were similar. By differential polymerase chain reaction, c-myc and N-myc were amplified separately in two large cell/anaplastic medulloblastomas. No cyclin D1 amplification, or beta- or gamma-catenin mutations were found. Kaplan-Meier analysis revealed no dissemination at diagnosis (Chang Grade M0) and gamma-catenin expression was correlated with good prognosis (p = 0.0002 and 0.003, respectively). Expression of gamma-catenin was also significant in the M0 group (p = 0.022). Expression of cyclin D1 showed a trend toward adverse outcome (p = 0.057) and all patients in whom cyclin D1 expression was found died of disease.

CONCLUSIONS

Expression of gamma-catenin is of great prognostic value and its immunohistochemistry may be useful for further stratification of treatment. Cyclin D expression may have the potential to be an adverse prognostic indicator.

Subtype-specific expression and genetic alterations of the chemokinereceptor gene CXCR4 in medulloblastomas

Recent findings indicate that the chemokine receptor Cxcr4 is essential for normal development of the cerebellar cortex. As medulloblastomas (MBs), the most common malignant brain tumors of childhood, are believed to arise from neuronal cerebellar precursors, we asked whether there is a potential role for Cxcr4 in the pathogenesis of MB. RT-PCR and immunohistochemistry revealed expression of Cxcr4 in different variants of MBs. Whereas 18/20 classic MBs showed very low levels of CXCR4 mRNA, high amounts were expressed in 17/18 desmoplastic and 6/7 extensively nodular MBs. In addition, a significant correlation of high CXCR4 mRNA levels and presence of the neurotrophin receptor p75NTR or expression of ATOH1 and GLI1 suggests that CXCR4 is a reliable marker for tumors derived from the cerebellar external granular layer. Because Cxcr4 is important for migration and cell cycle control of granular precursors, we screened for mutations in the coding region by SSCP and gene sequencing. In a series of 90 MBs and 8 MB cell lines, we found one germline and one somatic mutation resulting in amino acid substitutions in the first (Ile53Leu) and second (Asp97Asn) transmembrane regions, respectively. These data suggest that Cxcr4 may be involved in the pathogenesis of MBs.

Identification of a novel c-Myc protein interactor, JPO2, with transforming activity in medulloblastoma cells

c-myc oncogene activation is critical in the pathogenesis of a spectrum of human malignancies. The c-Myc NH2-terminal domain (MycNTD) is essential for cellular transformation, and mediates critical protein interactions that modulate c-Myc oncogenic properties. In medulloblastoma, the most common malignant pediatric brain tumor, deregulated c-myc expression is linked with poorer disease phenotypes and outcomes. The biological basis for these associations is, however, not well understood. To better understand mechanisms underlying Myc-mediated transformation of medulloblastoma, we sought to identify novel MycNTD protein interactors from a medulloblastoma cell line library using a unique two-hybrid system. We identified a novel MycNTD binding protein, JPO2, which shows nuclear colocalization with c-Myc, and interacts with c-Myc both in vitro and in mammalian cells. In Rat1a transformation assays, JPO2 potentiates c-Myc transforming activity, and can complement a transformation-defective Myc mutant. Immunohistochemical studies indicate tumor-specific JPO2 expression in human medulloblastoma, and an association of JPO2 expression with metastatic tumors. Significantly, JPO2 expression induces colony formation in UW228, a medulloblastoma cell line, whereas RNAi-mediated JPO2 knockdown impairs colony formation in UW228, and in Myc-transformed UW228 cells. These data provide evidence for biochemical and functional interaction between c-Myc and JPO2 in medulloblastoma transformation. JPO2 is closely related to JPO1, a Myc transcriptional target with transforming activity. As tumor-specific JPO1 expression in human and murine medulloblastoma has also been reported; these collective observations suggest important functional links between the novel JPO protein family and c-Myc in medulloblastoma transformation.

Survivin is a negative prognostic marker in medulloblastoma

Survivin is a member of the inhibitor of apoptosis protein family, which is over-expressed in many human cancers. Our aim was to analyse survivin expression in medulloblastoma, its association with aberrant activation of the WNT (wingless) pathway and to test the prognostic significance of survivin expression. We immuno histochemically analysed survivin expression and localization of beta-catenin, a downstream mediator of the WNT pathway, in 56 cases of medulloblastoma. Survivin was detected in the nuclei of tumour cells in all cases, but the proportion of positive nuclei varied from 0.5 to 31.3%. Survivin expression tended to be higher in medulloblastomas with an aberrant activation of the WNT pathway (nuclear localization of beta-catenin), but did not correlate with histological type, age group or dissemination via cerebrospinal fluid pathways. Survivin expression and dissemination status were two independent negative prognostic variables for the overall survival of patients with medulloblastoma. In conclusion, survivin is up-regulated in medulloblastomas. It is a negative prognostic marker and a potential therapeutic target.

Recent advances in embryonal tumours of the central nervous system

INTRODUCTION

Embryonal tumours of the central nervous system (CNS) are the commonest malignant paediatric brain tumours. This group includes medulloblastomas, supratentorial primitive neuroectodermal tumours, atypical teratoid/rhabdoid tumours, ependymoblastomas, and medulloepitheliomas. Earlier, all these tumours were grouped under a broad category of primitive neuroectodermal tumours (PNETs). However, the current WHO classification (2000) separates them into individual types based on significant progress in the understanding of their distinctive clinical, pathological, molecular genetic, histogenetic, and behavioural characteristics. Furthermore, advances in histopathology and molecular genetics have shown great promise for refining risk assessment in these tumours, especially medulloblastomas, thus providing a more accurate basis for tailoring therapies to individual patients. Correlation of histological changes with genetic events has also led to a new model of medulloblastoma tumorigenesis.

REVIEW

This review presents an updated comparative profile of these tumours, highlighting the clinical and biological relevance of the recent advances.

Wnt signalling and the mechanistic basis of tumour development

Abnormalities in the Wnt signalling pathway are found in a wide range of cancers. The diverse origin of these malignancies implies that the contribution that disrupted Wnt signalling makes to tumourigenesis is not limited to specific tissue types and thus can be regarded as a step which is 'generic' to the process of carcinogenesis. In recent years, rapid progress has been made in the understanding of the Wnt signalling pathway, giving an insight into how inappropriate activation of this pathway may facilitate the neoplastic conversion of a normal cell. Furthermore, elucidation of the mechanisms that regulate Wnt signalling has led to the possibility of manipulating these mechanisms in order to down-regulate Wnt signalling in established tumours. In this review, the Wnt signalling pathway is described. The role of aberrant Wnt signalling in tumour development is discussed together with its clinical implications for anti-tumour therapy.

No evidence for mutations or altered expression of the Suppressor of Fused gene (SUFU) in primitive neuroectodermal tumours

The sonic hedgehog (Shh) and the Wnt signalling pathways are involved in the development of medulloblastomas (MBs), the most frequent malignant brain tumours in children. Components of these two developmental and cancer-associated pathways, including (Patched) PTCH, SMOH, adenomatous polyposis coli (APC), beta-catenin and AXIN1 show somatic mutations in sporadic MBs. In this study we analysed SUFU (human Suppressor of Fused), which acts as a negative regulator of both the Shh and Wnt signalling pathways and therefore represents a putative tumour suppressor gene, to find out if it is also involved in the pathogenesis of sporadic MBs. We screened 145 primitive neuroectodermal tumours (PNETs) including 90 classic MBs, 42 of the desmoplastic variant and two medullomyoblastomas as well as 11 MB cell lines for mutations using single-strand conformational polymorphism (SSCP) and sequencing analysis. 18% of the MBs exhibited allelic losses on chromosome 10q. In contrast to a previous report, in which truncating mutations of SUFU have been identified in 9% of MBs, we were not able to identify somatic mutations of SUFU in our large tumour panel. We uncovered single nucleotide polymorphisms (SNPs) in exon 4, 8, 11 and in intron 2 in the SUFU gene. Expression analysis by competitive reverse transcription-polymerase chain reaction (RT-PCR) revealed no difference in SUFU mRNA levels of both MB subtypes and normal foetal or adult cerebellar tissues. Our results indicate that genetic alterations of the SUFU gene, do not contribute significantly to the molecular pathogenesis of MBs.

Molecular pathogenesis of childhood brain tumors

In the last decade, the molecular biology revolution has advanced considerably. These advances have enhanced our understanding of the genetic underpinnings of human brain tumors in general, and pediatric brain tumors in particular. We now know that many pediatric brain tumors arise from disturbances in developmentally regulated signaling pathways. The medulloblastoma, a tumor in which the developmental Hedgehog and WNT pathways have gone awry, is a prime example of this. New techniques in genetic engineering have allowed for the creation of sophisticated mouse models of brain tumors that recapitulate the human disease. Many laboratories are now using cDNA microarrays to study the expression level of thousands of genes that may be aberrantly expressed in brain tumors when compared to normal control cells. In the next decade, the use of several new molecular techniques to establish brain tumor diagnoses will likely become standard tools in the diagnostics and treatment stratification of children with central nervous system tumors.

Failure of a medulloblastoma-derived mutant of SUFU to suppress WNT signaling

Germline mutations of APC in patients with Turcot syndrome (colon cancer and medulloblastoma), was well as somatic mutations of APC, beta-catenin, and Axin in sporadic medulloblastomas (MBs) have shown the importance of WNT signaling in the pathogenesis of MB. A subset of children with MB have germline mutations of SUFU, a known inhibitor of Hedgehog signal transduction. A recent report suggested that murine Sufu can bind beta-catenin, export it from the nucleus, and thereby repress beta-catenin/T-cell factor (Tcf)-mediated transcription. We show that an MB-derived mutant of SUFU has lost the ability to decrease nuclear levels of beta-catenin, and cannot inhibit beta-catenin/Tcf-mediated transcription as compared to wild type SUFU. Our results suggest that loss of function of SUFU results in overactivity of both the Sonic Hedgehog, and the WNT signaling pathways, leading to excessive proliferation and failure to differentiate resulting in MB.

Medulloblastoma: signalling a change in treatment

Medulloblastoma is the most common malignant brain tumour that occurs during childhood. Multimodality treatment regimens have substantially improved survival in this disease; however, the tumour is incurable in about a third of patients with medulloblastoma, and current treatment has a detrimental effect on long-term survivors. Drugs that target cell-signalling pathways provide an alternative to conventional cytotoxic approaches to treatment of cancer. Several pathways have been implicated in medulloblastoma formation, and knowledge of these is now being used to develop new ways of treating children with medulloblastoma.

In vivo evidence in the brain for lithium inhibition of glycogen synthase kinase-3

There is considerable interest in the possibility that small-molecule glycogen synthase kinase-3 inhibitors may have utility in the treatment of bipolar disorder, since glycogen synthase kinase-3 is a target of lithium. Although the in vitro inhibition of glycogen synthase kinase-3 by lithium occurs with a K(i) of 1-2 mM, the degree of inhibition of this enzyme in the mammalian brain at therapeutically relevant concentrations has not fully been established. The transcription factor beta-catenin is an established marker of glycogen synthase kinase-3 inactivation because cytoplasmic levels are increased by inhibition of the enzyme. In this study, we measured beta-catenin protein levels after treatment with therapeutically relevant doses of lithium, valproate, and carbamazepine. Western blot revealed that 9 days of treatment with lithium and valproate, but not carbamazepine, increased beta-catenin protein levels in soluble fractions from the frontal cortex. The level of beta-catenin in the particulate fraction, which is not directly regulated by glycogen synthase kinase-3, did not change with any of the three drugs. Furthermore, real-time PCR revealed that lithium significantly decreased beta-catenin mRNA levels, which may represent compensation for an increase in beta-catenin stability. These results strongly suggest that lithium significantly inhibits brain glycogen synthase kinase-3 in vivo at concentrations relevant for the treatment of bipolar disorder.

Molecular biology of medulloblastoma therapy

Molecular biological studies have created a new understanding of medulloblastomas, revealing key cell signaling pathways that promote tumor growth. These studies have identified molecular markers that can serve as prognostic indicators and which will provide therapeutic targets in the very near future. In contrast to conventional histological techniques, molecular biological methods are designed to detect highly unstable molecules degraded by conventional tissue collection and fixation protocols. Consequently, a new approach to tissue collection is required for molecular analysis as we enter the next era of brain tumor therapy.

Detection of point mutations of the Axin1 gene in colorectal cancers

Axin is a recently identified tumor suppressor that plays an important role in liver and colon cancers. To gain further insights into the structure and function of Axin in controlling cell growth, we analyzed 54 colorectal cancer tissues for mutations in AXIN1 gene. We employed PCR amplification with 23 sets of primers against introns that encompassed the whole coding region of AXIN1 followed by single-strand conformation polymorphism (SSCP) analysis. After subcloning and sequencing analysis of the reamplified DNA from the aberrant bands, we found, in addition to 3 silent mutations, 6 missense point mutations in different functionally important regions. The missense mutation rate is hence 11%, suggesting that Axin deficiency may contribute to the onset of colorectal tumorigenesis.