Medulloblastomas and related primitive neuroectodermal brain tumors of childhood recapitulate molecular milestones in the maturation of neuroblasts

The interplay between TGF-β-stimulated TSC22 domain family proteins regulates cell-cycle dynamics in medulloblastoma cells

Proteins belonging to the TGFβ-stimulated clone 22 domain (TSC22D) family display a repertoire of activities, regulating cell proliferation and differentiation. The tumor suppressor activity of the first identified member of the family, TSC22D1 (formerly named TSC-22), has been extensively studied, but afterward a longer isoform encoded by the same gene turned out to play an opposite role. We have previously characterized the role of TSC22D1 and TSC22D4 in cell differentiation using granule neurons (GNs) isolated from the mouse cerebellum. However, the possibility to study the role of these factors in cell proliferation was limited by the fact that GNs readily exit from the cell-cycle and differentiate upon isolation and in vitro culture. To overcome this limitation, we have now exploited DAOY medulloblastoma cells, which are ontogenetically similar to cerebellar GNs and can be efficiently transfected with interfering RNA for gene knockdown purposes. Our findings indicate that TSC22D4-TSC22D1 short isoform heterodimers are involved in the escape from cell proliferation and exit from the cell-cycle, whereas, the TSC22D1 long isoform is required for cell proliferation, acting independently from TSC22D4. We also show that the silencing of specific expression of TSC22D4 or TSC22D1 isoforms affects the cell-cycle progression. These findings add a novel insight on the function of TSC22D proteins, with particular reference to the tumor suppressor activity of the TSC22D1 short isoform, which is re-framed within the context of a functional interplay with TSC22D4 and the mutually exclusive expression with the TSC22D1 long isoform.

A medulloblastoma showing an unusually long doubling time: reflection of its singular nature

CASE DESCRIPTION

In this paper, we present a case of a 4-year-old male diagnosed with a desmoplastic, SHH-type medulloblastoma. Retrospectively, we discovered that the patient underwent an MRI scan at 21 months for reasons unrelated, revealing a T1-enhanced lesion at the vermis, later recognized as the source of the tumor. This unique case provides us with a glimpse into the natural history of this tumor. Our ability to measure tumor volume at two defined time points, 31 months apart, enabled us to deduce the tumor's doubling time. This is defined as the time of one cell cycle divided by the amount of cycling cells, multiplied by cell loss factor. Potential doubling time (Tpot) and actual doubling time (Td), calculated using the Gompertzian model, are the most clinically relevant with regard to a tumor's response to radiotherapy. Here, we show an actual doubling-time (Td) of 78 days, and an extrapolated tumor diameter at the time of birth of 0.25 mm.

CLINICAL RELEVANCE

These results both support the medulloblastoma's embryonic origin, and indicating a threefold longer actual doubling time when compared to previous studies. Taking into account the reported range of medulloblastoma potential doubling time, we deduced a cell loss factor of between 48.9 and 95.5 %. These percentages fall in line with other malignant tumors. Although limited due to the obvious reliance on only two points in time and using the Gompertzian model to complete the remainder, to the best of our knowledge, this is the longest follow-up period reported for medulloblastoma. We have described how a unique turn of events enabled us to get a glimpse into the in situ development of a medulloblastoma over a 31-month period. Regarded sometimes as an idiosyncratic tumor comprised of an array of molecular changes, the complexity of medulloblastoma is displayed here, by revealing for the first time an actual doubling time three- to fourfold the previously known length.

Combining anatomic and molecularly targeted imaging in the diagnosis and surveillance of embryonal tumors of the nervous and endocrine systems in children

Combining anatomical and functional imaging can improve sensitivity and accuracy of tumor diagnosis and surveillance of pediatric malignancies. MRI is the state-of-the-art modality for demonstrating the anatomical location of brain tumors with contrast enhancement adding additional information regarding whether the tumor is neuronal or glial. Addition of SPECT imaging using a peptide that targets the somatostatin receptor (Octreoscan) can now differentiate medulloblastoma from a cerebellar pilocytic astrocytoma. Combined MRI and Octreoscan is now the most sensitive and accurate imaging modality for differentiating recurrent medulloblastoma from scar tissue. CT is the most common imaging modality for demonstrating the anatomical location of tumors in the chest and abdomen. Addition of SPECT imaging with either MIBG or Octreoscan has been shown to add important diagnostic information on the nature of tumors in chest and abdomen and is often more sensitive than CT for identification of metastatic lesions in bone or liver. Combined anatomical and functional imaging is particularly helpful in neuroblastoma and in neuroendocrine tumors such as gastrinoma and carcinoid. Functional imaging with MIBG and Octreoscan is predictive of response to molecularly targeted therapy with 131I-MIBG and 90Y-DOTA-tyr3-Octreotide. Dosimetry using combined anatomical and functional imaging is being developed for patient-specific dosing of targeted radiotherapy and as an extremely sensitive monitor of response to therapy. Both MIBG and Octreotide are now being adapted to PET imaging which will greatly improve the utility of PET in medulloblastoma as well as increase the sensitivity for detection of metastatic lesions in neuroblastoma and neuroendocrine tumors.

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.

Medulloblastoma: molecular genetics and animal models

Medulloblastoma is a primary brain tumor found in the cerebellum of children. The tumor occurs in association with two inherited cancer syndromes: Turcot syndrome and Gorlin syndrome. Insights into the molecular biology of the tumor have come from looking at alterations in the genes altered in these syndromes, PTC and APC, respectively. Murine models of medulloblastoma have been constructed based on these alterations. Additional murine models that, while mimicking the appearance of the human tumor, seem unrelated to the human tumor's molecular alterations have been made. In this review, the clinical picture, origin, molecular biology, and murine models of medulloblastoma are discussed. Although a great deal has been discovered about this tumor, the genetic alterations responsible for tumor development in a majority of patients have yet to be described.

Taurine Detection by Proton Magnetic Resonance Spectroscopy in Medulloblastoma: Contribution to Noninvasive Differential Diagnosis with Cerebellar Astrocytoma

OBJECTIVE:

We sought to evaluate whether taurine detection in short-echo (20 ms) proton magnetic resonance spectroscopy contributes to the noninvasive differential diagnosis between medulloblastoma and cerebellar astrocytoma in children and young adults. These two types of tumor have very different prognoses and may be difficult to differentiate by neuroradiological or clinical means.

METHODS:

Single-voxel proton magnetic resonance spectra of tumors were acquired at 1.5 T in 14 patients with biopsy-proven primary cerebellar tumors (six medulloblastomas, seven astrocytomas, and one mixed astroependymoma) using short-echo time (20 ms) and long-echo time (135 ms). For taurine assignment, qualitative analysis was performed on short-echo time spectra and results were compared in vitro with spectra of model solutions. Perchloric acid extracts of postsurgical tumor biopsies were performed in two medulloblastoma cases.

RESULTS:

Taurine detection was demonstrated in all patients with medulloblastoma and in none of those with astrocytoma. We were unable to ascertain any relationship between taurine and metastatic spread within the medulloblastoma group.

CONCLUSION:

Medulloblastomas characteristically seem to show taurine detectable in vivo by short-echo proton magnetic resonance spectroscopy, which may help to discriminate medulloblastoma from cerebellar astrocytoma.

Effects of basic fibroblastic growth factor on the growth of human medulloblastoma xenografts

The purpose of this study was to evaluate the effect of basic fibroblastic growth factor (bFGF) on the growth of human UM-MB1 medulloblastoma xenografts injected intracranially in nude mice. Under general anesthesia, a homogenous suspension of UM-MB1 cells (10(5)/10 microl) were injected in the caudoputamen nuclei of the right cerebral hemisphere using a stereotaxic apparatus. The treatment group (n = 9) received 10 microl of a bFGF solution (20 microg/ml) at 3 and 6 days following the inoculation of the cells at the injection site using the same stereotaxic coordinates. The control group (n = 9) were injected intracranially with a phosphate-buffered saline vehicle using a similar protocol. Mice were sacrificed 3 weeks following the xenograft surgery and the brains were prepared for histological observations as well as tumor volume evaluations. The mean volume of bFGF-treated tumors (mean volume +/- SD = 50.0 +/- 32.9 +/- mm3) was significantly smaller than for the non-treated xenografts (mean volume +/- SD = 199.0 +/- 42.1 mm3) (t-test, p < 0.001). Compared to non-treated tumor cells, bFGF-treated medulloblastoma cells had a greater cytoplasm volume and their nuclei contained more euchromatin suggesting that bFGF may initiate differentiation. In conclusion, our results suggest that bFGF may offer a new chemotherapeutic modality for the treatment of medulloblastoma.

Expression of the splicing regulator polypyrimidine tract-binding protein in normal and neoplastic brain

Polypyrimidine tract-binding protein (PTB) is a nuclear factor that binds to the polypyrimidine tract of pre-mRNA introns, where it is associated with negative regulation of RNA splicing and with exon silencing. We have previously demonstrated that PTB expression is increased during glial cell transformation and that this increase correlates brain and in glial and neuronal tumors. Paraffin sections were stained by using a primary monoclonal antibody against PTB. Tissues that were analyzed included normal with changes in the RNA splicing of the fibroblast growth factor receptor 1. In this paper we examine the specific cellular distribution of PTB expression in normal brain (n = 2) and tumors of various types (low-grade astrocytoma, n = 2; anaplastic astrocytoma, n = 2; glioblastoma, n = 4; medulloblastoma, n = 4; central neurocytoma, n = 2; dysplastic gangliocytoma, n = 1; ganglioglioma, n = 1; paraganglioma, n = 1). In glial cell populations the majority of astrocytes and oligodendrocytes were negative, but occasional positively staining cells were observed. Strongly positive PTB staining was observed in ependymocytes, choroid plexus epithelium, microglia, arachnoid membrane, and adenohypophysis, and weak staining was found in the neurohypophysis. In all cases vascular endothelium and smooth muscle stained strongly. In tumor samples, intense positive nuclear staining was observed in transformed cells of low-grade astrocytoma, anaplastic astrocytoma, glioblastoma multiforme, medulloblastoma, paraganglioma, and the glial population of both ganglioglioma and dysplastic gangliocytoma (the neuronal cells of both were negative). In medulloblastoma, neoplastic neuronal cells were positive, as were other cell lineages. In normal brain, all neuron populations and pineocytes were negative for PTB. We conclude that although glial cells show derepression of PTB expression, a similar mechanism is absent in both nonneoplastic neurons and in most neuronally derived tumor cells. Strong upregulation of PTB expression in tumor cells of glial or primitive neuroectodermal origin suggests involvement of this protein in cellular transformation. Whether PTB affects splicing of RNAs critical to cellular transformation or proliferation is an important question for future research.

The Wnt signaling pathway in solid childhood tumors

The Wnt signaling pathway has long been known to direct growth and patterning during embryonic development. Recent evidence also implicates this pathway in the development of childhood tumors of the liver, the kidney, the brain, and the pancreas. Here, we review the current evidence on how constitutive activation of the Wnt signaling pathway may occur in hepato-, nephro-, medullo- and pancreatoblastomas. With particular emphasis the mutational activation of CTNNB1, an emerging major oncogene in solid childhood tumors, is discussed.

Platelet-derived growth factor-B and -C and active alpha-receptors in medulloblastoma cells

The malignant childhood brain tumor medulloblastoma belongs to the group of primitive neuroectodermal tumours (PNETs). Medulloblastomas are thought to arise from remnants of the transient external germinal layer in the cerebellum. Proliferation, differentiation, and motility of cells in the central nervous system are regulated by growth factors, e.g., platelet-derived growth factor (PDGF). Recently, it was shown that higher level of PDGF alpha-receptor expression is characteristic of metastatic medulloblastomas. We have investigated five medulloblastoma/PNET cell lines and found that the PDGF alpha-receptor is actively signalling in most of them, an activity most likely driven by endogenously produced PDGF-C. PDGF-C is normally present in cells of the developing external germinal layer and our results are consistent with the idea that medulloblastomas are derived from such cells undergoing early neuronal differentiation. Moreover, the expression of PDGF and its receptors was associated with neuronal characteristics, but not with high levels of c-myc expression in the medullablastoma cells.

REST-VP16 activates multiple neuronal differentiation genes in human NT2 cells

The RE1-silencing transcription factor (REST)/neuron-restrictive silencer factor (NRSF) can repress transcription of a battery of neuronal differentiation genes in non-neuronal cells by binding to a specific consensus DNA sequence present in their regulatory regions. However, REST/NRSF(-/-) mice suggest that the absence of REST/NRSF-dependent repression alone is not sufficient for the expression of these neuronal differentiation genes and that the presence of other promoter/enhancer-specific activators is required. Here we describe the construction of a recombinant transcription factor, REST-VP16, by replacing repressor domains of REST/NRSF with the activation domain of a viral activator VP16. In transient transfection experiments, REST-VP16 was found to operate through RE1 binding site/neuron-restrictive enhancer element (RE1/NRSE), activate plasmid-encoded neuronal promoters in various mammalian cell types and activate cellular REST/NRSF target genes, even in the absence of factors that are otherwise required to activate such genes. Efficient expression of REST-VP16 through adenoviral vectors in NT2 cells, which resemble human committed neuronal progenitor cells, was found to cause activation of multiple neuronal genes that are characteristic markers for neuronal differentiation. Thus, REST-VP16 could be used as a unique tool to study neuronal differentiation pathways and neuronal diseases that arise due to the deregulation of this process.

Voltage- and gamma-aminobutyric acid-activated membrane currents in the human medulloblastoma cell line MHH-MED-3

The whole-cell patch clamp technique was used to characterize voltage- and neurotransmitter-activated currents in the medulloblastoma cell line MHH-MED-3 and cells from tissue slices and primary cultures of two medulloblastoma biopsies. These preparations revealed similar electrophysiological properties. All tested cells displayed 4-aminopyridine-sensitive delayed rectifying K(+) currents, gamma-aminobutyric acid(A) receptor-mediated Cl(-) currents and most of them inward rectifier K(+) currents. Transient inward currents were mainly carried by low-voltage activated T-type Ca(2+) channels in MHH-MED-3 cells, and tetrodotoxin-sensitive Na(+) channels in cells from the primary culture. From these characteristics we conclude that medulloblastoma cells share physiological features with developing cerebellar granule cells at an immature stage.

Expression of the neurotrophin receptor p75NTR in medulloblastomas is correlated with distinct histological and clinical features: evidence for a medulloblastoma subtype derived from the external granule cell layer

Medulloblastomas (MBs) are primitive neuroectodermal tumors (PNET) of the cerebellum. They represent the most frequent malignant pediatric brain tumors, but their origin still remains unresolved and controversial. MB cells correspond to different stages of neural development and differentiation as illustrated by their expression of neuronal and glial markers. In the present study, we examined the expression pattern of the common low-affinity neurotrophin receptor p75NTR in a series of 167 MBs by immunohistochemistry. While p75NTR was present in only 17% of classic MBs (CMB), we found expression of p75NTR in all desmoplastic (nodular) MBs (DMB) examined, and in 71% of those MBs with a significant desmoplastic component. Furthermore, both desmoplastic histology and p75NTR expression were present preferentially in those tumors of adolescents and adults that are frequently located laterally in the cerebellar hemispheres. In DMBs, p75NTR was expressed predominantly in the proliferative, reticulin-rich areas, which may show coexpression of GFAP. In the pale islands of DMB, p75NTR was expressed only weakly or was absent. The expression pattern showed an inverse relation to that of the synaptic vesicle protein synaptophysin that was predominant in p75NTR negative classic MBs. Since the neurotrophin receptor p75NTR is expressed in cells of the external granule cell layer (EGL) of the fetal cerebellum, our findings suggest that progenitor cells of the EGL are the cellular origin of a distinct subset of MB, namely the desmoplastic variant and MBs with a significant desmoplastic component.

Neurotrophins and Trk receptors in primitive neuroectodermal tumor cell lines

OBJECTIVE

Primitive neuroectodermal tumors (PNETs) are thought to be derived from early central nervous system precursors. Therefore, we hypothesized that the neurotrophins (nerve growth factor, brain-derived neurotrophic factor, and neurotrophin-3) and their receptors (TrkA, TrkB, and TrkC), which are involved in the proliferation, differentiation, and survival of neuronal cells, might be important in regulating tumor growth.

METHODS

Using ribonucleic acid (RNA) blotting and reverse transcription-polymerase chain reaction analysis, we investigated the expression of these ligands and their receptors in six PNET cell lines (Daoy, PFSK, D283 Med, UW288-1, CHP707m, and D341 Med). Neurotrophin protein levels were measured using enzyme-linked immunosorbent assay procedures. Receptor function was demonstrated by autophosphorylation. Induction of c-Fos expression and effects on cell proliferation were assessed after the addition of exogenous neurotrophin.

RESULTS

Three cell lines expressed messenger RNA for all neurotrophins, whereas the other three expressed two of the three neurotrophins. Neurotrophin protein levels were low. All cell lines expressed trkA messenger RNA. Five expressed the amino terminus of trkB, but three of these did not express the carboxyl terminus. All cell lines contained trkC messenger RNA, but the receptor was truncated in two cell lines. No cell line contained message for a receptor containing an insertion in the tyrosine kinase domain. The addition of neurotrophin to PNET cells resulted in phosphorylation of a protein that was immunoprecipitated with an anti-pan-Trk antibody. c-Fos expression and cell growth were increased by preincubation with neurotrophins, but only in the cell lines expressing the relevant full-length receptors.

CONCLUSION

The expression of neurotrophins and neurotrophin receptors by PNET cell lines is variable. The presence of activated Trk receptors in these cell lines may be required for rapid growth, via an autocrine loop mechanism. This will require further investigation.

Sonic hedgehog regulates the growth and patterning of the cerebellum

The molecular bases of brain development and CNS malignancies remain poorly understood. Here we show that Sonic hedgehog (Shh) signaling controls the development of the cerebellum at multiple levels. SHH is produced by Purkinje neurons, it is required for the proliferation of granule neuron precursors and it induces the differentiation of Bergmann glia. Blocking SHH function in vivo results in deficient granule neuron and Bergmann glia differentiation as well as in abnormal Purkinje neuron development. Thus, our findings provide a molecular model for the growth and patterning of the cerebellum by SHH through the coordination of the development of cortical cerebellar cell types. In addition, they provide a cellular context for medulloblastomas, childhood cancers of the cerebellum.

Molecular heterogeneity in medulloblastoma with implications for differing tumor biology

Medulloblastomas and related primitive neuroectodermal tumors are the second most common malignant tumors of childhood. In spite of improvements in cancer therapy, these tumors are still associated with significant morbidity and mortality. Although these tumors share similar histologic features, recent molecular studies suggest that they could represent a genetically mixed group of tumors. The genetic events that might play a role in the biology of these tumors also could allow a molecular subtyping of medulloblastomas. Such molecular subtyping of medulloblastomas could allow for the use of newer therapeutic techniques, such as gene therapy, for selective targeting of critical genetic events in subsets of medulloblastomas. It is becoming increasingly clear that in medulloblastomas, the morphologic similarity of "small blue" cells does not imply similar or shared molecular characteristics, with implications for differing tumor biology.

High expression of somatostatin receptor subtype 2 (sst2) in medulloblastoma: implications for diagnosis and therapy

Medulloblastoma is a pediatric malignancy, which arises in cerebellum. The neuropeptide somatostatin (SS-14) is a neuromodulator and growth regulator in the developing cerebellum. SS-14 has previously been demonstrated in medulloblastomas with immunohistochemical techniques, but somatostatin receptor (sst) expression is less well understood. We analyzed somatostatin and sst subtype expression (sst1-5) in central primitive neuroectodermal tumors (cPNET), including 23 medulloblastomas, 6 supratentorial PNET, and 10 cPNET cell lines. The expression of SS-14 and sst genes in cPNET was compared with expression of these genes in 17 tumors of the Ewing's sarcoma family of tumors using reverse transcriptase-PCR, Southern hybridization, quantitative in vitro receptor autoradiography, and competitive membrane binding assays. The sst1 subtype was expressed in similar frequency in cPNET (83%) and Ewing's sarcoma family of tumors (71%). Nine of the 10 cell lines and 76% of the cPNET expressed mRNA for sst2 compared with 35% of the Ewing's sarcoma family of tumors. High-affinity binding of SS-14 was demonstrated in cPNET by quantitative autoradiography as well as by competitive binding assays. The cPNET cell line D283 Med bound SS-14 and octreotide with high affinity; SS-14 inhibited proliferation of D283 Med cells as measured by a decrease in [3H]thymidine uptake. We conclude that both sst1 and sst2 are highly expressed in cPNET and suggest that somatostatin may regulate proliferation and differentiation in these developmental tumors.

Bone morphogenetic proteins-2 and -4 attenuate apoptosis in a cerebellar primitive neuroectodermal tumor cell line

Similarities between primitive neuroectodermal tumors and central nervous system (CNS) progenitor cells have evoked interest in the response of these tumors to endogenous growth factors. The bone morphogenetic proteins (BMPs) have recently been found to regulate survival and differentiation of CNS progenitor cell populations. In this study, we investigated the effects of BMP-2, BMP-4, and BMP-6 on the undifferentiated cerebellar primitive neuroectodermal tumor or medulloblastoma cell line DAOY. Analysis by reverse transcriptase-polymerase chain reaction showed that mRNAs for type IA and type II BMP receptors were present in control cultures. In cultures treated with BMP-2, mRNAs for BMP receptor type IB and the activin R-I receptor became evident. Cultures were analyzed for total cell counts, proliferating cell nuclear antigen (PCNA), and apoptotic DNA fragmentation. There was a significant increase in total cell number in the BMP-2 and BMP-4 treatment groups, without any change in PCNA reactivity, and a dramatic decrease in the proportion of apoptotic nuclei at concentrations of BMP-2 and BMP-4 above 5 ng/ml (P<0.001). These effects were not observed with BMP-6, TGF-beta1 or GDNF. These results suggest that the increase in total cell number is due to the attenuation of apoptosis by BMP-2 and BMP-4. The anti-apoptotic effect of BMP-2 and BMP-4 on this neuroectodermal cell line has potential clinical implications for neuroectodermal tumors.

Gangliosides and neutral glycolipids in ependymal, neuronal and primitive neuroectodermal tumors

Neutral glycolipid and ganglioside compositions were determined on 11 ependymal tumors, 12 medulloblastomas, 6 other neuronal tumors of the brain, 4 peripheral neuroblastomas, 1 cerebral primitive neuroectodermal tumor (PNET), and 1 PNET of the thoracic wall. Within the group of tumors that can demonstrate neuronal phenotypes, there was an association between the degree of neuronal differentiation usually demonstrated by these tumors and the proportions of both GD1a and 1b-pathway gangliosides. The amount of globoside also correlated with the amount of 1b pathway gangliosides. Patients with medulloblastomas whose 1b gangliosides made up over 15% of the total gangliosides survived longer that those with lower proportions of 1b gangliosides. The only gangliosides in the choroid plexus papilloma were GM3 and GD1a, but other ependymal tumors had significant amounts of GD1b and its metabolic precursors. Ependymoma and anaplastic ependymoma had similar neutral glycolipid compositions, which were different from subependymoma, which lacked ceramide monohexoside and ceramide dihexoside. These differences in glycolipid compositions suggest that there may be fundamental biological differences between these types of ependymal tumors.

Risk of primary childhood brain tumors related to birth characteristics: a Norwegian prospective study

Relations between birth characteristics and risk of primary brain tumor were explored in a prospective study of the 1,489,297 children born in Norway between 1967 and 1992. A total of 459 primary brain tumors, including 78 medulloblastomas and 168 astrocytomas, were diagnosed in the age interval 0-15 years. The overall risk of brain tumor depended on the season of birth (p = 0.01), with a higher risk for children born in winter than those born in spring [incidence rate ratio (IRR) = 1.52; 95% confidence interval (CI) 1.18-1.97]. An inverse association was observed with father's age at birth of child. The risk of medulloblastoma was positively associated with birth weight (IRR = 1.27/500 g; p = 0.05). Inverse relationships with length at birth were found for astrocytoma in the 0-1 and 5-10 year age intervals. Among 5-10-year-old children, birth weight was also inversely related to risk of astrocytoma. Our results suggest that risk factors may differ over age intervals and histological subgroups.

Medulloblastoma: survival and late recurrence after the Collins' risk period

Sixty-three patients with cerebellar medulloblastoma were treated between 1963 and 1992 at our institution. Among them, 10 patients have survived beyond the Collins' risk period. These included 6 males and 4 females who ranged in age from 6 months to 12 years at the time of diagnosis. A total removal of the tumor was achieved in 4 patients, while there was a subtotal removal in 3, and a partial removal in 3. Histologically, 6 tumors were classified as a classical type of medulloblastoma, and 4 were diagnosed as being a desmoplastic type. Postoperatively, 9 patients received craniospinal radiation therapy, and one received local radiation to the primary site. During the follow-up period of 3.9-25.4 years, 5 patients have been in continuous remission for from 14.2 to 25.4 years and are leading normal lives, 2 have survived for 18.1 and 18.5 years with mild to moderate neurological deficits, while the remaining 3 died after the Collins' risk period. Two out of these last 3 patients were under the age of one year at the time of onset, while the remaining one died after a second recurrence. We conclude that careful follow-up is needed for all long-term survivors even after the Collins' risk period, especially for those who were under the age of 1 year at onset and who failed in the initial treatments.

Anti-Hu immunolabeling as an index of neuronal differentiation in human brain tumors: a study of 112 central neuroepithelial neoplasms

Anti-Hu is a polyclonal immunoglobulin G associated with a syndrome of paraneoplastic sensory neuropathy/encephalomyelitis that principally afflicts patients with small cell lung carcinoma. Anti-Hu antibodies, which identify a family of RNA-binding proteins that are normally neuron restricted and that appear to be integral to neuronal differentiation and maintenance, selectively label the nuclei (and, less strongly, the cytoplasm) of neurons throughout the human neuraxis. Small cell carcinomas of the lung and many neuroblastomas are also labeled. We screened 112 tumors of central neuroepithelial lineage for immunohistochemical evidence of Hu expression with anti-Hu immunoglobulin G that was purified from patient sera and with a recombinant Fab fragment (Fab GLN 495) selected from a patient-derived combinatorial antibody phage display library using a recombinant Hu protein (HuD). Both antibodies uniformly labeled, in addition to native neurons, the nuclei of central neurocytomas (6 of 6) and the neuronal components of "classic" (12 of 12) and desmoplastic infantile (2 of 2) gangliogliomas. Of 33 embryonal tumors, 29 were anti-Hu reactive, including 87% of medulloblastomas (26 of 30). Glial neoplasms (n = 59) were anti-Hu negative save for one "oligodendroglioma" (of 17 oligodendroglial/oligoastrocytic tumors) that may have been an extraventricular neurocytoma. Anti-Hu immunoglobulin G/Fab GLN 495 identifies neoplasms of differentiated neuronal type and embryonal tumors with neuronogenic potential.

Neurotrophins in cerebellar granule cell development and medulloblastoma

Medulloblastomas may be derived from granule cells of the developing cerebellum. Children with tumors expressing high levels of the neurotrophin-3 receptor, TrkC, have a more favorable outcome. During development, TrkC is expressed in the most mature granule cells. Favorable medulloblastomas may be derived from more highly differentiated granule cells.

Neurotrophin signal transduction in medulloblastoma

The members of the neurotrophin family play key biological roles in the development of the nervous system. Based on studies initially in cell lines (e.g., the rat pheochromocytoma PC12 cells), neurotrophins have been found to be important mediators of proliferation, differentiation, and survival in the normal brain, but their role in brain tumors remains unclear. Since neurotrophins and neurotrophin receptors are frequently detected in biopsy samples of central nervous system medulloblastomas, efforts have been undertaken in several laboratories to elucidate the potential effects of neurotrophins on the growth and differentiation of these tumors. Results from these studies may have both basic and clinical implications because medulloblastomas resemble embryonic neuroectodermal stem cells and/or their immature neuronal and glial progeny. This review focuses on recent developments in our understanding of the role of neurotrophins in medulloblastomas, especially the ability of nerve growth factor to induce apoptosis in vitro in medulloblastomas.

Primitive neuroectodermal tumors of the central nervous system

Controversial issues relating to the pathobiology and classification of central nervous system primitive neuroectodermal tumors (PNETs) have plagued neuropathologists for more than 70 years. Hypotheses advanced in the mid-1920's have remained as fixed concepts in contemporary literature, largely consequent to repetitious support by a small number of neuropathologists despite a growing body of information discrediting these ideas from neuroembryologists, oncologists, neuroscientists and pathologists. Attention has largely focused upon PNETs arising in the cerebellum (commonly known as medulloblastomas ([MBs]), because about 80% of central nervous system (CNS) PNETs originate in this site. It has been asserted that the 20% which do not are biologically different, although most individuals agree that the histological features of PNETs that occur in different sites throughout the CNS are indistinguishable from those growing in the cerebellum. The historical aspects of this controversy are examined in the face of evidence that there is, in fact, a unique class of CNS tumors which should appropriately be regarded as primitive neuroectodermal in nature. Specifically, a number of different approaches to the problem have yielded data supporting this hypothesis. These approaches include the identification of patterns of expression among a variety of cellular antigens (demonstrated by the use of immunopathological techniques), molecular analyses of cell lines derived from these tumors, experimental production of PNETs and molecular genetic analyses. Differences of opinion among surgeons, oncologists and radiotherapists are typically resolved by conducting cooperative studies of patients with these tumors who are diagnosed and treated at multiple centers.

Metabolic studies of human primitive neuroectodermal tumour cells by proton nuclear magnetic resonance spectroscopy

Well-characterized cell lines established from primitive neuroectodermal tumours (PNETs) were examined by proton nuclear magnetic resonance (1H-NMR) spectroscopy and chromatographic analysis of perchloric acid extracts, following amplification in cell culture. A characteristic 1H-NMR spectroscopic metabolite pattern was found for medulloblastoma cell lines, which clearly discriminates these cells from PNETs of other locations in the central nervous system (CNS), on the basis of their N-acetyl aspartate (NAA) and aspartate expression. Medulloblastoma cell lines were heterogeneous in respect of their metabolite expression, possibly owing to the heterogeneity in their differentiation along lineages of the CNS. All PNET spectra displayed similar features, including decreased NAA and creatine peaks and increased signals from choline compounds (Cho) compared with normal cerebellum. The expression of NAA by the medulloblastoma lines was in the opposite order to the extent of neuronal differentiation, which may indicate their origin from a progenitor cell with the phenotype of an oligodendrocyte-type-2 astrocyte cell.

In vitro properties of a newly established medulloblastoma cell line, MCD-1

Medulloblastomas are poorly differentiated brain tumors believed to arise from primitive pleuripotential stem cells, and tend to express mixed neuronal and glial properties. In the present study, we examined immunohistochemical and neurotransmitter phenotypic properties in a newly established medulloblastoma cell line, MCD-1. MCD-1 cells were immortal, not contact-inhibited, but did not grow in soft agar. Immunohistochemical studies showed positive staining for neurofilament protein (NF), neuron-specific enolase (NSE), synaptophysin, MAP 2, tau, NCAM 180, vimentin, and S-100 protein. The cells expressed specific uptake of glutamate, serotonin, and choline, but not GABA or dopamine. A significant increase in process extension was seen in response to agents that enhance intracellular cyclic AMP, especially 3-isobutyl-1-methylxanthine (IBMX). Process formation induced by IBMX was associated with a decrease in cell proliferation as evidenced by a reduction in numbers of cells incorporating 5-bromo-2-deoxyuridine (BrdU). No increase in process extension was observed following exposure to NGF or retinoic acid. MCD-1 cells were shown to produce transforming growth factor beta (TGF beta), and were immunopositive for mutant p53. Transfection assays with the PG13-Luc reporter plasmid, which contains a p53-responsive enhancer element and a luciferase reporter gene, suggested MCD-1 cells are deficient in wild-type p53 and do not activate p53 on treatment with the anticancer agent adriamycin. The MCD-1 cell line is suggested to represent an abnormally differentiated cell type, which has some properties consistent with a multipotent neuronal phenotype while retaining some properties of immature cells of a glial lineage. The MCD-1 cell line can be used to provide a model of a medulloblastoma cell line that is resistant to growth-controlling and anticancer agents.

Cellular and molecular pathology of medulloblastoma

Medulloblastoma is a malignant embryonal tumor predominantly of childhood. It occurs principally in the midline cerebellar region but is prone to invade the meninges and cerebrospinal fluid spaces. It is the principal posterior fossa tumor in children and represents 20% of all brain tumors in this age group. Considerable advances have been made in characterizing the morphologic subtypes, immunophenotypes, and in vitro behavior of cell lines. However, the cell of origin and its relationship to other related primitive neuroectodermal tumors remains uncertain. Although recent advances in the application of proliferation markers and the use of apoptosis in situ labelling have been applied, a prognostically relevant marker applicable to surgical neuropathology remains to be developed. The fundamental molecular pathogenesis of tumor development remains unknown, although recent exciting advances have shown alterations in some members of the PAX family of genes as well as increased expression of neurotrophin receptors. These may prove to be of prognostic significance.

Expression of the neurotrophin receptor TrkC is linked to a favorable outcome in medulloblastoma

Medulloblastoma, the most common malignant brain tumor of childhood, has a variable prognosis. Although half of the children and young adults with the disease survive longer than 10 years after diagnosis, the others relapse and die despite identical therapy. We have examined the expression of neurotrophins and their receptors in medulloblastoma samples snap frozen in the operating room to preserve RNA integrity. All tumors (n = 12) were found to express mRNA encoding neurotrophin 3 and its receptor TrkC. The level of trkC expression was highly variable, with a more than 50-fold difference between the highest and lowest values. By Kaplan-Meier analysis, patients with tumors expressing high levels of trkC mRNA had significantly longer intervals without disease progression than those with low levels (log-rank, P = 0.03) and a more favorable overall survival (log-rank, P = 0.05). Thus, trkC expression is a prognostic indicator for patients with medulloblastoma.

Studies of childhood brain tumors using immunohistochemistry and microwave technology: methodological considerations

The immunohistochemical detection of antigens in archival tissue sections has been hampered by the poor reactivity of certain polypeptides in conventional formalin-fixed, paraffin-embedded material. For example, the poor reactivity of neurofilament proteins (NFPs) in surgical and autopsy specimens has been a major drawback of previous large, retrospective, clinicopathologic studies of pediatric primitive neuroectodermal tumors (PNETs), also known as medulloblastomas. We report our experience with a method of antigen retrieval which greatly enhanced the immunohistochemical detection of neuronal and glial intermediate filament proteins, retinal S-antigen (RSA), and the proliferating cell nuclear antigen (PCNA) in archival, paraffin-embedded, formalin or Bouin's-fixed, pediatric brain tumors, particularly PNETs. The technique involves adding a single brief step to an established avidin-biotin complex (ABC) immunohistochemical protocol (Vectastain Elite Kit). This step involves boiling tissue sections in distilled water for 5 min in a microwave oven. The specificity of staining was consistent with known cell and tissue specificities of the well-characterized monoclonal antibodies used and there was minimal background. Synaptophysin (SYN) staining was unaffected by heating and immunoreactivity of the low affinity nerve growth factor (p75NGFR) and the neural cell adhesion molecule (NCAM) were lost. The enhanced detection of neuronal and glial antigens in routinely prepared, formalin-fixed, archival material should facilitate large retrospective clinicopathologic studies designed to assess the prognostic implications of differentiation in PNETs and to better understand the biology of these tumors.

Genomic stability and instability in different neuroepithelial tumors. A role for chromosome structure?

Selected childhood and adult neoplasm exemplify fundamental differences in their propensity for genomic change. DNA replication is essential for the formation of neuroepithelial tumors, probably because the genome can be remodeled. Nonetheless, several differentiated and stable childhood neoplasms retain their nuclear controls for differentiation. In contrast, rapidly arising gliomas often show a variety of phenotypic changes. Genomic plasticity and instability allow gliomas to flexibly adapt to new environments. Gene changes (in DNA) can be limited in childhood tumors whereas more widespread genetic changes in malignant gliomas indicate a fundamental alteration in many chromosome regions. Can such regions be defined? We used one repeated DNA sequence (TTAGGG)n, present at the end of all normal human chromosomes, to investigate chromosome termini in more detail. Pulsed-field gel electrophoresis showed this region can be unusually variable, as several other multilocus probes did not reveal comparable changes. Because telomeres form unique chromosomal structures, and are thought to provide essential signals to position chromosomes in the interphase nucleus, it was pertinent to assess these regions by in situ hybridization. Many telomeric domains localized at variable as well as interior nuclear positions in glioma cells. These positions, which are presumably abnormal, may be generated by the DNA variants observed. Such position changes may contribute to the more general 'disorder' observed in glioma nuclei. Other chromosome domains with a unique DNA-protein structure may define additional genomic loci that are preferentially modified in neoplasia. A fundamental understanding of chromosome structure should clarify the problem of multilocus instability in glioblastoma.

In vivo and in vitro models of medulloblastomas and other primitive neuroectodermal brain tumors of childhood

Recent advances in understanding the basic biology of the neoplastic cells that populate childhood primitive neuroectodermal tumors (PNET) of the central nervous system (CNS) underline several unique properties of these common pediatric brain neoplasms. For example, studies of posterior fossa cerebellar medulloblastomas (MB), a prototypical group of brain tumors that comprise the largest class of PNET, suggest that the molecular phenotype of subpopulations of neoplastic cells in MB partially recapitulates stages in the acquisition of the neuronal phenotype by normal developing human CNS progenitor cells. However, as reviewed here, it appears that the neoplastic cells in MB exhibit one or more molecular defects in the sequence of normal maturational events that enable CNS progenitor cells to exit the cell cycle, become committed to the neuronal lineage, and undergo terminal differentiation into fully mature, permanently postmitotic CNS neurons. Indeed, since PNET emerge almost exclusively in early childhood, the induction of PNET may result from genetic lesions that arise in developing CNS progenitor cells thereby preventing these neural precursors from executing normal programs of lineage commitment and differentiation in the CNS. Clarification of how lineage commitment and maturation in PNET comprised of neuron-like tumor cells deviate from normal CNS development may clarify how oncogenes and tumor suppressor genes exert their effects in a cell type specific manner at different stages in the normal maturation of CNS cells. Recently, a number of potentially effective in vitro and in vivo model systems of PNET have been developed. Since these model systems could facilitate efforts to elucidate mechanisms of neoplastic transformation and tumor progression in the CNS, we review the potential utility of several recently described in vitro (e.g., MB cell lines) and in vivo (e.g., transgenic mice) experimental systems as models of authentic childhood CNS neoplasms.

Expression of neuronal and glial polypeptides during histogenesis of the human cerebellar cortex including observations on the dentate nucleus

In order to gain a more complete understanding of the sequential pattern of gene expression during neurogenesis and gliogenesis in humans, we followed the expression of well-characterized, developmentally regulated polypeptides in the cerebellar cortex and dentate nucleus by immunohistochemistry using monoclonal antibodies of highly defined specificity. At 8-10 weeks gestational age (GA), progenitor cells and their immediate progeny in the rhombencephalic ventricular zone expressed vimentin and nestin and, to a lesser extent, microtubule-associated protein 5 (MAP5) and glial fibrillary acidic protein (GFAP), but not the low affinity nerve growth factor receptor (NGFR). In contrast, postmitotic, migrating immature neurons in the intermediate zone gave strong reactions for MAP2, tau, and a nonphosphorylated form of middle molecular weight neurofilament (NF) protein (NF-M) and weak reactivity for NGFR. At 15 weeks GA, proliferating cells of the superficial part of the cerebellar external granular layer stained only for NGFR, while more deeply situated cells of the external granular layer stained positively for NGFR, MAP2, MAP5, tau, and chromogranin A, which correlates with the early outgrowth of parallel fibers. All phosphoisoforms of NF-M as well as the low (NF-L) and high (NF-H) molecular weight NF proteins and alpha-internexin were expressed in the somatodendritic domain of Purkinje cells and dentate nucleus neurons from about 20 weeks GA with a gradual compartmentalization of highly phosphorylated forms of NF-M and NF-H into axons by the end of gestation. Alpha-internexin was also expressed strongly in axons of the deep white matter from 20 weeks GA to adulthood. MAP2, synaptophysin, and NGFR showed early, transient expression in the somatodendritic domain of Purkinje cells followed by the appearance of a 220 kDa nestin-like peptide that continued to be expressed in adult Purkinje cells. Notably, developing dentate nucleus neurons expressed many of these proteins in a similar temporal sequence. Early in the developing cerebellar cortex, the expression of NF protein and synaptophysin occurred in discrete patches or columns similar to those described for other antigens (i.e., zebrins). Finally, radial glia were positive for vimentin, GFAP, and nestin from 8 weeks GA to 8 months postnatal. This study describes the distinct molecular programs of lineage commitment in cerebellar progenitor cells and in differentiating neurons and astrocytes of the human cerebellum. The acquisition of a mature molecular neuronal phenotype correlates with the establishment of structural polarity in cerebellar neurons.