Enteric neural crest differentiation in ganglioneuromas implicates Hedgehog signaling in peripheral neuroblastic tumor pathogenesis

Maturation of metastases in peripheral neuroblastic tumors (neuroblastoma) of children

Peripheral neuroblastic tumors of childhood exhibit 3 principal neural crest lineages: primitive neuroblastoma, ganglioneuroblastoma, and ganglioneuroma. They are unique in undergoing maturation of neurons (ganglion cells) and Schwann cells, thereby recapitulating normal fetal neuronal development in the brain. Precision in estimating neurogenesis is enhanced by immunoreactivities of markers of neuronal maturation. Whether organ tissue factors in different sites of metastases influence rates of maturation and whether metastases are similar to their primary neuroblastic tumor are incompletely documented. Four young children, 1 with a mixed primary adrenal tumor and 3 with metastases were studied at surgery or autopsy. Immunocytochemical reactivities included microtubule-associated protein-2, synaptophysin, chromogranin-A, somatostatin, keratan sulfate, vimentin, S-100β protein, and PHOX2B. Primary tumors were non-uniform with regions of either poor or enhanced maturation. Both neuronal and Schwannian lineages were represented in each tumor type but differed in proportions. Bi- or multi-nucleated ganglion cells matured equal to mononuclear forms. Ganglion cell maturation was similar in metastases regardless of the target organ. Metastases resembled primary tumors. Immunocytochemical markers of neuronal and of Schwann cell maturation provide greater diagnostic precision to supplement histological criteria. Interval between diagnosis of primary tumor and metastases, metastatic target tissues, and chemotherapy over an interval of time do not appear to influence neuroblastic or Schwann cell differentiation.

Tumor-suppressive disruption of cancer subtype-associated super enhancer circuits by small molecule treatment

Transcriptional cancer subtypes which correlate with traits such as tumor growth, drug sensitivity or the chances of relapse and metastasis, have been described for several malignancies. The core regulatory circuits (CRCs) defining these subtypes are established by chromatin super enhancers (SEs) driving key transcription factors (TFs) specific for the particular cell state. In neuroblastoma (NB), one of the most frequent solid pediatric cancer entities, two major SE-directed molecular subtypes have been described: A more lineage-committed adrenergic (ADRN) and a mesenchymal (MES) subtype. Here, we found that a small isoxazole molecule (ISX), a frequently used pro-neural drug, reprogrammed SE activity and switched NB cells from an ADRN subtype towards a growth-retarded MES-like state. The MES-like state shared strong transcriptional overlap with ganglioneuroma (GN), a benign and highly differentiated tumor of the neural crest. Mechanistically, ISX suppressed chromatin binding of N-MYC, a CRC-amplifying transcription factor, resulting in loss of key ADRN subtype-enriched components such as N-MYC itself, PHOX2B and ALK, while concomitently, MES subtype markers were induced. Globally, ISX treatment installed a chromatin accessibility landscape typically associated with low risk NB. In summary, we provide evidence that CRCs and cancer subtype reprogramming might be amenable to future therapeutic targeting.

Gene regulatory network from cranial neural crest cells to osteoblast differentiation and calvarial bone development

Calvarial bone is one of the most complex sequences of developmental events in embryology, featuring a uniquely transient, pluripotent stem cell-like population known as the cranial neural crest (CNC). The skull is formed through intramembranous ossification with distinct tissue lineages (e.g. neural crest derived frontal bone and mesoderm derived parietal bone). Due to CNC's vast cell fate potential, in response to a series of inductive secreted cues including BMP/TGF-β, Wnt, FGF, Notch, Hedgehog, Hippo and PDGF signaling, CNC enables generations of a diverse spectrum of differentiated cell types in vivo such as osteoblasts and chondrocytes at the craniofacial level. In recent years, since the studies from a genetic mouse model and single-cell sequencing, new discoveries are uncovered upon CNC patterning, differentiation, and the contribution to the development of cranial bones. In this review, we summarized the differences upon the potential gene regulatory network to regulate CNC derived osteogenic potential in mouse and human, and highlighted specific functions of genetic molecules from multiple signaling pathways and the crosstalk, transcription factors and epigenetic factors in orchestrating CNC commitment and differentiation into osteogenic mesenchyme and bone formation. Disorders in gene regulatory network in CNC patterning indicate highly close relevance to clinical birth defects and diseases, providing valuable transgenic mouse models for subsequent discoveries in delineating the underlying molecular mechanisms. We also emphasized the potential regenerative alternative through scientific discoveries from CNC patterning and genetic molecules in interfering with or alleviating clinical disorders or diseases, which will be beneficial for the molecular targets to be integrated for novel therapeutic strategies in the clinic.

Activation of Cilia-Independent Hedgehog/GLI1 Signaling as a Novel Concept for Neuroblastoma Therapy

Simple Summary

Elevated GLI1 expression levels are associated with improved survival in NB patients and GLI1 overexpression exerts tumor-suppressive traits in cultured NB cells. However, NB cells are protected from increased GLI1 levels as they have lost the ability to form primary cilia and transduce Hedgehog signals. This study identifies an isoxazole (ISX) molecule with primary cilia-independent GLI1-activating properties, which blocks NB cell growth. Mechanistically, ISX combines the removal of GLI3 repressor and the inhibition of class I HDACs, providing proof-of-principle evidence that small molecule-mediated activation of GLI1 could be harnessed therapeutically in the future.

Abstract

Although being rare in absolute numbers, neuroblastoma (NB) represents the most frequent solid tumor in infants and young children. Therapy options and prognosis are comparably good for NB patients except for the high risk stage 4 class. Particularly in adolescent patients with certain genetic alterations, 5-year survival rates can drop below 30%, necessitating the development of novel therapy approaches. The developmentally important Hedgehog (Hh) pathway is involved in neural crest differentiation, the cell type being causal in the etiology of NB. However, and in contrast to its function in some other cancer types, Hedgehog signaling and its transcription factor GLI1 exert tumor-suppressive functions in NB, rendering GLI1 an interesting new candidate for anti-NB therapy. Unfortunately, the therapeutic concept of pharmacological Hh/GLI1 pathway activation is difficult to implement as NB cells have lost primary cilia, essential organelles for Hh perception and activation. In order to bypass this bottleneck, we have identified a GLI1-activating small molecule which stimulates endogenous GLI1 production without the need for upstream Hh pathway elements such as Smoothened or primary cilia. This isoxazole compound potently abrogates NB cell proliferation and might serve as a starting point for the development of a novel class of NB-suppressive molecules.

Ganglioneuromas across age groups: Systematic review of individual patient data

BACKGROUND

Ganglioneuromas are very rare tumours of the sympathetic nervous system. Clinical and pathological knowledge is currently based on largely incomparable registries and case series that focus on paediatric or adrenal cases. To comprehensively characterize the full clinical spectrum across ages and locations, a meta-analysis was performed where amenable and complemented by systematic literature review of individual patient data (IPD).

DESIGN

Articles containing "ganglioneuroma" in English on humans, published from 1/1/1995-6/27/2018, were identified from PubMed. Aggregate data from 10 eligible patient series on 19 variables were considerably inhomogeneous, restricting meta-analysis to age and gender distribution. To determine basic disease characteristics across ages and locations, IPD were retrieved from case reports and small case series (PROSPERO CRD42018010247).

RESULTS

Individual patient data representing 364 cases revealed that 65.7% (60.6%-70.4%) were diagnosed in adults, more frequently in females (62%, 56.9%-66.9%). 24.5% (20.3%-39.1%) were discovered incidentally. Most often, ganglioneuromas developed in abdomen/pelvis (66.2, 32.1% adrenal). With age, the proportion of ganglioneuroma localizations with high post-surgical complication rate (35.6% head/neck and 16.3% thorax) decreased. Contrarily, the diagnosis of adrenal ganglioneuromas (<1% post-surgical complications) increased with age. Hormone production, hypertension or coincidence with another non-neuroblastic neural-crest-derived tumour component was more common for adrenal location. Recurrence and metastatic spread have not been reported for ganglioneuromas without secondary tumour component.

CONCLUSIONS

This work summarizes characteristics of the currently largest number of international GN patients across all ages. The data confirm a benign nature of GN, independent of age. Age-related differences in predominant tumour location, associated post-surgical complications and hormone production suggest case-centred management strategies.

Specific and spatial labeling of P0-Cre versus Wnt1-Cre in cranial neural crest in early mouse embryos

P0-Cre and Wnt1-Cre mouse lines have been widely used in combination with loxP-flanked mice to label and genetically modify neural crest (NC) cells and their derivatives. Wnt1-Cre has been regarded as the gold standard and there have been concerns about the specificity of P0-Cre because it is not clear about the timing and spatial distribution of the P0-Cre transgene in labeling NC cells at early embryonic stages. We re-visited P0-Cre and Wnt1-Cre models in the labeling of NC cells in early mouse embryos with a focus on cranial NC. We found that R26-lacZ Cre reporter responded to Cre activity more reliably than CAAG-lacZ Cre reporter during early embryogenesis. Cre immunosignals in P0-Cre and reporter (lacZ and RFP) activity in P0-Cre/R26-lacZ and P0-Cre/R26-RFP embryos was detected in the cranial NC and notochord regions in E8.0-9.5 (4-19 somites) embryos. P0-Cre transgene expression was observed in migrating NC cells and was more extensive in the forebrain and hindbrain but not apparent in the midbrain. Differences in the Cre distribution patterns of P0-Cre and Wnt1-Cre were profound in the midbrain and hindbrain regions, that is, extensive in the midbrain of Wnt1-Cre and in the hindbrain of P0-Cre embryos. The difference between P0-Cre and Wnt1-Cre in labeling cranial NC may provide a better explanation of the differential distributions of their NC derivatives and of the phenotypes caused by Cre-driven genetic modifications.

Risk Stratification of Pediatric Patients With Neuroblastoma Using Volumetric Parameters of 18F-FDG and 18F-DOPA PET/CT

PURPOSE

This study determined the prognostic value of volumetric parameters derived from pretreatment F-FDG and F-DOPA PET/CT of neuroblastoma and their correlation with clinical and histopathologic features.

PATIENTS AND METHODS

A total of 25 children with neuroblastoma underwent pretreatment F-FDG and F-DOPA PET/CT within 4 weeks. The SUVmax of primary tumors on F-FDG and F-DOPA PET were recorded as SUVFDG and SUVDOPA, respectively. For volumetric parameters of primary tumors, 40% of SUVmax was used to generate volume of interest. If the 40% of SUVmax was below 2.5, an SUV threshold of 2.5 was used instead. Metabolic tumor volume (MTV), total lesion glycolysis (TLG), dopaminergic tumor volume (DTV), and total lesion F-DOPA activity (TLDA) were recorded as F-FDG and F-DOPA volumetric parameters. All indices were compared between groups distinguished by survival status and clinical features, including bone marrow involvement, lymph node metastasis, amplification of the MYCN oncogene, invasive features on anatomic images, and risk categories. The Kaplan-Meier method and log-rank test were used to compare the survival curves between groups.

RESULTS

The median follow-up period was 28.2 months. Nonsurvivors (20%) tended to have lower SUVDOPA, DTV, and TLDA (P ≤ 0.05), and higher SUVFDG, MTV, and TLG (all P < 0.05). Lower F-DOPA uptake is associated with bone marrow and lymph node metastases (all P < 0.05). Higher F-FDG uptake is associated with MYCN amplification (all P < 0.05) and anatomic invasive features of tumors such as vascular encasement or adjacent organ invasion (TLG, P = 0.05). Only volumetric indices (DTV, TLDA, MTV, and TLG) significantly differed among risk groups (all P < 0.05).

CONCLUSIONS

Pretherapeutic F-DOPA and F-FDG PET provided complementary information, and both can be served for risk stratification. Volumetric indices of F-DOPA and F-FDG PET correlate more highly with risk grouping.

Smoothened-independent activation of hedgehog signaling by rearranged during transfection promotes neuroblastoma cell proliferation and tumor growth

BACKGROUND

Rearranged during transfection (RET) proto-oncogene encodes a receptor tyrosine kinase for glial cell line-derived neurotrophic factor (GDNF) signaling, and high RET expression is closely related to the tumorigenesis and malignancy of neuroblastoma(NB).

METHODS

We have investigated whether RET signals through hedgehog (HH) pathway in NB cell proliferation and tumor growth by in vitro cell culture and in vivo xenograft approaches.

RESULTS

The key members of both GDNF/RET and HH/GLI pathways are expressed in NB cell lines to different extents. Knockdown of RET in NB cells significantly attenuates the activity of HH signaling, whereas overexpression of RET robustly enhances the output of transcriptional activation by HH. Likewise, activation of RET by GDNF induces HH signaling, whereas knockdown of RET attenuates both basal and GDNF-induced activities of HH signaling. Moreover, protein kinase B lies on the downstream of GDNF/RET signaling module to inhibit the GSK3β, resulting in activation of HH signaling. Furthermore, either knockdown of RET by shRNA or inhibition of HH pathway by cyclopamine attenuates not only basal but also GDNF-induced proliferation of SH-SY5Y cells, and knockdown of either RET or smoothened in SH-SY5Y cell xenografts significantly attenuated the tumor growth. Finally, inhibition of HH signaling by GLI1 and GLI2 inhibitor, Gant61, reduces not only basal but also RET-induced proliferation of SH-SY5Y cells and outgrowth of xenografts.

CONCLUSION

GDNF/RET/AKT/GSK3β signaling module activates HH pathway to stimulate NB cells proliferation and tumor outgrowth.

GENERAL SIGNIFICANCE

Targeting HH pathway is a rational approach for therapeutic intervention of NB with high RET expression.

Hedgehog Pathway in Pediatric Cancers: They're Not Just for Brain Tumors Anymore

The Hedgehog (HH) pathway regulates fundamental processes in embryonic development, including stem cell maintenance, cell differentiation, tissue polarity, and cell proliferation. In the vertebrate pathway, Sonic hedgehog (SHH) binds to Patched1 (PTCH1), which relieves its inhibition of Smoothened (SMO), allowing the GLI family of transcription factors to translocate to the nucleus and activate HH target genes such as GLI1, GLI2, PTCH1, CYCLIN D1, BCL-2, and MYCN. The HH pathway is also an active participant in tumorigenesis. In 1996, loss-of-function mutation in PTCH1 was discovered to be the cause of nevoid basal cell carcinoma syndrome (NBCCS, or Gorlin syndrome), an autosomal dominant disease associated with increased rates of basal cell carcinoma (BCC), medulloblastoma (MB), and rarely, rhabdomyosarcoma. It is now estimated that 100% of sporadic BCC and up to 20% to 30% of MB also harbor activating HH pathway mutations. Together, these discoveries firmly established the linkage between HH pathway activation and cancer development. Intense research has since been focused on further defining the role of the HH pathway in BCC and MB and potential therapeutic strategies to inhibit HH signaling. Early clinical trials of SMO inhibitors have shown promising results in the treatment of adult BCC and SHH-driven MB. More recently, a number of other pediatric cancers have been reported to show HH activity, making these tumors potential candidates for HH inhibitor therapy. To date however, no HH pathway mutations have been identified in other pediatric cancers. This review will describe the HH pathway signaling in development and cancer with a focus on recent evidence for HH pathway activation in central nervous system (CNS) and non-CNS pediatric cancers.

Prognostic role of Gli1 expression in solid malignancies: a meta-analysis

Gli1 is a downstream transcriptional factor of Sonic hedgehog pathway in mammalians, and has been recognized as a proliferative indicator of carcinogenesis. However, its actual role in prognosis among solid malignancies remains unclear. Therefore we performed this meta-analysis aiming to discover the correlation between Gli1 positivity and clinical prognosis in patients suffering from diverse carcinomas. A total of 39 studies containing 4496 cases were selected into our quantitative analysis via electronic database search. Original data of 3-year, 5-year, 10-year overall survival and disease-free survival were extracted and calculated using odds ratio and Mantel-Haenszel model. Subgroup analysis was also conducted to clarify the possible confounding factors. P < 0.05 was considered significant in statistics. Gli1 redundancy was associated with worse 3-year, 5-year, 10-year overall survival and disease-free survival in solid malignancies. Different source regions, sample-size, mean-age and detection approaches had no impact on the negative prognostic effect of Gli1 over-expression. Nevertheless, stratified by cancer type and subcellular localization, cytoplasmic Gli1 expression and Gli1 positivity in intracranial tumors was not correlated to poorer 3-year and 5-year prognosis. The over-expression of Gli1 is a credible indicator of poorer prognosis in most of solid malignancies, irrespective of intracranial tumors.

ENS Development Research Since 1983: Great Strides but Many Remaining Challenges

The first enteric nervous system (ENS) conference, organized by Marcello Costa and John Furness, was held in Adelaide, Australia in 1983. In this article, we review what was known about the development of the ENS in 1983 and then summarize some of the major advances in the field since 1983.

Aspm sustains postnatal cerebellar neurogenesis and medulloblastoma growth in mice

Alterations in genes that regulate brain size may contribute to both microcephaly and brain tumor formation. Here, we report that Aspm, a gene that is mutated in familial microcephaly, regulates postnatal neurogenesis in the cerebellum and supports the growth of medulloblastoma, the most common malignant pediatric brain tumor. Cerebellar granule neuron progenitors (CGNPs) express Aspm when maintained in a proliferative state by sonic hedgehog (Shh) signaling, and Aspm is expressed in Shh-driven medulloblastoma in mice. Genetic deletion of Aspm reduces cerebellar growth, while paradoxically increasing the mitotic rate of CGNPs. Aspm-deficient CGNPs show impaired mitotic progression, altered patterns of division orientation and differentiation, and increased DNA damage, which causes progenitor attrition through apoptosis. Deletion of Aspm in mice with Smo-induced medulloblastoma reduces tumor growth and increases DNA damage. Co-deletion of Aspm and either of the apoptosis regulators Bax or Trp53 (also known as p53) rescues the survival of neural progenitors and reduces the growth restriction imposed by Aspm deletion. Our data show that Aspm functions to regulate mitosis and to mitigate DNA damage during CGNP cell division, causes microcephaly through progenitor apoptosis when mutated, and sustains tumor growth in medulloblastoma.

Tumors of the neural crest: Common themes in development and cancer

The neural crest (NC) is a remarkable transient structure in the vertebrate embryo that gives rise to a highly versatile population of pluripotent cells that contribute to the formation of multiple tissues and organs throughout the body. In order to achieve their task, NC-derived cells have developed specialized mechanisms to promote (1) their transition from an epithelial to a mesenchymal phenotype, (2) their capacity for extensive migration and cell proliferation, and (3) their ability to produce diverse cell types largely depending on the microenvironment encountered during and after their migratory path. Following embryogenesis, these same features of cellular motility, invasion, and proliferation can become a liability by contributing to tumorigenesis and metastasis. Ample evidence has shown that cancer cells have cleverly co-opted many of the genetic and molecular features used by developing NC cells. This review focuses on tumors that arise from NC-derived tissues and examines mechanistic themes shared during their oncogenic and metastatic development with embryonic NC cell ontogeny.

Gli1 protein regulates the S-phase checkpoint in tumor cells via Bid protein, and its inhibition sensitizes to DNA topoisomerase 1 inhibitors

Aberrant expression of hedgehog molecules, particularly Gli1, is common in cancers of many tissues and is responsible for their aggressive behavior and chemoresistance. Here we demonstrate a novel and tumor-specific role for aberrant Gli1 in the regulation of the S-phase checkpoint that suppresses replication stress and resistance to chemotherapy. Inhibition of Gli1 in tumor cells induced replication stress-mediated DNA damage response, attenuated their clonogenic potential, abrogated camptothecin (CPT)-induced Chk1 phosphorylation, and potentiated its cytotoxicity. However, in normal fibroblasts, Gli1 siRNAs showed no significant changes in CPT-induced Chk1 phosphorylation. Further analysis of ataxia telangiectasia and Rad3-related protein (ATR)/Chk1 signaling cascade genes in tumor cells revealed an unexpected mechanism whereby Gli1 regulates ATR-mediated Chk1 phosphorylation by transcriptional regulation of the BH3-only protein Bid. Consistent with its role in DNA damage response, Bid down-regulation in tumor cells abolished CPT-induced Chk1 phosphorylation and sensitized them to CPT. Correspondingly, Gli1 inhibition affected the expression of Bid and the association of replication protein A (RPA) with the ATR- interacting protein (ATRIP)-ATR complex, and this compromised the S-phase checkpoint. Conversely, complementation of Bid in Gli1-deficient cells restored CPT-induced Chk1 phosphorylation. An in silico analysis of the Bid promoter identified a putative Gli1 binding site, and further studies using luciferase reporter assays confirmed Gli1-dependent promoter activity. Collectively, our studies established a novel connection between aberrant Gli1 and Bid in the survival of tumor cells and their response to chemotherapy, at least in part, by regulating the S-phase checkpoint. Importantly, our data suggest a novel drug combination of Gli1 and Top1 inhibitors as an effective therapeutic strategy in treating tumors that expresses Gli1.

Gli1 transcriptional activity is negatively regulated by AKT2 in neuroblastoma

Activation of the Hedgehog (Hh) signaling pathway has been implicated in a variety of malignancies including neuroblastoma. Expression of Gli1, a downstream effector of Hh, correlates with a favorable prognosis in patients with neuroblastoma. Moreover, Gli1 overexpression reduces mitotic index and induces transcription of genes involved in the differentiation of neuroblastoma cells; however, much remains unknown regarding the regulation of Gli1 transcriptional activity. Here, we report a novel negative regulation of Gli1 transcriptional activity by PI3K/AKT2 signal transduction pathway. Constitutively active PI3K subunit, p110α, inhibited Gli1 transcriptional activity in neuroblastoma cells, whereas, overexpression of an inactive form of PI3K subunit, p85, enhanced its activity. Specifically, the AKT2 isoform inhibited Gli1 luciferase activity. Silencing AKT2 using siRNA increased Gli1 transcriptional activity and conversely, overexpression of constitutively active AKT2 (myr-AKT2) decreased Gli1 transcriptional activity. Furthermore, Gli1 overexpression-mediated decrease in anchorage-independent growth was rescued by AKT2 overexpression. We also demonstrated that AKT2 overexpression regulates the nuclear-cytoplasmic distribution of exogenous Gli1 protein in neuroblastoma cells by relieving a GSK3β-mediated destabilization of SUFU, a negative regulator of Gli1 nuclear translocation. Inhibition of nuclear Gli1 accumulation may explain for the suppression of the tumor-suppressive function of Gli1. Collectively, our findings suggest an important role of Gli1 as a tumor suppressor in neuroblastoma, and offer a mechanism by which AKT2 regulates the subcellular localization, and in turn, inhibits the tumor-suppressive function of Gli1 in neuroblastoma.

Hedgehog signaling in human medullary thyroid carcinoma: a novel signaling pathway

BACKGROUND

Locally or widely metastatic medullary thyroid carcinoma (MTC) is difficult to treat, and therapeutic options are limited. Recently, kinase inhibitors have shown partial efficacy in this cancer, but there is a continued need for the development of novel therapeutics. Within this context, the Hedgehog (Hh) pathway has been implicated in several types of human tumors, and early clinical trials with Hh antagonists have validated Hh as a novel therapeutic target. For the first time, we evaluated Hh pathway activity in MTC, and examined the effect of Hh pathway perturbation in highly characterized MTC cell lines.

METHODS

We examined immunohistochemical expression of the Hh signaling mediators Sonic Hedgehog (Shh) and Glioblastoma (Gli)2 in paraffin-embedded normal versus histologically characterized human MTC tissue. We examined pharmacologic disruption of Hh signaling in vitro using two established MTC cell lines (TT and MZ-CRC-1). Hh signaling was either pharmacologically activated (SAG) or inhibited (GDC-0449) in MTC cell lines; Hh activity was assessed by quantitative real-time polymerase chain reaction, Western blot analysis, and quantification of cellular growth and apoptotic activity.

RESULTS

Our data showed increased expression of Hh signaling factors in human MTC compared to normal tissue. In vitro, activation of the Hh pathway resulted in increased expression of key Hh signaling components Smoothened (Smo) and Gli2. Conversely, inhibition of the Hh pathway decreased expression of these genes, leading to significantly reduced cellular growth and increased apoptosis.

CONCLUSIONS

Hedgehog signaling components are markedly upregulated in MTC. Hh pathway inhibitors have potential as novel therapeutic options in patients with metastatic and/or surgically unresectable MTC.

Bax deficiency prolongs cerebellar neurogenesis, accelerates medulloblastoma formation and paradoxically increases both malignancy and differentiation

Neurogenesis requires negative regulation through differentiation of progenitors or their programmed cell death (PCD). Growth regulation is particularly important in the postnatal cerebellum, where excessive progenitor proliferation promotes medulloblastoma, the most common malignant brain tumor in children. We present evidence that PCD operates alongside differentiation to regulate cerebellar granule neuron progenitors (CGNPs) and to prevent medulloblastoma.

Here we show that genetic deletion of pro-apoptotic Bax disrupts regulation of cerebellar neurogenesis and promotes medulloblastoma formation. In Bax^−/− mice, the period of neurogenesis was extended into the third week of postnatal life, and ectopic neurons and progenitors collected in the molecular layer of the cerebellum and adjacent tectum. Importantly, genetic deletion of Bax in medulloblastoma-prone ND2:SmoA1 transgenic mice greatly accelerated tumorigenesis. Bax-deficient medulloblastomas exhibited strikingly distinct pathology, with reduced apoptosis, increased neural differentiation and tectal migration. Comparing Bax^+/+ and Bax^−/− medulloblastomas, we were able to identify up-regulation of Bcl-2 and nuclear exclusion of p27 as tumorigenic changes that are required to mitigate the tumor suppressive effect of Bax. Studies on human tumors confirmed the importance of modulating Bax in medulloblastoma pathogenesis.

Our results demonstrate that Bax-dependent apoptosis regulates postnatal cerebellar neurogenesis, suppresses medulloblastoma formation, and imposes selective pressure on tumors that form. Functional resistance to Bax-mediated apoptosis, required for medulloblastoma tumorigenesis, may be a tumor-specific vulnerability to be exploited for therapeutic benefit.

Hedgehog signaling pathway in neuroblastoma differentiation

PURPOSE

The hedgehog (Hh) signaling pathway is activated in some adult cancers. On the other hand, the Hh signaling pathway plays an important role in the development of the neural crest in embryos. The aim of this study is to show the activation of Hh signaling pathway in neuroblastoma (NB), a pediatric malignancy arising from neural crest cells, and to reveal the meaning of the Hh signaling pathway in NB development.

METHODS

This study analyzed the expression of Sonic hedgehog (Shh), GLI1, and Patched 1 (Ptch1), transactivators of Hh signaling pathway, by immunohistochemistry in 82 NB and 10 ganglioneuroblastoma cases. All 92 cases were evaluated for the status of MYCN amplification.

RESULTS

Of the 92 cases, 67 (73%) were positive for Shh, 62 cases (67%) were positive for GLI1, and 73 cases (79%) were positive for Ptch1. Only 2 (10%) of the 20 cases with MYCN amplification were positive for Shh and GLI1, and 4 cases (20%) were positive for Ptch1 (MYCN amplification vs no MYCN amplification, P ≦ .01). The percentage of GLI1-positive cells in the cases with INSS stage 1 without MYCN amplification was significantly higher than that with INSS stage 4. Of 72 cases without MYCN amplification, 60 were GLI1-positive. Twelve cases were GLI1-negative, and the prognosis of the GLI1-positive cases was significantly better than that of the GLI1-negative cases (P = .015).

CONCLUSIONS

Most of NBs without MYCN amplification were positive for Shh, GLI1, and Ptch1. In the cases without MYCN amplification, the high expression of GLI1 was significantly associated with early clinical stage and a good prognosis of the patients. In contrast to adult cancers, the activation of the Hh signaling pathway in NB may be associated with the differentiation of the NB.