Insulin-like growth factor II is involved in the proliferation control of medulloblastoma and its cerebellar precursor cells

Targeting the gp130/STAT3 Axis Attenuates Tumor Microenvironment Mediated Chemoresistance in Group 3 Medulloblastoma Cells

Medulloblastoma (MB) is the most common malignant pediatric brain tumor. Of the four molecular subgroups, Group 3 MB is the most aggressive and has the worst prognosis. To understand the origins of chemoresistance involving IL-6/STAT3 signaling, we used in vitro co-culture systems to investigate the contribution of microglia as a brain tumor microenvironment cellular source of paracrine cytokines that promotes acquired drug resistance in Group 3 MB. MB cells subjected to co-culture with microglia exhibited increased expression of phosphorylated JAK1 and STAT3, which was correlated with enhanced resistance to vincristine. We found that both microglia and MB cells co-cultured with microglia secreted significant quantities of IL-6, indicating that IL-6 is a paracrine and autocrine cytokine able to initiate and sustain STAT3 activity in MB cells. Surprisingly, IL-6R^−/− MB cells, which cannot respond to exogenous IL-6 stimuli, were responsive to microglia co-culture induced activation of STAT3 and chemoresistance. Subsequently, we found that MB cells conditioned in vitro with the IL-6 family cytokines, IL-6, OSM, LIF, or IL-11, exhibited enhanced JAK1/STAT3 activity and chemoresistance. Intriguingly, MB cells conditioned with any one of the IL-6 family cytokine secreted multiple IL-6 family cytokines, implicating a feedback network involving multiple cytokines. The IL-6 family cytokine receptors share a common signal transducing β-subunit, gp130, which may be targeted to mitigate tumor chemoresistance. We showed that microglia co-culture failed to induce chemoresistance of gp130^−/− MB cells, and that combination treatment using gp130 inhibitors, or with the JAK inhibitor ruxolitinib, effectively overcame the observed resistance to vincristine in gp130 expressing MB cells. Our in vitro studies highlight the gp130/JAK/STAT pathway as a therapeutic target in combating acquired treatment resistance in Group 3 MB.

The interplay between estrogen receptor beta and protein kinase C, a crucial collaboration for medulloblastoma cell proliferation and invasion

Medulloblastoma (MB) is the most common and aggressive pediatric intracranial tumor. Estrogen receptor β (ERβ) expression correlates with MB development and its phosphorylation modifies its transcriptional activity in a ligand-dependent or independent manner. Using in silico tools, we have identified several residues in ERβ protein as potential targets of protein kinases C (PKCs) α and δ. Using Daoy cells, we observed that PKCα and PKCδ associate with ERβ and induce its phosphorylation. The activation of ERβ promotes MB cells proliferation and invasion, and PKCs downregulation dysregulates these steroid receptor mediated processes. Our data suggest that these kinases may play a crucial role in the regulation of the ERβ transcriptional activity. Overexpression of both PKCα and PKCδ in MB biopsies samples supports their relevance in MB progression.

Autocrine IL-6/STAT3 signaling aids development of acquired drug resistance in Group 3 medulloblastoma

Medulloblastoma (MB) is a high-grade pediatric brain malignancy that originates from neuronal precursors located in the posterior cranial fossa. In this study, we evaluated the role of STAT3 and IL-6 in a tumor microenvironment mediated drug resistance in human MBs. We established that the Group 3 MB cell line, Med8A, is chemosensitive (hence Med8A-S), and this is correlated with a basal low phosphorylated state of STAT3, while treatment with IL-6 induced robust increases in pY705-STAT3. Via incremental selection with vincristine, we derived the stably chemoresistant variant, Med8A-R, that exhibited multi-drug resistance, enhanced IL-6 induced pY705-STAT3 levels, and increased IL6R expression. Consequently, abrogation of STAT3 or IL6R expression in Med8A-R led to restored chemosensitivity to vincristine, highlighting a prominent role for canonical IL-6/STAT3 signaling in acquired drug resistance. Furthermore, Med8A-S subjected to conditioning exposure with IL-6, termed Med8A-IL6+ cells, exhibited enhanced vincristine resistance, increased expression of pY705-STAT3 and IL6R, and increased secretion of IL-6. When cocultured with Med8A-IL6+ cells, Med8A-S cells exhibited increased pY705-STAT3 and increased IL-6 secretion, suggesting a cytokine feedback loop responsible for amplifying STAT3 activity. Similar IL-6 induced phenomena were also observed in the Group 3 MB cell lines, D283 and D341, including increased pY705-STAT3, drug resistance, IL-6 secretion and IL6R expression. Our study unveiled autocrine IL-6 as a promoter of STAT3 signaling in development of drug resistance, and suggests therapeutic benefits for targeting the IL-6/STAT3 signaling axis in Group 3 MBs.

Mini Review: Opposing Pathologies in Cancer and Alzheimer's Disease: Does the PI3K/Akt Pathway Provide Clues?

This minireview is a brief overview examining the roles of insulin-like growth factors (IGFs) and the PI3K/Akt pathway in two apparently unconnected diseases: Alzheimer's dementia and cancer. For both, increased age is a major risk factor, and, in accord with the global rise in average life expectancy, their prevalence is also increasing. Cancer, however, involves excessive cell proliferation and metastasis, whereas Alzheimer's disease (AD) involves cell death and tissue destruction. The apparent "inverse" nature of these disease states is examined here, but also some important commonalities in terms of the PI3K/Akt pathway, glucose utilization and cell deregulation/death. The focus here is on four key molecules associated with this pathway; notably, the insulin receptor substrate 1 (IRS-1), cellular tumor antigen p53 (p53), peptidyl-prolyl cis-trans isomerase NIMA-interacting 1 (PIN1) and low-density lipoprotein receptor-related protein-1 (LRP1), all previously identified as potential therapeutic targets for both diseases. The insulin-resistant state, commonly reported in AD brain, results in neuronal glucose deprivation, due to a dampening down of the PI3K/Akt pathway, including overactivity of the mammalian target of rapamycin 1 (mTORC1) complex, hyperphosphorylation of p53 and neuronal death. This contrasts with cancer, where there is overstimulation of the PI3K/Akt pathway and the suppression of mTORC1 and p53, enabling abundant energy and unrestrained cell proliferation. Although these disease states appear to be diametrically opposed, the same key molecules are controlling pathology and, with differential targeting of therapeutics, may yet provide a beneficial outcome for both.

miR-196B-5P and miR-200B-3P Are Differentially Expressed in Medulloblastomas of Adults and Children

Medulloblastoma is a highly aggressive brain tumor that typically affects children, while in adults it represents ~1% of all brain tumors. Little is known about microRNA expression profile of the rare adult medulloblastoma. The main aim of this study was to identify peculiar differences in microRNA expression between childhood and adult medulloblastoma. Medulloblastomas were profiled for microRNA expression using the Exiqon Human miRNome panel (I + II) analyzing 752 microRNAs in a training set of six adult and six childhood cases. Then, the most differentially expressed microRNAs were validated in a total of 21 adult and 19 childhood cases. Eight microRNAs (miR-196b-5p, miR-183-5p, miR-200b-3p, miR-196a-5p, miR-193a-3p, miR-29c-3p, miR-33b-5p, and miR-200a-3p) were differentially expressed in medulloblastoma of adults and children. Analysis of the validation set confirmed that miR-196b-5p and miR-200b-3p were significantly overexpressed in medulloblastoma of adults as compared with those of children. We followed an in silico approach to investigate direct targets and the pathways involved for the two microRNAs (miR-196b and miR-200b) differently expressed between adult and childhood medulloblastoma. Adult and childhood medulloblastoma have different miRNA expression profiles. In particular, the differential dysregulation of miR-196b-5p and miR-200b-3p characterizes the miRNA profile of adult medulloblastoma and suggests potential targets for novel diagnostic, prognostic, or therapeutic strategies.

Maternal Folic Acid Supplementation Mediates Offspring Health via DNA Methylation

The clinical significance of periconceptional folic acid supplementation (FAS) in the prevention of neonatal neural tube defects (NTDs) has been recognized for decades. Epidemiological data and experimental findings have consistently been indicating an association between folate deficiency in the first trimester of pregnancy and poor fetal development as well as offspring health (i.e., NTDs, isolated orofacial clefts, neurodevelopmental disorders). Moreover, compelling evidence has suggested adverse effects of folate overload during perinatal period on offspring health (i.e., immune diseases, autism, lipid disorders). In addition to several single-nucleotide polymorphisms (SNPs) in genes related to folate one-carbon metabolism (FOCM), folate concentrations in maternal serum/plasma/red blood cells must be considered when counseling FAS. Epigenetic information encoded by 5-methylcytosines (5mC) plays a critical role in fetal development and offspring health. S-adenosylmethionine (SAM), a methyl donor for 5mC, could be derived from FOCM. As such, folic acid plays a double-edged sword role in offspring health via mediating DNA methylation. However, the underlying epigenetic mechanism is still largely unclear. In this review, we summarized the link across DNA methylation, maternal FAS, and offspring health to provide more evidence for clinical guidance in terms of precise FAS dosage and time point. Future studies are, therefore, required to set up the reference intervals of folate concentrations at different trimesters of pregnancy for different populations and to clarify the epigenetic mechanism for specific offspring diseases.

The molecular biology of medulloblastoma metastasis

Medulloblastoma (MB) is the most common primary malignant brain tumor of childhood and a significant contributor to pediatric morbidity and death. While metastatic dissemination is the predominant cause of morbidity and mortality for patients with this disease, most research efforts and clinical trials to date have focused on the primary tumor; this is due mostly to the paucity of metastatic tumor samples and lack of robust mouse models of MB dissemination. Most current insights into the molecular drivers of metastasis have been derived from comparative molecular studies of metastatic and non-metastatic primary tumors. However, small studies on matched primary and metastatic tissues and recently developed mouse models of dissemination have begun to uncover the molecular biology of MB metastasis more directly. With respect to anatomical routes of dissemination, a hematogenous route for MB metastasis has recently been demonstrated, opening new avenues of investigation. The tumor micro-environment of the primary and metastatic niches has also been increasingly scrutinized in recent years, and further investigation of these tumor compartments is likely to result in a better understanding of the molecular mediators of MB colonization and growth in metastatic compartments.

Ceritinib-Induced Regression of an Insulin-Like Growth Factor-Driven Neuroepithelial Brain Tumor

The insulin-like growth factor (IGF) pathway plays an important role in several brain tumor entities. However, the lack of inhibitors crossing the blood–brain barrier remains a significant obstacle for clinical translation. Here, we targeted the IGF pathway using ceritinib, an off-target inhibitor of the IGF1 receptor (IGF1R) and insulin receptor (INSR), in a pediatric patient with an unclassified brain tumor and a notch receptor 1 (NOTCH1) germline mutation. Pathway analysis of the tumor revealed activation of the sonic hedgehog (SHH), the wingless and integrated-1 (WNT), the IGF, and the Notch pathway. The proliferation of the patient tumor cells (225ZL) was inhibited by arsenic trioxide (ATO), which is an inhibitor of the SHH pathway, by linsitinib, which is an inhibitor of IGF1R and INSR, and by ceritinib. 225ZL expressed INSR but not IGF1R at the protein level, and ceritinib blocked the phosphorylation of INSR. Our first personalized treatment included ATO, but because of side effects, we switched to ceritinib. After 46 days, we achieved a concentration of 1.70 µM of ceritinib in the plasma, and after 58 days, MRI confirmed that there was a response to the treatment. Ceritinib accumulated in the tumor at a concentration of 2.72 µM. Our data suggest ceritinib as a promising drug for the treatment of IGF-driven brain tumors.

IGF1R Is a Potential New Therapeutic Target for HGNET-BCOR Brain Tumor Patients

(1) Background: The high-grade neuroepithelial tumor of the central nervous system with BCOR alteration (HGNET-BCOR) is a highly malignant tumor. Preclinical models and molecular targets are urgently required for this cancer. Previous data suggest a potential role of insulin-like growth factor (IGF) signaling in HGNET-BCOR. (2) Methods: The primary HGNET-BCOR cells PhKh1 were characterized by western blot, copy number variation, and methylation analysis and by electron microscopy. The expression of IGF2 and IGF1R was assessed by qRT-PCR. The effect of chemotherapeutics and IGF1R inhibitors on PhKh1 proliferation was tested. The phosphorylation of IGF1R and downstream molecules was assessed by western blot. (3) Results: Phkh1 cells showed a DNA methylation profile compatible with the DNA methylation class "HGNET-BCOR" and morphologic features of cellular cannibalism. IGF2 and IGF1R were highly expressed by three HGNET-BCOR tumor samples and PhKh1 cells. PhKh1 cells were particularly sensitive to vincristine, vinblastine, actinomycin D (IC₅₀ < 10 nM for all drugs), and ceritinib (IC₅₀ = 310 nM). Ceritinib was able to abrogate the proliferation of PhKh1 cells and blocked the phosphorylation of IGF1R and AKT. (4) Conclusion: IGF1R is as an attractive target for the development of new therapy protocols for HGNET-BCOR patients, which may include ceritinib and vinblastine.

Insulin growth factor 2 (IGF2) as an emergent target in psychiatric and neurological disorders. Review

Insulin-like growth factor 2 (IGF2) is abundantly expressed in the central nervous system (CNS). Recent evidence highlights the role of IGF2 in the brain, sustained by data showing its alterations as a common feature across a variety of psychiatric and neurological disorders. Previous studies emphasize the potential role of IGF2 in psychiatric and neurological conditions as well as in memory impairments, targeting IGF2 as a pro-cognitive agent. New research on animal models supports that upcoming investigations should explore IGF2's strong promising role as a memory enhancer. The lack of effective treatments for cognitive disturbances as a result of psychiatric diseases lead to further explore IGF2 as a promising target for the development of new pharmacology for the treatment of memory dysfunctions. In this review, we aim at gathering all recent relevant studies and findings on the role of IGF2 in the development of psychiatric diseases that occur with cognitive problems.

IGFBP6 controls the expansion of chemoresistant glioblastoma through paracrine IGF2/IGF-1R signaling

BACKGROUND

Glioblastomas (GBMs), the most common and most lethal of the primary brain tumors, are characterized by marked intra-tumor heterogeneity. Several studies have suggested that within these tumors a restricted population of chemoresistant glioma cells is responsible for recurrence. However, the gene expression patterns underlying chemoresistance are largely unknown. Numerous efforts have been made to block IGF-1R signaling pathway in GBM. However, those therapies have been repeatedly unsuccessful. This failure may not only be due to the complexity of IGF receptor signaling, but also due to complex cell-cell interactions in the tumor mass. We hypothesized that differential expression of proteins in the insulin-like growth factor (IGF) system underlie cell-specific differences in the resistance to temozolomide (TMZ) within GBM tumors.

METHODS

Expression of IGF-1R was analyzed in cell lines, patient-derived xenograft cell lines and human biopsies by cell surface proteomics, flow cytometry, immunofluorescence and quantitative real time polymerase chain reaction (qRT-PCR). Using gain-of-function and loss-of-function strategies, we dissected the molecular mechanism responsible for IGF-binding protein 6 (IGFBP6) tumor suppressor functions both in in vitro and in vivo. Site direct mutagenesis was used to study IGFBP6-IGF2 interactions.

RESULTS

We determined that in human glioma tissue, glioma cell lines, and patient-derived xenograft cell lines, treatment with TMZ enhances the expression of IGF1 receptor (IGF-1R) and IGF2 and decreases the expression of IGFBP6, which sequesters IGF2. Using chemoresistant and chemosensitive wild-type and transgenic glioma cells, we further found that a paracrine mechanism driven by IGFBP6 secreted from TMZ-sensitive cells abrogates the proliferation of IGF-1R-expressing TMZ-resistant cells in vitro and in vivo. In mice bearing intracranial human glioma xenografts, overexpression of IGFBP6 in TMZ-resistant cells increased survival. Finally, elevated expression of IGF-1R and IGF2 in gliomas associated with poor patient survival and tumor expression levels of IGFBP6 directly correlated with overall survival time in patients with GBM.

CONCLUSIONS

Our findings support the view that proliferation of chemoresistant tumor cells is controlled within the tumor mass by IGFBP6-producing tumor cells; however, TMZ treatment eliminates this population and enriches the TMZ-resistant cell populationleading to accelerated growth of the entire tumor mass.

Duality of estrogen receptor β action in cancer progression

The physiological actions of estrogens are primarily mediated by the nuclear hormone receptors estrogen receptor alpha (ERα) and beta (ERβ). Activities of these nuclear steroid hormone receptors in etiology and progression of many hormone-responsive cancers are well-established, yet the specific role of each receptor, and their various expressed isoforms, in estrogen-responsive cancers remains unclear. Recent advances in nuclear receptor profiling, characterization of expressed splice variants, and the availability of new experimental cancer models, has extended the understanding of the complex interplay between the differentially expressed nuclear estrogen receptors. In this review, we discuss proposed roles of ERβ in several subtypes of cancers that lack significant ERα expression and define current understanding of how different ERs collaborate to regulate cellular processes.

Increased cytomegalovirus replication by 5-Azacytidine and viral-induced cytoplasmic expression of DNMT‑1 in medulloblastoma and endothelial cells

Among all brain tumors diagnosed in children, medulloblastomas (MBs) are associated with a poor prognosis. The etiology of MB is not fully understood, yet the impact of epigenetic alterations of oncogenes has previously been established. During the past decade, the human cytomegalovirus (HCMV) has been detected in several types of cancer, including MB. Since DNA methylation occurs in the cell nucleus and this is considered a host defence response, we studied the impact of HCMV infection on DNA methyltransferase (DNMT‑1) in MB (D324) cells, human umbilical vein endothelial cells (HUVECs) as well as in MB tissue sections. We hypothesized that infection and DNMT‑1 intracellular localization are linked. Uninfected and HCMV‑infected D324 cells and HUVECs were analyzed for HCMV immediate early (HCMV‑IE) protein, HCMV‑glycoprotein B (HCMV‑gB) and DNMT‑1 using immunofluorescence staining and quantitative ELISA. DNMT‑1 localized to the nucleus of uninfected and HCMV‑IE- expressing D324 cells and HUVECs, but accumulated in the extra nuclear space in all HCMV‑gB-positive cells. Inhibition of HCMV late protein expression by Cymevene® (ganciclovir) prevented the cytoplasmic localization of DNMT‑1. Treatment of HCMV‑ infected D324 cells and HUVECs with the methylation inhibitor 5-Azacytidine (5AZA), significantly increased HCMV‑IE and HCMV‑gB gene transcription and protein expression. Immunohistochemical staining of DNMT‑1 and HCMV proteins in MB cancer tissue sections revealed both nuclear and cytoplasmic DNMT‑1 localization. In conclusion, DNMT‑1 resides in the cytoplasm of HCMV‑gB-expressing HUVECs and D324 cells. Increased viral protein synthesis in 5AZA-treated cells suggests that HCMV replication may benefit from a DNA methyltransferase-free cellular environment. Our findings emphasize the importance of assessing potential viral activation in the treatment of MB patients with epigenetic drugs.

Activation of the basal cell carcinoma pathway in a patient with CNS HGNET-BCOR diagnosis: consequences for personalized targeted therapy

High grade neuroepithelial tumor of the central nervous system with BCOR alteration (CNS HGNET-BCOR) is a recently described new tumor entity with a dismal prognosis. The objective of this study was to identify and validate pathways deregulated in CNS HGNET-BCOR as basis for targeted therapy approaches.

We characterized the BCOR alteration in a pediatric patient with CNS HGNET-BCOR diagnosis by Sanger sequencing and demonstrated an elevated BCOR expression by qRT-PCR and western blot. By whole transcriptome sequencing and Ingenuity Pathway Analysis, we identified the activation of the Sonic Hedgehog (SHH) and of the WNT signaling pathway in two different regions of the primary tumor and of one inoculation metastasis compared to normal brain. We validated the activation of the SHH and of the WNT pathway by qRT-PCR analysis of GLI1 and AXIN2 respectively. GLI1 and AXIN2 were upregulated in the primary tumor and in two inoculation metastases compared to normal brain. Mutational analysis of SMO, PTCH1 and SUFU, three key components of the SHH pathway, revealed a Single Nucleotide Polymorphism (SNP) in PTCH1 (rs357564). We tested the effect of the GLI-inhibitor arsenic trioxide (ATO) on a short-term cell culture isolated from the metastasis. ATO was able to reduce the viability of the cells with an IC₅₀ of 1.3 μM.

In summary, these results provide functional evidence of altered BCOR expression and homogeneous coactivation of both the SHH and WNT signaling pathways, building the basis for potential novel therapeutic approaches for patients with a CNS HGNET-BCOR diagnosis.

mTORC1-Mediated Inhibition of 4EBP1 Is Essential for Hedgehog Signaling-Driven Translation and Medulloblastoma

Mechanistic target of rapamycin (MTOR) cooperates with Hedgehog (HH) signaling, but the underlying mechanisms are incompletely understood. Here we provide genetic, biochemical, and pharmacologic evidence that MTOR complex 1 (mTORC1)-dependent translation is a prerequisite for HH signaling. The genetic loss of mTORC1 function inhibited HH signaling-driven growth of the cerebellum and medulloblastoma. Inhibiting translation or mTORC1 blocked HH signaling. Depleting 4EBP1, an mTORC1 target that inhibits translation, alleviated the dependence of HH signaling on mTORC1. Consistent with this, phosphorylated 4EBP1 levels were elevated in HH signaling-driven medulloblastomas in mice and humans. In mice, an mTORC1 inhibitor suppressed medulloblastoma driven by a mutant SMO that is inherently resistant to existing SMO inhibitors, prolonging the survival of the mice. Our study reveals that mTORC1-mediated translation is a key component of HH signaling and an important target for treating medulloblastoma and other cancers driven by HH signaling.

Disparities in Cervical Cancer Incidence and Mortality: Can Epigenetics Contribute to Eliminating Disparities?

Screening for uterine cervical intraepithelial neoplasia (CIN) followed by aggressive treatment has reduced invasive cervical cancer (ICC) incidence and mortality. However, ICC cases and carcinoma in situ (CIS) continue to be diagnosed annually in the United States, with minorities bearing the brunt of this burden. Because ICC peak incidence and mortality are 10-15 years earlier than other solid cancers, the number of potential years of life lost to this cancer is substantial. Screening for early signs of CIN is still the mainstay of many cervical cancer control programs. However, the accuracy of existing screening tests remains suboptimal. Changes in epigenetic patterns that occur as a result of human papillomavirus infection contribute to CIN progression to cancer, and can be harnessed to improve existing screening tests. However, this requires a concerted effort to identify the epigenomic landscape that is reliably altered by HPV infection specific to ICC, distinct from transient changes.

In vitro models of medulloblastoma: Choosing the right tool for the job

The recently-defined four molecular subgroups of medulloblastoma have required updating of our understanding of in vitro models to include molecular classification and risk stratification features from clinical practice. This review seeks to build a more comprehensive picture of the in vitro systems available for modelling medulloblastoma. The subtype classification and molecular characterisation for over 40 medulloblastoma cell-lines has been compiled, making it possible to identify the strengths and weaknesses in current model systems. Less than half (18/44) of established medulloblastoma cell-lines have been subgrouped. The majority of the subgrouped cell-lines (11/18) are Group 3 with MYC-amplification. SHH cell-lines are the next most common (4/18), half of which exhibit TP53 mutation. WNT and Group 4 subgroups, accounting for 50% of patients, remain underrepresented with 1 and 2 cell-lines respectively. In vitro modelling relies not only on incorporating appropriate tumour cells, but also on using systems with the relevant tissue architecture and phenotype as well as normal tissues. Novel ways of improving the clinical relevance of in vitro models are reviewed, focusing on 3D cell culture, extracellular matrix, co-cultures with normal cells and organotypic slices. This paper champions the establishment of a collaborative online-database and linked cell-bank to catalyse preclinical medulloblastoma research.

Proneurotrophin-3 promotes cell cycle withdrawal of developing cerebellar granule cell progenitors via the p75 neurotrophin receptor

Cerebellar granule cell progenitors (GCP) proliferate extensively in the external granule layer (EGL) of the developing cerebellum prior to differentiating and migrating. Mechanisms that regulate the appropriate timing of cell cycle withdrawal of these neuronal progenitors during brain development are not well defined. The p75 neurotrophin receptor (p75(NTR)) is highly expressed in the proliferating GCPs, but is downregulated once the cells leave the cell cycle. This receptor has primarily been characterized as a death receptor for its ability to induce neuronal apoptosis following injury. Here we demonstrate a novel function for p75(NTR) in regulating proper cell cycle exit of neuronal progenitors in the developing rat and mouse EGL, which is stimulated by proNT3. In the absence of p75(NTR), GCPs continue to proliferate beyond their normal period, resulting in a larger cerebellum that persists into adulthood, with consequent motor deficits.

Medulloblastoma: molecular pathways and histopathological classification

Malignant brain tumors are the leading cause of cancer death among pediatric patients, and medulloblastoma constitutes 20% of them. Currently, the treatment is risk-adapted. Maximum surgical resection is recommended, always followed by chemotherapy and neuroaxis radiotherapy. In spite of the improving survival rate, survivors succumb to treatment-induced side effects. To reduce toxic effects, molecular-targeted treatment is proposed. Medulloblastoma research is very robust, and new articles on the subject are published daily. In the current review we have tried to bring together molecular pathophysiology of the neoplasm and current pathological classification, thus making an effort to relate tumor biology and the histological picture.

YB-1 is elevated in medulloblastoma and drives proliferation in Sonic hedgehog-dependent cerebellar granule neuron progenitor cells and medulloblastoma cells

Postnatal proliferation of cerebellar granule neuron precursors (CGNPs), proposed cells of origin for the SHH-associated subgroup of medulloblastoma, is driven by Sonic hedgehog (Shh) and insulin-like growth factor (IGF) in the developing cerebellum. Shh induces the oncogene Yes-associated protein (YAP), which drives IGF2 expression in CGNPs and mouse Shh-associated medulloblastomas. To determine how IGF2 expression is regulated downstream of YAP, we carried out an unbiased screen for transcriptional regulators bound to IGF2 promoters. We report that Y-box binding protein-1 (YB-1), an onco-protein regulating transcription and translation, binds to IGF2 promoter P3. We observed that YB-1 is upregulated across human medulloblastoma subclasses as well as in other varieties of pediatric brain tumors. Utilizing the cerebellar progenitor model for the Shh subgroup of medulloblastoma in mice, we show for the first time that YB-1 is induced by Shh in CGNPs. Its expression is YAP-dependent and it is required for IGF2 expression in CGNPs. Finally, both gain-of function and loss-of-function experiments reveal that YB-1 activity is required for sustaining CGNP and medulloblastoma cell (MBC) proliferation. Collectively, our findings describe a novel role for YB-1 in driving proliferation in the developing cerebellum and MBCs and they identify the SHH:YAP:YB1:IGF2 axis as a powerful target for therapeutic intervention in medulloblastomas.

Histology and molecular aspects of central neurocytoma

Central neurocytoma (CN) is a well-differentiated tumor of neural cells occurring within the ventricles. It is composed of monomorphic cells with round, regular nuclei within clear cytoplasm and must be distinguished from other clear cell tumors. Immunohistochemical markers of CN that aid in diagnosis include synaptophysin and neuronal nuclear antigen. The molecular biology of these tumors is becoming increasingly elucidated, particularly with the use of microarray analyses. Several oncogenic pathways have been suggested by these studies. Although progress continues to be made, knowledge of CN has yet to dictate targeted therapies in treating patients with these tumors.

SRC inhibition represents a potential therapeutic strategy in liposarcoma

Liposarcomas (LS) are the most common malignant mesenchymal tumors, with an overall long-term mortality rate of 60%. LS comprise three major subtypes, i.e., well-differentiated/dedifferentiated liposarcoma (WDLS/DDLS), myxoid/round cell liposarcoma (MLS) and pleomorphic liposarcoma (PLS). Aiming at the preclinical identification of novel therapeutic options, we here investigate the functional significance of SRC in primary human LS and in LS-derived cell lines. Immunohistochemical and Western blot analyses reveal relevant levels of activated p-(Tyr416)-SRC in LS of the different subtypes with particular activation in MLS and PLS. Dysregulation of the SRC modifiers CSK and PTP1B was excluded as major reason for the activation of the kinase. Consistent siRNA-mediated knockdown of SRC or inhibition by the SRC inhibitor Dasatinib led to decreased proliferation of LS cell lines of the different subtypes, with MLS cells reacting particularly sensitive in MTT assays. Flow cytometric analyses revealed that this effect was due to a significant decrease in mitotic activity and an induction of apoptosis. SRC inhibition by Dasatinib resulted in dephosphorylation of SRC itself, its interacting partners FAK and IGF-IR as well as its downstream target AKT. Consistent with a particular role of SRC in cell motility, Dasatinib reduced the migratory and invasive potential of MLS cells in Boyden chamber and Matrigel chamber assays. In summary, we provide evidence that SRC activation plays an important role in LS biology and therefore represents a potential therapeutic target, particularly in MLS and PLS.

Estrogen Receptor-β Up-Regulates IGF1R Expression and Activity to Inhibit Apoptosis and Increase Growth of Medulloblastoma

Medulloblastoma (Med) is the most common malignant brain tumor in children. The role of ESR2 [estrogen receptor (ER)-β] in promoting Med growth was comprehensively examined in three in vivo models and human cell lines. In a novel Med ERβ-null knockout model developed by crossing Esr2(-/-) mice with cerebellar granule cell precursor specific Ptch1 conditional knockout mice, the tumor growth rate was significantly decreased in males and females. The absence of Esr2 resulted in increased apoptosis, decreased B-cell lymphoma 2 (BCL2), and IGF-1 receptor (IGF1R) expression, and decreased levels of active MAPKs (ERK1/2) and protein kinase B (AKT). Treatment of Med in Ptch1(+/-) Trp53(-/-) mice with the antiestrogen chemotherapeutic drug Faslodex significantly increased symptom-free survival, which was associated with increased apoptosis and decreased BCL2 and IGF1R expression and signaling. Similar effects were also observed in nude mice bearing D283Med xenografts. In vitro studies in human D283Med cells metabolically stressed by glutamine withdrawal found that 17β-estradiol and the ERβ selective agonist 2,3-bis(4-hydroxyphenyl)-propionitrile dose dependently protected Med cells from caspase-3-dependent cell death. Those effects were associated with increased phosphorylation of IGF1R, long-term increases in ERK1/2 and AKT signaling, and increased expression of IGF-1, IGF1R, and BCL2. Results of pharmacological experiments revealed that the cytoprotective actions of estradiol were dependent on ERβ and IGF1R receptor tyrosine kinase activity and independent of ERα and G protein-coupled estrogen receptor 1 (G protein coupled receptor 30). The presented results demonstrate that estrogen promotes Med growth through ERβ-mediated increases in IGF1R expression and activity, which induce cytoprotective mechanisms that decrease apoptosis.

Coagulation and angiogenic gene expression profiles are defined by molecular subgroups of medulloblastoma: evidence for growth factor-thrombin cross-talk

BACKGROUND

The coagulation system becomes activated during progression and therapy of high-grade brain tumors. Triggering tissue factor (F3/TF) and thrombin receptors (F2R/PAR-1) may influence the vascular tumor microenvironment and angiogenesis irrespective of clinically apparent thrombosis. These processes are poorly understood in medulloblastoma (MB), in which diverse oncogenic pathways define at least four molecular disease subtypes (WNT, SHH, Group 3 and Group 4). We asked whether there is a link between molecular subtype and the network of vascular regulators expressed in MB.

METHODS

Using R2 microarray analysis and visualization platform, we mined MB datasets for differential expression of vascular (coagulation and angiogenesis)-related genes, and explored their link to known oncogenic drivers. We evaluated the functional significance of this link in DAOY cells in vitro following growth factor and thrombin stimulation.

RESULTS

The coagulome and angiome differ across MB subtypes. F3/TF and F2R/PAR-1 mRNA expression are upregulated in SHH tumors and correlate with higher levels of hepatocyte growth factor receptor (MET). Cultured DAOY (MB) cells exhibit an up-regulation of F3/TF and F2R/PAR-1 following combined SHH and MET ligand (HGF) treatment. These factors cooperate with thrombin, impacting the profile of vascular regulators, including interleukin 1β (IL1B) and chondromodulin 1 (LECT1).

CONCLUSIONS

Coagulation pathway sensors (F3/TF, F2R/PAR-1) are expressed in MB in a subtype-specific manner, and may be functionally linked to SHH and MET circuitry. Thus coagulation system perturbations may elicit subtype/context-specific changes in vascular and cellular responses in MB.

The anti-aging and tumor suppressor protein Klotho enhances differentiation of a human oligodendrocytic hybrid cell line

Klotho functions as an aging suppressor, which, in mice, extends lifespan when overexpressed and accelerates development of aging-like phenotypes when disrupted. Klotho is mainly expressed in brain and kidney and is secreted into the serum and CSF. We have previously shown that Klotho is reduced in brains of old monkeys, rats, and mice. We further reported the ability of Klotho to enhance oligodendrocyte differentiation and myelination. Here, we examined the signaling pathways induced by Klotho in MO3.13, a human oligodendrocytic hybrid cell line. We show that exogenous Klotho affects the ERK and Akt signaling pathways, decreases the proliferative abilities and enhances differentiation of MO3.13 cells. Furthermore, microarray analysis of Klotho-treated MO3.13 cells reveals a massive change in gene expression with 80 % of the differentially expressed genes being downregulated. Using gene set enrichment analysis, we predicted potential transcription factors involved in regulating Klotho-treated MO3.13 cells and found that these cells are highly enriched in the gene sets, that are similarly observed in cancer, cardiovascular disease, stress, aging, and hormone-related chemical and genetic perturbations. Since Klotho is downregulated in all brain tumors tested to date, enhancing Klotho has therapeutic potential for treating brain and other malignancies.

The emerging role of insulin and insulin-like growth factor signaling in cancer stem cells

Cancer cells frequently exploit the IGF signaling, a fundamental pathway mediating development, cell growth, and survival. As a consequence, several components of the IGF signaling are deregulated in cancer and sustain cancer progression. However, specific targeting of IGF-IR in humans has resulted efficacious only in small subsets of cancers, making researches wondering whether IGF system targeting is still worth pursuing in the clinical setting. Although no definite answer is yet available, it has become increasingly clear that other components of the IGF signaling pathway, such as IR-A, may substitute for the lack of IGF-IR, and induce cancer resistance and/or clonal selection. Moreover, accumulating evidence now indicates that IGF signaling is a central player in the induction/maintenance of epithelial mesenchymal transition (EMT) and cell stemness, two strictly related programs, which play a key role in metastatic spread and resistance to cancer treatments. Here we review the evidences indicating that IGF signaling enhances the expression of transcription factors implicated in the EMT program and has extensive cross-talk with specific pathways involved in cell pluripotency and stemness maintenance. In turn, EMT and cell stemness activate positive feed-back mechanisms causing up-regulation of various IGF signaling components. These findings may have novel translational implications.

Generating new neurons to circumvent your fears: the role of IGF signaling

Extinction of fear memory is a particular form of cognitive function that is of special interest because of its involvement in the treatment of anxiety and mood disorders. Based on recent literature and our previous findings (EMBO J 30(19):4071-4083, 2011), we propose a new hypothesis that implies a tight relationship among IGF signaling, adult hippocampal neurogenesis and fear extinction. Our proposed model suggests that fear extinction-induced IGF2/IGFBP7 signaling promotes the survival of neurons at 2-4 weeks old that would participate in the discrimination between the original fear memory trace and the new safety memory generated during fear extinction. This is also called "pattern separation", or the ability to distinguish similar but different cues (e.g., context). To understand the molecular mechanisms underlying fear extinction is therefore of great clinical importance.

PID1 (NYGGF4), a new growth-inhibitory gene in embryonal brain tumors and gliomas

PURPOSE

We present here the first report of PID1 (Phosphotyrosine Interaction Domain containing 1; NYGGF4) in cancer. PID1 was identified in 2006 as a gene that modulates insulin signaling and mitochondrial function in adipocytes and muscle cells.

EXPERIMENTAL DESIGN AND RESULTS

Using four independent medulloblastoma datasets, we show that mean PID1 mRNA levels were lower in unfavorable medulloblastomas (groups 3 and 4, and anaplastic histology) compared with favorable medulloblastomas (SHH and WNT groups, and desmoplastic/nodular histology) and with fetal cerebellum. In two large independent glioma datasets, PID1 mRNA was lower in glioblastomas (GBM), the most malignant gliomas, compared with other astrocytomas, oligodendrogliomas and nontumor brains. Neural and proneural GBM subtypes had higher PID1 mRNA compared with classical and mesenchymal GBM. Importantly, overall survival and radiation-free progression-free survival were longer in medulloblastoma patients whose tumors had higher PID1 mRNA (univariate and multivariate analyses). Higher PID1 mRNA also correlated with longer overall survival in patients with glioma and GBM. In cell culture, overexpression of PID1 inhibited colony formation in medulloblastoma, atypical teratoid rhabdoid tumor (ATRT), and GBM cell lines. Increasing PID1 also increased cell death and apoptosis, inhibited proliferation, induced mitochondrial depolaization, and decreased serum-mediated phosphorylation of AKT and ERK in medulloblastoma, ATRT, and/or GBM cell lines, whereas siRNA to PID1 diminished mitochondrial depolarization.

CONCLUSIONS

These data are the first to link PID1 to cancer and suggest that PID1 may have a tumor inhibitory function in these pediatric and adult brain tumors.

Multiple tumor types including leiomyoma and Wilms tumor in a patient with Gorlin syndrome due to 9q22.3 microdeletion encompassing the PTCH1 and FANC-C loci

Gorlin syndrome or nevoid basal cell carcinoma syndrome (NBCCS) is an autosomal dominant condition mainly characterized by the development of mandibular keratocysts which often have their onset during the second decade of life and/or multiple basal cell carcinoma (BCC) normally arising during the third decade. Cardiac and ovarian fibromas can be found. Patients with NBCCS develop the childhood brain malignancy medulloblastoma (now often called primitive neuro-ectodermal tumor [PNET]) in 5% of cases. The risk of other malignant neoplasms is not clearly increased, although lymphoma and meningioma can occur in this condition. Wilms tumor has been mentioned in the literature four times. We describe a patient with a 10.9 Mb 9q22.3 deletion spanning 9q22.2 through 9q31.1 that includes the entire codifying sequence of the gene PTCH1, with Wilms tumor, multiple neoplasms (lung, liver, mesenteric, gastric and renal leiomyomas, lung typical carcinoid tumor, adenomatoid tumor of the pleura) and a severe clinical presentation. We propose including leiomyomas among minor criteria of the NBCCS.

Identification of a neuronal transcription factor network involved in medulloblastoma development

BACKGROUND

Medulloblastomas, the most frequent malignant brain tumours affecting children, comprise at least 4 distinct clinicogenetic subgroups. Aberrant sonic hedgehog (SHH) signalling is observed in approximately 25% of tumours and defines one subgroup. Although alterations in SHH pathway genes (e.g. PTCH1, SUFU) are observed in many of these tumours, high throughput genomic analyses have identified few other recurring mutations. Here, we have mutagenised the Ptch+/- murine tumour model using the Sleeping Beauty transposon system to identify additional genes and pathways involved in SHH subgroup medulloblastoma development.

RESULTS

Mutagenesis significantly increased medulloblastoma frequency and identified 17 candidate cancer genes, including orthologs of genes somatically mutated (PTEN, CREBBP) or associated with poor outcome (PTEN, MYT1L) in the human disease. Strikingly, these candidate genes were enriched for transcription factors (p=2x10-5), the majority of which (6/7; Crebbp, Myt1L, Nfia, Nfib, Tead1 and Tgif2) were linked within a single regulatory network enriched for genes associated with a differentiated neuronal phenotype. Furthermore, activity of this network varied significantly between the human subgroups, was associated with metastatic disease, and predicted poor survival specifically within the SHH subgroup of tumours. Igf2, previously implicated in medulloblastoma, was the most differentially expressed gene in murine tumours with network perturbation, and network activity in both mouse and human tumours was characterised by enrichment for multiple gene-sets indicating increased cell proliferation, IGF signalling, MYC target upregulation, and decreased neuronal differentiation.

CONCLUSIONS

Collectively, our data support a model of medulloblastoma development in SB-mutagenised Ptch+/- mice which involves disruption of a novel transcription factor network leading to Igf2 upregulation, proliferation of GNPs, and tumour formation. Moreover, our results identify rational therapeutic targets for SHH subgroup tumours, alongside prognostic biomarkers for the identification of poor-risk SHH patients.

Synergism between Hedgehog-GLI and EGFR signaling in Hedgehog-responsive human medulloblastoma cells induces downregulation of canonical Hedgehog-target genes and stabilized expression of GLI1

Aberrant activation of Hedgehog (HH) signaling has been identified as a key etiologic factor in many human malignancies. Signal strength, target gene specificity, and oncogenic activity of HH signaling depend profoundly on interactions with other pathways, such as epidermal growth factor receptor-mediated signaling, which has been shown to cooperate with HH/GLI in basal cell carcinoma and pancreatic cancer. Our experimental data demonstrated that the Daoy human medulloblastoma cell line possesses a fully inducible endogenous HH pathway. Treatment of Daoy cells with Sonic HH or Smoothened agonist induced expression of GLI1 protein and simultaneously prevented the processing of GLI3 to its repressor form. To study interactions between HH- and EGF-induced signaling in greater detail, time-resolved measurements were carried out and analyzed at the transcriptomic and proteomic levels. The Daoy cells responded to the HH/EGF co-treatment by downregulating GLI1, PTCH, and HHIP at the transcript level; this was also observed when Amphiregulin (AREG) was used instead of EGF. We identified a novel crosstalk mechanism whereby EGFR signaling silences proteins acting as negative regulators of HH signaling, as AKT- and ERK-signaling independent process. EGFR/HH signaling maintained high GLI1 protein levels which contrasted the GLI1 downregulation on the transcript level. Conversely, a high-level synergism was also observed, due to a strong and significant upregulation of numerous canonical EGF-targets with putative tumor-promoting properties such as MMP7, VEGFA, and IL-8. In conclusion, synergistic effects between EGFR and HH signaling can selectively induce a switch from a canonical HH/GLI profile to a modulated specific target gene profile. This suggests that there are more wide-spread, yet context-dependent interactions, between HH/GLI and growth factor receptor signaling in human malignancies.

Mechanisms linking obesity and cancer

The incidence of obesity in US adults has been steadily increasing over the past few decades. Many comorbidities associated with obesity have been well-established such as type 2 diabetes and cardiovascular diseases. However, more recently an epidemiological relationship between obesity and the prevalence of a variety of cancers has also been uncovered. The shift of the paradigm surrounding white adipose tissue function from purely an energy storage tissue, to one that has both endocrine and metabolic relevance, has led to several mechanisms implicated in how obesity drives cancer prevalence and cancer deaths. Currently, there are four categories into which these mechanisms fall - increased lipids and lipid signaling, inflammatory responses, insulin resistance, and adipokines. In this review, we examine each of these categories and the mechanisms through which they drive cancer pathogenesis. Understanding the relationship(s) between obesity and cancer and especially the nodal points of control in these cascades will be essential in developing effective therapeutics or interventions for combating this deadly combination. This article is part of a Special Issue entitled Lipid Metabolism in Cancer.

Expression patterns of insulin-like growth factor binding protein isoforms in medulloblastoma subtypes and clinical correlation

BACKGROUND

Insulin-like growth factor binding proteins (IGFBPs) are known to be differentially expressed in brain tumours. The role of some IGFBPs in malignant CNS tumours, except glioblastoma, is unknown. We evaluated the protein expression of 3 IGFBP isoforms (IGFBP-2, -3, -5) in medulloblastoma and correlated them with histological subtypes and clinical parameters.

METHODS

The expression of IGFBP-2, -3 and -5 was analysed in 67 samples of medulloblastoma by immunohistochemistry and correlated with histological subtypes and patient prognosis.

RESULTS

IGFBP-3 expression was seen in 37.3% of cases and IGFBP-5 expression in 80.6% of cases. IGFBP-2 expression was totally absent in medulloblastoma. The extent of IGFBP-3 expression was higher in anaplastic when compared to classical and desmoplastic subtypes (p < 0.05). IGFBP-5 expression was significantly higher in classical and anaplastic subtypes when compared to desmoplastic medulloblastoma (p < 0.05). No influence of IGFBPs on survival was noted.

CONCLUSIONS

This is the first study to report expression of 3 cancer-related biomarkers - IGFBP-2, -3, -5 in medulloblastoma. Significantly higher extents of expression of IGFBP-3 in large cell variant and IGFBP-5 in classical and anaplastic subtypes suggest a plausible role of these molecules in specific molecular pathways of medulloblastoma.

Mismatch repair deficiency: a temozolomide resistance factor in medulloblastoma cell lines that is uncommon in primary medulloblastoma tumours

BACKGROUND

Tumours are responsive to temozolomide (TMZ) if they are deficient in O(6)-methylguanine-DNA methyltransferase (MGMT), and mismatch repair (MMR) proficient.

METHODS

The effect of TMZ on medulloblastoma (MB) cell killing was analysed with clonogenic survival assays. Expression of DNA repair genes and enzymes was investigated using microarrays, western blot, and immunohistochemistry. DNA sequencing and promoter methylation analysis were employed to investigate the cause of loss of the expression of MMR gene MLH1.

RESULTS

Temozolomide exhibited potent cytotoxic activity in D425Med (MGMT deficient, MLH1 proficient; IC(50)=1.7 μM), moderate activity against D341Med (MGMT proficient, MLH1 deficient), and DAOY MB cells (MGMT proficient, MLH1 proficient). MGMT inhibitor O(6)-benzylguanine sensitised DAOY, but not D341Med cells to TMZ. Of 12 MB cell lines, D341Med, D283Med, and 1580WÜ cells exhibited MMR deficiency due to MLH1 promoter hypermethylation. DNA sequencing of these cells provided no evidence for somatic genetic alterations in MLH1. Expression analyses of MMR and MGMT in MB revealed that all patient specimens (n=74; expression array, n=61; immunostaining, n=13) are most likely MMR proficient, whereas some tumours had low MGMT expression levels (according to expression array) or were totally MGMT deficient (3 out of 13 according to immunohistochemistry).

CONCLUSION

A subset of MB may respond to TMZ as some patient specimens are MGMT deficient, and tumours appear to be MMR proficient.

Analysis of the role of Igf2 in adrenal tumour development in transgenic mouse models

Adrenal cortical carcinomas (ACC) are rare but aggressive tumours associated with poor prognosis. The two most frequent alterations in ACC in patients are overexpression of the growth factor IGF2 and constitutive activation of Wnt/β-catenin signalling. Using a transgenic mouse model, we have previously shown that constitutive active β-catenin is a bona fide adrenal oncogene. However, although all these mice developed benign adrenal hyperplasia, malignant progression was infrequent, suggesting that secondary genetic events were required for aggressive tumour development. In the present paper, we have tested IGF2 oncogenic properties by developing two distinct transgenic mouse models of Igf2 overexpression in the adrenal cortex. Our analysis shows that despite overexpression levels ranging from 7 (basal) to 87 (ACTH-induced) fold, Igf2 has no tumour initiating potential in the adrenal cortex. However, it induces aberrant accumulation of Gli1 and Pod1-positive progenitor cells, in a hedgehog-independent manner. We have also tested the hypothesis that Igf2 may cooperate with Wnt signalling by mating Igf2 overexpressing lines with mice that express constitutive active β-catenin in the adrenal cortex. We show that the combination of both alterations has no effect on tumour phenotype at stages when β-catenin-induced tumours are benign. However, there is a mild promoting effect at later stages, characterised by increased Weiss score and proliferation. Formation of malignant tumours is nonetheless a rare event, even when Igf2 expression is further increased by ACTH treatment. Altogether these experiments suggest that the growth factor IGF2 is a mild contributor to malignant adrenocortical tumourigenesis.

Extra- and intracellular imaging of human matrix metalloprotease 11 (hMMP-11) with a cell-penetrating FRET substrate

Matrix metalloprotease 11 (MMP-11), a protease associated with invasion and aggressiveness of cancerous tissue, was postulated as a prognostic marker for pancreatic, breast, and colon cancer patients. Expression analysis, however, did not reveal localization and regulation of this protease. Thus, cellular tools for the visualization of MMP-11 are highly desirable to monitor presence and activity and to elucidate the functional role of MMP-11. Therefore, fluorescein-Dabcyl-labeled Foerster resonance energy transfer (FRET) substrates were developed. The design focused on enhanced peptide binding to human MMP-11, employing an unusual amino acid for the specificity pocket P1'. The addition of several arginines resulted in a cell-permeable FRET substrate SM-P124 (Ac-GRRRK(Dabcyl)-GGAANC(MeOBn)RMGG-fluorescein). In vitro evaluation of SM-P124 with human MMP-11 showed a 25-fold increase of affinity (k(cat)/K(m) = 9.16 × 10(3) m(-1) s(-1), K(m) = 8 μm) compared with previously published substrates. Incubation of pancreatic adenocarcinoma cell line MIA PaCa-2 and mamma adenocarcinoma cell line MCF-7 with the substrate SM-P124 (5 μm) indicated intra- and extracellular MMP-11 activity. A negative control cell line (Jurkat) showed no fluorescent signal either intra- or extracellularly. Negative control FRET substrate SM-P123 produced only insignificant extracellular fluorescence without any intracellular fluorescence. SM-P124 therefore enabled intra- and extracellular tracking of MMP-11-overexpressing cancers such as pancreatic and breast adenocarcinoma and might contribute to the understanding of the activation pathways leading to MMP-11-mediated invasive processes.

Promoter-specific expression and imprint status of marsupial IGF2

In mice and humans, IGF2 has multiple promoters to maintain its complex tissue- and developmental stage-specific imprinting and expression. IGF2 is also imprinted in marsupials, but little is known about its promoter region. In this study, three IGF2 transcripts were isolated from placental and liver samples of the tammar wallaby, Macropus eugenii. Each transcript contained a unique 5' untranslated region, orthologous to the non-coding exons derived from promoters P1–P3 in the human and mouse IGF2 locus. The expression of tammar IGF2 was predominantly from the P2 promoter, similar to humans. Expression of IGF2 was higher in pouch young than in the adult and imprinting was highly tissue and developmental-stage specific. Interestingly, while IGF2 was expressed throughout the placenta, imprinting seemed to be restricted to the vascular, trilaminar region. In addition, IGF2 was monoallelically expressed in the adult mammary gland while in the liver it switched from monoalleleic expression in the pouch young to biallelic in the adult. These data suggest a complex mode of IGF2 regulation in marsupials as seen in eutherian mammals. The conservation of the IGF2 promoters suggests they originated before the divergence of marsupials and eutherians, and have been selectively maintained for at least 160 million years.

Gene expression profiling of neural stem cells and their neuronal progeny reveals IGF2 as a regulator of adult hippocampal neurogenesis

Neural stem cells (NSCs) generate neurons throughout life in the hippocampal dentate gyrus (DG). How gene expression signatures differ among NSCs and immature neurons remains largely unknown. We isolated NSCs and their progeny in the adult DG using transgenic mice expressing a GFP reporter under the control of the Sox2 promoter (labeling NSCs) and transgenic mice expressing a DsRed reporter under the control of the doublecortin (DCX) promoter (labeling immature neurons). Transcriptome analyses revealed distinct gene expression profiles between NSCs and immature neurons. Among the genes that were expressed at significantly higher levels in DG NSCs than in immature neurons was the growth factor insulin-like growth factor 2 (IGF2). We show that IGF2 selectively controls proliferation of DG NSCs in vitro and in vivo through AKT-dependent signaling. Thus, by gene expression profiling of NSCs and their progeny, we have identified IGF2 as a novel regulator of adult neurogenesis.

Transcriptional targeting of glioblastoma by diphtheria toxin-A driven by both H19 and IGF2-P4 promoters

BACKGROUND

The H19-IGF2 locus is either highly expressed and/or shows aberrant allelic pattern of expression in a large array of human cancers, while rarely expressed in the corresponding normal tissue. Preclinical, clinical studies and human compassionate using a DNA plasmid containing H19 and/or IGF2-P4 regulatory sequences that drive the expression of an intracellular toxin [diphtheria toxin A-fragment (DTA)] have demonstrated promising results in several types of carcinomas. Recently we reported that a single construct that expresses DTA under the control of both H19 and IGF2 P4 promoters showed superior efficacy in vitro as well as in vivo, in comparison to a single promoter construct in bladder carcinoma. Here we extended this approach to glioblastoma and tested the antitumor efficacy of the double promoter DTA-expressing vector (H19-DTA-P4-DTA) in vitro as well as in heterotopic animal model. H19 gene expression was tested by in-situ hybridization (ISH) and by quantitative Real-Time PCR (qRT-PCR) in samples of diffuse glioma.

METHODS

IGF2-P4 gene expression was tested by qRT-PCR as well.

RESULTS

Both H19 and IGF2-P4 transcripts were highly expressed in high grade gliomas. Furthermore, significant H19 expression in other types of primary brain tumors as well as in brain metastases was detected by ISH. Both A172 and U87 human glioblastoma cell lines showed high expression of IGF2-P4 while the A172 cell line showed high expression of H19 RNA as well. H19-DTA-P4-DTA exhibited superior cytotoxic activity compared to the single promoter expression vectors, in U87 and A172 glioblastoma cell lines in vitro and showed antitumoral efficacy in heterotopic glioblastoma animal model.

CONCLUSIONS

Our findings indicate antitumoral efficacy against glioblastoma of the targeted double promoter vector H19-DTA-P4-DTA, both in-vitro and in-vivo. Thus, its test in orthotopic animal model of glioblastoma as well as in clinical trials is warranted.

An essential role for p38 MAPK in cerebellar granule neuron precursor proliferation

Development of the cerebellum occurs postnatally and is marked by a rapid proliferation of cerebellar granule neuron precursors (CGNPs). CGNPs are the cells of origin for SHH-driven medulloblastoma, the most common malignant brain tumor in children. Here, we investigated the role of ERK, JNK, and p38 mitogen-activated protein kinases in CGNP proliferation. We found high levels of p38α in proliferating CGNPs. Concomitantly, members of the p38 pathway, such as ASK1, MKK3 and ATF-2, were also elevated. Inhibition of the Shh pathway or CGNP proliferation blunts p38α levels, irrespective of Shh treatment. Strikingly, p38α levels were high in vivo in the external granule layer of the postnatal cerebellum, Shh-dependent mouse medulloblastomas and human medulloblastomas of the SHH subtype. Finally, knocking down p38α by short hairpin RNA-carrying lentiviruses as well as the pharmacologically inhibiting of its kinase activity caused a marked decrease in CGNP proliferation, underscoring its requirement for Shh-dependent proliferation in CGNPs. The inhibition of p38α also caused a decrease in Gli1 and N-myc transcript levels, consistent with reduced proliferation. These findings suggest p38 inhibition as a potential way to increase the efficacy of treatments available for malignancies associated with deregulated SHH signaling, such as basal cell carcinoma and medulloblastoma.

Proper cerebellar development requires expression of β1-integrin in Bergmann glia, but not in granule neurons

β1-class integrins play essential roles both in developmental biology as well as in cancer. Particularly, a Nestin-driven deletion of β1-integrin receptors results in severe abnormalities of brain development including a laminar disorganization of cerebellar granule neurons. However, since Nestin is expressed in all kinds of neural precursors, these data do not allow conclusions to be drawn about the role of β1-integrins in distinct neuronal and glial cell types. By generating conditional knockout mice using granule cell-specific Math1-promoter sequences, we show here that the expression of β1-integrins in granule neurons is dispensable for the development of the cerebellum. Also, deletion of β1-integrin from tumors that arise in a mouse model of granule cell precursor-derived medulloblastoma did not result in a significant survival benefit. Last, expression levels of β1-integrin in human medulloblastoma samples did not predict patient's outcome. However, a β1-integrin knockout using hGFAP-promoter sequences led to cerebellar hypoplasia, inappropriate positioning of Bergmann glia cells in the molecular layer, undirected outgrowth of radial glia fibers, and granule cell ectopia. We therefore conclude that β1-integrin expression in cerebellar granule neurons is not essential during normal development or medulloblastoma formation. In fact, it is the expression of β1-integrin in glia that is crucial for the proper development of the cerebellar cortex.

Canonical and noncanonical Hedgehog/GLI signaling in hematological malignancies

The highly conserved Hedgehog/GLI signaling pathway regulates multiple aspects of embryonic development and plays a decisive role in tissue homeostasis and the hematopoietic system by controlling cell fate decisions, stem cell self-renewal, and activation. Loss of negative control of Hedgehog signaling contributes to tumor pathogenesis and progression. In the classical view of canonical Hedgehog signaling, Hedgehog ligand binding to its receptor Patched culminates in the activation of the key pathway activator Smoothened, followed by activation of the GLI transcription factors. Its essential function and druggability render Smoothened well suited to therapeutic intervention. However, recent evidence suggests a critical role of Smoothened-independent regulation of GLI activity by several other signaling pathways including the PI3K/AKT and RAS/RAF/MEK/ERK axes. In addition, the contribution of canonical Hedgehog signaling via Patched and Smoothened to normal and malignant hematopoiesis has been the subject of recent controversies. In this review, we discuss the current understanding and controversial findings of canonical and noncanonical GLI activation in hematological malignancies in light of the current therapeutic strategies targeting the Hedgehog pathway.

Oncogenic YAP promotes radioresistance and genomic instability in medulloblastoma through IGF2-mediated Akt activation

Radiation therapy remains the standard of care for many cancers, including the malignant pediatric brain tumor medulloblastoma. Radiation leads to long-term side effects, while radio-resistance contributes to tumor recurrence. Radio-resistant medulloblastoma cells occupy the peri-vascular niche. They express Yes-associated protein (YAP), a Sonic hedgehog (Shh) target markedly elevated in Shh-driven medulloblastomas. Here we report that YAP accelerates tumor growth and confers radio-resistance, promoting ongoing proliferation after radiation. YAP activity enables cells to enter mitosis with un-repaired DNA through driving IGF2 expression and Akt activation, resulting in ATM/Chk2 inactivation and abrogation of cell cycle checkpoints. Our results establish a central role for YAP in counteracting radiation-based therapies and driving genomic instability, and indicate the YAP/IGF2/Akt axis as a therapeutic target in medulloblastoma.

Neurogenesis at the brain-cerebrospinal fluid interface

Cerebral cortical progenitor cells can be classified into several different types, and each progenitor type integrates cell-intrinsic and cell-extrinsic cues to regulate neurogenesis. On one hand, cell-intrinsic mechanisms that depend upon appropriate apical-basal polarity are established by adherens junctions and apical complex proteins and are particularly important in progenitors with apical processes contacting the lateral ventricle. The apical protein complexes themselves are concentrated at the ventricular surface, and apical complex proteins regulate mitotic spindle orientation and cell fate. On the other hand, remarkably little is known about how cell-extrinsic cues signal to progenitors and couple with cell-intrinsic mechanisms to instruct neurogenesis. Recent research shows that the cerebrospinal fluid, which contacts apical progenitors at the ventricular surface and bathes the apical complex of these cells, provides growth- and survival-promoting cues for neural progenitor cells in developing and adult brain. This review addresses how the apical-basal polarity of progenitor cells regulates cell fate and allows progenitors to sample diffusible signals distributed by the cerebrospinal fluid. We also review several classes of signaling factors that the cerebrospinal fluid distributes to the developing brain to instruct neurogenesis.

Severe alterations of cerebellar cortical development after constitutive activation of Wnt signaling in granule neuron precursors

The Wnt/β-catenin signaling pathway plays crucial roles in early hindbrain formation, and its constitutive activity is associated with a subset of human medulloblastoma, a malignant childhood tumor of the posterior fossa. However, the precise function of Wnt/β-catenin signaling during cerebellar development is still elusive. We generated Math1-cre::Apc(Fl/Fl) mice with a conditional knockout for the Adenomatosis polyposis coli (Apc) gene that displayed a constitutive activity of Wnt/β-catenin signaling in cerebellar granule neuron precursors. Such mice showed normal survival without any tumor formation but had a significantly smaller cerebellum with a complete disruption of its cortical histoarchitecture. The activation of the Wnt/β-catenin signaling pathway resulted in a severely inhibited proliferation and premature differentiation of cerebellar granule neuron precursors in vitro and in vivo. Mutant mice hardly developed an internal granular layer, and layering of Purkinje neurons was disorganized. Clinically, these mice presented with significantly impaired motor coordination and ataxia. In summary, we conclude that cerebellar granule neurons essentially require appropriate levels of Wnt signaling to balance their proliferation and differentiation.

Expression of BARHL1 in medulloblastoma is associated with prolonged survival in mice and humans

Medulloblastoma is the most common malignant brain tumor in childhood, and development of targeted therapies is highly desired. Although the molecular mechanisms of malignant transformation are not fully understood, it is known that medulloblastomas may arise from cerebellar granule neuron precursors. The homeodomain transcription factor Barhl1 is known to regulate migration and survival of granule cell precursors, but its functional role in medulloblastoma is unknown. We show here that the expression of BARHL1 is significantly upregulated during human cerebellar development and in human medulloblastoma samples as compared with the normal adult cerebellum. We also detected high levels of Barhl1 expression in medulloblastomas of Math1-cre:SmoM2 mice, a mouse model for Sonic hedgehog-associated medulloblastomas that we developed previously. To investigate Barhl1 function in vivo during tumor development, we generated Barhl1(-/-)Math1-cre:SmoM2 mice. Interestingly, tumors that developed in these mice displayed increased mitotic activity and decreased neuronal differentiation. Moreover, survival of these mice was significantly decreased. Similarly, low expression of BARHL1 in human medulloblastoma cases was associated with a less favorable prognosis for patients. These results suggest that the expression of Barhl1 decelerates tumor growth both in human and in murine medulloblastomas and should be further investigated with respect to potential implications for individualized therapeutic strategies.