The different role of Notch1 and Notch2 in astrocytic gliomas

RBM8A Promotes Glioblastoma Growth and Invasion Through the Notch/STAT3 Pathway

Background

Glioblastoma (GBM) is a prevalent brain malignancy with an extremely poor prognosis, which is attributable to its invasive biological behavior. The RNA-binding motif protein 8A (RBM8A) has different effects on various human cancers. However, the role of RBM8A in GBM progression remains unclear.

Methods

We investigated the expression levels of RBM8A in 94 GBM patients and explored the correlation between RBM8A expression and patient prognosis. Using in vitro and in vivo assays, combined with GBM sequencing data from the Cancer Genome Atlas (TCGA) and the Chinese Glioma Genome Atlas (CGGA), we examined whether and how RBM8A contributes to GBM progression.

Results

RBM8A was up-regulated in GBM tissues, and its higher expression correlated with worse prognosis. Knockdown of RBM8A inhibited GBM progression and invasion ability both in vitro and in vivo. On the contrary, overexpression of RBM8A promoted GBM progression and invasion ability. Enrichment analysis of differentially expressed genes in GBM data identified the Notch1/STAT3 network as a potential downstream target of RBM8A, and this was supported by molecular docking studies. Furthermore, we demonstrated that RBM8A regulates the transcriptional activity of CBF1. The γ-secretase inhibitor DAPT significantly reversed RBM8A-enhanced GBM cell proliferation and invasion, and was associated with down-regulation of p-STAT3 and Notch1 protein. Finally, the gene set variance analysis score of genes involved in regulation of the Notch1/STAT3 network by RBM8A showed good diagnostic and prognostic value for GBM.

Conclusions

RBM8A may promote GBM cell proliferation and migration by activating the Notch/STAT3 pathway in GBM cells, suggesting that RBM8A may serve as a potential therapeutic target for the treatment of GBM.

Oncolytic HSV-Infected Glioma Cells Activate NOTCH in Adjacent Tumor Cells Sensitizing Tumors to Gamma Secretase Inhibition

PURPOSE

To examine the effect of oncolytic herpes simplex virus (oHSV) on NOTCH signaling in central nervous system tumors.

EXPERIMENTAL DESIGN

Bioluminescence imaging, reverse phase protein array proteomics, fluorescence microscopy, reporter assays, and molecular biology approaches were used to evaluate NOTCH signaling. Orthotopic glioma-mouse models were utilized to evaluate effects in vivo.

RESULTS

We have identified that herpes simplex virus-1 (HSV-1; oncolytic and wild-type)-infected glioma cells induce NOTCH signaling, from inside of infected cells into adjacent tumor cells (inside out signaling). This was canonical NOTCH signaling, which resulted in activation of RBPJ-dependent transcriptional activity that could be rescued with dnMAML. High-throughput screening of HSV-1-encoded cDNA and miRNA libraries further uncovered that HSV-1 miR-H16 induced NOTCH signaling. We further identified that factor inhibiting HIF-1 (FIH-1) is a direct target of miR-H16, and that FIH-1 downregulation by virus encoded miR-H16 induces NOTCH activity. FIH-1 binding to Mib1 has been reported, but this is the first report that shows FIH-1 sequester Mib1 to suppress NOTCH activation. We observed that FIH-1 degradation induced NOTCH ligand ubiquitination and NOTCH activity. REMBRANDT and The Cancer Genome Atlas data analysis also uncovered a significant negative regulation between FIH-1 and NOTCH. Furthermore, combination of oHSV with NOTCH-blocking gamma secretase inhibitor (GSI) had a therapeutic advantage in two different intracranial glioma models treated with oncolytic HSV, without affecting safety profile of the virus in vivo.

CONCLUSIONS

To our knowledge this is the first report to identify impact of HSV-1 on NOTCH signaling and highlights the significance of combining oHSV and GSI for glioblastoma therapy.

Advancing towards Effective Glioma Therapy: MicroRNA Derived from Umbilical Cord Mesenchymal Stem Cells' Extracellular Vesicles

A glioma, especially a grade IV glioblastoma, is a malignant tumour with a poor prognosis despite growing medical advancements. Researchers have been looking for better and more effective treatments targeting the molecular pathways of gliomas due to glioblastomas’ ability to develop resistance to chemotherapies. Moreover, glioma stem cells (GSC) contribute to maintaining the glioma population, which benefits from its ability to self-renew and differentiate. Recent research has reported that through the introduction of umbilical cord mesenchymal stem cells (UCMSC) into glioma cells, the growth and development of the glioma cells can be downregulated. It has more currently been found out that UCMSC release extracellular vesicles (EVs) containing miRNA that are responsible for this phenomenon. Therefore, this review analyses literature to discuss all possible miRNAs contained within the UCMSC’s EVs and to elaborate on their molecular mechanisms in halting gliomas and GSC growth. This review will also include the challenges and limitations, to account for which more in vivo research is suggested. In conclusion, this review highlights how miRNAs contained within UCMSC’s EVs are able to downregulate multiple prominent pathways in the survival of gliomas.

Therapeutic Targeting of the Notch Pathway in Glioblastoma Multiforme

BACKGROUND

Glioblastoma (GBM) is the most common and deadly form of brain tumor. After standard treatment of resection, radiotherapy, and chemotherapy, the 5-year survival is <5%. In recent years, research has uncovered several potential targets within the Notch signaling pathway, which may lead to improved patient outcomes.

METHODS

A literature search was performed for articles containing the terms "Glioblastoma" and "Receptors, Notch" between 2003 and July 2015. Of the 62 articles retrieved, 46 met our criteria and were included in our review. Nine articles were identified from other sources and were subsequently included, leaving 55 articles reviewed.

RESULTS

Of the 55 articles reviewed, 47 used established human GBM cell lines. Seventeen articles used human GBM surgical samples. Forty-five of 48 articles that assessed Notch activity showed increased expression in GBM cell lines. Targeting the Notch pathway was carried out through Notch knockdown and overexpression and targeting δ-like ligand, Jagged, γ-secretase, ADAM10, ADAM17, and Mastermindlike protein 1. Arsenic trioxide, microRNAs, and several other compounds were shown to have an effect on the Notch pathway in GBM. Notch activity in GBM was also shown to be associated with hypoxia and certain cancer-related molecular pathways such as PI3K/AKT/mTOR and ERK/MAPK. Most articles concluded that Notch activity amplifies malignant characteristics in GBM and targeting this pathway can bring about amelioration of these effects.

CONCLUSIONS

Recent literature suggests targeting the Notch pathway has great potential for future therapies for GBM.

Molecular mechanism of Notch signaling with special emphasis on microRNAs: Implications for glioma

Glioma is the most aggressive primary brain tumor and is notorious for resistance to chemoradiotherapy. Although its associated mechanisms are still not completely understood, Notch signaling, an evolutionarily conserved pathway, appears to be the key processes involved. Nevertheless, its mechanisms are sophisticated, due to a variety of targets and signal pathways, especially microRNA. MicroRNAs, which are small noncoding regulatory RNA molecules, have been proposed as one of the key mechanisms in glioma pathogenesis. Among the known glioma associated microRNA, microRNA-129, microRNA-34 family, and microRNA-326 have been shown to influence the progress of glioma through Notch signaling. Evidence also indicates that recurrence is due to development or persistence of the glioma stem-like cells and active angiogenesis, which are tightly regulated by a variety of factors, including Notch signaling. In this review, we summarize the recent progress regarding the functional roles of Notch signaling in glioma, including Notch ligand, microRNA, intracellular crosstalk, glioma stem-like cells and active angiogenesis and explore their clinical implications as diagnostic or prognostic biomarkers and molecular therapeutic targets for glioma.

FoxM1 drives ADAM17/EGFR activation loop to promote mesenchymal transition in glioblastoma

Mesenchymal transition (MES transition) is a hallmark of glioblastoma multiforme (GBM), however, the mechanism regulating the process remains to be elucidated. Here we report that FoxM1 drives ADAM17/EGFR activation loop to promote MES transition in GBM. Firstly, FoxM1 expression was positively associated with ADAM17 expression, and their expression was correlated with the mesenchymal features and overall patient survival of GBM. Overexpressing FoxM1 or ADAM17 increased the mesenchymal phenotype of glioma cells, which could be reversed by silencing FoxM1 or ADAM17. Importantly, FoxM1 bound to the ADAM17 promoter to transcriptionally upregulate its expression. Using gain- and loss-of-function studies, we showed that FoxM1/ADAM17 axis promoted the MES transition in glioma cells. Moreover, tissue microarray analysis and orthotopic xenograft model further confirmed that FoxM1/ADAM17 axis played key roles in malignancy of GBM. Mechanistically, FoxM1/ADAM17 axis activated the EGFR/AKT/GSK3β signaling pathway and ADAM17/EGFR/GSK3β axis could maintain FoxM1 stability in glioma cells. Taken together, our study demonstrated that FoxM1/ADAM17 feedback loop controlled the MES transition and regulated the progression of GBM, raising the possibility that deregulation of this loop might improve the durability of therapies in GBM.

Loss of miR-107, miR-181c and miR-29a-3p Promote Activation of Notch2 Signaling in Pediatric High-Grade Gliomas (pHGGs)

The mechanisms by which microRNAs control pediatric high-grade gliomas (pHGGs) have yet to be fully elucidated. Our studies of patient-derived pHGG tissues and of the pHGG cell line KNS42 revealed down-regulation in these tumors of three microRNAs, specifically miR-107, miR-181c, and miR-29a-3p. This down-regulation increases the proliferation of KNS42 cells by de-repressing expression of the Notch2 receptor (Notch2), a validated target of miR-107 and miR-181c and a putative target of miR-29a-3p. Inhibition (either pharmacologic or genetic) of Notch2 or re-expression of the implicated microRNAs (all three combined but also individually) significantly reduced KNS42 cell proliferation. These findings suggest that Notch2 pathway activation plays a critical role in pHGGs growth and reveal a direct epigenetic mechanism that controls Notch2 expression, which could potentially be targeted by novel forms of therapy for these childhood tumors characterized by high-morbidity and high-mortality.

Notch1 ablation radiosensitizes glioblastoma cells

Broad specific Notch1 inhibitors suppress glioblastoma multiforme (GBM) growth but have significant gastrointestinal toxicities. Here, we examined Notch1 expression in GBM tissue specimens and its correlation with the overall survival (OS) of GBM patients. Furthermore, using the CRISPR/Cas9 system, we investigated the effects of Notch1 downregulation on clonogenic growth and angiogenesis of GBM cells and xenografts. Immunohistochemistry showed positive Notch1 expression in 71% (49/69) of GBM tissues. Our multivariate Cox regression analysis further revealed that Notch1 expression was an independent adverse prognostic factor for OS. Notch1 downregulation suppressed the growth of GBM cells U87MG and U251. The mean duration to reach 6 x the starting volume was 18.3 days for xenografts with Notch1 downregulation and 13.4 days for the control xenografts. Immunofluorescent staining further disclosed that Notch1 downregulation markedly increased the number of γH2AX foci and radiosensitized GBM cells. Notch1 downregulation also impaired angiogenesis and attenuated VEGF and hypoxic response to irradiation in xenografts. In conclusion, Notch1 ablation inhibited GBM cell proliferation and neovascularization and radiosensitized GBM cells and xenografts, suggesting a pivotal role of Notch1 in tumor growth, angiogenesis, and radioresistance in GBM.

Notch Signaling in Development, Tissue Homeostasis, and Disease

Notch signaling is an evolutionarily highly conserved signaling mechanism, but in contrast to signaling pathways such as Wnt, Sonic Hedgehog, and BMP/TGF-β, Notch signaling occurs via cell-cell communication, where transmembrane ligands on one cell activate transmembrane receptors on a juxtaposed cell. Originally discovered through mutations in Drosophila more than 100 yr ago, and with the first Notch gene cloned more than 30 yr ago, we are still gaining new insights into the broad effects of Notch signaling in organisms across the metazoan spectrum and its requirement for normal development of most organs in the body. In this review, we provide an overview of the Notch signaling mechanism at the molecular level and discuss how the pathway, which is architecturally quite simple, is able to engage in the control of cell fates in a broad variety of cell types. We discuss the current understanding of how Notch signaling can become derailed, either by direct mutations or by aberrant regulation, and the expanding spectrum of diseases and cancers that is a consequence of Notch dysregulation. Finally, we explore the emerging field of Notch in the control of tissue homeostasis, with examples from skin, liver, lung, intestine, and the vasculature.

Combinatorial therapy with adenoviral-mediated PTEN and a PI3K inhibitor suppresses malignant glioma cell growth in vitro and in vivo by regulating the PI3K/AKT signaling pathway

PURPOSE

Glioblastoma is a highly invasive and challenging tumor of the central nervous system. The mutation/deletion of the tumor suppressor phosphatase and tensin homolog (PTEN) gene is the main genetic change identified in glioblastomas. PTEN plays a critical role in tumorigenesis and has been shown to be an important therapeutic target. The phosphatidylinositol 3-kinase (PI3K) inhibitor LY294002 is commonly used to inhibit glioma cell growth via regulation of the PI3K/AKT signaling pathway. In this study, we examined the growth inhibitory effects of a combinatorial therapy of adenoviral-mediated PTEN (Ad-PTEN) and LY294002 on LN229 and U251 glioma cells in vitro and on tumor xenografts in vivo.

METHODS

In vitro, LN229 and U251 glioma cells were treated by combinatorial therapy with Ad-PTEN and LY294002. The growth ability was determined by MTT assay. The cell cycle distribution was analyzed by flow cytometry. Cell invasive ability was analyzed by transwell invasion assay and cell apoptosis analysis via FITC-Annexin V analysis. In vivo, U251 subcutaneous glioblastoma xenograft was used to assay anti-tumor effect of combinatorial therapy with Ad-PTEN and LY294002 by mean volume of tumors, immunohistochemistry and TUNEL method.

RESULTS

The combinatorial treatment clearly suppressed cell proliferation, arrested the cell cycle, reduced cell invasion and promoted cell apoptosis compared with the Ad-PTEN or LY294002 treatment alone. The treatment worked by inhibiting the PI3K/AKT pathway. In addition, the growth of U251 glioma xenografts treated with the combination of Ad-PTEN and LY294002 was significantly inhibited compared with those treated with Ad-PTEN or LY294002 alone.

CONCLUSIONS

Our data indicated that the combination of Ad-PTEN and LY294002 effectively suppressed the malignant growth of human glioma cells in vitro and in tumor xenografts, suggesting a promising new approach for glioma gene therapy that warrants further investigation.

Epigenetic regulation of NOTCH1 and NOTCH3 by KMT2A inhibits glioma proliferation

Glioblastomas are among the most fatal brain tumors; however, the molecular determinants of their tumorigenic behavior are not adequately defined. In this study, we analyzed the role of KMT2A in the glioblastoma cell line U-87 MG. KMT2A knockdown promoted cell proliferation. Moreover, it increased the DNA methylation of NOTCH1 and NOTCH3 and reduced the expression of NOTCH1 and NOTCH3. NOTCH1 or NOTCH3 activation inhibited U-87 MG cell proliferation, whereas NOTCH1 and NOTCH3 inhibition by shRNAs induced cell proliferation, thus demonstrating the tumor-suppressive ability of NOTCH1 and NOTCH3 in U-87 MG cells. The induced cell proliferation caused by KMT2A knockdown could be nullified by using either constitutively active NOTCH1 or constitutively active NOTCH3. This result demonstrates that KMT2A positively regulates NOTCH1 and NOTCH3 and that this mechanism is essential for inhibiting the U-87 MG cell proliferation. The role of KMT2A knockdown in promoting tumor growth was further confirmed in vivo by transplanting U-87 MG cells into the brains of zebrafish larvae. In conclusion, we identified KMT2A-NOTCH as a negative regulatory cascade for glioblastoma cell proliferation, and this result provides important information for KMT2A- or NOTCH-targeted therapeutic strategies for brain tumors.

Molecular targets in glioblastoma

Glioblastoma is the most lethal brain tumor. The poor prognosis results from lack of defined tumor margins, critical location of the tumor mass and presence of chemo- and radio-resistant tumor stem cells. The current treatment for glioblastoma consists of neurosurgery, followed by radiotherapy and temozolomide chemotherapy. A better understanding of the role of molecular and genetic heterogeneity in glioblastoma pathogenesis allowed the design of novel targeted therapies. New targets include different key-role signaling molecules and specifically altered pathways. The new approaches include interference through small molecules or monoclonal antibodies and RNA-based strategies mediated by siRNA, antisense oligonucleotides and ribozymes. Most of these treatments are still being tested yet they stay as solid promises for a clinically relevant success.

Notch1 and Notch2 in Podocytes Play Differential Roles During Diabetic Nephropathy Development

Notch pathway activation in podocytes has been shown to play an important role in diabetic kidney disease (DKD) development; however, the receptors and ligands involved in the process have not been identified. Here, we report that conditional deletion of Notch1 in podocytes using NPHS2(cre)Notch1(flox/flox) animals resulted in marked amelioration of DKD. On the contrary, podocyte-specific genetic deletion of Notch2 had no effect on albuminuria and mesangial expansion. Notch1-null podocytes were protected from apoptosis and dedifferentiation in vitro, likely explaining the protective phenotype in vivo. Deletion of Notch1 in podocytes also resulted in an increase in Notch2 expression, indicating an interaction between the receptors. At the same time, transgenic overexpression of Notch2 in podocytes did not induce phenotypic changes, while constitutive expression of Notch1 caused rapid development of albuminuria and glomerulosclerosis. In summary, our studies indicate that Notch1 plays a distinct (nonredundant) role in podocytes during DKD development.

A functional polymorphism in the pre‑miR‑146a gene influences the prognosis of glioblastoma multiforme by interfering with the balance between Notch1 and Notch2

The aim of the present study was to evaluate the association between a polymorphism (rs2910164) in the microRNA (miR)‑146a precursor and the prognosis of glioblastoma multiforme (GBM), as well as to examine the possible underlying mechanism in a Chinese population. A total of 380 patients with histologically confirmed GBM were recruited between 2008 and 2012, and were genotyped for the rs2910164 polymorphism using Sanger sequencing. The Kaplan‑Meier method was used to estimate overall survival (OS), and univariate and multivariate Cox proportional hazard regression analyses were used to evaluate the effect of miR‑146a polymorphisms on OS. It was identified that the rs2910164 CC genotype was significantly associated with a decreased OS among the patients with GBM (P=0.002). It was confirmed that Notch1 and Notch2 were targets of miR‑146a and it was demonstrated that the introduction of miR‑146a mimic suppressed the levels of Notch1 and Notch2 to different extents, resulting in a reduced Notch1/Notch2 ratio with an increase in miR‑146a mimic concentration in U251 cells. Additionally, resected tumor specimens were collected from 138 GBM patients and the expression levels of miR‑146a, Notch1 and Notch2 were examined using reverse transcription‑quantitative polymerase chain reaction and western blot analysis. Consistent with the in vitro study, lower levels of miR‑146a, higher levels of Notch1 and Notch2, and a higher Notch1/Notch2 ratio were identified in the CC genotype group compared with those of the GG/GC group. In the present study, the rs2910164 C allele was found to be associated with a reduced survival rate in patients with GBM, and the observed association between the CC genotype and poorer prognosis of GBM was at least partially mediated by the decreased expression of miR‑146a, which interfered with the balance of Notch1 and Notch2.

LRIG1 inhibits hypoxia-induced vasculogenic mimicry formation via suppression of the EGFR/PI3K/AKT pathway and epithelial-to-mesenchymal transition in human glioma SHG-44 cells

Leucine-rich repeats and immunoglobulin-like domains 1 (LRIG1) is a pan-negative regulator of the epidermal growth factor receptor (EGFR) signaling pathway. The aim of this study was to investigate the underlying mechanism of LRIG1 in the regulation of vasculogenic mimicry (VM) formation in glioma cells. We constructed an enhanced green fluorescent protein plasmid (pEGFP) system, pEGFP-C1-LRIG1, for overexpression of LRIG1, and transfected it into human glioma cell line SHG-44. Under hypoxic conditions induced by CoCl2, we investigated the effects of LRIG1 overexpression on VM formation and VM-dependent malignant behaviors including migration, invasion, and proliferation. Additionally, we explored the effects of LRIG1 on the expression levels of major components of the EGFR/PI3K/AKT pathway as well as E-cadherin and vimentin. We found that LRIG1 overexpression is able to inhibit hypoxia-induced VM formation, migration, invasion, and proliferation. Furthermore, LRIG1 overexpression counteracts hypoxia-induced increase in the expression of phosphorylated EGFR (pEGFR), PI3K (pPI3K), and AKT (pAKT) and reverts hypoxia-induced alteration in E-cadherin and vimentin expression levels. In LRIG1 knockdown SHG-44 cells, however, hypoxia-induced VM formation and alteration in E-cadherin and vimentin expression levels were exacerbated. These results suggest that the inhibitory effects of LRIG1 are most likely mediated by suppression of the EGFR/PI3K/AKT pathway and epithelial-mesenchymal transition (EMT) process. Our findings provide compelling evidence implicating LRIG1 in glioma pathophysiology, suggesting that gene therapy using LRIG1 may serve as a treatment for this disease.

Elevated expression of Notch-1 and EGFR induced apoptosis in glioblastoma multiforme patients

OBJECTIVE

The Notch signaling pathway has been well recognized as important adjuster in glioma tumorigenesis and could regulate the glioma cell proliferation through downstream factors such as epidermal growth factor receptor (EGFR). Our current study was aim to investigate the clinical association between Notch-1 gene and EGFR gene as well as cell survival rate in human glioblastoma multiforme (GBM) samples.

PATIENTS AND METHODS

Samples from 90 patients with GBMs and 20 normal brain tissues were analyzed in our study. Western blot and immunohistochemistry was used to detect Notch and EGFR protein expression. RT-PCR was used to detect Notch and EGFR mRNA expression. Apoptosis was detected with flow cytometry.

RESULTS

Results demonstrated that the Notch and EGFR gene mRNA and protein levels were dramatically higher in GBM tissues compared to normal brain. Further analysis found these increased mRNA levels were only associated with patient survival period, but not related to patient age, gender and tumor size. A positive correlation was observed between Notch and EGFR protein expression. The positive correlations were also exhibited between Notch-1, EGFR gene expression and apoptosis percentage.

CONCLUSION

Our study verified both Notch-1 and EGFR involved in GBM tumorigenesis and may provide important information for GBM clinical treatment and prognosis.

Notching on Cancer's Door: Notch Signaling in Brain Tumors

Notch receptors play an essential role in the regulation of central cellular processes during embryonic and postnatal development. The mammalian genome encodes for four Notch paralogs (Notch 1–4), which are activated by three Delta-like (Dll1/3/4) and two Serrate-like (Jagged1/2) ligands. Further, non-canonical Notch ligands such as epidermal growth factor like protein 7 (EGFL7) have been identified and serve mostly as antagonists of Notch signaling. The Notch pathway prevents neuronal differentiation in the central nervous system by driving neural stem cell maintenance and commitment of neural progenitor cells into the glial lineage. Notch is therefore often implicated in the development of brain tumors, as tumor cells share various characteristics with neural stem and progenitor cells. Notch receptors are overexpressed in gliomas and their oncogenicity has been confirmed by gain- and loss-of-function studies in vitro and in vivo. To this end, special attention is paid to the impact of Notch signaling on stem-like brain tumor-propagating cells as these cells contribute to growth, survival, invasion, and recurrence of brain tumors. Based on the outcome of ongoing studies in vivo, Notch-directed therapies such as γ-secretase inhibitors and blocking antibodies have entered and completed various clinical trials. This review summarizes the current knowledge on Notch signaling in brain tumor formation and therapy.

Short hairpin RNA targeting Notch2 inhibits U87 human glioma cell proliferation by inducing cell cycle arrest and apoptosis in vitro and in vivo

Notch signaling has been reported to be oncogenic or tumor suppressive, depending on the tissue context. To investigate the effects of Notch2 knockdown on U87 human glioma cell proliferation in vitro and in vivo, and the associated mechanisms, U87 cells were stably transfected with p green fluorescent protein (GFP)-V-RS Notch2 short hairpin (sh) RNA plasmid and pGFP-V-RS scramble-shRNA plasmid. The former was referred to as the Notch2-shRNA group and the latter as the negative-shRNA group. mRNA and protein expression, cell proliferation, cell cycle and apoptosis were measured by reverse transcription-polymerase chain reaction, western blot analysis, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide analysis and flow cytometry using propidium iodide, respectively. Tumor volume, tumor weight and cumulative survival rate were determined in a nude mouse xenograft tumor model. Notch2 mRNA and protein expression in the Notch2-shRNA group were reduced by 87.6 and 94.5% compared with the negative-shRNA group (P<0.001). Notch2 knockdown significantly inhibited U87 cell proliferation after three days of culture (P<0.05). Notch2 silencing induced cell cycle arrest at G₀/G₁ phase by upregulation of p21 protein expression and downregulation of mini chromosome maintenance complex 2 and cyclin-D1 protein expression. Furthermore, knockdown of Notch2 also induced U87 cell apoptosis. On day 50 after inoculation, tumor weight in the Notch2-shRNA group was significantly lower than that in the negative-shRNA group (0.55±0.10 vs. 1.23±0.52 g; P<0.01). The cumulative survival rate was significantly longer in the Notch2-shRNA group compared with the negative-shRNA group (log rank test P=0.01). In conclusion, Notch2 silencing inhibited U87 glioma cell proliferation by inducing cell cycle arrest and apoptosis in vitro and in vivo. Thus, Notch2 may be a key therapeutic target for the treatment of glioma.

Differential patterns of NOTCH1-4 receptor expression are markers of glioma cell differentiation

Background Notch signaling is deregulated in human gliomas and may play a role in their malignancy. However, the role of each Notch receptor in glioma cell differentiation and progression is not clear. We examined the expression pattern of Notch receptors and compared it with differentiation markers in glioma cell lines, primary human cultures, and biopsies of different grades. Furthermore, the effects of a γ-secretase inhibitor (GSI) on cell survival were assessed. Methods Notch receptors and markers of cellular differentiation were analyzed by reverse transcriptase PCR, Western blotting, immunohistochemistry, and immunocytochemistry. GSI sensitivity was assessed in both cell lines and primary cultures grown as monolayers or tumorspheres, by MTT assay. Results In cell lines, Notch1 and Notch2/4 levels paralleled those of glial fibrillary acidic protein (GFAP) and vimentin, respectively. In human gliomas and primary cultures, Notch1 was moderate/strong in low-grade tumors but weak in glioblastoma multiforme (GBM). Conversely, Notch4 increased from astrocytoma grade II to GBM. Primary GBM cultures grown in serum (monolayer) showed moderate/high levels of CD133, nestin, vimentin, and Notch4 and very low levels of GFAP and Notch1, which were reduced in tumorspheres. This effect was drastic for Notch4. GSI reduced cell survival with stronger effect in serum, whilst human primary cultures showed different sensitivity. Conclusion Data from cell lines and human gliomas suggest a correlation between expression of Notch receptors and cell differentiation. Namely, Notch1 and Notch4 are markers of differentiated and less differentiated glioma cells, respectively. We propose Notch receptors as markers of glioma grading and possible prognostic factors.

Identification of aberrant microRNA expression pattern in pediatric gliomas by microarray

Background

Brain tumor remains the leading cause of disease-related death in children. Many studies have focused on the complex biological process involved in pediatric brain tumors but little is know about the possible role of microRNAs in the genesis of these tumors.

Methods

In this study, we used a microRNA microarray assay to study the expression pattern of microRNAs in pediatric gliomas and matched normal tissues.

Results

We found 40 differentially expressed microRNAs, among which miR-1321, miR-513b, miR-769-3p were found be related to cancer genesis for the first time. The expression of selected microRNAs were then confirmed by qRT-PCR. Furthermore, GO and pathway analysis showed that the target genes of the 40 differentially expressed microRNAs were significantly enriched in nervous system-related and tumor-related biological processes and signaling pathways. Additionally, an apoptosis-related network of microRNA–mRNA interaction, representing the critical microRNAs and their targets, was constructed based on microRNA status.

Conclusions

In the present study we identified the changed expression pattern of microRNAs in pediatric gliamas. Our study also provides a better understanding of pediatric brain tumor biology and may assist in the development of less toxic therapies and in the search for better markers for disease stratification.

Virtual slides

The virtual slide(s) for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs/1323049861105720