Activation of Wnt/beta-catenin/Tcf signaling pathway in human astrocytomas

Shikonin Inhibits the Migration and Invasion of Human Glioblastoma Cells by Targeting Phosphorylated β-Catenin and Phosphorylated PI3K/Akt: A Potential Mechanism for the Anti-Glioma Efficacy of a Traditional Chinese Herbal Medicine

Shikonin is an anthraquinone derivative extracted from the root of lithospermum. Shikonin is traditionally used in the treatment of inflammatory and infectious diseases such as hepatitis. Shikonin also inhibits proliferation and induces apoptosis in various tumors. However, the effect of shikonin on gliomas has not been fully elucidated. In the present study, we aimed to investigate the effects of shikonin on the migration and invasion of human glioblastoma cells as well as the underlying mechanisms. U87 and U251 human glioblastoma cells were treated with shikonin at 2.5, 5, and 7.5 μmol/L and cell viability, migration and invasiveness were assessed with CCK8, scratch wound healing, in vitro Transwell migration, and invasion assays. The expression and activity of matrix metalloproteinase-2 (MMP-2) and matrix metalloproteinase-9 (MMP-9) and the expression of phosphorylated β-catenin (p-β-catenin) and phosphorylated PI3K/Akt were also checked. Results showed that shikonin significantly inhibited the cell proliferation, migration, invasion, and expression of MMP-2 and MMP-9 in U87 and U251 cells. The expression of p-β-catenin showed contrary trends in two cell lines. It was significantly inhibited in U87 cells and promoted in U251 cells. Results in this work indicated that shikonin displayed an inhibitory effect on the migration and invasion of glioma cells by inhibiting the expression and activity of MMP-2 and -9. In addition, shikonin also inhibited the expression of p-PI3K and p-Akt to attenuate cell migration and invasion and MMP-2 and MMP-9 expression in both cell lines, which could be reversed by the PI3K/Akt pathway agonist, insulin-like growth factor-1 (IGF-1).

Overexpression of FRAT1 is associated with malignant phenotype and poor prognosis in human gliomas

Glioma is the most common malignancy of the central nervous system. Approximately 40 percent of intracranial tumors are diagnosed as gliomas. Difficulties in treatment are associated closely with the malignant phenotype, which is characterized by excessive proliferation, relentless invasion, and angiogenesis. Although the comprehensive treatment level of brain glioma is continuously progressing, the outcome of this malignancy has not been improved drastically. Therefore, the identification of new biomarkers for diagnosis and therapy of this malignancy is of significant scientific and clinical value. FRAT1 is a positive regulator of the Wnt/β-catenin signaling pathway and is overexpressed in many human tumors. In the present study, we investigated the expression status of FRAT1 in 68 patients with human gliomas and its correlation with the pathologic grade, proliferation, invasion, angiogenesis, and prognostic significance. These findings suggest that FRAT1 may be an important factor in the tumorigenesis and progression of glioma and could be explored as a potential biomarker for pathological diagnosis, an indicator for prognosis, and a target for biological therapy of malignancy.

β-Catenin knockdown inhibits pituitary adenoma cell proliferation and invasion via interfering with AKT and gelatinases expression

Pituitary adenomas are among the most prevalent forms of intrinsic brain tumors. Although most pituitary adenomas are benign, some of them may become invasive and cause significant mass effect and hormonal dysfunction. We have previously shown that β-catenin is overexpressed in human pituitary adenomas and its level correlates to tumor grades. In the present study, we further investigated the role of β-catenin in pituitary adenoma cell proliferation and invasion in vitro. Stable β-catenin knockdown pituitary adenoma cell line was created by transfecting mouse growth hormone pituitary adenoma GT1.1 cells with β-catenin shRNA plasmid. Cell proliferation and invasion were assessed using CCK-8 kit and transwell assay, respectively. Our data demonstrated that knockdown of β-catenin with shRNA significantly inhibited the proliferation and invasion of GT1.1 cells. In β-catenin shRNA transfected cells, the expression of AKT, STAT3, cyclin D1 and CDK4 were significantly suppressed, which accounted for the observed growth retardation following β-catenin shRNA transfection. Moreover, β-catenin shRNA transfection led to a drastic reduction in MMP-2/9 secretion into the conditioned media, which might be responsible for the reduced invasiveness of β-catenin shRNA-transfected pituitary adenoma cells. These results indicate that β-catenin may regulate the expression of AKT, STAT3, cyclin D1, CDK4 and MMP-2/9 to promote pituitary adenoma cell proliferation and invasion.

The expression and significance of dishevelled in human glioma

BACKGROUND

The proto-oncogene dishevelled (Dvl) is a critical component of the Wnt/β-catenin signaling pathway, and its elevated expression in various tumor types is associated with malignancy. However, a role for Dvl in glioma has not been explored.

MATERIALS AND METHODS

To determine whether Dvl expression is elevated in human glioma, we examined the protein levels in 67 human glioma samples and 3 normal brain specimens by Western blotting and immunohistochemistry. To investigate a possible association of Dvl with the malignant phenotype in glioma, the correlation of the Dvl immunoreactivity score (IRS) with β-catenin IRS, the tumor proliferation index (PI), and tumor invasion index (II) were determined for each sample.

RESULTS

The Dvl IRS, β-catenin IRS, PI, and II increased significantly with the pathologic grade of glioma (P <0.001) with average scores of 3.46 ± 3.45, 3.92 ± 3.28, 30.93 ± 17.92, and 20.43 ± 11.79, respectively. Furthermore, the PI and II were significantly higher for the Dvl-positive group than the Dvl-negative group (P <0.001). Correlation analysis demonstrated that β-catenin IRS, PI, and II were positively correlated with Dvl IRS.

CONCLUSIONS

Dvl overexpression may contribute to the malignant proliferation and invasion of human glioma.

Brain metastases from lung cancer show increased expression of DVL1, DVL3 and beta-catenin and down-regulation of E-cadherin

The susceptibility of brain to secondary formation from lung cancer primaries is a well-known phenomenon. In contrast, the molecular basis for invasion and metastasis to the brain is largely unknown. In the present study, 31 brain metastases that originated from primary lung carcinomas were analyzed regarding over expression of Dishevelled-1 (DVL1), Dishevelled-3 (DVL3), E-cadherin (CDH1) and beta-catenin (CTNNB1). Protein expressions and localizations were analyzed by immunohistochemistry. Genetic alterations of E-cadherin were tested by polymerase chain reaction (PCR)/loss of heterozygosity (LOH). Heteroduplex was used to investigate mutations in beta-catenin. DVL1 and DVL3 showed over expression in brain metastasis in 87.1% and 90.3% of samples respectively. Nuclear staining was observed in 54.8% of cases for DVL1 and 53.3% for DVL3. The main effector of the Wnt signaling, beta-catenin, was up-regulated in 56%, and transferred to the nucleus in 36% of metastases. When DVL1 and DVL3 were up-regulated the number of cases with nuclear beta-catenin significantly increased (p=0.0001). Down-regulation of E-cadherin was observed in 80% of samples. Genetic analysis showed 36% of samples with LOH of the CDH1. In comparison to other lung cancer pathologies, the diagnoses adenocarcinoma and small cell lung cancer (SCLC) were significantly associated to CDH1 LOH (p=0.001). Microsatellite instability was detected in one metastasis from adenocarcinoma. Exon 3 of beta-catenin was not targeted. Altered expression of Dishevelled-1, Dishevelled-3, E-cadherin and beta-catenin were present in brain metastases which indicates that Wnt signaling is important and may contribute to better understanding of genetic profile conditioning lung cancer metastasis to the brain.

The expressions of Wnt/β-catenin pathway-related components in brainstem gliomas

BACKGROUND

The overall prognosis of brainstem gliomas is very poor, and the current treatment cannot significantly prolong the overall survival of these patients; therefore, studying the molecular biological mechanisms of the occurrence and development of brainstem gliomas has important significance for their treatment. The Wnt/β-catenin signaling pathway is closely associated with the occurrence and development of tumors, but its relationship with brainstem gliomas remains unclear.

METHODS

This study used Western blot and immunohistochemistry methods to detect the expressions of Wnt/β-catenin signaling pathway-related components such as Wnt-1, Wnt-2, β-catenin and C-myc in six cases of normal brain tissues and 24 cases of brainstem gliomas and analyzed the relationship between their expressions and clinicopathological characteristics.

RESULTS

Wnt-1 had no obvious expression in normal brain tissues and did not show any significant difference between high- and low-grade brainstem gliomas; the expressions of Wnt-2, β-catenin and C-myc in high-grade brainstem gliomas were significantly higher than that in low-grade brainstem gliomas and normal brain tissues and were positively correlated with the expression of Ki-67. Moreover, the expressions of Wnt-2 and C-myc were significantly associated with the prognosis of brainstem glioma patients; additionally, there was a trend toward increased β-catenin expression with shorter survival, but there was no statistical difference.

CONCLUSIONS

Wnt/β-catenin signaling pathway might be abnormally activated and plays an important role in the occurrence and development of brainstem gliomas. Wnt-2, β-catenin and C-myc may be potential targets for brainstem glioma treatment.

MiR-92b inhibitor promoted glioma cell apoptosis via targeting DKK3 and blocking the Wnt/beta-catenin signaling pathway

Background

MiR-92b was upregulated in gliomas. However, the association of miR-92b with glioma cell apoptosis and survival remains unknown.

Methods

Proliferation capability of glioma cells upon tranfection with miR-92b mimics or inhibitors was detected by mutiple analyses, including MTT assays, colony formation assay. Apoptosis abilities of glioma cells were detected by flow cytometric analysis. The target of miR-92b was determined by luciferase reporter and western blot. The association of miR-92b with outcome was examined in twenty glioma patients.

Results

MiR-92b expression was significantly increased in high-grade gliomas compared with low-grade gliomas, and positively correlated with the degree of glioma infiltration. Over-expression of miR-92b increased cell proliferation, whereas knockdown of miR-92b decreased cell proliferation via modulating the levels of the target, Target prediction analysis and a dual luciferase reporting assay confirmed that the inhibitory protein-coding Dickkopf-3 gene (DKK3) was a direct target of miR-92b. Furthermore, miR-92b could regulate the expression of downstream genes of the Wnt/beta-catenin signaling pathway, such as Bcl2, c-myc and p-c-Jun, in glioma cells. Finally, the increased level of miR-92b expression in high-grade gliomas confers poorer overall survival.

Conclusions

The present data indicates that miR-92b directly regulate cell proliferation and apoptosis by targeting DKK3 and act as prognostic factors for glioma patients.

TCTP promotes glioma cell proliferation in vitro and in vivo via enhanced β-catenin/TCF-4 transcription

Background The translationally controlled tumor protein (TCTP) is a multifunctional protein that plays important roles in immune responses, cell proliferation, tumorigenicity and cell apoptosis. Here, we examined the clinical value of TCTP in glioma patient survival and investigated the functional roles and mechanism of TCTP in glioma development. Methods TCTP expression was determined through immunohistochemical staining, immunoblotting, and quantitative real-time PCR (qRT-PCR). TCTP or TCF-4 expression was silenced using short hairpin (sh) RNA. In vitro cell proliferation was detected using MTT, BrdU and colony formation assays, and in vivo tumor growth was performed using the xenograft model. TCTP/TCF-4/β-catenin association was detected using a co-immunoprecipitation (co-IP) assay. TCF-4 transcription activity was detected using a TOPflash/FOPflash report gene assay. Wnt/β-catenin-targeted gene expression was detected through Western blotting. Results TCTP protein levels were significantly elevated in high-grade gliomas compared with low-grade gliomas and normal brain tissues. Importantly, the expression of TCTP was significantly associated with poorer overall survival and disease-free survival, and TCTP also reduced the survival rate after treatment with radiotherapy and temozolomide (RT-TMZ) for glioma patients. The ectopic expression of TCTP enhanced glioma cell proliferation both in vitro and in vivo, whereas the knockdown of TCTP inhibited this effect. Similarly, the overexpression of TCTP increased β-catenin binding to TCF-4, TOPflash report gene transcription activity, and the expression of Wnt/β-catenin signaling target genes including c-Myc and cyclin D1; notably, the knockdown of TCTP reduced these effects. The knockdown of TCF-4 using shRNA rescued the enhanced cell proliferation induced by the overexpression of TCTP. Conclusion TCTP is associated with reduced survival of glioma patients and induces glioma tumor growth through enhanced Wnt/β-catenin signaling.

Nonsteroidal anti-inflammatory drugs diclofenac and celecoxib attenuates Wnt/β-catenin/Tcf signaling pathway in human glioblastoma cells

Glioblastoma, the most common and aggressive primary brain tumors, carry a bleak prognosis and often recur even after standard treatment modalities. Emerging evidence suggests that deregulation of the Wnt/β-catenin/Tcf signaling pathway contributes to glioblastoma progression. Nonsteroidal anti-inflammatory drugs (NSAIDs) inhibit tumor cell proliferation by suppressing Wnt/β-catenin/Tcf signaling in various human malignancies. In this study, we sought to inhibit Wnt/β-catenin/Tcf signaling in glioblastoma cells by the NSAIDs diclofenac and celecoxib. Both diclofenac and celecoxib significantly reduced the proliferation, colony formation and migration of human glioblastoma cells. Diclofenac and celecoxib downregulated β-catenin/Tcf reporter activity. Western and qRT-PCR analysis showed that diclofenac and celecoxib reduced the expression of β-catenin target genes Axin2, cyclin D1 and c-Myc. In addition, the cytoplasmic accumulation and nuclear translocation of β-catenin was significantly reduced following diclofenac and celecoxib treatment. Furthermore, diclofenac and celecoxib significantly increased phosphorylation of β-catenin and reduced the phosphorylation of GSK3β. These results clearly indicated that diclofenac and celecoxib are potential therapeutic agents against glioblastoma cells that act by suppressing the activation of Wnt/β-catenin/Tcf signaling.

Aflatoxin B1 negatively regulates Wnt/β-catenin signaling pathway through activating miR-33a

MicroRNAs are known to play an important role in modulating gene expression in various diseases including cancers and cardiovascular disorders, but only a few of them are associated with the pathology of aflatoxin B1 (AFB1), a potent mycotoxin. Here, we discovered a novel regulatory network between AFB1, miR-33a and β-catenin in human carcinoma cells. The level of miR-33a was up-regulated in hepatocellular carcinoma (HCC) cells treated with AFB1, while in the same cells causing the decrease in β-catenin expression when treated at their IC50 values. miR-33a, specifically miR-33a-5p, was demonstrated to down-regulate the expression of β-catenin, affect the β-catenin pathway, and inhibit cell growth. Also, by employing a luciferase assay, we found that miR-33a down-regulated β-catenin by directly binding to the 3'-UTR of β-catenin. These results suggested that AFB1 might down-regulate β-catenin by up-regulating miR-33a. This understanding opens new lines of thought in the potential role of miR-33a in the clinical therapy of cancer.

Treatment of glioblastoma multiforme using a combination of small interfering RNA targeting epidermal growth factor receptor and β-catenin

BACKGROUND

Epidermal growth factor receptor (EGFR) and β-catenin are two key mediators of cell signal transduction implicated in the pathogenesis of a variety of tumors. There is emerging evidence indicating that they are overexpressed in glioblastoma multiforme (GBM) and both play significant roles in GBM carcinogenesis. Moreover, down-regulating EGFR individually only provides limited therapeutic efficacy. Therefore, we aimed to determine the feasibility and efficacy of gene therapy of GBM using combinatorial inhibition of EGFR and β-catenin in view of the cross-talk between these two signaling pathways.

METHODS

The down-regulatory effect of small interfering RNA (siRNA) targeting EGFR and β-catenin alone or in combination in human GBM cells U-87 MG was evaluated by Quantitative RT-PCR. Cell proliferation in the short- and long-term was investigated by alamar blue and clonogenic assays, respectively. An annexin-V assay was performed to detect apoptosis caused by siRNA treatment. The effect of downregulating EGFR and β-catenin on cell cycle progression, cell migration and invasive potential were also examined.

RESULTS

The siRNA treatment potently reduced gene expression of EGFR and β-catenin at the mRNA level. Simultaneous inhibition of EGFR and β-catenin greatly decreased GBM cell proliferation. Although no significant increase in apoptosis was demonstrated, combinatorial siRNA treatment delayed the progression of cell cycle with an increased proportion of cells arrested in the G0/1 phase. Furthermore, EGFR and β-catenin siRNA in combination significantly inhibited the migratory and invasive ability of GBM cells.

CONCLUSIONS

Simultaneous inhibition of EGFR and β-catenin expression could represent an effective therapy for human GBM, and warrants further study in vivo.

Bcl-w Enhances Mesenchymal Changes and Invasiveness of Glioblastoma Cells by Inducing Nuclear Accumulation of β-Catenin

Bcl-w a pro-survival member of the Bcl-2 protein family, is expressed in a variety of cancer types, including gastric and colorectal adenocarcinomas, as well as glioblastoma multiforme (GBM), the most common and lethal brain tumor type. Previously, we demonstrated that Bcl-w is upregulated in gastric cancer cells, particularly those displaying infiltrative morphology. These reports propose that Bcl-w is strongly associated with aggressive characteristic, such as invasive or mesenchymal phenotype of GBM. However, there is no information from studies of the role of Bcl-w in GBM. In the current study, we showed that Bcl-w is upregulated in human glioblastoma multiforme (WHO grade IV) tissues, compared with normal and glioma (WHO grade III) tissues. Bcl-w promotes the mesenchymal traits of glioblastoma cells by inducing vimentin expression via activation of transcription factors, β-catenin, Twist1 and Snail in glioblastoma U251 cells. Moreover, Bcl-w induces invasiveness by promoting MMP-2 and FAK activation via the PI3K-p-Akt-p-GSK3β-β-catenin pathway. We further confirmed that Bcl-w has the capacity to induce invasiveness in several human cancer cell lines. In particular, Bcl-w-stimulated β-catenin is translocated into the nucleus as a transcription factor and promotes the expression of target genes, such as mesenchymal markers or MMPs, thereby increasing mesenchymal traits and invasiveness. Our findings collectively indicate that Bcl-w functions as a positive regulator of invasiveness by inducing mesenchymal changes and that trigger their aggressiveness of glioblastoma cells.

The positive correlation between DJ-1 and β-catenin expression shows prognostic value for patients with glioma

The relationship between DJ-1 and β-catenin, and its impact on the prognosis for glioma patients has not been fully understood. This study determined the effect of DJ-1 on β-catenin and the prognostic significance of this interaction in glioma patients. We collected tumor specimens from 88 glioma patients and determined the expression of DJ-1, β-catenin and PTEN by using immunohistochemical staining. The involvement of DJ-1 and β-catenin in glioma cell lines was evaluated by immunohistochemistry and Western blotting. High DJ-1 expression (37.5%) and high β-catenin expression (34.1%) in glioma specimens were significantly associated with high grade and poor prognosis in glioma patients. However, only high levels of DJ-1 (P = 0.014) was a strong independent prognostic factor, correlated with a reduced overall survival time. In vitro DJ-1 expression was positively correlated with the expression levels of β-catenin and p-Akt, and negatively correlated with PTEN expression in U87, U251 MG, SWO-38 and SHG44 human glioma cell lines. After the knockdown of DJ-1, Akt, p-Akt or β-catenin expression levels were not affected in the PTEN-null cell lines (U87 and U251 MG). However, in the SWO-38 cell line, which has wild-type PTEN protein, the level of PTEN increased while Akt/p-Akt and β-catenin levels were reduced. Furthermore, β-catenin staining weakened in SWO-38 cells after DJ-1 levels decreased according to immunocytochemical analysis. In conclusion, DJ-1 and β-catenin may contribute to the development and recurrence of glioma and are valuable prognostic factors for glioma patients. DJ-1 may regulate β-catenin expression via PTEN and p-Akt.

Promoter methylation of WNT inhibitory factor-1 and expression pattern of WNT/β-catenin pathway in human astrocytoma: pathologic and prognostic correlations

WNT inhibitory factor-1 (WIF1) is an antagonist of the WNT signaling pathway. We investigated the relationship between WIF1 promoter methylation and regulation of the WNT/β-catenin signaling pathway, tumor grade, and survival in patients with astrocytoma. This study included 86 cases of astrocytoma, comprising 20 diffuse astrocytomas and 66 glioblastomas. In addition, 17 temporal lobectomy specimens from patients with epilepsy were included as controls. The ratio of methylated DNA to total methylated and unmethylated DNA (% methylation) was measured by methylation- and unmethylation-specific PCR. Representative tumor tissue was immunostained for WIF1, β-catenin, cyclin D1, c-myc, and isocitrate dehydrogenase 1. Levels of WIF1 promoter methylation, mRNA expression, and protein expression in a glioblastoma cell line were compared before and after demethylation treatment. The mean percent methylation of the WIF1 promoter in astrocytomas was higher than that in control brain tissue. WIF1 protein expression was lower in the tumor group with >5% methylation than in the group with <5% methylation. Cytoplasmic β-catenin staining was more frequently observed in tumors with a low WIF1 protein expression level. Demethylation treatment of a glioblastoma cell line increased WIF1 mRNA and protein expression. Increased WIF1 promoter methylation and decreased WIF1 protein expression were not related to patient survival. In conclusion, WIF1 expression is downregulated by promoter methylation and is an important mechanism of aberrant WNT/β-catenin pathway activation in astrocytoma pathogenesis.

Isoform level expression profiles provide better cancer signatures than gene level expression profiles

BACKGROUND

The majority of mammalian genes generate multiple transcript variants and protein isoforms through alternative transcription and/or alternative splicing, and the dynamic changes at the transcript/isoform level between non-oncogenic and cancer cells remain largely unexplored. We hypothesized that isoform level expression profiles would be better than gene level expression profiles at discriminating between non-oncogenic and cancer cellsgene level.

METHODS

We analyzed 160 Affymetrix exon-array datasets, comprising cell lines of non-oncogenic or oncogenic tissue origins. We obtained the transcript-level and gene level expression estimates, and used unsupervised and supervised clustering algorithms to study the profile similarity between the samples at both gene and isoform levels.

RESULTS

Hierarchical clustering, based on isoform level expressions, effectively grouped the non-oncogenic and oncogenic cell lines with a virtually perfect homogeneity-grouping rate (97.5%), regardless of the tissue origin of the cell lines. However, gene levelthis rate was much lower, being 75% at best based on the gene level expressions. Statistical analyses of the difference between cancer and non-oncogenic samples identified the existence of numerous genes with differentially expressed isoforms, which otherwise were not significant at the gene level. We also found that canonical pathways of protein ubiquitination, purine metabolism, and breast-cancer regulation by stathmin1 were significantly enriched among genes thatshow differential expression at isoform level but not at gene level.

CONCLUSIONS

In summary, cancer cell lines, regardless of their tissue of origin, can be effectively discriminated from non-cancer cell lines at isoform level, but not at gene level. This study suggests the existence of an isoform signature, rather than a gene signature, which could be used to distinguish cancer cells from normal cells.

MicroRNA-222 promotes tumorigenesis via targeting DKK2 and activating the Wnt/β-catenin signaling pathway

MiR-222 in glioma can regulate cell cycle progression and apoptosis. However, the relationship between miR-222 and Wnt/β-catenin signaling pathway in glioma remains unknown. Here, we found that the Dickkopf-2 gene (DKK2) was a direct target of miR-222 by target prediction analysis and dual luciferase reporter assay. RNA interference silencing of DKK2 proved that miR-222 overexpression led to constitutive activation of β-catenin through inhibition of DKK2 expression in glioma cells. Furthermore, miR-222 siRNA significantly inhibited tumorigenesis in vivo. Finally, Western blot analysis showed that miR-222 could regulate the expression of β-catenin and the downstream genes of Wnt/β-catenin signaling pathway. Taken together, our findings reveal a new regulatory mechanism of miR-222 and suggest that miR-222 might be a potential target in glioma therapy.

The antiproliferative effect of indomethacin-loaded lipid-core nanocapsules in glioma cells is mediated by cell cycle regulation, differentiation, and the inhibition of survival pathways

Despite recent advances in radiotherapy, chemotherapy, and surgical techniques, glioblastoma multiforme (GBM) prognosis remains dismal. There is an urgent need for new therapeutic strategies. Nanoparticles of biodegradable polymers for anticancer drug delivery have attracted intense interest in recent years because they can provide sustained, controlled, and targeted delivery. Here, we investigate the mechanisms involved in the antiproliferative effect of indomethacin-loaded lipid-core nanocapsules (IndOH-LNC) in glioma cells. IndOH-LNC were able to reduce cell viability by inducing apoptotic cell death in C6 and U138-MG glioma cell lines. Interestingly, IndOH-LNC did not affect the viability of primary astrocytes, suggesting that this formulation selectively targeted transformed cells. Mechanistically, IndOH-LNC induced inhibition of cell growth and cell-cycle arrest to be correlated with the inactivation of AKT and β-catenin and the activation of GSK-3β. IndOH-LNC also induced G0/G1 and/or G2/M phase arrest, which was accompanied by a decrease in the levels of cyclin D1, cyclin B1, pRb, and pcdc2 and an increase in the levels of Wee1 CDK inhibitor p21^WAF1. Additionally, IndOH-LNC promoted GBM cell differentiation, observed as upregulation of glial fibrillary acidic protein (GFAP) protein and downregulation of nestin and CD133. Taken together, the crosstalk among antiproliferative effects, cell-cycle arrest, apoptosis, and cell differentiation should be considered when tailoring pharmacological interventions aimed at reducing glioma growth by using formulations with multiples targets, such as IndOH-LNC.

MicroRNA-153 is tumor suppressive in glioblastoma stem cells

Glioblastoma multiforme (GBM) is lethal brain tumor thought to arise from GBM stem cells (GBM-SCs). MicroRNAs carry out post-transcriptional regulation of various cellular processes that modulate the stemness properties of GBM-SCs. Here, we investigated the critical role of miR-153 in GBM-SCs. First, GBM-SCs were isolated from six GBM specimens. These GBM-SCs formed GBM spheres, expressed markers associated with neural stem cells, and possessed the capacity for self-renewal and multilineage differentiation. Then qRT-PCR analysis showed that miR-153 expression was down-regulated in GBM tissues relative to normal brain tissues, and in CD133 positive cells relative to CD133 negative cells. This project demonstrates for the first time that transient transfection of miR-153 into GBM-SCs can inhibit their stemness properties, such as impairing self-renewal ability and inducing differentiation. Meanwhile, miR-153 can also repress GBM-SCs growth and induce apoptosis. Altogether, these results indicate that reactivation of miR-153 expression suggests novel therapeutic strategies for GBM-SCs.

AMPK activators suppress cervical cancer cell growth through inhibition of DVL3 mediated Wnt/β-catenin signaling activity

Recent evidence has suggested that AMPK activators may be applied as therapeutic drugs in suppressing cancer cell growth. However, the molecular mechanism of their suppressive function in cancer cells is still unclear. Here we show that AMPK activators impair cervical cancer cell growth through the reduction of DVL3, a positive regulator in Wnt/β-catenin signaling and an oncogenic player in cervical cancer tumorigenesis. By western blot and immunohistochemical analyses, we demonstrated that DVL3 was frequently upregulated and significantly associated with elevated β-catenin (P = 0.009) and CyclinD1 (P = 0.009) expressions in cervical cancer. Enforced expression of DVL3 elevated β-catenin and augmented cervical cancer cell growth, verifying that DVL3-mediated Wnt/β-catenin activation is involved in cervical cancer oncogenesis. On the other aspect, we noted that the cervical cancer cell growth was remarkably suppressed by AMPK activators and such cell growth inhibition was in concomitant with the reduction of DVL3 protein level in dose- and time-dependent manners. Besides, impaired mTOR signaling activity also reduced DVL3 expression. In contrast, co-treatment with Compound C (AMPK inhibitor) could significantly abrogate metformin induced DVL3 reduction. In addition, co-treatment with AM114 or MG132 (proteosomal inhibitors) could partially restore DVL3 expression under the treatment of metformin. Further in vivo ubiquitination assay revealed that metformin could reduce DVL3 by ubiquitin/proteasomal degradation. To our knowledge, this is the first report showing the probable molecular mechanisms of that the AMPK activators suppress cervical cancer cell growth by impairing DVL3 protein synthesis via AMPK/mTOR signaling and/or partially promoting the proteasomal degradation of DVL3.

Hsp27 (HSPB1): a possible surrogate molecular marker for loss of heterozygosity (LOH) of chromosome 1p in oligodendrogliomas but not in astrocytomas

In oligodendrogliomas, 1p loss of heterozygosity (LOH) is a predictor of good prognosis and treatment response. In contrast, in uveal melanomas, LOH of chromosome 3 has been linked to poor prognosis and downregulation of Hsp27. In the present study, we have analyzed the expression of heat-shock proteins (Hsps) to characterize subtypes of gliomas and their histopathologic features and to correlate with other molecular markers including LOH of 1p. Biopsies from patients with primary gliomas (n = 65) were analyzed by immunohistochemistry, chromogenic in situ hybridization and fluorescent in situ hybridization and methylation-specific PCR (MSP). Elevated Hsp27 and total Hsp70 expression levels were associated with high-grade astrocytomas (p = 0.0001 and p = 0.01, respectively). In grade III oligodendrogliomas, the Hsp27 levels were significantly higher (p = 0.03). Low O6-methylguanine-DNA methyltransferase (MGMT) expression was associated with grade II astrocytomas. Elevated β-catenin expression was associated with grade III/IV astrocytomas (p = 0.003); p53 (+) tumors were more frequently found in grade III/IV astrocytomas (p = 0,001). LOH on 1p was associated with oligodendroglial tumours. In addition, a higher Hsp27 expression correlated with LOH of 1p (p = 0.017); this was also tested in two glioma cell lines. MSP was successful in only six samples. No significant correlations were found for the other markers. In conclusion, in oligodendroglial tumors, Hsp27 appeared as a surrogate marker of LOH of 1p which could also help to predict the disease prognosis. In gliomas, p53, Hsp27, Hsp70, MGMT, and β-catenin correlated with histopathological characteristics, suggesting that these markers could predict the disease outcome and the response to treatments.

Stem cells in brain tumour development and therapy- two-sides of the same coin

Primary brain tumours are difficult to manage clinically due to their abilities to invade adjacent tissue and infiltrate distant neuropil. These contribute to challenges in surgical management and also limit the effectiveness of radiotherapy. Despite initial responses to chemotherapy, most tumours become chemo-resistant, leading to relapse. Recent identification and isolation of brain cancer stem cells (BCSCs) have broadened our understanding of the molecular pathogenesis and potential Achilles' heel of brain tumours. BCSCs are thought to drive and propagate the tumour and therefore present an important target for further investigations. This review explores the history of the discovery of BCSCs and the evolving concept of "cancer stem cells" in neuro-oncology. We attempt to present a balanced view on the subject and also to update the readers on the molecular biology of BCSCs. Lastly, we outline the potential strategies to target BCSCs which will translate into specific and effective therapies for brain tumours.

β-Catenin signaling initiates the activation of astrocytes and its dysregulation contributes to the pathogenesis of astrocytomas

Astrocytes are the most abundant cell of the CNS and demonstrate contact inhibition in which a nonproliferative, nonmotile cellular state is achieved once stable intercellular contacts are formed between mature cells. Cellular injury disrupts these intercellular contacts, causing a loss of contact inhibition and the rapid initiation of healing. Dysregulation of the molecular pathways involved in this process is thought to lead to an aggressive cellular state associated with neoplasia. We investigated whether a comparable correlation exists between the response of astrocytes to injury and the malignant phenotype of astrocytomas. We discovered that the loss of contact inhibition plays a critical role in the initiation and regulation of reactive astrocytes in the healing of wounds. In particular, injury of the astrocytes interrupts and destabilizes the cadherin-catenin complexes at the cell membrane leading to nuclear translocation of β-catenin and characteristic changes associated with the activation of astrocytes. Similar signaling pathways are found to be active--but dysregulated--in astrocytomas. Inhibition of β-catenin signaling diminished both the response of astrocytes to injury and induction of the malignant phenotype of astrocytomas. The findings shed light on a unique mechanism associated with the pathogenesis of astrocytomas and provide a model for the loss of contact inhibition that may broadly apply to understanding the mechanisms of tissue repair and tumorigenesis in the brain.

MicroRNA-200a suppresses the Wnt/β-catenin signaling pathway by interacting with β-catenin

The Wnt/β-catenin signaling pathway is crucial for human organ development and is involved in tumor progression of many cancers. Accumulating evidence suggests that the expression of β-catenin is, in part, regulated by specific microRNAs (miRNAs). The purpose of this study was to determine the expression of a recently identified epithelial to mesenchymal transition (EMT)-associated tumor suppressor microRNA (miR)-200a, in cancer cells. We also aimed to identify specific miR-200a target genes and to investigate the antitumor effects of miR-200a on the Wnt/β-catenin signaling pathway. We employed TOP/FOP flash luciferase assays to identify the effect of miR-200a on the Wnt/β-catenin pathway and we confirmed our observations using fluorescence microscopy. To determine target genes of miR-200a, a 3' untranslated region (3' UTR) luciferase assay was performed. Cell viability, invasion and wound healing assays were carried out for functional analysis after miRNA transfection. We further investigated the role of miR-200a in EMT by Western blot analysis. We found fluctuation in the expression of miR-200a that was accompanied by changes in the expression of members of the Wnt/β-catenin signaling pathway. We also determined that miR-200a can directly interact with the 3' UTR of CTNNB1 (the gene that encodes β-catenin) to suppress Wnt/β-catenin signaling. MiR-200a could also influence the biological activities of SGC790 and U251 cells. Our results demonstrate that miR-200a is a new tumor suppressor that can regulate the activity of the Wnt/β-catenin signaling pathway via two mechanisms. MiR-200a is a candidate target for tumor treatment via its regulation of the Wnt/β-catenin signaling pathway.

Wnt/beta-catenin signaling in glioma

Extensive data have shown that Wnt/beta-catenin signaling is associated with various disease pathologies, including an important role in tumorigenesis. Here, we review the regulation of Wnt/beta-catenin signaling in glioma, with particular focus on the expression signatures of the main components in Wnt/beta-catenin signaling, the role of key factors in Wnt/beta-catenin signaling, and crosstalk with other signaling pathways. Finally, we discuss the involvement of microRNAs in Wnt/beta-catenin signaling in glioma. This review reveals new insights into the role of Wnt/beta-catenin signaling in gliomagenesis, and highlights new therapeutic approaches for glioma, based on the modulation of the Wnt/beta-catenin pathway.

β-Catenin Signalling in Glioblastoma Multiforme and Glioma-Initiating Cells

Glioblastoma multiforme (GBM) is a commonly occurring brain tumor with a poor prognosis. GBM can develop both "de novo" or evolve from a previous astrocytoma and is characterized by high proliferation and infiltration into the surrounding tissue. Following treatment (surgery, radiotherapy, and chemotherapy), tumors often reappear. Glioma-initiating cells (GICs) have been identified in GBM and are thought to be responsible for tumors initiation, their continued growth, and recurrence. β-catenin, a component of the cell-cell adhesion complex and of the canonical Wnt pathway, regulates proliferation, adhesion, and migration in different cell types. β-catenin and components of the Wnt canonical pathway are commonly overexpressed in GBM. Here, we review previous work on the role of Wnt/β-catenin signalling in glioma initiation, proliferation, and invasion. Understanding the molecular mechanisms regulating GIC biology and glioma progression may help in identifying novel therapeutic targets for GBM treatment.

MicroRNA-200a suppresses the Wnt/β-catenin signaling pathway by interacting with β-catenin

The Wnt/β-catenin signaling pathway is crucial for human organ development and is involved in tumor progression of many cancers. Accumulating evidence suggests that the expression of β-catenin is, in part, regulated by specific microRNAs (miRNAs). The purpose of this study was to determine the expression of a recently identified epithelial to mesenchymal transition (EMT)-associated tumor suppressor microRNA (miR)-200a, in cancer cells. We also aimed to identify specific miR-200a target genes and to investigate the antitumor effects of miR-200a on the Wnt/β-catenin signaling pathway. We employed TOP/FOP flash luciferase assays to identify the effect of miR-200a on the Wnt/β-catenin pathway and we confirmed our observations using fluorescence microscopy. To determine target genes of miR-200a, a 3' untranslated region (3' UTR) luciferase assay was performed. Cell viability, invasion and wound healing assays were carried out for functional analysis after miRNA transfection. We further investigated the role of miR-200a in EMT by Western blot analysis. We found fluctuation in the expression of miR-200a that was accompanied by changes in the expression of members of the Wnt/β-catenin signaling pathway. We also determined that miR-200a can directly interact with the 3' UTR of CTNNB1 (the gene that encodes β-catenin) to suppress Wnt/β-catenin signaling. MiR-200a could also influence the biological activities of SGC790 and U251 cells. Our results demonstrate that miR-200a is a new tumor suppressor that can regulate the activity of the Wnt/β-catenin signaling pathway via two mechanisms. MiR-200a is a candidate target for tumor treatment via its regulation of the Wnt/β-catenin signaling pathway.

Shared molecular targets in pediatric gliomas and ependymomas

BACKGROUND

Recent advances in multidisciplinary treatment approaches have improved the overall prognosis of pediatric brain tumors, but some patients remain refractory to treatment and do poorly. Several molecularly targeted therapies are under development for the treatment of brain tumors, and high-grade gliomas in adults are a particular area of study.

PROCEDURE

To better understand if these new therapies can be used in pediatric populations, we examined the expression of the following seven marker genes involved in signaling pathways targeted by new therapies: β-catenin, suppressor of fused (SUFU), erythroblastic leukemia viral oncogene homolog (ERBB) 2, platelet-derived growth factor receptorα (PDGFRα), proliferating cell nuclear antigen (PCNA), secreted protein acid and rich in cysteine (SPARC), and granulocyte colony-stimulating factor receptor (G-CSFR). Samples from 27 patients with the primitive neuroectodermal tumor (PNET)/medulloblastomas (MBs) (n = 8), ependymomas (n = 5), or gliomas (n = 14) were assessed by quantitative real-time PCR. [Correction made here after initial online publication]. We assigned an EXP score to compare across samples and determined the levels of gene expression among tumor cell types.

RESULTS

Gene expression varied among the different tumors, but, within a tumor type, clear expression patterns were seen. The expression of SUFU, ERBB2, and PCNA in metastatic MBs were greater than that seen in non-metastatic MBs. Most glioma cases highly expressed PDGFRα and G-CSFR. Additionally, the expression patterns of gliomas and ependymomas were similar (r = 0.77, P = 0.04), but PNET/MBs substantially differed from gliomas (r = -0.37, P = 0.41) or ependymomas (r = 0.23, P = 0.62).

CONCLUSIONS

The development of new drugs targeting up-regulated pathways may be useful for the treatment of pediatric brain tumors. As new drugs are developed, gliomas and ependymomas may be treated with similar compounds.

The Wnt secretion protein Evi/Gpr177 promotes glioma tumourigenesis

Malignant astrocytomas are highly aggressive brain tumours with poor prognosis. While a number of structural genomic changes and dysregulation of signalling pathways in gliomas have been described, the identification of biomarkers and druggable targets remains an important task for novel diagnostic and therapeutic approaches. Here, we show that the Wnt-specific secretory protein Evi (also known as GPR177/Wntless/Sprinter) is overexpressed in astrocytic gliomas. Evi/Wls is a core Wnt signalling component and a specific regulator of pan-Wnt protein secretion, affecting both canonical and non-canonical signalling. We demonstrate that its depletion in glioma and glioma-derived stem-like cells led to decreased cell proliferation and apoptosis. Furthermore, Evi/Wls silencing in glioma cells reduced cell migration and the capacity to form tumours in vivo. We further show that Evi/Wls overexpression is sufficient to promote downstream Wnt signalling. Taken together, our study identifies Evi/Wls as an essential regulator of glioma tumourigenesis, identifying a pathway-specific protein trafficking factor as an oncogene and offering novel therapeutic options to interfere with the aberrant regulation of growth factors at the site of production.

Sensitization of glioma cells to tamoxifen-induced apoptosis by Pl3-kinase inhibitor through the GSK-3β/β-catenin signaling pathway

Malignant gliomas represent one of the most aggressive types of cancers and their recurrence is closely linked to acquired therapeutic resistance. A combination of chemotherapy is considered a promising therapeutic model in overcoming therapeutic resistance and enhancing treatment efficacy. Herein, we show by colony formation, Hochest 33342 and TUNEL staining, as well as by flow cytometric analysis, that LY294002, a specific phosphatidylinositide-3-kinase (PI3K) inhibitor, enhanced significantly the sensitization of a traditional cytotoxic chemotherapeutic agent, tamoxifen-induced apoptosis in C6 glioma cells. Activation of PI3K signaling pathway by IGF-1 protected U251 cells from apoptosis induced by combination treatment of LY294002 and tamoxifen. Interference of PI3K signaling pathway by PI3K subunit P85 siRNA enhanced the sensitization of U251 glioma cells to tamoxifen -induced apoptosis. By Western blotting, we found that combination treatment showed lower levels of phosphorylated Akt^Ser473 and GSK-3β^Ser9 than a single treatment of LY294002. Further, we showed a significant decrease of nuclear β-catenin by combination treatment. In response to the inhibition of β-catenin signaling, mRNA and protein levels of Survivin and the other three antiapoptotic genes Bcl-2, Bcl-xL, and Mcl-1 were significantly decreased by combination treatment. Our results indicated that the synergistic cytotoxic effect of LY294002 and tamoxifen is achieved by the inhibition of GSK-3β/β-catenin signaling pathway.

Increased β-catenin/Tcf signaling in pilocytic astrocytomas: a comparative study to distinguish pilocytic astrocytomas from low-grade diffuse astrocytomas

Although pilocytic and diffuse grade II astrocytomas considered as low-grade tumors, the distinction between them is still a major clinical problem. Previously we reported the activation of Wnt/β-catenin/Tcf signaling pathway in diffuse astrocytomas, however its role in pilocytic astrocytomas is not well understood. In this study, we investigated the Wnt/β-catenin/Tcf pathway in pilocytic astrocytomas and compared with diffuse astrocytomas. We observed the differential expression of β-catenin, Tcf4, Lef1 and c-Myc in astrocytomas particularly higher levels were observed in pilocytic astrocytomas and GBM while very little expression was documented in grade II tumors. Further, immunohistochemical analysis revealed the strong positivity of β-catenin, Tcf4, Lef1 and c-Myc in pilocytic astrocytomas than that of grade II tumors and also exhibited the strong positivity in vascular endothelial cells of pilocytic astrocytomas and GBM. Hence, Wnt/β-catenin/Tcf signaling pathway is differentially expressed in astrocytomas, activation of this pathway might be helpful in separating pilocytic astrocytomas from low-grade diffuse astrocytomas.

Antitumor effect of aspirin in glioblastoma cells by modulation of β-catenin/T-cell factor-mediated transcriptional activity

OBJECT

The goal in this study was to investigate the antitumor effect of aspirin in glioblastoma cells and the molecular mechanism involved in its antineoplastic activities.

METHODS

The authors used the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide method, flow cytometry, the annexin V method, and Transwell cell invasion test to detect the proliferation and invasive activity of U87 and A172 glioma cells before and after being treated with aspirin. To determine the effects of aspirin on β-catenin/T-cell factor (TCF) transcription activity, reporter constructs containing 3 repeats of the wild-type (TOPflash) or mutant (FOPflash) TCF-binding sites were used. Reverse transcriptase polymerase chain reaction and Western blot analyses were used to detect the expression of multiple β-catenin/TCF target genes following aspirin treatment.

RESULTS

The transcriptional activity of the β-catenin/TCF complex was strongly inhibited by aspirin. Increasing the concentration of aspirin resulted in decreased expression of c-myc, cyclin D1, and fra-1 mRNA and protein in U87 and A172 cells in a dose-dependent manner. Aspirin inhibited glioma cell proliferation and invasive ability, and induced apoptotic cell death.

CONCLUSIONS

The results suggest that aspirin is a potent antitumor agent, and that it exerts its antineoplastic action by inhibition of the β-catenin/TCF signaling pathway in glioma cells.

High β-catenin/Tcf-4 activity confers glioma progression via direct regulation of AKT2 gene expression

Recent data suggest that the β-catenin/Tcf-4 signaling pathway plays an important role in human cancer tumorigenesis. However, the mechanism of β-catenin/Tcf-4 signaling in tumorigenesis is poorly understood. In this study, we show that Tcf-4 protein levels were significantly elevated in high-grade gliomas in comparison with low-grade gliomas and that Tcf-4 levels correlated with levels of AKT2. Reduction of β-catenin/Tcf-4 activity inhibited glioma cell proliferation and invasion in vitro and tumor growth in vivo. This effect of β-catenin/Tcf-4 activity was mediated by AKT2, and in vivo binding of β-catenin/Tcf-4 to the AKT2 promoter was validated using the chromatin immunoprecipitation assay and luciferase reporter assays. Taken together, we have demonstrated that Tcf-4 is associated with glioma progression and that AKT2 is a new member of the genes that are regulated by β-catenin/Tcf-4.

Interruption of β-catenin suppresses the EGFR pathway by blocking multiple oncogenic targets in human glioma cells

Malignant gliomas are the most common type of intrinsic central nervous system (CNS) tumors with high mortality and morbidity. β-catenin is overexpressed in human glioblastoma and knockdown of β-catenin inhibits glioblastoma cell proliferation and invasive ability, and induces apoptotic cell death. Furthermore, treating the nude mice carrying established subcutaneous LN229 gliomas with siRNA targeting β-catenin intratumorally also delayed the tumor growth. However, the mechanisms of down-regulation of β-catenin that represses glioblastoma malignancy behavior remain to be elucidated. We utilized text-mining of MEDLINE abstracts with natural language processing to establish the β-catenin biologic association network, and identified several interactions of this network with the EGFR pathway. In both in vitro and in vivo studies, our results confirmed down-regulation of β-catenin induced reduced expression of EGFR, STAT3 and AKT1 mRNA and protein, besides, the level of phosphorylated Akt also decreased. A similar reduction in expression of CyclinD1, MMP2 and MMP9, downstream genes of the EGFR pathway, was observed. These results suggest that the Wnt/β-catenin pathway regulates glioma cell proliferation and invasion, in part via the EGFR pathway.

MicroRNA roles in beta-catenin pathway

β-catenin, a key factor in the Wnt signaling pathway, has essential functions in the regulation of cell growth and differentiation. Aberrant β-catenin signaling has been linked to various disease pathologies, including an important role in tumorigenesis. Here, we review the regulation of the Wnt signaling pathway as it relates to β-catenin signaling in tumorigenesis, with particular focus on the role of microRNAs. Finally, we discuss the potential of β-catenin targeted therapeutics for cancer treatment.

Wnt/beta-Catenin pathway in human glioma: expression pattern and clinical/prognostic correlations

Gliomas are the most common primary intracranial tumors. Understanding the molecular basis of gliomas' progression is required to develop more effective therapies. The Wnt/β-catenin signaling cascade is an important signal transduction pathway in human cancers. Although, overactivation of this pathway is a hallmark of several forms of cancer, little is known about its role in human gliomas. Here, we aimed to determine the clinical significance of Wnt/β-catenin pathway components in gliomas. Immunohistochemical staining was performed to detect the expression patterns of Wnt1, β-catenin and Cyclin D1 in the biopsies from 96 patients with primary gliomas. Kaplan-Meier survival and Cox regression analyses were performed to evaluate the prognosis of patients. Cytoplasmic staining pattern of Wnt1, membranous, cytoplasmic and nuclear accumulation of β-catenin, and nuclear localization of Cyclin D1 were demonstrated by immunohistochemical staining. The Wnt1 expression significantly correlated with the expression of Cyclin D1 (P < 0.0001). The ratio of tumors with a cytoplasmic-nuclear pattern or a cytoplasmic pattern of β-catenin was significantly higher in Wnt1-positive (P < 0.01) and Cyclin D1-positive (P < 0.01) tumors than in Wnt1-negative and Cyclin D1-negative tumors, respectively. The protein expression levels of Wnt1, β-catenin and Cyclin D1 were all positively correlated with the Karnofsky performance scale (KPS) score and World Health Organization (WHO) grades of patients with gliomas. Furthermore, Wnt1, cytoplasmic-nuclear β-catenin and Cyclin D1 status were all the independent prognostic factors for glioma patients (P = 0.01, 0.007 and 0.005, respectively). These results provide convincing evidence that the Wnt/β-catenin pathway correlated closely with the progression of gliomas and might be a novel prognostic marker for this neoplasm.

Downregulation of WIF-1 by hypermethylation in astrocytomas

Wnt inhibitory factor-1 (WIF-1) acts as a Wnt antagonist and tumor suppressor, but hypermethylation of WIF-1 gene promoter and low expression of WIF-1 activate Wnt signaling aberrantly and induce the development of several human tumors. By using RT-PCR, immunohistochemistry and methylation-specific PCR, we analyzed the expression and methylation of WIF-1 in 4 normal brain tissues, 35 freshly resected astrocytoma tissues and 4 glioblastoma-derived cell lines. Significant downregulation of WIF-1 mRNA and protein expression levels was observed in astrocytoma tissues compared with normal brain tissues. Significant association between WIF-1 downregulation and pathological grade of astrocytomas was found. WIF-1 gene aberrant methylation was observed in 19 of 35 (54.29%) tumor samples. The promoter methylation tumors showed low WIF-1 protein and mRNA expression, whereas the promoter unmethylation tumors displayed high protein and mRNA expression levels. Moreover, complete absence of WIF-1 mRNA expression was observed in four cell lines, whereas treatment with demethylating agent, 5-aza-2'-deoxycytidine, restored WIF-1 expression. Our results suggested that the WIF-1 gene is frequently silenced in astrocytoma by aberrant promoter methylation. This may be an important mechanism in astrocytoma carcinogenesis.

Expression and aberrant promoter methylation of Wnt inhibitory factor-1 in human astrocytomas

BACKGROUND

Wnt inhibitory factor-1(WIF-1) acts as a Wnt-antagonists and tumor suppressor, but hypermethylation of WIF-1 gene promoter and low expression activate Wnt signaling aberrantly and induce the development of various human tumors. With this work we intended to investigate the expression and promoter methylation status of WIF-1 gene in human astrocytomas.

METHODS

The tissue samples consisted of 53 astrocytomas and 6 normal brain tissues. The expression levels of WIF-1 were determined by immunohistochemistry and semiquantitative RT-PCR. The results were analyzed in correlation with clinicopathological data. Methylation status of WIF-1 gene promoter was investigated using methylation specific PCR. The relationship between methylation and expression of the genes was analyzed.

RESULTS

The average expression levels of WIF-1 protein and mRNA in astrocytomas were decreased significantly compared with normal control tissues. The protein and mRNA expression of WIF-1 gene in astrocytomas was decreased with the increase of pathological grade. Furthermore, WIF-1 promoter methylation was observed by MS-PCR in astrocytomas which showed significant reduction of WIF-1 expression. The WIF-1 promoter hypermethylation was associated with reduced expression of WIF-1 expression.

CONCLUSION

Our results demonstrate that the WIF-1 gene is frequently down-regulated or silenced in astrocytomas by aberrant promoter methylation. This may be an important mechanism in astrocytoma carcinogenesis.

β-Catenin overexpression in malignant glioma and its role in proliferation and apoptosis in glioblastma cells

β-Catenin, a core component of Wnt/β-catenin signaling, has been shown to be a crucial factor in a broad range of tumors, while its role in glioma is not well understood. In this study, the expression of β-catenin in astrocytic glioma tissues with different grade and human normal cerebral tissues was examined using reverse transcription-polymerase chain reaction (RT-PCR) and immunohistochemistry. We found a higher expression level of β-catenin in astrocytic glioma patients with high grade in comparison with the normal controls. Additionally, siRNA was transfected into human U251 glioblastoma cells by liposome after the design of siRNA was confirmed to effectively inhibit the expression of β-catenin by RT-PCR. Compared to the control siRNA group, siRNA-mediated knockdown of β-catenin in human U251 cells inhibited cell proliferation, resulted in cell apoptosis, and arrested cell cycle in G₀/G₁. Additionally, downregulation of β-catenin decreased the expression level of cyclin D1, c-Myc and c-jun. Taken together, these results indicate that overexpression of β-catenin may be an important contributing factor to glioma progression.

The expression profile of FRAT1 in human gliomas

FRAT1 was originally characterized as a protein frequently rearranged in advanced T cell lymphoma, which inhibits GSK-3-mediated phosphorylation of beta-catenin and positively regulates the Wnt signaling pathway. FRAT1 has been identified as a proto-oncogene involved in tumorigenesis. Previous studies have shown that FRAT1 is strikingly overexpressed in some human cancers. However, the relationship between FRAT1 and human gliomas is unclear. In this study, we detected the expression of FRAT1 in human gliomas by immunohistochemistry, Western blot and RT-PCR. FRAT1 was found to be specifically expressed in the majority of glioma samples, and their expression levels increased markedly with the increase of WHO grades. In addition, there was a positive correlation between FRAT1 immunoreactivity score (IRS) and beta-catenin IRS. Our results suggest that FRAT1 may be an important factor in the tumorigenesis and progression of gliomas, and could be used as a potential molecular marker for pathological diagnosis and a target for biological therapy.

Differentiation of the brain vasculature: the answer came blowing by the Wnt

Vascularization of the vertebrate brain takes place during embryonic development from a preformed perineural vascular plexus. As a consequence of the intimate contact with neuroectodermal cells the vessels, which are entering the brain exclusively via sprouting angiogenesis, acquire and maintain unique barrier properties known as the blood-brain barrier (BBB). The endothelial BBB depends upon the close association of endothelial cells with pericytes, astrocytes, neurons and microglia, which are summarized in the term neuro-vascular unit. Although it is known since decades that the CNS tissue provides the cues for BBB induction and differentiation in endothelial cells, the molecular mechanism remained obscure.Only recently, the canonical Wnt/beta-catenin pathway and the Wnt7a/7b growth factors have been implicated in brain angiogenesis on the one hand and in BBB induction on the other. This breakthrough in understanding the differentiation of the brain vasculature prompted us to review these findings embedded in the emerging concepts of Wnt signaling in the vasculature. In particular, interactions with other pathways that are crucial for vascular development such as VEGF, Notch, angiopoietins and Sonic hedgehog are discussed. Finally, we considered the potential role of the Wnt pathway in vascular brain pathologies in which BBB function is hampered, as for example in glioma, stroke and Alzheimer's disease.