Functions In Glioblastoma Research Articles

SynCAM, a novel putative tumor suppressor, suppresses growth and invasiveness of glioblastoma

SynCAM, also named by TSLC1, SgIGSF and IGSF4, was identified as a neural tissue-specific immunoglobulin-like cell-cell adhesion molecule. However, the role of SynCAM in tumorigenesis remains elusive. We aimed to clarify its epigenetic regulation and biological functions in glioblastoma. SynCAM was silenced in 72% (5/7) glioblastoma cell lines. A significant downregulation was also detected in paired glioblastoma tumors compared with adjacent non-cancerous tissues. In contrast, SynCAM was readily expressed in various normal adult brain tissues. Ectopic expression of SynCAM in the silenced cancer cell line T98G significantly reduced colony formation and cell proliferation, induced cell cycle arrests and repressed cell invasive ability. Nude mice were subcutaneously injected into the flank with T98G cells and treated with normal saline, pcDNA3.1 (vector) or pcDNA3.1-SynCAM, respectively. Treatment with pcDNA3.1-SynCAM retarded growth in the xenografts, which contributed to a 58% decrease in tumor volume compared to controls. In conclusion, our results suggest that SynCAM suppressions growth of glioblastoma and may serve as a novel functional tumor-suppressor gene.

MiR-145 functions as a tumor-suppressive RNA by targeting Sox9 and adducin 3 in human glioma cells

MicroRNAs (miRNAs) are increasingly being recognized as being involved in cancer development and progression in gliomas. Using a model cell system developed in our lab to study glioma progression comprising human neuroglial culture (HNGC)-1 and HNGC-2 cells, we report here that miR-145 is one of the miRNAs significantly downregulated during malignant transformation in glioblastoma multiforme (GBM). In a study using tumor samples derived from various glioma grades, we show that expression of miR-145 is decreased in a graded manner, with GBM patients showing lowest expression relative to lower-grade gliomas (P < .05) and normal brain tissues (P < .0001). Functional studies involving ectopic expression of miR-145 in glioma cells had a negative impact on cell proliferation and tumor development, as well as invasion and induced apoptosis, providing further support to the concept that inactivation of miR-145 is important for glioma disease pathogenesis. More notably, these growth-suppressive effects of miR-145 are mediated through its target proteins Sox9 and the cell adhesion-associated molecule adducin 3 (ADD3). Inhibiting Sox9 and ADD3 rescued effects of miR-145 loss. Interestingly, miR-145 loss in glioma cells led to overexpression of molecules involved in cell proliferation, like cyclin D1, c-myc, and N-myc, as well as enhanced expression of cell adhesion- and invasion-related molecules N-cadherin and E-cadherin, an effect which was again restored upon miR-145 overexpression in glioma cells. The miR-145 promoter was methylated at its cytosine-phosphate-guanine (CpG) islands in the glioma cell lines studied. Our study demonstrates that miR-145 has a tumor-suppressive function in glioblastoma in that it reduces proliferation, adhesion, and invasion of glioblastoma cells, apparently by suppressing the activity of oncogenic proteins Sox9 and ADD3. Reduced levels of miR-145 may lead to neoplastic transformation and malignant progression in glioma due to unregulated activity of these proteins.

Abstract 837: Identification of non-canonical NF-κB signaling as a critical mediator of Smac mimetic-stimulated migration and invasion of glioblastoma cells.

Abstract Since inhibitor of apoptosis (IAP) proteins can regulate additional signaling pathways beyond apoptosis, we investigated the effect of the Smac mimetic BV6, which antagonizes IAP proteins, on non-apoptotic functions in glioblastoma (GBM). Here, we identify non-canonical NF-κB signaling and a TNFα/TNFR1 autocrine/paracrine loop as critical mediators of BV6-stimulated migration and invasion of GBM cells. In addition to GBM cell lines, BV6 triggers cell elongation, migration and invasion in primary, patient-derived GBM cells at non-toxic concentrations, which do not affect cell viability or proliferation, and also increases infiltrative tumor growth in vivo underscoring the relevance of these findings. Molecular studies reveal that BV6 causes rapid degradation of cIAP proteins, accumulation of NIK, processing of p100 to p52, translocation of p52 into the nucleus, increased NF-κB DNA binding and enhanced NF-κB transcriptional activity. EMSA supershift shows that the NF-κB DNA binding subunits consist of p50, p52 and RelB further confirming activation of the non-canonical NF-κB pathway. BV6-stimulated NF-κB activation leads to elevated mRNA levels of TNFα and additional NF-κB target genes involved in migration (i.e. IL-8, MCP-1, CXCR4) and invasion (i.e. MMP9). Importantly, inhibition of NF-κB by overexpression of dominant-negative IκBα superrepressor prevents the BV6-stimulated cell elongation, migration and invasion. Similarly, specific inhibition of non-canonical NF-κB signaling by RNA interference-mediated silencing of NIK suppresses the BV6-induced cell elongation, migration and invasion as well as upregulation of NF-κB target genes. Intriguingly, pharmacological or genetic inhibition of the BV6-stimulated TNFα autocrine/paracrine loop by the TNFα-blocking antibody Enbrel or by knockdown of TNFR1 abrogates the BV6-induced cell elongation, migration and invasion. By demonstrating that the Smac mimetic BV6 at non-toxic concentrations promotes migration and invasion of GBM cells via non-canonical NF-κB signaling, our findings have Citation Format: Aurelie Tchoghandjian, Claudia Jennewein, Ines Eckhardt, Krishna Rajalingam, Simone Fulda. Identification of non-canonical NF-κB signaling as a critical mediator of Smac mimetic-stimulated migration and invasion of glioblastoma cells. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 837. doi:10.1158/1538-7445.AM2013-837

Identification of non-canonical NF-κB signaling as a critical mediator of Smac mimetic-stimulated migration and invasion of glioblastoma cells

As inhibitor of apoptosis (IAP) proteins can regulate additional signaling pathways beyond apoptosis, we investigated the effect of the second mitochondrial activator of caspases (Smac) mimetic BV6, which antagonizes IAP proteins, on non-apoptotic functions in glioblastoma (GBM). Here, we identify non-canonical nuclear factor-κB (NF-κB) signaling and a tumor necrosis factor-α (TNFα)/TNF receptor 1 (TNFR1) autocrine/paracrine loop as critical mediators of BV6-stimulated migration and invasion of GBM cells. In addition to GBM cell lines, BV6 triggers cell elongation, migration and invasion in primary, patient-derived GBM cells at non-toxic concentrations, which do not affect cell viability or proliferation, and also increases infiltrative tumor growth in vivo underscoring the relevance of these findings. Molecular studies reveal that BV6 causes rapid degradation of cellular IAP proteins, accumulation of NIK, processing of p100 to p52, translocation of p52 into the nucleus, increased NF-κB DNA binding and enhanced NF-κB transcriptional activity. Electrophoretic mobility shift assay supershift shows that the NF-κB DNA-binding subunits consist of p50, p52 and RelB further confirming the activation of the non-canonical NF-κB pathway. BV6-stimulated NF-κB activation leads to elevated mRNA levels of TNFα and additional NF-κB target genes involved in migration (i.e., interleukin 8, monocyte chemoattractant protein 1, CXC chemokine receptor 4) and invasion (i.e., matrix metalloproteinase-9). Importantly, inhibition of NF-κB by overexpression of dominant-negative IκBα superrepressor prevents the BV6-stimulated cell elongation, migration and invasion. Similarly, specific inhibition of non-canonical NF-κB signaling by RNA interference-mediated silencing of NIK suppresses the BV6-induced cell elongation, migration and invasion as well as upregulation of NF-κB target genes. Intriguingly, pharmacological or genetic inhibition of the BV6-stimulated TNFα autocrine/paracrine loop by the TNFα-blocking antibody Enbrel or by knockdown of TNFR1 abrogates BV6-induced cell elongation, migration and invasion. By demonstrating that the Smac mimetic BV6 at non-toxic concentrations promotes migration and invasion of GBM cells via non-canonical NF-κB signaling, our findings have important implications for the use of Smac mimetics as cancer therapeutics.

Abstract 2117: The Wnt inhibitory factor 1 (WIF-1) has tumor suppressing functions in glioblastoma potentially by inducing cellular senescence

Abstract Glioblastoma multiforme is the most aggressive form of human glioma and despite recent progress in therapy the prognosis remains dismal with a median survival of 15 months. Expression based prediction of gene alterations identified Wnt inhibitory factor I (WIF1) as a new candidate tumor suppressor gene involved in glioblastoma. WIF1 encodes a secreted Wnt antagonist and it was strongly down-regulated in most glioblastoma as compared to normal brain, implying deregulation of Wnt signaling. Silencing of the WIF1 gene was found to be mediated by deletion and WIF1 promoter hypermethylation. Ectopic expression of WIF1 in glioblastoma cell lines revealed a dose dependent decrease of Wnt pathway activity. To further dissect the biological effects of WIF1 re-expression, we established WIF1 overexpressing glioblastoma cell lines. We observed that WIF1 re-expression inhibited cell proliferation in vitro and strongly reduced anchorage independent growth. The ability of forming colonies in soft agar was reduced to less than 11% of the control. Moreover, the expression of WIF1 was able to completely abolish tumorigenicity in a respective xenograft model in nude mice. Interestingly, WIF1 overexpression in glioblastoma cells induced a senescence-like phenotype characterized by the appearance of enlarged flattened and multinucleated cells positive for the presence of β-galactosidase, a late marker of senescence. These results provide evidence that WIF1 has tumor suppressing properties in glioblastoma, hence, the implication of a deregulated Wnt pathway may render glioblastoma sensitive to Wnt signaling inhibitors, potentially by diverting the tumor cells into a senescence-like state. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2117. doi:10.1158/1538-7445.AM2011-2117

Abstract 17: Bcl-2 is a downstream target of ATF5 that mediates ATF5's pro-survival function in a cell type-dependent manner

Abstract The activating transcription factor 5 (ATF5) is a member of the ATF/CREB family of basic zipper (bZIP) proteins. Recent reports showed that ATF5 loss-of-function causes apoptotic cell death in glioblastoma and breast cancer cells but not in non-transformed astrocytes and human breast epithelial cells. The mechanism for ATF5's cell type-dependent survival function is unknown. We report here that the anti-apoptotic factor Bcl-2 is a downstream target that mediates ATF5-promoted cancer-cell survival in C6 glioma cells and MCF-7 breast cancer cells. ATF5 binds to an ATF5-specific regulatory element (ARE) that is downstream of and adjacent to the negative regulatory element (NRE) in the Bcl-2 P2 promoter, stimulating Bcl-2 expression. Highlighting the importance of Bcl-2 in ATF5-dependent cancer-cell survival, expression of Bcl-2 blocks death of C6 and MCF-7 cells induced by d/nATF5 and depletion of Bcl-2 impairs ATF5-promoted cell survival. Moreover, we found that Bcl-2 expression is not regulated by ATF5 in non-transformed rat astrocytes, MEFs, and human breast epithelial cells (HBEC), where knock-down of Bcl-2 but not that of ATF5 evokes cell death. These findings identify Bcl-2 as an essential mediator for ATF5's cancer-specific cell survival function in glioblastoma and breast cancer cells and provide direct evidence that the cell type-specific function of ATF5 derives from the differential regulation of downstream targets by ATF5 in different types of cells. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 17. doi:10.1158/1538-7445.AM2011-17

Acyclovir inhibition of IDO to decrease Tregs as a glioblastoma treatment adjunct

Regulatory T cells, Tregs, are a subset of lymphocytes that have immunosuppressive attributes. They are elevated in blood of glioblastoma patients and within this tumor's tissue itself. Indoleamine 2,3-dioxygenase, IDO, converts tryptophan to kynurenine. IDO activity enhances Treg formation by pathways that are unknown. Experimentally, inhibition of IDO decreases Treg function and number in rodents. The common anti-viral agent acyclovir inhibits IDO. Acyclovir may thereby decrease Treg function in glioblastoma. If it can be confirmed that Treg counts are elevated in glioblastoma patients' tumor tissue, and if we can document acyclovir's lowering of tissue Treg counts by a small trial of acyclovir in pre-operative glioblastoma patients, a trial of acyclovir effect on survival should be done given the current poor prognosis of glioblastoma and the well-established safety and low side effect burden of acyclovir.

167 MicroRNA-34 family in triple-negative/basal-like breast cancer

MicroRNAs are endogenously expressed regulatory noncoding RNAs. Altered expression levels of several microRNAs have been observed in glioblastomas. Functions and direct mRNA targets for these microRNAs have been relatively well studied over the last years. According to these data, it is now evident, that impairment of microRNA regulatory network is one of the key mechanisms in glioblastoma pathogenesis. MicroRNA deregulation is involved in processes such as cell proliferation, apoptosis, cell cycle regulation, invasion, glioma stem cell behavior, and angiogenesis. In this review, we summarize the current knowledge of miRNA functions in glioblastoma with an emphasis on its significance in glioblastoma oncogenic signaling and its potential to serve as a disease biomarker and a novel therapeutic target in oncology.

Epigenetic Regulation of Wnt Pathway Antagonists in Human Glioblastoma Multiforme

Epigenetic inactivation of tumor suppressor genes is common in human cancer. Using a large-scale whole-genome approach in an earlier study, the authors identified epigenetically silenced genes with potential tumor suppressor function in glioblastoma (GBM). Three genes identified in this analysis-DKK1, SFRP1, and WIF1-are potent inhibitors of the Wnt signal transduction pathway. Here, the authors confirm decreased expression of these genes in GBM tumor tissue samples relative to nontumor brain tissue samples using real-time PCR. They then show that expression of all 3 genes is restored in T98 GBM cells by treatment with the histone deacetylase inhibitor Trichostatin A (TSA), but only DKK1 expression is restored by treatment with the demethylating agent 5-azacytidine. Bisulfite sequencing did not reveal significant methylation in the promoter region of DKK1, whereas histone acetylation and chromatin accessibility increased significantly for all 3 genes after TSA treatment. Ectopic expression of DKK1 significantly reduces colony formation and increases chemotherapy-induced apoptosis in T98 cells. Ectopic expression of the canonical Wnt pathway inhibitors WIF1 and SFRP1 shows a relative lack of response. Chronic Wnt3a stimulation only partially reverses growth suppression after DKK1 reexpression, whereas a specific inhibitor of the JNK pathway significantly reverses the effect of DKK1 reexpression on colony formation and apoptosis in T98 cells. These results support a potential growth-suppressive function for epigenetically silenced DKK1 in GBM and suggest that DKK1 restoration could modulate Wnt signaling through both canonical and noncanonical pathways.

MicroRNA involvement in glioblastoma pathogenesis

MicroRNAs are endogenously expressed regulatory noncoding RNAs. Altered expression levels of several microRNAs have been observed in glioblastomas. Functions and direct mRNA targets for these microRNAs have been relatively well studied over the last years. According to these data, it is now evident, that impairment of microRNA regulatory network is one of the key mechanisms in glioblastoma pathogenesis. MicroRNA deregulation is involved in processes such as cell proliferation, apoptosis, cell cycle regulation, invasion, glioma stem cell behavior, and angiogenesis. In this review, we summarize the current knowledge of miRNA functions in glioblastoma with an emphasis on its significance in glioblastoma oncogenic signaling and its potential to serve as a disease biomarker and a novel therapeutic target in oncology.

Expression of highly sulfated keratan sulfate synthesized in human glioblastoma cells

Keratan sulfate (KS) proteoglycan is expressed in the extracellular matrix or cell surface in numerous tissues, predominantly in those of the cornea, cartilage, and brain. However, its structure, function, and regulation remain poorly understood. Our investigation of KS expression in glioblastoma cell lines using Western-blot and flow cytometry with anti-KS antibody (5D4) revealed that LN229 glioblastoma cell highly expresses KS on a cell surface. Real-time PCR analysis showed that LN229 expresses a high level of keratan sulfate Gal-6-sulfotransferase. Results of this study also demonstrate that recombinant 5D4-reactive aggrecan is produced in LN229. Taken together, these results suggest that LN229 produces 5D4-reactive highly sulfated KS and is useful to investigate the KS structure and function in glioblastoma.