A novel function of OLIG2 to suppress human glial tumor cell growth via p27Kip1 transactivation

Computing microRNA-gene interaction networks in pan-cancer using miRDriver

DNA copy number aberrated regions in cancer are known to harbor cancer driver genes and the short non-coding RNA molecules, i.e., microRNAs. In this study, we integrated the multi-omics datasets such as copy number aberration, DNA methylation, gene and microRNA expression to identify the signature microRNA-gene associations from frequently aberrated DNA regions across pan-cancer utilizing a LASSO-based regression approach. We studied 7294 patient samples associated with eighteen different cancer types from The Cancer Genome Atlas (TCGA) database and identified several cancer-specific and common microRNA-gene interactions enriched in experimentally validated microRNA-target interactions. We highlighted several oncogenic and tumor suppressor microRNAs that were cancer-specific and common in several cancer types. Our method substantially outperformed the five state-of-art methods in selecting significantly known microRNA-gene interactions in multiple cancer types. Several microRNAs and genes were found to be associated with tumor survival and progression. Selected target genes were found to be significantly enriched in cancer-related pathways, cancer hallmark and Gene Ontology (GO) terms. Furthermore, subtype-specific potential gene signatures were discovered in multiple cancer types.

Difference in the malignancy between RAS and GLI1-transformed astrocytes is associated with frequency of p27KIP1-positive cells in xenograft tissues

We demonstrate that the introduction of GLI1 is sufficient for immortalized human astrocytes to be transformed whereas FOXM1 fails to induce malignant transformation, suggesting differences between GLI1 and FOXM1 in terms of transforming ability despite both transcription factors being overexpressed in malignant gliomas. Moreover, in investigations of mechanisms underlying relatively less-malignant features of GLI1-transformed astrocytes, we found that p27KIP1-positive cells were frequently observed in xenografts derived from GLI1-transformed astrocytes compared to those from RAS-transformed cells. As shRNA-mediated knockdown of p27KIP1 accelerates tumor progression of GLI1-transformed astrocytes, downregulation of p27KIP1 contributes to malignant features of transformed astrocytes. We propose that the models using immortalized/transformed astrocytes are useful to identify the minimal and most crucial set of changes required for glioma formation.

Tet2-mediated epigenetic drive for astrocyte differentiation from embryonic neural stem cells

DNA methylation and demethylation at CpG di-nucleotide sites plays important roles in cell fate specification of neural stem cells (NSCs). We have previously reported that DNA methyltransferases, Dnmt1and Dnmt3a, serve to suppress precocious astrocyte differentiation from NSCs via methylation of astroglial lineage genes. However, whether active DNA demethylase also participates in astrogliogenesis remains undetermined. In this study, we discovered that a Ten-eleven translocation (Tet) protein, Tet2, which was critically involved in active DNA demethylation through oxidation of 5-Methylcytosine (5mC), drove astrocyte differentiation from NSCs by demethylation of astroglial lineage genes including Gfap. Moreover, we found that an NSC-specific bHLH transcription factor Olig2 was an upstream inhibitor for Tet2 expression through direct association with the Tet2 promoter, and indirectly inhibited astrocyte differentiation. Our research not only revealed a brand-new function of Tet2 to promote NSC differentiation into astrocytes, but also a novel mechanism for Olig2 to inhibit astrocyte formation.

A strategy for designing allosteric modulators of transcription factor dimerization

Transcription factors in the bHLH family are potentially relevant for tumor growth. Activation requires homodimerization or heterodimerization. Thus, the dimerization step is a likely significant drug target. The oligodendrocyte transcription factor 2 (OLIG2) is overexpressed in gliomas. Here, we developed a fluorescence cross-correlation spectroscopy protocol to examine 10 compounds selected using a pharmacophore-based computational strategy targeting OLIG2 dimerization. We showed that the potency to interact with OLIG2 dimerization in live cells correlates with carcinostatic efficacy. The data indicate a promising approach toward drug development targeting transcription factor overactivity and protein–protein interaction more generally.

Transcription factors (TFs) are fundamental in the regulation of gene expression in the development and differentiation of cells. They may act as oncogenes and when overexpressed in tumors become plausible targets for the design of antitumor agents. Homodimerization or heterodimerization of TFs are required for DNA binding and the association interface between subunits, for the design of allosteric modulators, appears as a privileged structure for the pharmacophore-based computational strategy. Based on this strategy, a set of compounds were earlier identified as potential suppressors of OLIG2 dimerization and found to inhibit tumor growth in a mouse glioblastoma cell line and in a whole-animal study. To investigate whether the antitumor activity is due to the predicted mechanism of action, we undertook a study of OLIG2 dimerization using fluorescence cross-correlation spectroscopy (FCCS) of live HEK cells transfected with 2 spectrally different OLIG2 clones. The selected compounds showed an effect with potency, which correlated with the earlier observed antitumor activity. The OLIG2 proteins showed change in diffusion time under compound treatment in line with dissociation from DNA. The data suggest a general approach of drug discovery based on the design of allosteric modulators of protein–protein interaction.

Role of MEK partner-1 in cancer stemness through MEK/ERK pathway in cancerous neural stem cells, expressing EGFRviii

Background

Glioma stem cells (GSCs) are a major cause of the frequent relapse observed in glioma, due to their high drug resistance and their differentiation potential. Therefore, understanding the molecular mechanisms governing the ‘cancer stemness’ of GSCs will be particularly important for improving the prognosis of glioma patients.

Methods

We previously established cancerous neural stem cells (CNSCs) from immortalized human neural stem cells (F3 cells), using the H-Ras oncogene. In this study, we utilized the EGFRviii mutation, which frequently occurs in brain cancers, to establish another CNSC line (F3.EGFRviii), and characterized its stemness under spheroid culture.

Results

The F3.EGFRviii cell line was highly tumorigenic in vitro and showed high ERK1/2 activity as well as expression of a variety of genes associated with cancer stemness, such as SOX2 and NANOG, under spheroid culture conditions. Through meta-analysis, PCR super-array, and subsequent biochemical assays, the induction of MEK partner-1 (MP1, encoded by the LAMTOR3 gene) was shown to play an important role in maintaining ERK1/2 activity during the acquisition of cancer stemness under spheroid culture conditions. High expression of this gene was also closely associated with poor prognosis in brain cancer.

Conclusion

These data suggest that MP1 contributes to cancer stemness in EGFRviii-expressing glioma cells by driving ERK activity.

Electronic supplementary material

The online version of this article (doi:10.1186/s12943-017-0703-y) contains supplementary material, which is available to authorized users.

Targeting the bHLH transcriptional networks by mutated E proteins in experimental glioma

Glioblastomas (GB) are aggressive primary brain tumors. Helix-loop-helix (HLH, ID proteins) and basic HLH (bHLH, e.g., Olig2) proteins are transcription factors that regulate stem cell proliferation and differentiation throughout development and into adulthood. Their convergence on many oncogenic signaling pathways combined with the observation that their overexpression in GB correlates with poor clinical outcome identifies these transcription factors as promising therapeutic targets. Important dimerization partners of HLH/bHLH proteins are E proteins that are necessary for nuclear translocation and DNA binding. Here, we overexpressed a wild type or a dominant negative form of E47 (dnE47) that lacks its nuclear localization signal thus preventing nuclear translocation of bHLH proteins in long-term glioma cell lines and in glioma-initiating cell lines and analyzed the effects in vitro and in vivo. While overexpression of E47 was sufficient to induce apoptosis in absence of bHLH proteins, dnE47 was necessary to prevent nuclear translocation of Olig2 and to achieve similar proapoptotic responses. Transcriptional analyses revealed downregulation of the antiapoptotic gene BCL2L1 and the proproliferative gene CDC25A as underlying mechanisms. Overexpression of dnE47 in glioma-initiating cell lines with high HLH and bHLH protein levels reduced sphere formation capacities and expression levels of Nestin, BCL2L1, and CDC25A. Finally, the in vivo induction of dnE47 expression in established xenografts prolonged survival. In conclusion, our data introduce a novel approach to jointly neutralize HLH and bHLH transcriptional networks activities, and identify these transcription factors as potential targets in glioma.

Global identification of genes targeted by DNMT3b for epigenetic silencing in lung cancer

The maintenance cytosine DNA methyltransferase DNMT1 and de novo methyltransferase DNMT3b cooperate to establish aberrant DNA methylation and chromatin complexes to repress gene transcription during cancer development. The expression of DNMT3b was constitutively increased 5-20-fold in hTERT/CDK4-immortalized human bronchial epithelial cells (HBECs) before treatment with low doses of tobacco carcinogens. Overexpression of DNMT3b increased and accelerated carcinogen-induced transformation. Genome-wide profiling of transformed HBECs identified 143 DNMT3b-target genes, many of which were transcriptionally regulated by the polycomb repressive complex 2 (PRC2) complex and silenced through aberrant methylation in non-small-cell lung cancer cell lines. Two genes studied in detail, MAL and OLIG2, were silenced during transformation, initially through enrichment for H3K27me3 and H3K9me2, commonly methylated in lung cancer, and exert tumor suppressor effects in vivo through modulating cancer-related pathways. Re-expression of MAL and OLIG2 to physiological levels dramatically reduced the growth of lung tumor xenografts. Our results identify a key role for DNMT3b in the earliest stages of initiation and provide a comprehensive catalog of genes targeted for silencing by this methyltransferase in non-small-cell lung cancer.

Prox1 regulates Olig2 expression to modulate binary fate decisions in spinal cord neurons

Specification of spinal cord neurons depends on gene regulation networks that impose distinct fates in neural progenitor cells (NPCs). Olig2 is a key transcription factor in these networks by inducing motor neuron (MN) specification and inhibiting interneuron identity. Despite the critical role of Olig2 in nervous system development and cancer progression, the upstream molecular mechanisms that control Olig2 gene transcription are not well understood. Here we demonstrate that Prox1, a transcription repressor and downstream target of proneural genes, suppresses Olig2 expression and therefore controls ventral spinal cord patterning. In particular, Prox1 is strongly expressed in V2 interneuron progenitors and largely excluded from Olig2+ MN progenitors (pMN). Gain- and loss-of-function studies in mouse NPCs and chick neural tube show that Prox1 is sufficient and necessary for the suppression of Olig2 expression and proper control of MN versus V2 interneuron identity. Mechanistically, Prox1 interacts with the regulatory elements of Olig2 gene locus in vivo and it is critical for proper Olig2 transcription regulation. Specifically, chromatin immunoprecipitation analysis in the mouse neural tube showed that endogenous Prox1 directly binds to the proximal promoter of the Olig2 gene locus, as well as to the K23 enhancer, which drives Olig2 expression in the pMN domain. Moreover, plasmid-based transcriptional assays in mouse NPCs suggest that Prox1 suppresses the activity of Olig2 gene promoter and K23 enhancer. These observations indicate that Prox1 controls binary fate decisions between MNs and V2 interneurons in NPCs via direct repression of Olig2 gene regulatory elements.

Uptake by human glioma cell lines and biological effects of a peptide-nucleic acids targeting miR-221

MicroRNAs are a family of small noncoding RNAs regulating gene expression by sequence-selective mRNA targeting, leading to a translational repression or mRNA degradation. The oncomiR miR-221 is highly expressed in human gliomas, as confirmed in this study in samples of low and high grade gliomas, as well in the cell lines U251, U373 and T98G. In order to alter the biological functions of miR-221, a peptide nucleic acid targeting miR-221 (R8-PNA-a221) was produced, bearing a oligoarginine peptide (R8) to facilitate uptake by glioma cells. The effects of R8-PNA-a221 were analyzed in U251, U373 and T98G glioma cells and found to strongly inhibit miR-221. In addition, the effects of R8-PNA-a221 on p27(Kip1) (a target of miR-221) were analyzed in U251 and T98G cells by RT-qPCR and by Western blotting. No change of p27(Kip1) mRNA content occurs in U251 cells in the presence of PNA-a221 (lacking the R8 peptide), whereas significant increase of p27(Kip1) mRNA was observed with the R8-PNA-a221. These data were confirmed by Western blot assay. A clear increment of p27(Kip1) protein expression in the samples treated with R8-PNA-a221 was detected. In addition, R8-PNA-a221 was found able to increase TIMP3 expression (another target of miR-221) in T98G cells. These results suggest that PNAs against oncomiRNA miR-221 might be proposed for experimental treatment of human gliomas.

OLIG2 over-expression impairs proliferation of human Down syndrome neural progenitors

Mental retardation and early Alzheimer's disease (AD) have generally been attributed to progressive neuronal loss in the developing and mature Down syndrome (DS) brain. However, reduced neuronal production during development could also contribute to the smaller brain size and simplified gyral patterning seen in this disorder. Here, we show impairments in proliferation within the ventricular zone (VZ) of early DS fetal cortex and in cultured early passage DS human neural progenitors (HNPs). We find that the reduced proliferative rates correspond temporally with increased expression of the chromosome 21 (HSA21) associated, oligodendrocyte transcription factor OLIG2 at 14-18 weeks gestational age (GA) (period of neurogenesis). Moreover, the DS HNPs adopt more oligodendrocyte-specific features including increased oligodendrocyte marker expression, as well as a reduction in KCNA3 potassium channel expression and function. We further show that OLIG2 inhibition or over-expression regulates potassium channel expression levels and that activation or inhibition of these channels influences the rate of progenitor proliferation. Finally, neural progenitors from Olig2 over-expressing transgenic mice exhibit these same impairments in proliferation and potassium channel expression. These findings suggest that OLIG2 over-expression inhibits neural progenitor proliferation through changes in potassium channel activity, thereby contributing to the reduced neuronal numbers and brain size in DS.

Glypican-1 stimulates Skp2 autoinduction loop and G1/S transition in endothelial cells

The heparan sulfate proteoglycan glypican-1 (GPC1) is involved in tumorigenesis and angiogenesis and is overexpressed frequently in tumor and endothelial cells (ECs) in human gliomas. We demonstrated previously that in brain EC, GPC1 regulates mitotic cyclins and securin as well as mitosis and that GPC1 is required for progression through the cell cycle. To characterize the molecular mechanism underlying cell cycle regulation by GPC1, we systematically investigated its effects on key G(1)/S checkpoint regulators and on major signaling pathways reportedly activated by Dally (Division abnormally delayed) the Drosophila GPC1 homologue. We found that elevated GPC1 affected a wide range of G(1)/S checkpoint regulators, leading to inactivation of the G(1)/S checkpoint and increased S phase entry, apparently by activating the mitogen-independent Skp2 autoinduction loop. Specifically, GPC1 suppressed CDK inhibitors (CKIs), including p21, p27, p16, and p19, and the D cyclins, and induced CDK2 and Skp2. GPC1 may trigger the Skp2 autoinduction loop at least partially by suppressing p21 transcription as knockdown of p21 by RNAi can mimic the effect of GPC1 on the cell cycle regulators related to the loop. Moreover, multiple mitogenic signaling pathways, including ERK MAPK, Wnt and BMP signaling, were significantly stimulated by GPC1 as has been reported for Dally in Drosophila. Notably, the c-Myc oncoprotein, which is frequently up-regulated by both ERK and Wnt signaling and functions as a potent transcription repressor for CKIs as well as D cyclins, was also significantly induced by GPC1. These findings provide mechanistic insights into how GPC1 regulates the cell cycle and proliferation.

NKX2.2 suppresses self-renewal of glioma-initiating cells

Glioblastoma (GBM) is the most aggressive and destructive form of brain cancer. Animal models that can unravel the mechanisms underlying its progression are needed to develop rational and effective molecular therapeutic approaches. In this study, we report the development of mouse models for spontaneous gliomas representing distinct progressive stages of disease that are governed by defined genetic alterations. Neural stem/progenitor cell (NPC)-specific constitutive Ras activation in vivo plus p53 deficiency led to development of primarily anaplastic astrocytoma (grade III), whereas combined loss of p53 plus p16(Ink4a)/p19(Arf) led to development of GBM (grade IV) at 100% penetrance within 6 weeks. These glioma models showed enhanced stem cell properties (stemness) accompanied by malignant progression. Notably, we determined that, in our models and in human specimens, downregulation of the homeodomain transcription factor NKX2.2, which is essential for oligodendroglial differentiation, was correlated with increased tumor malignancy. NKX2.2 overexpression by GBM-derived glioma-initiating cells (GIC) induced oligodendroglial differentiation and suppressed self-renewal capacity. By contrast, Nkx2.2 downregulation in mouse NPCs accelerated GBM formation. Importantly, the inhibitory effects of NXK2.2 on GIC self-renewal were conserved in human cells. Thus, our mouse models offer pathobiologically significant advantages to investigate the nature of brain tumors, with improved opportunities to develop novel mechanism-based therapeutic approaches.

Gain-of-function of Olig transcription factors enhances oligodendrogenesis and myelination

The basic helix-loop-helix transcription factors Olig1 and Olig2 are required for oligodendrocyte specification and differentiation during central nervous system (CNS) development but the effects of overexpression of these factors in murine development are not well understood. To test whether Olig1 and Olig2 may reprogram CNS stem/progenitors toward an oligodendroglial fate for myelination, we generated transgenic mice with doxycycline (Dox)-inducible expression of Olig1 or Olig2 in nestin-expressing stem/progenitor cells of the CNS. Overexpression of Olig1 or Olig2 from E8.5 to E12.5 was sufficient to promote the generation of platelet-derived growth factor receptor alpha + oligodendrocyte precursors (OPCs) in the spinal cord. We also demonstrated that overexpression of Olig2, but not Olig1, enhanced the stem/progenitor cell proliferation and generation of motoneuron precursors and inhibited the development of V3 interneurons. In the postnatal brain, Dox-inducible expression of Olig2 but not Olig1 in nestin+ stem/progenitors of the subventricular zone increased the generation of OPCs that migrated and differentiated into mature oligodendrocytes in the corpus callosum, cortex and olfactory bulb, leading to increased and precocious myelination. Altogether, our data indicate that Olig2 is a potential therapeutic target to enhance myelination and remyelination in the CNS.

Analysis of an alternative human CD133 promoter reveals the implication of Ras/ERK pathway in tumor stem-like hallmarks

Background

An increasing number of studies support the presence of stem-like cells in human malignancies. These cells are primarily responsible for tumor initiation and thus considered as a potential target to eradicate tumors. CD133 has been identified as an important cell surface marker to enrich the stem-like population in various human tumors. To reveal the molecular machinery underlying the stem-like features in tumor cells, we analyzed a promoter of CD133 gene using human colon carcinoma Caco-2 and synovial sarcoma Fuji cells, which endogenously express CD133 gene.

Results

A reporter analysis revealed that P5 promoter, located far upstream in a human CD133 gene locus, exhibits the highest activity among the five putative promoters (P1 to P5). Deletion and mutation analysis identified two ETS binding sites in the P5 region as being essential for its promoter activity. Electrophoretic mobility shift assays demonstrated the specific binding between nuclear factors and the ETS binding sequence. Overexpression of dominant-negative forms of Ets2 and Elk1 resulted in the significant decrease of P5 activity. Furthermore, treatment of Fuji cells with a specific MEK/ERK inhibitor, U0126, also markedly decreased CD133 expression, but there was no significant effect in Caco-2 cells, suggesting cell type-specific regulation of CD133 expression. Instead, the side population, another hallmark of TSLCs, was dramatically diminished in Caco-2 cells by U0126. Finally, Ras-mediated oncogenic transformation in normal human astrocytes conferred the stem-like capability to form neurosphere-like colonies with the increase of CD133 mRNA expression.

Conclusions

In conclusion, the Ras/ERK pathway at least in part contributes to the maintenance and the acquisition of stem-like hallmarks, although the extent of its contribution is varied in a cell type-specific manner. These findings could help our comprehensive understanding of tumor stemness, and also improve the development of eradicative therapies against human malignancies.

Quantitative analysis of mitotic Olig2 cells in adult human brain and gliomas: implications for glioma histogenesis and biology

The capacity of adult human glial progenitor cells (AGPs), to proliferate and undergo multipotent differentiation, positions them as ideal candidate cells of origin for human gliomas. To investigate this potential role we identified AGPs as mitotically active Olig2 cells in nonneoplastic adult human brain and gliomas. We conservatively estimated that one in 5,000 human temporal lobe neocortical gray or subcortical white matter cells is mitotic. Extrapolating from a mean Olig2/Mib-1 labeling index (LI) of 52% and total cell number of 100 billion, we estimated the overall prevalence of mitotic Olig2 AGPs in nonneoplastic human brain parenchyma at 10 million. These data identify a large reservoir of Olig2 AGPs which could be potential targets for human gliomagenesis. The vast majority of mitotic cells in Grade II and Grade III gliomas of all histologic subtypes expressed Olig2 (mean LI 75%) but rarely S100B (LI 0.6%), identifying the Olig2 cell as a distinct contributor to the proliferating cell population of human gliomas of both oligodendroglial and astrocytic lineages. In the most malignant Grade IV glioma, or glioblastoma multiforme (GBM), the prevalence of Olig2/Mib-1 cells was significantly decreased (24.5%). The significantly lower Olig2/Mib-1 LI in GBMs suggests that a decrease in the prevalence of Olig2 cells to the total mitotic cell pool accompanies increasing malignancy. The novel framework provided by this quantitative and comparative analysis supports future studies to examine the histogenetic role of Olig2 AGPs in adult gliomas, their potential contribution to the tumor stroma and the molecular role of Olig2 in glioma pathogenesis.

Promoter hypomethylation regulates CD133 expression in human gliomas

Brain tumor-initiating cells (BTICs) have been enriched using antibodies against the cell surface protein CD133; however, the biological relevance and the regulatory mechanism of CD133 expression in human gliomas are not yet understood. In this study, we initially demonstrated that CD133 was overexpressed in high-grade human glioblastomas where CD133-positive cells were focally observed as a micro-cluster. In addition, CD133 transcripts with exon 1A, 1B, or 1C were predominantly expressed in glioblastomas. To elucidate the mechanism regulating this aberrant expression of CD133, three proximal promoters (P1, P2, and P3) containing a CpG island were isolated. In U251MG and T98G glioblastoma cells, the P1 region flanking exon 1A exhibited the highest activity among the three promoters, and this activity was significantly inactivated by in vitro methylation. After treatment with the demethylating agent 5-azacytidine and/or the histone deacetylase inhibitor valproic acid, the expression level of CD133 mRNA was significantly restored in glioma cells. Importantly, hypomethylation of CpG sites within the P1, P2, and P3 regions was observed by bisulfite sequencing in human glioblastoma tissues with abundant CD133 mRNA. Taken together, our results indicate that DNA hypomethylation is an important determinant of CD133 expression in glioblastomas, and this epigenetic event may be associated with the development of BTICs expressing CD133.

Olig2-regulated lineage-restricted pathway controls replication competence in neural stem cells and malignant glioma

Recent studies have identified stem cells in brain cancer. However, their relationship to normal CNS progenitors, including dependence on common lineage-restricted pathways, is unclear. We observe expression of the CNS-restricted transcription factor, OLIG2, in human glioma stem and progenitor cells reminiscent of type C transit-amplifying cells in germinal zones of the adult brain. Olig2 function is required for proliferation of neural progenitors and for glioma formation in a genetically relevant murine model. Moreover, we show p21(WAF1/CIP1), a tumor suppressor and inhibitor of stem cell proliferation, is directly repressed by OLIG2 in neural progenitors and gliomas. Our findings identify an Olig2-regulated lineage-restricted pathway critical for proliferation of normal and tumorigenic CNS stem cells.

Oligodendrocyte lineage transcription factor 2 inhibits the motility of a human glial tumor cell line by activating RhoA

The basic helix-loop-helix transcription factor, oligodendrocyte lineage transcription factor 2 (OLIG2), is specifically expressed in the developing and mature central nervous system and plays an important role in oligodendrogenesis from neural progenitors. It is also expressed in various types of glial tumors, but rarely in glioblastoma. Although we previously showed that OLIG2 expression inhibits glioma cell growth, its role in tumorigenesis remains incompletely understood. Here, we investigated the effect of OLIG2 expression on the migration of the human glioblastoma cell line U12-1. In these cells, OLIG2 expression is controlled by the Tet-off system. Induction of OLIG2 expression inhibited both the migration and invasiveness of U12-1 cells. OLIG2 expression also increased the activity of the GTPase RhoA as well as inducing the cells to form stress fibers and focal adhesions. Experiments using short interfering RNA against p27(Kip1) revealed that up-regulation of the p27(Kip1) protein was not essential for RhoA activation, rather it contributed independently to the decreased motility of OLIG2-expressing U12-1 cells. Alternatively, semiquantitative reverse transcription-PCR analysis revealed that mRNA expression of RhoGAP8, which regulates cell migration, was decreased by OLIG2 expression. Furthermore, expression of C3 transferase, which inhibits Rho via ADP ribosylation, attenuated the OLIG2-induced inhibition of cell motility. Imaging by fluorescence resonance energy transfer revealed that in U12-1 cells lacking OLIG2, the active form of RhoA was localized to protrusions of the cell membrane. In contrast, in OLIG2-expressing cells, it lined almost the entire plasma membrane. Thus, OLIG2 suppresses the motile phenotype of glioblastoma cells by activating RhoA.

Signaling adaptor protein Crk is indispensable for malignant feature of glioblastoma cell line KMG4

Signaling adaptor protein Crk has been shown to be involved in pathogenesis of human cancers including brain tumor where Crk was reported to be overexpressed. In this study, we addressed whether Crk is indispensable for malignant phenotype of brain tumor. In 20 surgical specimens of glioma, mRNA of both CrkI and CrkII was found to be elevated in malignant tumor. To define a precise role of Crk, we have established Crk-knockdown cell lines of glioblastoma KMG4 by siRNA, and early phase of cell adhesion to laminin was found to be suppressed. Wound healing assay revealed the decreased cell motility in Crk knockdown cells, and suppression of both anchorage-dependent and -independent growth were demonstrated in these cells. Furthermore, in vivo tumor forming potential was also markedly suppressed. These results suggest that Crk is required for early attachment to laminin, cell motility, and growth of glioblastoma cell line KMG4.

The selective RNA-binding protein quaking I (QKI) is necessary and sufficient for promoting oligodendroglia differentiation

Quaking I (QKI) is a selective RNA-binding protein essential for myelination of the central nervous system. Three QKI isoforms with distinct C termini and subcellular localization, namely QKI-5, QKI-6, and QKI-7, are expressed in oligodendroglia progenitor cells (OPCs) prior to the initiation of myelin formation and implicated in promoting oligodendrocyte lineage development. However, the functional requirement for each QKI isoform and the mechanisms by which QKI isoforms govern OPC development still remain elusive. We report here that exogenous expression of each QKI isoform is sufficient to enhance differentiation of OPCs with different efficiency, which is abolished by a point mutation that abrogates the RNA binding activity of QKI. Reciprocally, small interfering RNA-mediated QKI knockdown blocks OPC differentiation, which can be partly rescued by QKI-5 and QKI-6 but not by QKI-7, indicating the differential requirement of QKI isoform function in advancing OPC differentiation. Furthermore, we found that abrogation of OPC differentiation, as a result of QKI deficiency, is not due to altered proliferation capacity or cell cycle progression. These results indicate that QKI isoforms are necessary and sufficient for promoting OPC development, which must involve direct influence of QKI on differentiation/maturation of OPCs independent of cell cycle exit, likely via regulating the expression of the target mRNAs of QKI that support OPC differentiation.