[Retracted] Role of the AKT pathway in microRNA expression of human U251 glioblastoma cells.

Following the publication of the above article, a concerned reader drew to the Editor's attention that, regarding the western blots featured in Fig. 3B on p. 670, the bands featured in the U251 and U251­MC lanes for the miR­21 and U6 experiments appeared to be duplicates of each other. Moreover, certain of these data were strikingly similar to data that appeared in another article published at around the same time featuring some of the same authors (again, with apparent duplications of bands within the same gel slices, as they were presented). After having conducted an internal investigation of this matter, the Editor of International Journal of Oncology has judged that the apparently anomalous grouping of the data could not have been attributed to pure coincidence. Therefore, the Editor has decided that this article should be retracted from the publication on the grounds of an overall lack of confidence in the data. The authors were asked for an explanation to account for these concerns, but the Editorial Office did not receive a reply. The Editor sincerely apologizes to the readership for any incovenience caused, and we thank the reader for bringing this matter to our attention. [International Journal of Oncology 36: 665­672, 2010; DOI: 10.3892/ijo_00000542].

The role of PKN1 in glioma pathogenesis and the antiglioma effect of raloxifene targeting PKN1.

PKN1 (protein kinase N1), a serine/threonine protein kinase family member, is associated with various cancers. However, the role of PKN1 in gliomas has rarely been studied. We suggest that PKN1 expression in glioma specimens is considerably upregulated and positively correlates with the histopathological grading of gliomas. Knocking down PKN1 expression in glioblastoma (GBM) cells inhibits GBM cell proliferation, invasion and migration and promotes apoptosis. In addition, yes-associated protein (YAP) expression, an essential effector of the Hippo pathway contributing to the oncogenic role of gliomagenesis, was also downregulated. In contrast, PKN1 upregulation enhances the malignant characteristics of GBM cells and simultaneously upregulates YAP expression. Therefore, PKN1 is a promising therapeutic target for gliomas. Raloxifene (Ralo), a commonly used selective oestrogen-receptor modulator to treat osteoporosis in postmenopausal women, was predicted to target PKN1 according to the bioinformatics team from the School of Mathematics, Tianjin Nankai University. We showed that Ralo effectively targets PKN1, inhibits GBM cells proliferation and migration and sensitizes GBM cells to the major chemotherapeutic drug, Temozolomide. Ralo also reverses the effect of PKN1 on YAP activation. Thus, we confirm that PKN1 contributes to the pathogenesis of gliomas and may be a potential target for Ralo adjuvant glioma therapy.

miR-19a/b promote EMT and proliferation in glioma cells via SEPT7-AKT-NF-κB pathway.

miR-19a/b belong to the miR-17-92 family. We have demonstrated previously that miR-19a/b are overexpressed in glioma and glioma cell lines. However, the role of miR-19a/b in glioma remains unclear. In the present study, we aim to identify the biological function and molecular mechanism of miR-19a/b in glioma cell proliferation and epithelial-mesenchymal transition (EMT). Knocking down miR-19a/b in LN308 glioblastoma (GBM) cells with higher expression of miR-19a/b inhibits cell proliferation and invasion, induces apoptosis, and suppresses EMT by downregulating the expression of Akt, phosphorylated p-Akt, nuclear factor κB (NF-κB), Snail, N-cadherin, and Vimentin and upregulating E-cadherin in vitro and in vivo. Enhanced proliferation and EMT are also observed when miR-19a/b are transfected into SNB19 GBM cells, with lowered expression of miR-19a/b. miR-19a is more effective than miR-19b in the regulation of biological behavior of glioma cells. miR-19a/b modulate molecular events for the promotion of EMT via the Akt-NF-κB pathway. SEPT7 has been confirmed as the target gene of miR-19a/b. The effect of miR-19a/b on proliferation and EMT of glioma cells and the Akt-NF-κB pathway could be reversed by transfection with SEPT7. Our study strongly suggests that miR-19a/b play a significant role in glioma progression and EMT through regulating target gene-SEPT7 and the SEPT7-Akt-NF-κB pathway.

The emerging role of miR-19 in glioma.

Glioma has been regarded as the most common, highly proliferative and invasive brain tumour. Advances in research of miRNAs in glioma are toward further understanding of the pathogenesis of glioma. MiR-19, a member of miR-17~92 cluster, was reported to play an oncogenic role in tumourigenesis. Here we review the identified data about the effect of miR-19 on proliferation, apoptosis, migration and invasion of glioma cells, the target genes regulated by miR-19, and correlation of miR-19 with the sensitivity of glioma cells to chemotherapy and radiotherapy. It is concluded that miR-19 plays an important role in the pathogenesis of glioma and can be a potential target for gene therapy of glioma.

RUNX3 inhibits glioma survival and invasion via suppression of the ß-catenin/TCF-4 signaling pathway.

INTRODUCTION: Runt-related transcription factor 3 (RUNX3) exerts a tumor suppressor gene associated with gastric and other cancers, including glioma. However, how its anti-tumor mechanism in functions glioma is unclear. METHODS: We assayed expression of RUNX3 with a tissue microarray (TMA), frozen cancer tissues and malignant glioma cell lines using immunohistochemistry, qRT-PCR and Western bolt analysis. Cell proliferation, invasion, cell cycle distribution and apoptosis were also examined to confirm the effect of RUNX3 medicated malignant phenotype. TOP/FOP experiment was used to detect the ß-catenin/Tcf-4 transcription activity by RUNX3. RESULTS: Enforced RUNX3 expression inhibited proliferation and invasion, induced cell cycle arrest and promoted apoptosis in vitro and in vivo, Bim siRNA partically reversed the effect of RUNX3-induced apoptosis in LN229 and U87 cells, suggesting a dependent role of Bim-caspase pathway. Moreover, Mechanism investigations revealed that restoration of RUNX3 suppressed ß-catenin/Tcf-4 transcription activity. CONCLUSIONS: RUNX3 plays a pivotal role in glioma initiation and progression as a tumor suppressor via attenuation of Wnt signaling, highlighting it as a potential therapeutic target for glioma.

MiR-19 regulates the proliferation and invasion of glioma by RUNX3 via ß-catenin/Tcf-4 signaling.

Accumulating data demonstrates that the network dysregulation of microRNA-medicated target genes is involved in glioma. We have previously found miR-19a/b overexpression in glioma cell lines and specimens with various tumour grades. However, there was no report on the function and regulatory mechanism of miR-19a/b in glioma. In this study, based on our previous research data, we first determine the inverse relationship between miR-19 (miR-19a and miR-19b) and RUNX3 which is also identified the reduced expression in tumour tissues by real-time PCR and IHC. Luciferase reporter assay and western blot analysis revealed that RUNX3 was a direct target of miR-19. Down-regulation of miR-19 dramatically inhibited proliferation, invasion and induced the cell cycle G1 arrest and apoptosis, at least partly via the up-regulation of RUNX3. Furthermore, Mechanistic investigation indicated that knockdown of miR-19 repressed the ß-catenin/TCF4 transcription activity. In conclusion, our study validates a pathogenetic role of miR-19 in glioma and establishes a potentially regulatory and signaling involving miR-19 /RUNX3/ß-catenin, also suggesting miR-19 may be a candidate therapeutic target in glioma.

The role of transcriptional coactivator TAZ in gliomas.

The transcriptional coactivator with PDZ-binding motif (TAZ) is one of the important downstream effectors of Hippo pathway. In this study, the potential implication of TAZ in gliomagenesis was explored. TAZ expression was identified to be upregulated in glioma specimens and positively correlated with tumor grade. Meanwhile, its expression in nucleus was increased more significantly with the ascending order of tumor grade. Knocking down TAZ inhibited glioma cell proliferation, invasion and promoted apoptosis. Conversely, enforced upregulation of TAZ promoted proliferation, invasion of glioma cells, and suppressed apoptosis in vitro. When orthotopic glioblastoma mouse model implanted with TAZ knocked down cells, glioma growth was inhibited and survival period was prolonged. Expression of Ki67, MMP-9, Cyclin D1, Bcl-2 and C-myc was varied in accordance with the level of TAZ in glioma cell. The biomarkers of EMT (epithelial-mesenchymal transition), vimentin and N-cadherin, were downregulated when TAZ was suppressed. Using Co-immunoprecipitation TAZ was identified to bind to TEAD4. Therefore, our findings indicate that TAZ is overexpressed in glioma and translocated more into nucleus in high grade glioma. TAZ is involved in gliomagenesis by promoting glioma growth and may benefit to EMT progression. This result suggests that TAZ serves as a potential target for the treatment of glioma.

MicroRNAs let-7b/i suppress human glioma cell invasion and migration by targeting IKBKE directly.

We demonstrated that IKBKE is overexpressed in human gliomas and that the downregulation of IKBKE markedly inhibits the proliferative and invasive abilities of glioma cells, which is consistent with the results reported by several different research groups. Therefore, IKBKE represents a promising therapeutic target for the treatment of glioma. In the present study, we verified that the microRNAs let-7b and let-7i target IKBKE through luciferase assays and found that let-7b/i mimics can knock down IKBKE and upregulate E-cadherin through western blot analysis. Moreover, the expression levels of let-7b/i were significantly lower in glioma cell lines than that in normal brain tissues, as determined by quantitative real-time PCR. Furthermore, let-7b/i inhibit the invasion and migration of glioma cells, as determined through wound healing and Transwell assays. The above-mentioned data suggest that let-7b/i inhibit the invasive ability of glioma cells by directly downregulating IKBKE and indirectly upregulating E-cadherin.

Resveratrol inhibits glioma cell growth via targeting oncogenic microRNAs and multiple signaling pathways.

Resveratrol (Res), a natural polyphenolic compound, has anticancer activity in a variety of cancers. In the present study, the antitumor effect and underlying molecular mechanism of Res on rat C6 glioma growth was studied. The results demonstrated that Res inhibited glioma cell proliferation, arrested cell cycle in S phase and induced apoptosis in vitro. Res also suppressed intracranial C6 tumor growth in vivo and prolonged survival in a fraction of the rats bearing intracranial gliomas. Res significantly downregulated the specific miRs, including miR-21, miR-30a-5p and miR-19, which have been identified as oncomiRs in our previous studies, and altered the expression of their targeting and crucial genes for glioma formation and progression such as p53, PTEN, EGFR, STAT3, COX-2, NF-κB and PI3K/AKT/mTOR pathway. Therefore, the anti-glioma effect of Res, at least in part, is through the regulation of oncogenic miRNAs. The effect of Res on non-coding RNAs should be studied further. Res is a potential multi-targeting drug for the treatment of gliomas.

A lentivirus-mediated miR-23b sponge diminishes the malignant phenotype of glioma cells in vitro and in vivo.

microRNA (miRNA) sponges are RNA molecules with repeated miRNA binding sequences that can sequester miRNAs from their endogenous target mRNAs, and a stably expressed miRNA sponge is particularly valuable for long-term loss-of-function studies in vitro and in vivo. Glioblastoma multiforme (GBM) is the most common primary brain tumor in adults and is characterized by extraordinarily angiogenic, invasive and migratory capabilities, hallmark features that make the disease incurable. Nonetheless, improvements in clinical treatment and a better understanding of the underlying molecular mechanisms have been achieved within the past few decades. miR-23b has previously been found to function as a tumor oncogene in GBM. In the present study, we employed an microRNA sponge that was forcibly expressed using a lentiviral vector to knock down the expression of miR-23b in vitro and in vivo and assessed the pleiotropic effects on glioma angiogenesis, invasion and migration. We demonstrated that the inhibition of miR-23b in glioma cell lines and orthotopic tumor mouse models resulted in a reduction in tumor malignancy, through the downregulation of HIF-1α, ß-catenin, MMP2, MMP9, VEGF and ZEB1 and increased expression of VHL and E-cadherin. Therefore, we suggest that this miR-23b sponge could be developed into a promising anticancer therapy either alone or in combination with current targeted therapies.

miR-19a and miR-19b overexpression in gliomas.

Astrocytic gliomas are the most common type of human primary brain tumors with poor prognosis. MicroRNAs(miRs) are frequently deregulated in gliomas and play an oncogenic or tumor suppressor role. In our previous study we found that miR-19a and miR-19b were up-regulated in malignant glioma cell lines by microRNA array. For further validation of this finding, the expression of miR-19a and miR-19b was detected by qRT-PCR and in situ hybridization(ISH) in 8 malignant glioma cell lines, 43 freshly resected glioma samples and 75 archival paraffin embedded glioma specimens with different grades of malignancy in the present study. The results demonstrate that miR-19a and miR-19b are overexpressed in glioma cell lines and astrocytic glioma tissues, and their expression level is positively correlated with tumor grades. Additionally, the tumor suppressor gene PTEN is identified as the target of miR-19a and miR-19b by Luciferase assay. It is speculated that miR-19a and miR-19b may have an oncogenic role in gliomagenesis at least partially via the negative regulation of PTEN and the molecular mechanism of gliomagenesis in which miR 19a and miR-19b involved should be investigated further.

Analysis of hsa-miR-30a-5p expression in human gliomas.

Our previous study demonstrated that miR-30a-5p was upregulated in six malignant glioma cell lines by microRNA(miRNA) array. For further verification of this finding, the expression of miR-30a-5p in 7 more malignant glioma cell lines, 43 freshly resected glioma samples and 75 archival paraffin embedded glioma specimens with different grade of malignancy were examined by qRT-PCR and in situ hybridization(ISH). Here, we present the first evidence that miR-30a-5p is overexpressed in glioma cell lines and glioma samples as compared to the normal brain tissues (NBTs), and its expression level is positively correlated with tumor grade of malignancy. It is concluded that miR-30a-5p may have the potential as a diagnostic or prognostic marker of gliomas and as the target of miRNA-based glioma therapy in further studies.

Down-regulation of miR-106b suppresses the growth of human glioma cells.

Recently, many studies have found that the miR-106b ~25 cluster plays an oncogenic role in tumor progression. However, the precise role of each microRNAs (miRNAs) in the cluster is not yet clear. In the present study, we examined the expression of miR-106b in glioma samples and a tissue microarray by real-time PCR and in situ hybridization (ISH), respectively, finding that miR-106b is overexpressed in the majority of gliomas. Meanwhile, the expression of miR-106b was positively correlated with tumor grade (p < 0.05). The transfection of a miR-106b anti-sense oligonucleotide (ASON) into three human glioma cell lines (U251, LN229 and TJ905) suppressed the proliferation of these cells. Moreover, the growth of xenograft tumors in nude mice treated with miR-106b ASON was significantly impaired. A bioinformatics analysis predicted that RBL2 may be the target of miR-106b, and dual-luciferase reporter assays identified RBL2, but not RB1 or RBL1, as a target of miR-106b. These results suggest that miR-106b facilitates glioma cell growth by promoting cell cycle progression through the negative regulation of RBL2.

MiR-30a-5p antisense oligonucleotide suppresses glioma cell growth by targeting SEPT7.

MicroRNAs (miRNAs) are small noncoding RNAs that regulate gene expression by targeting the mRNAs of hundreds of human genes. Variations in miRNA expression levels were shown to be associated with glioma. We have previously found miR-30a-5p overexpression in glioma cell lines and specimens. Bioinformatics analyses predict that several miRNAs, including miR-30a-5p, are involved in the post-transcriptional regulation of SEPT7. SEPT7 is a member of the septin family, which is a highly conserved subfamily of GTPases implicated in exocytosis, apoptosis, synaptogenesis, neurodegeneration and tumorigenesis. Our previous study has also demonstrated that SEPT7 expression is decreased in astrocytic gliomas with different grades and plays a tumor suppressor role. In the present study, we knocked down miR-30a-5p with antisense oligonucleotide (miR-30a-5p AS) in LN229 and SNB19 glioblastoma(GBM) cells, and found that cell growth and invasion were inhibited, while apoptosis was induced. miR-30a-5p AS treated cells showed upregulation of SEPT7 and downregulation of PCNA, cyclin D1, Bcl2, MMP2 and MMP9. In contrast, when miR-30a-5p mimics were transfected into LN229 and SNB19 GBM cells, cell growth and invasion were promoted and the expression of relevant proteins increased. Meanwhile, the effect of miR-30a-5p mimics on glioma cells can be reversed by transfection of SEPT7 construct. Additionaly, miR-30a-5p directly targeting SEPT7 was identified by the reporter gene assay. Our study demonstrates,for the first time, that miR-30a-5p is a bona fide negative regulator of SEPT7 and the oncogenic activity of miR-30a-5p in human gliomas is at least in part through the repression of SEPT7.

The different role of Notch1 and Notch2 in astrocytic gliomas.

It is well known that Notch signaling plays either oncogenic or tumor suppressive role in a variety of tumors, depending on the cellular context. However, in our previous study, we found that Notch1 was overexpressed while Notch2 downregulated in the majority of astrocytic gliomas with different grades as well as in glioblastoma cell lines U251 and A172. We had knocked down Notch1 by siRNA in glioblastoma cells, and identified that the cell growth and invasion were inhibited, whereas cell apoptosis was induced either in vitro or in vivo. For further clarification of the role of Notch2 in pathogenesis of gliomas, enforced overexpression of Notch2 was carried out with transfection of Notch2 expression plasmid in glioma cells and the cell growth, invasion and apoptosis were examined in vitro and in vivo in the present study, and siRNA targeting Notch1 was used as a positive control in vivo. The results showed that upregulating Notch2 had the effect of suppressing cell growth and invasion as well as inducing apoptosis, just the same as the results of knocking down Notch1. Meanwhile, the activity of core signaling pathway-EGFR/PI3K/AKT in astrocytic glioma cells was repressed. Thus, the present study reveals, for the first time, that Notch1 and Notch2 play different roles in the biological processes of astrocytic gliomas. Knocking down the Notch1 or enforced overexpression of Notch2 both modulate the astrocytic glioma phenotype, and the mechanism by which Notch1 and 2 play different roles in the glioma growth should be further investigated.

LncRNA profile of glioblastoma reveals the potential role of lncRNAs in contributing to glioblastoma pathogenesis.

Long non-coding RNAs (lncRNAs) have recently emerged as a major class of regulatory molecules involved in a broad range of biological processes and complex diseases. Our aim was to identify important lncRNAs that might play an important role in contributing to glioblastoma (GBM) pathogenesis by conducting lncRNA and mRNA profile comparison between GBM and normal brain tissue. The differentially expressed lncRNA and mRNA profiles of the tissue between GBM patient and age-matched donor without GBM diseases were analyzed using microarrays. We propose a novel model for the identification of lncRNA-mRNA targeting relationships that combine the potential targets of the differentially expressed lncRNAs with the differentially expressed mRNA abundance data. Bioinformatic analysis of the predicted target genes (gene ontology, pathway and network analysis) was performed for further research. The lncRNA microarray reveals differentially expressed lncRNAs between GBM and normal brain tissues. In the GBM group, 654 lncRNAs were upregulated and 654 were downregulated (fold change ≥4.0 or ≤0.25, P<0.01). We found 104 matched lncRNA-mRNA pairs for 91 differentially expressed lncRNAs and 84 differentially expressed genes. Target gene-related pathway analysis showed significant changes in PPAR pathways in the GBM group compared with the normal brain group (P<0.05). By further conducting lncRNA gene network analysis, we found that ASLNC22381 and ASLNC2081 were likely to play roles in the regulation of glioma signaling pathways. In conclusion, our results indicated that the lncRNA expression profile in GBM tissue was significantly altered. These results may provide important insights into the mechanisms responsible for GBM progression and pathogenesis. This study also suggests that ASLNC22381 and ASLNC20819 may play important roles via their target IGF-1 in the recurrence and malignant progression of GBM.

miR-221/222 is the regulator of Cx43 expression in human glioblastoma cells.

The miR-221/222 cluster is significantly upregulated in malignant glioma cells and regulates the expression of multiple genes associated with glioma cell proliferation, invasion and apoptosis, which was shown in our previous studies. Cx43 has been identified as a tumor suppressor and major component for the establishment of gap junction intercellular communication (GJIC) in glial cells, which is frequently reduced or deleted in high-grade gliomas. According to bioinformatic analysis, connexin 43 (Cx43) may be one of the target genes of miR-221/222. The aim of the present study was to validate Cx43 as a target gene of miR-221/222 and to determine whether overexpression of miR-221/222 is one of the molecular mechanisms for the reduced expression of Cx43 in malignant gliomas. We transfected miR-221/222 antisense oligonucleotides (AS-miR-221/222) into U251 human glioblastoma cells using a lipofectamine method. Northern blot analysis was conducted to detect the expression of the miR-221/222 cluster. Luciferase reporter assays were exploited to confirm Cx43 as a target gene of miR-221/222. Cx43 expression was assessed by western blotting and immunofluorescence staining. Scrape loading and dye transfer (SLDT) assays were used for examination of GJIC. Proliferation and invasion of U251 cells were evaluated by MTT and transwell assays, respectively. Cell cycle kinetics and apoptosis were determined with flow cytometry. We found that expression of the miR-221/222 cluster was significantly reduced while Cx43 expression was upregulated in U251 cells transfected with AS-miR-221/222, and the GJIC deficiency in parental U251 cells was re-established. Moreover, the luciferase activity determined by the luciferase reporter assay was enhanced in AS-miR-221/222-treated cells, and cell proliferation and invasion were suppressed while apoptosis was induced. We conclude that miR-221/222 function as oncogenic microRNAs in human gliomas, at least in part, by targeting Cx43.

MicroRNA miR-451 downregulates the PI3K/AKT pathway through CAB39 in human glioma.

The microRNA miR-451 is downregulated in gliomas, this has been suggested by several different research groups and is consistent with our data. Our previous study also confirmed that miR-451 has a repressive role in glioma by inhibiting cell growth, proliferation and by inducing cell apoptosis. In the present study, we identified a target gene of miR-451 in human glioma and investigated the mechanism for the glioma suppressive effect of miR-451 functions. Expression of miR-451 in gliomas was identified by quantitative real-time PCR and fluorescence in situ hybridization. Human glioma cell lines (U251, U87, LN229 and A172) were transfected with miR-451 mimics to restore miR-451 expression. The tumor suppressive effects of miR-451 were further verified by subcutaneous assays in nude mice, in addition to our previous in vitro data. A candidate target gene was tested by Western blotting and luciferase reporter assays. Some PI3K/AKT pathway factors were tested by Western blotting. We found that miR-451 expression was downregulated in glioma samples and was inversely correlated with WHO grades of gliomas. In vivo assays confirmed that miR-451 had tumor suppressive traits. CAB39-3'UTR luciferase reporter assay confirmed CAB39 as a direct target gene of miR-451. Significant alterations in the expression of PI3K/AKT pathway factors were observed by Western blot assays. We conclude that miR-451 represses glioma in vitro and in vivo, likely through targeting CAB39 directly and inhibiting the PI3K/AKT pathway indirectly.

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

Recent data suggest that the ß-catenin/Tcf-4 signaling pathway plays an important role in human cancer tumorigenesis. However, the mechanism of ß-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 ß-catenin/Tcf-4 activity inhibited glioma cell proliferation and invasion in vitro and tumor growth in vivo. This effect of ß-catenin/Tcf-4 activity was mediated by AKT2, and in vivo binding of ß-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 ß-catenin/Tcf-4.

MicroRNA-221 and -222 regulate radiation sensitivity by targeting the PTEN pathway.

PURPOSE: MicroRNAs (miRNAs) are noncoding RNAs inhibiting expression of numerous target genes by posttranscriptional regulation. miRNA-221 and miRNA-222 (miRNA-221/-222) expression is elevated in radioresistant tumor cell lines; however, it is not known whether and how miRNAs control cellular responses to ionizing irradiation. METHODS AND MATERIALS: We used bioinformatic analyses, luciferase reporter assay, and genetic knockdown and biochemical assays to characterize the regulation pathways of miRNA-221/-222 in response to radiation treatment. RESULTS: We identified the PTEN gene as a target of miRNA-221/-222. Furthermore, we found that knocking down miRNA-221/-222 by antisense oligonucleotides upregulated PTEN expression. Upregulated PTEN expression suppressed AKT activity and increased radiation-induced apoptosis, resulting in enhancement of radiosensitivity in tumor cells. CONCLUSIONS: miRNA-221/-222 control radiation sensitivity by regulating the PTEN/AKT pathway and can be explored as novel targets for radiosensitization.