Overexpression of NNMT in Glioma Aggravates Tumor Cell Progression: An Emerging Therapeutic Target.

PURPOSE: Increasing evidence has revealed that nicotinamide N-methyltransferase (NNMT) is a key factor influencing the prognosis of tumors. The present study aimed to investigate the role of NNMT in glioma and to elucidate the associated functional mechanisms. METHODS: Clinical samples were analyzed by immunohistochemical staining and Western blotting to evaluate NNMT expression in glioma and normal brain tissues. The correlation between NNMT expression and glioma was analyzed using the Cancer Genome Atlas (TCGA) database. Additionally, NNMT was knocked down in two types of glioma cells, U87 and U251, to evaluate the invasive ability of these cells. Quantitative real-time polymerase chain reaction (qRT-PCR) was used to validate NNMT knockdown in the cells. Furthermore, ELISA was used to determine the balance between nicotinamide adenine dinucleotide and nicotinamide adenine dinucleotide hydrogen (NAD/NADH ratio), which verified the altered methylation patterns in the cells. The glioma xenograft mouse models were used to verify the regulatory role of NNMT, GAP43, and SIRT1. RESULTS: Analysis based on our clinical glioma samples and TCGA database revealed that overexpression of NNMT was associated with poor prognosis of patients. Knockdown of NNMT reduced the invasive ability of glioma cells, and downregulation of its downstream protein GAP43 occurred due to altered cellular methylation caused by NNMT overexpression. Gene Set Enrichment Analysis confirmed that NNMT modulated the NAD-related signaling pathway and showed a negative association between NNMT and SIRT1. Moreover, the regulatory roles of NNMT, GAP43, and SIRT1 were confirmed in glioma xenograft mouse models. CONCLUSION: Overexpression of NNMT causes abnormal DNA methylation through regulation of the NAD/NADH ratio, which in turn leads to the downregulation of GAP43 and SIRT1, eventually altering the biological behavior of tumor cells.

Ubiquitin-specific protease 22 acts as an oncoprotein to maintain glioma malignancy through deubiquitinating B cell-specific Moloney murine leukemia virus integration site 1 for stabilization.

Ubiquitin-specific protease 22 (USP22) is a member of the "death-from-cancer" signature, which plays a key role in cancer progression. Previous evidence has shown that USP22 is overexpressed and correlates with poor prognosis in glioma. The effect and mechanism of USP22 in glioma malignancy, especially cancer stemness, remain elusive. Herein, we find USP22 is more enriched in stem-like tumorspheres than differentiated glioma cells. USP22 knockdown inhibits cancer stemness in glioma cell lines. With a cell-penetrating TAT-tag protein, B cell-specific Moloney murine leukemia virus integration site 1 (BMI1), a robust glioma stem-cell marker, is found to mediate the effect of USP22 on glioma stemness. By immunofluorescence, USP22 and BMI1 are found to share similar intranuclear expression in glioma cells. By analysis with immunohistochemistry and bioinformatics, USP22 is found to positively correlate with BMI1 at the post-translational level only rather than at the transcriptional level. By immunoprecipitation and in vivo deubiquitination assay, USP22 is found to interact with and deubiquitinate BMI1 for protein stabilization. Microarray analysis shows that USP22 and BMI1 mutually regulate a series of genes involved in glioma stemness such as POSTN, HEY2, PDGFRA and ATF3. In vivo study with nude mice confirms the role of USP22 in promoting glioma tumorigenesis by regulating BMI1. All these findings indicate USP22 as a novel deubiquitinase of BMI1 in glioma. We propose a working model of the USP22-BMI1 axis, which promotes glioma stemness and tumorigenesis through oncogenic activation. Thus, targeting USP22 might be an effective strategy to treat glioma especially in those with elevated BMI1 expression.

FBW7 is associated with prognosis, inhibits malignancies and enhances temozolomide sensitivity in glioblastoma cells.

F-box and WD repeat domain-containing 7 (FBW7) is a SCF-type E3 ubiquitin ligase targeting a multitude of oncoproteins for degradation. Acting as one of the most important tumor suppressors, it is frequently inactivated in various tumors. In this study we aimed to evaluate the relationship of FBW7 with glioma pathology and prognosis, and examine its effect in glioma malignancies and temozolomide (TMZ)-based therapy. Clinical tissues and TCGA database analysis revealed that FBW7 expression was correlated inversely with glioma histology and positively with patient survival time. Lentivirus transfection-induced FBW7 overexpression significantly suppressed proliferation, invasion and migration of U251 and U373 cells, whereas knockdown of FBW7 by targeted shRNA promoted proliferation, invasion and migration of glioma cells. Most importantly, the expression level of FBW7 was found to affect the 50% inhibitory concentration (IC50) of U251 and the TMZ-resistant variant. Combining TMZ with FBW7 overexpression notably increased the cytotoxicity compared to TMZ treatment alone, which was conversely attenuated by FBW7 knockdown. Moreover, flow cytometry (FC) analysis showed overexpression of FBW7, TMZ or the combination-increased proportion of G2/M arrest and the apoptotic rate, whereas FBW7 inhibition reduced G2/M arrest and apoptosis in U251 cells. Finally, mechanistic study found that FBW7 overexpression downregulated Aurora B, Mcl1 and Notch1 levels in a time-dependent pattern and this expressional suppression was independent of TMZ. These findings collectively demonstrate the critical role of FBW7 as a prognostic factor and a potential target to overcome chemoresistance of glioblastoma.

Overexpression of ubiquitin specific proteases 44 promotes the malignancy of glioma by stabilizing tumor-promoter securin.

Ubiquitin specific peptidase 44 (USP44) has been identified as an important component of spindle assemble checkpoint (SAC) to prevent the formation of aneuploidy. However, recent study raised a controversy about the effect of USP44 in tumor. Here, we first confirmed the intranuclear localization of USP44 by testing several specific antibodies to recognize endogenous USP44. Then, data from IHC and qRT-PCR assay indicated that the high expression of USP44 existed in high-grade glioma tissues and signified a poor prognosis. Knockdown of USP44 inhibited proliferation, migration and invasion, induced apoptosis, and arrested cell cycle in G2/M phase in the established glioma cell lines. Down-regulation of oncoprotein securin was detected in USP44 deficient cells, and the interaction of endogenous USP44 and securin was confirmed by immunoprecipitation in U251MG cells, which indicated that securin was a substrate of USP44, and might be stabilized by USP44. In vivo, knockdown of USP44 inhibited the tumorigenicity of U87MG cells significantly. Consequently, our findings suggested that overexpression of USP44 could enhance the malignancy of glioma via securin. USP44 might serve as a predictive biomarker, and the USP44-securin pathway might provide a new therapeutic strategy for the treatment of glioma.

RIZ1 negatively regulates ubiquitin-conjugating enzyme E2C/UbcH10 via targeting c-Myc in meningioma.

RIZ1 has been considered as an important tumor suppressor gene. Our previous studies have already demonstrated that the expression of RIZ1 is closely related to the occurrence and development of meningioma. In addition, we also found that the expression of UbcH10 was related to the pathologic grade of meningioma which also affected the prognosis of these patients. However, we are lack of the understanding of the effect of UbcH10 on cell proliferation, cell apoptosis, cell cycle and other functions in meningioma cells. Besides, the regulation mechanism between RIZ1 and UbcH10 still remains unclear. In this study, we attempted to demonstrated that UbcH10 was a downstream target of RIZ1 and reported that UbcH10 silencing might negatively regulate cell proliferation, migration, invasion and promote apoptosis, which is similar to the cell phenotype that of over expressed RIZ1. Mechanistically, we proved that UbcH10 was a c-Myc target gene and that RIZ1 regulated UbcH10 expression in a c-Myc-dependent manner. For the first time, our study demonstrated that UbcH10 played a key role in the proliferation, metastasis and apoptosis of primary human malignant meningioma cells. In addition, the mechanism of RIZ1 regulating UbcH10 is also clear. Our study can also provide a potential target and new idea for the follow-up molecular intervention in clinical malignant meningiomas.

Tissue thioredoxin-interacting protein expression predicted recurrence in patients with meningiomas.

BACKGROUND: The redox regulatory protein, thioredoxin-interacting protein (TXNIP), has been confirmed as an important tumor suppressor gene in various types of human cancers. In previous studies, we found that overexpression of tumor suppressor gene RIZ1 in meningiomas can significantly improve the expression of TXNIP by microarray data analysis. Therefore, we hypothesized that TXNIP was associated with the initiation and progression of meningiomas. METHODS: First, we evaluated the expression of TXNIP and Ki-67 in meningioma tissues from 65 patients using immunohistochemistry. We also analyzed the correlation between TXNIP immunoreactivity and clinicopathological features, as well as patient prognostic factors. RESULTS: According to immunohistochemistry results, high-grade meningioma tissues had significantly lower expression of TXNIP than benign meningioma tissues (29.31 ± 18.70 vs 74.61 ± 7.51, P < 0.0001). TXNIP and Ki67 were negatively correlated (P < 0.0001). Moreover, the expression of TXNIP was higher in nonrecurrent high-grade meningiomas (P < 0.05). In addition, Kaplan-Meier analysis indicated that expression of TXNIP and Ki-67 was related to recurrence-free time. Multivariate Cox analysis showed that TXNIP expression level was the only independent predictor for meningioma prognosis. CONCLUSION: Our results demonstrated that high expression of TXNIP indicates a lower pathological grade of meningnioma, and is also associated with longer recurrence-free time. Therefore, TXNIP could be regarded as a potential molecular marker to predict recurrence in patients with meningiomas.

Down-regulation of long non-coding RNA FOXD3 antisense RNA 1 (FOXD3-AS1) inhibits cell proliferation, migration, and invasion in malignant glioma cells.

Growing evidence indicates that long non-coding RNAs (lncRNAs) play key roles in cancer initiation and progression. However, little is known about the therapeutic significance of lncRNAs in glioma. In this study, we explored the tumorigenic role of a classical lncRNA, FOXD3 antisense RNA 1 (FOXD3-AS1) in glioma. Systemic analysis of the patient specimens and clinical data showed that FOXD3-AS1 was markedly up-regulated in high-grade glioma tissues (WHO grade III-IV) compared with that in low-grade glioma (WHO grade I-II) and normal brain tissues (both P<0.01), and patients with low FOXD3-AS1 expression had grater survival probability. Multivariate regression analysis showed that increased FOXD3-AS1 expression was a significant independent indicator of poor prognosis in glioma patients (P=0.034). To understand the tumorigenic mechanism of FOXD3-AS1, the expression pattern and functional role of FOXD3-AS1 in glioma were detected using real-time PCR and Smart Silencer-mediated knockdown study. In related cell biological assays, we discovered that FOXD3-AS1 knockdown significantly inhibited cell proliferation, induced cell cycle S-phase arrest, and impaired cell migration and invasion in malignant glioma cells. As expected, we also found that the expression of FOXD3-AS1 was positively correlated with FOXD3 mRNA. Knockdown of FOXD3-AS1 reduced the protein level of FOXD3 in cultured U251 and A172 cell lines. These results suggest that FOXD3-AS1 is an oncogenic lncRNA, which may promote the occurrence and development of glioma through transcriptional regulation of FOXD3.

RNA interference against TMEM97 inhibits cell proliferation, migration, and invasion in glioma cells.

Gliomas are the most common form of primary brain tumor in the adult central nervous system. Altered expression and prognostic value of transmembrane protein 97 (TMEM97) has been recently reported in different types of human tumors. However, the association of TMEM97and glioma is poorly defined. Here, we reported that TMEM97 was significantly increased in glioma tissues compared to non-tumorous brain tissues. Furthermore, TMEM97 levels were progressively increased with increasing histologic tumor grade in glioma. Higher TMEM97 expression level was correlated with shorter survival time of patients with glioma. Downregulation of TMEM97 through RNA interference inhibited cell proliferation and G1/S transition in two glioma cell lines, U87 and U373. More importantly, TMEM97 silencing induced a significant decrease in the expression of G1/S transition key regulators, cyclin D1, cyclin E, CDK2, and CDK4. Additionally, downregulation of TMEM97 in glioma cells notably repressed cell migration and cell invasion. Further analysis suggested that the decreased invasion was associated with alterations in EMT markers, including E-cadherin, ß-catenin, and Twist. Since expression of TMEM97 seems to be associated with the oncogenic potential of glioma, and suppression of its expression can inhibit cancer cell growth and metastasis, TMEM97 may be a potential therapeutic target in human glioma.

Knockdown of TMEM45A inhibits the proliferation, migration and invasion of glioma cells.

Gliomas are the most common and aggressive type of primary adult brain tumor. Although high expression and prognostic value of TMEM45A has been recently reported in various types of human tumors, the association of TMEM45A expression and glioma is still unknown. Here, we reported that TMEM45A was significantly overexpressed in glioma tissues compared to non-tumorous brain tissues. Furthermore, TMEM45A mRNA levels were gradually increased with the increasing severity of histological grade of glioma. Moreover, high TMEM45A expression level was correlated with short survival time of glioma patients. Down-regulation of TMEM45A in two glioma cell lines, U251 and U373 by transected with TMEM45A siRNA resulted in a significant reduction of cell proliferation and G1-phase arrest. Additionally, we found that suppressing of TMEM45A expression in glioma cells remarkably suppressed cell migration and cell invasion. More importantly, TMEM45A siRNA treatment significantly down-regulated the proteins promoting cell cycles transition (Cyclin D1, CDK4 and PCNA) and cell invasion (MMP-2 and MMP-9), which indicted a possible mechanism underlying its functions on glioma. In summary, our study suggests that TMEM45A may work as an oncogene and a new effective therapeutic target for glioma treatment.

The expression of SALL4 in patients with gliomas: high level of SALL4 expression is correlated with poor outcome.

The spalt-like transcription factor 4 (SALL4) gene has been demonstrated to be overexpressed in many malignancies, but little is known about its expression in gliomas. To explore the expression of SALL4 in patients with gliomas and the relationship between SALL4 expression and clinicopathologic characteristics, qPCR and immunohistochemical staining were used to investigate the SALL4 expression level in 54 glioma specimens and seven normal brain tissues. In vitro, siRNAs against SALL4 in U251 cell line were constructed and cell proliferation was evaluated by CCK8 assay. The SALL4 expression level in glioma was significantly higher than that in normal brain tissues (P < 0.05). Both qPCR and immunohistochemical analysis found that the expression of SALL4 was tightly correlated with glioma pathology grade (P < 0.05). Analysis using glioma and normal brain tissues revealed that SALL4 was positively proportionated to glioma cell differentiation with high sensitivity (92.59 %) and specificity (85.71 %). Survival analysis indicated the SALL4 expression was an independent prognostic factor. High level of SALL4 expression was correlated with poor outcome in patients with gliomas. This result agreed with the negative correlation between SALL4 expression and overall survival period obtaining in GBM patients from the cancer genome atlas database. The CCK8 experiments demonstrated SALL4 could significantly inhibit cell proliferation in U251 cell line (P < 0.05). The findings of the current study indicated that the SALL4 may play an important role in progression, development and maintenance of glioma.

LncRNA and mRNA interaction study based on transcriptome profiles reveals potential core genes in the pathogenesis of human glioblastoma multiforme.

OBJECTIVES: To study the expression profiles of lncRNA and mRNA in glioblastoma multiforme (GBM) and to find potential core genes in the pathogenesis of this high malignant disease. METHODS: Agilent Microarray (Arrystar v2.0) was used to detect the expressions of 33,045 lncRNAs and 30,215 coding transcripts in 5 GBM and 5 normal brain samples. Differentially expressed lncRNAs and mRNAs were identified through Volcano Plot filtering. The expressions of six lncRNAs were further detected by qPCR to validate the results of microarray. The function of differential mRNA was determined by pathway and GO analysis, and the function of lncRNAs was studied by subgroup analysis and by their physical or functional relationships with corresponding mRNAs. RESULTS: A total of 815 lncRNAs and 738 mRNAs are found to be differentially expressed between the GBM and normal brain groups. With the expression of these differentially expressed genes, the two group samples could be clearly differentiated. The result of qPCR has showed a good consistency with the microarray, thus proving the accuracy of the microarray data. GO and Pathway analyses have proved that the functions of differentially expressed mRNAs in GBM related closely with many processes that important in the cancer pathogenesis. Core lncRNAs and mRNAs that may play important roles in the pathogenesis of GBM are revealed and listed according to various methods. CONCLUSION: The GBM shows an aberrant expression profile of lncRNA and mRNA. Potential core genes are revealed by the lncRNA and mRNA interaction study based on transcriptome profiles in GBM.

SAMSN1 is highly expressed and associated with a poor survival in glioblastoma multiforme.

OBJECTIVES: To study the expression pattern and prognostic significance of SAMSN1 in glioma. METHODS: Affymetrix and Arrystar gene microarray data in the setting of glioma was analyzed to preliminarily study the expression pattern of SAMSN1 in glioma tissues, and Hieratical clustering of gene microarray data was performed to filter out genes that have prognostic value in malignant glioma. Survival analysis by Kaplan-Meier estimates stratified by SAMSN1 expression was then made based on the data of more than 500 GBM cases provided by The Cancer Genome Atlas (TCGA) project. At last, we detected the expression of SAMSN1 in large numbers of glioma and normal brain tissue samples using Tissue Microarray (TMA). Survival analysis by Kaplan-Meier estimates in each grade of glioma was stratified by SAMSN1 expression. Multivariate survival analysis was made by Cox proportional hazards regression models in corresponding groups of glioma. RESULTS: With the expression data of SAMSN1 and 68 other genes, high-grade glioma could be classified into two groups with clearly different prognoses. Gene and large sample tissue microarrays showed high expression of SAMSN1 in glioma particularly in GBM. Survival analysis based on the TCGA GBM data matrix and TMA multi-grade glioma dataset found that SAMSN1 expression was closely related to the prognosis of GBM, either PFS or OS (P<0.05). Multivariate survival analysis with Cox proportional hazards regression models confirmed that high expression of SAMSN1 was a strong risk factor for PFS and OS of GBM patients. CONCLUSION: SAMSN1 is over-expressed in glioma as compared with that found in normal brains, especially in GBM. High expression of SAMSN1 is a significant risk factor for the progression free and overall survival of GBM.