Circular RNA Pleiotrophin promotes carcinogenesis in glioma via regulation of microRNA-122/SRY-box transcription factor 6 axis.

BACKGROUND: Circular RNAs (circRNAs) are recently identified as gene regulators in mammals and play important roles in carcinogenesis of cancer. For example, circRNA_PTN has been recognized as a biomarker of human cancer and is overexpressed in glioma. The molecular function of circRNA_PTN and its downstream targets in glioma, however, remains elusive. METHODS: Quantitative polymerase chain reaction analysis was used to measure the expression of circular RNA pleiotrophin (circ_PTN) and miR-122. 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2-H-tetrazolium bromide, propidium iodide and Annexin-V/propidium iodide assay were performed to determine cell proliferation and apoptosis of glioma cells. Circular RNA Interactome and TargetScan were used to predict the potential microRNA targeting of circ_PTN and the potential targets of miR-122, respectively. Luciferase activity assay was used to validate these interactions. Downstream molecular mechanisms, including SRY-box transcription factor 6 (SOX6), extracellular regulated protein kinases (ERK), Cyclin D1, B-cell lymphoma-2 (BCL-2) and BCL2 associated X, apoptosis regulator (BAX), were determined by western blot. RESULTS: Circ_PTN was overexpressed in glioma cells, and its knockdown induced cell proliferation inhibition, cell cycle arrest and apoptosis in glioma cells. The target microRNA of circ_PTN was predicted to be miR-122, the expression of which was negatively correlated with circ_PTN in glioma cells. Moreover, SOX6 was predicted as a potential target of miR-122, and miR-122 overexpression decreased SOX6 expression. MiR-122 inhibitor reversed the tumor-suppressing effects of circ_PTN knockdown, while overexpression of SOX6 impaired the miR-122 overexpression-induced cell growth inhibition and apoptosis. In addition, mitogen activated kinase-like protein (MAPK)/ERK pathway was involved in circ_PTN/miR-122/SOX6 axis. CONCLUSIONS: Circ_PTN acted as a sponge of miR-122 and upregulated miR-122 target SOX6, thus promoting carcinogenesis of glioma cells.

MicroRNA-15b suppresses the growth and invasion of glioma cells through targeted inhibition of cripto-1 expression.

Gliomas are the most common type of malignant brain tumor. Studies have identified that miR­15b is negatively correlated with cripto-1 expression in glioma cells, and these molecules serve an important role in cancer development and progression. The current study was undertaken to further examine the association between these two molecules. Fluorescent quantitative PCR confirmed that miR­15b expression was significantly downregulated in glioma tissue while cripto­1 expression was significantly increased. Subsequent to transfection with miR­15b mimics, cripto­1 expression was significantly suppressed, and dual luciferase reporter assays further demonstrated that miR­15b regulates cripto­1 in a targeted manner. Furthermore, miR­15b inhibited proliferation and invasion, and promoted apoptosis of glioma cells while downregulating the expression of MMP­2 and MMP­9. In contrast, cripto­1 expression had the opposite effects. Co­transfection with miR­15b mimics and the cripto­1 overexpression vector overcame the inhibitory action of miR­15b on cripto­1. Therefore, it is suggested that miR­15b modulates cell growth and invasion through targeted regulation of cripto­1 expression in glioma cells. This observation may provide novel targets for the prevention and treatment of gliomas.

The short chain cell-permeable ceramide (C6) restores cell apoptosis and perifosine sensitivity in cultured glioblastoma cells.

Primary glioblastoma multiforme is the most malignant form of astrocytic tumor with an average survival of approximately 12-14 months. The combination of novel Akt inhibitors with anti-cancer therapeutics has achieved improved anti-tumor efficiency. In the current study, we examined the synergistic anti-cancer ability of Akt inhibitor perifosine in combination with short-chain ceramide (C6) against glioblastoma cells (U87MG and U251MG), and studied the underlying mechanisms. We found that perifosine, which blocked Akt/mammalian target of rapamycin activation, only induced moderate cell death and few cell apoptosis in cultured glioblastoma cells. On the other hand, perifosine administration induced significant protective autophagy, which inhibited cell apoptosis induction. Inhibition of autophagy by 3-methyaldenine or by autophagy-related gene-5 RNA interference significantly enhanced perifosine-induced apoptosis and cytotoxicity. We found that the short chain cell-permeable ceramide (C6) significantly enhanced cytotoxic effects of perifosine in cultured glioblastoma cells. For mechanism study, we observed that ceramide (C6) inhibited autophagy induction to restore cell apoptosis and perifosine sensitivity. In conclusion, our study suggests that autophagy inhibition by ceramide (C6) restores perifosine-induced apoptosis and cytotoxicity in glioblastoma cells.

MiR-21 modulates hTERT through a STAT3-dependent manner on glioblastoma cell growth.

BACKGROUND AND PURPOSE: As an important oncogenic miRNA, miR-21 has been reported to play crucial roles in glioblastoma (GBM) carcinogenesis. However, the precise biological function and molecular mechanism of miR-21 in GBM remain elusive. This study is designed to explore the mechanism of miR-21 involved in the control of GBM cell growth. METHODS AND RESULTS: MTT assay, cell cycle analysis, and apoptosis analysis showed that reduction of miR-21 inhibited cell growth in U87 and LN229 GBM cells. Further, reduction of miR-21 decreased the expression of human telomerase reverse transcriptase (hTERT) and repressed STAT3 expression and STAT3 phosphorylation. STAT3 inhibition led to a remarkable depletion of hTERT at both mRNA and protein levels by binding to the hTERT gene promoter by performing luciferase reporter assay and chromatin Immunoprecipitation PCR. Finally, knockdown of miR-21 considerably inhibited tumor growth and diminished the expression of STAT3 and hTERT in xenograft model. CONCLUSION: Our findings indicate that miR-21 regulates hTERT expression mediated by STAT3, therefore controlling GBM cell growth.