Phosphoglycerate dehydrogenase induces glioma cells proliferation and invasion by stabilizing forkhead box M1.

Phosphoglycerate dehydrogenase (PHGDH) is the first enzyme branching from glycolysis in the three-step serine biosynthetic pathway. Recent evidence has shown that PHGDH is amplified in human breast cancer and melanoma and plays a key role in cancer metabolism. However, PHGDH expression in glioma and a potential non-metabolic role in tumorigenesis have not been reported. We analyzed PHGDH levels in specimens from glioma patients and found that PHGDH, although negative in normal brain tissues, was highly expressed in astrocytic tumors and increasingly expressed in more aggressive cancer types. Inhibition of PHGDH expression in glioma cells downregulated the expression of VEGF, MMP-2, CHK2 and cyclin D1 and reduced glioma cell proliferation, invasion and tumorigenicity in vitro and in vivo. Interestingly, we found that the oncogenic transcription factor FOXM1 was also downregulated in PHDGH-silenced glioma cells. Using LC/LC MS analysis, we identified PHGDH as a novel binding partner of FOXM1. PHGDH interacted with and stabilized FOXM1 at the protein level, promoting the proliferation, invasion and tumorigenicity of glioma cells. Our data identified PHGDH as a potential prognostic marker of glial brain tumors and identified a non-metabolic role for PHGDH in glioma tumorigenesis, providing a novel angle of targeting the PHGDH-FOXM1 axis in future brain tumor therapy.

LRRC8A potentiates temozolomide sensitivity in glioma cells via activating mitochondria-dependent apoptotic pathway.

Chloride (Cl-), a primary anion in the extracellular fluid, plays an important role in a variety of physiological and pathological processes, such as cell apoptosis and proliferation. However, the information about Cl- in cancer cell apoptosis and chemoresistance is poorly understood. In the present study, we found that temozolomide (TMZ) treatment led to a decrease in intracellular concentration of Cl- ([Cl-]i) in both U87 and TMZ-resistant U87/R glioma cells. The decrease in [Cl-]i was more noticeable in U87 cells than in U87/R cells. Moreover, the expression of LRRC8A was reduced in U87/R cells compared with U87 cells. LRRC8A downregulation inhibited TMZ, induced the decrease in [Cl-]i and abolished the difference of [Cl-]i between U87 cells and U87/R cells. Knockdown of LRRC8A using small interfering RNA attenuated TMZ-induced U87 cell growth inhibition and apoptosis, while overexpression of LRRC8A by adenoviral infection enhanced the effect of TMZ on U87 and U87/R cell viability and apoptosis. Furthermore, LRRC8A downregulation inhibited TMZ-induced mitochondria-dependent apoptosis, including elevated Bcl-2 expression, reduced Bax expression, cytochrome c release, and caspase nine and caspase three activation. On the contrary, upregulation of LRRC8A augmented the activation of mitochondria-dependent apoptotic pathway in U87 and U87/R cells. In conclusion, this study demonstrates that LRRC8A potentiates TMZ-induced glioma cell apoptosis via promoting mitochondria-dependent apoptosis, suggesting that LRRC8A can be represented as a novel target for drug resistance treatment in glioma cells.

[Study on inhibitory effect of arsenic trioxide on growth of rat C6 glioma cells].

OBJECTIVE: To explore the inhibitory effect of arsenic trioxide (A(s2)O3) on the growth of rat C6 glioma cells (C6 cells) as well as finding out the feasibility of using As2O3 as chemotherapy of gliomas. METHOD: C6 cells were treated by different dose of As2O3 (1, 2, 4, 6 and 8 micromol L(-1)). MTT assay and staining for PCNA were used for cell proliferation. Cell apoptosis was determined by TUNEL method and Bcl-2 expression was studied by Western blot. Parental rat C6 cells (5 x 10(5)/15 microL) were implanted into right caudate nucleus of male SD rats as control group. Rats bearing cerebral C6 gliomas as treated group were treated with 1 mmol x L(-1) As2O3. The general manifestation, survival time, MRI dynamic scanning and histopathological changes of all rats were observed. RESULT: All the treated cells showed decreased proliferation in vitro as detected by MTT method (P < 0.01) and staining for PCNA. In situ labeling apoptotic DNA fragment of the treated cells demonatrated that the cell apoptosis significantly increased following treatment with As2O3 (P < 0.01). Western blot showed that the expression of Bcl-2 protein was decreased. All rats in control group died of cerebral gliomas within 3 weeks after implantation of C6 cells (17.8 +/- 0.92) d. Eight out of 10 rats in treated group died within 24-36 days (32.1 +/- 1.35) d and other 2 ones kept alive beyond 120 days with one treated rat being totally disappear of the tumor foci and another having a little residue of tumor. CONCLUSION: The result demonstrates the potential efficacy of As2O3 in the treatment of gliomas. It also suggests that As2O3 may be a good candidate for chemotherapy of human gliomas.

[Connexin 43 gene in the in vivo treatment of cerebral glioma in C6 rats].

OBJECTIVE: To study the role of connexin gene (Cx43) in the suppression of C6 glioma. METHODS: Cx43 gene depleted parental C6 rats (control group) and C6 cells transfected with Cx43 cDNA (transfection group) were implanted into the right caudate nucleus of SD rats. Rats bearing cerebral C6 gliomas were treated with Cx43 cDNA (treatment group) with another group treated with empty vector (empty vector group) serving as control. The general manifestation, survival time, MRI dynamic scanning and histopathological changes in all rats were observed. Cx43 mRNA and its protein were examined by in situ hybridization and immunohistochemistry. Proliferation activity was monitored by the average number of AgNOR stain. Cell apoptosis was examined by the Tolt-mediated x-duTP nick end labeling (TUNEL) method. RESULTS: All rats in the control and empty vector groups died of cerebral glioma within 3 weeks after implantation of C6 cells. Six in the transfection group and 8 in the treatment group were alive beyond 120 days with complete disappearance of the tumor foci, except one in this group having some residue of tumor. In the glioma of transfection and treatment groups, Cx43 gene expression was up-regulated, proliferation activity reduced while the apoptotic cells did not increase. CONCLUSION: The development of glioma is greatly suppressed by the transfection of Cx43 gene, which has great effectiveness in rats bearing cerebral malignant gliomas. This could become a target of choice in the gene treatment of malignant gliomas.

[Preliminary study on the mechanism of connexin 43 gene transfection in the control of glioma cell proliferation].

OBJECTIVE: To study the mechanism involved in the control of glioma cell proliferation with transfection of connexin (Cx) 43 gene. METHODS: C6 rat glioma and TJ905 human glioblastoma cell lines without Cx43 gene expression were transfected with Cx43cDNA mediated by lipofectamine. Northern blot, in situ hybridization and immunohistochemical technology were used to detect the expression of Cx43mRNA and its protein with MTT assay and silver colloid stain for the detection of cell proliferation, TUNEL method for determination of cell apoptosis, scrape loading dye transfer (SLDT) for GJIC, Western blot and immunohistochemical technology for bFGF, PDGF, EGFR, IGF-I and IGFBP3 expression. RESULTS: Cx 43 gene transfected glioma cells showed decreased proliferation, restored GJIC and decreased bFGF, PDGF, IGFBP3, except EGFR expression and cell apoptosis which showed no change. CONCLUSION: The mechanism of Cx 43 gene inhibiting gliomas cell proliferation is the restoration of GJIC and decreased autocrine growth factors.