Endogenous GABAA receptor activity suppresses glioma growth.

Although genome alterations driving glioma by fueling cell malignancy have largely been resolved, less is known of the impact of tumor environment on disease progression. Here, we demonstrate functional GABAA receptor-activated currents in human glioblastoma cells and show the existence of a continuous GABA signaling within the tumor cell mass that significantly affects tumor growth and survival expectancy in mouse models. Endogenous GABA released by tumor cells, attenuates proliferation of the glioma cells with enriched expression of stem/progenitor markers and with competence to seed growth of new tumors. Our results suggest that GABA levels rapidly increase in tumors impeding further growth. Thus, shunting chloride ions by a maintained local GABAA receptor activity within glioma cells has a significant impact on tumor development by attenuating proliferation, reducing tumor growth and prolonging survival, a mechanism that may have important impact on therapy resistance and recurrence following tumor resection.

Quiescence and γH2AX in neuroblastoma are regulated by ouabain/Na,K-ATPase.

BACKGROUND: Cellular quiescence is a state of reversible proliferation arrest that is induced by anti-mitogenic signals. The endogenous cardiac glycoside ouabain is a specific ligand of the ubiquitous sodium pump, Na,K-ATPase, also known to regulate cell growth through unknown signalling pathways. METHODS: To investigate the role of ouabain/Na,K-ATPase in uncontrolled neuroblastoma growth we used xenografts, flow cytometry, immunostaining, comet assay, real-time PCR, and electrophysiology after various treatment strategies. RESULTS: The ouabain/Na,K-ATPase complex induced quiescence in malignant neuroblastoma. Tumour growth was reduced by >50% when neuroblastoma cells were xenografted into immune-deficient mice that were fed with ouabain. Ouabain-induced S-G2 phase arrest, activated the DNA-damage response (DDR) pathway marker γH2AX, increased the cell cycle regulator p21(Waf1/Cip1) and upregulated the quiescence-specific transcription factor hairy and enhancer of split1 (HES1), causing neuroblastoma cells to ultimately enter G0. Cells re-entered the cell cycle and resumed proliferation, without showing DNA damage, when ouabain was removed. CONCLUSION: These findings demonstrate a novel action of ouabain/Na,K-ATPase as a regulator of quiescence in neuroblastoma, suggesting that ouabain can be used in chemotherapies to suppress tumour growth and/or arrest cells to increase the therapeutic index in combination therapies.

The glycogen synthase kinase (GSK) 3beta represses RNA polymerase I transcription.

Several oncogenic proteins and tumour suppressors target the RNA polymerase I and interfere with rRNA synthesis. Here, we show that the glycogen synthase kinase (GSK) 3beta, which phosphorylates the tumour suppressor PTEN (phosphatase and tensin homologue deleted on chromosome 10), is selectively enriched in nucleoli of RAS-transformed cells. Immunoprecipitation and chromatin immunoprecipitation assays performed on epithelial and endothelial cells transformed with oncogenic RAS show that GSK3beta and PTEN are part of the same complex and associate with promoter and coding region of the rDNA. An active GSK3beta mutant abolished nucleolar BrUTP incorporation and associated with the member of the selectivity factor 1 complex TAF(I)110. Finally, GSK3beta inhibition upregulated 45S, 18S and 28S rRNA synthesis in RAS-transformed epithelial cells as revealed by semiquantitative real-time PCR and promoted cellular proliferation. Our results underscore a repressive function for GSK3beta in rRNA biogenesis supporting its role as a tumour supressor.

Interaction between hammerhead ribozyme and RNA substrates measured by a surface plasmon resonance biosensor.

Dynamic interactions between hammerhead ribozymes and RNA substrates were measured using the surface plasmon resonance (SPR) technology. Two in vitro transcribed substrates (non-cleavable and cleavable) were immobilised on streptavidin-coated dextran matrices and subsequently challenged with non-related yeast tRNA or two hammerhead ribozymes, both of which had previously been shown to exhibit functional binding and cleavage of complementary target RNAs. The target-binding domain of one of the ribozymes was fully complementary to a 16-ribonucleotide stretch on the immobilised substrates, while the other ribozyme had a nine-ribonucleotide complementarity. The two ribozymes could readily be differentiated with regard to affinity. Cleavage could be measured, using the ribozyme with full target complementarity to the cleavable substrate. In contrast, the ribozyme with lower affinity lacked cleavage activity. We suggest that SPR will be useful for investigations of ribozyme-substrate interactions.

Differentiation of mesothelioma cells is influenced by the expression of proteoglycans.

Malignant mesothelioma characteristically shows epithelial and/or sarcomatous morphology, this phenotypic differentiation being correlated to the prognosis. The present study was undertaken to see whether proteoglycan (PG) expression influences mesothelioma differentiation. To assess this hypothesis, we studied a mesothelioma model, where the cells were induced to differentiate into epithelial or fibroblast-like morphology, mimicking the biphasic growth of this sarcoma. Series of PGs were analyzed in parallel by semiquantitative reversed transcriptase polymerase chain reaction, showing increased expression of syndecan-2, syndecan-4, and hyaluronan synthase in the epithelial phenotype, whereas the fibroblast-like cells expressed more matrix PGs: versican, decorin, and biglycan. Western blotting confirms these differences and provides evidence of extensive shedding and rapid turnover of cell membrane PGs. Experimental down-regulation of the studied syndecans by antisense targeting resulted in a change in shape from polygonal to spindle-like morphology, while syndecan-1 and -4, but not syndecan-2, could be associated with cell aggregation, indicating distinct functions of different syndecans. The PG profile is thus closely associated with the morphology and biological behavior of tumor cells, mesotheliomas showing a different profile than true epithelial tumors.

Dose-response resistance to HIV-1/MuLV pseudotype virus ex vivo in a hairpin ribozyme transgenic mouse model.

We have investigated the efficacy of a hairpin ribozyme targeting the 5' leader sequence of HIV-1 RNA in a transgenic model system. Primary spleen cells derived from transgenic or control mice were infected with HIV-1/MuLV pseudotype virus. A significantly reduced susceptibility to infection in ribozyme-expressing transgenic spleen cells (P = 0.01) was shown. Variation of transgene-expression levels between littermates revealed a dose response between ribozyme expression and viral resistance, with an estimated cut off value below 0.2 copies of hairpin ribozyme per cell. These findings open up possibilities for studies on ribozyme efficacy and anti-HIV-1 gene therapy.

IL-6 antisense oligonucleotides inhibit IgE production in IL-4 and anti-CD40-stimulated human B-lymphocytes.

Stimulation of tonsillar B-lymphocytes with CD40 antibodies and IL-4 leads to homotypic adhesion, proliferation, and differentiation into Ig-producing cells. It also leads to the production of IL-6, a pleiotropic cytokine involved in B-cell maturation and differentiation. To assess the importance of IL-6 in the differentiation process, an antisense oligonucleotide to IL-6 was added to tonsillar B-cells together with CD40 antibodies and IL-4. This led to clearly reduced levels of IL-6 as well as to a specific inhibition of IgE production. Also, IgG secretion was somewhat reduced while IgM appeared to be unaffected. The effects were not due to toxicity of the oligonucleotide since proliferation proceeded normally or was slightly enhanced in the presence of the antisense. The findings show that endogenous IL-6 is an important co-factor for the generation of B-cells secreting IgE and IgG but that it is not required for IgM production. They further indicate that IL-6 may not be necessary as a co-factor in CD40/IL-4 induced proliferation.

A novel ribozyme target site located in the HIV-1 nef open reading frame.

We have tested the sequence UUC CAG UCA GAC CU, at position 9016--9029 within the HIV-1(SF2) nef open reading frame, for accessibility to antisense and hammerhead ribozyme attack. The accessibility was first studied using a phosphorothioate-modified 14-nt DNA oligo (complementary to the nef9016--9029 site). A dose-dependent repression of HIV-1(SF2) growth was observed in human peripheral blood mononuclear cells after exogenous administration of the oligo to the cell culture medium. A hammerhead ribozyme with a 6+7-nt antisense specificity for the nef9016--9029 site (hhRz.nef9016--9029) was constructed and transfected into the human T-cell line HUT78. Again, a dose-dependent repression of virus growth was observed when different individual clones expressing hhRz.nef9016--9029 were infected with HIV-1(SF2). A complete abrogation of virus production was observed after infection with a low (0.5 TCID50) HIV-1 titer. Increasing doses (2.5 and 12.5 TCID50) of HIV-1 virus yielded a low production (10(3)-fold reduced) of virus particles in most cases; but a complete, or close to complete, abrogation was observed even in individual cultures infected with the highest dose. Presence of proviral pol and gag sequences in hhRz.nef9016--9029-expressing HUT78 clones was assayed, using PCR. Interestingly, since no pol and gag PCR products could be detected, the results strongly indicated that the hammerhead ribozyme was already acting on the infecting HIV RNA before its reverse transcription and integration as proviral DNA. In summary, the results obtained in this study support the nef9016--9029 site as a strong new candidate for ribozymal gene therapy against HIV-1 infection.

A method for production of 13C/15N double labelled RNA in E. coli, and subsequent in vitro synthesis of ribonucleotide 5' triphosphates.

In this paper we describe an enhanced method for the large scale production of high quality 13C/15N labelled NTPs. High amounts of labelled RNA was obtained from E. coli cells grown in 13C/15N enriched medium and treated with chloramphenicol. Total RNA was extracted from spheroplasted cells in the presence of SDS and proteinase K and subsequently degraded to NMPs by nuclease P1 and high concentrations of nuclease S1 in a low salt buffer. To avoid non-specific degradation of the RNA, nuclease digestion was performed in a short term reaction on native, not heat-denatured RNA. CMP, AMP, GMP and UMP were chromatographically separated and converted to the corresponding NTPs by a mixture of kinases in the presence of a coupled redox system based on thioredoxin and dithiothreitol. The quality of the 13C/15N labelled NTPs was tested by in vitro transcription.

Reduced beta 2-microglobulin mRNA levels in transgenic mice expressing a designed hammerhead ribozyme.

We have generated three artificial hammerhead ribozymes, denoted 'Rz-b', 'Rz-c' and 'Rz-d', with different specificities for exon II of the mouse beta-2-microglobulin (beta 2M) mRNA. In this study we tested for ribozyme mediated reduction of beta 2M mRNA in a cell line and in transgenic mice. Transfections of either of the Rz-b, Rz-c or Rz-d plasmids into a mouse cell-line (NIH/3T3) revealed reductions of beta 2M mRNA substrate in each case. Ribozyme expression in individual transfected clones was accompanied with an up to 80% reduction of beta 2M mRNA levels. Rz-c was selected for a transgenic study. Seven Rz-c transgenic founder animals were identified from which three ribozyme expressing families were established and analysed. Expression of the ribozyme transgene was tested for and detected in lung, kidney and spleen. Expression was accompanied with reduction of the beta 2M mRNA levels of heterozygous (Rz+/-) animals compared to non-transgenic litter mates. The effect was most pronounced in lung with more than 90% beta 2M mRNA reduction in individual mice. In summary, expression of our ribozymes in a cell free system, in a cell-line and in transgenic mice were all accompanied with reductions of beta 2M mRNA levels.