Superinduction of cytotoxic interferon-beta in glioma cells

Protein synthesis inhibitors, gene superinduction and memory: too little or too much protein?

To date, the effects of protein synthesis inhibitors (PSI) in learning and memory processes have been attributed to translational arrest and consequent inhibition of de novo protein synthesis. Here we argue that amnesia produced by PSI can be the direct result of their abnormal induction of mRNA-a process termed gene superinduction. This action exerted by PSI involves an abundant and prolonged accumulation of mRNA transcripts of genes that are normally transiently induced. We summarize experimental evidence for the multiple mechanisms and signaling pathways mediating gene superinduction and consider its relevance for PSI-induced amnesia. This mechanistic alternative to protein synthesis inhibition is compared to models of electroconvulsive seizures and fragilexsyndrome associated with enhanced mRNA/protein levels and cognitive deficits.

Susceptibility to exogenously added interferon-beta protein depends on intracellular interferon-beta mRNA level in human glioma cells

Exogenously added human interferon-beta (HuIFN-beta) protein possesses a remarkable antiproliferative activity in human glioma and melanoma. Endogenous HuIFN-beta protein, which is produced by its gene transfer using cationic liposomes, has much more effective antiproliferative activity against these tumors, even in cells resistant to exogenously added HuIFN-beta protein. As the first step to elucidate the possible difference in antiproliferative mechanisms between exogenous and endogenous HuIFN-beta protein, we here investigated the relationship between the intracellular level of its mRNA and susceptibility to exogenously added HuIFN-beta protein. In this study, we used seven human glioma cell lines (SK-MG-1, SK-MG-4, SK-AO2, U87MG, U251SP, U251MG and T98) and one human melanoma cell line (MMAN). At first, we examined the relationship between spontaneous expression of HuIFN-beta mRNA and susceptibility to exogenously added HuIFN-beta protein (50 IU/ml) in human glioma cells and then confirmed a significant correlation between them. Next, we confirmed that administration of 0-100 IU/ml exogenously added HuIFN-beta protein upregulated the HuIFN-beta mRNA in a dose-dependent manner using the RT-PCR technique and that the HuIFN-beta mRNA was suppressed by siRNA for HuIFN-beta in SK-MG-1 and MMAN cells. Furthermore, we confirmed that the siRNA for HuIFN-beta significantly suppressed the antiproliferative effect of SK-MG-1 cells treated with 10-100 IU/ml HuIFN-beta protein and MMAN cells with 25 and 50 IU/ml HuIFN-beta protein. We found this phenomenon in another human glioma cell line, U87MG cells, as well. This finding would suggest that susceptibility to exogenously added HuIFN-beta protein is related to the amount of intracellular HuIFN-beta mRNA in human glioma and melanoma cells.

Synergism between mild hyperthermia and interferon-beta gene expression

In the present study, the synergistic effect of mild hyperthermia in combination with gene expression of interferon-beta (IFN-beta) was examined in vitro in the human glioma cell line U87MG. The cells transiently expressed the IFN-beta gene under the control of the mouse mammary tumor virus promoter and were then subjected to temperature elevation (41 degrees C for 1 h). In terms of the cell killing effect, the optimum scheme was obtained by transfection for 4 days before hyperthermia, i.e. rate in the time course of IFN-beta gene expression. The relative specific growth rate decreased to 32% compared with the control while it was only 40% under the hyperthermic conditions. These observations suggest that IFNbeta expression was able to enhance the sensitivity of transfected glioma cells to mild hyperthermia.