No abstract

Interferon (IFN)-inducible human MxA protein mediates resistance against influenza and several other RNA viruses. The MxA gene is under the control of type I IFN and, in certain cell types, is also directly activated by viruses. Here we show that in human macrophages, MxA mRNA levels are upregulated by very low doses of IFN-alpha in a dose-dependent manner. A similar, albeit much weaker, dose-dependent induction was seen with IFN-gamma. The induction was rapid and independent of protein synthesis. Interleukin-6 (IL-6) or tumor necrosis factor-alpha (TNF-alpha) did not influence MxA mRNA levels alone or in combination with IFNs, in spite of the presence of putative response elements of these cytokines in the MxA promoter. We show that the promoter of the MxA gene contains two functional IFN-stimulated response elements (ISRE) near the transcription start site and one homologous ISRE-like element, which is apparently nonfunctional, further upstream. The two proximal ISRE sites are essential for IFN-alpha-induced transcription and appear to be binding sites for IFN-stimulated gene factor 3 complex. In addition, EMSA and DNAse I footprinting analysis demonstrated that Spl binds with high affinity to a region encompassing nucleotides -25 and -50 and, thus, may provide means of interaction with the basal transcriptional machinery.

Ca2؉ may trigger programmed cell death (apoptosis) and regulate death-specific enzymes. Therefore, the development of strategies to control Ca 2؉ homeostasis may represent a potential approach to prevent or enhance cell apoptosis. To test this hypothesis, the plasma membrane Na/Ca exchanger (NCX1.7 isoform) was stably overexpressed in insulin-secreting tumoral cells. homeostasis that could, on the contrary, prevent the process of apoptosis that mediates, in part, ␤-cell autoimmune destruction in type 1 diabetes. NCX1.7 overexpression increased apoptosis induced by endoplasmic reticulum (ER) Ca

No abstract

To characterize the role played by Na/Ca exchange in the pancreatic beta-cell, phosphorothioated antisense oligonucleotides (AS-oligos) were used to knock down the exchanger in rat pancreatic beta-cells. Na/Ca exchange activity was evaluated by measuring cytosolic free Ca2+ concentration ([Ca2+]i) in single cells using fura-2. Exposure of beta-cells to 500 nmol/l of the AS-oligos for 24 h inhibited Na/Ca exchange activity by approximately 77%. In contrast, control oligonucleotides (scrambled and mismatched) did not affect Na/Ca exchange activity. In AS-oligo-treated cells, the increase in [Ca2+]i induced by membrane depolarization (K+ or the hypoglycemic sulfonylurea, tolbutamide) was reduced by 28 or 40%, respectively. Likewise, the rate of [Ca2+]i decrease after K+ or tolbutamide removal was reduced by 72 or 40%, respectively. AS-oligos treatment also abolished the nifedipine-resistant increase in [Ca2+]i induced by K+ and profoundly altered the oscillatory or sustained increases in [Ca2+]i induced by 11.1 mmol/l glucose. The present study shows that AS-oligos may specifically inhibit Na/Ca exchange in rat pancreatic beta-cells. In those cells, Na/Ca exchange appears to mediate Ca2+ entry in response to membrane depolarization and to be responsible for up to 70% of Ca2+ removal from the cytoplasm upon membrane repolarization.