NUCLEAR FACTOR OF ACTIVATED T-CELLS (NFAT) AS A NEW COMPONENT OF THE SIGNAL-TRANSDUCTION PATHWAY IN GLIOMA-CELLS

Cyclosporin A (CsA) exerts its immunosuppressive effect by inhibiting the activity of nuclear factor of activated T cells (NFAT), thus preve nting transcriptional induction of several cytokine genes. This effect is mediated through inactivation of the phosphatase calcineurin, whic h inhibits translocation of an NFAT component to the nucleus. We have previously reported that CsA inhibits the growth of rat C6 glioma cell s in a dose-dependent manner and induces apoptotic cell death. Here, w e report that NFAT DNA-binding activity is present in the nuclear extr acts from C6 glioma cells and that CsA treatment inhibits the formatio n of a functional NFAT complex. We provide evidence for the presence o f a group of NFATc proteins in proliferating glioma cells. Immunoblot analyses show that stimulation of C6 glioma cells with a calcium-induc ing agent, ionomycin, alters NFATc migration on sodium dodecyl sulfate -polyacrylamide gel electrophoresis. This alteration is inhibited by s imultaneous treatment with CsA, suggesting a calcineurin involvement i n the regulation of glioma NFATc proteins. Direct immunofluorescence r eveals the presence of NFATc proteins in nuclei of proliferating gliom a cells and their disappearance in CsA-treated cells. These data point to a new mechanism of transcription regulation in glioma cells and pr ovide an explanation for the observed sensitivity of glioma cells to C sA.