RECOMBINANT NFAT1 (NFATP) IS REGULATED BY CALCINEURIN IN T-CELLS AND MEDIATES TRANSCRIPTION OF SEVERAL CYTOKINE GENES

Transcription factors of the NFAT family play a key role in the transc ription of cytokine genes and other genes during the immune response. We have identified two new isoforms of the transcription factor NFAT1 (previously termed NFATp) that are the predominant isoforms expressed in murine and human T cells. When expressed in Jurkat T cells, recombi nant NFAT1 is regulated, as expected, by the calmodulin-dependent phos phatase calcineurin, and its function is inhibited by the immunosuppre ssive agent cyclosporin A (CsA). Transactivation by recombinant NFAT1 in Jurkat T cells requires dual stimulation with ionomycin and phorbol 12-myristate 13-acetate; this activity is potentiated by coexpression of constitutively active calcineurin and is inhibited by CsA. Immunoc ytochemical analysis indicates that recombinant NFAT1 localizes in the cytoplasm of transiently transfected T cells and translocates into th e nucleus in a CsA-sensitive manner following ionomycin stimulation. W hen expressed in COS cells, however, NFAT1 is capable df transactivati on, but it is not regulated correctly: its subcellular localization an d transcriptional function are not affected by stimulation of the COS cells with ionomycin and phorbol 12-myristate 13-acetate. Recombinant NFAT1 can mediate transcription of the interleukin-2, interleukin-4, t umor necrosis factor alpha, and granulocyte-macrophage colony-stimulat ing factor promoters in T cells, suggesting that NFAT1 contributes to the CsA-sensitive transcription of these genes during the immune respo nse.