CALCINEURIN-DEPENDENT NUCLEAR TRANSLOCATION OF A MURINE TRANSCRIPTIONFACTOR NFATX - MOLECULAR-CLONING AND FUNCTIONAL-CHARACTERIZATION

Members of the nuclear factor of activated T cells (NFAT) are involved in the induction of a number of cytokine genes. We report here cDNA c loning and chromosomal localization of a murine homologue of human NFA Tx, designated as mNFATx1, and its splicing variants nMFATx2 and m Del ta NFATx. Northern blot analysis showed mNFATx1 to be predominantly ex pressed in the thymus. nMFATx1, but not m Delta NFATx, produced in COS -7 cells, bound to all NFAT-binding sites of the interleukin (IL)-2 an d IL-4 promoters tested. Immunofluorescence assay showed that both mNF ATx1 and m Delta NFATx introduced into COS-7 cells localized predomina ntly to the cytoplasm, but did translocate to the nucleus, either by c otransfection with an active form of calcineurin or wild-type calcineu rin followed by stimulation with calcium ionophore. Translocation of m NFATx1 correlated well with activation of the murine IL-2 promoter; mN FATx1 translocated under conditions described above, in combination wi th phorbol 12-myristate 13-acetate, activated the transiently transfec ted murine IL-2 promoter. Thus, nuclear-translocated mNFATx1 is involv ed in activation of the IL-2 promoter. These results provide the first evidence for the requirement of calcineurin in the control of mNFATx imported from the cytoplasm to the nucleus and implies that mNFATx may possibly be a substrate of calcineurin in vivo.