CARBOXYL-TERMINAL 15-AMINO ACID SEQUENCE OF NFATX1 IS POSSIBLY CREATED BY TISSUE-SPECIFIC SPLICING AND IS ESSENTIAL FOR TRANSACTIVATION ACTIVITY IN T-CELLS

NFAT regulates transcription of a number of cytokine and other immunor egulatory genes. We have isolated NFATx, which is one of four members of the NFAT family of transcription factors and is preferentially expr essed in the thymus and peripheral blood leukocytes, and an isoform of NFATx, NFATx1. Here we provide evidence showing that 15 amino acids i n the carboxyl-terminal end of NFATx1 are required for its maximum tra nsactivation activity in Jurkat T cells,A fusion between these 15 amin o acids and the GALA DNA binding domain was capable of transactivating reporters driven by the GAL4 DNA binding site. Interestingly, this. 1 5-amino acid transactivation sequence is well conserved in NFAT family proteins, although the sequences contiguous to the carboxyl-terminal regions of the NFAT family are much less consented. We also report thr ee additional isoforms of NFATx, designated NFATx2, NFATx3, and NFATx4 . This transactivation sequence is altered by tissue-specific alternat ive splicing in newly isolated NFATx isoforms, resulting in lower tran sactivation activity in Jurkat T cells. NFATx1 is expressed predominan tly in the thymus and peripheral blood leukocyte, while the skeletal m uscle expressed primarily NFATx2. In Jurkat cells, transcription from the NFAT site of the IL-2 promoter is activated strongly by NFATx1 but only weakly by NFATx2. These data demonstrate that the U-amino acid s equence of NFATx1 is a major transactivation sequence required for ind uction of genes by NFATx1 in T cells and possibly regulates NFAT activ ity through tissue-specific alternative splicing.