Requirement for integration of phorbol 12-myristate 13-acetate and calciumpathways is preserved in the transactivation domain of NFAT1

The transcription factor NFAT integrates signals from both calcium- and pho rbol ester-stimulated signaling pathways. The calcium signal activates the calmodulin (CaM)-dependent phosphatase calcineurin, which dephosphorylates the regulatory domain of NFAT and promotes its nuclear import, while the ph orbol ester signal results in synthesis and activation of Fos and Jun, tran scription factors that bind cooperatively with the NFAT DNA-binding domain in the nucleus to mediate the transcription of many target genes. Here we s how that transactivation by a GAL4 fusion protein containing the strong aci dic N-terminal transactivation domain (TAD) of NFAT1 also requires both cal cium and phorbol ester stimulation. The calcium requirement can be mimicked by coexpression of activated versions of two CaM-dependent enzymes, calcin eurin and CaM kinase IV. Our data indicate that a 144-amino acid segment of NFAT1, containing the N-terminal TAD but lacking the DNA-binding and Fos/J un interaction domains, resembles the full-length protein in requiring a co mbined input from two separate signaling pathways for optimal function in c ells.