NFAT-1 DNA Binding Complex in Activated T Cells Contains Fra-1 and JunB

摘要

Activation of T cells induces transciption of the interleukin-2 (IL-2) gene. IL-2expression is regulated through the binding of transcription factors to multiple sites within the IL-2 enhancer. One such cis-acting element within the IL-2 enhancer is the NFAT-1 (nuclear factor of activated T cells) binding site. NFAT-1 binding activity is absent in resting cells but is induced upon T-cell activation. The induction of NFAT-1 binding activity can be inhibited by cyclosporin A, potentially accounting for the ability of cyclosporin A to inhibit IL-2 production by T cells. We have previously reported that the NFAT-1 binding complex is composed of at least two proteins and that the 5' portion of the NFAT-1 sequence acts as a binding site for one or more proteins from the Ets family of transcription factors. We now report that the 3' portion of the NFAT-1 sequence contains a variant AP-1 binding site. NFAT-1 binding can be specifically inhibited by oligonucleotides containing a consensus AP-1 site. Moreover, mutation of the AP-1 site at the 3' end of the NFAT-1 sequence inhibits both NFAT-1 binding and the ability of the NFAT-1 binding site to activate expression from a reporter plasmid upon T-cell activation. Since AP-1 sites bind dimeric protein complexes composed of individual members of the Fos and Jun families of transcription factors, we used antibodies specific for individual Fos and Jun family members to determine whether they are present in the NFAT-1 binding complex. These experiments demonstrated that the NFAT-1 binding complex contains JunB and Fra-1 proteins. Northern (RNA) blot analyses demonstrate that both fra-1 and junB mRNAs are induced upon T-cell activation, although fra-1 mRNA is present even in q