Molecular Mechanism of NFAT Family Proteins for Differential Regulation of the IL-2 and TNF-α Promoters

Abstract

Nuclear factor of activated T cells (NFAT) is a family of transcription factors that regulates activation-induced transcription of many immunologically important genes. Although all NFAT family proteins contain a highly conserved DNA-binding domain and also bind cooperatively with AP-1 proteins to the interleukin-2 (IL-2) promoter NFAT site, each member shows characteristic site preferences to other promoters. Previously, we have shown that NFATc.β, an isoform of NFATc, is different from NFATp in both DNA binding and transactivation of the TNF-α promoter. To further characterize target gene specificity of NFATc and NFATp, we generated deletion mutants as well as mutants swapping the C-terminal region of their DNA binding domains, and analyzed their DNA-binding specificity to different target sites. Our results show that the C-terminal one third of DNA binding domain confers different binding specificity of NFATc and NFATp to an NFAT site in the TNF-α promoters. Transient expression of the mutant NFAT proteins also demonstrates that transcriptional activation of the target promoters is consistent with the DNA binding specificity of the mutant NFATs. These results strongly suggest that a binding site preference and availability of different NFAT proteins may program the temporal expression of distinct cytokine genes. Importantly, the C-terminal region of the DNA binding domain plays an important role in determining the binding site preferences at least of NFATp and NFATc members.