NFAT proteins are transcription factors that were first identified as inducers of the immune response. As demonstrated later, these proteins also play varied roles in cell differentiation and adaptation for vascular endothelial cells or skeletal muscle cells. There are four NFAT family members (NFAT1-4, NFAT2 is also called NFATc or NFATc1) from which numerous isoforms are generated by alternative splicing1. NFAT mRNAs are found in peripheral blood lymphocytes, spleen (NFAT1 and 2) and thymus (NFAT4). NFATs modulate the expression of numerous cytokines such as IL-2, IL-3, IL-4, IL-5, IL-8, IL-13, GM-CSF, IFNa, IFNg and CD40L. In resting cells, NFATc1 is confined to the cytoplasm, where it is maintained in a phosphorylated state by the action of constitutive kinases. Upon stimulation, NFATc1 is dephosphorylated by calcineurin, a Ca2+-dependent phosphatase, and migrates to the nucleus. NFATc1 dephosphorylation is stimulated by Ca2+-coupled membrane receptors, such as T cell and B cell receptors, and the CD40, FceRI, CD16 and G protein-associated receptors (thrombin or H1 histamine receptors). NFATc1 can also be activated by calcium ionophores. Cyclosporin A and FK506 immunosuppressor drugs inhibit calcineurin activity on NFAT. Receptors not associated with calcium movement are not expected to stimulate NFAT. When calcium levels drop, calcineurin becomes inactive, and NFATc1 is rephosphorylated by kinases and exported back into the cytoplasm.

NFAT phosphoproteins share two conserved domains:  a DNA-binding domain (DBD) displaying limited similarity to the Rel protein family DBD, and modulating interactions with AP-1 dimers; and a NFAT homology region (NHR), upstream of the DBD that regulates translocation and DNA-binding activity. The regulatory domain is dephosphorylated by the calcium- and calmodulin-dependent phosphatase calcineurin, which controls NFAT nuclear translocation. Transactivation domains can be found at the N- and C-terminal ends of the NFAT proteins. NFATs bind to the DNA consensus motif 5´-T/AGGAAA-3´ as monomers. NFATs can cooperatively interact with AP-1 and GATA proteins for DNA binding. NFAT can also bind to certain kB-like sites. Vitamin D3 receptor heterodimers (RXR:VDR) can abrogate NFAT modulation of IL-2 by binding to a site which overlaps the NFAT distal site. Sites in IL-2 and GM-CSF promoters can accommodate both NFAT and the Ets-family member, Elf-1.