NFAT
Nuclear Factor of Activated T-cells (NFAT) is a family of transcription factors that regulate gene expression in response to calcium signaling, primarily through dephosphorylation by the phosphatase calcineurin, enabling their translocation to the nucleus where they cooperate with other factors to control diverse cellular processes.[1] Originally identified in activated T lymphocytes for their role in cytokine production, NFAT proteins are expressed across various cell types and are essential for immune responses, development, and adaptation to environmental cues.[2] The NFAT family comprises five members: NFAT1 (also known as NFATc2), NFAT2 (NFATc1), NFAT3 (NFATc4), NFAT4 (NFATc3), and NFAT5 (TonEBP), with NFAT1–4 being calcium/calcineurin-dependent and sharing a conserved Rel homology domain for DNA binding to consensus sequences like (A/T)GGAAA, while NFAT5 operates independently and is constitutively nuclear.[3] Activation occurs upon antigen receptor or other stimuli-induced calcium influx, which binds calmodulin to activate calcineurin; this enzyme then dephosphorylates serine-rich regions in the NFAT regulatory domain, promoting nuclear import and interaction with partners such as AP-1 (Fos-Jun) to drive transcription of target genes.[1] This process is reversible, as kinases like GSK-3 rephosphorylate NFAT, exporting it back to the cytoplasm, and is inhibited by immunosuppressive drugs such as cyclosporine A and FK506.[2] In the immune system, NFAT proteins are pivotal for T-cell development, activation, differentiation into effector subsets (e.g., Th1, Th2, Treg), and tolerance mechanisms, including the induction of anergy-associated genes like GRAIL and ITCH; they also influence cytokine expression in B cells, dendritic cells, mast cells, and natural killer T cells.[1] Beyond immunity, NFAT regulates cardiac and skeletal muscle differentiation, heart valve formation, neuronal development, osteogenesis, adipocyte function, and keratinocyte responses to stress.[2] Dysregulated NFAT activity contributes to pathologies, including autoimmune diseases, transplant rejection, and cancers such as lymphomas, breast, and pancreatic tumors, where it promotes proliferation, survival, migration, and angiogenesis.[1] Additionally, NFAT modulates cell cycle progression by controlling cyclins (e.g., cyclin D1, A2) and CDK inhibitors (e.g., p21, p15), as well as apoptosis through targets like FasL (pro-apoptotic) and Bcl-2 (anti-apoptotic).[3]Family and Structure
Members of the NFAT Family
The NFAT (Nuclear Factor of Activated T-cells) family comprises five principal members: NFAT1 (encoded by NFATC2), NFAT2 (encoded by NFATC1), NFAT3 (encoded by NFATC4), NFAT4 (encoded by NFATC3), and NFAT5 (also known as TONEBP, encoded by NFAT5). These proteins are transcription factors that regulate gene expression in response to cellular signals, primarily in immune and stress contexts. In humans, the genes are located as follows: NFATC1 on chromosome 18q23, NFATC2 on chromosome 20q13.2, NFATC3 on chromosome 16q22.1, NFATC4 on chromosome 14q12, and NFAT5 on chromosome 16q22.1.[4][5][6][7][8] Their predicted molecular weights vary due to isoforms and post-translational modifications, but representative sizes include approximately 100 kDa for NFAT1, 101 kDa for NFAT2, 95 kDa for NFAT3, 115 kDa for NFAT4, and 166 kDa for NFAT5.| Member | Gene | Chromosomal Location | Approximate Molecular Weight (kDa) |
|---|---|---|---|
| NFAT1 | NFATC2 | 20q13.2 | 100 |
| NFAT2 | NFATC1 | 18q23 | 101 |
| NFAT3 | NFATC4 | 14q12 | 95 |
| NFAT4 | NFATC3 | 16q22.1 | 115 |
| NFAT5 | NFAT5 | 16q22.1 | 166 |