Regulation of NFAT and NFkB, key transcription factors in activated T cells

NFAT and NFkB transcription factors are quickly activated upon stimulation of many cell types, including antigen-stimulated T cells. (a) NFAT. When we entered the field in ~1991, cytokine production by activated T cells was known to be sensitive to the clinically important immunosuppressive agents cyclosporin A (CsA) and FK506, and a region of the IL-2 promoter had been shown to drive CsA-sensitive reporter activity and to bind a nuclear factor (NFAT) in a CsA-sensitive manner in electrophoretic mobility shift assays. It had also just been shown that the target of CsA and FK506 was calcineurin, a calcium/ calmodulin-dependent phosphatase. However, NFAT had not been purified and its molecular nature was completely unknown. By working in the mouse instead of the human system, we realized that NFAT was composed of two components, a cytoplasmic component that we termed NFATp (for preexisting and phosphorylated) and a nuclear component that we identified as the unrelated transcription factor AP-1 (homodimers and heterodimers of Fos and Jun proteins). We used this information to purify, clone and molecularly characterize the founding member of the NFAT family, NFAT1; define its interactions with Fos and Jun; and show that NFAT was highly phosphorylated in resting cells and directly dephosphorylated by calcineurin upon T cell activation ([1, 2]; collaboration with Dr. Patrick Hogan). We made the first mouse knockout for NFAT1 (collaboration with Tom Curran; PMID 8629027); determined the structure of the NFAT:AP-1 complex (collaboration with Steve Harrison; PMID 9510247); discovered the related protein NFAT5, a key regulator of the response to osmotic stress (PMID 10377394); identified the many phosphorylation sites of NFAT1 by mass spectrometry (collaboration with Jun Qin; PMID 11030334); used an innovative peptide selection technique to select a high-affinity peptide inhibitor of the NFAT-calcineurin interaction, later shown to have clinical potential (collaboration with Lew Cantley and Mike Yaffe) [3]; and identified DYRK, GSK3 and CK1 kinases as an essential triad of NFAT kinases (PMID 15121840, 16511445).

(b) NFkB. In a brief sabbatical at a start-up biotechnology company in San Diego, I directed a project that led to the first molecular identification of two key upstream regulators of NFkB, a family of transcription factors crucial for cell survival, inflammation and cancer: IKK-1 (CHUK) and IKK-2 (IKBKB), IkB kinases [4]. These were discovered simultaneously and independently by two other groups: Goeddel (Genentech) and Karin (UCSD). Our studies on NFAT and NFkB were paradigm-shifting and revolutionized the field. Reviews on NFAT from our lab: PMID: 9143705, 12975316.

1. Jain J, McCaffrey PG, Miner Z, Kerppola TK, Lambert JN, Verdine GL, Curran T, Rao A. The T cell transcription factor NFATp is a substrate for calcineurin and interacts with the DNA-binding domains of Fos and Jun. Nature 1993; 365: 352-355.

2. McCaffrey PG, Luo C, Kerppola TK, Jain J, Badalian TM, Ho AM, Burgeon E, Lane WS, Lambert JL, Curran T, Verdine GL, Rao A, Hogan PG. Isolation of the cyclosporin-sensitive T cell transcription factor NFATp. Science 1993; 262: 750-754.

3. Aramburu J, Yaffe MB, Lopez-Rodriguez C, Cantley LC, Hogan PG, Rao, A. Affinity-driven peptide selection of an NFAT inhibitor more selective than cyclosporin A.  Science 1999; 285: 2129-2133.

4. Mercurio F, Zhu H, Murray BW, Shevchenko A, Bennett BL, Li J, Young D, Barbosa M, Mann M, Manning A, Rao A. IKK-1 and IKK-2, Cytokine-activated IkB kinases essential for NF-kB activation. Science 1997; 278: 860-865.