Proteolytic regulation of nuclear factor of activated T (NFAT) c2 cells and NFAT activity by caspase-3.

The nuclear factor of activated T (NFAT) cell family of transcription factors is important in regulating the expression of a broad array of genes, including cytokines, T cell surface receptors, and other transcription factors. NFATc1 and NFATc2 are two principal NFAT members that are expressed in peripheral T cells. Levels of NFAT expression in T cells are partly transcriptionally regulated, but less is understood regarding their post-transcriptional control. We show here that NFATc1 and NFATc2 are rapidly degraded in apoptotic T cells. NFATc2 is highly sensitive to cleavage by caspase-3, whereas NFATc1 is only weakly sensitive to caspase-3 or caspase-8. Two potential caspase-3 cleavage sites were identified in the N-terminal transactivation domain. These sites were confirmed by in vitro caspase cleavage assays. Abolition of NFATc2 cleavage by mutation of these two cleavage sites resulted in augmented NFAT transcriptional activity. Furthermore, NFAT activity could be augmented in wild-type effector T cells by inhibition of caspase activity. Of particular interest was that non-apoptotic T cells from cellular FLIP long transgenic (c-FLIP(L)-Tg) mice that manifest elevated caspase activity have greatly reduced levels of NFATc2 protein and NFAT transcriptional activity. Our findings reveal a new post-transcriptional regulation of NFATc2 that operates, not only during apoptosis, but also in non-apoptotic effector T cells.