Cytotoxic T lymphocytes are effector CD8+ T cells that eradicate infected and malignant cells. Here we show that the transcription factor NFATc1 controls the cytotoxicity of mouse cytotoxic T lymphocytes. Activation of Nfatc1 −/− cytotoxic T lymphocytes showed a defective cytoskeleton organization and recruitment of cytosolic organelles to immunological synapses. These cells have reduced cytotoxicity against tumor cells, and mice with NFATc1-deficient T cells are defective in controlling Listeria infection. Transcriptome analysis shows diminished RNA levels of numerous genes in Nfatc1 −/− CD8+ T cells, including Tbx21, Gzmb and genes encoding cytokines and chemokines, and genes controlling glycolysis. Nfatc1 −/−, but not Nfatc2 −/− CD8+ T cells have an impaired metabolic switch to glycolysis, which can be restored by IL-2. Genome-wide ChIP-seq shows that NFATc1 binds many genes that control cytotoxic T lymphocyte activity. Together these data indicate that NFATc1 is an important regulator of cytotoxic T lymphocyte effector functions.

In effector T and B cells immune receptor signals induce within minutes a rise of intracellular Ca++, the activation of the phosphatase calcineurin and the translocation of NFAT transcription factors from cytosol to nucleus. In addition to this first wave of NFAT activation, in a second step the occurrence of NFATc1/αA, a short isoform of NFATc1, is strongly induced. Upon primary stimulation of lymphocytes the induction of NFATc1/αA takes place during the G1 phase of cell cycle. Due to an auto-regulatory feedback circuit high levels of NFATc1/αA are kept constant during persistent immune receptor stimulation. Contrary to NFATc2 and further NFATc proteins which dampen lymphocyte proliferation, induce anergy and enhance activation induced cell death (AICD), NFATc1/αA supports antigen-mediated proliferation and protects lymphocytes against rapid AICD. Whereas high concentrations of NFATc1/αA can also lead to apoptosis, in collaboration with NF-κB-inducing co-stimulatory signals they support the survival of mature lymphocytes in late phases after their activation. However, if dysregulated, NFATc1/αA appears to contribute to lymphoma genesis and – as we assume – to further disorders of the lymphoid system. While the molecular details of NFATc1/αA action and its contribution to lymphoid disorders have to be investigated, NFATc1/αA differs in its generation and function markedly from all the other NFAT proteins which are expressed in lymphoid cells. Therefore, it represents a prime target for causal therapies of immune disorders in future.

NFAT transcription factors control the proliferation and survival of peripheral lymphocytes. We have reported previously that the short isoform NFATc1/αA whose generation is induced by immune receptor stimulation supports the proliferation and inhibits the activation-induced cell death of peripheral T and B cells. We will show in this study that in novel bacterial artificial chromosome transgenic mice that express EGFP under the control of entire Nfatc1 locus the Nfatc1/Egfp transgene is expressed as early as in double-negative thymocytes and in nonstimulated peripheral T and B cells. Upon immune receptor stimulation, Nfatc1/Egfp expression is elevated in B, Th1, and Th2 cells, but only weakly in T regulatory, Th9, and Th17 cells in vitro whose generation is affected by TGFβ. In naive lymphocytes, persistent immune receptor signals led to a 3–5 increase in NFATc1/αA RNA levels during primary and secondary stimulation, but a much stronger induction was observed at the protein level. Whereas anti-CD3+CD28 stimulation of primary T cells induces both NFATc1/αA and their proliferation and survival, anti-IgM stimulation of B cells induces NFATc1/αA and proliferation, but activation-induced cell death after 3-d incubation in vitro. The anti-IgM–mediated activation-induced cell death induction of B cells in vitro is suppressed by anti-CD40–, LPS-, and CpG-mediated signals. In addition to inducing NF-κB factors, together with anti-IgM, these signals also support the generation of NFATc1/αA. According to these data and the architecture of its promoter region, the Nfatc1 gene resembles a primary response gene whose induction is affected at the posttranscriptional level.

Epicutaneous application of Aldara cream containing the TLR7 agonist imiquimod (IMQ) to mice induces skin inflammation that exhibits many aspects of psoriasis, an inflammatory human skin disease. Here we show that mice depleted of B cells or bearing interleukin (IL)-10-deficient B cells show a fulminant inflammation upon IMQ exposure, whereas ablation of NFATc1 in B cells results in a suppression of Aldara-induced inflammation. In vitro, IMQ induces the proliferation and IL-10 expression by B cells that is blocked by BCR signals inducing NFATc1. By binding to HDAC1, a transcriptional repressor, and to an intronic site of the Il10 gene, NFATc1 suppresses IL-10 expression that dampens the production of tumour necrosis factor-α and IL-17 by T cells. These data indicate a close link between NFATc1 and IL-10 expression in B cells and suggest NFATc1 and, in particular, its inducible short isoform, NFATc1/αA, as a potential target to treat human psoriasis.