ABSTRACT
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 TGFß. 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.
Subject(s)
B-Lymphocytes/drug effects , NFATC Transcription Factors/genetics , Th1 Cells/drug effects , Th2 Cells/drug effects , Animals , Antibodies/pharmacology , B-Lymphocytes/immunology , B-Lymphocytes/metabolism , Cell Proliferation/drug effects , Chromosomes, Artificial, Bacterial/genetics , Gene Expression/drug effects , Gene Expression/immunology , Genes, Reporter , Green Fluorescent Proteins , Lipopolysaccharides/pharmacology , Lymphocyte Activation/drug effects , Mice , Mice, Inbred C57BL , Mice, Transgenic , NF-kappa B/genetics , NF-kappa B/immunology , NFATC Transcription Factors/agonists , NFATC Transcription Factors/immunology , Promoter Regions, Genetic , Protein Isoforms/agonists , Protein Isoforms/genetics , Protein Isoforms/immunology , T-Lymphocytes, Regulatory/drug effects , T-Lymphocytes, Regulatory/immunology , T-Lymphocytes, Regulatory/metabolism , Th1 Cells/immunology , Th1 Cells/metabolism , Th17 Cells/drug effects , Th17 Cells/immunology , Th17 Cells/metabolism , Th2 Cells/immunology , Th2 Cells/metabolism , Transforming Growth Factor beta/genetics , Transforming Growth Factor beta/immunologyABSTRACT
Threshold levels of individual NFAT factors appear to be critical for apoptosis induction in effector T cells. In these cells, the short isoform A of NFATc1 is induced to high levels due to the autoregulation of the NFATc1 promoter P1 by NFATs. P1 is located within a CpG island in front of exon 1, represents a DNase I hypersensitive chromatin site, and harbors several sites for binding of inducible transcription factors, including a tandemly arranged NFAT site. A second promoter, P2, before exon 2, is not controlled by NFATs and directs synthesis of the longer NFATc1/B+C isoforms. Contrary to other NFATs, NFATc1/A is unable to promote apoptosis, suggesting that NFATc1/A enhances effector functions without promoting apoptosis of effector T cells.
