A Costimulation-Initiated Signaling Pathway Regulates NFATc1 Transcription in T Lymphocytes

T cell activation and differentiation is accompanied and mediated by transcriptional reprogramming. The NFATc1 transcription factor is strongly induced upon T cell activation and controls numerous genes involved in the T cell effector function. However, its regulation by physiological stimuli in primary T cells has not been well understood. We previously found that ICOS synergizes with TCR and CD28 to greatly enhance NFATc1 expression in primary T cells. In this study, we have examined the signaling mechanisms whereby costimulation regulates NFATc1 expression. We found that CD28 and ICOS regulate sustained PI3K activity in primary T cells, which is required for NFATc1 up-regulation. CD28 and ICOS costimulation, possibly through Itk, a Tec kinase downstream of the PI3K, enhanced phosphorylation of phospholipase C gamma1 and increased and sustained Ca(2+) flux in T cells. Costimulation of T cells potentiated transcription of the Nfatc1 gene P1 promoter in a PI3K-dependent manner. This work demonstrates an important role for costimulatory receptors in sustaining T cell activation programs leading to Nfatc1 gene transcription and has implications in our understanding of the immune response and tolerance

Epigenetic Changes and Suppression of the Nuclear Factor of Activated T Cell 1 (NFATC1) Promoter in Human Lymphomas with Defects in Immunoreceptor Signaling

The nuclear factor of activated T cell 1 (Nfatc1) locus is a common insertion site for murine tumorigenic retroviruses, suggesting a role of transcription factor NFATc1 in lymphomagenesis. Although NFATc1 is expressed in most human primary lymphocytes and mature human T- and B-cell neoplasms, we show by histochemical stainings that NFATc1 expression is suppressed in anaplastic large cell lymphomas and classical Hodgkin’s lymphomas (HLs). In HL cell lines, NFATc1 silencing correlated with a decrease in histone H3 acetylation, H3-K4 trimethylation, and Sp1 factor binding but with an increase in HP1 binding to the NFATC1 P1 promoter. Together with DNA hypermethylation of the NFATC1 P1 promoter, which we detected in all anaplastic large cell lymphoma and many HL lines, these observations reflect typical signs of transcriptional silencing. In several lymphoma lines, methylation of NFATC1 promoter DNA resulted in a “window of hypomethylation,” which is flanked by Sp1-binding sites. Together with the under-representation of Sp1 at the NFATC1 P1 promoter in HL cells, this suggests that Sp1 factors can protect P1 DNA methylation in a directional manner. Blocking immunoreceptor signaling led to NFATC1 P1 promoter silencing and to a decrease in H3 acetylation and H3-K4 methylation but not DNA methylation. This shows that histone modifications precede the DNA methylation in NFATC1 promoter silencing