Regulation of nuclear factor of activated T-cell family transcription factors during T-cell development in the thymus

Abstract

Background: T lymphocytes undergo a series of developmental events in the thymus, and signaling through the T-cell antigen receptor is crucial in this differential program. The nuclear factor of activated T cells (NFATs) may be involved in transcriptional induction of cytokine genes and other immunoregulatory genes in T cells. Objectives: We have examined the distribution of 3 NFAT family members (NFAT1, NFATc, and NFATx) in human fetal thymocytes, by using semiquantitative RT-PCR and electrophoretic mobility shift assay. Results: The messenger RNA of NFATx was expressed in all T-lymphocyte subsets tested, and expression was highest in CD4+CD8+ thymocytes. Conversely, mRNA of NFAT1 was preferentially expressed in mature CD4+ single-positive cells. NFATc mRNA was present at low levels in all subsets but was strongly induced by treatment with phorbol ester plus calcium ionophore. Using electrophoretic mobility shift assay, we observed stimulation-dependent NFAT-DNA binding in CD4+CD8+ thymocytes, which was largely dependent on NFATx protein. This DNA-binding activity was inhibited by cyclosporin A, which indicated that NFATx nuclear translocation in CD4+CD8+ thymocytes was regulated by calcineurin phosphatase. In contrast, NFAT1 and NFATc (and to some extent NFATx) were responsible for NFAT DNA binding in the CD4+ cells. Conclusions: Expression of NFAT family members is differentially regulated during T-cell development, and NFATx may be involved in T-cell antigen receptor/calcineurin-dependent signaling in CD4+CD8+ thymocytes.