Nickel differentially regulates NFAT and NF-κB activation in T cell signaling

Nickel is a potent hapten that induces contact hypersensitivity in human skin. While nickel induces the maturation of dendritic cells via NF-κB and p38 MAPK activation, it also exerts immunosuppressive effects on T cells through an unknown mechanism. To elucidate the molecular mechanisms of its effects on T cells, we examined the effects of NiCl(2) on mRNA expression in human CD3+ T cells stimulated with CD3 and CD28 antibodies. Using a DNA microarray and Gene Ontology, we identified 70 up-regulated (including IL-1β, IL-6 and IL-8) and 61 down-regulated (including IL-2, IL-4, IL-10 and IFN-γ) immune responsive genes in NiCl(2)-treated T cells. The DNA microarray results were verified using real-time PCR and a Bio-Plex(TM) suspension protein array. Suppression of IL-2 and IFN-γ gene transcription by NiCl(2) was also confirmed using Jurkat T cells transfected with IL-2 or IFN-γ luciferase reporter genes. To explore the NiCl(2)-regulated signaling pathway, we examined the binding activity of nuclear proteins to NFAT, AP-1, and NF-κB consensus sequences. NiCl(2) significantly and dose-dependently suppressed NFAT- and AP-1-binding activity, but augmented NF-κB-binding activity. Moreover, NiCl(2) decreased nuclear NFAT expression in stimulated T cells. Using Jurkat T cells stimulated with PMA/ionomycin, we demonstrated that NiCl(2) significantly suppressed stimulation-evoked cytosolic Ca(2+) increases, suggesting that NiCl(2) regulates NFAT signals by acting as a blocker of Ca(2+) release-activated Ca(2+) (CRAC) channels. These data showed that NiCl(2) decreases NFAT and increases NF-κB signaling in T cells. These results shed light on the effects of nickel on the molecular regulation of T cell signaling.