Loss of T Regulatory Cell Suppression following Signaling through Glucocorticoid-induced Tumor Necrosis Receptor (GITR) Is Dependent on c-Jun N-terminal Kinase Activation

Naturally occurring Foxp3(+)CD4(+)CD25(+) T regulatory cell (nTreg)-mediated suppression of lung allergic responses is abrogated following ligation of glucocorticoid-induced tumor necrosis receptor (GITR) family-related protein. In vitro stimulation of nTregs with GITR ligand increased phosphorylation of c-Jun N-terminal kinase (JNK) but not extracellular signal-regulated protein kinase (ERK) or p38 MAPK. SP600125, a known JNK inhibitor, prevented GITR-mediated phosphorylation of JNK. Activation of JNK was associated with increases in the upstream mitogen-activated protein kinase kinase 7 (MKK7) and the downstream transcription factor NF-kappa beta. Phosphorylated c-Jun (p-c-Jun), indicative of the activation of JNK, was detected in the immunoprecipitates of nTregs from wild-type but not JNK- or GITR-deficient mice. Treatment with an inhibitor of JNK phosphorylation resulted in complete reversal of all GITR-induced changes in nTreg phenotype and function, with full restoration of suppression of in vivo lung allergic responses and in vitro proliferation of activated CD4(+)CD25(-) T cells. Thus, regulation of JNK phosphorylation plays a central role in T regulatory cell function with therapeutic implications for the treatment of asthma and autoimmune diseases.