ABNORMAL REGULATION OF THE IL-2 PROMOTER IN LPR CD4(-)CD8(-) T-LYMPHOCYTES RESULTS IN CONSTITUTIVE EXPRESSION OF A NOVEL NUCLEAR FACTOR OF ACTIVATED T-CELLS-BINDING FACTOR

The inert quality of MRL-lpr/lpr(lpr) peripheral CD4(-)CD8(-) (CD4(-)8 (-)) T cells manifests primarily as an inability to proliferate or pro duce IL-2 in response to TCR or mitogenic stimulation. Yet these same cells do initiate early TCR-mediated signaling events, such as generat ion of inositol phosphates and increased intracellular calcium. They a lso display constitutively high levels of p59(fyn) and CD3 zeta tyrosi ne phosphorylation, The generation of second messengers in T cells nor mally leads to downstream signaling that results in transcriptional ac tivation of the IL-2 gene. We, therefore, compared the activation stat e of the IL-2 gene promoter region in freshly isolated and stimulated lpr CD4(-)8(-) T cells with that of normal T lymphocytes. Levels of th e octamer, NF-kappa B (p50-p65 heterodimer), and AP-1 transcriptional factors are constitutively elevated in freshly isolated lpr CD4(-)8(-) T cells, consistent with the activated phenotype of these cells. Upon stimulation with mitogens, formation of the transactivating complex, nuclear factor of activated T cells (NF-AT), occurs with normal kineti cs in lpr CD4(-)8(-) T cells. Yet, the levels of the activating NF-AT complex never reach those observed in similarly stimulated normal T ce lls. Furthermore, nuclear extracts from lpr CD4(-)8(-) T cells display high levels of a novel specific binding activity at the NF-AT site, w hich is present at much lower levels in freshly isolated normal T lymp hocytes. Upon mitogenic stimulation, the binding activity of the novel NF-AT-binding factor is rapidly down-regulated in normal T cells, but persists at high levels in lpr CD4(-)8(-) T cells. These two abnormal ities at the NF-AT site provide a potential mechanism to account for t he defect in IL-2 production from lpr CD4(-)8(-) T cells.