Signaling requirements for the expression of the transactivating factor NF-AT in human T lymphocytes.

A protein called nuclear factor of activated T cells (NF-AT) binds to DNA sequences within the enhancer region of the interleukin 2 (IL 2) gene and appears necessary for both the inducibility and T cell specificity of IL 2 expression. IL 2 production is regulated by multiple signals including those generated via activation of the T cell antigen receptor complex (TcR/CD3), CD2 antigen, protein kinase C (PKC) or elevation of intracellular free calcium concentration ([Ca2+]i). We have, therefore, explored the role of these different stimuli in regulating the nuclear expression of NF-AT in human peripheral blood-derived lymphocytes. Results presented herein indicate that maximal expression of NF-AT in T cells requires at least two signals: PKC activation and TcR/CD3 or CD2 triggering, [Ca2+]i increases and TcR/CD3 or CD2 triggering. Data are presented that indicate that either the [Ca2+]i or PKC signal generated via the TcR/CD3 complex would not alone induce NF-AT expression, and that the TcR/CD3 complex probably regulates NF-AT expression because of its ability to regulate multiple intracellular signals in T cells, and not via any single biochemical event. The combination of CD2 mAb GT2/OKT11 used in the present study to trigger the CD2 antigen is able to act in synergy with phorbol 12,13-dibutyrate or ionomycin to induce NF-AT expression. However, these CD2 mAb do not elevate [Ca2+]i or activate PKC, suggesting that signals other than [Ca2+]i or PKC can regulate NF-AT expression in peripheral blood-derived T cells.