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⁺]_j 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.