Functionally distinct NF-kappa B binding sites in the immunoglobulin kappa and IL-2 receptor alpha chain genes.

The interleukin-2 receptor alpha (IL-2R alpha) chain gene contains a sequence similar to the immunoglobulin (Ig) kappa (kappa) enhancer NF-kappa B binding site. This site, which is bound by the nuclear protein, NF-kappa B, is critical for Ig kappa gene expression. The major T cell nuclear factor that binds to the IL-2R alpha site in vitro appears indistinguishable from NF-kappa B. NF-kappa B binds to IL-2R alpha and kappa sequences with similar affinities; however, only the kappa site potently activates transcription from heterologous promoters. Thus, high-affinity NF-kappa B binding in vitro cannot be equated with transcriptional activation in vivo. Mutation of the NF-kappa B binding site in the context of an IL-2 R alpha promoter construct markedly diminished promoter activity in human T cell lymphotropic virus type I (HTLV-I)-transformed MT-2 cells but not in phorbol myristate acetate-stimulated Jurkat T cells.