A T cell nuclear factor resembling NF-AT binds to an NF-KB site and to the conserved lymphokine promoter sequence "cytokine-1"

Nuclear extracts from a nontransformed murine T lymphocyte clone contained two inducible factors that bound to a nuclear factor κB (NF-κB) site. One factor was NF-κB, and the other was differentiated from NF-κB by its mobility in the electrophoretic mobility shift assay and its lack of sensitivity to protein kinase C depletion. Competition and methylation interference assays showed that the binding site for the novel factor was limited to nucleotides in the 3′ half of the κB site. This part of the κB site resembled sequences in the binding site for a second inducible nuclear factor of T cells, NF-AT, as well as a conserved sequence found in several lymphokine genes, termed "cytokine-1" (CK-1). Competition and methylation interference analysis showed that both NF-AT and CK-1 sequences bound a factor similar to the novel κB-binding factor and that binding involved a four-nucleotide sequence (TTCC) that the κB, CK-1, and NF-AT sites have in common. The complexes that form with each site have characteristics of NF-AT: they are induced upon T cell receptor stimulation, are sensitive to protein synthesis inhibitors and cyclosporin A, and are not sensitive to protein kinase C depletion. Thus, a factor or factors similar to NF-AT can bind to three distinct promoter sequences which occur commonly in several T cell activation genes. These results raise the possibility that related factors binding to κB, CK-1, and NF-AT sequences could play a role in the coordinate induction of T cell activation genes. In addition, our results suggest that κB and CK-1 sites represent potential cyclosporin-sensitive promoter elements by virtue of their ability to bind an NF-AT-like factor.