An activation-responsive element in single C motif-1 lymphotactin promoteris a site of constitutive and inducible DNA-protein interactions involvingnuclear factor of activated T cell

Single C motif-1 (SCM-1)/lymphotactin is a C-type chemokine whose expressio n is activation dependent, cyclosporin A sensitive and restricted to CD8(+) T cells, double-negative thymocytes, gamma delta-type T cells, and NK cell s. In humans, there are two highly homologous genes encoding SCM-1 alpha an d SCM-1 beta. Here we examined the regulatory mechanism of the SCM-1 genes. The luciferase reporter gene under the control of the 5' flanking region o f 0.7 kb was strongly induced upon activation with anti-CD3 or PHA plus PMA only in SCM-1-producer T cell lines through a cyclosporin A-sensitive mech anism. An element termed E1 located at -108 to -95 nt relative to the major transcription start site was found to be critical for the promoter activit y. In electrophoretic mobility shift assays using the E1 oligonucleotide as probe, nuclear extracts from unstimulated T and B cell lines formed a cons titutive complex termed complex I, while nuclear extracts from stimulated S CM-1-producer T cell lines formed a higher mobility complex termed complex II with a concomitant decrease in complex I. The shift from complex I to co mplex II seen only in SCM-1-producer T cell lines upon activation was compl etely suppressed by cyclosporin A. Both complexes were critically dependent on the NF-AT core sequence TTTCC in the E1 element and were partially supe rshifted by anti-NF-ATp. One-hybrid assays in yeast isolated NF-ATp as an E l binding protein, and transfection of NF-ATp into T and B cell lines stron gly enhanced the activation-dependent SCM-1 promoter activity. Collectively , a unique mechanism involving NF-ATp appears to regulate the cell type-spe cific and activation-dependent expression of the SCM-1 genes.