THE CD40L PROMOTER CONTAINS NUCLEAR FACTOR OF ACTIVATED T-CELLS-BINDING MOTIFS WHICH REQUIRE AP-1 BINDING FOR ACTIVATION OF TRANSCRIPTION

Four nuclear factor of activated T cells (NF-AT) binding motifs were f ound in the murine CD40 ligand promoter. Electrophoretic mobility shif t assays using 18-base pair (bp) long oligonucleotides corresponding t o the proximal site and nuclear extracts from activated T cells reveal ed two complexes which were inhibited by cyclosporin A and contained N F-ATc and NF-ATp. Neither complex contained AP-1 proteins. Multimers o f the 18-bp oligonncleotides were not active in transient transfection assays using luciferase reporter gene constructs. In contrast, a 30-b p long oligonucleotide bound AP-1 proteins in addition to NP-AT protei ns and its multimers strongly induced luciferase gene expression. Thes e results suggested that NF-AT proteins play an important role in the expression of the CD40L gene and that their transcriptional activity r equires AP-1 binding.