HTLV-I TAX TRANSACTIVATES THE PROMOTER OF HUMAN PROINTERLEUKIN 1β GENE

Abstract

P014 HTLV-I, which infects a wide variety of mammalian cells, encodes a transactivating protein designated as Tax. We now report that Tax induces the human proIL-1 β (IL1B) gene promoter. In our transient transfection assays using Jurkat CD4+ T and THP-1 monocytic cells, a chloramphenicol acetyltransferase (CAT) construct containing the IL1B promoter sequence between positions −131 and +12 showed significant increases in activity following cotransfection of a Tax expression vector in both CD4+ T and monocytic cells. In addition, Tax synergistically transactivated the IL1B promoter with LPS in monocytes. Analyses of specific nucleotide substitutions further indicated that the Tax-induced transcriptional activation requires two transcription factor binding motifs within the IL1B promoter in monocytes; One is a binding site for NF-IL6 (CCAAT/enhancer binding protein β, C/EBP β), which belongs to basic region-leucine zipper (bZIP) family and the other for Spi-1 (PU.1), which is an Ets family protein found principally in monocytes, macrophages and B lymphocytes. On the other hand, in Jurkat T cells, the NF-IL6 binding site but not the Spi-1 site is required for Tax induction of the IL1B promoter. In gel shift assays (EMSA), Tax expression in cells increased binding of the two factors to their target IL1B promoter sequences. Additional EMSA using in vitro translated proteins also showed that recombinant Tax enhances DNA binding activities of both of recombinant NF-IL6 and Spi-1 proteins. These data were further supported by our glutathione S-transferase (GST)-pulldown data, which indicated that Tax physically interacts with the two proteins. Based upon the results obtained from the present study, we conclude that the IL1B promoter is a Tax-responsive sequence in human T cells and monocytes.