HUMAN T-CELL LEUKEMIA-VIRUS TYPE-I TAX TRANSACTIVATES THE PROMOTER OFHUMAN PROINTERLEUKIN-1-BETA GENE THROUGH ASSOCIATION WITH 2 TRANSCRIPTION FACTORS, NUCLEAR FACTOR-INTERLEUKIN-6 AND SPI-1

The human T-cell leukemia virus type I (HTLV-I), which infects a wide variety of mammalian cells including monocytes and macrophages, encode s a transactivating protein designated as Tax. We now report that Tax induces the human prointerleukin-1 beta (IL1B) gene promoter in monocy tic cells. In our transient transfection assays using human THP-1 mono cytic cells, a chloramphenicol acetyltransferase (CAT) construct conta ining the IL1B promoter sequence between positions -131 and +12 showed an approximately 90-fold increase in activity following cotransfectio n of a Tax expression vector. Moreover, Tax synergized with lipopolysa ccharide (LPS) to induce the IL1B promoter activity. Analyses of speci fic nucleotide substitutions further indicated that the Tax-induced tr anscriptional activation requires two transcription factor binding mot ifs within the IL1B promoter; one is a binding site for nuclear factor (NF)-IL6 (CCAAT/enhancer binding protein beta, C/EBP beta), which bel ongs to the basic region-leucine zipper (bZIP) family and the other fo r Spi-1 (PU.1), which is an Ets family protein found principally in mo nocytes, macrophages, and B lymphocytes. In electrophoretic mobility s hift assays (EMSA) using in vivo THP-1 nuclear extracts, Tax expressio n in THP-1 monocytic cells significantly increased binding of the two factors to their target IL1B promoter sequences. However, in contrast to NF-IL6 and Spi-1, DNA binding activity of Oct-1, an ubiquitously ex pressed octamer-binding protein was not affected by Tax. Additional EM SA using in vitro translated proteins also showed that recombinant Tax enhances DNA binding of both of recombinant NF-IL6 and Spi-1 proteins . These data were supported by our glutathione S-transferase (GST)-pul l-down data, which indicated that Tax physically interacts with the tw o proteins. Based on the results obtained from the present study, we c onclude that the IL1B promoter is a Tax-responsive sequence as a resul t of ability of Tax to induce binding of NF-IL6 and Spi-1 to the IL1B promoter sequence through protein-protein interaction. (C) 1997 by The American Society of Hematology.