MONOCYTE EXPRESSION OF THE HUMAN PROINTERLEUKIN 1-BETA GENE (IL1B) ISDEPENDENT ON PROMOTER SEQUENCES WHICH BIND THE HEMATOPOIETIC TRANSCRIPTION FACTOR SPI-1 PU.1/

Interleukin-1 beta (IL-1 beta) is produced primarily by stimulated mon ocytes, suggesting that the IL1B gene, which codes for this protein, d epends upon at least one cell-type-specific factor. Our previous chara cterization of the IL1B promoter indicated that the region between -13 1 and +12 is sufficient to direct cell-type-specific expression of a r eporter gene (F. Shirakawa, K. Saito, C. A. Bonagura, D. L. Galson, M. J. Fenton, A. C. Webb, and P. E. Auron, Mel. Cell. Biol. 13:1332-1344 , 1993). We now show that a sequence located between positions -50 and -39 of the IL1B promoter binds the tissue-restricted Ets domain trans cription factor Spi-1/PU.1 (Spi-1). Mutation of this site abrogates bi nding of this factor and reduces the ability of the IL1B promoter to f unction in macrophages. A second Spi-1 binding site located between po sitions -115 and -97 also is required for maximal IL1B promoter activi ty in the presence of the proximal Spi-1 binding site. In addition, an activation domain-deficient Spi-1 expression vector acts as a dominan t-negative inhibitor of reporter gene expression in a monocyte cell li ne. Finally, the IL1B promoter, which is inactive in Spi-1-deficient H eLa cells, is activated in these cells by cotransfection with a Spi-1 expression vector. Thus, the cell-type-specific expression of the IL1B promoter appears to be dependent on the binding of Spi-1.