Autocrine induction of the human pro-IL-1β gene promoter by IL-1β in monocytes

IL-1beta is produced primarily by activated monocytes/macrophages. We report in this study that IL-1beta induces the human pro-IL-1beta (IL1B) gene promoter in human THP-1 monocytic cells. The -131 to +12 minimal IL1B promoter was induced by IL-1beta in a dose-dependent manner. The promoter possesses two important transcription factor binding motifs, one for an ETS family transcription factor Spi-1 (PU.1), and the other a binding site for NF-IL6 (CCAAT/enhancer binding protein beta). Autocrine promoter activity was completely inhibited by mutation of the Spi-1 site. Mutation of the NF-IL6 binding motif caused partial loss of activity. EMSAs using THP-1 cell nuclear extracts indicated that IL-1beta significantly induced Spi-1 binding to its target site within the IL1B promoter that was maximal at I h after stimulation, correlating with the kinetics of IL-1beta induction. The importance of Spi-1 was supported by our observation that Spi-1-deficient EL4 thymocytes exhibited IL-1beta-induced activity only after transfection with a Spi-1 expression vector. Moreover, TNFR-associated factor 6 also required Spi-1 to activate the promoter. Transfection studies using Spi-1 mutant constructs showed that the TATA-binding protein binding and glutamine-rich domains of Spi-1 were important for IL-1beta induction, whereas LPS induction required the proline, glutamic acid, serine, and threonine-rich domain containing serine 148 as well as the TATA-binding protein and glutamine-rich domains. We conclude that the IL1B promoter is an IL-1beta-responsive sequence as a result of its ability to bind Spi-1 in response to IL-1beta.