The NF-κB repressing factor is involved in basal repression and interleukin (IL)-1-induced activation of IL-8 transcription by binding to a conserved NF-κB-flanking sequence element

Interleukin (IL)-8, a prototypic chemokine, is rapidly induced by the pro-inflammatory cytokine IL-1 but is barely detectable in noninduced cells. Although there is clear evidence that the transcription factor NF-kappaB plays a central role in inducible IL-8 transcription, very little is known about the cis-elements and trans-acting factors involved in silencing of the IL-8 promoter. By sequence comparison with the interferon-beta promoter, we found a negative regulatory element (NRE) in the IL-g promoter overlapping partially with the NF-kappaB response element. Here we show that an NF-kappaB-repressing factor (NRF) binds to the IL-8 promoter NF-kappaB-NRE. Reduction of cellular NRF by expressing NRF antisense RNA results in spontaneous IL-8 gene expression. In contrast, IL-1-induced IL-8 secretion is strongly impaired by expressing NRF antisense RNA. Mutation of the NRE site results in loss of NRF binding and increased basal IL-8 transcription. On the other hand IL-I-induced IL-8 transcription is decreased by mutating the NRE, These data provide evidence for a dual role of the NRF in IL-8 transcription. Although in the absence of stimulation it is involved in transcriptional silencing, in IL-l-induced cells it is required for full induction of the IL-8 promoter.