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-κB 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-β promoter, we found a negative regulatory element (NRE) in the IL-8 promoter overlapping partially with the NF-κB response element. Here we show that an NF-κB-repressing factor (NRF) binds to the IL-8 promoter NF-κB-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-1-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-1-induced cells it is required for full induction of the IL-8 promoter.