Interaction of AP-1 with a cluster of NF-kappa B binding elements in the human TNF promoter region

Transcriptional activation of the human TNF gene involves multiple regulato ry elements whose functional properties vary between stimuli and cell types . Here we have used a COS-7 expression system to dissect the transactivatin g potential of NF-kappaB binding sites in the human TNF promoter region fro m other regulatory influences. In this model, NF-kappaB acts largely throug h a dense cluster of three binding sites located 600 nt upstream of the tra nscription start site. We show that the transcriptional activity of this co mplex is highly sensitive to the p65:p50 ratio that is expressed. We demons trate that the AP-1 complex c-Jun/Fra2 is capable of binding to this region and that this inhibits the transactivating effects of NF-kappaB These resu lts are suggestive of a complex regulatory element that mediates fine contr ol rather than acting as a simple on-off switch for TNF gene expression. (C ) 2001 Academic Press.