Functional Consequences of a Polymorphism Affecting NF-κB p50-p50 Binding to the TNF Promoter Region

Abstract

Stimulation of the NF-κB pathway often causes p65-p50 and p50-p50 dimers to be simultaneously present in the cell nucleus. A natural polymorphism at nucleotide −863 in the human TNF promoter (encoding tumor necrosis factor [TNF]) region provides an opportunity to dissect the functional interaction of p65-p50 and p50-p50 at a single NF-κB binding site. We found that this site normally binds both p65-p50 and p50-p50, but a single base change specifically inhibits p50-p50 binding. Reporter gene analysis in COS-7 cells expressing both p65-p50 and p50-p50 shows that the ability to bind p50-p50 reduces the enhancer effect of this NF-κB site. Using an adenoviral reporter assay, we found that the variant which binds p50-p50 results in a reduction of lipopolysaccharide-inducible gene expression in primary human monocytes. This finding adds to a growing body of experimental evidence that p50-p50 can inhibit the transactivating effects of p65-p50 and illustrates the potential for genetic modulation of inflammatory gene regulation in humans by subtle nucleotide changes that alter the relative binding affinities of different forms of the NF-κB complex.

ACKNOWLEDGMENTS

We thank Vincent Vidal and Meike Hensmann for technical help and critical comments and Scott Silverman for assistance with manuscript preparation.

This work was supported by the Medical Research Council (I.A.U., A.R., and D.K.) and by the Arthritis Research Campaign (C.S. and B.F.) A.D. was supported by an EU Training and Mobility of Researchers Award.