IDENTIFICATION AND CHARACTERIZATION OF A NOVEL REPRESSOR SITE IN THE HUMAN TUMOR-NECROSIS-FACTOR-ALPHA GENE

In human monocytic cell lines, tumor necrosis factor alpha (TNF alpha) expression is induced by phorbol myristate acetate (PMA). We have ide ntified positive and negative cis-acting elements in the TNF alpha pro moter by deletion analysis. Here we present the initial characterizati on of the repressor element. The repressor element was shown to functi on in either orientation and at various distances upstream from the po sitive element of the TNF alpha promoter. The TNF alpha repressor site (TRS) has been localized to a 25 bp region between base pairs - 254 a nd - 230 in the promoter. This region contains a 10 bp sequence with h omology to the binding site of the activator protein AP-2. Mutation of the 6 C's of this 10 bp AP-2-like site abolish TRS repressor function . However, this AP-2-like site is not a binding site for AP-2 protein based on gel retardation analysis. In addition, a well-characterized A P-2 binding site placed upstream of the positive element of the TNF al pha gene did not cause repression. Therefore, this repression is very likely mediated by a novel protein(s) which interacts with the AP-2 co nsensus site in the TRS.