TNF stimulates expression of mouse MHC class I genes by inducing an NF kappa B-like enhancer binding activity which displaces constitutive factors.

We have dissected the mouse H-2Kb gene promoter in order to define the sequences responsible for induction by tumour necrosis factor (TNF-alpha). An enhancer element (-187 to -158) composed of two imperfect direct palindromic repeats has been shown to be necessary and sufficient for TNF-alpha induction of a heterologous promoter. A multimer of either repeat is also responsive, while a single copy is not: this is the situation in the beta 2-microglobulin (beta 2-m) promoter which contains a single palindrome and does not respond to TNF-alpha. We had previously found that the two repeats can bind a factor named KBF1. We show here that in the uninduced state the transcription factor AP2 binds to the interpalindromic region, while in TNF-treated cells an NF kappa B-like activity is induced which displaces both KBF1 and AP2 and binds to the two palindromes. This strongly suggests that induction of an NF kappa B-like activity is responsible for TNF-alpha stimulation of mouse MHC class I genes.