Reduced binding activity of transcription factor NF-kappa B accounts for MHC class I repression in adenovirus type 12 E 1-transformed cells.

The early region 1 (E1) of human adenovirus (Ad) type 12 represses the expression of major histocompatibility (MHC) Class I genes in transformed primary rodent cells. In this paper we show that both NF-kappa B and KBF1 (p50 dimer) binding activity to the H2TF1 element in the Class I promoter is reduced in Ad12-13S-E1A-transformed cells compared to Ad5E1- or Ad12-12S-E1A-transformed cells. Consistently, in Ad12E1A-13S-transformed cells the H2TF1 element does not contribute to transcriptional activity in transient expression assays, whereas it does contribute in Ad12E1A-12S-transformed cells. Therefore, the most likely explanation is that reduced binding of NF-kappa B and KBF1 to the H2TF1 element accounts for the down-regulation of MHC Class I expression in Ad12E1- and Ad12E1A-13S-transformed cells.