Conservation of the H-2 BF1 binding motif 5' of the H-2Ds, Ks and Dq genes

Transduction of a murine dominant negative activation transcription factor 1 increases cell surface expression of the class I MHC on a human epidermoid tumor cell line

The transcription of the MHC class I genes is regulated by interaction of cis-elements, located in the 5' genomic flanking regions, with sequence-specific trans-factors. We have identified a cis-regulatory element, 5'-TGACGCG-3', of the H-2D(d) gene. This cyclic adenosine-3',5'-monophosphate regulatory element (CRE)-like sequence, named H-2 binding factor 1 (H-2 BF1) binding motif, is highly conserved among species. In addition, we found that homo- and heterodimers of activation transcription factor 1 (ATF-1) and CRE binding protein (CREB) associate with the H-2 BF1 binding motif and activate transcription of the H-2D(d) gene. Here we demonstrate that a homologue of ATF-1, originally isolated and designated ATF-1DN, acts as a dominant repressor, blocking the ability of wild-type ATF-1 and CREB to bind to the H-2 BF1 probe in electrophoretic mobility shift assays (EMSA). We have utilized this molecule to analyze the participation of the H-2 BF1 complexes, consisting of the H-2 BF1 binding motif and ATF-1/CREB trans-factors, in the physiological regulation of MHC class I expression in tissue culture cells. A human epidermoid carcinoma cell line, A431, was transfected with ATF-1DN and clones expressing the gene transcripts were selected. When analyzed in the EMSA, nuclear proteins prepared from these clones exhibited a decreased shift of the H-2 BF1 probe corresponding to the levels of the ATF-1DN gene expression. Additionally, MHC class I expression of cells with reduced H-2 BF1 activity was significantly higher than in control cells lacking ATF-1DN. These findings indicate that in these carcinoma cells, the H-2 BF1 complexes negatively regulate the constitutive expression of MHC class I.