Binding of nuclear factors of the IFN-γ consensus sequence of the human HLA-DRα gene: Effects of IFN-γ on tumor cell lines

The binding of nuclear proteins from human tumor cells to synthetic double stranded oligonucleotides mimicking upstream regions of the HLA-DRα gene was studied. As the HLA-DRα gene is inducible by interferon(IFN)-γ, nuclear extracts were also purified from IFN-γ treated cells. Our data indicate that a) nuclear binding proteins (named IFN-γ-B3 and Z-BI/B2) are detectable, specific for the IFN-γ and Z boxes of the human HLA-DRα gene; b) both IFN-γ-B3 and Z-BI/B2 are present in HLA-D negative cell lines and c) the content of IFN-γ-B3 and Z-BI/B2 is not modulated by IFN-γ treatment. These data suggest that the presence in the nuclear compartment of these factors, presumably necessary for the correct regulation of the HLA-DRα gene, is not sufficient to explain its differential constitutive and induced expression in a variety of in vitro cultured cell lines of different lineage.