FUNCTION OF NF-KAPPA-B REL BINDING-SITES IN THE MAJOR HISTOCOMPATIBILITY COMPLEX CLASS-II INVARIANT CHAIN PROMOTER IS DEPENDENT ON CELL-SPECIFIC BINDING OF DIFFERENT NF-KAPPA-B/REL SUBUNITS/

The promoter of the human major histocompatibility complex class II-as sociated invariant-chain gene (Ii) contains two NF-kappa B/Rel binding sites located at -109 to -118 (Ii kappa B-1) and -163 to -172 (Ii kap pa B-2) from the transcription start site. We report here that the dif ferential function of each of these NF-kappa B/Rel sites in several di stinct cell types depends on cell-specific binding of NF-kappa B/Rel t ranscription factors. Ii kappa B-1 is a positive regulatory element in B-cell lines and in the Ii-expressing T-cell line, H9, but acts as a negative regulatory element in myelomonocytic and glial cell lines. In vivo protein-DNA contacts are detectable at Ii kappa B-1 in cell line s in which this site is functional as either a positive or negative re gulator. Electrophoretic mobility supershift assays determine that mem bers of the NF-kappa B/Rel family of transcription factors can bind to this site in vitro and that DNA-binding complexes that contain p50, p 52, p65, and cRel correlate with positive regulation whereas the prese nce of p50 correlates with negative regulation. Ii kappa B-2 is a site of positive regulation in B-cell lines and a site of negative regulat ion in H9 T cells, myelomonocytic, and glial cell lines. In vivo occup ancy of this site is observed only in the H9 T-cell line. Again, in vi tro supershift studies indicate that the presence of p50, p52, p65, an d cRel correlates with positive function whereas the presence of only p50 and p52 correlates with negative function. This differential bindi ng of specific NF-kappa B/Re subunits is likely to mediate the dispara te functions of these two NF-kappa B/Rel binding sites.