NF-kappa B activity is required for the deregulation of c-myc expression by the immunoglobulin heavy chain enhancer

The c-myc gene is translocated to one of the immunoglobulin genes in Burkit t's lymphoma resulting in deregulated expression of c-myc. Several enhancer s have been shown to be important for expression of the immunoglobulin heav y chain gene. Four enhancer regions (murine-hypersensitive sites (MHS) 1, 2 , 3, and 4) located 3' of the murine immunoglobulin heavy chain gene play a role in activating expression of the translocated c-myc gene. The enhancer regions also result in a shift in transcriptional initiation from the P2 p romoter to P1 that is characteristic of the translocated c-myc allele. We f ound that the most 3' enhancer region (MHS4) activated the c-myc promoter b y 46-fold in the Raji Burkitt's lymphoma cell line, and it was the most act ive enhancer in these cells. The addition of enhancer regions MHS1,2 and 3 to MHS4 increased c-myc transcription by an additional 3-fold and resulted in the full promoter shift from Pa to P1. By deletion analysis of enhancer region MHS4, we located a region that was critical for the transcriptional activity of MHS4. Electrophoretic mobility shift assay analysis revealed th at NF-kappa B/Rel family members bound to this region. Mutation of the NF-k appa B binding site abolished both the enhancer activity and the promoter s hift activity of MHS4. An active NF-kappa B site was also identified in the human HS4 enhancer. Inhibition of c-myc promoter activity driven by the im munoglobulin enhancers was observed with expression of a super-repressor I kappa B alpha construct. These results indicate that the NF-kappa B/Rel tra nscription factors play an important role in the deregulation of the transl ocated c-myc gene in Burkitt's lymphoma and suggest that interference with NF-kappa B function may represent a new approach to the treatment of Burkit t's lymphoma.