Critical elements of the immunoglobulin heavy chain gene enhancers for deregulated expression of bcl-2.

Translocation of the bcl-2 gene to the immunoglobulin heavy chain gene is the most common alteration in follicular lymphoma. The result is the deregulated expression of bcl-2 and increased resistance to cell death. Regulation of the immunoglobulin heavy chain gene is controlled in part by four DNase I-hypersensitive regions located 3' of the gene. Here, we show that these four enhancer regions also contribute to bcl-2 up-regulation in t(14;18) cells. The enhancers are able to individually or in combination activate bcl-2 promoter activity. The HS4 enhancer region was found to impart the largest positive effect on the bcl-2 promoter, activating it by 6-fold, whereas addition of the HS1,2 region with HS4 increased promoter activity by approximately 9-fold. Nuclear factor kappaB binding sites were shown to be primarily responsible for the positive activity contributed by the HS1,2 and HS4 regions, and we observed the in vivo interaction of these factors with the human immunoglobulin heavy chain gene enhancer regions in t(14;18) cells. In addition, two Sp1 binding sites in HS4 were also found to positively influence bcl-2 activity, and Sp1 was observed to interact with the human HS4 enhancer in vivo. These results suggest that the interactions of the nuclear factor kappaB and Sp1 transcription factors with the immunoglobulin heavy chain enhancer region are important for bcl-2 deregulation in t(14;18) cells.