The role of immunoglobulin kappa elements in c-myc activation

Burkitt's lymphoma cells are characterized by chromosomal translocations involving the proto-oncogene c-myc on chromosome 8 and one of the immunoglobulin gene loci on chromosome 2, 14 or 22. The translocated c-myc allele is transcriptionally activated, shows a preferential usage of promoter P1 over P2 (promoter shift) and lacks the ability to retain the transcription complex at the P2 promoter. In order to define the elements of the immunoglobulin kappa gene involved in deregulation of c-myc in a t(2;8) translocation, we designed constructs consisting of c-myc and different parts of the immunoglobulin kappa gene locus. Chromatin analysis of these stably transfected constructs revealed DNase I hypersensitive sites within the c-myc 5' region characteristic for an actively transcribed c-myc gene and three sites within the immunoglobulin kappa locus corresponding to the matrix attachment region, the intron and 3' enhancers, respectively. These three regulatory elements were necessary and sufficient for maximal c-myc activation and formation of the promoter shift. Kinetic nuclear run on experiments were performed to study the distribution of transcription complexes on c-myc exon 1 on constructs with and without the immunoglobulin kappa regulatory elements. The absence of a pausing polymerase complex at the c-myc P2 promoter could be demonstrated for constructs consisting of c-myc and the two kappa enhancers. Therefore the two enhancers are sufficient to relief the elongational block at the P2 promoter, however, the matrix attachment region is additionally required for maximal c-myc activation observed in Burkitt's lymphoma cells.