THE ROLE OF IMMUNOGLOBULIN-KAPPA ELEMENTS IN C-MYC ACTIVATION

Burkitt's lymphoma cells are characterized by chromosomal translocatio ns involving the proto-oncogene c-myc on chromosome 8 and one of the i mmunoglobulin gene loci on chromosomes 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 reta in the transcription complex at the P2 promoter. In order to define th e elements of the immunoglobulin kappa gene involved in deregulation o f c-myc in a t(2;8) translocation, we designed constructs consisting o f c-myc and different parts of the immunoglobulin kappa gene locus. Ch romatin 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 immunogl obulin 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 format ion of the promoter shift. Kinetic nuclear run on experiments were per formed to study the distribution of transcription complexes on c-myc e xon 1 on constructs with and without the immunoglobulin kappa regulato ry elements. The absence of a pausing polymerase complex at the c-myc P2 promoter could be demonstrated for constructs consisting of c-myc a nd the two kappa enhancers. Therefore the two enhancers are sufficient to relief the elongational block at the P2 promoter, however, the mat rix attachment region is additionally required for maximal c-myc activ ation observed in Burkitt's lymphoma cells.