Activation of c-myc promoter P1 by immunoglobulin kappa gene enhancers in Burkitt lymphoma: functional characterization of the intron enhancer motifskappa B, E box 1 and E box 2, and of the 3 ' enhancer motif PU

Deregulated expression of the proto-oncogene c-myc in Burkitt lymphoma (BL) cells carrying a t(2;8) translocation is mediated by a synergistic interac tion of the translocated immunoglobulin (Ig) kappa gene intron (kappa Ei) a nd 3' (kappa E3') enhancers and characterized by a strong activation of the promoter P1, We have investigated the functional role of distinct kappa en hancer sequence motifs in P1 activation on both minichromosomes and reporte r gene constructs, Stable and transient transfections of BL cells revealed critical roles of the kappa Ei and kappa E3' elements kappa B and PU, respe ctively, Joint mutation of kappa B and PU completely abolished P1 activity, implying that an interaction of kappa B- and PU-binding factors is essenti al for the enhancer synergism, Mutation of the E box 1 and E box 2 motifs m arkedly decreased P1 activity in transient but not in stable transfection e xperiments. Co-expression of the NF-kappa B subunit p65(RelA) and Sp1, an e ssential factor for P1 transcription, in Drosophila melanogaster SL2 cells synergistically enhanced promoter activity. Our results support a model whi ch proposes cross-talk between promoter and enhancer binding factors as the basic mechanism for kappa enhancer-mediated c-myc activation in BL cells.