Regulation of immunoglobulin transcription

Abstract: Each Ig V-region has its own upstream promoter and the promoter of a mature Ig gene is thereby selected during the V(D)J recombination process. Upon comparison, it is evident that only one transcription factor binding site, the octamer, is preserved within all promoters. The octamer motif and the binding Oct-proteins are crucial for Ig promoter function, but not sufficient for a high level of transcription. We have compared mouse and human Igk promoters in detail and found that other DNA elements were conserved between subgroups of V regions. This was true also between related mouse and human subgroups. To study Ig promoter function, we have used the SP6 k promoter as a model promoter. This promoter contains several sites that are conserved in certain Igk promoter subgroups, in addition to the octamer. The promoter is dependent on a functional octamer but needs the other regions to stimulate transcription at a high level. Mutations of the octamer that lowered the affinity for Oct-proteins were functionally compensated for by the surrounding regions of the SP6 k promoter, indicating that Oct-proteins are qualitative, rather than quantitative, regulators of Igk promoter function. In the region between the octamer and TATA-box we could detect two octamer-dependent costimulatory regions, A and B, centered around a CCCT-motif and an E-box. Two proteins, FA and FB, were found to bind the sequences and the A region functioned in a differentiation-specific manner. Ig transcription is also dependent on NFkB. NFkB is an attractive drug target and we used its role in Ig transcription to test six different N-substituted benzamides for NFkB-inhibitory properties. Using a model system based on the 70Z/3 cell line, we could show that compounds with a N-acetyl substitution were able to interfere with NFkB and that a chloride substitution also gave apoptosis-inducing properties.