Repression of an interleukin-4-responsive promoter requires cooperative BCL-6 function.
BCL-6 functions as a potent transcriptional repressor that binds with specificity to DNA elements bearing marked similarity to STAT recognition sequences. Previous studies have demonstrated that BCL-6 and Stat6 can both bind and regulate the Iepsilon promoter that controls immunoglobulin heavy chain class switching to IgE. Examination of BCL-6-/- and BCL-6-/-Stat6-/- mice has demonstrated that BCL-6 is a repressor of IgE and that Stat6 is still required for the interleukin-4 (IL-4) induction of class switching to IgE in B cells lacking BCL-6. To define the mechanisms by which BCL-6 represses IL-4 function, we analyzed the role of BCL-6 in repressing the Iepsilon promoter. There are three BCL-6-binding sites within this IL-4-responsive promoter. Analysis of Iepsilon promoters that have mutated BCL-6-binding sites demonstrates that at least two of these sites are required for maximal BCL-6 repression of this locus. Footprinting analysis demonstrates that BCL-6 binds cooperatively to the two upstream binding sites in the Iepsilon promoter. This cooperative binding requires the POZ domain of BCL-6. Furthermore, activated Stat6 molecules can displace BCL-6 from one of these binding sites. These data demonstrate that cooperative interaction between BCL-6 molecules is required for repression of the Iepsilon promoter.
Harris
Miera B
MB
Integrated Program in Cellular, Molecular, and Biophysical Sciences and the Departments of Medicine and Microbiology, Columbia University College of Physicians and Surgeons, New York, New York 10032, USA.
Mostecki
Justin
J
Rothman
Paul B
PB
D000818:Animals; D001665:Binding Sites; D001667:Binding, Competitive; D022782:CCAAT-Enhancer-Binding Protein-beta / Q000378:metabolism; D002460:Cell Line; D004268:DNA-Binding Proteins / Q000378:metabolism / Q000502:physiology*; D003850:Deoxyribonuclease I / Q000378:metabolism; D017930:Genes, Reporter; D005982:Glutathione Transferase / Q000378:metabolism; D015847:Interleukin-4 / Q000037:antagonists & inhibitors / Q000235:genetics*; D051379:Mice; D009154:Mutation; D010957:Plasmids / Q000378:metabolism; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D011518:Proto-Oncogene Proteins / Q000378:metabolism / Q000502:physiology*; D051560:Proto-Oncogene Proteins c-bcl-6; D011994:Recombinant Proteins / Q000737:chemistry; D014157:Transcription Factors / Q000378:metabolism / Q000502:physiology*; D014158:Transcription, Genetic; D014162:Transfection
D022782:CCAAT-Enhancer-Binding Protein-beta; D004268:DNA-Binding Proteins; D011518:Proto-Oncogene Proteins; D051560:Proto-Oncogene Proteins c-bcl-6; D011994:Recombinant Proteins; D014157:Transcription Factors; D015847:Interleukin-4; D005982:Glutathione Transferase; D003850:Deoxyribonuclease I