BCL3 is induced by IL-6 via Stat3 binding to intronic enhancer HS4 and represses its own transcription.
BCL3 is a proto-oncogene affected by chromosomal translocations in some patients with chronic lymphocytic leukemia. It is an IkappaB family protein that is involved in transcriptional regulation of a number of NF-kappaB target genes. In this study, interleukin (IL)-6-induced BCL3 expression and its effect on survival of multiple myeloma (MM) cells were examined. We demonstrate the upregulation of BCL3 by IL-6 in INA-6 and other MM cell lines. Sequence analysis of the BCL3 gene locus revealed four potential signal transducer and activator of transcription (Stat) binding sites within two conserved intronic enhancers regions: one located within enhancer HS3 and three within HS4. Chromatin immunoprecipitation experiments showed increased Stat3 binding to both enhancers upon IL-6 stimulation. Silencing Stat3 expression by small interfering RNA (siRNA) abrogated BCL3 expression by IL-6. Using reporter gene assays, we demonstrate that BCL3 transcription depends on HS4. Mutation of the Stat motifs within HS4 abolished IL-6-dependent BCL3 induction. Furthermore, BCL3 transcription was inhibited by its own gene product. This repressive feedback is mediated by NF-kappaB sites within the promoter and HS3. Finally, we show that overexpression of BCL3 increases apoptosis, whereas BCL3-specific siRNA does not affect the viability of INA-6 cells suggesting that BCL3 is not essential for the survival of these cells.
Brocke-Heidrich
K
K
Institute of Clinical Immunology and Transfusion Medicine, University of Leipzig, Leipzig, Germany. kheid@medizin.uni-leipzig.de
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Cvijic
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Pfeifer
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Löffler
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Henze
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McKeithan
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Horn
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D000081242:B-Cell Lymphoma 3 Protein; D001483:Base Sequence; D045744:Cell Line, Tumor; D047369:Chromatin Immunoprecipitation; D017931:DNA Primers; D004742:Enhancer Elements, Genetic; D020868:Gene Silencing; D006801:Humans; D015850:Interleukin-6 / Q000378:metabolism*; D007438:Introns; D009101:Multiple Myeloma / Q000378:metabolism / Q000473:pathology; D011485:Protein Binding; D000090063:Proto-Oncogene Mas; D011518:Proto-Oncogene Proteins / Q000096:biosynthesis*; D050796:STAT3 Transcription Factor / Q000378:metabolism*; D014157:Transcription Factors / Q000096:biosynthesis*; D014158:Transcription, Genetic
D000081242:B-Cell Lymphoma 3 Protein; C000631344:BCL3 protein, human; D017931:DNA Primers; D015850:Interleukin-6; C000715470:MAS1 protein, human; D000090063:Proto-Oncogene Mas; D011518:Proto-Oncogene Proteins; D050796:STAT3 Transcription Factor; D014157:Transcription Factors