title: BCL-6 negatively regulates macrophage proliferation by suppressing autocrine IL-6 production.
abstract: The transcription repressor BCL-6 is known to play critical roles in B-cell lymphomagenesis, germinal center formation, and balanced Th1/Th2 differentiation. In macrophages, although BCL-6 has also been shown to regulate the expression of several chemokine genes, its function in other aspects of macrophage biology has not been studied. In addition, the precise role of BCL-6 in cell proliferation is poorly understood in general. Here we report that BCL-6(-/-) macrophages hyperproliferate due to an accelerated G(1)/S transition accompanied by increased cyclin D2 and c-myc and decreased expression of p27. Crucial to this enhanced proliferation is spontaneous interleukin 6 (IL-6) production and signal transducer and activator of transcription 3 (STAT3) activation in BCL-6(-/-) macrophages. In colony-forming assays, BCL- 6(-/-) bone marrow progenitor cells form spontaneous macrophage colonies that can be inhibited by anti-IL-6 antibodies. Gene expression studies demonstrate that BCL-6 binds to several sequence motifs scattered in the IL-6 locus and can repress IL-6 transcription both in 293T cells and in macrophages. In conclusion, our results indicate that BCL-6 negatively regulates proliferation of the monocytic/macrophage lineage by suppressing an autocrine IL-6/STAT3-mediated gene expression program. Our work also suggests that BCL-6 prevents abnormal Th2 differentiation by suppressing basal level IL-6 production in antigen-presenting cells (APCs).
authors.affiliation: Department of Cell Biology, Albert Einstein College of Medicine, 1300 Morris Park Ave, Bronx, NY 10461, USA.
authors.forename: Raymond Yick-Loi
authors.initials: RY
authors.lastname: Yu
authors.forename: Xing
authors.initials: X
authors.lastname: Wang
authors.forename: Fiona J
authors.initials: FJ
authors.lastname: Pixley
authors.forename: J Jessica
authors.initials: JJ
authors.lastname: Yu
authors.forename: Alexander L
authors.initials: AL
authors.lastname: Dent
authors.forename: Hal E
authors.initials: HE
authors.lastname: Broxmeyer
authors.forename: E Richard
authors.initials: ER
authors.lastname: Stanley
authors.forename: B Hilda
authors.initials: BH
authors.lastname: Ye
mesh_terms: D000818:Animals; D019898:Autocrine Communication / Q000235:genetics; D018797:Cell Cycle Proteins / Q000037:antagonists & inhibitors / Q000096:biosynthesis; D049109:Cell Proliferation; D002478:Cells, Cultured; D016922:Cellular Senescence / Q000235:genetics; D003114:Colony-Forming Units Assay; D004268:DNA-Binding Proteins / Q000037:antagonists & inhibitors / Q000172:deficiency / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D015536:Down-Regulation / Q000235:genetics; D016193:G1 Phase / Q000235:genetics; D006412:Hematopoietic Stem Cells / Q000166:cytology / Q000378:metabolism; D015850:Interleukin-6 / Q000096:biosynthesis* / Q000235:genetics / Q000502:physiology; D008264:Macrophages / Q000166:cytology* / Q000378:metabolism; D051379:Mice; D018345:Mice, Knockout; D011518:Proto-Oncogene Proteins / Q000037:antagonists & inhibitors / Q000172:deficiency / Q000235:genetics / Q000502:physiology*; D051560:Proto-Oncogene Proteins c-bcl-6; D012097:Repressor Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000502:physiology*; D016196:S Phase / Q000235:genetics; D050796:STAT3 Transcription Factor; D015398:Signal Transduction / Q000235:genetics; D015534:Trans-Activators / Q000378:metabolism / Q000502:physiology; D014157:Transcription Factors / Q000037:antagonists & inhibitors / Q000172:deficiency / Q000235:genetics / Q000502:physiology*; D015854:Up-Regulation / Q000235:genetics; D000093242:Interleukin-6 Inhibitors
chemical_list: D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D015850:Interleukin-6; D011518:Proto-Oncogene Proteins; D051560:Proto-Oncogene Proteins c-bcl-6; D012097:Repressor Proteins; D050796:STAT3 Transcription Factor; D015534:Trans-Activators; D014157:Transcription Factors; D000093242:Interleukin-6 Inhibitors; C494087:Stat3 protein, mouse