PU.1 and multiple IFN regulatory factor proteins synergize to mediate transcriptional activation of the human IL-1 beta gene.
Both lymphoid and myeloid cells express two related members of the IFN regulatory factor (IRF) family of transcription factors, specifically IRF-4 and IFN consensus binding protein (ICSBP or IRF-8). We previously reported that macrophages express IRF-4 and in combination with the ETS-like protein PU.1 can synergistically activate a human IL-1beta reporter gene. Here we report that this synergy is mediated by a composite PU.1/IRF element located within an upstream enhancer known to confer cytokine- and LPS-inducible expression. In macrophages, synergistic activation of IL-1beta reporter gene expression was preferentially mediated by IRF-4, whereas IRF-4 and ICSBP were equally capable of synergizing with PU.1 when coexpressed in fibroblasts. Furthermore, coexpression of IRF-1 and IRF-2 dramatically increased the capacity of both PU.1/IRF-4 and PU.1/ICSBP to induce IL-1beta reporter gene expression in fibroblasts. The additional synergy observed with IRF-1 and IRF-2 coexpression is mediated by a region of DNA distinct from either the IL-1beta enhancer or promoter. We also assessed the capacity of these transcription factors to activate endogenous IL-1beta gene when overexpressed in human embryonic kidney 293 cells. Although ectopic expression of PU.1 alone was sufficient to activate modest levels of IL-1beta transcripts, endogenous IL-1beta expression was markedly increased following coexpression of additional IRF proteins. Thus, maximal expression of both a human IL-1beta reporter gene and the endogenous IL-1beta gene was observed in cells that coexpressed PU.1, IRF-4 (or ICSBP), IRF1, and IRF2. Together, our observations suggest that these factors may function together as an enhanceosome.
Marecki
S
S
Pulmonary Center and Department of Pathology, Boston University School of Medicine, Boston MA 02118, USA.
Riendeau
C J
CJ
Liang
M D
MD
Fenton
M J
MJ
D016475:3T3 Cells; D020121:5' Untranslated Regions / Q000235:genetics / Q000276:immunology; D000818:Animals; D001483:Base Sequence; D002460:Cell Line; D004268:DNA-Binding Proteins / Q000096:biosynthesis / Q000378:metabolism / Q000502:physiology; D004357:Drug Synergism; D004742:Enhancer Elements, Genetic / Q000276:immunology; D006801:Humans; D050856:Interferon Regulatory Factor-1; D050836:Interferon Regulatory Factor-2; D050835:Interferon Regulatory Factors; D007371:Interferon-gamma / Q000378:metabolism*; D007375:Interleukin-1 / Q000096:biosynthesis / Q000235:genetics* / Q000378:metabolism*; D051379:Mice; D010750:Phosphoproteins / Q000096:biosynthesis / Q000378:metabolism / Q000502:physiology; D011485:Protein Binding / Q000235:genetics; D011518:Proto-Oncogene Proteins / Q000096:biosynthesis / Q000378:metabolism / Q000502:physiology*; D012097:Repressor Proteins / Q000378:metabolism / Q000502:physiology; D015534:Trans-Activators / Q000096:biosynthesis / Q000378:metabolism / Q000502:physiology*; D014157:Transcription Factors / Q000378:metabolism / Q000502:physiology; D015533:Transcriptional Activation / Q000276:immunology*; D015854:Up-Regulation / Q000235:genetics / Q000276:immunology; D000099185:Interferon Regulatory Factor-8; D000099232:Proto-Oncogene Protein Spi-1; D000099218:Interferon Regulatory Factor-4
D020121:5' Untranslated Regions; D004268:DNA-Binding Proteins; D050856:Interferon Regulatory Factor-1; D050836:Interferon Regulatory Factor-2; D050835:Interferon Regulatory Factors; D007371:Interferon-gamma; D007375:Interleukin-1; D010750:Phosphoproteins; D011518:Proto-Oncogene Proteins; D012097:Repressor Proteins; D015534:Trans-Activators; D014157:Transcription Factors; D000099185:Interferon Regulatory Factor-8; D000099232:Proto-Oncogene Protein Spi-1; D000099218:Interferon Regulatory Factor-4; C494257:IRF1 protein, human; C494229:IRF2 protein, human; C494258:Irf1 protein, mouse; C494230:Irf2 protein, mouse