Interaction between PU.1 and another Ets family transcription factor promotes macrophage-specific Basal transcription initiation.
Numerous macrophage-restricted promoters lack TATA boxes or other conventional initiation motifs but contain high affinity binding sites (PU boxes) for the macrophage-restricted Ets family transcription factor PU.1. In RAW264 murine macrophages, multimerized PU boxes were not active as enhancers when placed upstream of a minimal promoter. To model their role in basal promoters, we inserted PU boxes into a promoterless luciferase reporter plasmid. Two sites, regardless of orientation, were necessary and sufficient to direct reporter gene expression in transient transfections of the RAW264 macrophage-like cell line. This activity was absent in transfected 3T3 fibroblasts but could be induced by PU.1 coexpression. Both the model promoter and the macrophage-specific mouse and human c-fms promoters were activated in RAW264 cells by other Ets family transcription factors, Ets-2 and Elf-1. In fibroblasts, the effects of PU.1 and Ets-2 were multiplicative, whereas overexpression of PU.1 in RAW264 cells reduced activation of c-fms or model promoters by the other Ets factors. The PU.1 and Ets-2 binding sites of the mouse c-fms promoter have been located by DNase footprinting. A conserved Ets-like motif at the transcription site, CAGGAAC, that bound only weakly to PU.1, was identified as an additional critical basal c-fms promoter element. Comparison of studies on the model promoter, c-fms and other myeloid promoters provides evidence for a conserved mechanism that involves three separate and functionally distinct Ets-like motifs.
Ross
I L
IL
Department of Microbiology, University of Queensland, Brisbane 4072, Australia.
Yue
X
X
Ostrowski
M C
MC
Hume
D A
DA
D016475:3T3 Cells; D000818:Animals; D001665:Binding Sites; D018983:DNA Footprinting; D004742:Enhancer Elements, Genetic; D006367:HeLa Cells; D006801:Humans; D008264:Macrophages / Q000378:metabolism*; D051379:Mice; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D050783:Proto-Oncogene Proteins c-ets; D016186:Receptor, Macrophage Colony-Stimulating Factor / Q000235:genetics; D015534:Trans-Activators / Q000378:metabolism*; D014157:Transcription Factors / Q000378:metabolism*; D014158:Transcription, Genetic; D014162:Transfection; D000099232:Proto-Oncogene Protein Spi-1
D011518:Proto-Oncogene Proteins; D050783:Proto-Oncogene Proteins c-ets; D016186:Receptor, Macrophage Colony-Stimulating Factor; D015534:Trans-Activators; D014157:Transcription Factors; D000099232:Proto-Oncogene Protein Spi-1