Multiple Ets factors and interferon regulatory factor-4 modulate CD68 expression in a cell type-specific manner.
CD68 is a transmembrane glycoprotein expressed in all cells of the mononuclear phagocyte lineage including monocytes and tissue resident macrophages. Deletion analysis of the 5'-flanking sequences of the gene demonstrated that the proximal -150-bp sequence of the CD68 promoter exhibits high level promoter activity in macrophages. Mutations that abolish Ets factor binding at positions -106 and -89 reduce promoter activity in macrophages to 12 and 30%, respectively. Band shift experiments show that PU.1 associates with the -89 site whereas, Elf-1 preferentially binds the -106 Ets binding site and enhances CD68 activity in vitro. Furthermore, chromatin immunoprecipitation experiments confirm that Elf-1 and PU.1 associate with the CD68 proximal promoter in vivo in THP-1 cells. PU.1 does not bind to the CD68 promoter alone but instead forms heterocomplexes with members of the interferon regulatory factor family (IRF) including IRF-4 and IRF-8. IRF-4 and IRF-8 typically mediate transcriptional activation when associated with PU.1 on composite elements. However, our data show that PU.1/IRF-4 and IRF-8 heterocomplexes down-regulate CD68 promoter activity in macrophages and repression is dependent on the integrity of both the IRF and PU.1 half-sites of this composite element. Chromatin immunoprecipitation data reveal that neither IRF-4 nor IRF-8 associate with the CD68 proximal promoter in macrophages in vivo but IRF-4 is associated with the promoter in B lymphocytes. We propose that expression of CD68 in myeloid cells requires the Ets transcription factors Elf-1 and PU.1 and CD68 expression is down-regulated in lymphoid cells by combinatorial interactions between PU.1 and IRF-4.
O'Reilly
Dawn
D
Sir William Dunn School of Pathology, University of Oxford, South Parks Road, Oxford OX1 3RE, United Kingdom.
Quinn
Carmel M
CM
El-Shanawany
Tariq
T
Gordon
Siamon
S
Greaves
David R
DR
D020816:Amino Acid Motifs; D000818:Animals; D015703:Antigens, CD / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism; D015214:Antigens, Differentiation, Myelomonocytic / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism; D001402:B-Lymphocytes / Q000378:metabolism; D001483:Base Sequence; D001665:Binding Sites; D015153:Blotting, Western; D019556:COS Cells; D002460:Cell Line; D004268:DNA-Binding Proteins / Q000378:metabolism*; D015536:Down-Regulation; D017930:Genes, Reporter; D005822:Genetic Vectors; D018922:HL-60 Cells; D006801:Humans; D050835:Interferon Regulatory Factors; D008214:Lymphocytes / Q000378:metabolism; D008264:Macrophages / Q000378:metabolism; D051379:Mice; D008957:Models, Genetic; D008969:Molecular Sequence Data; D009154:Mutation; D009687:Nuclear Proteins; D010957:Plasmids / Q000378:metabolism; D016133:Polymerase Chain Reaction; D011233:Precipitin Tests; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D012097:Repressor Proteins / Q000378:metabolism; D013997:Time Factors; D015534:Trans-Activators / Q000378:metabolism; D014157:Transcription Factors / Q000378:metabolism*; D014158:Transcription, Genetic; D015533:Transcriptional Activation; D014407:Tumor Cells, Cultured; D020298:U937 Cells; D000099185:Interferon Regulatory Factor-8; D000099232:Proto-Oncogene Protein Spi-1; D000099218:Interferon Regulatory Factor-4; D000097382:CD68 Molecule
D015703:Antigens, CD; D015214:Antigens, Differentiation, Myelomonocytic; D004268:DNA-Binding Proteins; D050835:Interferon Regulatory Factors; D009687:Nuclear Proteins; D011518:Proto-Oncogene Proteins; D012333:RNA, Messenger; 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; C067980:CD68 antigen, human; D000097382:CD68 Molecule; C512897:ELF1 protein, human; C512896:Elf1 protein, mouse