The C/EBP bZIP domain can mediate lipopolysaccharide induction of the proinflammatory cytokines interleukin-6 and monocyte chemoattractant protein-1.
C/EBPalpha, beta, and delta are all expressed by bone marrow-derived macrophages. Ectopic expression of any of these transcription factors is sufficient to confer lipopolysaccharide (LPS)-inducible expression of interleukin-6 (IL-6) and monocyte chemoattractant protein-1 (MCP-1) to a B lymphoblast cell line, which normally lacks C/EBP factors and does not display LPS induction of proinflammatory cytokines. Thus, the activities of C/EBPalpha, beta, and delta are redundant in regard to expression of IL-6 and MCP-1. Surprisingly, the bZIP region of C/EBPbeta, which lacks any previously described activation domains, can also confer LPS-inducible expression of IL-6 and MCP-1 in stable transfectants. Transient transfections reveal that the bZIP regions of C/EBPbeta, C/EBPdelta, and, to a lesser extent, C/EBPalpha can activate the IL-6 promoter and augment its induction by LPS. Furthermore, the transdominant inhibitor, LIP, can activate expression from the IL-6 promoter. The ability of the C/EBPbeta bZIP region to activate the IL-6 promoter in transient transfections is completely dependent upon an intact NF-kappaB-binding site, supporting a model where the bZIP protein primarily functions to augment the activity of NF-kappaB. Replacement of the leucine zipper of C/EBPbeta with that of GCN4 yields a chimeric protein that can dimerize and specifically bind to a C/EBP consensus sequence, but shows a markedly reduced ability to activate IL-6 and MCP-1 expression. These results implicate the leucine zipper domain in some function other than dimerization with known C/EBP family members, and suggest that C/EBP redundancy in regulating cytokine expression may result from their highly related bZIP regions.
Hu
H M
HM
Department of Microbiology, Michigan State University, East Lansing, Michigan 48824-1101, USA.
Tian
Q
Q
Baer
M
M
Spooner
C J
CJ
Williams
S C
SC
Johnson
P F
PF
Schwartz
R C
RC
D000818:Animals; D001402:B-Lymphocytes; D001665:Binding Sites; D022782:CCAAT-Enhancer-Binding Protein-beta; D022762:CCAAT-Enhancer-Binding Proteins; D002460:Cell Line; D018932:Chemokine CCL2 / Q000096:biosynthesis* / Q000235:genetics; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D019281:Dimerization; D005656:Fungal Proteins / Q000235:genetics; D005786:Gene Expression Regulation; D015850:Interleukin-6 / Q000096:biosynthesis* / Q000235:genetics; D016350:Leucine Zippers / Q000235:genetics*; D008070:Lipopolysaccharides / Q000494:pharmacology*; D051379:Mice; D016328:NF-kappa B / Q000378:metabolism; D009687:Nuclear Proteins / Q000032:analysis / Q000235:genetics / Q000378:metabolism*; D011401:Promoter Regions, Genetic; D020033:Protein Isoforms / Q000378:metabolism; D011494:Protein Kinases / Q000235:genetics; D011993:Recombinant Fusion Proteins / Q000235:genetics; D012097:Repressor Proteins / Q000494:pharmacology; D029701:Saccharomyces cerevisiae Proteins; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D015533:Transcriptional Activation; D014162:Transfection
D022782:CCAAT-Enhancer-Binding Protein-beta; D022762:CCAAT-Enhancer-Binding Proteins; D018932:Chemokine CCL2; D004268:DNA-Binding Proteins; D005656:Fungal Proteins; D015850:Interleukin-6; D008070:Lipopolysaccharides; D016328:NF-kappa B; D009687:Nuclear Proteins; D020033:Protein Isoforms; D011993:Recombinant Fusion Proteins; D012097:Repressor Proteins; D029701:Saccharomyces cerevisiae Proteins; D014157:Transcription Factors; D011494:Protein Kinases