Expression of the gene encoding alpha 1-acid glycoprotein in rabbit liver under acute-phase conditions involves induction and activation of beta and delta CCAAT-enhancer-binding proteins.
Transcription of the gene encoding alpha 1-acid glycoprotein is highly induced during acute inflammation which has been previously shown to be mediated by some inducible members of the CCAAT-enhancer-binding (C/EBP) transcription-factor family. In this study, we demonstrate that the involved inducible C/EBP isoforms are C/EBP-beta and C/EBP-delta, and together they control the high-level induction of the alpha 1-acid glycoprotein gene in response to inflammatory signals. We observed that dephosphorylation severely inhibits the DNA-binding ability of C/EBP-delta and its transactivating potential increases in the presence of cellular phosphatase inhibitors, such as okadaic acid and sodium orthovanadate. These results suggest that C/EBP-delta is regulated by phosphorylation. Transient transfections using expression vectors of C/EBP-alpha, C/EBP-beta and C/EBP-delta have shown that while individually all three isoforms can transactivate the alpha 1-acid glycoprotein-chloramphenicol-acetyltransferase gene transcription, co-expression of C/EBP-alpha and C/EBP-beta isoforms results in lower levels of reporter gene expression than the levels predicted from their additive transactivation level. In vitro DNA-binding studies have shown that C/EBP-alpha and C/EBP-beta isoforms both interact and form complexes with the alpha 1-acid glycoprotein gene C/EBP-binding element under normal noninduced conditions during which alpha 1-acid glycoprotein is expressed at a very low level. Higher than additive levels of reporter gene expression are observed when combinations of C/EBP-delta and C/EBP-beta or C/EBP-delta and C/EBP-alpha are used. Together, these data demonstrate that C/EBP-beta and C/EBP-delta are the major proteins responsible for the acute-phase induction of alpha 1-acid-glycoprotein gene expression and they require phosphorylation for transactivation potential.
Ray
B K
BK
Department of Veterinary Microbiology, University of Missouri 65211.
Ray
A
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D000210:Acute-Phase Reaction / Q000235:genetics* / Q000378:metabolism; D000818:Animals; D001483:Base Sequence; D001665:Binding Sites; D015152:Blotting, Northern; D022762:CCAAT-Enhancer-Binding Proteins; D002460:Cell Line; D004268:DNA-Binding Proteins / Q000378:metabolism*; D015870:Gene Expression; D008099:Liver / Q000378:metabolism* / Q000473:pathology; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000378:metabolism*; D009961:Orosomucoid / Q000235:genetics*; D010766:Phosphorylation; D011401:Promoter Regions, Genetic / Q000235:genetics; D012313:RNA / Q000032:analysis; D011817:Rabbits; D014157:Transcription Factors / Q000378:metabolism*; D014158:Transcription, Genetic / Q000187:drug effects / Q000235:genetics; D015533:Transcriptional Activation
D022762:CCAAT-Enhancer-Binding Proteins; D004268:DNA-Binding Proteins; D009687:Nuclear Proteins; D009961:Orosomucoid; D014157:Transcription Factors; D012313:RNA