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BACKGROUND The transcription factor CCAAT/enhancer-binding protein β (C/EBPβ) is implicated in diverse processes and diseases. Its two isoforms, namely liver-enriched activator protein (LAP) and liver-enriched inhibitor protein (LIP) are translated from the same mRNA. They share the same C-terminal DNA binding domain except LAP has an extra N-terminal activation domain. Probably due to its higher affinity for its DNA cognate sequences, LIP can inhibit LAP transcriptional activity even at substoichiometric levels. However, the regulatory mechanism of C/EBPβ gene expression and the LAP: LIP ratio is unclear. METHODS In this study, the C/EBPβ promoter sequence was scanned for conserved P53 response element (P53RE), and binding of P53 to the C/EBPβ promoter was tested by Electrophoretic Mobility Shift Assay (EMSA) and chromatin immunoprecipitation assay. P53 over-expression and dominant negative P53 expression plasmids were transfected into rat lung fibroblasts and tested for C/EBPβ gene transcription and expression. Western blot analysis was used to test the regulation of C/EBPβ LAP and LIP isoforms. Constructs containing the LAP 5'untranslated region (5'UTR) or the LIP 5'UTR region were used to test the importance of 5'UTR in the control of C/EBPβ LAP and LIP translation. RESULTS The C/EBPβ promoter sequence was found to contain a conserved P53 response element (P53RE), which binds P53 as demonstrated by Electrophoresis Mobility Shift Assay and chromatin immunoprecipitation assays. P53 over-expression suppressed while dominant negative P53 stimulated C/EBPβ gene transcription and expression. Western blot analysis showed that P53 differentially regulated the translation of the C/EBPβ LAP and LIP isoforms through the regulation of eIF4E and eIF4E-BP1. Further studies with constructs containing the LAP 5'untranslated region (5'UTR) or the LIP 5'UTR region showed that the 5'UTR is important in differential control of C/EBPβ LAP and LIP translation. CONCLUSIONS Analysis of the effects of P53 on C/EBPβ expression revealed a novel mechanism by which P53 could antagonize the effects of C/EBPβ on its target gene expression. For the first time, P53 is shown to be a repressor of C/EBPβ gene expression at both transcriptional and translational levels, with a differential effect in the magnitude of the effect on LAP vs. LIP isoforms.
Biao Hu, and
Tianju Liu, and
Zhe Wu, and
Sem H Phan
September 2013,
Neurobiology of aging,
Biao Hu, and
Tianju Liu, and
Zhe Wu, and
Sem H Phan
January 2014,
PloS one,
Biao Hu, and
Tianju Liu, and
Zhe Wu, and
Sem H Phan
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Annals of the rheumatic diseases,
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Tianju Liu, and
Zhe Wu, and
Sem H Phan
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Molecular and cellular endocrinology,
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Tianju Liu, and
Zhe Wu, and
Sem H Phan
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Biology of reproduction,
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Tianju Liu, and
Zhe Wu, and
Sem H Phan
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Molecular medicine reports,
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Tianju Liu, and
Zhe Wu, and
Sem H Phan
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Molecular and cellular biology,
Biao Hu, and
Tianju Liu, and
Zhe Wu, and
Sem H Phan
April 2017,
Cytokine,
Biao Hu, and
Tianju Liu, and
Zhe Wu, and
Sem H Phan
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Yi chuan = Hereditas,
Biao Hu, and
Tianju Liu, and
Zhe Wu, and
Sem H Phan
June 2012,
The Journal of biological chemistry,
