Document Detail

Transactivation of the ApoCIII promoter by ATF-2 and repression by members of the Jun family.
MedLine Citation:
PMID:  9760243     Owner:  NLM     Status:  MEDLINE    
It was shown previously that cytokines such as tumor necrosis factor-alpha that stimulate signal transduction pathways involving transcription factors ATF-2 and Jun repress apoCIII promoter activity in HepG2 cells. In the present study, DNase I footprinting analysis established that ATF-2 protected three regions in the apoCIII promoter. One region (-747/-726) present in the apoCIII enhancer is within the previously identified footprint I and has overlapping boundaries with the binding sites of Sp1 (-764/-742) and HNF-4 (-736/-714). The other two regions represent new footprints and have been designated D/E (-219/-199) and B/C (-102/-75). The B/C region overlaps with the previously identified footprint B which contains an HNF-4 binding site (-87/-63). Cotransfection experiments in HepG2 cells showed that ATF-2 transactivated the -890/+24 apoCIII promoter 1.6-fold. In addition, mutations in the proximal D/E (-219/-199) and distal I (-747/-726) ATF-2-binding sites reduced the apoCIII promoter strength to 33 and 9% of control, respectively, indicating that ATF-2 is a positive regulator of apoCIII gene transcription. Cotransfections with ATF-2 and HNF-4 expression plasmids resulted in additive transactivation of the apoCIII promoter. Furthermore, apoCIII promoter constructs bearing mutations in the D/E and I ATF-2 binding sites were efficiently transactivated by HNF-4, suggesting that these two factors contribute independently to the apoCIII promoter strength. Members of the Jun family (c-Jun, JunB, and JunD) caused a dose-dependent inhibition of the -890/+24 apoCIII promoter activity. A synthetic promoter containing the apoCIII enhancer in front of the minimal AdML promoter was also repressed by Jun. In contrast, apoCIII promoter segments lacking the enhancer region were transactivated by Jun. The findings suggest that homodimers of Jun or heterodimers of Jun with other AP-1 subunits could be responsible for the observed repression by interfering with the function(s) of the apoCIII enhancer. Repression by Jun could be reversed in the presence of ATF-2 and HNF-4, suggesting that ATF2 and possibly Jun/ATF-2 heterodimers exert a positive effect on apoCIII gene transcription, as opposed to Jun homodimers or heterodimers with other AP-1 members. These findings suggest a role for members of the Jun family and ATF-2 that participate in signal transduction pathways in basal or induced apoCIII promoter activity in cells of hepatic origin.
M Hadzopoulou-Cladaras; S N Lavrentiadou; V I Zannis; D Kardassis
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Publication Detail:
Type:  Journal Article; Research Support, U.S. Gov't, Non-P.H.S.; Research Support, U.S. Gov't, P.H.S.    
Journal Detail:
Title:  Biochemistry     Volume:  37     ISSN:  0006-2960     ISO Abbreviation:  Biochemistry     Publication Date:  1998 Oct 
Date Detail:
Created Date:  1998-11-04     Completed Date:  1998-11-04     Revised Date:  2008-11-21    
Medline Journal Info:
Nlm Unique ID:  0370623     Medline TA:  Biochemistry     Country:  UNITED STATES    
Other Details:
Languages:  eng     Pagination:  14078-87     Citation Subset:  IM    
Department of Medicine and Biochemistry, Cardiovascular Institute, Boston University Medical Center, Massachusetts 02118, USA.
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MeSH Terms
Activating Transcription Factor 2
Apolipoprotein C-III
Apolipoproteins C / genetics*,  metabolism
Base Sequence
Binding Sites / genetics
Carcinoma, Hepatocellular
Cyclic AMP Response Element-Binding Protein / genetics,  physiology*
Enhancer Elements, Genetic / physiology
Molecular Sequence Data
Promoter Regions, Genetic*
Proto-Oncogene Proteins c-jun / physiology*
Repressor Proteins / physiology*
Transcription Factors / genetics,  physiology*
Transcriptional Activation*
Tumor Cells, Cultured
Grant Support
Reg. No./Substance:
0/ATF2 protein, human; 0/Activating Transcription Factor 2; 0/Apolipoprotein C-III; 0/Apolipoproteins C; 0/Cyclic AMP Response Element-Binding Protein; 0/Proto-Oncogene Proteins c-jun; 0/Repressor Proteins; 0/Transcription Factors

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