E1A represses apolipoprotein AI enhancer activity in liver cells through a pRb- and CBP-independent pathway.
The apolipoprotein AI (apoAI) promoter/enhancer contains multiple cis -acting elements on which a variety of hepatocyte-enriched and ubiquitous transcription factors function synergistically to regulate liver-specific transcription. Adenovirus E1A proteins repress tissue-specific gene expression and disrupt the differentiated state in a variety of cell types. In this study expression of E1A 12Sor 13S in hepatoblastoma HepG2 cells repressed apoAI enhancer activity 8-fold. Deletion mapping analysis showed that inhibition by E1A was mediated by the apoAI promoter site B. E1A selectively inhibited the ability of HNF3beta and HNF3alpha to transactivate reporter genes controlled by the apoAI site B and the HNF3 binding site from the transthyretin promoter. The E1A-mediated repression of HNF3 activity was not reversed by overexpression of HNF3beta nor did E1A alter nuclear HNF3beta protein levels or inhibit HNF3 binding to DNA in mobility shift assays. Overexpression of two cofactors known to interact with E1A, pRb and CBP failed to overcome inhibition of HNF3 activity. Similarly, mutations in E1A that disrupt its interaction with pRb or CBP did not compromise its ability to repress HNF3beta transcriptional activity. These data suggest that E1A inhibits HNF3 activity by inactivating a limiting cofactor(s) distinct from pRb or CBP.
Kilbourne
E J
EJ
Department of Nuclear Receptors, Wyeth-Ayerst Research, 145 King of Prussia Road, Radnor, PA 19087, USA.
Evans
M J
MJ
Karathanasis
S K
SK
D017500:Adenovirus E1A Proteins / Q000378:metabolism*; D016632:Apolipoprotein A-I / Q000096:biosynthesis* / Q000235:genetics*; D001665:Binding Sites; D006528:Carcinoma, Hepatocellular; D015500:Chloramphenicol O-Acetyltransferase / Q000096:biosynthesis; D004268:DNA-Binding Proteins / Q000378:metabolism; D004742:Enhancer Elements, Genetic; D005786:Gene Expression Regulation; D017930:Genes, Reporter; D051541:Hepatocyte Nuclear Factor 3-alpha; D051542:Hepatocyte Nuclear Factor 3-beta; D006801:Humans; D008099:Liver / Q000378:metabolism*; D008113:Liver Neoplasms; D008156:Luciferases / Q000096:biosynthesis; D009687:Nuclear Proteins / Q000378:metabolism; D009928:Organ Specificity; D011401:Promoter Regions, Genetic; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis; D011994:Recombinant Proteins / Q000096:biosynthesis; D016385:TATA Box; D014157:Transcription Factors; D015533:Transcriptional Activation; D014162:Transfection; D014407:Tumor Cells, Cultured
D017500:Adenovirus E1A Proteins; D016632:Apolipoprotein A-I; D004268:DNA-Binding Proteins; C496499:FOXA1 protein, human; C496502:FOXA2 protein, human; D051541:Hepatocyte Nuclear Factor 3-alpha; D009687:Nuclear Proteins; D011993:Recombinant Fusion Proteins; D011994:Recombinant Proteins; D014157:Transcription Factors; D051542:Hepatocyte Nuclear Factor 3-beta; D008156:Luciferases; D015500:Chloramphenicol O-Acetyltransferase