Antagonism between apolipoprotein AI regulatory protein 1, Ear3/COUP-TF, and hepatocyte nuclear factor 4 modulates apolipoprotein CIII gene expression in liver and intestinal cells.
Apolipoprotein CIII (apoCIII), a lipid-binding protein involved in the transport of triglycerides and cholesterol in the plasma, is synthesized primarily in the liver and the intestine. A cis-acting regulatory element, C3P, located at -90 to -66 upstream from the apoCIII gene transcriptional start site (+1), is necessary for maximal expression of the apoCIII gene in human hepatoma (HepG2) and intestinal carcinoma (Caco2) cells. This report shows that three members of the steroid receptor superfamily of transcription factors, hepatocyte nuclear factor 4 (HNF-4), apolipoprotein AI regulatory protein 1 (ARP-1), and Ear3/COUP-TF, act at the C3P site. HNF-4 activates apoCIII gene expression in HepG2 and Caco2 cells, while ARP-1 and Ear3/COUP-TF repress its expression in the same cells. HNF-4 activation is abolished by increasing amounts of ARP-1 or Ear3/COUP-TF, and repression by ARP-1 or Ear3/COUP-TF is alleviated by increasing amounts of HNF-4. HNF-4 and ARP-1 bind with similar affinities to the C3P site, suggesting that their opposing transcriptional effects may be mediated by direct competition for DNA binding. HNF-4 and ARP-1 mRNAs are present within the same cells in the liver and intestine, and protein extracts from hepatic tissue, HepG2, and Caco2 cells contain significantly more HNF-4 than ARP-1 or Ear3/COUP-TF binding activities. These findings suggest that the transcription of the apoCIII gene in vivo is dependent, at least in part, upon the intracellular balance of these positive and negative regulatory factors.
Mietus-Snyder
M
M
Department of Cardiology, Children's Hospital, Boston, Massachusetts 02115.
Sladek
F M
FM
Ginsburg
G S
GS
Kuo
C F
CF
Ladias
J A
JA
Darnell
J E
JE
Karathanasis
S K
SK
D053305:Apolipoprotein C-III; D001056:Apolipoproteins C / Q000235:genetics / Q000378:metabolism*; D001483:Base Sequence; D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; D051838:COUP Transcription Factor I; D051837:COUP Transcription Factor II; D051836:COUP Transcription Factors; D002277:Carcinoma / Q000378:metabolism; D006528:Carcinoma, Hepatocellular / Q000378:metabolism; D003110:Colonic Neoplasms / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism; D015972:Gene Expression Regulation, Neoplastic; D051557:Hepatocyte Nuclear Factor 4; D006801:Humans; D008113:Liver Neoplasms / Q000378:metabolism; D008969:Molecular Sequence Data; D010750:Phosphoproteins; D011401:Promoter Regions, Genetic / Q000235:genetics*; D011987:Receptors, Steroid; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D014018:Tissue Distribution; D014157:Transcription Factors / Q000378:metabolism*; D014158:Transcription, Genetic; D014407:Tumor Cells, Cultured
D053305:Apolipoprotein C-III; D001056:Apolipoproteins C; D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; D051838:COUP Transcription Factor I; D051837:COUP Transcription Factor II; D051836:COUP Transcription Factors; D004268:DNA-Binding Proteins; D051557:Hepatocyte Nuclear Factor 4; D010750:Phosphoproteins; D011987:Receptors, Steroid; D011993:Recombinant Fusion Proteins; D014157:Transcription Factors; C403128:MLX protein, human; C497589:NR2F1 protein, human; C095569:NR2F2 protein, human