Suppression of cholesterol 7alpha-hydroxylase transcription and bile acid synthesis by an alpha1-antitrypsin peptide via interaction with alpha1-fetoprotein transcription factor.
alpha1-Antitrypsin (alpha1-AT) is a serum protease inhibitor that is synthesized mainly in the liver, and its rate of synthesis markedly increases in response to inflammation. This increase in alpha1-AT synthesis results in an increase in peptides, like its carboxyl-terminal C-36 peptide (C-36), resulting from alpha1-AT cleavage by proteases. Atherosclerosis is a form of chronic inflammation, and one of the risk factors is elevated plasma cholesterol levels. Because of the correlation between atherosclerosis, plasma cholesterol content, inflammation, and alpha1-AT rate of synthesis, we investigated the effect of the C-36 serpin peptide on hepatic bile acid biosynthesis. We discovered that C-36 is a powerful and specific transcriptional down-regulator of bile acid synthesis in primary rat hepatocytes, through inhibition of the cholesterol 7alpha-hydroxylase/CYP7A1 (7alpha-hydroxylase) promoter. Mice injected with the C-36 peptide also showed a decrease in 7alpha-hydroxylase mRNA. A mutated but very similar peptide did not have any effect on 7alpha-hydroxylase mRNA or its promoter. The sterol 12alpha-hydroxylase/CYP8B1 (12alpha-hydroxylase) promoter is also down-regulated by the C-36 peptide in HepG2 cells but not by the mutated peptide. The DNA element involved in the C-36-mediated regulation of 7alpha- and 12alpha-hydroxylase promoters mapped to the alpha1-fetoprotein transcription factor (FTF) site in both promoters. The C-36 peptide prevented binding of FTF to its target DNA recognition site by direct interaction with FTF. We hypothesize that the C-36 peptide specifically interacts with FTF and induces a conformational change that results in loss of its DNA binding ability, which results in suppression of 7alpha- and 12alpha-hydroxylase transcription. These results suggest that peptides derived from specific serum proteins may alter hepatic gene expression in a highly specific manner.
Gerbod-Giannone
Marie-Christine
MC
Department of Microbiology and Immunology, Medical College of Virginia Campus, Virginia Commonwealth University, Richmond, Virginia 23298, USA.
Del Castillo-Olivares
Antonio
A
Janciauskiene
Sabina
S
Gil
Gregorio
G
Hylemon
Phillip B
PB
D000595:Amino Acid Sequence; D000818:Animals; D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; D001647:Bile Acids and Salts / Q000096:biosynthesis*; D002784:Cholesterol / Q000378:metabolism; D002790:Cholesterol 7-alpha-Hydroxylase / Q000235:genetics* / Q000378:metabolism; D004268:DNA-Binding Proteins; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects*; D051557:Hepatocyte Nuclear Factor 4; D022781:Hepatocytes / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D008156:Luciferases / Q000235:genetics / Q000378:metabolism; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000737:chemistry / Q000494:pharmacology*; D010750:Phosphoproteins / Q000378:metabolism; D011401:Promoter Regions, Genetic; D051381:Rats; D017207:Rats, Sprague-Dawley; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D015843:Serpins / Q000494:pharmacology; D014157:Transcription Factors / Q000378:metabolism; D014158:Transcription, Genetic / Q000187:drug effects*; D014162:Transfection; D000515:alpha 1-Antitrypsin / Q000737:chemistry / Q000494:pharmacology*
D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; D001647:Bile Acids and Salts; D004268:DNA-Binding Proteins; D051557:Hepatocyte Nuclear Factor 4; C403128:MLX protein, human; D010446:Peptide Fragments; D010750:Phosphoproteins; D011993:Recombinant Fusion Proteins; D015843:Serpins; C501970:Tcfl4 protein, mouse; D014157:Transcription Factors; D000515:alpha 1-Antitrypsin; D002784:Cholesterol; D008156:Luciferases; D002790:Cholesterol 7-alpha-Hydroxylase