A novel bile acid-activated vitamin D receptor signaling in human hepatocytes.
Calcitriol/*metabolism; Calcitriol/pharmacology; Cell Membrane/drug effects/metabolism; Cell Nucleus/drug effects/metabolism; Cholesterol 7-alpha-Hydroxylase/antagonists & inhibitors/genetics; Enzyme Activation/drug effects; Extracellular Signal-Regulated MAP Kinases/antagonists & inhibitors; Genetic/genetics; Hep G2 Cells; Hepatocyte Nuclear Factor 4/metabolism; Hepatocytes/*drug effects/enzymology/*metabolism; Humans; Intracellular Space/drug effects/metabolism; Ligands; Lithocholic Acid/*pharmacology; Mitogen-Activated Protein Kinase Kinases/metabolism; Phosphorylation/drug effects; Phosphotyrosine/metabolism; Promoter Regions; Protein Kinase Inhibitors/pharmacology; Protein Transport/drug effects; Proto-Oncogene Proteins c-raf/metabolism; Receptors; Retinoid X Receptor alpha/metabolism; Signal Transduction/*drug effects; src-Family Kinases/metabolism; Steroid Hydroxylases/genetics/metabolism; Vitamin D3 24-Hydroxylase
Vitamin D receptor (VDR) is activated by natural ligands, 1alpha,
Han Shuxin; Li Tiangang; Ellis Ewa; Strom Stephen; Chiang John Y L
Molecular endocrinology (Baltimore, Md.)
2010
2010-06
Article information provided for research and reference use only. All rights are retained by the journal listed under publisher and/or the creator(s).
<a href="http://doi.org/10.1210/me.2009-0482" target="_blank" rel="noreferrer noopener">10.1210/me.2009-0482</a>
Insulin regulation of cholesterol 7alpha-hydroxylase expression in human hepatocytes: roles of forkhead box O1 and sterol regulatory element-binding protein 1c.
*Gene Expression Regulation; *Transcriptional Activation; Adolescent; Adult; Animals; Child; Cholesterol 7-alpha-Hydroxylase/*biosynthesis/genetics; Enzymologic; Female; Forkhead Box Protein O1; Forkhead Transcription Factors/*physiology; Hepatocytes/*enzymology; Humans; Insulin/metabolism/*physiology; Male; Middle Aged; Preschool; Rats; Sterol Regulatory Element Binding Protein 1/*physiology; Transcription Factors/*physiology
Bile acid synthesis and pool size increases in diabetes, whereas insulin inhibits bile acid synthesis. The objective of this study is to elucidate the mechanism of insulin regulation of cholesterol 7alpha-hydroxylase gene expression in human hepatocytes. Real-time PCR assays showed that physiological concentrations of insulin rapidly stimulated cholesterol 7alpha-hydroxylase (CYP7A1) mRNA expression in primary human hepatocytes but inhibited CYP7A1 expression after extended treatment. The insulin-regulated forkhead box O1 (FoxO1) and steroid regulatory element-binding protein-1c (SREBP-1c) strongly inhibited hepatocyte nuclear factor 4alpha and peroxisome proliferator-activated receptor gamma coactivator-1alpha trans-activation of the CYP7A1 gene. FoxO1 binds to an insulin response element in the rat CYP7A1 promoter, which is not present in the human CYP7A1 gene. Insulin rapidly phosphorylates and inactivates FoxO1, whereas insulin induces nuclear SREBP-1c expression in human primary hepatocytes. Chromatin immunoprecipitation assay shows that insulin reduced FoxO1 and peroxisome proliferators-activated receptor gamma-coactivator-1alpha but increased SREBP-1c recruitment to CYP7A1 chromatin. We conclude that insulin has dual effects on human CYP7A1 gene transcription; physiological concentrations of insulin rapidly inhibit FoxO1 activity leading to stimulation of the human CYP7A1 gene, whereas prolonged insulin treatment induces SREBP-1c, which inhibits human CYP7A1 gene transcription. Insulin may play a major role in the regulation of bile acid synthesis and dyslipidemia in diabetes.
Li Tiangang; Kong Xiaoying; Owsley Erika; Ellis Ewa; Strom Stephen; Chiang John Y L
The Journal of biological chemistry
2006
2006-09
Article information provided for research and reference use only. All rights are retained by the journal listed under publisher and/or the creator(s).
<a href="http://doi.org/10.1074/jbc.M605815200" target="_blank" rel="noreferrer noopener">10.1074/jbc.M605815200</a>
Overexpression of cholesterol 7alpha-hydroxylase promotes hepatic bile acid synthesis and secretion and maintains cholesterol homeostasis.
Animals; ATP Binding Cassette Transporter; ATP-Binding Cassette Transporters/metabolism; Bile Acids and Salts/*metabolism; Cholesterol 7-alpha-Hydroxylase/*biosynthesis; Cholesterol/*metabolism; Cytoplasmic and Nuclear/agonists; Hepatocytes/drug effects; Homeostasis; Humans; Isoxazoles/pharmacology; Knockout; Lipoproteins/metabolism; Liver/*metabolism; Member 5; Member 8; Mice; Receptors; Subfamily G
UNLABELLED: We reported previously that mice overexpressing cytochrome P450 7a1 (Cyp7a1; Cyp7a1-tg mice) are protected against high fat diet-induced hypercholesterolemia, obesity, and insulin resistance. Here, we investigated the underlying mechanism of bile acid signaling in maintaining cholesterol homeostasis in Cyp7a1-tg mice. Cyp7a1-tg mice had two-fold higher Cyp7a1 activity and bile acid pool than did wild-type mice. Gallbladder bile acid composition changed from predominantly cholic acid (57%) in wild-type to chenodeoxycholic acid (54%) in Cyp7a1-tg mice. Cyp7a1-tg mice had higher biliary and fecal cholesterol and bile acid secretion rates than did wild-type mice. Surprisingly, hepatic de novo cholesterol synthesis was markedly induced in Cyp7a1-tg mice but intestine fractional cholesterol absorption in Cyp7a1-tg mice remained the same as wild-type mice despite the presence of increased intestine bile acids. Interestingly, hepatic but not intestinal expression of several cholesterol (adenosine triphosphate-binding cassette G5/G8 [ABCG5/G8], scavenger receptor class B, member 1) and bile acid (ABCB11) transporters were significantly induced in Cyp7a1-tg mice. Treatment of mouse or human hepatocytes with a farnesoid X receptor (FXR) agonist GW4064 or bile acids induced hepatic Abcg5/g8 expression. A functional FXR binding site was identified in the Abcg5 gene promoter. Study of tissue-specific Fxr knockout mice demonstrated that loss of the Fxr gene in the liver attenuated bile acid induction of hepatic Abcg5/g8 and gallbladder cholesterol content, suggesting a role of FXR in the regulation of cholesterol transport. CONCLUSION: This study revealed a new mechanism by which increased Cyp7a1 activity expands the hydrophobic bile acid pool, stimulating hepatic cholesterol synthesis and biliary cholesterol secretion without increasing intestinal cholesterol absorption. This study demonstrated that Cyp7a1 plays a critical role in maintaining cholesterol homeostasis and underscores the importance of bile acid signaling in regulating overall cholesterol homeostasis.
Li Tiangang; Matozel Michelle; Boehme Shannon; Kong Bo; Nilsson Lisa-Mari; Guo Grace; Ellis Ewa; Chiang John Y L
Hepatology (Baltimore, Md.)
2011
2011-03
Article information provided for research and reference use only. All rights are retained by the journal listed under publisher and/or the creator(s).
<a href="http://doi.org/10.1002/hep.24107" target="_blank" rel="noreferrer noopener">10.1002/hep.24107</a>
Hepatocyte growth factor signaling pathway inhibits cholesterol 7alpha-hydroxylase and bile acid synthesis in human hepatocytes.
Bile Acids and Salts/*biosynthesis; Cells; Cholesterol 7-alpha-Hydroxylase/*biosynthesis; Cultured; Hepatocyte Growth Factor/*metabolism; Hepatocytes/*metabolism; Humans; Signal Transduction
UNLABELLED: Bile acid synthesis in the liver is regulated by the rate-limiting enzyme cholesterol 7alpha-hydroxylase (CYP7A1). Transcription of the CYP7A1 gene is inhibited by bile acids and cytokines. The rate of bile acid synthesis is reduced immediately after partial hepatectomy and during the early stage of liver regeneration. Hepatocyte growth factor (HGF) released from stellate cells activates a receptor tyrosine kinase c-Met, in hepatocytes and stimulates signaling pathways that regulate cell growth, proliferation, and apoptosis. This study demonstrated that HGF strongly and rapidly repressed CYP7A1 mRNA expression and the rate of bile acid synthesis in primary human hepatocytes. HGF rapidly induced c-Jun and small heterodimer partner mRNA and protein expression and increased phosphorylation of ERK1/2, JNK, and c-Jun. Specific inhibitors of protein kinase C, extracellular signal-regulated kinase 1/2 (ERK1/2), and c-Jun
Song Kwang-Hoon; Ellis Ewa; Strom Stephen; Chiang John Y L
Hepatology (Baltimore, Md.)
2007
2007-12
Article information provided for research and reference use only. All rights are retained by the journal listed under publisher and/or the creator(s).
<a href="http://doi.org/10.1002/hep.21878" target="_blank" rel="noreferrer noopener">10.1002/hep.21878</a>