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>
Forkhead box transcription factor O1 inhibits cholesterol 7alpha-hydroxylase in human hepatocytes and in high fat diet-fed mice.
Adenoviridae/genetics; Animals; Bile Acids and Salts/biosynthesis; Cell Line; Cell Nucleus/drug effects/metabolism; Cholesterol 7-alpha-Hydroxylase/*antagonists & inhibitors/genetics/metabolism; Dietary Fats/*administration & dosage/*pharmacology; Down-Regulation/drug effects; Enzymologic/drug effects; Feeding Behavior/*drug effects; Forkhead Box Protein O1; Forkhead Transcription Factors/genetics/*metabolism; Gene Expression Regulation; Gene Knockdown Techniques; Gene Transfer Techniques; Hepatocytes/drug effects/*enzymology; Humans; Inbred C57BL; Insulin Resistance; Insulin/metabolism; Male; Messenger/genetics/metabolism; Mice; RNA; RNA Interference/drug effects; Tumor
The conversion of cholesterol to bile acids is the major pathway for cholesterol catabolism. Bile acids are metabolic regulators of triglycerides and glucose metabolism in the liver. This study investigated the roles of FoxO1 in the regulation of cholesterol 7alpha-hydroxylase (CYP7A1) gene expression in primary human hepatocytes. Adenovirus-mediated expression of a phosphorylation defective and constitutively active form of FoxO1 (FoxO1-ADA) inhibited CYP7A1 mRNA expression and bile acid synthesis, while siRNA knockdown of FoxO1 resulted in a approximately 6-fold induction of CYP7A1 mRNA in human hepatocytes. Insulin caused rapid exclusion of FoxO1 from the nucleus and resulted in the induction of CYP7A1 mRNA expression, which was blocked by FoxO1-ADA. In high fat diet-fed mice, CYP7A1 mRNA expression was repressed and inversely correlated to increase hepatic FoxO1 mRNA expression and FoxO1 nuclear retention. In conclusion, our current study provides direct evidence that FoxO1 is a strong repressor of CYP7A1 gene expression and bile acid synthesis. Impaired regulation of FoxO1 may cause down-regulation of CYP7A1 gene expression and contribute to dyslipidemia in insulin resistance.
Li Tiangang; Ma Huiyan; Park Young Joo; Lee Yoon-Kwang; Strom Stephen; Moore David D; Chiang John Y L
Biochimica et biophysica acta
2009
2009-10
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/10.1016/j.bbalip.2009.05.004" target="_blank" rel="noreferrer noopener">10.1016/j.bbalip.2009.05.004</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>
Bile acids activate fibroblast growth factor 19 signaling in human hepatocytes to inhibit cholesterol 7alpha-hydroxylase gene expression.
Butadienes/pharmacology; Carcinoma; Cell Line; Chenodeoxycholic Acid/*pharmacology; Cholesterol 7-alpha-Hydroxylase/*biosynthesis; Cytoplasmic and Nuclear/metabolism/physiology; DNA-Binding Proteins/metabolism; Fibroblast Growth Factor; Fibroblast Growth Factors/drug effects/*physiology; Gene Expression/drug effects; Hepatocellular/metabolism; Hepatocytes/metabolism; Humans; Isoxazoles/pharmacology; Mitogen-Activated Protein Kinase 1/metabolism; Mitogen-Activated Protein Kinase 3/metabolism; Nitriles/pharmacology; Receptor; Receptors; Signal Transduction/drug effects; Transcription Factors/metabolism; Tumor; Type 4/antagonists & inhibitors
UNLABELLED: Mouse fibroblast growth factor 15 (FGF15) and human ortholog FGF19 have been identified as the bile acid-induced intestinal factors that mediate bile acid feedback inhibition of cholesterol 7alpha-hydroxylase gene (C YP7A1) transcription in mouse liver. The mechanism underlying FGF15/FGF19 inhibition of bile acid synthesis in hepatocytes remains unclear. Chenodeoxycholic acid (CDCA) and the farnesoid X receptor (FXR)-specific agonist GW4064 strongly induced FGF19 but inhibited CYP7A1 messenger RNA (mRNA) levels in primary human hepatocytes. FGF19 strongly and rapidly repressed CYP7A1 but not small heterodimer partner (SHP) mRNA levels. Kinase inhibition and phosphorylation assays revealed that the mitogen-activated protein kinase/extracellular signal-regulated kinase 1/2 (MAPK/Erk1/2) pathway played a major role in mediating FGF19 inhibition of CYP7A1. However, small interfering RNA (siRNA) knockdown of SHP did not affect FGF19 inhibition of CYP7A1. Interestingly, CDCA stimulated tyrosine phosphorylation of the FGF receptor 4 (FGFR4) in hepatocytes. FGF19 antibody and siRNA specific to FGFR4 abrogated GW4064 inhibition of CYP7A1. These results suggest that bile acid-activated FXR is able to induce FGF19 in hepatocytes to inhibit CYP7A1 by an autocrine/paracrine mechanism. CONCLUSION: The hepatic FGF19/FGFR4/Erk1/2 pathway may inhibit CYP7A1 independent of SHP. In addition to inducing FGF19 in the intestine, bile acids in hepatocytes may activate the liver FGF19/FGFR4 signaling pathway to inhibit bile acid synthesis and prevent accumulation of toxic bile acid in human livers.
Song Kwang-Hoon; Li Tiangang; Owsley Erika; Strom Stephen; Chiang John Y L
Hepatology (Baltimore, Md.)
2009
2009-01
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.22627" target="_blank" rel="noreferrer noopener">10.1002/hep.22627</a>