201
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Orphan nuclear receptor SHP interacts with and represses hepatocyte nuclear factor-6 (HNF-6) transactivation. Biochem J 2008; 413:559-69. [PMID: 18459945 DOI: 10.1042/bj20071637] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
SHP (small heterodimer partner; NR0B2) is an atypical orphan NR (nuclear receptor) that functions as a transcriptional co-repressor by interacting with a diverse set of NRs and transcriptional factors. HNF-6 (hepatocyte nuclear factor-6) is a key regulatory factor in pancreatic development, endocrine differentiation and the formation of the biliary tract, as well as glucose metabolism. In this study, we have investigated the function of SHP as a putative repressor of HNF-6. Using transient transfection assays, we have shown that SHP represses the transcriptional activity of HNF-6. Confocal microscopy revealed that both SHP and HNF-6 co-localize in the nuclei of cells. SHP physically interacted with HNF-6 in protein-protein association assays in vitro. EMSAs (electrophoretic mobility-shift assays) and ChIP (chromatin immunoprecipitation) assays demonstrated that SHP inhibits the DNA-binding activity of HNF-6 to an HNF-6-response element consensus sequence, and the HNF-6 target region of the endogenous G6Pase (glucose 6-phosphatase) promoter respectively. Northern blot analysis of HNF-6 target genes in cells infected with adenoviral vectors for SHP and SHP siRNAs (small inhibitory RNAs) indicated that SHP represses the expression of endogenous G6Pase and PEPCK (phosphoenolpyruvate carboxykinase). Our results suggest that HNF-6 is a novel target of SHP in the regulation of gluconeogenesis.
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202
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Henry RR. Evolving concepts of type 2 diabetes management with oral medications: new approaches to an old disease. Curr Med Res Opin 2008; 24:2189-202. [PMID: 18573228 DOI: 10.1185/03007990802212981] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
BACKGROUND Type 2 diabetes is often accompanied by co-morbid conditions such as hypertension and dyslipidemia, which, coupled with persistent hyperglycemia, result in significant macrovascular and microvascular complications. Type 2 diabetes treatments focus primarily on controlling hyperglycemia, hypertension, and dyslipidemia to stabilize the disease and minimize complications. Despite treatment, control of hyperglycemia and the conditions associated with type 2 diabetes are suboptimal in the majority of patients. Research efforts have concentrated on the development of new therapies for type 2 diabetes, including agents that could be used both as monotherapy and in combination with established oral antidiabetic agents to improve glycemic control and reduce the disease burden on patients. OBJECTIVE To review published literature on oral agents in development for type 2 diabetes, with a focus on their mechanism of action and impact on concomitant risk factors. METHODS After identifying oral agents in late-stage development for type 2 diabetes using the R&D Insight database, a literature review was conducted through PubMed for studies (preferably randomized, controlled trials) on dipeptidyl peptidase-IV inhibitors, CB(1) cannabinoid receptor blockers, and bile acid sequestrants. Where limited published data were available, abstracts from recent major conferences were searched. Other emerging therapies targeting pathways involved in modifying insulin resistance, glycogenolysis, and gluconeogenesis are also discussed. CONCLUSIONS A variety of novel therapies for type 2 diabetes are in development, which will provide patients and diabetes care providers more choices for the management of this disease. Importantly, many of these treatments offer the potential to significantly improve multiple metabolic parameters.
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203
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Seo HY, Kim YD, Lee KM, Min AK, Kim MK, Kim HS, Won KC, Park JY, Lee KU, Choi HS, Park KG, Lee IK. Endoplasmic reticulum stress-induced activation of activating transcription factor 6 decreases insulin gene expression via up-regulation of orphan nuclear receptor small heterodimer partner. Endocrinology 2008; 149:3832-41. [PMID: 18450959 PMCID: PMC2488228 DOI: 10.1210/en.2008-0015] [Citation(s) in RCA: 91] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
The highly developed endoplasmic reticulum (ER) structure of pancreatic beta-cells is a key factor in beta-cell function. Here we examined whether ER stress-induced activation of activating transcription factor (ATF)-6 impairs insulin gene expression via up-regulation of the orphan nuclear receptor small heterodimer partner (SHP; NR0B2), which has been shown to play a role in beta-cell dysfunction. We examined whether ER stress decreases insulin gene expression, and this process is mediated by ATF6. A small interfering RNA that targeted SHP was used to determine whether the effect of ATF6 on insulin gene expression is mediated by SHP. We also measured the expression level of ATF6 in pancreatic islets in Otsuka Long Evans Tokushima Fatty rats, a rodent model of type 2 diabetes. High glucose concentration (30 mmol/liter glucose) increased ER stress in INS-1 cells. ER stress induced by tunicamycin, thapsigargin, or dithiotreitol decreased insulin gene transcription. ATF6 inhibited insulin promoter activity, whereas X-box binding protein-1 and ATF4 did not. Adenovirus-mediated overexpression of active form of ATF6 in INS-1 cells impaired insulin gene expression and secretion. ATF6 also down-regulated pancreatic duodenal homeobox factor-1 and RIPE3b1/MafA gene expression and repressed the cooperative action of pancreatic duodenal homeobox factor-1, RIPE3b1/MafA, and beta-cell E box transactivator 2 in stimulating insulin transcription. The ATF6-induced suppression of insulin gene expression was associated with up-regulation of SHP gene expression. Finally, we found that expression of ATF6 was increased in the pancreatic islets of diabetic Otsuka Long Evans Tokushima Fatty rats, compared with their lean, nondiabetic counterparts, Long-Evans Tokushima Otsuka rats. Collectively, this study shows that ER stress-induced activation of ATF6 plays an important role in the development of beta-cell dysfunction.
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Affiliation(s)
- Hye-Young Seo
- Department of Internal Medicine, Kyungpook National University School of Medicine, 50 Samduk-2ga, Jung-gu, Daegu 700-721, Republic of Korea
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204
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Chanda D, Kim SJ, Lee IK, Shong M, Choi HS. Sodium arsenite induces orphan nuclear receptor SHP gene expression via AMP-activated protein kinase to inhibit gluconeogenic enzyme gene expression. Am J Physiol Endocrinol Metab 2008; 295:E368-79. [PMID: 18505831 DOI: 10.1152/ajpendo.00800.2007] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Sodium arsenite has been demonstrated to alter the expression of genes associated with glucose homeostasis in tissues involved in the pathogenesis of type 2 diabetes; however, the underlying molecular mechanism has not been fully elucidated yet. In this study, we report that the sodium arsenite-induced gene expression of the small heterodimer partner (SHP; NR0B2), an atypical orphan nuclear receptor, regulates the expression of hepatic gluconeogenic genes. Sodium arsenite augments hepatic SHP mRNA levels in an AMP-activated protein kinase (AMPK)-dependent manner. Sodium arsenite activated AMPK and was shown to perturb cellular ATP levels. The arsenite-induced SHP mRNA level was blocked by adenoviral overexpression of dominant negative AMPK (Ad-dnAMPKalpha) or by the AMPK inhibitor compound C in hepatic cell lines. We demonstrated the dose-dependent induction of SHP mRNA levels by sodium arsenite and repressed the forskolin/dexamethasone-induced gene expression of the key hepatic gluconeogenic genes phosphoenolpyruvate carboxykinase (PEPCK) and glucose-6-phosphatase (G6Pase). Ad-dnAMPKalpha blocked the repressive effects of arsenite-induced SHP on PEPCK and G6Pase. Sodium arsenite inhibited the promoter activity of PEPCK and G6Pase, and this repression was abolished by small interfering (si)RNA SHP treatments. The knockdown of SHP expression by oligonucleotide siRNA SHP or adenoviral siRNA SHP released the sodium arsenite-mediated repression of forskolin/dexamethasone-stimulated PEPCK and G6Pase gene expression in a variety of hepatic cell lines. Results from our study suggest that sodium arsenite induces SHP via AMPK to inhibit the expression of hepatic gluconeogenic genes and also provide us with a novel molecular mechanism of arsenite-mediated regulation of hepatic glucose homeostasis.
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Affiliation(s)
- Dipanjan Chanda
- Hormone Research Center, School of Biological Sciences and Technology, Chonnam National University, Gwangju, Republic of Korea
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205
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Chanda D, Park JH, Choi HS. Molecular basis of endocrine regulation by orphan nuclear receptor Small Heterodimer Partner. Endocr J 2008; 55:253-68. [PMID: 17984569 DOI: 10.1507/endocrj.k07e-103] [Citation(s) in RCA: 91] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Abstract
Nuclear receptors (NRs) are a unique superfamily of transcription factors (TFs) which are involved in and play a crucial role in almost all aspects of mammalian physiology. Small Heterodimer Partner (SHP; NR0B2), an exceptional member of this superfamily of NRs, have been identified as a key regulatory factor of the transcription of a variety of genes involved in diverse metabolic pathways, and are thereby an important factor in a variety of physiological functions. Since its discovery a decade ago, considerable progress has been made in the elucidation of the underlying mechanism by which SHP regulates various metabolic processes, and the results of previous studies support its importance in the maintenance of metabolic homeostasis. In this review, we have evaluated the current state of understanding of the molecular mechanisms and the resultant physiological interpretations governed by SHP.
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Affiliation(s)
- Dipanjan Chanda
- Hormone Research Center, School of Biological Sciences and Technology, Chonnam National University, Gwangju, Republic of Korea
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206
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Pascussi JM, Gerbal-Chaloin S, Duret C, Daujat-Chavanieu M, Vilarem MJ, Maurel P. The tangle of nuclear receptors that controls xenobiotic metabolism and transport: crosstalk and consequences. Annu Rev Pharmacol Toxicol 2008; 48:1-32. [PMID: 17608617 DOI: 10.1146/annurev.pharmtox.47.120505.105349] [Citation(s) in RCA: 215] [Impact Index Per Article: 13.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
The expression of many genes involved in xenobiotic/drug metabolism and transport is regulated by at least three nuclear receptors or xenosensors: aryl hydrocarbon receptor (AhR), constitutive androstane receptor (CAR), and pregnane X receptor (PXR). These receptors establish crosstalk with other nuclear receptors or transcription factors controlling signaling pathways that regulate the homeostasis of bile acids, lipids, glucose, inflammation, vitamins, hormones, and others. These crosstalks are expected to modify profoundly our vision of xenobiotic/drug disposition and toxicity. They provide molecular mechanisms to explain how physiopathological stimuli affect xenobiotic/drug disposition, and how xenobiotics/drugs may affect physiological functions and generate toxic responses. In addition, the possibility that xenosensors may control other signaling pathways opens the way to new pharmacological opportunities.
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207
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Kim YD, Park KG, Lee YS, Park YY, Kim DK, Nedumaran B, Jang WG, Cho WJ, Ha J, Lee IK, Lee CH, Choi HS. Metformin inhibits hepatic gluconeogenesis through AMP-activated protein kinase-dependent regulation of the orphan nuclear receptor SHP. Diabetes 2008; 57:306-14. [PMID: 17909097 DOI: 10.2337/db07-0381] [Citation(s) in RCA: 313] [Impact Index Per Article: 19.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
OBJECTIVE Metformin is an antidiabetic drug commonly used to treat type 2 diabetes. The aim of the study was to determine whether metformin regulates hepatic gluconeogenesis through the orphan nuclear receptor small heterodimer partner (SHP; NR0B2). RESEARCH DESIGN AND METHODS We assessed the regulation of hepatic SHP gene expression by Northern blot analysis with metformin and adenovirus containing a constitutive active form of AMP-activated protein kinase (AMPK) (Ad-AMPK) and evaluated SHP, PEPCK, and G6Pase promoter activities via transient transfection assays in hepatocytes. Knockdown of SHP using siRNA SHP was conducted to characterize the metformin-induced inhibition of hepatic gluconeogenic gene expression in hepatocytes, and metformin-and adenovirus SHP (Ad-SHP)-mediated hepatic glucose production was measured in B6-Lep(ob/ob) mice. RESULTS Hepatic SHP gene expression was induced by metformin, 5-aminoimidazole-4-carboxamide-1-beta-d-ribofuranoside (AICAR), and Ad-AMPK. Metformin-induced SHP gene expression was abolished by adenovirus containing the dominant negative form of AMPK (Ad-DN-AMPK), as well as by compound C. Metformin inhibited hepatocyte nuclear factor-4alpha-or FoxA2-mediated promoter activity of PEPCK and G6Pase, and the inhibition was blocked with siRNA SHP. Additionally, SHP knockdown by adenovirus containing siRNA SHP inhibited metformin-mediated repression of cAMP/dexamethasone-induced hepatic gluconeogenic gene expression. Furthermore, oral administration of metformin increased SHP mRNA levels in B6-Lep(ob/ob) mice. Overexpression of SHP by Ad-SHP decreased blood glucose levels and hepatic gluconeogenic gene expression in B6-Lep(ob/ob) mice. CONCLUSIONS We have concluded that metformin inhibits hepatic gluconeogenesis through AMPK-dependent regulation of SHP.
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Affiliation(s)
- Yong Deuk Kim
- Hormone Research Center, School of Biological Sciences & Technology, Chonnam National University, Gwangju, 500-757, Republic of Korea
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208
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Differential inhibition of nuclear hormone receptor-dependent hepatitis B virus replication by the small heterodimer partner. J Virol 2008; 82:3814-21. [PMID: 18234786 DOI: 10.1128/jvi.02507-07] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
The nuclear hormone receptors hepatocyte nuclear factor 4 (HNF4) and retinoid X receptor alpha (RXRalpha) plus peroxisome proliferator-activated receptor alpha (PPARalpha) heterodimer support hepatitis B virus (HBV) pregenomic RNA synthesis and viral replication in nonhepatoma cells. Small heterodimer partner (SHP), an orphan nuclear hormone receptor lacking a DNA binding domain, inhibits nuclear hormone receptor-mediated viral transcription and replication. The inhibition of HBV replication by SHP is dependent on the presence of nuclear hormone receptors. HBV replication that is dependent on HNF4 is considerably more sensitive to SHP-mediated inhibition than RXRalpha/PPARalpha-directed viral biosynthesis. SHP inhibition of HBV biosynthesis in HepG2 cells suggests that multiple nuclear hormone receptors mediate viral replication in this human hepatoma cell line. These observations suggest that the physiological regulation of HBV biosynthesis by SHP in the liver will depend on both the level of SHP expression and the relative contribution of HNF4 and RXRalpha/PPARalpha, plus potentially additional nuclear hormone receptors, to HBV RNA synthesis and replication.
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209
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Higashiyama H, Kinoshita M, Asano S. Immunolocalization of farnesoid X receptor (FXR) in mouse tissues using tissue microarray. Acta Histochem 2008; 110:86-93. [PMID: 17963822 DOI: 10.1016/j.acthis.2007.08.001] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2007] [Revised: 08/01/2007] [Accepted: 08/01/2007] [Indexed: 11/30/2022]
Abstract
Farnesoid X receptor (FXR) is a member of the nuclear receptor family and is known to play important roles in bile acid homeostasis, and lipid and glucose metabolism. In this study, to elucidate the systemic physiological functions of FXR, comprehensive immunohistochemical analysis of cell/subcellular localization of FXR and its heterodimer partner, retinoid X receptor (RXR)-alpha, in adult mice tissues was performed using tissue microarray (TMA)-based immunohistochemistry. FXR immunolabeling was observed in the enterohepatic system--including absorptive epithelium in the intestines, hepatocytes and gall bladder epithelium, several epithelial lineage cells including the basal cells of stratified epithelium in the tongue, esophagus, forestomach--skin, corneal epithelium and ciliary body epithelium in the eye and adrenocortical cells--including glandular cells in the zona reticularis/fasciculata. In these FXP-positive cells, FXR was preferentially localized to the nucleus. RXR-alpha was ubiquitously distributed in the nucleus of most cell types, including FXR-positive cell types in the examined tissues. These data suggest that FXR might have various physiological roles, not only in bile acid homeostasis, and lipid and glucose metabolism, but also in the epithelial cell barrier, visual and urinary function through multiple organ systems.
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Affiliation(s)
- Hiroyuki Higashiyama
- Tsukuba Research Laboratories, Pharmacology Department, GlaxoSmithKline, 43 Wadai, Tsukuba, Ibaraki 300-4247, Japan
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210
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Zhang Y, Edwards PA. FXR signaling in metabolic disease. FEBS Lett 2007; 582:10-8. [PMID: 18023284 DOI: 10.1016/j.febslet.2007.11.015] [Citation(s) in RCA: 155] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2007] [Accepted: 11/06/2007] [Indexed: 11/25/2022]
Abstract
Farnesoid X receptor (FXR), a member of the nuclear receptor superfamily, has been shown to be important in controlling numerous metabolic pathways; these include roles in maintaining bile acid, lipid and glucose homeostasis, in preventing intestinal bacterial infection and gallstone formation and in modulating liver regeneration and tumorigenesis. The accumulating data suggest that FXR may be a pharmaceutical target for the treatment of certain metabolic diseases.
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Affiliation(s)
- Yanqiao Zhang
- Department of Biological Chemistry, University of California at Los Angeles, 47-105 CHS, 10833 Le Conte Avenue, Los Angeles, CA 90095, USA.
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211
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212
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Murakami T, Walczak R, Caron S, Duhem C, Vidal V, Darteil R, Staels B. The farnesoid X receptor induces fetuin-B gene expression in human hepatocytes. Biochem J 2007; 407:461-9. [PMID: 17655523 PMCID: PMC2275064 DOI: 10.1042/bj20070658] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
FXR (farnesoid X receptor), a nuclear receptor activated by BAs (bile acids), is a key factor in the regulation of BA, lipid and carbohydrate metabolism. The recent development of synthetic FXR agonists and knockout mouse models has accelerated the discovery of FXR target genes. In the present study, we identify human fetuin-B as a novel FXR target gene. Treatment with FXR agonists increased fetuin-B expression in human primary hepatocytes and in the human hepatoma HepG2 cell line. In contrast, fetuin-B expression was not responsive to FXR agonist treatment in murine primary hepatocytes. Fetuin-B induction by FXR agonist was abolished upon FXR knockdown by siRNA (small interfering RNA). In addition to the previously described P1 promoter, we show that the human fetuin-B gene is also transcribed from an alternative promoter, termed P2. Transcription via the P2 promoter was induced by FXR agonist treatment, whereas P1 promoter activity was not sensitive to FXR agonist treatment. Two putative FXR-response elements [IR-1 (inverted repeat-1)] were identified in the region -1.6 kb upstream of the predicted P2 transcriptional start site. Both motifs bound FXR-RXR (retinoid X receptor) complexes in vitro and were activated by FXR in transient transfection reporter assays. Mutations in the IR-1 sites abolished FXR-RXR binding and activation. Taken together, these results identify human fetuin-B as a new FXR target gene in human hepatocytes.
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Affiliation(s)
- Takeshi Murakami
- *Tokyo New Research Laboratories I, Pharmaceutical Division, Kowa Company Ltd, 2-17-43 Noguchicho, Higashimurayama, Tokyo, Japan
| | | | - Sandrine Caron
- ‡Institut Pasteur de Lille, Lille F-59019, France
- §Inserm, U545, Lille F-59019, France
- ¶Faculté de Pharmacie et Faculté de Médecine, Université de Lille 2, Lille F-59006, France
| | - Christian Duhem
- ‡Institut Pasteur de Lille, Lille F-59019, France
- §Inserm, U545, Lille F-59019, France
- ¶Faculté de Pharmacie et Faculté de Médecine, Université de Lille 2, Lille F-59006, France
| | | | | | - Bart Staels
- ‡Institut Pasteur de Lille, Lille F-59019, France
- §Inserm, U545, Lille F-59019, France
- ¶Faculté de Pharmacie et Faculté de Médecine, Université de Lille 2, Lille F-59006, France
- To whom correspondence should be addressed (email )
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213
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Abstract
Bile acids promote bile formation and facilitate dietary lipid absorption. Animal and human studies showing disturbed bile acid metabolism in diabetes mellitus suggest a link between bile acids and glucose control. Bile acids are activating ligands of the farnesoid X receptor (FXR), a nuclear receptor with an established role in bile acid and lipid metabolism. Evidence suggests a role for FXR also in maintenance of glucose homeostasis. Animal and human studies employing bile acid sequestrants (bile acid binding agents), which interrupt the enterohepatic circulation of bile acids and effectively reduce plasma cholesterol, support a link between bile acid and glucose metabolism. In lipid-lowering trials, bile acid sequestrants, such as colesevelam hydrochloride, colestyramine (cholestyramine) and colestilan (colestimide), have also been shown to lower plasma glucose and glycosylated haemoglobin levels, suggesting the utility of these agents as a potential therapy for type 2 diabetes. In this article, we review the relationship between bile acid metabolism and glucose homeostasis, and present data demonstrating the utility of bile acid sequestrants in the management of diabetes.
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214
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Chang KO, George DW. Bile acids promote the expression of hepatitis C virus in replicon-harboring cells. J Virol 2007; 81:9633-40. [PMID: 17609266 PMCID: PMC2045404 DOI: 10.1128/jvi.00795-07] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
Hepatitis C virus (HCV) is a cause of chronic liver disease, with more than 170 million persistently infected individuals worldwide. Although the combination therapy of alpha interferon (IFN-alpha) and ribavirin is effective for chronic HCV infection, around half of all patients infected with HCV genotype 1 fail to show sustained virologic responses and remain chronically infected. Previously, we demonstrated that bile acids were essential for growth of porcine enteric calicivirus in cell culture in association with down-regulation of IFN responses. Because hepatocytes are exposed to high concentrations of bile acids in the liver, we hypothesized that bile acids have similar effects on HCV replication. We incubated HCV replicon-harboring cells (genotype 1b, Con1) in the presence of various bile acids and monitored the expression of HCV RNA and protein (NS5B). The addition of an individual bile acid (deoxycholic acid, chenodeoxycholic acid, ursodeoxycholic acid, or glycochenodeoxycholic acid) in the medium increased the levels of HCV RNA and proteins up to fivefold at 48 h of incubation. An antagonist of bile acid receptor farnesoid X receptor (FXR), Z-guggulsterone, reduced the bile acid-mediated increase of HCV RNA. When IFN (alpha or gamma) and each bile acid were incubated together, we observed that bile acid significantly reduced the anti-HCV effect of IFN. These results indicated that bile acids are factors in the failure of IFN treatment for certain patients infected with HCV genotype 1. Our finding may also contribute to the establishment of better regimens for treatment of chronic HCV infections by including agents altering the bile acid-mediated FXR pathway.
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Affiliation(s)
- Kyeong-Ok Chang
- Department of Diagnostic Medicine and Pathobiology, College of Veterinary Medicine, Kansas State University, 1800 Denison Avenue, Manhattan, KS 66506, USA.
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215
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Fiorucci S, Rizzo G, Donini A, Distrutti E, Santucci L. Targeting farnesoid X receptor for liver and metabolic disorders. Trends Mol Med 2007; 13:298-309. [PMID: 17588816 DOI: 10.1016/j.molmed.2007.06.001] [Citation(s) in RCA: 155] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2006] [Revised: 05/01/2007] [Accepted: 06/04/2007] [Indexed: 02/08/2023]
Abstract
The farnesoid X receptor (FXR) is a metabolic nuclear receptor expressed in the liver, intestine, kidney and adipose tissue. By regulating the expression and function of genes involved in bile acid (BA) synthesis, uptake and excretion, FXR has emerged as a key gene involved in the maintenance of cholesterol and BA homeostasis. FXR ligands are currently under clinical investigation for the treatment of cholestasis, dyslipidemic disorders and conditions of insulin resistance in type 2 diabetes and non-alcoholic steatohepatitis (NASH). Because activation of FXR impacts a considerable number of genes, development of FXR modulators that selectively regulate specific pathways will limit potentially undesirable side effects. Interaction of FXR with other BAs and xenobiotics sensors such as the constitutive androstane receptor and the pregnane X receptor might allow the development of combination therapies for liver and metabolic disorders.
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Affiliation(s)
- Stefano Fiorucci
- Dipartimento di Medicina Clinica e Sperimentale, University of Perugia, Perugia, Italy.
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216
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Kim HI, Koh YK, Kim TH, Kwon SK, Im SS, Choi HS, Kim KS, Ahn YH. Transcriptional activation of SHP by PPAR-gamma in liver. Biochem Biophys Res Commun 2007; 360:301-6. [PMID: 17601490 DOI: 10.1016/j.bbrc.2007.05.171] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2007] [Accepted: 05/18/2007] [Indexed: 10/23/2022]
Abstract
The mechanism of how PPARgamma decrease gluconeogenic gene expressions in liver is still unclear. Since PPARgamma is a transcriptional activator, it requires a mediator to decrease the transcription of gluconeogenic genes. Recently, SHP has been shown to mediate the bile acid-dependent down regulation of gluconeogenic gene expression in liver. This led us to explore the possibility that SHP may mediate the antigluconeogenic effect of PPARgamma. In the present study, we have identified and characterized the presence of functional PPRE in human SHP promoter. We show the binding of PPARgamma/RXRalpha heterodimer to the PPRE and increased SHP expression by rosiglitazone in primary rat hepatocytes. Taken together with the previous reports about the function of SHP on gluconeogenesis, our results indicate that SHP can mediate the acute antigluconeogenic effect of PPARgamma.
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Affiliation(s)
- Ha-il Kim
- Department of Biochemistry and Molecular Biology, Yonsei University College of Medicine, 134 Shinchon-dong, Seodaemoon-gu, Seoul 120-752, Republic of Korea
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217
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Cariou B, Staels B. FXR: a promising target for the metabolic syndrome? Trends Pharmacol Sci 2007; 28:236-43. [PMID: 17412431 DOI: 10.1016/j.tips.2007.03.002] [Citation(s) in RCA: 101] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2006] [Revised: 02/12/2007] [Accepted: 03/21/2007] [Indexed: 12/23/2022]
Abstract
The metabolic syndrome is an insulin-resistant state that is characterized by a cluster of cardiovascular risk factors, including abdominal obesity, hyperglycemia, elevated blood pressure and combined dyslipidemia. In this review, we discuss the role of the bile-acid-activated farnesoid X receptor (FXR) in the modulation of the metabolic syndrome. Owing to its regulatory actions in lipid and glucose homeostasis, FXR is a potential pharmacological target. Moreover, the observation that FXR also influences endothelial function and atherosclerosis indicates a regulatory role in the cardiovascular complications that are associated with the metabolic syndrome. The pharmacological activation of FXR leads to a complex response that integrates beneficial actions and potentially undesirable side-effects. Thus, the identification of selective FXR modulators (selective bile acid receptor modulators) is required for the development of compounds that can be used to treat the metabolic syndrome.
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Affiliation(s)
- Bertrand Cariou
- Centre Hospitalier Universitaire Hôtel-Dieu, Nantes 44093, France.
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218
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Park M, Kong H, Kim H, Kim H, Kim J, Cheong J. Transcriptional repression of the gluconeogenic gene PEPCK by the orphan nuclear receptor SHP through inhibitory interaction with C/EBPalpha. Biochem J 2007; 402:567-74. [PMID: 17094771 PMCID: PMC1863575 DOI: 10.1042/bj20061549] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
SHP (short heterodimer partner) is an orphan nuclear receptor that plays an important role in regulating glucose and lipid metabolism. A variety of transcription factors are known to regulate transcription of the PEPCK (phosphoenolpyruvate carboxykinase) gene, which encodes a rate-determining enzyme in hepatic gluconeogenesis. Previous reports identified glucocorticoid receptor and Foxo1 as novel downstream targets regulating SHP inhibition [Borgius, Steffensen, Gustafsson and Treuter (2002) J. Biol. Chem. 277, 49761-49796; Yamagata, Daitoku, Shimamoto, Matsuzaki, Hirota, Ishida and Fukamizu (2004) J. Biol. Chem. 279, 23158-23165]. In the present paper, we show a new molecular mechanism of SHP-mediated inhibition of PEPCK transcription. We also show that the CRE1 (cAMP regulatory element 1; -99 to -76 bp relative to the transcription start site) of the PEPCK promoter is also required for the inhibitory regulation by SHP. SHP repressed C/EBPalpha (CCAAT/enhancer-binding protein alpha)-driven transcription of PEPCK through direct interaction with C/EBPalpha protein both in vitro and in vivo. The formation of an active transcriptional complex of C/EBPalpha and its binding to DNA was inhibited by SHP, resulting in the inhibition of PEPCK gene transcription. Taken together, these results suggest that SHP might regulate a level of hepatic gluconeogenesis driven by C/EBPalpha activation.
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Affiliation(s)
- Min Jung Park
- *Department of Molecular Biology, Pusan National University, Busan 609-735, Korea
| | - Hee Jeong Kong
- †Laboratory of Molecular Growth Regulation, National Institute of Child Health and Development, National Institutes of Health, Bethesda, Maryland 20892-2753, U.S.A
| | - Hye Young Kim
- *Department of Molecular Biology, Pusan National University, Busan 609-735, Korea
| | - Hyeong Hoe Kim
- ‡Department of Laboratory Medicine, College of Medicine, Pusan National University, Busan 602-739, Korea
| | - Joon Hong Kim
- §Department of Internal Medicine, College of Medicine, Pusan National University, Busan 602-739, Korea
| | - Jae Hun Cheong
- *Department of Molecular Biology, Pusan National University, Busan 609-735, Korea
- To whom correspondence should be addressed (email )
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219
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Park KG, Lee KM, Seo HY, Suh JH, Kim HS, Wang L, Won KC, Lee HW, Park JY, Lee KU, Kim JG, Kim BW, Choi HS, Lee IK. Glucotoxicity in the INS-1 rat insulinoma cell line is mediated by the orphan nuclear receptor small heterodimer partner. Diabetes 2007; 56:431-7. [PMID: 17259388 DOI: 10.2337/db06-0753] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Prolonged elevations of glucose concentration have deleterious effects on beta-cell function. One of the hallmarks of such glucotoxicity is a reduction in insulin gene expression, resulting from decreased insulin promoter activity. Small heterodimer partner (SHP; NR0B2) is an atypical orphan nuclear receptor that inhibits nuclear receptor signaling in diverse metabolic pathways. In this study, we found that sustained culture of INS-1 cells at high glucose concentrations leads to an increase in SHP mRNA expression, followed by a decrease in insulin gene expression. Inhibition of endogenous SHP gene expression by small interfering RNA partially restored high-glucose-induced suppression of the insulin gene. Adenovirus-mediated overexpression of SHP in INS-1 cells impaired glucose-stimulated insulin secretion as well as insulin gene expression. SHP downregulates insulin gene expression via two mechanisms: by downregulating PDX-1 and MafA gene expression and by inhibiting p300-mediated pancreatic duodenal homeobox factor 1-and BETA2-dependent transcriptional activity from the insulin promoter. Finally, the pancreatic islets of diabetic OLETF rats express SHP mRNA at higher levels than the islets from LETO rats. These results collectively suggest that SHP plays an important role in the development of beta-cell dysfunction induced by glucotoxicity.
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Affiliation(s)
- Keun-Gyu Park
- Department of Internal Medicine, Kyungpook National University Hospital, 50 Samduk-2ga, Jung-gu, Daegu 700-721, Republic of Korea
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220
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Lee YS, Chanda D, Sim J, Park YY, Choi HS. Structure and function of the atypical orphan nuclear receptor small heterodimer partner. INTERNATIONAL REVIEW OF CYTOLOGY 2007; 261:117-58. [PMID: 17560281 DOI: 10.1016/s0074-7696(07)61003-1] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
The small heterodimer partner (SHP; NROB2) is a member of the nuclear receptor superfamily and is classified as an "orphan" subgroup, as its ligand has not yet been identified. SHP lacks the classical DNA-binding domain found in most nuclear receptors and functions as a transcriptional coregulator by directly interacting with nuclear receptors and other transcription factors. SHP regulates the transcription of a variety of target genes and controls a variety of physiological functions. For the past 10 years, great progress has been made in our understanding of the mechanism of action of SHP and the regulation of SHP gene expression. Many of the results imply that SHP has a variety of roles in the regulation of metabolic homeostasis. In this review, we discuss the current state of understanding of the structure, expression, and function of the orphan nuclear receptor, SHP.
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Affiliation(s)
- Yong-Soo Lee
- Hormone Research Center, School of Biological Sciences and Technology, Chonnam National University, Gwangju 500-757, Korea
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221
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Edgerton DS, Jacobson PB, Opgenorth TJ, Zinker B, Beno D, von Geldern T, Ohman L, Scott M, Neal D, Cherrington AD. Selective antagonism of the hepatic glucocorticoid receptor reduces hepatic glucose production. Metabolism 2006; 55:1255-62. [PMID: 16919547 DOI: 10.1016/j.metabol.2006.05.011] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/16/2006] [Accepted: 05/29/2006] [Indexed: 01/07/2023]
Abstract
A liver-selective glucocorticoid (GC) receptor antagonist (A-348441) was used to determine the effect of reduced hepatic GC signaling on hepatic glucose production. Fasted conscious dogs were studied in the presence (GRA, n = 6) or absence (CON, n = 6) of the intraduodenally administered GC receptor antagonist (100 mg/kg). All dogs were maintained on a pancreatic clamp and in a euglycemic state for 7 hours to ensure that any changes in glucose metabolism were the direct result of the effects of A-348441, which was given at the start of a 5-hour experimental period. In the GRA group, the arterial plasma insulin level was 4.6 +/- 0.7 and 4.8 +/- 0.6 microU/mL during the basal and the last 30 minutes of the experimental periods, respectively. In the CON group, it was 4.0 +/- 0.3 and 4.5 +/- 0.5 microU/mL in the 2 periods, respectively. The arterial plasma glucagon level was 49 +/- 4 and 46 +/- 3 pg/mL in the 2 periods in the GRA group, and 45 +/- 3 and 42 +/- 3 pg/mL in the CON group. Net hepatic glucose balance progressively decreased in the GRA group from 1.31 +/- 0.18 to 0.49 +/- 0.30 mg/kg per minute, whereas in the CON group, net hepatic glucose balance was 1.17 +/- 0.09 and 1.43 +/- 0.18 mg/kg per minute during the basal and last 30 minutes of the experimental periods, respectively. No significant change in net renal or gut glucose balance or nonhepatic glucose uptake was observed in either group. This study demonstrates that the GC receptor plays an important role in the regulation of basal hepatic glucose production and represents a significant potential therapeutic target.
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Affiliation(s)
- Dale S Edgerton
- Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, TN 37232, USA.
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222
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Tobin JF, Freedman LP. Nuclear receptors as drug targets in metabolic diseases: new approaches to therapy. Trends Endocrinol Metab 2006; 17:284-90. [PMID: 16870465 DOI: 10.1016/j.tem.2006.07.004] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/10/2006] [Revised: 07/10/2006] [Accepted: 07/12/2006] [Indexed: 10/24/2022]
Abstract
Nuclear receptors represent novel targets for the development of therapeutic agents for the treatment of numerous diseases, including type 2 diabetes, obesity dyslipidemia, atherosclerosis and the metabolic syndrome. There have been many recent advances in the development of new therapeutic agents for a subset of these receptors, including the peroxisome proliferator-activated receptors, the liver X receptors and the farnesoid X receptor. To date, the synthesis of selective modulators that regulate the activity of these receptors has been empirical. However, a detailed understanding of the molecular basis for selective modulation, as well as new insights into the biology of these receptors, might open the door to the rational design of a new generation of therapeutic agents with improved safety and efficacy.
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Affiliation(s)
- James F Tobin
- Department of Cardiovascular and Metabolic Diseases, Wyeth Research, 200 Cambridge Park Drive, Cambridge, MA 02140, USA.
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223
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Nakae J, Cao Y, Daitoku H, Fukamizu A, Ogawa W, Yano Y, Hayashi Y. The LXXLL motif of murine forkhead transcription factor FoxO1 mediates Sirt1-dependent transcriptional activity. J Clin Invest 2006; 116:2473-83. [PMID: 16917544 PMCID: PMC1550275 DOI: 10.1172/jci25518] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2005] [Accepted: 06/27/2006] [Indexed: 11/17/2022] Open
Abstract
The forkhead transcription factor FoxO1 has been identified as a negative regulator of insulin/IGF-1 signaling. Its function is inhibited by phosphorylation and nuclear exclusion through a PI3K-dependent pathway. However, the structure/function relationship of FoxO1 has not been elucidated completely. In this study, we carried out mutation analysis of the FoxO1 coactivator-interacting LXXLL motif (amino acids 459-463). Expression of a 3A/LXXAA mutant, in which 3 Akt phosphorylation sites (T24, S253, and S316) and 2 leucine residues in the LXXLL motif (L462 and L463) were replaced by alanine, decreased both Igfbp-1 and G6Pase promoter activity and endogenous Igfbp-1 and G6Pase gene expression in simian virus 40-transformed (SV40-transformed) hepatocytes. Importantly, mutagenesis of the LXXLL motif eliminated FoxO1 interaction with the nicotinamide adenine dinucleotide-dependent (NAD-dependent) deacetylase sirtuin 1 (Sirt1), sustained the acetylated state of FoxO1, and made FoxO1 nicotinamide and resveratrol insensitive, supporting a role for this motif in Sirt1 binding. Furthermore, intravenous administration of adenovirus encoding 3A/LXXAA FoxO1 into Lepr db/db mice decreased fasting blood glucose levels and improved glucose tolerance and was accompanied by reduced G6Pase and Igfbp-1 gene expression and increased hepatic glycogen content. In conclusion, the LXXLL motif of FoxO1 may have an important role for its transcriptional activity and Sirt1 binding and should be a target site for regulation of gene expression of FoxO1 target genes and glucose metabolism in vivo.
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Affiliation(s)
- Jun Nakae
- Department of Clinical Molecular Medicine, Division of Diabetes, Digestive and Kidney Disease, Kobe University Graduate School of Medicine, Kobe, Japan.
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224
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Lee FY, Lee H, Hubbert ML, Edwards PA, Zhang Y. FXR, a multipurpose nuclear receptor. Trends Biochem Sci 2006; 31:572-80. [PMID: 16908160 DOI: 10.1016/j.tibs.2006.08.002] [Citation(s) in RCA: 259] [Impact Index Per Article: 14.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2006] [Revised: 07/14/2006] [Accepted: 08/03/2006] [Indexed: 12/20/2022]
Abstract
The farnesoid X receptor (FXR) is a ligand-activated transcription factor and a member of the nuclear receptor superfamily. In the past six years, remarkable inroads have been made into determining the functional importance of FXR. This receptor has been shown to have crucial roles in controlling bile acid homeostasis, lipoprotein and glucose metabolism, hepatic regeneration, intestinal bacterial growth and the response to hepatotoxins. Thus, the development of FXR agonists might prove useful for the treatment of diabetes, cholesterol gallstones, and hepatic and intestinal toxicity.
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Affiliation(s)
- Florence Y Lee
- Department of Biological Chemistry, University of California at Los Angeles, Los Angeles, CA 90095, USA
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225
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Modica S, Moschetta A. Nuclear bile acid receptor FXR as pharmacological target: are we there yet? FEBS Lett 2006; 580:5492-9. [PMID: 16904670 DOI: 10.1016/j.febslet.2006.07.082] [Citation(s) in RCA: 72] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2006] [Revised: 07/11/2006] [Accepted: 07/20/2006] [Indexed: 12/12/2022]
Abstract
The farnesoid X receptor (FXR) is a member of the nuclear receptor superfamily that is primarily expressed in the enterohepatic system where it functions as intracellular sensor for bile acids. Ligand dependent FXR activation induces transcriptional responses to coordinately regulate bile acid, cholesterol, triglyceride and glucose metabolism, and to protect the intestinal mucosa from bacterial overgrowth and inflammatory insults. Here we discuss the latest discoveries in FXR-driven metabolic pathways with relevance to pathophysiology and novel therapeutic approaches of several conditions such as hypertriglyceridemia, type 2 diabetes, cholesterol gallstone disease, steato-hepatitis and metabolic syndrome.
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Affiliation(s)
- Salvatore Modica
- Department of Cell Biology and Oncology, Consorzio Mario Negri Sud, Via Nazionale 8A, Santa Maria Imbaro Chieti, CH, Chieti 66030, Italy
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226
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Li T, Kong X, Owsley E, Ellis E, Strom S, Chiang JY. Insulin regulation of cholesterol 7alpha-hydroxylase expression in human hepatocytes: roles of forkhead box O1 and sterol regulatory element-binding protein 1c. J Biol Chem 2006; 281:28745-54. [PMID: 16885156 PMCID: PMC1576296 DOI: 10.1074/jbc.m605815200] [Citation(s) in RCA: 73] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
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.
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Affiliation(s)
- Tiangang Li
- Department of Microbiology, Immunology and Biochemistry, Northeastern Ohio Univ’s College of Medicine, Rootstown, OH 44272
| | - Xiaoying Kong
- Department of Microbiology, Immunology and Biochemistry, Northeastern Ohio Univ’s College of Medicine, Rootstown, OH 44272
| | - Erika Owsley
- Department of Microbiology, Immunology and Biochemistry, Northeastern Ohio Univ’s College of Medicine, Rootstown, OH 44272
| | - Ewa Ellis
- Department of Pathology, University of Pittsburgh Medical Center, Pittsburgh, PA 15213
| | - Stephan Strom
- Department of Pathology, University of Pittsburgh Medical Center, Pittsburgh, PA 15213
| | - John Y.L. Chiang
- Department of Microbiology, Immunology and Biochemistry, Northeastern Ohio Univ’s College of Medicine, Rootstown, OH 44272
- Corresponding author address: John Y. L. Chiang, Department of Microbiology, Immunology and Biochemistry, Northeastern Ohio Univ’s College of Medicine, 4209 State Route 44, Rootstown, OH 44272, Tel: 330-325-6694, Fax: 330-325-5910, e-mail:
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227
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Heishi M, Ichihara J, Teramoto R, Itakura Y, Hayashi K, Ishikawa H, Gomi H, Sakai J, Kanaoka M, Taiji M, Kimura T. Global gene expression analysis in liver of obese diabetic db/db mice treated with metformin. Diabetologia 2006; 49:1647-55. [PMID: 16752183 DOI: 10.1007/s00125-006-0271-y] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/06/2006] [Accepted: 03/07/2006] [Indexed: 12/19/2022]
Abstract
AIMS/HYPOTHESIS Metformin is widely used as a hypoglycaemic reagent for type 2 diabetes. While the reduction of hepatic gluconeogenesis is thought to be a key effect, the detailed molecular mechanism of action of metformin remains to be elucidated. To gain insight into this, we performed a global gene expression profiling study. MATERIALS AND METHODS We performed DNA microarray analysis to study global gene expression in the livers of obese diabetic db/db mice 2 h after a single administration of metformin (400 mg/kg). RESULTS This analysis identified 14 genes that showed at least a 1.5-fold difference in expression following metformin treatment, including a reduction of glucose-6-phosphatase gene expression. The mRNA levels of glucose-6-phosphatase showed one of the best correlations with blood glucose levels among 12,000 genes. Enzymatic activity of glucose-6-phosphatase was also reduced in metformin-treated liver. Moreover, intensive analysis of the expression profile revealed that metformin effected significant alterations in gene expression across at least ten metabolic pathways, including those involved in glycolysis-gluconeogenesis, fatty acid metabolism and amino acid metabolism. CONCLUSIONS/INTERPRETATION These results suggest that reduction of glucose-6-phosphatase activity, as well as suppression of mRNA expression levels of this gene, in liver is of prime importance for controlling blood glucose levels in vivo, at least at early time points after metformin treatment. Our results also suggest that metformin not only affects expression of specific genes, but also alters the expression level of multiple genes linked to the metabolic pathways involved in glucose and lipid metabolism in the liver.
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Affiliation(s)
- M Heishi
- Dainippon Sumitomo Pharma, 3-1-98, Kasugade-naka, Konohana, Osaka, 554-0022, Japan
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228
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Abstract
The nuclear farnesoid X receptor (FXR) plays a pivotal role in maintaining bile acid homeostasis by regulating key genes involved in bile acid synthesis, metabolism and transport, including CYP7A1, UGT2B4, BSEP, MDR3, MRP2, ASBT, I-BABP, NTCP and OSTalpha-OSTbeta in humans. Altered expression or malfunction of these genes has been described in patients with cholestatic liver diseases. This review examines the rationale for the use of FXR ligand therapy in various cholestatic liver disorders and includes potential concerns.
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Affiliation(s)
- Shi-Ying Cai
- Liver Center, Department of Medicine, Yale University School of Medicine, P.O. Box 208019, New Haven, CT 06520-8019, USA
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229
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Bilz S, Samuel V, Morino K, Savage D, Choi CS, Shulman GI. Activation of the farnesoid X receptor improves lipid metabolism in combined hyperlipidemic hamsters. Am J Physiol Endocrinol Metab 2006; 290:E716-22. [PMID: 16291572 DOI: 10.1152/ajpendo.00355.2005] [Citation(s) in RCA: 77] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The transcription factor farnesoid X receptor (FXR) has recently been implicated in the control of hepatic triglyceride production. Activation of FXR may ameliorate hypertriglyceridemia, a cardinal feature of the metabolic syndrome. Because hamsters share many characteristic features of human lipid metabolism, we used a high-fructose-fed hamster model to study the impact of FXR activation with chenodeoxycholic acid (CDCA) on plasma lipoprotein metabolism. Male Syrian hamsters fed a diet containing 60% kcal from fructose for 2 wk developed hypertriglyceridemia and hypercholesterolemia (+120 and +60%, P = 0.005 and 0.0004 vs. controls) due to increased hepatic lipoprotein production. This could be largely attributed to enhanced hepatic de novo lipogenesis, as indicated by increased expression of sterol regulatory element-binding protein-1, fatty acid synthase, and steaoryl-CoA desaturase-1. Lipoprotein analysis demonstrated that the increase in plasma triglycerides occurred in the VLDL density range, whereas increases in VLDL, IDL/LDL, and HDL cholesterol accounted for the elevated plasma cholesterol concentrations. Addition of 0.1% CDCA to the high-fructose diet decreased hepatic de novo lipogenesis and consequently triglyceride production and prevented the increases in plasma triglycerides and cholesterol (-40 and -18%, P = 0.03 and 0.03 vs. high fructose-fed animals). CDCA-treated animals had lower VLDL triglycerides and decreased VLDL and IDL/LDL cholesterol plasma concentrations. These data demonstrate that activation of FXR with CDCA effectively lowers plasma triglyceride and cholesterol concentrations, mainly by decreasing de novo lipogenesis and hepatic secretion of triglyceride-rich lipoproteins. Our studies identify activators of FXR as promising new tools in the therapy of hypertriglyceridemic states, including the insulin resistance syndrome and type 2 diabetes.
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Affiliation(s)
- Stefan Bilz
- Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut 06536-8012, USA
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230
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Ma K, Saha PK, Chan L, Moore DD. Farnesoid X receptor is essential for normal glucose homeostasis. J Clin Invest 2006; 116:1102-9. [PMID: 16557297 PMCID: PMC1409738 DOI: 10.1172/jci25604] [Citation(s) in RCA: 655] [Impact Index Per Article: 36.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2005] [Accepted: 01/31/2006] [Indexed: 12/13/2022] Open
Abstract
The bile acid receptor farnesoid X receptor (FXR; NR1H4) is a central regulator of bile acid and lipid metabolism. We show here that FXR plays a key regulatory role in glucose homeostasis. FXR-null mice developed severe fatty liver and elevated circulating FFAs, which was associated with elevated serum glucose and impaired glucose and insulin tolerance. Their insulin resistance was confirmed by the hyperinsulinemic euglycemic clamp, which showed attenuated inhibition of hepatic glucose production by insulin and reduced peripheral glucose disposal. In FXR-/- skeletal muscle and liver, multiple steps in the insulin signaling pathway were markedly blunted. In skeletal muscle, which does not express FXR, triglyceride and FFA levels were increased, and we propose that their inhibitory effects account for insulin resistance in that tissue. In contrast to the results in FXR-/- mice, bile acid activation of FXR in WT mice repressed expression of gluconeogenic genes and decreased serum glucose. The absence of this repression in both FXR-/- and small heterodimer partner-null (SHP-/-) mice demonstrated that the previously described FXR-SHP nuclear receptor cascade also targets glucose metabolism. Taken together, our results identify a link between lipid and glucose metabolism mediated by the FXR-SHP cascade.
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Affiliation(s)
- Ke Ma
- Department of Molecular and Cellular Biology and
Section of Endocrinology and Metabolism, Departments of Molecular and Cellular Biology and Medicine, Baylor College of Medicine, Houston, Texas, USA
| | - Pradip K. Saha
- Department of Molecular and Cellular Biology and
Section of Endocrinology and Metabolism, Departments of Molecular and Cellular Biology and Medicine, Baylor College of Medicine, Houston, Texas, USA
| | - Lawrence Chan
- Department of Molecular and Cellular Biology and
Section of Endocrinology and Metabolism, Departments of Molecular and Cellular Biology and Medicine, Baylor College of Medicine, Houston, Texas, USA
| | - David D. Moore
- Department of Molecular and Cellular Biology and
Section of Endocrinology and Metabolism, Departments of Molecular and Cellular Biology and Medicine, Baylor College of Medicine, Houston, Texas, USA
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231
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Houten SM, Watanabe M, Auwerx J. Endocrine functions of bile acids. EMBO J 2006; 25:1419-25. [PMID: 16541101 PMCID: PMC1440314 DOI: 10.1038/sj.emboj.7601049] [Citation(s) in RCA: 414] [Impact Index Per Article: 23.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2005] [Accepted: 02/24/2006] [Indexed: 12/19/2022] Open
Abstract
Bile acids (BAs), a group of structurally diverse molecules that are primarily synthesized in the liver from cholesterol, are the chief components of bile. Besides their well-established roles in dietary lipid absorption and cholesterol homeostasis, it has recently emerged that BAs are also signaling molecules, with systemic endocrine functions. BAs activate mitogen-activated protein kinase pathways, are ligands for the G-protein-coupled receptor TGR5, and activate nuclear hormone receptors such as farnesoid X receptor alpha. Through activation of these diverse signaling pathways, BAs can regulate their own enterohepatic circulation, but also triglyceride, cholesterol, energy, and glucose homeostasis. Thus, BA-controlled signaling pathways are promising novel drug targets to treat common metabolic diseases, such as obesity, type II diabetes, hyperlipidemia, and atherosclerosis.
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Affiliation(s)
- Sander M Houten
- Laboratory Genetic Metabolic Diseases, Academic Medical Center, Amsterdam, The Netherlands
| | - Mitsuhiro Watanabe
- Institut de Génétique et Biologie Moléculaire et Cellulaire (IGBMC), CNRS/INSERM/ULP, Illkirch, France
| | - Johan Auwerx
- Institut de Génétique et Biologie Moléculaire et Cellulaire (IGBMC), CNRS/INSERM/ULP, Illkirch, France
- Institut Clinique de la Souris, Illkirch, France
- Laboratoire de Biochimie Générale et Spécialisée, Hôpitaux Universitaires de Strasbourg, Strasbourg, France
- Institut de Génétique et Biologie Moléculaire et Cellulaire, 1 rue Laurent Fries, Parc d'Innovation, BP10142, 67404 Illkirch, France. Tel.: +33 388 653425; Fax: +33 388 653201; E-mail:
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232
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Furihata T, Hosokawa M, Masuda M, Satoh T, Chiba K. Hepatocyte nuclear factor-4alpha plays pivotal roles in the regulation of mouse carboxylesterase 2 gene transcription in mouse liver. Arch Biochem Biophys 2006; 447:107-17. [PMID: 16527247 DOI: 10.1016/j.abb.2006.01.015] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2005] [Revised: 01/25/2006] [Accepted: 01/25/2006] [Indexed: 10/25/2022]
Abstract
The mouse carboxylesterase 2 isozyme, mCES2, is thought to play important roles in lipid metabolism and is expressed in the liver, kidney, and small intestine at high levels. In this study, we examined the molecular mechanisms controlling this tissue-specific expression of mCES2, and demonstrated that hepatocyte nuclear factor-4alpha (HNF-4alpha) could enhance transcription of the mCES2 gene in vitro and in vivo. It was found that effects of HNF-4alpha on the level of mCES2 promoter activity were repressed by small heterodimer partner (SHP) and chenodeoxycholic acid (CDCA) in luciferase assays. Accordingly, mCES2 gene transcription was repressed by CDCA treatment in mouse immortalized hepatocytes. Our results suggested that this repression resulted from the combined effects of both inhibition of HNF-4alpha transactivation ability by SHP and reduction of HNF-4alpha expression level. These findings show that HNF-4alpha plays an important role in the regulation of mCES2 gene transcription.
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Affiliation(s)
- Tomomi Furihata
- Laboratory of Pharmacology and Toxicology, Graduate School of Pharmaceutical Sciences, Chiba University, Chiba 260-8675, Japan
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Cariou B, van Harmelen K, Duran-Sandoval D, van Dijk TH, Grefhorst A, Abdelkarim M, Caron S, Torpier G, Fruchart JC, Gonzalez FJ, Kuipers F, Staels B. The farnesoid X receptor modulates adiposity and peripheral insulin sensitivity in mice. J Biol Chem 2006; 281:11039-49. [PMID: 16446356 DOI: 10.1074/jbc.m510258200] [Citation(s) in RCA: 411] [Impact Index Per Article: 22.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
The farnesoid X receptor (FXR) is a bile acid (BA)-activated nuclear receptor that plays a major role in the regulation of BA and lipid metabolism. Recently, several studies have suggested a potential role of FXR in the control of hepatic carbohydrate metabolism, but its contribution to the maintenance of peripheral glucose homeostasis remains to be established. FXR-deficient mice display decreased adipose tissue mass, lower serum leptin concentrations, and elevated plasma free fatty acid levels. Glucose and insulin tolerance tests revealed that FXR deficiency is associated with impaired glucose tolerance and insulin resistance. Moreover, whole-body glucose disposal during a hyperinsulinemic euglycemic clamp is decreased in FXR-deficient mice. In parallel, FXR deficiency alters distal insulin signaling, as reflected by decreased insulin-dependent Akt phosphorylation in both white adipose tissue and skeletal muscle. Whereas FXR is not expressed in skeletal muscle, it was detected at a low level in white adipose tissue in vivo and induced during adipocyte differentiation in vitro. Moreover, mouse embryonic fibroblasts derived from FXR-deficient mice displayed impaired adipocyte differentiation, identifying a direct role for FXR in adipocyte function. Treatment of differentiated 3T3-L1 adipocytes with the FXR-specific synthetic agonist GW4064 enhanced insulin signaling and insulin-stimulated glucose uptake. Finally, treatment with GW4064 improved insulin resistance in genetically obese ob/ob mice in vivo. Although the underlying molecular mechanisms remain to be unraveled, these results clearly identify a novel role of FXR in the regulation of peripheral insulin sensitivity and adipocyte function. This unexpected function of FXR opens new perspectives for the treatment of type 2 diabetes.
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Affiliation(s)
- Bertrand Cariou
- Institut Pasteur de Lille, Département d'Athérosclérose, Lille, F-59019, France
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234
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Zhang Y, Lee FY, Barrera G, Lee H, Vales C, Gonzalez FJ, Willson TM, Edwards PA. Activation of the nuclear receptor FXR improves hyperglycemia and hyperlipidemia in diabetic mice. Proc Natl Acad Sci U S A 2006; 103:1006-11. [PMID: 16410358 PMCID: PMC1347977 DOI: 10.1073/pnas.0506982103] [Citation(s) in RCA: 711] [Impact Index Per Article: 39.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2005] [Indexed: 02/06/2023] Open
Abstract
Farnesoid X receptor (FXR) plays an important role in maintaining bile acid and cholesterol homeostasis. Here we demonstrate that FXR also regulates glucose metabolism. Activation of FXR by the synthetic agonist GW4064 or hepatic overexpression of constitutively active FXR by adenovirus-mediated gene transfer significantly lowered blood glucose levels in both diabetic db/db and wild-type mice. Consistent with these data, FXR null mice exhibited glucose intolerance and insulin insensitivity. We further demonstrate that activation of FXR in db/db mice repressed hepatic gluconeogenic genes and increased hepatic glycogen synthesis and glycogen content by a mechanism that involves enhanced insulin sensitivity. In view of its central roles in coordinating regulation of both glucose and lipid metabolism, we propose that FXR agonists are promising therapeutic agents for treatment of diabetes mellitus.
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Affiliation(s)
- Yanqiao Zhang
- Department of Biological Chemistry, University of California, Los Angeles, CA 90095, USA
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235
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Abstract
Liver X receptors (LXRs) and farnesoid X receptor (FXR) are nuclear receptors that function as intracellular sensors for sterols and bile acids, respectively. In response to their ligands, these receptors induce transcriptional responses that maintain a balanced, finely tuned regulation of cholesterol and bile acid metabolism. LXRs also permit the efficient storage of carbohydrate- and fat-derived energy, whereas FXR activation results in an overall decrease in triglyceride levels and modulation of glucose metabolism. The elegant, dual interplay between these two receptor systems suggests that they coevolved to constitute a highly sensitive and efficient system for the maintenance of total body fat and cholesterol homeostasis. Emerging evidence suggests that the tissue-specific action of these receptors is also crucial for the proper function of the cardiovascular, immune, reproductive, endocrine pancreas, renal, and central nervous systems. Together, LXRs and FXR represent potential therapeutic targets for the treatment and prevention of numerous metabolic and lipid-related diseases.
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Affiliation(s)
- Nada Y Kalaany
- Whitehead Institute for Biomedical Research, Massachusetts Institute of Technology, Cambridge, Massachusetts 02142, USA.
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236
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Nozawa H. Xanthohumol, the chalcone from beer hops (Humulus lupulus L.), is the ligand for farnesoid X receptor and ameliorates lipid and glucose metabolism in KK-A(y) mice. Biochem Biophys Res Commun 2005; 336:754-61. [PMID: 16140264 DOI: 10.1016/j.bbrc.2005.08.159] [Citation(s) in RCA: 88] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2005] [Accepted: 08/21/2005] [Indexed: 11/17/2022]
Abstract
We have examined the modulating action of xanthohumol (XN) on the farnesoid X receptor (FXR) in vitro and in vivo. In the transient transfection assay, XN dose-dependently increased the BSEP promoter-driven luciferase activity. XN-fed KK-A(y) mice exhibited lowered levels of plasma glucose, plasma, and hepatic triglyceride. They also showed decreased amounts of water intake, lowered weights of white adipose tissue, and exhibited increased levels of plasma adiponectin, indicating that XN attenuated diabetes in KK-A(y) mice. The hepatic gene expression of XN-fed mice showed lowered levels of SREBP-1c including its targets involved in fatty acid synthesis and lowered levels of gluconeogenetic genes. However, the expression of cholesterol 7-hydroxylase (CYP7A1) was significantly induced in the liver of XN-fed mice. From the present results, it is suggested that XN acts on FXR through a selective bile acid receptor modulator (SBARM) like guggulsterone or polyunsaturated fatty acids, which have previously been reported as SBARMs.
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Affiliation(s)
- Hajime Nozawa
- R&D Laboratory, Functional Food Division, Kirin Brewery Co., Ltd., 3 Miyahara, Takasaki, Gunma 370-1295, Japan.
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237
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Claudel T, Staels B, Kuipers F. The Farnesoid X receptor: a molecular link between bile acid and lipid and glucose metabolism. Arterioscler Thromb Vasc Biol 2005; 25:2020-30. [PMID: 16037564 DOI: 10.1161/01.atv.0000178994.21828.a7] [Citation(s) in RCA: 350] [Impact Index Per Article: 18.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Bile acids are the end products of cholesterol metabolism. They are synthesized in the liver and secreted via bile into the intestine, where they aid in the absorption of fat-soluble vitamins and dietary fat. Subsequently, bile acids return to the liver to complete their enterohepatic circulation. The Farnesoid X receptor (FXR) is a member of the nuclear receptor superfamily and has emerged as a key player in the control of multiple metabolic pathways. On its activation by bile acids, FXR regulates bile acid synthesis, conjugation, and transport, as well as various aspects of lipid and glucose metabolism. This review summarizes recent advances in deciphering the role of FXR in the context of hepatic lipid and glucose homeostasis and discusses the potential of FXR as a pharmacological target for therapeutic applications.
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Affiliation(s)
- Thierry Claudel
- Center for Liver, Digestive, and Metabolic Diseases, University Medical Center Groningen, 9700 RB Groningen, The Netherlands.
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238
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Cariou B, van Harmelen K, Duran-Sandoval D, van Dijk T, Grefhorst A, Bouchaert E, Fruchart JC, Gonzalez FJ, Kuipers F, Staels B. Transient impairment of the adaptive response to fasting in FXR-deficient mice. FEBS Lett 2005; 579:4076-80. [PMID: 16023103 DOI: 10.1016/j.febslet.2005.06.033] [Citation(s) in RCA: 64] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2005] [Accepted: 06/17/2005] [Indexed: 10/25/2022]
Abstract
The farnesoid X receptor (FXR) has been suggested to play a role in gluconeogenesis. To determine whether FXR modulates the response to fasting in vivo, FXR-deficient (FXR-/-) and wild-type mice were submitted to fasting for 48 h. Our results demonstrate that FXR modulates the kinetics of alterations of glucose homeostasis during fasting, with FXR-/- mice displaying an early, accelerated hypoglycaemia response. Basal hepatic glucose production rate was lower in FXR-/- mice, together with a decrease in hepatic glycogen content. Moreover, hepatic PEPCK gene expression was transiently lower in FXR-/- mice after 6h of fasting and was decreased in FXR-/- hepatocytes. FXR therefore plays an unexpected role in the control of fuel availability upon fasting.
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Affiliation(s)
- Bertrand Cariou
- Research Unit 545 INSERM, Atherosclerosis Department, Pasteur Institute of Lille, Faculty of Pharmacy, Lille2 University, Lille, France
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239
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Duran-Sandoval D, Cariou B, Fruchart JC, Staels B. Potential regulatory role of the farnesoid X receptor in the metabolic syndrome. Biochimie 2005; 87:93-8. [PMID: 15733743 DOI: 10.1016/j.biochi.2004.11.018] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2004] [Accepted: 11/23/2004] [Indexed: 01/12/2023]
Abstract
Dyslipidemia and gallbladder diseases are two current anomalies observed in patients suffering from the metabolic syndrome and type 2 diabetes. The bile acid-activated nuclear receptor farnesoid X receptor (FXR) controls bile acid as well as lipid metabolism. Recent observations indicate a role for FXR also in carbohydrate metabolism. Hepatic FXR expression is altered in diabetic animal models in vivo and regulated by hormones and nutrients in vitro. At the molecular level, FXR activation modifies the transcriptional activity of different transcription factors controlling gluconeogenesis and lipogenesis, thus affecting in concert bile acid, lipid and carbohydrate metabolism. The present review focuses on recent advances in our understanding of the modulation of carbohydrate metabolism by FXR. These observations raise the intriguing possibility for a modulatory role of this receptor also in the metabolic syndrome.
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Affiliation(s)
- Daniel Duran-Sandoval
- U.R.545 Inserm, Département d'Atherosclerosis, Institut Pasteur de Lille et Faculté de Pharmacie, Université de Lille 2, 1, rue du Professeur-Calmette, BP245, 59019 Lille, France
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240
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Duran-Sandoval D, Cariou B, Percevault F, Hennuyer N, Grefhorst A, van Dijk TH, Gonzalez FJ, Fruchart JC, Kuipers F, Staels B. The farnesoid X receptor modulates hepatic carbohydrate metabolism during the fasting-refeeding transition. J Biol Chem 2005; 280:29971-9. [PMID: 15899888 DOI: 10.1074/jbc.m501931200] [Citation(s) in RCA: 174] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The liver plays a central role in the control of blood glucose homeostasis by maintaining a balance between glucose production and utilization. The farnesoid X receptor (FXR) is a bile acid-activated nuclear receptor. Hepatic FXR expression is regulated by glucose and insulin. Here we identify a role for FXR in the control of hepatic carbohydrate metabolism. When submitted to a controlled fasting-refeeding schedule, FXR(-/-) mice displayed an accelerated response to high carbohydrate refeeding with an accelerated induction of glycolytic and lipogenic genes and a more pronounced repression of gluconeogenic genes. Plasma insulin and glucose levels were lower in FXR(-/-) mice upon refeeding the high-carbohydrate diet. These alterations were paralleled by decreased hepatic glycogen content. Hepatic insulin sensitivity was unchanged in FXR(-/-) mice. Treatment of isolated primary hepatocytes with a synthetic FXR agonist attenuated glucose-induced mRNA expression as well as promoter activity of L-type pyruvate kinase, acetyl-CoA carboxylase 1, and Spot14. Moreover, activated FXR interfered negatively with the carbohydrate response elements regions. These results identify a novel role for FXR as a modulator of hepatic carbohydrate metabolism.
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Affiliation(s)
- Daniel Duran-Sandoval
- U.R. 545 INSERM, Atherosclerosis Department, Pasteur Institute of Lille and the Faculty of Pharmacy, Lille2 University, France
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241
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Abstract
There is increasing evidence that Forkhead box 'Other' (FoxO) proteins, a subgroup of the Forkhead transcription factor family, have an important role in mediating the effects of insulin and growth factors on diverse physiological functions, including cell proliferation, apoptosis and metabolism. Genetic studies in Caenorhabditis (Caenorhabditis elegans) and Drosophila demonstrate that FoxO proteins are ancient targets of insulin-like signaling involved in the regulation of metabolism and longevity. Studies in mammalian cells reveal that FoxO proteins regulate cell cycle progression and promote resistance to oxidative stress; both in vivo and cell culture studies support the concept that FoxO proteins have an important role in mediating the effects of insulin on metabolism, including its effects on hepatic glucose production. Phosphorylation and acetylation modulate FoxO function and control nuclear-cytoplasmic shuttling, DNA binding and protein-protein interactions. FoxO transcription factors exert positive and negative effects on gene expression, through direct binding to DNA target sites and protein-protein interactions with other transcription factors and coactivators. This paper provides an overview of studies leading to the identification of FoxO proteins as targets of insulin action and the mechanisms mediating the effects of insulin-like signaling on FoxO function, emphasizing the role of FoxO proteins in mediating the effects of insulin on metabolism.
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Affiliation(s)
- Andreas Barthel
- Department of Endocrinology, Diabetes and Rheumatology, University Hospital Düsseldorf, Moorenstrasse 5, D-40225 Düsseldorf, Germany
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242
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Anisfeld AM, Kast-Woelbern HR, Lee H, Zhang Y, Lee FY, Edwards PA. Activation of the nuclear receptor FXR induces fibrinogen expression: a new role for bile acid signaling. J Lipid Res 2005; 46:458-68. [PMID: 15604525 DOI: 10.1194/jlr.m400292-jlr200] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Three genes, fibrinogen-alpha (FBGalpha), -beta, and -gamma, encode proteins that make up the mature FBG protein complex. This complex is secreted from the liver and plays a key role in coagulation in response to vascular disruption. We identified all three FBG genes in a screen designed to isolate genes that are regulated by the farnesoid X receptor (FXR; NR1H4). Treatment of human hepatoma cells with either naturally occurring or synthetic [3-(2,6-dichlorophenyl)-4-(3'-carboxy-2-chloro-stilben-4-yl)-oxymethyl-5-isopropyl-isoxazole] FXR ligands resulted in the induction of transcripts for all three genes. The induction of FBGbeta mRNA in response to activated FXR appears to be a primary transcriptional response, as it is blocked by actinomycin D but not by cycloheximide. Four FXR isoforms were recently identified that differ either at their N termini and/or by the presence of four amino acids in the hinge region. Interestingly, the activities of the human FBGbeta promoter-reporter constructs were highly induced by FXR isoforms that lack the four amino acid insert. The observation that all three FBG subunits are induced by specific FXR isoforms, in response to FXR ligands, suggests that bile acids and FXR modulate fibrinolytic activity.
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Affiliation(s)
- Andrew M Anisfeld
- Department of Biological Chemistry and Medicine, University of California Los Angeles, Los Angeles, CA 90095, USA
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243
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Cariou B, Duran-Sandoval D, Kuipers F, Staels B. Farnesoid X receptor: a new player in glucose metabolism? Endocrinology 2005; 146:981-3. [PMID: 15713939 DOI: 10.1210/en.2004-1595] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Affiliation(s)
- Bertrand Cariou
- Unité de Recherche 545, Institut National de la Santé et de la Recherche Médicale, Départment d'Athérosclérose, Institut Pasteur de Lille & Faculté de Pharmacie, Université de Lille 2, BP245-59019 Lille, France
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244
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Stayrook KR, Bramlett KS, Savkur RS, Ficorilli J, Cook T, Christe ME, Michael LF, Burris TP. Regulation of carbohydrate metabolism by the farnesoid X receptor. Endocrinology 2005; 146:984-91. [PMID: 15564327 DOI: 10.1210/en.2004-0965] [Citation(s) in RCA: 215] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
The farnesoid X receptor (FXR; NR1H4) is a nuclear hormone receptor that functions as the bile acid receptor. In addition to the critical role FXR plays in bile acid metabolism and transport, it regulates a variety of genes important in lipoprotein metabolism. We demonstrate that FXR also plays a role in carbohydrate metabolism via regulation of phosphoenolpyruvate carboxykinase (PEPCK) gene expression. Treatment of either H4IIE or MH1C1 rat hepatoma cell lines as well as primary rat or human hepatocytes with FXR agonists led to stimulation of PEPCK mRNA expression to levels comparable to those obtained with glucocorticoid receptor agonists. We examined the physiological significance of FXR agonist-induced enhancement of PEPCK expression in primary rat hepatocytes. In addition to inducing PEPCK expression in primary hepatocytes, FXR agonists stimulated glucose output to levels comparable to those observed with a glucocorticoid receptor agonist. Consistent with these observations, treatment of C57BL6 mice with GW4064 significantly increased hepatic PEPCK expression. Activation of FXR initiated a cascade involving induction of peroxisome proliferator-activated receptor alpha and TRB3 expression that is consistent with stimulation of PEPCK gene expression via interference with a pathway that may involve Akt-dependent phosphorylation of Forkhead/winged helix transcription factor (FOXO1). The FXR-peroxisome proliferator-activated receptor alpha-TRB3 pathway was conserved in rat hepatoma cell lines, mice, as well as primary human hepatocytes. Thus, in addition to its role in the regulation of lipid metabolism, FXR regulates carbohydrate metabolism.
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Affiliation(s)
- Keith R Stayrook
- Lilly Research Laboratories, Lilly Corporate Center, Indianapolis, Indiana 46285, USA
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245
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Kim JY, Kim HJ, Kim KT, Park YY, Seong HA, Park KC, Lee IK, Ha H, Shong M, Park SC, Choi HS. Orphan nuclear receptor small heterodimer partner represses hepatocyte nuclear factor 3/Foxa transactivation via inhibition of its DNA binding. Mol Endocrinol 2004; 18:2880-94. [PMID: 15358835 DOI: 10.1210/me.2004-0211] [Citation(s) in RCA: 67] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Small heterodimer partner (SHP; NR0B2) is an atypical orphan nuclear receptor and acts as a coregulator of various nuclear receptors. Herein, we examined a novel cross talk between SHP and a forkhead transcription factor HNF3 (hepatocyte nuclear factor 3/Foxa. Transient transfection assay demonstrated that SHP inhibited the transcriptional activity of all three isoforms of HNF3, HNF3alpha, beta, and gamma. In vivo and in vitro protein interaction studies showed that SHP physically interacted with HNF3. Adenovirus-mediated overexpression of SHP significantly decreased the mRNA levels of glucose-6-phosphase (G6Pase), cholesterol 7-alpha-hydroxylase (CYP7A1), and phosphoenolpyruvate carboxykinase (PEPCK) in HepG2 cells and rat primary hepatocytes. Moreover, the mRNA level of G6Pase was notably increased by down-regulation of SHP with small interfering RNA. Interestingly, HNF3 transactivity was still repressed by SHPDelta128-139 that fails to repress nuclear receptors. Mapping of interaction domain revealed that SHP interacted with forkhead DNA binding domain of HNF3alpha. Gel mobility shift and chromatin immunoprecipitation assays demonstrated that SHP inhibits DNA binding of HNF3. These results suggest that SHP is involved in the regulation of G6Pase, CYP7A1, and PEPCK gene expression via novel mechanism of inhibition of HNF3 activity and expand the role of SHP as a coregulator of other family of transcription factors in addition to nuclear receptors.
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Affiliation(s)
- Joon-Young Kim
- Hormone Research Center, Chonnam National University, Gwangju 500-757, Korea
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246
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Hirokane H, Nakahara M, Tachibana S, Shimizu M, Sato R. Bile acid reduces the secretion of very low density lipoprotein by repressing microsomal triglyceride transfer protein gene expression mediated by hepatocyte nuclear factor-4. J Biol Chem 2004; 279:45685-92. [PMID: 15337761 DOI: 10.1074/jbc.m404255200] [Citation(s) in RCA: 125] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Microsomal triglyceride transfer protein (MTP) is involved in the transfer of triglycerides, cholesterol esters, and phospholipids to newly synthesized apolipoprotein (apo) B. It is therefore essential for lipoprotein synthesis and secretion in the liver and the small intestine. Although several recent experiments have revealed the transcriptional regulation of the MTP gene, little has been revealed to date about hepatocyte nuclear factor-4 (HNF-4)-dependent regulation. We here report that the human MTP gene promoter contains a pair of functional responsive elements for HNF-4 and HNF-1, the latter of which is another target gene of HNF-4. Chromatin immunoprecipitation assays provide evidence that endogenous HNF-4 and HNF-1 can bind these elements in chromatin. In Hep G2 cells overexpression of either a dominant negative form of HNF-4 or small interfering RNAs (siRNAs) against HNF-4 dramatically reduces the activities of both the wild type and the HNF-4 site mutant MTP promoter. This suggests that HNF-4 regulates MTP gene expression either directly or indirectly through elevated HNF-1 levels. When Hep G2 cells were cultured with chenodeoxycholic acid (CDCA), a ligand for the farnesoid X receptor (FXR), mRNA levels for MTP and apo B were reduced because of increased expression of the factor small heterodimer partner (SHP), which factor suppresses HNF-4 activities. Chenodeoxycholic acid, but not a synthetic FXR ligand, attenuated expression of HNF-4, bringing about a further suppression of MTP gene expression. Over time the intracellular MTP protein levels and apo B secretion in the culture medium significantly declined. These results indicate that two nuclear receptors, HNF-4 and FXR, are closely involved in MTP gene expression, and the results provide evidence for a novel interaction between bile acids and lipoprotein metabolism.
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Affiliation(s)
- Hisako Hirokane
- Department of Applied Biological Chemistry, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Tokyo 113-8657, Japan
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