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Orphan nuclear receptor small heterodimer partner (SHP) plays a key role in transcriptional repression of gluconeogenic enzyme gene expression. Here, we show that SHP inhibited protein kinase A-mediated transcriptional activity of cAMP-response element-binding protein (CREB), a major regulator of glucose metabolism, to modulate hepatic gluconeogenic gene expression. Deletion analysis of phosphoenolpyruvate carboxykinase (PEPCK) promoter demonstrated that SHP inhibited forskolin-mediated induction of PEPCK gene transcription via inhibition of CREB transcriptional activity. In vivo imaging demonstrated that SHP inhibited CREB-regulated transcription coactivator 2 (CRTC2)-mediated cAMP-response elementdriven promoter activity. Furthermore, overexpression of SHP using adenovirus SHP decreased CRTC2-dependent elevations in blood glucose levels and PEPCK or glucose-6-phosphatase (G6Pase) expression in mice. SHP and CREB physically interacted and were co-localized in vivo. Importantly, SHP inhibited both wild type CRTC2 and S171A (constitutively active form of CRTC2) coactivator activity and disrupted CRTC2 recruitment on the PEPCK gene promoter. In addition, metformin or overexpression of a constitutively active form of AMPK (Ad-CA-AMPK) inhibited S171A-mediated PEPCK and G6Pase gene expression, and hepatic glucose production and knockdown of SHP partially relieved the metformin-and Ad-CA-AMPK-mediated repression of hepatic gluconeogenic enzyme gene expression in primary rat hepatocytes. In conclusion, our results suggest that a delayed effect of metformin-mediated induction of SHP gene expression inhibits CREB-dependent hepatic gluconeogenesis.Glucose homeostasis is regulated by the opposing actions of insulin and glucagon (1-3), and glucose production in the liver is controlled primarily by gluconeogenesis (4). The regulation of hepatic gluconeogenesis involves the transcriptional regulation of key metabolic enzymes, including PEPCK 6 and G6Pase. The gluconeogenic program is largely regulated at the level of transcription and the process is coordinated by CREB via its direct binding to the cAMP-response element (CRE) site on the promoter of PEPCK, G6Pase, or PGC-1␣ (PPAR␥ coactivator-1␣) (5).Metformin has been shown to activate AMP-activated protein kinase (AMPK) via an LKB1-dependent mechanism (6). AMPK is a serine/threonine kinase that functions as an intracellular energy sensor and has been implicated in the modulation of glucose and fatty acid metabolism (7). AMPK is activated by physiological stimuli, including exercise, muscle contraction, and hormones, such as adiponectin and leptin, as well as by physiological stresses, glucose deprivation, hypoxia, oxidative stress, and osmotic shock conditions (8, 9). In the liver, activation of AMPK suppresses hepatic gluconeogenesis acutely by direct phosphorylation of its substrates, including CREB-binding protein (CBP) (10), CRTC2 (11), and GSK3␤ (glycogen synthase kinase 3␤) (12). Recent studies also suggest that AMPK induces SHP gene expression and inhibits hepatic g...

Prox1, an early specific marker for developing liver and pancreas in foregut endoderm has recently been shown to interact with ␣-fetoprotein transcription factor and repress cholesterol 7␣-hydroxylase (CYP7A1) gene transcription. Using a yeast two-hybrid assay, we found that Prox1 strongly and specifically interacted with hepatocyte nuclear factor (HNF)4␣, an important transactivator of the human CYP7A1 gene in bile acid synthesis and phosphoenolpyruvate carboxykinase (PEPCK) gene in gluconeogenesis. A real time PCR assay detected Prox1 mRNA expression in human primary hepatocytes and HepG2 cells. Reporter assay, GST pull-down, coimmunoprecipitation, and yeast two-hybrid assays identified a specific interaction between the N-terminal LXXLL motif of Prox1 and the activation function 2 domain of HNF4␣. Prox1 strongly inhibited HNF4␣ and peroxisome proliferators-activated receptor ␥ coactivator-1␣ co-activation of the CYP7A1 and PEPCK genes. Knock down of the endogenous Prox1 by small interfering RNA resulted in significant increase of CYP7A1 and PEPCK mRNA expression and the rate of bile acid synthesis in HepG2 cells. These results suggest that Prox1 is a novel co-regulator of HNF4␣ that may play a key role in the regulation of bile acid synthesis and gluconeogenesis in the liver. CYP7A12 catalyzes the first and rate-limiting step in the conversion of cholesterol to bile acids and plays an important role in maintaining whole body lipid homeostasis (1). Bile acids are physiological detergents that facilitate absorption, transport and distribution of sterols and lipid-soluble vitamins, and disposal of toxic metabolites and xenobiotics. Bile acid synthesis and CYP7A1 gene transcription is feedback inhibited by bile acids returning to the liver via enterohepatic circulation of bile (1). Recent studies have identified farnesoid X receptor (NR1H4) as a bile acid-activated receptor that induces an atypical nuclear receptor small heterodimer partner (SHP, NR0B2), which interacts with FTF (NR5A2) and HNF4␣ (NR2A1) bound to an overlapping sequence located in the bile acid response element II (Ϫ144/Ϫ126) and represses CYP7A1 gene transcription (2). However, the molecular mechanism by which FTF and HNF4␣ regulate the CYP7A1 gene is not completely understood.HNF4␣ is the most abundant nuclear receptor expressed in the liver and is involved in early liver development (3). Conditional knock-out of the HNF4␣ gene in mouse liver caused accumulation of lipids in the liver, markedly reduced serum cholesterol and triglycerides, and increased serum bile acids (4). CYP7A1, Na ϩ -taurocholate co-transport peptide, organic anion transporter 1, apolipoprotein B100, and scavenger receptor B-1 expression are reduced in these mice (4). It appears that HNF4␣ is a key regulator of bile acid and lipoprotein metabolism and plays a central role in lipid homeostasis (5). HNF4␣ is involved in diabetes; mutation of the HNF4␣ gene causes maturity onset diabetes of the young type 1 (MODY1) (6). HNF4␣ regulates the HNF1␣ gene, a MODY 3 gene (7). The tr...

Hepatic gluconeogenesis is tightly balanced by opposing stimulatory (glucagon) and inhibitory (insulin) signaling pathways. Hepatocyte growth factor (HGF) is a pleiotropic growth factor that mediates diverse biological processes. In this study, we investigated the effect of HGF and its family member, macrophage-stimulating factor (MSP), on hepatic gluconeogenesis in primary hepatocytes. HGF and MSP significantly repressed expression of the key hepatic gluconeogenic enzyme genes, phosphoenolpyruvate carboxykinase (PEPCK), and glucose-6-phosphatase (Glc-6-Pase) and reduced glucose production. HGF and MSP activated small heterodimer partner (SHP) gene promoter and induced SHP mRNA and protein levels, and the effect of HGF and MSP on SHP gene expression was demonstrated to be mediated via activation of the AMP-activated protein kinase (AMPK) signaling pathway. We demonstrated that upstream stimulatory factor-1 (USF-1) specifically mediated HGF effect on SHP gene expression, and inhibition of USF-1 by dominant negative USF-1 significantly abrogated HGF-mediated activation of the SHP promoter. Elucidation of the mechanism showed that USF-1 bound to E-box-1 in the SHP promoter, and HGF increased USF-1 DNA binding on the SHP promoter via AMPK and DNA-dependent protein kinase-mediated pathways. Adenoviral overexpression of USF-1 significantly repressed PEPCK and Glc-6-Pase gene expression and reduced glucose production. Knockdown of endogenous SHP expression significantly reversed this effect. Finally, knockdown of SHP or inhibition of AMPK signaling reversed the ability of HGF to suppress hepatocyte nuclear factor 4␣-mediated up-regulation of PEPCK and Glc-6-Pase gene expression along with the HGFand MSP-mediated suppression of gluconeogenesis. Overall, our results suggest a novel signaling pathway through HGF/ AMPK/USF-1/SHP to inhibit hepatic gluconeogenesis.

B ile acids are physiological detergents that facilitate absorption, transport, and distribution of sterols and lipid-soluble vitamins and disposal of toxic metabolites and xenobiotics. Bile acid synthesis and cholesterol 7␣-hydroxylase (CYP7A1) 2 gene transcription are inhibited by bile acids returning to the liver via enterohepatic circulation of bile acids. 1 Because bile acids are amphipathic molecules that function as powerful detergents, their concentrations in hepatocytes have to be tightly regulated to prevent cell damage. 2 Bile acids are also signaling molecules that activate nuclear receptors including farnesoid X receptor (FXR), pregnane X receptor, and vitamin D3 receptor and play important roles in the regulation of bile acid synthesis, cholesterol metabolism, and drug metabolism. 2 It has been reported that bile acid synthesis and CYP7A1 activity are suppressed after partial hepatectomy and during liver regeneration in animals and human patients. [3][4][5] The increase of bile acids in the remaining hepatocytes after partial hepatectomy and in the early stage of liver regeneration and injury inhibits bile acid synthesis and increases bile acid excretion to protect the liver from accumulating toxic bile acids. A recent study showed that bile acids and FXR are involved in liver regeneration in mice, as FXR-null mice had a lower rate of liver regeneration. 6 However, the molecular mechanism underlying the bile acid effect on liver regeneration remains unclear. Abbreviations: CBP, cAMP response element binding protein

Metabolic syndrome (MS) is a complex disorder defined by a cluster of abdominal obesity, atherogenic dyslipidemia, hyperglycemia, and hypertension; the condition is recognized as a risk factor for diabetes and cardiovascular disease. This study assessed the effects of the Sasang constitution group (SCG) on the risk of MS in Korean subjects. We have analyzed 1,617 outpatients of Korean oriental medicine hospitals who were classified into three SCGs, So-Yang, So-Eum, and Tae-Eum. Significant differences were noted in the prevalence of MS and the frequencies of all MS risk factors among the three SCGs. The odds ratios for MS as determined via multiple logistic regression analysis were 2.004 for So-Yang and 4.521 for Tae-Eum compared with So-Eum. These results indicate that SCG may function as a significant risk factor of MS; comprehensive knowledge of Sasang constitutional medicine may prove helpful in predicting susceptibility and developing preventive care techniques for MS.

The orphan nuclear receptor Nur77 (NR4A1) is a member of the nuclear receptor superfamily and plays an important role in the regulation of genes involved in steroidogenesis and cell death. Northern blot analysis revealed that the expression of Nur77 mRNA was increased after puberty in mouse testis, and hCG treatment of peripubertal animals induced this gene expression in the testis. Moreover, LH treatment induced a transient increase in Nur77 mRNA, and this induction was LH dose dependent in mouse Leydig tumor cell line, K28. Western blot analysis showed that LH transiently induced Nur77 protein. The protein kinase inhibitor H-89, bisindolymaleimide I, and wortmannin strongly inhibited this inductive effect of LH on Nur77 gene expression. Transient transfection assay demonstrated that LH significantly increased the Nur77 promoter-driven luciferase reporter activity in a dose-dependent manner, and LH also increased the activity of a luciferase reporter gene driven by a promoter containing multi copies of a Nur77-responsive element. Moreover, EMSA showed that Nur77 DNA-binding activity was increased in response to LH. Finally, overexpression of dominant negative Nur77 reduced LH-mediated progesterone biosynthesis. Taken together, these results demonstrate that LH induces Nur77 gene expression, and Nur77 may play an important role in the LH-mediated steroidogenesis in Leydig cells.

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