HNF1 and/or HNF3 may contribute to the tissue specific expression of glucokinase gene

Tumor-suppressive activity of Hnf1β in Wilms' tumor

Hepatocyte nuclear factor 1β (HNF1β) is a transcription factor belonging to the HNF-1 family and has been implicated in a number of cancers, but its role in Wilms' tumor (nephroblastoma) has not been addressed. Here, we compared its expression between Wilms' tumor patient kidney tissue and adjacent tissue based on the Oncomine database ( www.oncomine.com ). Cell proliferation, apoptosis, migration, and HNF1β expression level were analyzed in Wilms' tumor-derived G401 cells. Using a variety of mouse tissues (lung, heart, kidney, etc.), we found that HNF1β is the highest expression in the kidneys. Oncomine analysis further demonstrated that HNF1β has a lower expression in Wilms' tumor tissue than in paracancerous tissues. Overexpression of HNF1β decreased cell proliferation and migration, but promoted cell apoptosis. Knockdown of HNF1β produced the opposite results. These results indicated that HNF1β may play important roles in kidney development and function, and its activation may negatively regulate Wilms' tumor progression.

Expression of the human glucokinase gene: important roles of the 5' flanking and intron 1 sequences

Background

Glucokinase plays important tissue-specific roles in human physiology, where it acts as a sensor of blood glucose levels in the pancreas, and a few other cells of the gut and brain, and as the rate-limiting step in glucose metabolism in the liver. Liver-specific expression is driven by one of the two tissue-specific promoters, and has an absolute requirement for insulin. The sequences that mediate regulation by insulin are incompletely understood.

Methodology/Principal Findings

To better understand the liver-specific expression of the human glucokinase gene we compared the structures of this gene from diverse mammals. Much of the sequence located between the 5′ pancreatic beta-cell-specific and downstream liver-specific promoters of the glucokinase genes is composed of repetitive DNA elements that were inserted in parallel on different mammalian lineages. The transcriptional activity of the liver-specific promoter 5′ flanking sequences were tested with and without downstream intronic sequences in two human liver cells lines, HepG2 and L-02. While glucokinase liver-specific 5′ flanking sequences support expression in liver cell lines, a sequence located about 2000 bases 3′ to the liver-specific mRNA start site represses gene expression. Enhanced reporter gene expression was observed in both cell lines when cells were treated with fetal calf serum, but only in the L-02 cells was expression enhanced by insulin.

Conclusions/Significance

Our results suggest that the normal liver L-02 cell line may be a better model to understand the regulation of the liver-specific expression of the human glucokinase gene. Our results also suggest that sequences downstream of the liver-specific mRNA start site have important roles in the regulation of liver-specific glucokinase gene expression.

The Fox genes in the liver: from organogenesis to functional integration

Formation and function of the liver are highly controlled, essential processes. Multiple signaling pathways and transcriptional regulatory networks cooperate in this complex system. The evolutionarily conserved FOX, for Forkhead bOX, class of transcriptional regulators is critical to many aspects of liver development and function. The FOX proteins are small, mostly monomeric DNA binding factors containing the so-called winged helix DNA binding motif that distinguishes them from other classes of transcription factors. We discuss the biochemical and genetic roles of Foxa, Foxl1, Foxm1, and Foxo, as these have been shown to regulate many processes throughout the life of the organ, controlling both formation and function of the liver.

The role of hepatocyte nuclear factor-1beta in the pathogenesis of clear cell carcinoma of the ovary

PROBLEM

Clear cell carcinoma (CCC) of the ovary has a number of features distinguishing it from other epithelial ovarian carcinomas (EOC) because of its characteristic histology and biology, frequent concurrence with endometriotic lesion, and highly chemoresistant nature resulting in an extremely poor prognosis. The incidence of CCC has been steadily increasing in Japan. They comprise approximately 20% of all EOC. Understanding the mechanisms of CCC development and elucidating pathogenesis and pathophysiology are intrinsic to prevention and effective therapies for CCC.

METHOD OF STUDY

This article reviews the English language literature for biology, pathogenesis, and pathophysiological studies on endometriosis-associated EOC. Several data are discussed in the context of endometriosis and CCC biology.

RESULTS

Recent studies based on genome-wide expression analysis technology have noted specific expression of hepatocyte nuclear factor-1beta (HNF-1beta) in endometriosis and CCC, suggesting that early differentiation into the clear cell lineage takes place in the endometriosis. The HNF-1beta-dependent pathway of CCC will be discussed, which are providing new insights into regulation of apoptosis and glycogen synthesis and resistance of CCC to anticancer agents.

CONCLUSIONS

This review summarizes recent advances in the HNF-1beta and its target genes; the potential challenges to the understanding of carcinogenesis, pathogenesis, and pathophysiology of CCC; and a possible novel model is proposed.

Engineered glucagon-like peptide-1-producing hepatocytes lower plasma glucose levels in mice

Glucagon-like peptide (GLP)-1 is an incretin hormone with well-characterized antidiabetic properties, including glucose-dependent stimulation of insulin secretion and enhancement of beta-cell mass. GLP-1 agonists have recently been developed and are now in clinical use for the treatment of type 2 diabetes. Rapid degradation of GLP-1 by enzymes including dipeptidyl-peptidase (DPP)-IV and neutral endopeptidase (NEP) 24.11, along with renal clearance, contribute to a short biological half-life, necessitating frequent injections to maintain therapeutic efficacy. Gene therapy may represent a promising alternative approach for achieving long-term increases in endogenous release of GLP-1. We have developed a novel strategy for glucose-regulated production of GLP-1 in hepatocytes by expressing a DPP-IV-resistant GLP-1 peptide in hepatocytes under control of the liver-type pyruvate kinase promoter. Adenoviral delivery of this construct to hepatocytes in vitro resulted in production and secretion of bioactive GLP-1 as measured by a luciferase-based bioassay developed to detect the NH2-terminally modified GLP-1 peptide engineered for this study. Transplantation of encapsulated hepatocytes into CD-1 mice resulted in an increase in plasma GLP-1 levels that was accompanied by a significant reduction in fasting plasma glucose levels. The results from this study demonstrate that a gene therapy approach designed to induce GLP-1 production in hepatocytes may represent a novel strategy for long-term secretion of bioactive GLP-1 for the treatment of type 2 diabetes.

Regulation of insulin secretion, glucokinase gene transcription and beta cell proliferation by adipocyte-derived Wnt signalling molecules

AIMS/HYPOTHESIS

Adipocytes secrete signalling molecules that elicit responses from target cells, including pancreatic beta cells. Wnt signalling molecules have recently been identified as novel adipocyte-derived factors. They also regulate insulin secretion in pancreatic beta cells and the cell cycle. The aim of this study was to investigate the effect of adipocyte-derived Wnt signalling molecules on insulin secretion and beta cell proliferation.

METHODS

Human adipocytes were isolated to generate fat cell-conditioned medium (FCCM). Ins-1 cells were stimulated with FCCM and transiently transfected with reporter genes. Proliferation assays using [3H]thymidine incorporation were carried out in Ins-1 cells and primary islet cells. Insulin secretion from primary islets was assessed by radioimmunoassay. Gene expression in primary islets was assessed by Taqman PCR.

RESULTS

Treatment with human FCCM increased the transcription of a T cell-specific transcription factor reporter gene (TOPFLASH) in Ins-1 cells (241%, p < 0.05). FCCM induced the proliferation of Ins-1 cells (1.8 fold, p < 0.05) and primary mouse islet cells (1.6 fold, p < 0.05). Antagonizing Wnt signalling with secreted Frizzled-related protein 1 (FRP-1) inhibited the proliferative effect induced by Wnt3a and FCCM on Ins-1 cells by 49 and 41%, respectively. In addition, FCCM led to a twofold (p < 0.05) induction of cyclin D1 promoter activity in Ins-1 cells. Furthermore, FCCM stimulated insulin secretion (204% of controls, p > 0.05) in primary mouse islets, and this stimulation was inhibited by sFRP-1. At a molecular level, canonical Wnt signalling induced glucokinase gene transcription in a peroxisome proliferator-activated receptor gamma-dependent fashion, thereby defining the glucokinase gene as a novel Wnt target gene.

CONCLUSIONS/INTERPRETATION

Taken together, these data show that adipocyte-derived Wnt signalling molecules induce beta cell proliferation and insulin secretion in vitro, suggesting a novel mechanism linking obesity to hyperinsulinaemia.

The human carcinoembryonic antigen (CEA) GPI anchor mediates anoikis inhibition by inactivation of the intrinsic death pathway

Human carcinoembryonic antigen (CEA) is a cell surface adhesion molecule member of the Immunoglobulin Superfamily (IgSF). Aberrant upregulation of CEA is a common feature found in a wide variety of human cancers such as colon, breast and lung. Previous in vitro and in vivo results have demonstrated that CEA can have tumorigenic effects including the inhibition of cell differentiation and anoikis, a specific type of apoptosis triggered by the absence of extracellular matrix-cell contacts. In the present work, we investigate the involvement of the caspase cascade in CEA-mediated inhibition of anoikis and the structural requirements for this signal. Expression of CEA and/or a chimeric protein consisting of the NCAM extracellular domain attached to the CEA-GPI anchor correlates with an early inactivation of caspase-9 and activation of the PI3-K/Akt survival pathway, and at later times, inactivation of caspase-8. The CEA-mediated caspase inactivation as well as activation of Akt was not observed by expression of a CEA molecule incapable of self-binding (DeltaNCEA). These results suggest that the intrinsic caspase pathway is involved in the inhibitory effects of anoikis by CEA and this signal is dependent on the presence of self-adhesive extracellular domains and a CEA-GPI anchor.

Transcriptional regulation of the distal promoter of the rat pyruvate carboxylase gene by hepatocyte nuclear factor 3beta/Foxa2 and upstream stimulatory factors in insulinoma cells

PC (pyruvate carboxylase) plays a crucial role in intermediary metabolism including glucose-induced insulin secretion in pancreatic islets. In the present study, we identified two regions of the 1.2 kb distal promoter, the -803/-795 site and the -408/-403 E-box upstream of the transcription start site, as the important cis-acting elements for transcriptional activation of the luciferase reporter gene. Site-directed mutagenesis of either one of these sites in the context of this 1.2 kb promoter fragment, followed by transient transfections in the insulinoma cell line, INS-1, abolished reporter activity by approx. 50%. However, disruption of either the -803/-795 or the -408/-403 site did not affect reporter gene activity in NIH 3T3 cells, suggesting that this promoter fragment is subjected to cell-specific regulation. The nuclear proteins that bound to these -803/-795 and -408/-403 sites were identified by gel retardation assays as HNF3beta (hepatocyte nuclear factor 3beta)/Foxa2 (forkhead/winged helix transcription factor box2) and USFs (upstream stimulatory factors), USF1 and USF2, respectively. Chromatin immunoprecipitation assays using antisera against HNF3beta/Foxa2, USF1 and USF2 demonstrated that endogenous HNF3beta/Foxa2 binds to the -803/-795 Foxa2 site, and USF1 and USF2 bind to the -408/-403 E-box respectively in vivo, consistent with the gel retardation assay results. Although there are weak binding sites located at regions -904 and -572 for PDX1 (pancreatic duodenal homeobox-1), a transcription factor that controls expression of beta-cell-specific genes, it did not appear to regulate PC expression in INS-1 cells in the context of the 1.2 kb promoter fragment. The results presented here show that Foxa2 and USFs regulate the distal promoter of the rat PC gene in a cell-specific manner.

Immunohistochemical detection of hepatocyte nuclear factor 1β in ovarian and endometrial clear-cell adenocarcinomas and nonneoplastic endometrium

Recent studies have noted specific expression of hepatocyte nuclear factor (HNF) 1beta in ovarian clear-cell adenocarcinoma (CCA). In this study, we aimed to determine whether HNF-1beta can be a specific marker of CCA in both the ovary and the endometrium and to assess the pathological significance of HNF-1beta expression in CCAs. We examined HNF-1beta expression immunohistochemically in 186 ovarian carcinomas, including 40 CCAs; 33 endometrial carcinomas, including 5 CCAs; 22 endometria at different stages of the menstrual cycle (5 in the proliferative, 12 in the secretory, and 5 in the menstrual phases); and 7 gestational endometria. The incidence of HNF-1beta immunoreactivity differed significantly between CCAs and other histology in both the ovary (100% in the former versus 2% in the latter) and the endometrium (100% in the former versus 0% in the latter) (P < .0001 each). In nonneoplastic endometrium, 25% or more immunoreactive cells were confined to the mid-to-late secretory phase of the menstrual cycle and gestational endometrium. HNF-1beta would be an excellent marker for distinguishing CCAs from other lesions in both the ovary and the endometrium. HNF-1beta expression seems to be associated with physiopathological cytoplasmic glycogen accumulation in these organs.

Genomic structure, alternative maturation and tissue expression of the human BBOX1 gene

Gamma-butyrobetaine hydroxylase (BBOX1) is the enzyme responsible for the biosynthesis of l-carnitine, a key molecule of fatty acid metabolism. This cytosolic dimeric protein belongs to the dioxygenase family. In human, enzyme activity has been detected in kidney, liver and brain. The human gene encoding gamma-butyrobetaine hydroxylase is located on chromosome 11. Although the protein structure and activity have been extensively described, little information is available concerning BBOX1 structure and expression. In this study, the organization of the human gene was determined. The structure and functions of the 5'- and 3'-untranslated regions of the human BBOX1 mRNA were characterized in kidney, liver and brain. Our experiments revealed that the transcription initiation of the human BBOX1 gene might occur at 3 different exons, and that the expression level of each type of transcript is organ-specific. We showed that the use of 3 different promoters is responsible for the 5'-end heterogeneity. Investigations on BBOX1 mRNA maturation highlighted an alternative polyadenylation mechanism that generates two 3'-untranslated regions differing by their length. This alternative polyadenylation exhibited a tissue specificity.

Host Cells Reduce Glucose Uptake and Glycogen Deposition in Response to Hepatic Insulin Gene Therapy

BACKGROUND

Hepatic insulin gene therapy (HIGT) restores weight gain and near-normal glycemia in rodent models of insulin-deficient diabetes mellitus. However, the effect of transgenic insulin on endogenous genes and recipient cell function is relatively unexplored. To investigate hepatocellular effects of transgenic insulin expression, we evaluated intermediary glucose metabolism in primary cultured hepatocytes treated with HIGT.

METHODS

Rat hepatocytes were transduced with adenovirus expressing a glucose-responsive human insulin transgene and cultured in high-glucose and high-insulin conditions. We determined glycogen content in cell cultures and intact liver directly. Glycogenolysis was compared using glucose production of cultured cells. Glucose uptake, oxidative, and glycolytic processing were determined by radiotracer analysis or direct end-product assessment. Quantitative real-time reverse transcriptase polymerase chain reaction was used to determine expression of glucose transporter 2 (GLUT2) and glucokinase genes. GLUT2 protein abundance was determined by Western blot analysis.

RESULTS

HIGT-treated hepatocytes contained significantly less glycogen than either untreated hepatocytes or those treated with an empty virus. Glucose release owing to glycogenolysis remained normal. However, HIGT treatment significantly impaired glucose uptake and processing. Metabolic synthetic processes were not generally inhibited, as indicated by enhanced beta-hydroxybutyrate secretion. While preserving cell viability, HIGT treatment diminished expression of both glucokinase and GLUT2. In HIGT-treated streptozocin-treated diabetic rats, total liver glycogen was intermediate between diabetic animals and normal controls.

CONCLUSIONS

These results suggest gene-specific effects in recipient hepatocytes following HIGT treatment and underscore the need for expanded studies examining host cell responses to the transfer of metabolically active transgenes.

Hepatic nuclear factor 3 and nuclear factor 1 regulate 5-aminolevulinate synthase gene expression and are involved in insulin repression

Although the negative regulation of gene expression by insulin has been widely studied, the transcription factors responsible for the insulin effect are still unknown. The purpose of this work was to explore the molecular mechanisms involved in the insulin repression of the 5-aminolevulinate synthase (ALAS) gene. Deletion analysis of the 5'-regulatory region allowed us to identify an insulin-responsive region located at -459 to -354 bp. This fragment contains a highly homologous insulin-responsive (IRE) sequence. By transient transfection assays, we determined that hepatic nuclear factor 3 (HNF3) and nuclear factor 1 (NF1) are necessary for an appropriate expression of the ALAS gene. Insulin overrides the HNF3beta or HNF3beta plus NF1-mediated stimulation of ALAS transcriptional activity. Electrophoretic mobility shift assay and Southwestern blotting indicate that HNF3 binds to the ALAS promoter. Mutational analysis of this region revealed that IRE disruption abrogates insulin action, whereas mutation of the HNF3 element maintains hormone responsiveness. This dissociation between HNF3 binding and insulin action suggests that HNF3beta is not the sole physiologic mediator of insulin-induced transcriptional repression. Furthermore, Southwestern blotting assay shows that at least two polypeptides other than HNF3beta can bind to ALAS promoter and that this binding is dependent on the integrity of the IRE. We propose a model in which insulin exerts its negative effect through the disturbance of HNF3beta binding or transactivation potential, probably due to specific phosphorylation of this transcription factor by Akt. In this regard, results obtained from transfection experiments using kinase inhibitors support this hypothesis. Due to this event, NF1 would lose accessibility to the promoter. The posttranslational modification of HNF3 would allow the binding of a protein complex that recognizes the core IRE. These results provide a potential mechanism for the insulin-mediated repression of IRE-containing promoters.

Orphan nuclear receptor small heterodimer partner, a novel corepressor for a basic helix-loop-helix transcription factor BETA2/neuroD

Small heterodimer partner (SHP; NR0B2) is an atypical orphan nuclear receptor that lacks a conventional DNA binding domain (DBD) and represses the transcriptional activity of various nuclear receptors. In this study, we examined the novel cross talk between SHP and BETA2/NeuroD, a basic helix-loop-helix transcription factor. In vitro and in vivo protein interaction studies showed that SHP physically interacts with BETA2/NeuroD, but not its heterodimer partner E47. Moreover, confocal microscopic study and immunostaining results demonstrated that SHP colocalized with BETA2 in islets of mouse pancreas. SHP inhibited BETA2/NeuroD-dependent transactivation of an E-box reporter, whereas SHP was unable to repress the E47-mediated transactivation and the E-box mutant reporter activity. In addition, SHP repressed the BETA2-dependent activity of glucokinase and cyclin-dependent kinase inhibitor p21 gene promoters. Gel shift and in vitro protein competition assays indicated that SHP inhibits neither dimerization nor DNA binding of BETA2 and E47. Rather, SHP directly repressed BETA2 transcriptional activity and p300-enhanced BETA2/NeuroD transcriptional activity by inhibiting interaction between BETA2 and coactivator p300. We also showed that C-terminal repression domain within SHP is also required for BETA2 repression. However, inhibition of BETA2 activity was not observed by naturally occurring human SHP mutants that cannot interact with BETA2/NeuroD. Taken together, these results suggest that SHP acts as a novel corepressor for basic helix-loop-helix transcription factor BETA2/NeuroD by competing with coactivator p300 for binding to BETA2/NeuroD and by its direct transcriptional repression function.

Targeting of therapeutic gene expression to the liver by using liver-type pyruvate kinase proximal promoter and the SV40 viral enhancer active in multiple cell types

To achieve the liver-directed expression in sufficient amounts of therapeutic genes for successful and safe gene therapy, natural liver-specific promoters can be used to direct the expression of therapeutic genes in the liver, whereas strong viral enhancers were used to obtain sufficient amounts of expressed therapeutic gene products. However, very often use of either the former or the latter does not guarantee both potent and liver-specific therapeutic gene expression. Here we conglomerate them and thus create a potent tissue-specific promoter by characterizing and using the liver-type pyruvate kinase proximal promoter (LPKPP) harboring its TATA box and a HNF-1alpha binding site. Alone it hardly activated its reporter gene expression in non-hepatocytes or hepatocytes. However, in the presence of the SV40 viral enhancer (SV40VE), which is active in multiple cell types, it was able to potently activate its reporter gene expression specifically in hepatocytes. The tissue-specific activation of the LPKPP by the viral enhancer was attributed to HNF-1alpha binding to the LPKPP. Taken together, these results support the idea that the constitutively active SV40VE could be used to activate the LPKPP in a tissue-specific manner in the presence of HNF-1alpha. To our knowledge, this is the first study to utilize HNF-1alpha and its binding site, in the context of the LPKPP, to generate a basal promoter that is transcriptionally activated potently in a tissue-specific manner by a viral enhancer that is active in multiple cell types.

Investigation of the role of epigenetic modification of the rat glucokinase gene in fetal programming

Fetal malnutrition is associated with development of impaired glucose tolerance, diabetes and hypertension in later life in humans and several mammalian species. The mechanisms that underlie this phenomenon of fetal programming are unknown. We hypothesize that adverse effects in utero and early life may influence the basal expression levels of certain genes such that they are re-set with long-term consequences for the organism. An excellent candidate mechanism for this re-setting process is DNA methylation, since post-natal methylation patterns are largely established in utero. We have sought to test this hypothesis by investigating the glucokinase gene (Gck) in rat offspring programmed using a maternal low protein diet model (MLP). Northern blot reveals that fasting levels of Gck expression are reduced after programming, although this distinction disappears after feeding. Bisulphite sequencing of the hepatic Gck promoter indicates a complete absence of methylation at the 12 CpG sites studied in controls and MLP animals. Non-expressing cardiac tissue also showed no DNA methylation in this region, whereas brain and all fetal tissues were fully methylated. These findings are not consistent with the hypothesis that programming results from differential methylation of Gck. However, it remains possible that programming may influence methylation patterns in Gck at a distance from the promoter, or in genes encoding factors that regulate basal Gck expression.

Genome-wide expression analysis of mouse liver reveals CLOCK-regulated circadian output genes

CLOCK is a positive component of a transcription/translation-based negative feedback loop of the central circadian oscillator in the suprachiasmatic nucleus in mammals. To examine CLOCK-regulated circadian transcription in peripheral tissues, we performed microarray analyses using liver RNA isolated from Clock mutant mice. We also compared expression profiles with those of Cryptochromes (Cry1 and Cry2) double knockout mice. We identified more than 100 genes that fluctuated from day to night and of which expression levels were decreased in Clock mutant mice. In Cry-deficient mice, the expression levels of most CLOCK-regulated genes were elevated to the upper range of normal oscillation. Most of the screened genes had a CLOCK/BMAL1 binding site (E box) in the 5'-flanking region. We found that CLOCK was absolutely concerned with the circadian transcription of one type of liver genes (such as DBP, TEF, and Usp2) and partially with another (such as mPer1, mPer2, mDec1, Nocturnin, P450 oxidoreductase, and FKBP51) because the latter were damped but remained rhythmic in the mutant mice. Our results showed that CLOCK and CRY proteins are involved in the transcriptional regulation of many circadian output genes in the mouse liver. In addition to being a core component of the negative feedback loop that drives the circadian oscillator, CLOCK also appears to be involved in various physiological functions such as cell cycle, lipid metabolism, immune functions, and proteolysis in peripheral tissues.

Hepatocyte nuclear factor 1 negatively regulates amylin gene expression

Maturity-onset diabetes of the young (MODY) is a monogenic subtype of Type 2 diabetes, defined as having an early age of onset, with a dominant inheritance pattern. Hepatocyte nuclear factor 1 (HNF1), which is encoded by the MODY3 gene, has been shown to bind the insulin promoter. Since the promoters of three pancreas-specific genes involved in glucose homeostasis-insulin, glucokinase, and amylin bind similar transcription factors, we were interested in whether HNF1 could also regulate amylin expression. In the present study, we used the electrophoretic mobility shift assay, to demonstrate that the HNF1 transcription factor can specifically bind to the amylin promoter. Moreover, co-transfection of an HNF1 expression vector with an amylin-CAT reporter plasmid decreased the activity of the amylin promoter by 85%. These data support the hypothesis that the amylin gene is regulated by HNF1 in a negative manner and may explain partially how HNF1 mutations result in diabetes.