The mouse fetoprotein transcription factor (FTF) gene promoter is regulated by three GATA elements with tandem E box and Nkx motifs, and FTF in turn activates the Hnf3beta, Hnf4alpha, and Hnf1alpha gene promoters

Trps1 acts as a regulator of Sf-1 transcription and testosterone synthesis in mouse Leydig cells

Infertility has attracted global concern, and disruption of testosterone is a common cause of male infertility. Exploring the critical factors in testosterone biosynthesis may provide new insights for disease research and clinical therapy. Research on trichorhinophalangeal syndrome-1 (Trps1) gene has recently been focus on cancers; it is yet unknown whether Trps1 produces a marked effect in the male reproductive system. In the current study, single-cell RNA sequencing analysis of trichorhinophalangeal syndrome-1 gene (Trps1) expression in mouse testes and cleavage under targets and tagmentation and RNA sequencing were utilized to investigate the functionality of Trps1 in mouse Leydig cells. Knockdown of Trps1 increased testosterone synthesis in vitro and vivo using adeno-associated viral delivery and conditional knockout models. The results showed that Trps1 was abundantly expressed in Leydig cells. The expression levels of both steroidogenic factor-1 (Sf-1) and steroidogenic enzymes (Cyp11a1, Hsd3b, Cyp17a1, and Hsd17b3) as well as testosterone secretion were increased after Trps1 deficiency in vivo and vitro. Furthermore, disruption of Trps1 reduced histone deacetylase 1/2 activity and increased histone H3 acetylation in the Sf-1 promoter, thereby promoting testosterone secretion. Interestingly, Sf-1 also regulated the transcription of Trps1 through activating transcription factor 2. These results indicate that Trps1 targets Sf-1 to affect steroidogenesis through histone acetylation and shed light on the critical role of Trps1 functioning in the mouse Leydig cells.

Screening and Identification of Differential Ovarian Proteins before and after Induced Ovulation via Seminal Plasma in Bactrian Camels

Simple Summary

Camelidae are induced ovulators whose ovulation is tightly regulated by multiple factors. Understanding the biological mechanisms underlying follicular development, hormone secretion, and ovulation requires investigating the potential molecular pathways involved in these mechanisms. However, little is known about these molecular pathways in Bactrian camels. To screen and identify candidate biomarkers after seminal plasma (SP)-induced ovulation in the ovaries, we performed comprehensive proteomic and molecular biological analyses of the ovaries from camels that were intramuscularly injected with either seminal plasma or phosphate-buffered saline. Identification of these candidate biomarkers will enable a better understanding of reproduction in Bactrian camels. Our findings suggest candidate proteins for further studies on the molecular mechanisms of induced ovulation.

Abstract

Camelidae are induced ovulators whose ovulation is tightly regulated by multiple factors. Understanding the biological mechanisms underlying follicular development, hormone secretion, and ovulation requires investigating the potential molecular pathways involved. However, little is known about these pathways in Bactrian camels. To screen and identify candidate biomarkers after inducing ovulation, this study performed comprehensive proteomic and molecular biological analyses of the ovaries from two camel groups (n = 6). We identified 5075 expressed ovarian proteins, of which 404 were differentially expressed (264 upregulated, 140 downregulated) (p < 0.05 or p < 0.01), in samples from plasma-induced versus control camels. Gene ontology annotation identified the potential functions of the differentially expressed proteins (DEPs). These results validated the differential expression for a subset of these proteins using Western blot (p < 0.05) and immunofluorescence staining. Three DEPs (FST, NR5A1, and PRL) were involved in neurochemical signal transduction, as well as endocrine and reproductive hormone regulatory processes. The Kyoto Encyclopedia of Genes and Genomes analysis indicated the involvement of several pathways, including the calcium, cAMP, gonadotropin-releasing hormone, MAPK, and neuroactive ligand–receptor signaling pathways, suggesting that induced ovulation depends on the hypothalamic–pituitary–ovarian axis. Identifying these candidate biomarkers enables a better understanding of Bactrian camel reproduction. Ovarian proteomic profiling and the measurement of selected proteins using more targeted methods is a promising approach for studying induced-ovulation mechanisms.

The Medicinal Chemistry and Therapeutic Potential of LRH-1 Modulators

The ligand-activated transcription factor liver receptor homologue 1 (LRH-1, NR5A2) is involved in the regulation of metabolic homeostasis, including cholesterol and glucose balance. Preliminary evidence points to therapeutic potential of LRH-1 modulation in diabetes, hepatic diseases, inflammatory bowel diseases, atherosclerosis, and certain cancers, but because of a lack of suitable ligands, pharmacological control of LRH-1 has been insufficiently studied. Despite the availability of considerable structural knowledge on LRH-1, only a few ligand chemotypes have been developed, and potent, selective, and bioavailable tools to explore LRH-1 modulation in vivo are lacking. In view of the therapeutic potential of LRH-1 in prevalent diseases, improved chemical tools are needed to probe the beneficial and adverse effects of pharmacological LRH-1 modulation in sophisticated preclinical models and to further elucidate the receptor's molecular function.

Emerging functions of the nuclear receptor LRH-1 in liver physiology and pathology

Nuclear receptors play pleiotropic roles in cell differentiation, development, proliferation, and metabolic processes to govern liver physiology and pathology. The nuclear receptor, liver receptor homolog-1 (LRH-1, NR5A2), originally identified in the liver as a regulator of bile acid and cholesterol homeostasis, was recently recognized to coordinate a multitude of other hepatic metabolic processes, including glucose and lipid processing, methyl group sensing, and cellular stress responses. In this review, we summarize the physiological and pathophysiological functions of LRH-1 in the liver, as well as the molecular mechanisms underlying these processes. This review also focuses on the recent advances highlighting LRH-1 as an attractive target for liver-associated diseases, such as non-alcoholic fatty liver disease (NAFLD) and hepatocellular carcinoma (HCC).

Time for a paradigm shift in treating type 1 diabetes mellitus: coupling inflammation to islet regeneration

Type 1 diabetes mellitus (T1DM) is an autoimmune disease that targets the destruction of islet beta-cells resulting in insulin deficiency, hyperglycemia and death if untreated. Despite advances in medical devices and longer-acting insulin, there is still no robust therapy to substitute and protect beta-cells that are lost in T1DM. Attempts to refrain from the autoimmune attack have failed to achieve glycemic control in patients highlighting the necessity for a paradigm shift in T1DM treatment. Paradoxically, beta-cells are present in T1DM patients indicating a disturbed equilibrium between the immune attack and beta-cell regeneration reminiscent of unresolved wound healing that under normal circumstances progression towards an anti-inflammatory milieu promotes regeneration. Thus, the ultimate T1DM therapy should concomitantly restore immune self-tolerance and replenish the beta-cell mass similar to wound healing. Recently the agonistic activation of the nuclear receptor LRH-1/NR5A2 was shown to induce immune self-tolerance, increase beta-cell survival and promote regeneration through a mechanism of alpha-to-beta cell phenotypic switch. This trans-regeneration process appears to be facilitated by a pancreatic anti-inflammatory environment induced by LRH-1/NR5A2 activation. Herein, we review the literature on the role of LRH1/NR5A2 in immunity and islet physiology and propose that a cross-talk between these cellular compartments is mandatory to achieve therapeutic benefits.

LRH-1 drives hepatocellular carcinoma partially through induction of c-myc and cyclin E1, and suppression of p21

Background

To explore potential therapeutic target is one of the areas of great interest in both clinical and basic hepatocellular carcinoma (HCC) studies. Nuclear receptor liver receptor homolog-1 (LRH-1, NR5A2) is proved to play a positive role in several cancers including breast cancer, pancreatic cancer and intestinal cancer in recent years. However, the exact role of LRH-1 in the development and progression of HCC is not fully elucidated.

Methods

The LRH-1 expression level in HCC clinical samples was examined by immunohis-tochemistry (IHC). Stable LRH-1-suppressed HepG2 clones (HepG2^LRH-1/-) were generated by transcription activator-like effector nucleases (TALENs) and both in vitro and in vivo experiments were conducted.

Results

We confirmed that LRH-1 showed an increased expression pattern in HCC clinical samples. Our in vitro and in vivo results indicated that suppression of LRH-1 in HepG2 significantly attenuated its proliferation rate and tumorigenic capacity. Gene expression microarray analysis indicated that LRH-1mostly regulated gene expression involved in cell cycle. In addition, our gain-of-function experiments indicated that ectopic expression of LRH-1 dramatically induced the mRNA and protein levels of c-myc and cyclin E1, while attenuating the expression of p21.

Conclusion

Our results suggest that LRH-1 might be a potential therapeutic target for clinical HCC treatment.

Iterative use of nuclear receptor Nr5a2 regulates multiple stages of liver and pancreas development

The stepwise progression of common endoderm progenitors into differentiated liver and pancreas organs is regulated by a dynamic array of signals that are not well understood. The nuclear receptor subfamily 5, group A, member 2 gene nr5a2, also known as Liver receptor homolog-1 (Lrh-1) is expressed in several tissues including the developing liver and pancreas. Here, we interrogate the role of Nr5a2 at multiple developmental stages using genetic and chemical approaches and uncover novel pleiotropic requirements during zebrafish liver and pancreas development. Zygotic loss of nr5a2 in a targeted genetic null mutant disrupted the development of the exocrine pancreas and liver, while leaving the endocrine pancreas intact. Loss of nr5a2 abrogated exocrine pancreas markers such as trypsin, while pancreas progenitors marked by ptf1a or pdx1 remained unaffected, suggesting a role for Nr5a2 in regulating pancreatic acinar cell differentiation. In the developing liver, Nr5a2 regulates hepatic progenitor outgrowth and differentiation, as nr5a2 mutants exhibited reduced hepatoblast markers hnf4α and prox1 as well as differentiated hepatocyte marker fabp10a. Through the first in vivo use of Nr5a2 chemical antagonist Cpd3, the iterative requirement for Nr5a2 for exocrine pancreas and liver differentiation was temporally elucidated: chemical inhibition of Nr5a2 function during hepatopancreas progenitor specification was sufficient to disrupt exocrine pancreas formation and enhance the size of the embryonic liver, suggesting that Nr5a2 regulates hepatic vs. pancreatic progenitor fate choice. Chemical inhibition of Nr5a2 at a later time during pancreas and liver differentiation was sufficient to block the formation of mature acinar cells and hepatocytes. These findings define critical iterative and pleiotropic roles for Nr5a2 at distinct stages of pancreas and liver organogenesis, and provide novel perspectives for interpreting the role of Nr5a2 in disease.

The nuclear hormone receptor family member NR5A2 controls aspects of multipotent progenitor cell formation and acinar differentiation during pancreatic organogenesis

The orphan nuclear receptor NR5A2 is necessary for the stem-like properties of the epiblast of the pre-gastrulation embryo and for cellular and physiological homeostasis of endoderm-derived organs postnatally. Using conditional gene inactivation, we show that Nr5a2 also plays crucial regulatory roles during organogenesis. During the formation of the pancreas, Nr5a2 is necessary for the expansion of the nascent pancreatic epithelium, for the subsequent formation of the multipotent progenitor cell (MPC) population that gives rise to pre-acinar cells and bipotent cells with ductal and islet endocrine potential, and for the formation and differentiation of acinar cells. At birth, the NR5A2-deficient pancreas has defects in all three epithelial tissues: a partial loss of endocrine cells, a disrupted ductal tree and a >90% deficit of acini. The acinar defects are due to a combination of fewer MPCs, deficient allocation of those MPCs to pre-acinar fate, disruption of acinar morphogenesis and incomplete acinar cell differentiation. NR5A2 controls these developmental processes directly as well as through regulatory interactions with other pancreatic transcriptional regulators, including PTF1A, MYC, GATA4, FOXA2, RBPJL and MIST1 (BHLHA15). In particular, Nr5a2 and Ptf1a establish mutually reinforcing regulatory interactions and collaborate to control developmentally regulated pancreatic genes by binding to shared transcriptional regulatory regions. At the final stage of acinar cell development, the absence of NR5A2 affects the expression of Ptf1a and its acinar specific partner Rbpjl, so that the few acinar cells that form do not complete differentiation. Nr5a2 controls several temporally distinct stages of pancreatic development that involve regulatory mechanisms relevant to pancreatic oncogenesis and the maintenance of the exocrine phenotype.

Therapeutic potential of Liver Receptor Homolog-1 modulators

Liver Receptor Homolog-1 (LRH-1; NR5A2) belongs to the orphan nuclear receptor superfamily, and plays vital roles in early development, cholesterol homeostasis, steroidogenesis and certain diseases, including cancer. It is expressed in embryonic stem cells, adult liver, intestine, pancreas and ovary. It binds to DNA as a monomer and is regulated by various ligand-dependent and -independent mechanisms. Recent work identified synthetic ligands for LRH-1; such compounds may yield useful therapeutics for a range of pathologic conditions associated with aberrant expression and activity of LRH-1.

Transcriptional control of hepatocyte differentiation

The liver is the largest glandular organ in the body and plays a central role in controlling metabolism. During hepatogenesis, complex developmental processes must generate an array of cell types that are spatially arranged to generate a hepatic architecture that is essential to support liver function. The processes that control the ultimate formation of the liver are diverse and complex and in many cases poorly defined. Much of the focus of research during the past three decades has been on understanding how hepatocytes, which are the predominant liver parenchymal cells, differentiate during embryogenesis. Through a combination of mouse molecular genetics, embryology, and molecular biochemistry, investigators have defined a myriad of transcription factors that combine to control formation and function of hepatocytes. Here, we will review the major discoveries that underlie our current understanding of transcriptional regulation of hepatocyte differentiation.

Nuclear Receptors in Regulation of Mouse ES Cell Pluripotency and Differentiation

Embryonic stem (ES) cells have great therapeutic potential because they are capable of indefinite self-renewal and have the potential to differentiate into over 200 different cell types that compose the human body. The switch from the pluripotent phenotype to a differentiated cell involves many complex signaling pathways including those involving LIF/Stat3 and the transcription factors Sox2, Nanog and Oct-4. Many nuclear receptors play an important role in the maintenance of pluripotence (ERRβ, SF-1, LRH-1, DAX-1) repression of the ES cell phenotype (RAR, RXR, GCNF) and also the differentiation of ES cells (PPARγ). Here we review the roles of the nuclear receptors involved in regulating these important processes in ES cells.

The liver receptor homolog-1 (LRH-1) is expressed in human islets and protects {beta}-cells against stress-induced apoptosis

Liver receptor homolog (LRH-1) is an orphan nuclear receptor (NR5A2) that regulates cholesterol homeostasis and cell plasticity in endodermal-derived tissues. Estrogen increases LRH-1 expression conveying cell protection and proliferation. Independently, estrogen also protects isolated human islets against cytokine-induced apoptosis. Herein, we demonstrate that LRH-1 is expressed in islets, including β-cells, and that transcript levels are modulated by 17β-estradiol through the estrogen receptor (ER)α but not ERβ signaling pathway. Repression of LRH-1 by siRNA abrogated the protective effect conveyed by estrogen on rat islets against cytokines. Adenoviral-mediated overexpression of LRH-1 in human islets did not alter proliferation but conferred protection against cytokines and streptozotocin-induced apoptosis. Expression levels of the cell cycle genes cyclin D1 and cyclin E1 as well as the antiapoptotic gene bcl-xl were unaltered in LRH-1 expressing islets. In contrast, the steroidogenic enzymes CYP11A1 and CYP11B1 involved in glucocorticoid biosynthesis were both stimulated in transduced islets. In parallel, graded overexpression of LRH-1 dose-dependently impaired glucose-induced insulin secretion. Our results demonstrate the crucial role of the estrogen target gene nr5a2 in protecting human islets against-stressed-induced apoptosis. We postulate that this effect is mediated through increased glucocorticoid production that blunts the pro-inflammatory response of islets.

Role of nuclear receptors in hepatitis B and C infections

Nuclear receptors are key regulators of many cellular functions including energy supply by the direct control of the expression of target genes. They constitute a super-family of transcription factors activated by ligands, hormones or metabolites, and therefore, sensible to host metabolic stimuli. Viral replication and production requires energy and elementary building blocks from the infected cells. Hepatitis B and C virus replication is modulated in part by liver nuclear receptors that regulate the glucose and lipid metabolism. However, nuclear receptors control the two viruses' replication by different mechanisms. The expression of hepatitis B virus genes is directly under the control of nuclear receptors, which bind to the viral genome regulatory regions. Viral replication and production may, therefore, be optimal when cells receive the correct metabolic signals. Hepatitis C virus replication and production depend to a large extent on lipidogenesis and lipoprotein secretion. The role of nuclear receptors in controlling hepatitis C replication may be to turn on the cellular mode that would provide the appropriate metabolic environment for viral replication.

Emerging actions of the nuclear receptor LRH-1 in the gut

Liver receptor homolog-1 (NR5A2) is a nuclear receptor originally identified in the liver and mostly known for its regulatory role in cholesterol and bile acid homeostasis. More recently, liver receptor homolog-1 has emerged as a key regulator of intestinal function, coordinating unanticipated actions, such as cell renewal and local immune function with important implications to common intestinal diseases, including colorectal cancer and inflammatory bowel disease. Unlike most of the other nuclear receptors, liver receptor homolog-1 acts as a constitutively active transcription factor to drive the transcription of its target genes. Liver receptor homolog-1 activity however is to a major extent regulated by different corepressors and posttranslational modifications, which may account for its tissue-specific functions. This review will provide an update on the molecular aspects of liver receptor homolog-1 action and focus on some emerging aspects of its function in normal and diseased gut. This article is part of a Special Issue entitled: Translating nuclear receptors from health to disease.

Identification and characterization of alternative promoters of zebrafish Rtn-4/Nogo genes in cultured cells and zebrafish embryos

In mammals, the Nogo family consists of Nogo-A, Nogo-B and Nogo-C. However, there are three Rtn-4/Nogo-related transcripts were identified in zebrafish. In addition to the common C-terminal region, the N-terminal regions of Rtn4-n/Nogo-C1, Rtn4-m/Nogo-C2 and Rtn4-l/Nogo-B, respectively, contain 9, 25 and 132 amino acid residues. In this study, we isolated the 5'-upstream region of each gene from a BAC clone and demonstrated that the putative promoter regions, P1-P3, are functional in cultured cells and zebrafish embryos. A transgenic zebrafish Tg(Nogo-B:GFP) line was generated using P1 promoter region to drive green fluorescent protein (GFP) expression through Tol2-mediated transgenesis. This line recapitulates the endogenous expression pattern of Rtn4-l/Nogo-B mRNA in the brain, brachial arches, eyes, muscle, liver and intestines. In contrast, GFP expressions by P2 and P3 promoters were localized to skeletal muscles of zebrafish embryos. Several GATA and E-box motifs are found in these promoter regions. Using morpholino knockdown experiments, GATA4 and GATA6 were involved in the control of P1 promoter activity in the liver and intestine, while Myf5 and MyoD for the control of P1 and P3 promoter activities in muscles. These data demonstrate that zebrafish Rtn4/Nogo transcripts might be generated by coupling mechanisms of alternative first exons and alternative promoter usage.

Multiple nuclear receptors may regulate hepatitis B virus biosynthesis during development

Hepatitis B virus (HBV) replicates by the reverse transcription of the viral 3.5 kb pregenomic RNA. Therefore the level of expression of this transcript in the liver is a primary determinant of HBV biosynthesis. In vivo neonatal transcription of the HBV 3.5 kb pregenomic RNA is developmental regulated by hepatocyte nuclear factor 4α (HNF4α). In addition, viral biosynthesis in non-hepatoma cells can be supported directly by this nuclear receptor. However HBV transcription and replication can be supported by additional nuclear receptors including the retinoid X receptor α/peroxisome proliferator-activated receptor α (RXRα/PPARα), retinoid X receptor α/farnesoid X receptor α (RXRα/FXRα), liver receptor homolog 1 (LRH1) and estrogen-related receptors (ERR) in non-hepatoma cells. Therefore during neonatal liver development, HNF4α may progressively activate viral transcription and replication by binding directly to the proximal HNF4α recognition sequence within the nucleocapsid promoter. Alternatively, HNF4α may support viral biosynthesis in vivo indirectly by activating a network of liver-enriched nuclear receptors that, in combination, direct HBV 3.5 kb pregenomic RNA transcription and replication.

VEGF and IHH rescue definitive hematopoiesis in Gata-4 and Gata-6-deficient murine embryoid bodies

OBJECTIVE

Murine embryonic stem cells can be differentiated into embryoid bodies (EBs), which serve as an in vitro model recapitulating many aspects of embryonic yolk sac hematopoiesis. Differentiation of embryonic stem cells deficient in either Gata-4 or Gata-6 results in EBs with disrupted visceral endoderm (VE). While lack of VE has detrimental effects on hematopoiesis in vivo, it is unclear whether lack of VE affects hematopoiesis in EBs. Therefore, we compared Gata-4 null (G4N) and Gata-6 null (G6N) EBs with wild-type EBs to assess their ability to commit to hematopoietic cells.

MATERIALS AND METHODS

EB VE formation was examined using cell-sorting techniques and analysis visceral endoderm gene expression. Hematopoietic progenitor potential of EBs cultured under various conditions was assessed using colony-forming assays.

RESULTS

Definitive erythroid, granulocyte-macrophage, and mixed colonies were significantly reduced in G4N and G6N EBs compared to wild-type EBs. Vascular endothelial growth factor (VEGF) expression and secretion were also reduced in both G4N and G6N EBs, consistent with VE serving as a site of VEGF production. Addition of exogenous VEGF(165), to EB cultures completely rescued definitive colony-forming cells in G4N and G6N EBs. This rescue response could be blocked by addition of soluble Flk-1 Fc to EB cultures. Similarly, addition of exogenous Indian hedgehog to EB cultures also recovers the diminishment in definitive hematopoiesis in a reversible manner.

CONCLUSION

These results suggest that the absence of VE in G4N and G6N EBs does not prevent emergence of definitive progenitors from EBs. However, the decreased level of VEGF and Indian hedgehog production in VE devoid G4N and G6N EBs attenuates definitive hematopoietic progenitor cell expansion.

Microarray analysis of gene-expression profile in hepatocellular carcinoma cell, BEL-7402, with stable suppression of hLRH-1 via a DNA vector-based RNA interference

To establish a cell line with a permanent suppression of hLRH-1 in this study, a stable RNAi vector (pSineohLRH-1) targeting hLRH-1 was constructed and introduced into hepatocellular carcinoma cell, BEL-7402. By semiquantitative RT-PCR analysis, the expression of hLRH-1 in BEL-7402 cells carrying pSineohLRH-1 was shown to be significantly suppressed by up to approximately 60%. In addition, microarray analysis was carried out to assess the extent of altered gene expression in BEL-7402 cells with stable knockdown of hLRH-1. Direct comparison of gene-expression profiles of more than 18,000 genes showed that 405 of the expressed genes in hLRH-1-knockdown cells differed dramatically in expression levels from those in controls, which suggested the even extensive biological functions of hLRH-1. Interestingly, among those differentially expressed genes, some are cancer-associated such as Gadd45beta and PTEN, and their expressions were further validated. Although the identification of the exact relationship between these genes and hLRH-1 awaits intensive investigation, the findings of this study provide new insights into the mechanism by which hLRH-1 is involved in tumorigenesis.

PIASy inhibits LRH-1-dependent CYP11A1 expression by competing for SRC-1 binding

The orphan nuclear receptor LRH-1 (liver receptor homologue-1; NR5A2) plays a critical role in development, bile acid synthesis and cholesterol metabolism. LRH-1 is also expressed in the ovary where it is implicated in the regulation of steroidogenic genes for steroid hormone synthesis. In the present study, we investigated the molecular mechanisms of the transcriptional regulation of CYP11A1 by LRH-1 and found that LRH-1-mediated transactivation was markedly repressed by PIASy [protein inhibitor of activated STAT (signal transducer and activator of transcription) y], the shortest member of the PIAS family. The suppression of LRH-1 activity requires the N-terminal repression domain. Although PIAS proteins also function as E3 SUMO (small ubiquitin-related modifier) ligases and enhance SUMO conjugation, PIASy-mediated repression was independent of LRH-1 SUMOylation status. In addition, histone deacetylase activity was not involved in the inhibition of LRH-1 by PIASy. Immunoprecipitation and mammalian two-hybrid analyses indicated that PIASy interacted with LRH-1 through the C-terminal region, including the AF-2 (activation function-2) motif, which was also involved in the interaction between LRH-1 and the co-activator SRC-1 (steroid receptor co-activator-1). PIASy inhibited the binding of SRC-1 to LRH-1, although overexpression of SRC-1 partially overcame the PIASy inhibition of LRH-1 induction of the CYP11A1 promoter. The results of the present study suggest that competition with co-activators may be an important mechanism underlying the PIASy repression of LRH-1-mediated transactivation.

Tissue-specific transcription factors in progression of epithelial tumors

Dedifferentiation and epithelial-mesenchymal transition are important steps in epithelial tumor progression. A central role in the control of functional and morphological properties of different cell types is attributed to tissue-specific transcription factors which form regulatory cascades that define specification and differentiation of epithelial cells during embryonic development. The main principles of the action of such regulatory systems are reviewed on an example of a network of hepatocyte nuclear factors (HNFs) which play a key role in establishment and maintenance of hepatocytes--the major functional type of liver cells. HNFs, described as proteins binding to promoters of most hepatospecific genes, not only control expression of functional liver genes, but are also involved in regulation of proliferation, morphogenesis, and detoxification processes. One of the central components of the hepatospecific regulatory network is nuclear receptor HNF4alpha. Derangement of the expression of this gene is associated with progression of rodent and human hepatocellular carcinomas (HCCs) and contributes to increase of proliferation, loss of epithelial morphology, and dedifferentiation. Dysfunction of HNF4alpha during HCC progression can be either caused by structural changes of this gene or occurs due to modification of up-stream regulatory signaling pathways. Investigations preformed on a model system of the mouse one-step HCC progression have shown that the restoration of HNF4alpha function in dedifferentiated cells causes partial reversion of malignant phenotype both in vitro and in vivo. Derangement of HNFs function was also described in other tumors of epithelial origin. We suppose that tissue-specific factors that underlie the key steps in differentiation programs of certain tissues and are able to receive or modulate signals from the cell environment might be considered as promising candidates for the role of tumor suppressors in the tissue types where they normally play the most significant role.

Compromised intestinal lipid absorption in mice with a liver-specific deficiency of liver receptor homolog 1

Bile acids (BAs) are water-soluble end products from cholesterol metabolism and are essential for efficient absorption of dietary lipids. By using targeted somatic mutagenesis of the nuclear receptor liver receptor homolog 1 (LRH-1) in mouse hepatocytes, we demonstrate here that LRH-1 critically regulates the physicochemical properties of BAs. The absence of LRH-1 and subsequent deficiency of Cyp8b1 eliminate the production of cholic acid and its amino acid conjugate taurocholic acid and increase the relative amounts of less amphipathic BA species. Intriguingly, while the expression of Cyp8b1 is almost extinguished in the livers of mice that lack LRH-1, the expression of the rate-limiting enzyme of BA synthesis, i.e., Cyp7a1, remains unchanged. The profound remodeling of the BA composition significantly reduces the efficacy of intestinal absorption of lipids and reuptake of BAs and facilitates the removal of lipids from the body. Our studies unequivocally demonstrate a pivotal role for LRH-1 in determining the composition of BAs, which, in turn has major consequences on whole-body lipid homeostasis.

Age-related changes in bile acid synthesis and hepatic nuclear receptor expression

BACKGROUND

Recent data highlighted the role of nuclear receptors in the transcriptional regulation of the limiting enzyme of bile acid synthesis, cholesterol 7alpha-hydroxylase, in cellular and animal models. This study was designed to analyze the effects of age on cholesterol 7alpha-hydroxylase and related nuclear receptor expression in human livers.

DESIGN

Surgical liver biopsies were obtained in 23 patients requiring operation on the gastrointestinal tract. mRNA levels of cholesterol 7alpha-hydroxylase and related nuclear receptors and co-activators were assayed by quantitative real-time RT-PCR. Serum levels of 7alpha-hydroxy-4-cholesten-3-one, a marker of bile acid synthesis, were assayed by gas-liquid chromatography:mass spectrometry.

RESULTS

Ageing was inversely correlated with serum 7alpha-hydroxy-4-cholesten-3-one and with cholesterol 7alpha-hydroxylase mRNA levels (r = -0.44 and r = -0.45 on a semi-log scale, respectively, P < 0.05). Among different nuclear factors, cholesterol 7alpha-hydroxylase mRNA best correlated with hepatocyte nuclear factor-4 (r = 0.55 on a log scale, P < 0.05); hepatocyte nuclear factor-4 levels were also inversely correlated with age (r = -0.64 on a semi-log scale, P < 0.05). Age was inversely correlated with serum insulin-like growth factor-I levels, which were directly correlated with hepatocyte nuclear factor-4 and cholesterol 7alpha-hydroxylase expression. No suppressive effect of short heterodimer partner expression on cholesterol 7alpha-hydroxylase was observed.

CONCLUSIONS

Ageing associates with reduced bile acid synthesis, possibly related to decreased hepatic expression of hepatocyte nuclear factor-4 and consequently of cholesterol 7alpha-hydroxylase. Age-related modifications of the growth hormone/insulin-like growth factor axis might play a role. These findings may help to elucidate the pathophysiology of age-related modifications of cholesterol metabolism.

Impaired progesterone production in Nr5a2+/- mice leads to a reduction in female reproductive function

NR5A2 is an orphan nuclear receptor involved in cholesterol metabolism and embryogenesis. The high level of expression of NR5A2 in the ovary and its involvement in the regulation of steroidogenic gene expression also suggest a role for this transcription factor in female reproductive function. In vivo evidence for a role for NR5A2 in fertility, however, is still lacking. In order to address this possibility, we used Nr5a2+/- mice to demonstrate that heterozygosity for a null mutation of Nr5a2 leads to a decreased fertility in females. Our results indicate that although Nr5a2+/- mice display normal follicular development, ovulation, and estrogen production, they exhibit altered luteal function. More specifically, we show that the reduced reproductive ability of Nr5a2+/- females arises from a reduction in circulating progesterone concentrations and can be rescued by exogenous progesterone supplementation. This study therefore provides the first in vivo evidence for a role of NR5A2 in reproductive function and steroidogenesis.

Identification and functional analysis of a novel human CYP2E1 far upstream enhancer

Both transcriptional and post-transcriptional CYP2E1 regulatory mechanisms are known, resulting in 20-fold or greater variation in CYP2E1 expression. To evaluate functional regulatory elements controlling transcription, CYP2E1 promoter constructs were used to make adenovirus vectors containing CYP2E1 promoter-driven luciferase reporters for analyses in both primary human hepatocytes and HepG2 cells. A 1.2-kilobase pair portion of the CYP2E1 promoter was associated with 5- to 10-fold greater luciferase activity. This upstream region contained five direct repeats of 59 base pairs (bp) that increased thymidine kinase-driven luciferase reporter activity in HepG2 cells more than 5-fold, regardless of orientation. Electrophoretic mobility shift assays (EMSAs) identified sequence-specific nuclear protein binding to the 59-bp repeats that was dependent on a 17-bp sequence containing a canonical GATA binding site (WGATAR). Competitive and supershift EMSA identified the participation of GATA4, another GATA family member or GATA-like factor, and a third factor unrelated to the GATA family. Involvement of the tricho-rhino-phalangeal syndrome-1 factor, which also binds a GATA sequence, was eliminated. Rather, competitive EMSA using known binding sequences for the orphan nuclear receptors, steroidogenic factor-1 (or NR5A1), and fetoprotein transcription factor (or NR5A2) implicated an NR5A member in binding a sequence overlapping the canonical GATA. Chromatin immunoprecipitation assay demonstrated in vivo binding of NR5A2 to the enhancer sequence in human hepatocytes. The enhancer sequence is conserved within the human population but seems species-specific. The identification of this novel enhancer and its putative mechanism adds to the complexities of human CYP2E1 regulation.

Nuclear receptor NR5A2 is required for proper primitive streak morphogenesis

NR5A2, also known as liver receptor homologue 1 (LRH-1) and fetoprotein transcription factor (FTF), is an orphan nuclear receptor involved in the regulation of cholesterol metabolism and steroidogenesis in the adult. NR5A2 was also shown to be expressed during early mouse embryogenesis. Consistent with its early expression pattern, a targeted disruption of this gene leads to embryonic lethality around the gastrulation period. To characterize the embryonic phenotype resulting from NR5A2 loss of function, we undertook morphological and marker gene analyses and showed that NR5A2-/- embryos display growth retardation, epiblast disorganization, a mild embryonic-extraembryonic constriction, as well as abnormal thickening of the proximo-posterior epiblast. We demonstrated that, although initial specification of the anterior-posterior axis occurred in the absence of NR5A2, primitive streak formation was impaired and neither embryonic nor extraembryonic mesoderm was generated. Moreover, although the visceral endoderm does not show major morphological abnormalities in NR5A2-/- embryos, a decrease in the expression level of HNF4 and GATA4 was observed. Aggregation experiments demonstrated that, in the presence of wild-type tetraploid cells, NR5A2 mutant cells in the epiblast are capable of undergoing normal gastrulation. Therefore, our results suggest a requirement for NR5A2 in extraembryonic tissues and identify a novel role of this gene in proper primitive streak morphogenesis.

Expression profiling of liver receptor homologue 1 (LRH-1) in mouse tissues using tissue microarray

Liver receptor homologue 1 (LRH-1) is a nuclear receptor that plays important roles in lipid homeostasis and embryogenesis. To elucidate systemic physiological functions of LRH-1, we used tissue microarray-based immunohistochemistry to examine the tissue distribution and localization of LRH-1 in adult mouse tissues. LRH-1 immunoreactivity was observed in the nucleus of multiple epithelial lineage cells in the digestive system (including absorptive epithelial cells in the small and large intestines, goblet cells, acinar cells of the exocrine glands, chief cells and mucus neck cells in the stomach, granular and prickle layer cells in the tongue and forestomach, and gall bladder epithelium); respiratory system (alveolar type II cells); and urinary system (transitional epithelium). Nuclear LRH-1 immunoreactivity was also localized in cells involved in fatty acid/glucose metabolism, including hepatocytes, brown adipocytes, and cardiomyocytes, and neurons involved in the regulation of food intake, including the arcuate nucleus in the hypothalamus and paraventricular nucleus of thalamus. Additionally, LRH-1 immunoreactivity was observed in testicular Leydig cells and ovarian follicular cells. These data suggest that LRH-1 functions in multiple organ systems to regulate epithelial cell physiology and differentiation, energy metabolism, and reproduction.

Evolution of the mechanisms and molecular control of endoderm formation

Endoderm differentiation and movements are of fundamental importance not only for subsequent morphogenesis of the digestive tract but also to enable normal patterning and differentiation of mesoderm- and ectoderm-derived organs. This review defines the tissues that have been called endoderm in different species, their cellular origin and their movements. We take a comparative approach to ask how signaling pathways leading to embryonic and extraembryonic endoderm differentiation have emerged in different organisms, how they became integrated and point to specific gaps in our knowledge that would be worth filling. Lastly, we address whether the gastrulation movements that lead to endoderm internalization are coupled with its differentiation.

Expression of mouse liver receptor homologue 1 in embryonic stem cells is directed by a novel promoter

Liver receptor homologue 1 (LRH-1) plays important roles in many physiological processes and embryogenesis. However, little is known about the developmental regulation of lrh-1 expression. We identified a novel transcript of mouse lrh-1 (mlrh-1v2) from embryonic stem (ES) cells. mlrh-1v2 is expressed throughout embryogenesis and in several adult tissues, while the known transcript (mlrh-1v1) appears later during embryogenesis. mlrh-1v2 expression is directed by a new promoter which displays a strong activity in ES cells. The generation of the new transcript is conserved in rats. The identification of novel mlrh-1 variant and promoter is critical for elucidating LRH-1 functions in development and adult tissues.

Chicken LRH-1 gene is transcribed from multiple promoters in steroidogenic organs

Liver receptor homolog-1 (LRH-1) is a homolog of FTZ-F1, a transcription factor of the fruit fly, and belongs to the orphan nuclear receptor family. LRH-1 is expressed in organs derived from the endoderm, including intestine, liver and exocrine pancreas and plays a predominant role in development, bile-acid homeostasis, and reverse cholesterol transport. Recent research has revealed that mammalian LRH-1 is also expressed in the steroidogenic organs and has suggested that LRH-1 shares a role in steroidogenesis with steroidogenic factor-1 (SF-1), which is a paralog of LRH-1. In this study, we determined transcription initiation sites of chicken LRH-1 and showed that LRH-1 is expressed as several splicing variants in chicken steroidogenic organs. From three steroidogenic organs, the adrenal glands, ovaries, and testes, several cDNA fragments including different lengths and sequences were amplified by 5'-RACE and these were mainly classified into five types. Using these sequences, chicken genomic database was searched and four types of first exons were identified in chromosome 8. However, the database sequence of these regions included several gaps. So we cloned gap regions by PCR cloning from chicken genomic DNA and found the other type of first exons in the gaps. Moreover, RT-PCR showed the expression of LRH-1 in chicken steroidogenic organs as many splicing variants. We concluded that the chicken LRH-1 gene is transcribed from at least five different transcription initiation sites and alternative splicing produces several types of mRNA in steroidogenic organs.

Experimental Study on the Suppression of Human Nuclear Receptor hLRH-1 via a Vector-based RNA Interference

To explore the inhibitions of human nuclear receptor hLRH-1 via RNA interference, siRNAs expressing vectors pShLRH-1.1 and pShLRH-1.2, and targeting hLRH-1 were designed and constructed. The recombinants were introduced into hepatocellular carcinoma cells, BEL-7402, mediated by lipofectamin. RT-PCR was carried out to examine the inhibition ratio of hLRH-1 expression. The same method was also applied to analyze the expression of farnesyl pyrophosphate synthetase (FPPS) gene. Our results demonstrated that after transient transfection, both pShLRH-1.1 and pShLRH-1.2 could trigger the efficient inhibition of hLRH-1 in cultured cells, BEL-7402. The inhibition ratios were up to 80%. By comparing with non-transfection and vector-transfection control, the expression of FPPS in cells with inhibition of hLRH-1 was up-regulated significantly. Thus, the inhibition of expression of hLRH-1 in cultured cells was achieved via RNA interference in this study. Our results also suggested that hLRH-1 acts as a negative regulator in FPPS expression.

Over-expression and purification of isotopically labeled recombinant ligand-binding domain of orphan nuclear receptor human B1-binding factor/human liver receptor homologue 1 for NMR studies

The human hepatitis B virus enhancer II B1 binding factor (hB1F), which regulates the expression of hepatitis B virus genes, is identified as a nuclear receptor. It regulates several liver-specific genes and plays an important role in the bile acid biosynthesis pathway. A significantly optimized protocol has been worked out to prepare 15N and/or 13C-labeled hB1F ligand-binding domain in minimal medium with high yields for NMR studies. Under the various conditions optimized for the purification of His6-hB1F ligand-binding domain, the yield of the purified protein is estimated to be 25-30 mg from 0.5 L of M9 minimal media. Electrospray ionization mass spectrometry data confirm the correctness of the primary sequence. Dynamic light scattering experiment proves that the protein exists as a monomeric form. In addition, the circular dichroism results show that the protein has a well-regulated secondary structure and a high alpha-helical content in ammonium bicarbonate buffer at 20 degrees C and pH 7.4. Finally, uniformly 15N-labeled protein is characterized by a TROSY-HSQC spectrum, and the dispersion of 15N-1H cross-peaks in the spectrum indicates the presence of well-ordered and properly folded protein as a monomer.

Protein kinase A-dependent synergism between GATA factors and the nuclear receptor, liver receptor homolog-1, regulates human aromatase (CYP19) PII promoter activity in breast cancer cells

Cancers, including that of the breast, are the result of multiple contributing factors including aberrant gene expression. Indeed, the CYP19 gene encoding P450 aromatase, the key enzyme for estrogen biosynthesis, is up-regulated in breast tumors predominantly via the cAMP-responsive gonad-type PII promoter, ultimately leading to increased intratumoral estrogen production and tumor growth. Thus, identifying the molecular factors involved in aromatase PII promoter regulation is essential for our understanding and treatment of the disease. Because we have previously shown activity of the murine aromatase PII promoter to be markedly up-regulated by GATA factors with respect to the gonads, we hypothesized that GATA factors are also key determinants of human PII promoter-driven aromatase transcription in breast tumors. We now show that GATA3 and GATA4 are indeed expressed in several breast cancer cells lines. Consistent with the cAMP dependence of the PII promoter, activation elicited by GATA3 or GATA4 alone and the striking synergism between GATA3 or GATA4 and the nuclear receptor liver receptor homolog (LRH)-1 was intimately linked to forskolin treatment or overexpression of protein kinase A (PKA) catalytic subunit. PKA-mediated phosphorylation increases the interaction between GATA3 and LRH-1 and the requirement for PKA in aromatase PII promoter stimulation involves at least three specific amino acid residues: GATA3 Ser308, GATA4 Ser261, and LRH-1 Ser469. Finally, we show that the human LRH-1 promoter is itself a target for GATA factors. Thus, taken together, our results suggest that GATA factors likely contribute to aberrant aromatase expression in breast tumors through two distinct, yet complementary mechanisms.

The Gem interacting protein (GMIP) gene is associated with major depressive disorder

Major depressive disorder (MDD) is a mood disorder with a significant heritable component. Structural neuronal impairment has been considered to be implicated in MDD, as it leads to brain morphological alterations such as hippocampal atrophy. The Gem interacting protein, GMIP, is a novel Rho GTPase-activating protein known to play important roles in neurite growth and axonal guidance. We examined the GMIP gene for possible association in a Japanese sample of 164 patients with MDD and 164 controls matched for sex. We found a significant association with MDD for one single nucleotide polymorphism (SNP) (-525G/A) located on the 5'-upstream region of the GMIP gene (p=0.039, odds ratio 1.66, 95% CI 1.05-2.69) and stronger evidence for association in a multimarker haplotype analysis (p=0.004). We then performed a promoter-luciferase reporter assay; the promoter activity for -525A allele, which was in excess in the MDD patients, was significantly decreased compared with the -525G allele in transient transfection experiments using three types of cell lines. Our results suggest that genetic variations in the GMIP gene can confer susceptibility to MDD, and the associated promoter SNP might play a role in the transcriptional regulation of the GMIP gene. Further study needs to be undertaken to validate the association between the GMIP gene and MDD.

Suppression of hLRH-1 mediated by a DNA vector-based RNA interference results in cell cycle arrest and induction of apoptosis in hepatocellular carcinoma cell BEL-7402

RNA interference (RNAi) is the process by which double-stranded RNA directs sequence-specific degradation of mRNA. A DNA vector-based approach has been shown to be able to trigger RNA interference in mammalian cells successfully. LRH-1 is an orphan nuclear receptor predominantly expressed in tissues of endodermal origin, where it controls development and cholesterol homeostasis. In the present study, we demonstrated that the expression of hLRH-1 and cyclin E1 in BEL-7402 cells could be suppressed by up to approximately 80% via DNA vector-based RNA interference. The suppression of hLRH-1 resulted in cell cycle arrest mediated by the down-regulation of cyclin E1. Induction of apoptosis and down-regulation of Gadd45beta were also shown in hLRH-1 knock down BEL-7402 cells. These results, together with the findings that Gadd45beta remained unchanged in cyclin E1 RNAi cells, suggested that the induction of apoptosis by knock down of hLRH-1 was closely related to the down-regulation of Gadd45beta.

Global analysis of RAR-responsive genes in the Xenopus neurula using cDNA microarrays

Retinoid signaling is important for patterning the vertebrate hindbrain and midaxial regions. We recently showed that signaling through retinoic acid receptors (RARs) is essential for anteroposterior patterning along the entire body axis. To further investigate the mechanisms through which RARs act, we used microarray analysis to investigate the effects of modulating RAR activity on target gene expression. We identified 334 up-regulated genes (92% of which were validated), including known RA-responsive genes, known genes that have never been proposed as RA targets and many hypothetical and unidentified genes (n = 166). Sixty-seven validated down-regulated genes were identified, including known RA-responsive genes and anterior marker genes. The expression patterns of selected up-regulated genes (n = 45) were examined at neurula stages using whole-mount in situ hybridization. We found that most of these genes were expressed in the neural tube and many were expressed in anterior tissues such as neural crest, brain, eye anlagen, and cement gland. Some were expressed in tissues such as notochord, somites, pronephros, and blood islands, where retinoic acid (RA) plays established roles in organogenesis. Members of this set of newly identified RAR target genes are likely to play important roles in neural patterning and organogenesis under the control of RAR signaling pathways, and their further characterization will expand our understanding of RA signaling during development.

Orphan nuclear receptor LRH-1 is required to maintain Oct4 expression at the epiblast stage of embryonic development

Oct4 plays an essential role in maintaining the inner cell mass and pluripotence of embryonic stem (ES) cells. The expression of Oct4 is regulated by the proximal enhancer and promoter in the epiblast and by the distal enhancer and promoter at all other stages in the pluripotent cell lineage. Here we report that the orphan nuclear receptor LRH-1, which is expressed in undifferentiated ES cells, can bind to SF-1 response elements in the proximal promoter and proximal enhancer of the Oct4 gene and activate Oct4 reporter gene expression. LRH-1 is colocalized with Oct4 in the inner cell mass and the epiblast of embryos at early developmental stages. Disruption of the LRH-1 gene results in loss of Oct4 expression at the epiblast stage and early embryonic death. Using LRH-1(-/-) ES cells, we also show that LRH-1 is required to maintain Oct4 expression at early differentiation time points. In vitro and in vivo results show that LRH-1 plays an essential role in the maintenance of Oct4 expression in ES cells at the epiblast stage of embryonic development, thereby maintaining pluripotence at this crucial developmental stage prior to segregation of the primordial germ cell lineage at gastrulation.

Liver receptor homolog 1 contributes to intestinal tumor formation through effects on cell cycle and inflammation

Liver receptor homolog 1 (LRH-1) is an orphan nuclear receptor that synergizes with beta-catenin/T cell factor 4 signaling to stimulate intestinal crypt cell renewal. We evaluated here the impact of haploinsufficiency of LRH-1 on intestinal tumorigenesis by using two independent mouse models of human colon tumorigenesis. Haploinsufficiency of LRH-1 blunts intestinal tumorigenesis in the ApcMin/+ mice, a genetic model of intestinal cancer. Likewise, Lrh-1+/- mice are protected against the formation of aberrant crypt foci in the colon of mice exposed to the carcinogen azoxymethane. LRH-1 gene expression is reduced in tumors that express elevated levels of the proinflammatory cytokine TNF-alpha. Reciprocally, decreased LRH-1 expression in Lrh-1+/- mice attenuates TNF-alpha expression. Compared with normal human colon, expression and subcellular localization of LRH-1 is significantly altered in neoplastic colon. In combination, these data suggest a role of LRH-1 in the initiation of intestinal tumorigenesis both by affecting cell cycle control as well as through its impact on inflammatory pathways.

LRH-1: an orphan nuclear receptor involved in development, metabolism and steroidogenesis

The liver receptor homolog-1 (LRH-1; NR5A2) and steroidogenic factor-1 (SF-1; NR5A1) are two orphan members of the Ftz-F1 subfamily of nuclear receptors. LRH-1 is expressed in tissues derived from endoderm, including intestine, liver and exocrine pancreas, as well as in the ovary. In these tissues, LRH-1 plays a predominant role in development, reverse cholesterol transport, bile-acid homeostasis and steroidogenesis. SF-1 expression is confined to steroidogenic tissues and the hypothalamo-pituitary-adrenal axis, where it is involved in the control of development, differentiation, steroidogenesis and sexual determination. In this article, we will review data concerning the structure, regulation and function of LRH-1. These data highlight structural similarities between LRH-1 and other Ftz-F1 members but also underscore important functional differences, assigning to LRH-1 a unique position among nuclear receptors.

Transcription factor HNF-6/OC-1 inhibits the stimulation of the HNF-3alpha/Foxa1 gene by TGF-beta in mouse liver

A network of liver-enriched transcription factors controls differentiation and morphogenesis of the liver. These factors interact via direct, feedback, and autoregulatory loops. Previous work has suggested that hepatocyte nuclear factor (HNF)-6/OC-1 and HNF-3alpha/FoxA1 participate coordinately in this hepatic network. We investigated how HNF-6 controls the expression of Foxa1. We observed that Foxa1 expression was upregulated in the liver of Hnf6(-/-) mouse embryos and in bipotential mouse embryonic liver (BMEL) cell lines derived from embryonic Hnf6(-/-) liver, suggesting that HNF-6 inhibits the expression of Foxa1. Because no evidence for a direct repression of Foxa1 by HNF-6 was found, we postulated the existence of an indirect mechanism. We found that the expression of a mediator and targets of the transforming growth factor beta (TGF-beta) signaling was increased both in Hnf6(-/-) liver and in Hnf6(-/-) BMEL cell lines. Using these cell lines, we demonstrated that TGF-beta signaling was increased in the absence of HNF-6, and that this resulted from upregulation of TGF-beta receptor II expression. We also found that TGF-beta can stimulate the expression of Foxa1 in Hnf6(+/+) cells and that inhibition of TGF-beta signaling in Hnf6(-/-) cells down-regulates the expression of Foxa1. In conclusion, we propose that Foxa1 upregulation in the absence of HNF-6 results from increased TGF-beta signaling via increased expression of the TGF-beta receptor II. We further conclude that HNF-6 inhibits Foxa1 by inhibiting the activity of the TGF-beta signaling pathway. This identifies a new mechanism of interaction between liver-enriched transcription factors whereby one factor indirectly controls another by modulating the activity of a signaling pathway.

Synergy between LRH-1 and beta-catenin induces G1 cyclin-mediated cell proliferation

LRH-1 is an orphan nuclear receptor predominantly expressed in tissues of endodermal origin, where it controls development and cholesterol homeostasis. We show here that LRH-1 induces cell proliferation through the concomitant induction of cyclin D1 and E1, an effect that is potentiated by its interaction with beta-catenin. Whereas beta-catenin coactivates LRH-1 on the cyclin E1 promoter, LRH-1 acts as a potent tissue-restricted coactivator of beta-catenin on the cyclin D1 promoter. The implication of LRH-1 in cell proliferation highlights an unanticipated crosstalk between LRH-1 and the beta-catenin/Tcf4 signaling pathway, which is relevant for the renewal of intestinal crypt cells.

Gene expression profile in liver of hB1F transgenic mice

AIM: To analyze the tissue morphologic phenotype and liver gene expression profile of hB1F transgenic mice.

METHODS: Transgene expression was analyzed with RT-PCR and Western blotting. For one of the transgenic mouse lines, tissue expression pattern of the transgene was also examined with immunochemical methods. Pathological analysis was used to examine the tissue morphologic phenotype of established transgenic mice. The liver gene expression profile of transgenic mice was analyzed with microchip, and some of the differentially expressed genes were verified with RT-PCR.

RESULTS: The expressions of hB1F were shown in livers from 6 of 7 transgenic mouse lines. The overexpression of hB1F transgene did not cause pathological changes. Expressions of three genes were up-regulated, while down-regulation was observed for 25 genes.

CONCLUSION: The overexpression of hB1F transgene may cause changes of gene expression profiles in the liver of transgenic mice.

Prospero-Related Homeobox (Prox1) Is a Corepressor of Human Liver Receptor Homolog-1 and Suppresses the Transcription of the Cholesterol 7-α-Hydroxylase Gene

Cholesterol 7-α-hydroxylase (CYP7A1) catalyzes a rate-limiting step in bile acid synthesis in liver, and its gene transcription is under complex regulation by multiple nuclear receptors in response to bile acids, cholesterol derivatives, and hormones. The liver receptor homolog-1 (LRH-1), a member of the fushi tarazu factor 1 subfamily of nuclear receptors, has emerged as an essential regulator for the expression of cyp7a1. In this report, we demonstrate Prox1, a prospero-related homeobox transcription factor, identified through a yeast two-hybrid screening, can directly interact with human LRH-1 (hLRH-1) and suppresses hLRH-1-mediated transcriptional activation of human cyp7a1 gene. Biochemical analysis demonstrates that Prox1 interacts with both the ligand binding domain (LBD) and the DNA binding domain (DBD) of hLRH-1. An LRKLL motif in Prox1 is important for the interaction with the LBD but not the DBD of hLRH-1. In hLRH-1 LBD, helices 2 and 10 are essential for Prox1 recruitment. The suppression by Prox1 on the transcriptional activity of hLRH-1 can be mediated through its interaction with the LBD or the DBD of hLRH-1. Gel shift assays reveal that Prox1 impairs the binding of hLRH-1 to the promoter of human cyp7a1 gene.

The orphan nuclear receptor LRH-1 activates the ABCG5/ABCG8 intergenic promoter

The ATP binding cassette (ABC) half-transporters ABCG5 and ABCG8 facilitate biliary and intestinal removal of neutral sterols. Here, we identify a binding site for the orphan nuclear receptor liver receptor homolog-1 (LRH-1) at nt 134-142 of the ABCG5/ABCG8 intergenic region necessary for the activity of both the ABCG5 and ABCG8 promoters. Mutating this LRH-1 binding site reduced promoter activity of the human ABCG5/ABCG8 intergenic region more than 7-fold in HepG2 and Caco2 cells. Electrophoretic mobility shift assays with HepG2 nuclear extracts demonstrated specific binding of LRH-1 to the LRH-1 binding motif in the human ABCG5/ABCG8 intergenic region. LRH-1 overexpression increased promoter activity up to 1.6-fold and 3-fold in Caco2 and 293 cells, respectively. Finally, deoxycholic acid repressed the ABCG5 and ABCG8 promoters, consistent with bile acid regulation via the farnesoid X receptor-small heterodimeric partner-LRH-1 pathway. These results demonstrate that LRH-1 is a positive transcription factor for ABCG5 and ABCG8 and, in conjunction with studies on LRH-1 activation of other promoters, identify LRH-1 as a "master regulator" for genes involved in sterol and bile acid secretion from liver and intestine.

Quantitative trait loci that determine lipoprotein cholesterol levels in an intercross of 129S1/SvImJ and CAST/Ei inbred mice

To identify genetic determinants of lipoprotein levels, we are performing quantitative trait locus (QTL) analysis on a series of mouse intercrosses in a "daisy chain" experimental design, to increase the power of detecting QTL and to identify common variants that should segregate in multiple intercrosses. In this study, we intercrossed strains CAST/Ei and 129S1/SvImJ, determined HDL, total, and non-HDL cholesterol levels, and performed QTL mapping using Pseudomarker software. For HDL cholesterol, we identified two significant QTL on chromosome (Chr) 1 (Hdlq5, 82 cM, 60-100 cM) and Chr 4 (Hdlq10, 20 cM, 10-30 cM). For total cholesterol, we identified three significant QTL on Chr 1 (Chol7, 74 cM, 65-80 cM), Chr 4 (Chol8, 12 cM, 0-30 cM), and Chr 17 (Chol9, 54 cM, 20-60 cM). For non-HDL cholesterol, we identified significant QTL on Chr 8 (Nhdlq1, 34 cM, 20-60 cM) and Chr X (Nhdlq2, 6 cM, 0-18 cM). Hdlq10 was the only QTL detected in two intercrosses involving strain CAST/Ei. Hdlq5, Hdlq10, Nhdlq1, and two suggestive QTL at D7Mit246 and D15Mit115 coincided with orthologous human lipoprotein QTL. Our analysis furthers the knowledge of the genetic control of lipoprotein levels and points to the importance of Hdlq10, which was detected repeatedly in multiple studies.

The fetoprotein transcription factor (FTF) gene is essential to embryogenesis and cholesterol homeostasis and is regulated by a DR4 element

The fetoprotein transcription factor (FTF) gene was inactivated in the mouse, with a lacZ gene inserted inframe into exon 4. LacZ staining of FTF+/- embryos shows that the mFTF gene is activated at initial stages of zygotic transcription. FTF gene activity is ubiquitous at the morula and blastocyst stages and then follows expression patterns indicative of multiple FTF functions in fetal development. FTF-/- embryos die at E6.5-7.5, with features typical of visceral endoderm dysfunction. Adult FTF+/- mice are hypocholesterolemic, and express liver FTF at about 40% of the normal level. Overexpression of liver FTF in transgenic mice indicates in vivo that FTF is an activator of CYP7A1. However, CYP7A1 expression is increased in FTF+/- liver. Gene expression profiles indicate that higher CYP7A1 expression is caused by attenuated liver cell stress signaling. Diet experiments support a model where FTF is quenched both by activated c-Jun, and by SHP as a stronger feedback mechanism to repress CYP7A1. A DR4 element is conserved in the FTF gene promoter and activated by LXR-RXR and TR-RXR, qualifying the FTF gene as a direct metabolic sensor. Liver FTF increases in rats treated with thyroid hormone or a high cholesterol diet. The FTF DR4 element tightens functional links between FTF and LXRalpha in cholesterol homeostasis and can explain transient surges of FTF gene activities during development and FTF levels lower than predicted in FTF+/- liver. The FTF-lacZ mouse establishes a central role for FTF in developmental, nutritive, and metabolic functions from early embryogenesis through adulthood.

Gene regulatory factors in pancreatic development

The intensity of research on pancreatic development has increased markedly in the past 5 years, primarily for two reasons: we now know that the insulin-producing beta-cells normally arise from an endodermally derived, pancreas-specified precursor cell, and successful transplants of islet cells have been performed, relieving patients with type I diabetes of symptoms for extended periods after transplantation. Combining in vitro beta-cell formation from a pancreatic biopsy of a diabetic patient or from other stem-cell sources followed by endocrine cell transplantation may be the most beneficial route for a future diabetes therapy. However, to achieve this, a thorough understanding of the genetic components regulating the development of beta-cells is required. The following review discusses our current understanding of the transcription factor networks necessary for pancreatic development and how several genetic interactions coming into play at the earliest stages of endodermal development gradually help to build the pancreatic organ. Developmental Dynamics 229:176-200, 2004.