Vitamin D-binding protein gene transcription is regulated by the relative abundance of hepatocyte nuclear factors 1alpha and 1beta

New aspects of vitamin D metabolism and action - addressing the skin as source and target

Vitamin D has a key role in stimulating calcium absorption from the gut and promoting skeletal health, as well as many other important physiological functions. Vitamin D is produced in the skin. It is subsequently metabolized to its hormonally active form, 1,25-dihydroxyvitamin D (1,25(OH)₂D), by the 1-hydroxylase and catabolized by the 24-hydroxylase. In this Review, we pay special attention to the effect of mutations in these enzymes and their clinical manifestations. We then discuss the role of vitamin D binding protein in transporting vitamin D and its metabolites from their source to their targets, the free hormone hypothesis for cell entry and HSP70 for intracellular transport. This is followed by discussion of the vitamin D receptor (VDR) that mediates the cellular actions of 1,25(OH)₂D. Cell-specific recruitment of co-regulatory complexes by liganded VDR leads to changes in gene expression that result in distinct physiological actions by 1,25(OH)₂D, which are disrupted by mutations in the VDR. We then discuss the epidermis and hair follicle, to provide a non-skeletal example of a tissue that expresses VDR that not only makes vitamin D but also can metabolize it to its hormonally active form. This enables vitamin D to regulate epidermal differentiation and hair follicle cycling and, in so doing, to promote barrier function, wound healing and hair growth, while limiting cancer development.

Induction of α cell-restricted Gc in dedifferentiating β cells contributes to stress-induced β-cell dysfunction

Diabetic β cell failure is associated with β cell dedifferentiation. To identify effector genes of dedifferentiation, we integrated analyses of histone methylation as a surrogate of gene activation status and RNA expression in β cells sorted from mice with multiparity-induced diabetes. Interestingly, only a narrow subset of genes demonstrated concordant changes to histone methylation and RNA levels in dedifferentiating β cells. Notable among them was the α cell signature gene Gc, encoding a vitamin D-binding protein. While diabetes was associated with Gc induction, Gc-deficient islets did not induce β cell dedifferentiation markers and maintained normal ex vivo insulin secretion in the face of metabolic challenge. Moreover, Gc-deficient mice exhibited a more robust insulin secretory response than normal controls during hyperglycemic clamps. The data are consistent with a functional role of Gc activation in β cell dysfunction, and indicate that multiparity-induced diabetes is associated with altered β cell fate.

A reduced protein diet modulates enzymes of vitamin D and cholesterol metabolism in young ruminants

Besides other adverse effects, a low protein diet has been shown to modulate cholesterol and vitamin D metabolism in monogastric species like rats and humans. As ruminants can increase the efficiency of the rumino-hepatic circulation of urea, it is assumed that goats should be able to compensate for a low dietary protein intake better. After a dietary protein restriction (9% vs. 20%) for six weeks, plasma concentrations of urea, albumin, 1,25-dihydroxyvitamin D₃ and calcium were decreased, while plasma 25-hydroxyvitamin D₃ (25-OHD₃), and total cholesterol were significantly increased in young goats. Because this was not accompanied by any decrease in expression of CYP24A1 mRNA, we investigated mRNA expression of additional enzymes with known 24- and/or 25-hydroxylase activities (CYP2R1, CYP2J2, CYP3 A24, CYP27A1), receptors involved in their regulation (VDR, PXR, RXRα) and vitamin D binding protein (VDBP). CYP2R1expression was stimulated with the low dietary protein intake, negatively correlated with plasma urea and positively associated with serum 25-OHD₃. The greater plasma concentrations of total cholesterol could be explained with the reduction of CYP2J2 and CYP27A1 expression. None of the receptors investigated were affected by the dietary protein restriction but mRNA expression of VDBP was slightly reduced. Taken together our results show that dietary protein restriction has an impact on vitamin D and cholesterol metabolism in ruminants, too. Therefore, further investigations are needed before dietary interventions aiming at diminishing nitrogen excretion can be implemented.

Vitamin D Binding Protein: A Historic Overview

Vitamin D and all its metabolites are bound to a specific vitamin D binding protein, DBP. This protein was originally first discovered by its worldwide polymorphism and called Group-specific Component (GC). We now know that DBP and GC are the same protein and appeared early in the evolution of vertebrates. DBP is genetically the oldest member of the albuminoid family (including albumin, α-fetoprotein and afamin, all involved in transport of fatty acids or hormones). DBP has a single binding site for all vitamin D metabolites and has a high affinity for 25OHD and 1,25(OH)2D, thereby creating a large pool of circulating 25OHD, which prevents rapid vitamin D deficiency. DBP of higher vertebrates (not amphibians or reptiles) binds with very high affinity actin, thereby preventing the formation of polymeric actin fibrils in the circulation after tissue damage. Megalin is a cargo receptor and is together with cubilin needed to reabsorb DBP or the DBP-25OHD complex, thereby preventing the urinary loss of these proteins and 25OHD. The total concentrations of 25OHD and 1,25(OH)2D in DBP null mice or humans are extremely low but calcium and bone homeostasis remain normal. This is the strongest argument for claiming that the "free hormone hypothesis" also applies to the vitamin D hormone, 1,25(OH)2D. DBP also transports fatty acids, and can play a role in the immune system. DBP is genetically very polymorphic with three frequent alleles (DBP/GC 1f, 1s, and 2) but in total more than 120 different variants but its health consequences, if any, are not understood. A standardization of DBP assays is essential to further explore the role of DBP in physiology and diseases.

The application of post-translational modification oriented serum proteomics to assess experimental diabetes with complications

Proteome analysis of serum from type 2 diabetics with complications may lead to the discovery of diagnostic or prognostic biomarkers. To circumvent the principal barrier of serum proteomics, our investigation aimed to evaluate whether a study of post-translational modification enriched serum proteins could be valuable for the discovery of biomarkers or metabolic pathways related to type 2 diabetes pathogenesis. Type 2 diabetes was induced from high-fat diet fed Sprague Dawley rats with streptozotocin injection. Once diabetic status was confirmed, serum samples from either fasted healthy or diabetic rats were pooled and profiled by two-dimensional difference gel electrophoresis or comparative 2D electrophoresis after protein enrichments using immobilized metal ion, concanavalin A, and lentil affinity chromatography, respectively. Differential expressed proteins were identified and the associated networks were established by an Ingenuity Pathway Analysis. As a result, induced rats became severe diabetic and accompanied by hyperlipidemia, fatty liver, and glomerular hypertrophy. There were 3 total, 14 phosphorylated and 23 glycosylated protein targets differentially expressed. Proteins could be linked to HNF4A, HNF1A, and NF_κB transcriptional factors and antigen presentation, humoral immune response, and inflammatory response pathways. Predicted organ toxicity in kidney, heart, and liver matched with our histopathological results. In conclusion, post-translational modification based serum protein enrichment could be a valuable approach to enhance the resolution of serum proteomics without depleting potentially valuable abundant proteins. Our results also indicated the potential association of the hepatic secretome and hepatocyte nuclear factors in the pathogenesis of type 2 diabetes and its complications.

Fine mapping of a QTL on bovine chromosome 6 using imputed full sequence data suggests a key role for the group-specific component (GC) gene in clinical mastitis and milk production

BACKGROUND

Clinical mastitis is an inflammation of the mammary gland and causes significant costs to dairy production. It is unfavourably genetically correlated to milk production, and, thus, knowledge of the mechanisms that underlie these traits would be valuable to improve both of them simultaneously through breeding. A quantitative trait locus (QTL) that affects both clinical mastitis and milk production has recently been fine-mapped to around 89 Mb on bovine chromosome 6 (BTA6), but identification of the gene that underlies this QTL was not possible due to the strong linkage disequilibrium between single nucleotide polymorphisms (SNPs) within this region. Our aim was to identify the gene and, if possible, the causal polymorphism(s) responsible for this QTL through association analysis of high-density SNPs and imputed full sequence data in combination with analyses of transcript and protein levels of the identified candidate gene.

RESULTS

Associations between SNPs and the studied traits were strongest for SNPs that were located within and immediately upstream of the group-specific component (GC) gene. This gene encodes the vitamin D-binding protein (DBP) and has multiple roles in immune defense and milk production. A 12-kb duplication that was identified downstream of this gene covered its last exon and segregated with the QTL allele that is associated with increased mastitis susceptibility and milk production. However, analyses of GC mRNA levels on the available samples revealed no differences in expression between animals having or lacking this duplication. Moreover, we detected no differences in the concentrations of DBP and its ligand vitamin D between the animals with different GC genotypes that were available for this study.

CONCLUSIONS

Our results suggest GC as the gene that underlies the QTL for clinical mastitis and milk production. However, since only healthy animals were sampled for transcription and expression analyses, we could not draw any final conclusion on the absence of quantitative differences between animals with different genotypes. Future studies should investigate GC RNA expression and protein levels in cows with different genotypes during an infection.

Discovery of serum protein biomarkers in drug-free patients with major depressive disorder

OBJECTIVE

Major depressive disorder (MDD) is a systemic and multifactorial disorder involving complex interactions between genetic predisposition and disturbances of various molecular pathways. Its underlying molecular pathophysiology remains unclear, and no valid and objective diagnostic tools for the condition are available.

METHODS

We performed large-scale proteomic profiling to identify novel peripheral biomarkers implicated in the pathophysiology of MDD in 25 drug-free female MDD patients and 25 healthy controls. First, quantitative serum proteome profiles were obtained and analyzed by liquid chromatography-tandem mass spectrometry using serum samples from 10 MDD patients and 10 healthy controls. Next, candidate biomarker sets, including differentially expressed proteins from the profiling experiment and those identified in the literature, were verified using multiple-reaction monitoring in 25 patients and 25 healthy controls. The final panel of potential biomarkers was selected using multiparametric statistical analysis.

RESULTS

We identified a serum biomarker panel consisting of six proteins: apolipoprotein D, apolipoprotein B, vitamin D-binding protein, ceruloplasmin, hornerin, and profilin 1, which could be used to distinguish MDD patients from controls with 68% diagnostic accuracy. Our results suggest that modulation of the immune and inflammatory systems and lipid metabolism are involved in the pathophysiology of MDD.

CONCLUSIONS

Our findings of functional proteomic changes in the peripheral blood of patients with MDD further clarify the molecular biological pathway underlying depression. Further studies using larger, independent cohorts are needed to verify the role of these candidate biomarkers for the diagnosis of MDD.

WITHDRAWN: Expression and functional characterization of guanylyl cyclase C receptor in HepG2 cells: Two-step regulation by dexamethasone and hepatocyte nuclear factor 4 (HNF4)

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The mouse alpha-albumin (afamin) promoter is differentially regulated by hepatocyte nuclear factor 1α and hepatocyte nuclear factor 1β

Alpha-albumin (AFM), a member of the albumin gene family that also includes albumin, alpha-fetoprotein, and vitamin D-binding protein, is expressed predominantly in the liver and activated at birth. Here, we identify two hepatocyte nuclear factor 1 (HNF1)-binding sites in the AFM promoter that are highly conserved in different mammals. These two sites bind HNF1α and HNF1β. The distal site (centered at -132, relative to AFM exon 1) is more important than proximal site (centered at -58), based on HNF1 binding and mutational analysis in transfected cells. Our data indicate that HNF1α is a more potent activator of AFM promoter than is HNF1β. However, HNF1β can act in a dominant manner to inhibit HNF1α-dependent transactivation of the AFM promoter when both proteins are expressed together. This suggests that the differential timing with which the albumin family genes are activated in the liver may be influenced by their responsiveness to HNF1α and HNF1β. Our comparison of HNF1-binding sites in the promoters in the albumin family of genes indicates that the primordial albumin-like gene contained two HNF1 sites; one of these sites was lost from the albumin promoter, but both sites still are present in other members of this gene family.

The alpha-fetoprotein enhancer region activates the albumin and alpha-fetoprotein promoters during liver development

The four members of the albumin gene family encode the serum transport proteins albumin, alpha-fetoprotein, alpha-albumin, and vitamin D-binding protein. These genes are transcribed primarily in the liver with each having a different pattern of developmental expression. The tight linkage of these genes, particularly that of albumin, alpha-fetoprotein and alpha-albumin, and their liver-specific expression, has led to the suggestion that these genes share common regulatory elements. To directly examine whether the alpha-fetoprotein enhancer region could regulate the albumin gene family, expression of these genes was monitored in mice in which this region was deleted by homologous recombination. Our data indicate that this enhancer region is required for alpha-fetoprotein and albumin activation early in liver development and alpha-fetoprotein reactivation during liver regeneration, but that albumin, alpha-albumin, and vitamin D-binding protein expression later in hepatic development is not affected by the absence of these enhancers. We also demonstrate that RNA polymerase II loading on the alpha-fetoprotein and albumin promoters is reduced in the absence of this enhancer region, indicating a direct role for these enhancers in the assembly of the RNA Polymerase II complex during liver development.

Alpha-fetoprotein related gene (ARG): a new member of the albumin gene family that is no longer functional in primates

The serum albumin gene family is comprised of albumin, alpha-fetoprotein, alpha-albumin (afamin), and the more distantly related Vitamin D binding protein. These genes arose from a common ancestor through a series of duplication events, are expressed primarily in the liver and tightly linked in all species where this has been investigated. Here, we describe a fifth member of the albumin gene family that we have named Alpha-fetoprotein Related Gene (ARG) since it exhibits greatest similarity to this family member. ARG is activated in the liver perinatally, but is expressed at very low levels. The ARG gene is present and intact in the mouse, rat, dog and horse genomes. In contrast, the ARG gene in human, chimpanzee, rhesus monkey, and marmoset contains a number of mutations common to all four species, indicating that this gene has been an inactive pseudogene in primates for at least 40 million years. Low expression and aberrant splicing of the ARG gene in the mouse liver suggests that ARG may have less functional significance than other members of the serum albumin gene family even in species where it is still intact.

Identification of an inter-transcription factor regulatory network in human hepatoma cells by Matrix RNAi

Transcriptional regulation by transcriptional regulatory factors (TRFs) of their target TRF genes is central to the control of gene expression. To study a static multi-tiered inter-TRF regulatory network in the human hepatoma cells, we have applied a Matrix RNAi approach in which siRNA knockdown and quantitative RT-PCR are used in combination on the same set of TRFs to determine their interdependencies. This approach focusing on several liver-enriched TRF families, each of which consists of structurally homologous members, revealed many significant regulatory relationships. These include the cross-talks between hepatocyte nuclear factors (HNFs) and the other TRF groups such as CCAAT/enhancer-binding proteins (CEBPs), retinoic acid receptors (RARs), retinoid receptors (RXRs) and RAR-related orphan receptors (RORs), which play key regulatory functions in human hepatocytes and liver. In addition, various multi-component regulatory motifs, which make up the complex inter-TRF regulatory network, were identified. A large part of the regulatory edges identified by the Matrix RNAi approach could be confirmed by chromatin immunoprecipitation. The resultant significant edges enabled us to depict the inter-TRF TRN forming an apparent regulatory hierarchy of (FOXA1, RXRA) → TCF1 → (HNF4A, ONECUT1) → (RORC, CEBPA) as the main streamline.

Role of HNF-1α and HNF-1β on insulin, IGF-1 and other potential target genes

Hepatocyte nuclear factor (HNF)-1α and HNF-1β are transcription factors that regulate many target genes in various tissues including liver, pancreas and kidney. Heterozygous mutations in the HNF-1α and HNF-1β genes result in maturity-onset diabetes of the young (MODY)3 and MODY5, respectively. The discovery of these 'hepatocyte nuclear factors' as MODY-responsible genes provided a breakthrough in the field of diabetes. Patients with HNF-1α and HNF-1β mutations, as well as their model mice, show impaired pancreatic β-cell function. The mechanism of impaired β-cell function and the target genes has been intensively investigated by considerable in vitro and in vivo studies. The insulin gene is one of the target genes of HNF-1α and HNF-1β in the β-cells, and may contribute to the diabetes. The IGF-1 gene is also regulated by HNF-1α and HNF-1β, and its decreased expression may contribute to growth failure and impaired β-cell proliferation. Mutations in HNF-1β result in symptoms in multiple organs, including kidney and liver, and several target genes have been reported to be involved in the pathogenesis. HNF-1α and HNF-1β may be one of the master regulators of hepatocyte and islet transcription, and further investigations by microarray and genome-scale analyses are providing information for the better understanding of the complex transcriptional network involving HNF-1α and -1β.

Expression of hepatocyte nuclear factor-1alpha mRNA in human anaplastic thyroid cancer cell lines and tumors

BACKGROUND

Hepatocyte nuclear factor (HNF)-1alpha and HNF-1beta are related transcription factors that are mainly expressed in liver cells. Our previous study showed that HNF-1beta was highly expressed in papillary thyroid cancer cell lines and tumors. HNF-1alpha mRNA, however, was not detected in differentiated thyroid cancer cell lines. The objective of this study was to determine whether HNF-1alpha is expressed in dedifferentiated anaplastic thyroid cancer cells.

METHODS

Total RNA isolated from six anaplastic thyroid cancer cell lines and 38 surgical samples was analyzed for HNF-1alpha mRNA by conventional reverse-transcription polymerase chain reaction (RT-PCR) or real-time RT-PCR. HNF-1alpha DNA binding activity was measured by gel retardation assay and HNF-1alpha protein was identified by Western blotting.

RESULTS

HNF-1alpha mRNA was expressed in four of the six anaplastic cell lines. The presence of HNF-1alpha protein and DNA binding activity was detected in three lines with higher HNF-1alpha mRNA level. Three cell lines also expressed HNF-1beta. HNF-1alpha transcripts were also detected in five out of six anaplastic tumors, but not in the papillary tumors except one with weak PCR signal.

CONCLUSION

HNF-1alpha mRNA was detected in high frequency in anaplastic thyroid cancer cell lines and tumors. HNF-1alpha might play a role in the pathogenesis of anaplastic thyroid cancer.

An intronic locus control region plays an essential role in the establishment of an autonomous hepatic chromatin domain for the human vitamin D-binding protein gene

The human vitamin D-binding protein (hDBP) gene exists in a cluster of four liver-expressed genes. A minimal hDBP transgene, containing a defined set of liver-specific DNase I hypersensitive sites (HSs), is robustly expressed in mouse liver in a copy-number-dependent manner. Here we evaluate these HSs for function. Deletion of HSI, located 5' to the promoter (kb -2.1) had no significant effect on hDBP expression. In contrast, deletion of HSIV and HSV from intron 1 repressed hDBP expression and eliminated copy number dependency without a loss of liver specificity. Chromatin immunoprecipitation analysis revealed peaks of histone H3 and H4 acetylation coincident with HSIV in the intact hDBP locus. This region contains a conserved array of binding sites for the liver-enriched transcription factor C/EBP. In vitro studies revealed selective binding of C/EBPalpha to HSIV. In vivo occupancy of C/EBPalpha at HSIV was demonstrated in hepatic chromatin, and depletion of C/EBPalpha in a hepatic cell line decreased hDBP expression. A nonredundant role for C/EBPalpha was confirmed in vivo by demonstrating a reduction of hDBP expression in C/EBPalpha-null mice. Parallel studies revealed in vivo occupancy of the liver-enriched factor HNF1alpha at HSIII (at kb 0.13) within the hDBP promoter. These data demonstrate a critical role for elements within intron 1 in the establishment of an autonomous and productive hDBP chromatin locus and suggest that this function is dependent upon C/EBPalpha. Cooperative interactions between these intronic complexes and liver-restricted complexes within the target promoter are likely to underlie the consistency and liver specificity of the hDBP activation.

Hepatocyte nuclear factor1 transcription factors are essential for the UDP-glucuronosyltransferase 1A9 promoter response to hepatocyte nuclear factor 4α

In humans, UDP-glucuronosyltransferase 1A9 is known to glucuronidate numerous lipophilic substances of pharmacological and toxicological importance. Although it has been established that individuals vary in their capacity to express this detoxification enzyme, little is known about the mechanisms that dictate the regulation of UGT1A9. In particular, it is not understood why, while the proximal regulatory regions of the UGT1A7-10 gene cluster are highly similar, UGT1A9 is the sole hepatic isoform of the four. Recent data have suggested that the human UGT1A9 promoter is controlled by hepatocyte nuclear factor 4alpha. In this work, we confirm that the human UGT1A9 promoter can indeed be upregulated by human hepatocyte nuclear factor 4alpha in vitro. Our results, however, show that the previously-reported hepatocyte nuclear factor 4alpha-binding site only plays a minor role in this response. Instead, upregulation was found to require a more proximal response element, which was not preserved in the UGT1A7, UGT1A8 or UGT1A10 promoters. Furthermore, hepatocyte nuclear factor 4alpha-mediated transcription from the human UGT1A9 promoter was discovered to be entirely dependent on hepatocyte nuclear factor 1. We have established that two hepatocyte nuclear factor 1-binding elements are involved in this phenomenon, the more distal of which is unique to the UGT1A9 promoter. Interestingly, this second site had no significant role in hepatocyte nuclear factor 1alpha-mediated induction of the UGT1A9 promoter in vitro, yet was critical for upregulation by human hepatocyte nuclear factor 4alpha. The discovery of two unique and cooperative liver-enriched transcription factor binding sites in the UGT1A9 promoter is a significant step towards understanding the unique hepatic expression of UGT1A9 amongst the UGT1A7-10 gene cluster.

Abnormal changes of plasma acute phase proteins in schizophrenia and the relation between schizophrenia and haptoglobin (Hp) gene

In this study we focused on detecting schizophrenia related changes of plasma proteins using proteomic technology and examining the relation between schizophrenia and haptoglobin (Hp) genotype. We investigated plasma proteins from schizophrenic subjects (n = 42) and healthy controls (n = 46) by two-dimensional gel electrophoresis (2-DE) in combination with mass spectrometry. To further reveal the genetic relationship between acute phase proteins (APPs) and schizophrenia disease, we tested Hp alpha1/Hp alpha2 (Hp 1/2) polymorphism and two single nucleotide polymorphisms (SNPs) of Hp, rs2070937 and rs5473, for associations with schizophrenia in the Chinese Han population. With the relatively high number of samples for 2-DE work, we found that four proteins in the family of positive APPs were all up-regulated in patients. In genetic association study, we found significant associations existing between schizophrenia and Hp polymorphisms, Hp 1/2 and rs2070937 variants. Schizophrenia is accompanied by both an altered expression of Hp protein and a different genotype distribution of Hp gene, demonstrating that Hp is associated with schizophrenia. The results from proteomic and genomic aspects both indicate that acute phase reaction is likely to be an aetiological agent in the pathophysiology of schizophrenia, but not just an accompanying symptom. The positive APPs are schizophrenic related proteins, with the highly concordant results on four positive APPs.

Altered vitamin D metabolism in type II diabetic mouse glomeruli may provide protection from diabetic nephropathy

The db/db mouse develops features of type II diabetes mellitus as the result of impaired signaling through its abnormal leptin receptor. In spite of accurate metabolic features of diabetes, renal disease manifestations in these mice are not as severe as in humans suggesting the presence of protective genes. There is a growing body of evidence in humans for the relevance of vitamin D in diabetes. Here we followed a large cohort of db/db mice and their non-diabetic db/+ littermates. Transcriptional profiling revealed significant upregulation of 23 genes involved in Ca2+ homeostasis and vitamin D metabolism in db/db glomeruli relative to db/+ glomeruli. Increased glomerular expression of vitamin D3 1alpha-hydroxylase, vitamin D binding protein, calbindins D9K and D28K, and calcyclin mRNA was confirmed by quantitative reverse transcription-polymerase chain reaction in 20-, 36-, and 52-week-old db/db glomeruli. Although vitamin D3 1alpha-hydroxylase protein was primarily expressed and upregulated in db/db renal tubules, it was also expressed in glomerular podocytes in vivo. Serum 1,25-dihydroxyvitamin D3 and urinary Ca2+ excretion were increased >3-fold in db/db mice compared to db/+ mice. Cultured glomerular podocytes had mRNA for vitamin D3 1alpha-hydroxylase, vitamin D receptor, and calbindin D28K, each of which was increased in high glucose conditions. High glucose also led to enhanced production of fibronectin and collagen IV protein, which was blocked by 1,25-dihydroxyvitamin D3. These results show that vitamin D metabolism is altered in db/db mice leading to metabolic and transcriptional effects. The podocyte is affected by paracrine and potentially autocrine effects of vitamin D, which may explain why db/db mice are resistant to progressive diabetic nephropathy.

The human vitamin D-binding protein gene contains locus control determinants sufficient for autonomous activation in hepatic chromatin

The human vitamin D-binding protein (hDBP) gene is a member of a cluster that includes albumin, alpha-fetoprotein and alpha-albumin genes. The common origin, physical linkage and hepatic expression of these four genes predict shared regulatory element(s). However, separation of hDBP from the other three genes by 1.5 Mb argues that hDBP may be under autonomous control. To test for hDBP autonomy, mouse lines were generated with a transgene containing the hDBP gene along with extensive flanking sequences. Expression of this transgene was hepatic, robust and proportional to transgene copy number. DNase I hypersensitive site (HS) mapping revealed five liver-specific HS at the hDBP locus: HSI and HSIII at -2.1 kb and -0.13 kb upstream of the transcription initiation site, HSIV and HSV within intron 1 and HSVII located 3' to the poly(A) site. A second transgene with minimal flanking sequences confirmed the sufficiency of these gene-proximal determinants for hepatic activation. The hepatic-specific HS aligned with segments of phylogenetically conserved non-coding sequences. These data demonstrate the autonomy of the hDBP locus and suggest that this control is mediated by chromatin-based locus control determinants in close proximity to, and within the transcription unit.

Histone deacetylase inhibitor depsipeptide represses nicotinamide N-methyltransferase and hepatocyte nuclear factor-1beta gene expression in human papillary thyroid cancer cells

Nicotinamide N-methyltransferase (NNMT) catalyzes N-methylation of nicotinamide and other structural analogues. NNMT gene expression is enhanced in many papillary thyroid cancer cells and activated by hepatocyte nuclear factor (HNF)-1beta. In this work, we studied the effects of depsipeptide, a histone deacetylase inhibitor, on NNMT gene expression in BHP 18-21 papillary thyroid cancer cells. Depsipeptide reduced NNMT mRNA level in a dose-dependent and time-dependent manner as determined by semiquantitative reverse transcriptase-polymerase chain reaction (RT-PCR). In contrast, expression of the sodium iodide symporter (NIS), a gene with differentiated function, waas enhanced in the treated cells. NNMT protein level determined by Western blot analysis and NNMT catalytic activity was also reduced significantly in the depsipeptide-treated cells. To study the mechanism of NNMT gene repression by depsipeptide, effects of depsipeptide on NNMT promoter activity were determined by luciferase reporter gene assay. NNMT promoter activity was significantly reduced in the HNF-1beta-positive BHP 18-21 cells but not in the HNF-1beta-negative BHP 14-9 papillary cancer cells. A mutant reporter construct with mutations in a HNF-1 site in the NNMT basal promoter region did not respond to depsipeptide in both HNF-1beta protein levels, and abolished activity of DNA binding to the HNF-1 site in the NNMT promoter region. Protein synthesis inhibitor cycloheximide and proteasome inhibitor MG-132 enhanced HNF-1beta stability in the depsipeptide-treated cells. In summary, depsipeptide represses NNMT and HNF-1beta gene expression in some papillary thyroid cancer cells. the repression of NNMT by depsipeptide is at the transcription level through downregulation of transcription activator HNF-1beta.

Sequence variation within the 5' regulatory regions of the vitamin D binding protein and receptor genes and prostate cancer risk

BACKGROUND

The vitamin D receptor (VDR) and binding protein (DBP) mediate the cellular transport, activity, and anti-tumor action of 1,25-dihydroxyvitamin D3 [1,25-(OH)(2)D3]. The purpose of this investigation is to determine whether novel single nucleotide polymorphisms (SNPs) within the transcriptional regulatory regions of the VDR and DBP are associated with prostate cancer risk.

METHODS

Novel SNPs were identified in the VDR and DBP transcription regulatory gene regions and genotyped in a case-control study using male subjects with (n=258) or without (n=434) prostate cancer.

RESULTS

African-American men who possessed at least one variant VDR-5132 C allele had a increased risk of prostate cancer (OR=1.83; 95% CI: 1.02, 3.31). Further study revealed that the VDR-5132 T/C SNP eliminates a GATA-1 transcription factor-binding site.

CONCLUSION

The VDR-5132 T/C SNP, resulting in potential elimination of the GATA-1 transcription factor-binding site, may increase prostate cancer susceptibility in African-Americans. Confirmation of these findings is needed in larger observational studies.

Identification and Characterization of Functional Hepatocyte Nuclear Factor 1‐Binding Sites in UDP‐Glucuronosyltransferase Genes

The hepatocyte nuclear factor 1 (HNF1) transcription factor family is composed of two closely related homeodomain proteins with similar but distinct expression profiles. Homodimers and heterodimers of these transcription factors, HNF1alpha and HNF1beta, increase transcription from target genes through direct physical interaction with one or more elements of sufficient similarity to a 13 nucleotide-inverted dyad consensus-binding sequence. Potential HNF1-binding sites have been found in the proximal upstream regulatory regions of most known human UDP-glucuronosyltransferase (UGT) genes. As the liver and gastrointestinal tract are both important sites of glucuronidation and express significant levels of one or both HNF1 proteins, it is thought that these homeoproteins may play a role in transcriptional regulation of UGTs. This chapter explores the current evidence that HNF1 transcription factors are explicitly involved in the transcription of mammalian UGT genes. Most data supporting this hypothesis come from in vitro reporter assays, site-directed mutagenesis, and electrophoretic mobility-shift assays, for which methods are detailed. However, as in vitro functionality of transcription factors does not necessarily imply significance in vivo, some of the limitations of these techniques are also examined. In addition, available in vivo data are discussed, with particular attention given to contributions made by HNF1alpha knockout mouse models and microarray studies of human tissue. Finally, possible scenarios in which HNF1-mediated regulation of UGT expression may be clinically relevant are suggested.

Cloning and characterization of the human beta2-glycoprotein I (beta2-GPI) gene promoter: roles of the atypical TATA box and hepatic nuclear factor-1alpha in regulating beta2-GPI promoter activity

Beta2-glycoprotein I (beta2-GPI) is a plasma glycoprotein primarily synthesized in the liver. The interindividual variability of beta2-GPI expression in subjects with various metabolic syndromes and disease states suggests that it may have clinical importance. However, the regulation of beta2-GPI gene expression has not been clarified. To gain more insight into the control of beta2-GPI gene expression, we cloned the 4.1-kb 5'-flanking region and characterized the proximal promoter of the beta2- GPI gene in this study. Cis -acting elements required for beta2-GPI promoter activity were identified with transient transfection assays in the hepatoma cell lines HepG2 and Huh7 and in non-hepatic HeLa cells. Serial deletion analyses of the beta2-GPI 5'-flanking sequence revealed that the region from -197 to +7 had strong promoter activity in hepatoma cells but not in HeLa cells. Truncation and site-directed mutagenesis of putative cis -elements within this region showing an atypical TATA box and a HNF-1 (hepatic nuclear factor-1) element were both essential for the beta2-GPI promoter activity. Subsequent gel mobility shift assays confirmed the interaction of HNF-1alpha with the HNF-1 site residing downstream of the TATA box. Co-transfection of beta2-GPI promoter-luciferase vector with HNF-1alpha expression vector in Huh7 and HNF-1-deficient HeLa cells demonstrated the transactivation effect of HNF-1alpha on beta2-GPI promoter activity. In addition, overexpression of HNF-1alpha enhanced the endogenous beta2-GPI expression. These results suggest that the atypical TATA box and HNF-1 cis-element are critical for beta2-GPI transcription and HNF-1alpha may play an important role in cell-specific regulation of beta2-GPI gene expression.

Activation of nicotinamide N-methyltransferase gene promoter by hepatocyte nuclear factor-1beta in human papillary thyroid cancer cells

We previously demonstrated that the human nicotinamide N-methytransferase (NNMT) gene was highly expressed in many papillary thyroid cancers and cell lines. The expression in other papillary and follicular cancers or cell lines and normal thyroid cells was low or undetectable. To gain an understanding of the molecular mechanism of this cell-specific expression, the NNMT promoter was cloned and studied by luciferase reporter gene assay. The promoter construct was expressed highly in papillary cancer cell lines, including those with higher (e.g. BHP 2-7) and lower (e.g. BHP 14-9) NNMT gene expression, and expressed weakly in follicular thyroid cancer cell lines. Further study with 5'-deletion promoter construct suggested that the NNMT promoter was regulated differently in BHP 2-7 and BHP 14-9 cells. In BHP 2-7 cells, promoter activity was dependent on an upstream sequence. In BHP 14-9 cells, sequence in the basal promoter region contributed notably to the overall promoter activity. RT-PCR or Western blot analysis indicated that hepatocyte nuclear factor-1beta (HNF-1beta) was expressed in only papillary cancer cell lines with high NNMT gene expression. HNF-1beta was not expressed or expressed very weakly in other papillary, follicular, and Hurthle cancer cell lines and primary cultures of normal thyroid cells and benign thyroid conditions. A HNF-1 binding site was identified in the NNMT basal promoter region. Mutations in this site decreased NNMT promoter activity in the HNF-1beta-positive BHP 2-7 cells, but not in the HNF-1beta-negative BHP 14-9 cells. HNF-1beta bound to the HNF-1 site specifically as a homodimer as determined by gel retardation assays with HNF-1beta-specific antibody. Cotransfection of a HNF-1beta expression plasmid increased NNMT promoter activity significantly in both HNF-1beta-positive and -negative thyroid cancer cell lines and Hep G2 liver cancer cells. Furthermore, transient expression of HNF-1beta in BHP 14-9 cells increased endogenous NNMT protein levels. In summary, HNF-1beta functions as a transcription activator for NNMT gene expression in some papillary thyroid cancer cells.

Promoter-specific repression of hepatocyte nuclear factor (HNF)-1 beta and HNF-1 alpha transcriptional activity by an HNF-1 beta missense mutant associated with Type 5 maturity-onset diabetes of the young with hepatic and biliary manifestations

Mutations in the hepatocyte nuclear factor (HNF)-1 beta lead to type 5 maturity-onset diabetes of the young (MODY5). HNF-1 beta forms a homodimer or a heterodimer with HNF-1 alpha and regulates various target genes. HNF-1 beta mutations are rare, and no functional analysis has been performed in conjunction with HNF-1 alpha. HNF-1 beta is expressed in the liver and biliary system and controls liver-specific and bile acid-related genes. Moreover, liver-specific Hnf-1 beta knockout mice present with severe jaundice. However, no patients with HNF-1 beta mutations have biliary manifestations. In this report, we found a novel missense mutation in the HNF-1 beta gene in a patient with neonatal cholestasis and liver dysfunction together with the common features of MODY5. Functional analysis revealed that the mutant HNF-1 beta had diminished transcriptional activity by loss of the DNA binding activity. The mutant had a promoter-specific dominant-negative transcriptional effect on wild-type HNF- and inhibited its DNA binding. Moreover, the mutant had a promoter- and cell-specific transcriptional repressive effect on HNF-1 alpha and a promoter-specific inhibitory effect on HNF-1 alpha DNA binding. From these results, we considered that the different phenotype of patients with HNF-1 beta mutations might be caused by the different HNF-1 beta activity in conjunction with the different repression of HNF-1 alpha activity in selected promoters and tissues.

Hereditary persistence of alpha-fetoprotein is due to both proximal and distal hepatocyte nuclear factor-1 site mutations

BACKGROUND AND AIMS

The molecular mechanism of hereditary persistence of alpha-fetoprotein (HPAFP) has been previously described in a large Scottish family, consisting of a -119G>A substitution in the distal hepatocyte nuclear factor 1 (HNF-1) binding site of the alpha-fetoprotein (AFP) gene promoter. We report here the molecular mechanisms of HPAFP in 2 new unrelated families.

METHODS

Family 1 was of Bengali origin, and family 2 was Italian. Four of 5 subjects (family 1) and 3 of 9 (family 2) showed HPAFP. The AFP gene promoter was studied in all available family members.

RESULTS

All subjects with high AFP levels had mutated promoter sequences. Family 1 showed the reported -119G>A substitution. Family 2 showed -55C>A and -65C>T substitutions in the proximal putative HNF-1 binding region of the promoter. The -55C>A mutation increased the similarity of the proximal HNF-1 binding region to a consensus binding region. Gel shift assays confirmed its increased affinity toward HNF-1, and transfection experiments revealed an increased level of gene transcription. The -65C>T substitution theoretically created a CCAAT box. However, gel shift and transfection experiments failed to show any biological effect of this substitution that is associated with the -55C>A mutation.

CONCLUSIONS

Two different mutations localized in either HNF-1 binding sites of the AFP gene promoter may result in HPAFP. This highlights the importance of HNF-1 in AFP gene expression. Unexplained persistent AFP should lead to family study and/or AFP gene promoter sequencing to avoid inappropriate explorations and treatment decisions.

HNF-1alpha and endodermal transcription factors cooperatively activate Fabpl: MODY3 mutations abrogate cooperativity

Hepatocyte nuclear factor (HNF)-1alpha plays a central role in intestinal and hepatic gene regulation and is required for hepatic expression of the liver fatty acid binding protein gene (Fabpl). An Fabpl transgene was directly activated through cognate sites by HNF-1alpha and HNF-1beta, as well as five other endodermal factors: CDX-1, C/EBPbeta, GATA-4, FoxA2, and HNF-4alpha. HNF-1alpha activated the Fabpl transgene by as much as 60-fold greater in the presence of the other five endodermal factors than in their absence, accounting for up to one-half the total transgene activation by the group of six factors. This degree of synergistic interaction suggests that multifactor cooperativity is a critical determinant of endodermal gene activation by HNF-1alpha. Mutations in HNF-1alpha that result in maturity onset diabetes of the young (MODY3) provide evidence for the in vivo significance of these synergistic interactions. An R131Q HNF-1alpha MODY3 mutant exhibits complete loss of synergistic activation in concert with the other endodermal transcription factors despite wild-type transactivation ability in their absence. Furthermore, whereas wild-type HNF-1alpha exhibited pairwise cooperative synergy with each of the other five factors, the R131Q mutant could synergize only with GATA-4 and C/EBPbeta. Selective loss of synergy with other endodermal transcription factors accompanied by retention of native transactivation ability in an HNF-1alpha MODY mutant suggests in vivo significance for cooperative synergy.

Hepatocyte nuclear factor (HNF)-4 alpha/gamma, HNF-1 alpha, and vHNF-1 regulate the cell-specific expression of the human dihydrodiol dehydrogenase (DD)4/AKR1C4 gene

Recently, we found a region A (a hepatocyte nuclear factor (HNF)-4-binding site from nucleotides -701 to -684) and a region B (an HNF-1-binding site from nucleotides -682 to -666) as cis-acting elements necessary for the transcriptional activation of the human dihydrodiol dehydrogenase (DD)4 gene in human hepatoblastoma HepG2 cells, which express DD4 mRNA. Thus, to investigate the mechanism(s) responsible for the cell-type-specific expression of DD4 mRNA, we constructed a reporter plasmid, pDD4 Foot A+B: -95/+28, in which regions A and B were linked to the human DD4 minimal promoter (-95 to +28) fused to the luciferase gene. The luciferase activity was detectable in HepG2 cells but not in human renal adenocarcinoma ACHN cells transfected with the pDD4 Foot A+B: -95/+28, which do not express DD4 mRNA. A supershift assay using antibodies to HNF-4 alpha, -4 gamma, -1 alpha, or valiant HNF (vHNF)-1 revealed that HNF-4 alpha, -4 gamma, and -1 alpha recognized regions A and B in HepG2 cells and that only vHNF-1 bound to regions A and B in ACHN cells. Semiquantitative reverse-transcribed polymerase chain reaction showed that a large amount of vHNF-1-C, which lacked transcriptional activation domain, was expressed in ACHN cells. Transfection of ACHN cells with an expression plasmid of vHNF-1-C did not activate the pDD4 Foot A+B: -95/+28 reporter gene. Taken together, we conclude that the cell-type-specific expression of DD4 mRNA is regulated by vHNF-1-C.

Bile system morphogenesis defects and liver dysfunction upon targeted deletion of HNF1β

The inactivation of the Hnf1β gene identified an essential role in epithelial differentiation of the visceral endoderm and resulted in early embryonic death. In the present study, we have specifically inactivated this gene in hepatocytes and bile duct cells using the Cre/loxP system. Mutant animals exhibited severe jaundice caused by abnormalities of the gallbladder and intrahepatic bile ducts (IHBD). The paucity of small IHBD was linked to a failure in the organization of duct structures during liver organogenesis, suggesting an essential function of Hnf1b in bile duct morphogenesis. Mutant mice also lacked interlobular arteries. As HNF1β is not expressed in these cells, it further emphasizes the link between arterial and biliary formation. Hepatocyte metabolism was also affected and we identified hepatocyte-specific HNF1β target genes involved in bile acids sensing and in fatty acid oxidation.

Sucrase-isomaltase gene transcription requires the hepatocyte nuclear factor-1 (HNF-1) regulatory element and is regulated by the ratio of HNF-1 alpha to HNF-1 beta

The mouse sucrase-isomaltase (SI) gene is an enterocyte-specific gene expressed in a complex developmental pattern. We previously reported that a short, evolutionarily conserved gene promoter regulates developmental expression of SI in mouse small intestine. Herein, we investigated the role of a hepatocyte nuclear factor-1 (HNF-1) cis-acting element to regulate SI gene expression in vivo. Transgenic SI gene constructs with a mutated HNF-1 element (SIF3) revealed a strong reduction in promoter activity in comparison with a wild-type construct in mice and during Caco-2 cell differentiation. Nuclear proteins isolated from enterocytes showed increased binding of the HNF-1 alpha complex with a concomitant decrease in the HNF-1 beta-containing complex to the SIF3 element both during the suckling-weaning developmental transition and Caco-2 cell differentiation. These changes coincided with a strong induction of SI gene transcription. In transfection experiments, HNF-1 alpha activated the SI promoter via the SIF3 element, and co-expression of HNF-1 beta impaired this transcriptional activation. These findings demonstrate the essential role of the HNF-1 regulatory element to support SI gene transcription in vivo and suggest that the ratio of HNF-1 alpha to HNF-1 beta plays a role in the transcriptional activity of this gene during intestinal development.

A pancreatic beta -cell-specific enhancer in the human PDX-1 gene is regulated by hepatocyte nuclear factor 3beta (HNF-3beta ), HNF-1alpha, and SPs transcription factors

The PDX-1 transcription factor plays a key role in pancreas development. Although expressed in all cells at the early stages, in the adult it is mainly restricted to the beta-cell. To characterize the regulatory elements and potential transcription factors necessary for human PDX-1 gene expression in beta-cells, we constructed a series of 5' and 3' deletion fragments of the 5'-flanking region of the gene, fused to the luciferase reporter gene. In this report, we identify by transient transfections in beta- and non-beta-cells a novel beta-cell-specific distal enhancer element located between -3.7 and -3.45 kilobases. DNase I footprinting analysis revealed two protected regions, one binding the transcription factors SP1 and SP3 and the other hepatocyte nuclear factor 3beta (HNF-3beta) and HNF-1alpha. Cotransfection experiments suggest that HNF-3beta, HNF-1alpha, and SP1 are positive regulators of the herein-described human PDX-1 enhancer element. Furthermore, mutations within each motif abolished the binding of the corresponding factor(s) and dramatically impaired the enhancer activity, therefore suggesting cooperativity between these factors.

The multifunctional properties and characteristics of vitamin D-binding protein

In recent years, our understanding of the many physiological, biochemical, and molecular functions and attributes of vitamin D-binding protein (DBP) has seen exciting and significant advances. Since its identification in 1959, many important functions of this abundant serum protein have been discovered. These range from the transport of vitamin D metabolites to possible roles in the immune system and host defense. With these discoveries, many questions regarding the biology of DBP have been raised and many remain to be answered. Our current understanding of the classic and less-recognized activities of DBP is discussed here.

Distant enhancers stimulate the albumin promoter through complex proximal binding sites

The albumin-alpha-fetoprotein locus epitomizes the main features of transcriptional regulation of fetal and adult hepatocyte-specific genes: developmentally regulated promoters and strong distant enhancers. Full enhancer activity required only a proximal albumin-promoter region containing the TATA box, hepatic nuclear factor 1 (HNF1), and nuclear factor Y (NF-Y) sites. Deletion of the HNF1 site abrogated enhancer and promoter activity, whereas methylation of the site reduced all activity by about 3-fold. Deletion of the NF-Y site attenuated activity by about half, but much of the activity could be replaced by juxtaposition of an upstream region (designated distal element IV). Gel shift and competition analysis demonstrated that binding of architectural factors overlapped NF-Y binding. Moreover, a mutation that eliminated NF-Y binding but only minimally perturbed the surrounding region did not affect enhancer function. In plasmids with a second promoter, the enhancers simultaneously stimulated both albumin and alpha-fetoprotein promoters with minimal competition, but surprisingly some mutations in the albumin promoter attenuated expression from both promoters, whereas another uncoupled their expression. With single promoters, the function of the proximal promoter region was controlled by three parameters in the following hierarchy: HNF1 binding > local architecture > NF-Y binding, but integrated two-promoter function had a much greater dependence on NF-Y.

The alpha-fetoprotein promoter is the target of Afr1-mediated postnatal repression

The alpha-fetoprotein (AFP) gene is transcribed at high levels in the fetal liver and is repressed at birth, leading to low but detectable levels of AFP mRNA in the adult liver. This repression is regulated, in part, by a locus that is unlinked to AFP called Alpha-fetoprotein regulator 1 (Afr1). Previous studies showed that Afr1 regulation is independent of the AFP enhancers but requires the 1-kb AFP promoter/repressor region. Here, we demonstrate that a transgene with the 250-bp AFP promoter region linked to AFP enhancer element EII is expressed in the fetal liver and is postnatally repressed. In addition, this transgene is regulated by Afr1. These data indicate that the promoter is involved in postnatal AFP repression. Furthermore, we provide a high-resolution map of the Afr1 locus on mouse chromosome 15.