Suppression of cholesterol 7alpha-hydroxylase transcription and bile acid synthesis by an alpha1-antitrypsin peptide via interaction with alpha1-fetoprotein transcription factor

SERPINA1 long transcripts produce non-secretory alpha1-antitrypsin isoform: In vitro translation in living cells

SERPINA1 is a well-studied serpin gene due to its dramatic impact on human health. Translation initiation at the main SERPINA1 start codon produces the only known alpha1-antitrypsin (AAT) isoform intended for secretion. AAT performs essential functions by inhibiting proteases and modulating immunity. However, SERPINA1 expression at the level of translation is not sufficiently studied. Here we hypothesize that the main SERPINA1 ORF can be alternatively translated, producing a non-secretory AAT isoform by either masking or excluding a signal peptide. We defined SERPINA1 long mRNA isoforms specific for prostate (DU145) and liver (HepG2) cell lines and studied their individual expression by in vitro assay. We found that all long transcripts produce both glycosylated secretory AAT-eGFP fusion protein and non-glycosylated intracellular AAT-eGFP (initiated from an alternative AUG-2 start codon), with the proportion regulated by the SERPINA1 5'-UTR. Both fusion proteins localize to distinct cellular compartments: in contrast to a fusion with the secretory AAT accumulating in the ER, the intracellular one exhibits nuclear-cytoplasmic shuttling. We detected putative endogenous AAT isoform enriching the nuclear speckles. CONCLUSION: Alternative translation initiation might be a mechanism through which SERPINA1 expands the biological diversity of its protein products. Our findings open up new prospects for the study of SERPINA1 gene expression.

Mice inflammatory responses to inhaled aerosolized LPS: effects of various forms of human alpha1-antitrypsin

Rodent models of lipopolysaccharide (LPS)-induced pulmonary inflammation are used for anti-inflammatory drug testing. We aimed to characterize mice responses to aerosolized LPS alone or with intraperitoneal (i.p.) delivery of alpha1-antitrypsin (AAT). Balb/c mice were exposed to clean air or aerosolized LPS (0.21 mg/mL) for 10 min per day, for 3 d. One hour after each challenge, animals were treated i.p. with saline or with (4 mg/kg body weight) one of the AAT preparations: native (AAT), oxidized (oxAAT), recombinant (recAAT), or peptide of AAT (C-36). Experiments were terminated 6 h after the last dose of AATs. Transcriptome data of mice lungs exposed to clean air versus LPS revealed 656 differentially expressed genes and 155 significant gene ontology terms, including neutrophil migration and toll-like receptor signaling pathways. Concordantly, mice inhaling LPS showed higher bronchoalveolar lavage fluid neutrophil counts and levels of myeloperoxidase, inducible nitric oxide synthase, IL-1β, TNFα, KC, IL-6, and granulocyte-macrophage colony-stimulating factor (GM-CSF). Plasma inflammatory markers did not increase. After i.p. application of AATs, about 1% to 2% of proteins reached the lungs but, except for GM-CSF, none of the proteins significantly influenced inflammatory markers. All AATs and C-36 significantly inhibited LPS-induced GM-CSF release. Surprisingly, only oxAAT decreased the expression of several LPS-induced inflammatory genes, such as Cxcl3, Cd14, Il1b, Nfkb1, and Nfkb2, in lung tissues. According to lung transcriptome data, oxAAT mostly affected genes related to transcriptional regulation while native AAT or recAAT affected genes of inflammatory pathways. Hence, we present a feasible mice model of local lung inflammation induced via aerosolized LPS that can be useful for systemic drug testing.

Multiplex quantification of C-terminal alpha-1-antitrypsin peptides provides a novel approach for characterizing systemic inflammation

C-terminal peptides (CAAPs) of the highly abundant serine protease alpha-1-antitrypsin (A1AT) have been identified at various lengths in several human materials and have been proposed to serve as putative biomarkers for a variety of diseases. CAAPs are enzymatically formed and these enzymatic activities are often associated with excessive immune responses (e.g. sepsis, allergies). However, most of those CAAPs have been either detected using in vitro incubation experiments or in human materials which are not easily accessible. To gain a comprehensive understanding about the occurrence and function of CAAPs in health and disease, a LC-MS/MS method for the simultaneous detection of nine CAAPs was developed and validated for human plasma (EDTA and lithium-heparin) and serum. Using this newly developed method, we were able to detect and quantify five CAAPs in healthy individuals thereby providing an initial proof for the presence of C36, C37, C40 and C44 in human blood. Concentrations of four CAAPs in a clinical test cohort of patients suffering from sepsis were significantly higher compared to healthy controls. These results reveal that in addition to C42 other fragments of A1AT seem to play a crucial role during systemic infections. The proposed workflow is simple, rapid and robust; thus this method could be used as diagnostic tool in routine clinical chemistry as well as for research applications for elucidating the diagnostic potential of CAAPs in numerous diseases. To this end, we also provide an overview about the current state of knowledge for CAAPs identified in vitro and in vivo.

Development of anti-inflammatory peptidomimetics based on the structure of human alpha1-antitrypsin

Human α1-antitrypsin (hAAT) has two distinguishing functions: anti-protease activity and regulation of the immune system. In the present study we hypothesized that those two protein functions are mediated by different structural domains on the hAAT surface. Indeed, such biologically active immunoregulatory sites (not associated with canonical anti-protease activity) on the surface of hAAT were identified by in silico methods. Several peptides were derived from those immunoregulatory sites. Four peptides exhibited impressive biological effects in pharmacological concentration ranges. Peptidomimetic (14) was developed, based on the structure of the most druggable and active peptide. The compound exhibited a potent anti-inflammatory activity in vitro and in vivo. Such a compound could be used as a basis for developing novel anti-inflammatory drug candidates and as a research tool for better understanding hAAT functions.

A metabolomic-based study on disturbance of bile acids metabolism induced by intratracheal instillation of nickel oxide nanoparticles in rats

Nickel oxide nanoparticles (Nano NiO) evoke hepatotoxicity, while whether it affects the hepatic metabolism remains unclear. The aim of this study was to explore the differential metabolites and their metabolic pathways in rat serum and to further verify the potential mechanism of bile acids' (BAs) metabolism dysregulation after Nano NiO exposure. Sixteen male Wistar rats were intratracheally instilled with Nano NiO (0.24 mg/kg body weight) twice a week for 9 weeks. Liquid chromatography/mass spectrometry was applied to filter the differentially expressed metabolites in rat serum. Western blot was employed to detect the protein contents. Twenty-one differential metabolites that associated with BAs, lipid and phospholipid metabolism pathways were identified in rat serum after Nano NiO exposure. Decreased cholic acid and deoxycholic acid implied that the BAs metabolism was disturbed. The nickel content increased in liver after Nano NiO exposure. The protein expression of cholesterol 7α-hydroxylase (CYP7A1) was down-regulated, and the bile salt export pump was up-regulated after Nano NiO administration in rat liver. Moreover, dehydroepiandrosterone sulphotransferase (SULT2A1) and cytochrome P450 (CYP) 3A4 were elevated in the exposure group. In conclusion, Nano NiO might trigger the disturbances of BAs, lipid and phospholipid metabolism pathways in rats. The diminished serum BAs induced by Nano NiO might be related to the down-regulation of synthetase and to the overexpression of transmembrane protein and detoxification enzymes in BAs metabolism.

A Novel Mouse Monoclonal Antibody C42 against C-Terminal Peptide of Alpha-1-Antitrypsin

The C-terminal-fragments of alpha1-antitrypsin (AAT) have been identified and their diverse biological roles have been reported in vitro and in vivo. These findings prompted us to develop a monoclonal antibody that specifically recognizes C-36 peptide (corresponding to residues 359–394) resulting from the protease-associated cleavage of AAT. The C-36-targeting mouse monoclonal Immunoglobulin M (IgM) antibody (containing κ light chains, clone C42) was generated and enzyme-linked immunosorbent assay (ELISA)-tested by Davids Biotechnologie GmbH, Germany. Here, we addressed the effectiveness of the novel C42 antibody in different immunoassay formats, such as dot- and Western blotting, confocal laser microscopy, and flow cytometry. According to the dot-blot results, our novel C42 antibody detects the C-36 peptide at a range of 0.1–0.05 µg and shows no cross-reactivity with native, polymerized, or oxidized forms of full-length AAT, the AAT-elastase complex mixture, as well as with shorter C-terminal fragments of AAT. However, the C42 antibody does not detect denatured peptide in SDS-PAGE/Western blotting assays. On the other hand, our C42 antibody, unconjugated as well as conjugated to DyLight488 fluorophore, when applied for immunofluorescence microscopy and flow cytometry assays, specifically detected the C-36 peptide in human blood cells. Altogether, we demonstrate that our novel C42 antibody successfully recognizes the C-36 peptide of AAT in a number of immunoassays and has potential to become an important tool in AAT-related studies.

Post-Translational Modifications of Circulating Alpha-1-Antitrypsin Protein

Alpha-1-antitrypsin (AAT), an acute-phase protein encoded by the SERPINA1 gene, is a member of the serine protease inhibitor (SERPIN) superfamily. Its primary function is to protect tissues from enzymes released during inflammation, such as neutrophil elastase and proteinase 3. In addition to its antiprotease activity, AAT interacts with numerous other substances and has various functions, mainly arising from the conformational flexibility of normal variants of AAT. Therefore, AAT has diverse biological functions and plays a role in various pathophysiological processes. This review discusses major molecular forms of AAT, including complex, cleaved, glycosylated, oxidized, and S-nitrosylated forms, in terms of their origin and function.

Identification and Replication of Six Loci Associated With Gallstone Disease

Gallstone disease is a common complex disease that confers a substantial economic burden on society. The genetic underpinnings of gallstone disease remain incompletely understood. We aimed to identify genetic associations with gallstone disease using publicly available data from the UK Biobank and two large Danish cohorts. We extracted genetic associations with gallstone disease from the Global Biobank Engine (GBE), an online browser of genome-wide associations in UK Biobank participants (14,940 cases and 322,268 controls). Significant associations (P < 5 × 10^-8 ) were retested in two Copenhagen cohorts (comprising 1,522 cases and 18,266 controls). In the Copenhagen cohorts, we also tested whether a genetic risk score was associated with gallstone disease and whether individual gallstone loci were associated with plasma levels of lipids, lipoproteins, and liver enzymes. We identified 19 loci to be associated with gallstone disease in the GBE. Of these, 12 were replicated in the Copenhagen cohorts, including six previously unknown loci (in hepatocyte nuclear factor 4 alpha [HNF4A], fucosyltransferase 2, serpin family A member 1 [SERPINA1], jumonji domain containing 1C, AC074212.3, and solute carrier family 10A member 2 [SLC10A2]) and six known loci (in adenosine triphosphate binding cassette subfamily G member 8 [ABCG8], sulfotransferase family 2A member 1, cytochrome P450 7A1, transmembrane 4 L six family member 4, ABCB4, and tetratricopeptide repeat domain 39B). Five of the gallstone associations are protein-altering variants, and three (HNF4A p.Thr139Ile, SERPINA1 p.Glu366Lys, and SLC10A2 p.Pro290Ser) conferred per-allele odds ratios for gallstone disease of 1.30-1.36. Individuals with a genetic risk score >2.5 (prevalence 1%) had a 5-fold increased risk of gallstones compared to those with a score <1.0 (11%). Of the 19 lithogenic loci, 11 and ten exhibited distinct patterns of association with plasma levels of lipids and liver enzymes, respectively. Conclusion: We identified six susceptibility loci for gallstone disease.

Dynamic and structural insights into tick serpin from Ixodes ricinus

Ixodid ticks have a crucial impact on people and domestic animals worldwide. These parasites also pose a serious threat to livestock. To date, vaccination of hosts against ticks is a safer, more sustainable alternative to chemical control of ticks and the disease agents they transmit. Because of their roles in tick physiology, serpins (serine protease inhibitors) from tick saliva are among the candidates for anti-tick vaccines. Inhibitory serpins employ a suicide inhibition mechanism to inhibit proteases, where the serpin reactive centre loop (RCL) is cleaved, by the targeted protease, and then inserted into the main β-sheet of the serpin. This causes a massive conformational change called the 'stressed to relaxed' (S→R) transition, leading to the breakdown of serpin into two regions (core domain and cleaved polypeptide). Recently, the first tick serpin crystal structure from Ixodes ricinus in R-state was reported. We thus employed molecular dynamics simulations to better understand serpin structure and dynamics in atomic detail. Overall, R-state serpin showed high rigidity, especially the core domain. The most flexible region is the terminal of the cleaved polypeptide, due to its high-water exposure, while the rest of the cleaved polypeptide is stably trapped behind the core domain. T363, D367 and N375 are found to play a vital role in protein-protein attachment. This finding can be used to explain the high stability of the R-state serpin at the atomic level and provides insight into this tick serpin which will be useful for rational anti-tick vaccine development. AbbreviationsMDMolecular DynamicsRCLReactive centre loopCommunicated by Ramaswamy H. Sarma.

Human cytochrome P450 enzymes 5-51 as targets of drugs and natural and environmental compounds: mechanisms, induction, and inhibition - toxic effects and benefits

Cytochrome P450 (P450, CYP) enzymes have long been of interest due to their roles in the metabolism of drugs, pesticides, pro-carcinogens, and other xenobiotic chemicals. They have also been of interest due to their very critical roles in the biosynthesis and metabolism of steroids, vitamins, and certain eicosanoids. This review covers the 22 (of the total of 57) human P450s in Families 5-51 and their substrate selectivity. Furthermore, included is information and references regarding inducibility, inhibition, and (in some cases) stimulation by chemicals. We update and discuss important aspects of each of these 22 P450s and questions that remain open.

Identification of Novel Short C-Terminal Transcripts of Human SERPINA1 Gene

Human SERPINA1 gene is located on chromosome 14q31-32.3 and is organized into three (IA, IB, and IC) non-coding and four (II, III, IV, V) coding exons. This gene produces α1-antitrypsin (A1AT), a prototypical member of the serpin superfamily of proteins. We demonstrate that human peripheral blood leukocytes express not only a product corresponding to the transcript coding for the full-length A1AT protein but also two short transcripts (ST1C4 and ST1C5) of A1AT. In silico sequence analysis revealed that the last exon of the short transcripts contains an Open Reading Frame (ORF) and thus putatively can produce peptides. We found ST1C4 expression across different human tissues whereas ST1C5 was mainly restricted to leukocytes, specifically neutrophils. A high up-regulation (10-fold) of short transcripts was observed in isolated human blood neutrophils after activation with lipopolysaccharide. Parallel analyses by liquid chromatography-mass spectrometry identified peptides corresponding to C-terminal region of A1AT in supernatants of activated but not naïve neutrophils. Herein we report for the first time a tissue specific expression and regulation of short transcripts of SERPINA1 gene, and the presence of C-terminal peptides in supernatants from activated neutrophils, in vitro. This gives a novel insight into the studies on the transcription of SERPINA1 gene.

Serpin A1 C-Terminal Peptides as Collagen Turnover Modulators

The modulation of collagen turnover can be a relevant pharmacological target in the context of treating either pathological or pathophysiological conditions, such as collagen-related diseases and skin aging. Our recent work has focused on the search for short-chain peptides as lead compounds for further development of compounds that enhance the production of type I collagen. In this study we selected and synthesized overlapping peptides of the C-terminal portion of serpin A1 (residues 393-418), the impact of which on collagen production has been reported previously, in order to identify shorter and still active fragments and to provide insight on the mechanisms involved. The biological activity of each fragment was evaluated with cultured normal human dermal fibroblasts, and changes in the amounts of collagen were monitored in collected culture media by a sandwich ELISA technique developed in house. Interestingly, we identified a decapeptide, termed SA1-III (Ac-MGKVVNPTQK-NH2 ), as a promising candidate for our purposes; it is able to induce a significant increase in type I collagen levels in the culture medium of treated cells at micromolar concentrations.

Identification of transcription factors and single nucleotide polymorphisms of Lrh1 and its homologous genes in Lrh1-knockout pancreas of mice

BACKGROUND

To identify transcription factors (TFs) and single nucleotide polymorphisms (SNPs) of Lrh1 (also named Nr5a2) and its homologous genes in Lrh1-knockout pancreas of mice.

METHODS

The RNA-Seq data GSE34030 were downloaded from Gene Expression Omnibus (GEO) database, including 2 Lrh1 pancreas knockout samples and 2 wild type samples. All reads were processed through TopHat and Cufflinks package to calculate gene-expression level. Then, the differentially expressed genes (DEGs) were identified via non-parametric algorithm (NOISeq) methods in R package, of which the homology genes of Lrh1 were identified via BLASTN analysis. Furthermore, the TFs of Lrh1 and its homologous genes were selected based on TRANSFAC database. Additionally, the SNPs were analyzed via SAM tool to record the locations of mutant sites.

RESULTS

Total 15683 DEGs were identified, of which 23 was Lrh1 homology genes (3 up-regulated and 20 down-regulated). Fetoprotein TF (FTF) was the only TF of Lrh1 identified and the promoter-binding factor of FTF was CYP7A. The SNP annotations of Lrh1 homologous genes showed that 92% of the mutation sites were occurred in intron and upstream. Three SNPs of Lrh1 were located in intron, while 1819 SNPs of Phkb were located in intron and 1343 SNPs were located in the upstream region.

CONCLUSION

FTF combined with CYP7A might play an important role in Lrh1 regulated pancreas-specific transcriptional network. Furthermore, the SNPs analysis of Lrh1 and its homology genes provided the candidate mutant sites that might affect the Lrh1-related production and secretion of pancreatic fluid.

Stearoyl CoA desaturase (SCD) facilitates proliferation of prostate cancer cells through enhancement of androgen receptor transactivation

Stearoyl-CoA desaturase (SCD), the rate-limiting enzyme in the biosynthesis of monounsaturated fatty acids, is highly expressed in prostate cancer although the SCD protein has been known to be rapidly turned over by proteolytic cleavage. The present data demonstrate that SCD can promote proliferation of androgen receptor (AR)-positive LNCaP prostate cancer cells and enhance dihydrotestosterone (DHT)-induced AR transcriptional activity, resulting in increased expression of prostate-specific antigen (PSA) and kallikrein-related peptidase 2 (KLK2). Interestingly, among the previously reported SCD-derived peptides produced by proteolytic cleavage of SCD, a peptide spanning amino acids 130-162 of SCD (SCD-CoRNR) contained the CoRNR box motif (LFLII) and enhanced AR transcriptional activity. In contrast, a mutant SCD-CoRNR in which Leu136 was replaced by Ala had no effect on AR transcriptional activity. Moreover, SCD-CoRNR directly interacted with AR and inhibited RIP140 suppression of AR transactivation. Knockdown of the SCD gene by SCD microRNA suppressed AR transactivation with decreased cell proliferation, suggesting that SCD may regulate the proliferation of LNCaP cells via modulation of AR transcriptional activity. Moreover, ectopic expression of SCD in LNCaP cells facilitated LNCaP tumor formation and growth in nude mice. Together, the data indicate that SCD plays a key role in the regulation of AR transcriptional activity in prostate cancer cells.

Nuclear receptors: mediators and modifiers of inflammation-induced cholestasis

Inflammation-induced cholestasis (IIC) is a frequently occurring phenomenon. A central role in its pathogenesis is played by nuclear receptors (NRs). These ligand-activated transcription factors not only regulate basal expression of hepatobiliary transport systems, but also mediate adaptive responses to inflammation and possess anti-inflammatory characteristics. The latter two functions may be exploited in the search for new treatments for IIC as well as for cholestasis in general. Current knowledge of the pathogenesis of IIC and the dual role NRs in this process are reviewed. Special interest is given to the use of NRs as potential targets for intervention.

Serpin A1 and CD91 as host instruments against HIV-1 infection: are extracellular antiviral peptides acting as intracellular messengers?

Serpin A1 (alpha1-antitrypsin, alpha1-proteinase inhibitor) has been shown to be a non-cytolytic antiviral factor present in blood and effective against HIV infection. The best known physiological role of serpin A1 is to inhibit neutrophil elastase, a proteinase which is secreted by neutrophils at sites of infection and inflammation. Decreased HIV-infectivity is associated with decreased density of membrane-associated elastase. The enzyme may facilitate binding of the HIV membrane protein gp120 to host cells, and it specifically cleaves SDF-1, the physiological ligand of the HIV-1 co-receptor CXCR4. It has been suggested that one of the actions of serpin A1 as antiviral agent is to reduce HIV infectivity, and this property could be due to elastase inhibition. However, the most dramatic effect of serpin A1 is inhibition of HIV production. In vitro experiments indicate that the C-terminal peptide of serpin A1, produced during the formation of the complex of serpin with serine proteinases, may be responsible for the inhibition of HIV-1 expression in infected cells. This peptide, an integral part of the serpin-enzyme complex, is internalized by several scavenger receptors. Peptides corresponding to the C-terminal section of serpin A1 inhibit HIV-1 long-terminal-repeat-driven transcription and interact with nuclear proteins, such as alpha1-fetoprotein transcription factor. LDL-receptor-related protein 1 (LRP1/CD91), the best known receptor for serpin-enzyme complexes, is up-regulated in monocytes of HIV-1-infected true non-progressors. CD91 could be one of the major players in host resistance against HIV-1. It has the capacity of internalizing antiviral peptides such as serpin C-terminal fragments and alpha-defensins, and is at the same time the receptor for heat-shock proteins in antigen-presenting cells, in which chaperoned viral peptides could lead to the induction of cytotoxic T-cell responses.

The C-terminal 26-residue peptide of serpin A1 is an inhibitor of HIV-1

Serpin A1 (alpha1-proteinase inhibitor) inhibits human immunodeficiency virus 1 (HIV-1) production by mechanisms which remain to be elucidated. The complex formation of serpin A1 with proteinases eliminates the proteolytic activity and generates a fragment corresponding to the serpin C-terminal 36-residue peptide. Here, we show that the C-terminal 26-residue peptide of serpin A1 (A1-C26) inhibits HIV-long terminal repeat (LTR)-driven transcription in epithelial cells transfected with HIV-1 LTR promoter-driven genes. A1-C26 increased STAT1 phosphorylation and strongly reduced viral expression in a monocytic cell line infected with HIV-1 NL4-3. This reduction of expression was also observed in HIV-1 infected, PHA-activated peripheral blood mononuclear cells. In HIV-1 infected cells, the inhibitory activity of HIV-1 caused by B9-C23 and C1-C26, the A1-C26 homologues corresponding to the C-terminal sections of serpin B9 and serpin C1, was much lower than that obtained with A1-C26. These serpin peptides represent a novel class of antiviral agents.

The C-terminal 26-residue peptide of serpin A1 stimulates proliferation of breast and liver cancer cells: role of protein kinase C and CD47

C26, the C-terminal 26 residue peptide of serpin A1, significantly increased cell proliferation in cultures of hepatoma cells, but not in porcine kidney epithelial cells, human skin fibroblasts or keratinocytes. The mitogenic activity of C26 was preferentially inhibited with a protein kinase C (PKC) inhibitor, an antibody against CD47 and CD47 short interfering RNA. The mutant C26-K19R,N22M, imitating a thrombospondin-like cell adhesion motif, increased the mitogenic activity in both Hep G2 cells and MCF-7 breast cancer cells. Phosphorylation of C26 at T24 (a putative PKC phosphorylation site) resulted in a 1.9-2.5 increase in mitogenic activity over C26 in MCF-7 cells.

Divergent effects of alpha1-antitrypsin on neutrophil activation, in vitro

alpha1-Antitrypsin (AAT) is a major circulating serine proteinase inhibitor in humans. The anti-proteinase activity of AAT is inhibited by chemical modification. These include inter- or intramolecular polymerisation, oxidation, complex formation with target proteinases (e.g., neutrophil elastase), and/or cleavage by multi-specific proteinases. In vivo, several modified forms of AAT have been identified which stimulate biological activity in vitro unrelated to inhibition of serine proteinases. In this study we have examined the effects of native and polymerised AAT and C-36 peptide, a proteolytic cleavage product of AAT, on human neutrophil activation, in vitro. We show that the C-36 peptide displays striking concentration-dependent pro-inflammatory effects on human neutrophils, including induction of neutrophil chemotaxis, adhesion, degranulation, and superoxide generation. In contrast to C-36 peptide, native and polymerised AAT at similar and higher concentrations showed no effects on neutrophil activation. These results suggest that cleavage of AAT may not only abolish its proteinase inhibitor activity, but can also generate a powerful pro-inflammatory activator for human neutrophils.

The role of alpha1-fetoprotein transcription factor/LRH-1 in bile acid biosynthesis: a known nuclear receptor activator that can act as a suppressor of bile acid biosynthesis

Two key regulatory enzymes in the bile acid biosynthesis pathway are cholesterol 7alpha-hydroxylase/CYP7A1 (7alpha-hydroxylase) and sterol 12alpha-hydroxylase/CYP8B1 (12alpha-hydroxylase). It has been shown previously that hepatocyte nuclear factor-4alpha (HNF-4) and the alpha(1)-fetoprotein transcription factor (FTF) are activators of 7alpha-and 12alpha-hydroxylase transcription and that the small heterodimer partner (SHP) suppresses bile acid biosynthesis by heterodimerizing with FTF. However, the role of FTF in bile acid biosynthesis has been studied only in tissue culture systems. In heterozygous FTF knockout mice, 7alpha- and 12alpha-hydroxylase genes were expressed at 5-7-fold higher levels than in wild-type mice, an apparent direct contradiction to previous in vitro observations. This higher expression of the 7alpha- and 12alpha-hydroxylase genes resulted in a 33% higher bile acid pool in their gallbladders, bile more enriched in cholic acid, and a 13% decrease in plasma cholesterol levels. Adenovirus-mediated FTF overexpression in wild-type mice resulted in 10-fold lower expression of the 7alpha- and 12alpha-hydroxylase genes and up to 8-fold higher SHP expression, highlighting the dual role that FTF plays in different promoters. Shorter overexpression times still resulted in lower 7alpha- and 12alpha-hydroxylase expression, but unchanged SHP expression, suggesting that two different mechanisms are involved in the FTF-mediated suppression of 7alpha- and 12alpha-hydroxylase expression. This FTF-mediated suppression of the expression of two bile acid biosynthesis genes resulted in a 3-fold lower rate of bile acid synthesis in a rat bile fistula animal model. Based on these observations and on protein binding studies performed in vitro and by chromatin immunoprecipitation, we hypothesize that FTF has two synergetic effects that contribute to its role in bile acid biosynthesis: 1) it has the ability to activate the expression of SHP, which in turn heterodimerizes and suppresses FTF transactivation activity; and 2) it occupies the FTF/HNF-4 recognition site within the 7alpha- and 12alpha-hydroxylase promoters, which can otherwise be occupied by a factor (HNF-4) that cannot be suppressed by SHP.

Changes in mRNA expression of 3-hydroxy-3-methylglutaryl coenzyme A reductase and cholesterol 7 alpha-hydroxylase in chickens

3-Hydroxy-3-methylglutaryl coenzyme A reductase (HMGR) and cholesterol 7 alpha-hydroxylase (CYP7A1), essential enzymes of cholesterol synthesis and excretion, respectively, were isolated from a chicken liver cDNA library. When their recombinant proteins were overexpressed in HNK293 cells, corresponding enzyme activities were observed. The complete open reading frames of MHGR and CYP7A1 contained (i) 2625 base pairs (bp), predicting a protein of 875 amino acids, and (ii) 1539 bp, predicting a protein of 513 amino acids, respectively. By Northern blot analysis, chicken HMGR mRNA expression was detected in most tissues examined, however, the highest levels were found in liver, brain and ileum. CYP7A1 mRNA was detected only in the liver. Changes in chicken HMGR and CYP7A1 mRNA expression with nutritional state were examined and were shown to respond to certain nutritional treatments, i.e. fast refeeding and cholesterol supplementation. HMGR and CYP7A1 mRNA levels were significantly increased with maturation (i.e. egg producing), when compared to immature chickens. However, these stimulations were not associated with estrogen, although this does enhance triacylglycerol and very low density lipoprotein secretion by the chicken liver. The present study is the first to report the molecular characterization of HMGR and CYP7A1, key enzymes of cholesterol metabolism in avian species.