Capsule ofStreptococcus pyogenesIs Essential for Delayed Death of Mice in a Model of Streptococcal Toxic Shock Syndrome

We have previously reported a mouse model of severe group A streptococcal infection (Microbiol. Immunol. 45: 777-786, 2001). When we injected Streptococcus pyogenes strains intramuscularly, the mice suffered from acute phase of infection for a few days but recovered from the illness and gained body weight. These mice, however, began to die after 3 weeks of infection, which we called 'delayed death.' Bacterial strains isolated from organs of the dead mice showed thick capsules. We, therefore, constructed a hyaluronic acid capsule gene, hasA, knockout mutant by homologous recombination and the effect of capsule on the death was observed. hasA knockout strain did not cause delayed death, though it caused acute death at high doses of infection. According to this result, the capsule is a critical pathogenic factor for causing the delayed death in our mouse model.

A Single Minor Histocompatibility Antigen Encoded by UGT2B17 and Presented by Human Leukocyte Antigen-A*2902 and -B*4403

BACKGROUND

T-cell responses to minor histocompatibility antigens are mediators of graft-versus-host disease and organ graft rejection. We previously identified a human minor histocompatibility antigen that is recognized by CD8 cytotoxic T lymphocytes (CTLs) and encoded by the UDP glycosyltransferase 2 family, polypeptide B17 (UGT2B17) gene, which is highly expressed in the liver, colon, and small intestine. The UGT2B17 is presented by human leukocyte antigen (HLA)-A*2902, and the immunogenicity of this minor histocompatibility antigen results from differential protein expression in donor and recipient cells as a consequence of a UGT2B17 gene deletion.

METHODS

An HLA-B*4403-restricted CD8 CTL clone was isolated from the same hematopoietic stem cell transplant recipient that exhibited an HLA-A*2902-restricted UGT2B17-specific response. The minor histocompatibility antigen recognized by the HLA-B*4403-restricted clone was identified, and the ability of the peptide to be presented by HLA-B*4402 was examined.

RESULTS

The HLA-B*4403-restricted CTL clone recognized a peptide encoded by UGT2B17, which is identical to the peptide presented by HLA-A*2902. Peptide binding assays revealed this UGT2B17 peptide binds with comparable affinity to HLA-B*4402 as to HLA-B*4403. This patient had acute graft-versus-host disease involving liver and gastrointestinal tract, suggesting the T-cell response directed against UGT2B17 is involved in graft-versus-host disease.

CONCLUSIONS

A single peptide encoded by UGT2B17 can be presented by HLA-A*2902, B*4402 and B*4403, and may serve as an immunodominant minor histocompatibility antigen in individuals with these HLA alleles that undergo transplantation of stem cells or organ grafts from UGT2B17 disparate donors.

Adeno-associated Virus Vector Serotypes Mediate Sustained Correction of Bilirubin UDP Glucuronosyltransferase Deficiency in Rats

Crigler-Najjar (CN) patients have no bilirubin UDP glucuronosyltransferase (UGT1A1) activity and suffer brain damage because of bilirubin toxicity. Vectors based on adeno-associated virus (AAV) serotype 2 transduce liver cells with relatively low efficiency. Recently, AAV serotypes 1, 6, and 8 have been shown to be more efficient for liver cell transduction. We compared AAV serotypes 1, 2, 6, and 8 for correction of UGT1A1 deficiency in the Gunn rat model of CN disease. Adult Gunn rats were injected with CMV-UGT1A1 AAV vectors. Serum bilirubin was decreased over the first year by 64% for AAV1, 16% for AAV2, 25% for AAV6, and 35% for AAV8. Antibodies to UGT1A1 were detected after injection of all AAV serotypes. An AAV1 UGT1A1 vector with the liver-specific albumin promoter corrected serum bilirubin levels but did not induce UGT1A1 antibodies. Two years after injection of AAV vectors all animals had large lipid deposits in the liver. These lipid deposits were not seen in age-matched control animals. AAV1 vectors are promising candidates for CN gene therapy because they can mediate a reduction in serum bilirubin levels in Gunn rats that would be therapeutic in humans.

Monospecific Antipeptide Antibodies Against Human Hepatic UDP-Glucuronosyltransferase 1A Subfamily (UGT1A) Isoforms

Expression of UDP-glucuronosyltransferases (UGT) in mammals is thought to be regulated in both a tissue- and developmental-specific manner. Furthermore, induction of genes encoding UGT occurs after exposure to xenobiotics including drugs, environmental pollutants and dietary compounds. In human, isoforms of UGT 1A subfamily catalyze the glucuronidation of a greater proportion of drugs, suggesting that the expression of UGT1A isoforms is responsible for the clearance of a diverse range of drugs. To analyze the expression of human UGT1A isoforms, we have developed polyclonal antibodies against specific peptide regions within the isoforms (UGT1A1, 1A3, 1A4, 1A6 and 1A9). The prepared antipeptide antibodies were found to be highly monospecific for each UGT1A isoform and no cross-reactivity with UGT2B isoforms was detected. Analysis of UGT1A protein levels in hepatic microsomes using these antibodies demonstrated interindividual differential expression of each isoform. These highly specific antipeptide antibodies provide an important tool to analyze tissue distribution and interindividual expression levels of human UGT1As.

Immune response to lentiviral bilirubin UDP-glucuronosyltransferase gene transfer in fetal and neonatal rats

Gene therapy for inherited disorders might cause an immune response to the therapeutic protein. A solution would be to introduce the gene in the fetal or neonatal period, which should lead to tolerization. Lentiviral vectors mediate long-term gene expression, and are well suited for gene therapy early in development. A model for fetal or neonatal gene therapy is the inherited disorder of bilirubin metabolism, Crigler-Najjar disease (CN). The absence of bilirubin UDP-glucoronyltransferase (UGT1A1) activity in CN patients causes high serum levels of unconjugated bilirubin and brain damage in infancy. CN is attractive for the development of gene therapy because the mutant Gunn rat closely mimics the human disease. Injection of UGT1A1 lentiviral vectors corrected the hyperbilirubinemia for more than a year in rats injected as fetuses and for up to 18 weeks in rats injected the day of birth. UGT1A1 gene transfer was confirmed by the presence of bilirubin glucuronides in bile. All animals injected with UGT1A1 lentiviral vectors developed antibodies to UGT1A1. Animals injected with green fluorescent protein (GFP) lentiviral vectors did not develop antibodies to GFP. Our results indicate that fetal and neonatal gene therapy with immunogenic proteins such as UGT1A1 does not necessarily lead to tolerization.

High levels of autoantibodies against drug-metabolizing enzymes in SLA/LP-positive AIH-1 sera

Autoimmune hepatitis type 1 (AIH-1) is characterized by the detection of smooth muscle autoantibodies, antinuclear antibodies and antineutrophil cytoplasmic autoantibodies, and AIH-2 is characterized by the presence of autoantibodies against LKM, which contain drug-metabolizing enzymes. In this study, we measured the levels of drug-metabolizing enzymes in AIH-1 patients (ANA-positive). We exhaustively investigated the level of autoantibodies against major CYPs and UDP-glucuronosyltransferases of typical phase II drug-metabolizing enzymes, a transporter (MDR1), and NADPH-cytochrome P450 reductase in 4 patients with AIH-1 and 6 controls, as a case report. Two (Patients 3 and 4) of the AIH patients exhibited high levels of autoantibodies, while two (Patients 1 and 2) of the patients and the controls did not. The levels of autoantibodies against CYP2C19, CYP2D6, CYP2E1, UGT1A6 and human liver microsomes in Patients 3 and 4 sera were over 2(3) times the levels in Patient 1, Patient 2 and the control sera. Meanwhile, the levels of autoantibodies against CYP1A2, CYP2A6, CYP2C9, UGT2B7, MDR1 and NADPH-cytochrome P450 reductase were 2-2(2) higher in Patients 3 and 4 than in the other subjects. We found that the pattern of elevation in the Patient 3 serum was not parallel with that in Patient 4. Thus, we found high levels of autoantibodies against drug-metabolizing enzymes in AIH-1 patients.

A UGT2B17-positive donor is a risk factor for higher transplant-related mortality and lower survival after bone marrow transplantation

We recently identified a human minor histocompatibility (H) antigen, encoded by UDP glycosyltransferase 2 family, polypeptide B17 (UGT2B17), whose immunogenicity results from differential expression in donor and recipient cells as a consequence of a homozygous deletion of the UGT2B17 gene. UGT2B17 is highly expressed in the liver and colon, which are major targets for graft-versus-host disease (GVHD). To assess the significance of homozygous UGT2B17 gene deletion in allogeneic haematopoietic stem cell transplantation (HSCT), we analysed DNA from 435 stem cell transplant recipients with a haematological malignancy and their human leucocyte antigen-identical unrelated bone marrow donors using sequence-specific primer polymerase chain reaction. Homozygous deletion of the UGT2B17 gene was observed in 85% of normal donors and in 82% of patients. The analysis showed no significant association between UGT2B17 mismatch in the GVHD direction and the incidence of acute GVHD, chronic GVHD, relapse, or survival. However, the use of a UGT2B17-positive donor was an independent risk factor for higher transplant-related mortality and lower survival after transplantation. UGT2B17 is a metabolic enzyme for hormones, drugs, and potentially toxic exogenous compounds and is expressed in subsets of haematopoietic cells. Thus, the enzyme function of UGT2B17 in donor cells may affect the outcome of allogeneic HSCT.

Autoantibodies directed against the UDP-glucuronosyltransferases in human autoimmune hepatitis

Liver-Kidney Microsomes Type 3 (LKM3) autoantibodies (aAbs) have been described in chronic hepatitis D virus infection in 1983. The detection of such aAbs in autoimmune hepatitis (AIH) Type 2 was thereafter reported. The molecular targets of LKM3 aAbs have been identified as enzymes belonging to the UDP-glucuronosyltransferase family 1. Since 20-30% of suspected AIH are negative for the classical autoimmune serological markers, such as aAbs directed against antinuclear autoantibodies, smooth muscle autoantibodies and Liver-Kidney Microsomes Type 1 aAbs, LKM3 aAbs could be of great interest in the diagnosis of such negative AIH. In this review, we discuss the sensitivity and specificity of these aAbs in AIH in order to stress out their potential clinical use as a marker.

Characterization and profiling of hepatic cytochromes P450 and phase II xenobiotic-metabolizing enzymes in beluga whales (Delphinapterus leucas) from the St. Lawrence River Estuary and the Canadian Arctic

Cytochromes P450 (CYP, phase I) and conjugating (phase II) enzymes can be induced by and influence the toxicokinetics (metabolism) and toxicity of xenobiotic contaminants in exposed organisms. Beluga whale (Delphinapterus leucas) from the endangered St. Lawrence (SL) River Estuary population exhibit deleterious health effects and various severe pathologies that have been associated with contaminant exposure. In contrast, such effects (e.g. reproductive and immunological impairment) are generally less frequent in less exposed populations in the Canadian Arctic (CA). In the present study, opportunistic sampling resulted in the collection immediately after death of liver tissue from a single female neonate SL beluga (SL6) and male and female CA beluga (n=10) from the Arviat region of western Hudson Bay, in addition to sampling of stranded carcasses of male and female SL beluga (n=5) at least 12 h postmortem. We immunologically characterized cross-reactive proteins of hepatic microsomal CYP1A, CYP2B, CYP3A, CYP2E, epoxide hydrolase (EH) and uridine diphosphoglucuronosyl transferase (UDPGT) isozymes. Cross-reactive proteins were found in all SL and CA beluga using anti-rat CYP1A1, anti-rainbow trout CYP3A, anti-human CYP2E1, anti-rabbit EH and anti-human UDPGT1A1 polyclonal antibodies (Abs), whereas faintly cross-reactive CYP2B proteins were only found in SL6 and the CA samples using an anti-rabbit CYP2B1 Ab. In corresponding catalytic activity assessments, only SL6 and all CA beluga microsomal samples exhibited CYP1A-mediated 7-ethoxyresorufin O-deethylase (EROD) activity (51-260 pmol/mg/min), CYP3A-mediated activity (113-899 pmol/mg/min) based on the formation of 6beta-hydroxytestosterone using a testosterone hydroxylase assay, and UDPGT activity (830-4956 pmol/mg/min) based on 1-naphthylglucuronide formation. The marginal cross-reactivity with the anti-CYP2B1 Ab and lack of catalytically measurable hydroxytestosterone isomers associated with CYP2B-type activity in all the SL and CA animals is suggestive of low CYP2B-type enzyme expression in beluga. The absence of measurable total P450 enzyme levels and catalytic activities in samples from the stranded SL belugas suggested catalytically inactive enzymes as a consequence of tissue degradation related due to the time delay of sample collection after death. However, all SL and CA animals demonstrated similar, immunologically cross-reactive phase I and II hepatic enzyme profiles, which is suggestive of the importance of metabolism in the toxicokinetics and fate of xenobiotics in animals from both populations

Human uridine diphosphate-glucuronosyltransferase UGT2B7 conjugates mineralocorticoid and glucocorticoid metabolites

Mineralocorticoid and glucocorticoid hormones are metabolized as glucuronide conjugates. Using labeled [(14)C]uridine diphosphate glucuronic acid and microsomal preparations from human embryonic kidney 293 cells stably expressing the different human and monkey uridine diphosphate glucuronosyltransferase (UGT)2B enzymes, it is demonstrated that the two human allelic variants UGT2B7H((268)) and UGT2B7Y((268)) conjugate aldosterone, its A-ring reduced metabolites (5alpha-dihydroaldosterone and 3alpha,5beta-tetrahydroaldosterone), and both 5alpha- and 5beta-tetrahydrocortisone epimers. The two variants of UGT2B4 also glucuronidate tetrahydroaldosterone, whereas all enzymes tested were inefficient to produce cortisol glucuronide derivatives. Kinetic analyses reveal that UGT2B7 polymorphisms glucuronidate mineralocorticoids with a 5.5- to 20-fold higher affinity than glucocorticoids. For the first time, a significant difference between the two allelic variants of UGT2B7 is described, because UGT2B7H((268)) possesses an 11-fold higher aldosterone glucuronidation efficiency (ratio Vmax((app.))/Km((app.))) than UGT2B7Y((268)). RT-PCR experiments demonstrate the expression of UGT2B7 in human kidney and in renal proximal tubule epithelial cells, suggesting that mineralocorticoids and glucocorticoids are metabolized in their target tissue. Measurement of aldosterone glucuronidation and normalization with the UGT2B protein contents in monkey tissues demonstrate that liver and kidney glucuronidate this hormone with a similar velocity. Immunohistochemical studies performed in monkey kidney cortex reveal a restrictive expression of UGT2B proteins in the epithelial cells of the proximal tubules. Because expression of the mineralocorticoid receptor was detected in the distal tubule epithelial cells, the present data suggest a two-cell mechanism of aldosterone action and metabolism in the kidney.

A human minor histocompatibility antigen resulting from differential expression due to a gene deletion

Minor histocompatibility antigens (minor H antigens) are targets of graft-versus-host disease and graft-versus-leukemia responses after allogeneic human leukocyte antigen identical hematopoietic stem cell transplantation. Only a few human minor H antigens have been molecularly characterized and in all cases, amino acid differences between homologous donor and recipient proteins due to nucleotide polymorphisms in the respective genes were responsible for immunogenicity. Here, we have used cDNA expression cloning to identify a novel human minor H antigen encoded by UGT2B17, an autosomal gene in the multigene UDP-glycosyltransferase 2 family that is selectively expressed in liver, intestine, and antigen-presenting cells. In contrast to previously defined human minor H antigens, UGT2B17 is immunogenic because of differential expression of the protein in donor and recipient cells as a consequence of a homozygous gene deletion in the donor. Deletion of individual members of large gene families is a common form of genetic variation in the population and our results provide the first evidence that differential protein expression as a consequence of gene deletion is a mechanism for generating minor H antigens in humans.

Immune-mediated drug-induced liver disease

Drug-induced immune-mediated hepatic injury is an adverse immune response against the liver that results in a disease with hepatitic, cholestatic, or mixed clinical features. Drugs such as halothane, tienilic acid, dihydralazine, and anticonvulsants trigger a hepatitic reaction, and drugs such as chlorpromazine, erythromycins, amoxicillin-calvulanic acid, sulfonamides and sulindac trigger a cholestatic or mixed reaction. Unstable metabolites derived from the metabolism of the drug may bind to cellular proteins or macromolecules, leading to a direct toxic effect on hepatocytes. Protein adducts formed in the metabolism of the drug may be recognized by the immune system as neoantigens. Immunocyte activation may then generate autoantibodies and cell-mediated immune responses, which in turn damage the hepatocytes. Cytochromes 450 are the major oxidative catalysts in drug metabolism, and they can form a neoantigen by covalently binding with the drug metabolite that they produce. Autoantibodies that develop are selectively directed against the particular cytochrome isoenzyme that metabolized the parent drug. The hapten hypothesis proposes that the drug metabolite can act as a hapten and can modify the self of the individual by covalently binding to proteins. The danger hypothesis proposes that the immune system only responds to a foreign antigen if the antigen is associated with a danger signal, such as cell stress or cell death. Most clinically overt adverse hepatic events associated with drugs are unpredictable, and they have intermediate (1 to 8 weeks) or long latency (up to 12 months) periods characteristic of hypersensitivity reactions. Immune-mediated drug-induced liver disease nearly always disappears or becomes quiescent when the drug is removed. Methyldopa, minocycline, and nitrofurantoin can produce a chronic hepatitis resembling AIH if the drug is continued.

Cytotoxic immune response blunts long-term transgene expression after efficient retroviral-mediated hepatic gene transfer in rat

Vectors derived from oncoretroviruses can transduce a small proportion of hepatocytes when injected in the regenerating liver. Transgene expression may be sustained for months without immune response. In striking contrast, we observed a rapid extinction when the intravenous injection of a high input of nuclear beta-galactosidase (beta-gal) expression vector, one day after partial hepatectomy, led to a significant proportion of transduced cells in the liver. Extinction was associated with liver inflammation on tissue sections and appearance of antibodies against the transgene product, while vector genomes became undetectable in liver tissue by PCR. These observations suggested the elimination of transduced cells by an immune response. Transgenic rats tolerant for cytoplasmic beta-gal, or normal rats depleted in CD8 T lymphocytes, steadily expressed the beta-gal vector. In the spleen of normal rats, we detected cytotoxic cells directed against cells expressing beta-gal after the injection of the beta-gal vector. In jaundiced Gunn rats deficient in bilirubin glucuronosyl transferase (BGT1) and treated with a human BGT1 cDNA expression vector, we observed the same kinetics of extinction as well as the appearance of anti-BGT1 antibodies. This study demonstrates that retrovirus-mediated gene transfer may induce cytotoxic T lymphocytes specifically directed against transgene-expressing cells.

Nuclear UDP-glucuronosyltransferases: identification of UGT2B7 and UGT1A6 in human liver nuclear membranes

We have demonstrated the subcellular localization of the human UDP-glucuronosyltransferases (UGTs), UGT2B7 and UGT1A6, in endoplasmic reticulum (ER) and nuclear membrane from human hepatocytes and cell lines, by in situ immunostaining and Western blot. Double immunostaining for UGT2B7 and calnexin, an ER resident protein, showed that UGT2B7 was equally present in ER and nuclear membrane whereas calnexin was present almost exclusively in ER. Immunogold labeling of HK293 cells expressing UGT2B7 established the presence of UGT2B7 in both nuclear membranes. Enzymatic assays with UGT2B7 substrates confirmed the presence of functional UGT2B7 protein in ER, whole nuclei, and both outer and inner nuclear membranes. This study has identified, for the first time, the presence of UGT2B7 and UGT1A6 in the nucleus and of UGT2B7 in the inner and outer nuclear membranes. This localization may play an important functional role within nuclei: protection from toxic compounds and/or control of steady-state concentrations of nuclear receptor ligands.

Role of CsrR, hyaluronic acid, and SpeB in the internalization of Streptococcus pyogenes M type 3 strain by epithelial cells

Internalization of group A streptococcus by human epithelial cells has been extensively studied during the past 6 years. It is now clear that multiple mechanisms are involved in this process. We have previously demonstrated that the CsrR global regulator controls the internalization of an invasive M type 3 strain through regulation of the has (hyaluronic acid synthesis) operon, as well as another, unknown gene(s). Recently, it was reported that the CsrR-regulated cysteine protease (SpeB) is also involved in bacterial uptake. In this study we have examined the roles of CsrR, hyaluronic acid capsule, and SpeB in streptococcal internalization. We have constructed isogenic mutants of the M3 serotype deficient in the csrR, hasA, and speB genes and tested their ability to be internalized by HEp-2 epithelial cells. Inactivation of csrR abolished internalization, while inactivation of either hasA or speB increased the internalization efficiency. Mutation in csrR derepressed hasA transcription and lowered the activity of SpeB, while no effect on speB transcription was observed. The speB mutant expressed smaller amounts of capsule, while the hasA mutant transcribed more csrR and speB mRNAs. Thus, it seems that complex interactions between CsrR, SpeB, and capsule are involved in modulation of group A streptococcus internalization.

Acetaminophen UDP-glucuronosyltransferase in ferrets: species and gender differences, and sequence analysis of ferret UGT1A6

The principal objective of this study was to determine whether ferrets glucuronidate acetaminophen more slowly compared with other species, and if so investigate the molecular basis for the difference. Acetaminophen-UDP-glucuronosyltransferase (UGT) activities were measured using hepatic microsomes from eight ferrets, four humans, four cats, four dogs, rat, mouse, cow, horse, monkey, pig and rabbit. Gender differences between male and female ferret livers were explored using enzyme kinetic analysis. Immunoblotting of microsomal proteins was also performed using UGT-specific antibodies. Finally, the exon 1 region of UGT1A6, a major acetaminophen-UGT, was sequenced. Glucuronidation of acetaminophen was relatively slow in ferret livers compared with livers from all other species except cat. Gender differences were also apparent, with intrinsic clearance (Vmax/Km) values significantly higher in male compared with female ferret livers. Furthermore, Vmax values correlated with densitometric measurements of two protein bands identified with a UGT1A subfamily-specific antibody. No deleterious mutations were identified in the exon 1 or flanking regions of the ferret UGT1A6 gene. In conclusion, like cats, ferret livers glucuronidate acetaminophen relatively slowly. However, unlike cats, in which UGT1A6 is encoded by a pseudogene and dysfunctional, there are no defects in the ferret UGT1A6 gene which could account for the low activity.

Characterization of autoantibodies against uridine-diphosphate glucuronosyltransferase in patients with inflammatory liver diseases

Uridine diphosphate glucuronosyltransferase (UGT) was identified as an antigenic target in a subgroup of liver-kidney microsomal autoantibodies and was termed LKM-3. To evaluate the nature of LKM-3 antibodies, we screened sera from 80 untreated patients with autoimmune hepatitis (AIH) type 1 and 2, primary biliary cirrhosis (PBC), AIH/PBC, hepatitis C virus (HCV) infection, and 12 healthy individuals (controls) against 7 recombinant human UGT isoenzymes (UGT1A1, UGT1A4, UGT1A6, UGT1A7, UGT1A9, UGT1A10, and UGT2B7). Autoantibodies reacting against various UGT isoenzymes were observed in sera from 3 of 18 AIH type 2 and 1 of 27 of the HCV patients. The anti-UGT-positive sera from AIH type 2 patients revealed the strongest immunoreactivity against UGT1A1, the main UGT-isoform involved in the bilirubin glucuronidation. Additionally, these sera were able to block UGT-mediated substrate glucuronidation in vitro. The prevalence for UGT1A1 was shown by 2 independent techniques: (1) UGT1A1 was identified as the main antigen by Western blotting. Preabsorption of sera with UGT1A1 prevented reaction against all tested UGT-isoforms. (2) In vitro immunoinhibition experiments showed that glucuronidation of the anticancer drug flavopiridol by UGT1A1 was more strongly inhibited than its UGT1A9-mediated biotransformation. In contrast, the serum from the HCV-patient reacted predominately with UGT1A6, and moreover, the immunoreactivity pattern was different from that of the AIH group. To summarize, we show the subtype preference of antibodies against UGT1A1 in a subgroup of AIH type 2 patients. These autoantibodies inhibit UGT-mediated glucuronidation in vitro, but it is unlikely that anti-UGT antibodies will have a marked effect on the patients capacity for drug biotransformation, as serum bilirubin levels in patients remained within the normal range.

LKM3 autoantibodies in hepatitis C cirrhosis: a further phenomenon of the HCV-induced autoimmunity

Chronic hepatitis C is frequently associated with laboratory markers-including LKM1 autoantibodies--of autoimmunity. A 62-yr-old woman with hepatitis C cirrhosis presented autoantibodies against liver and kidney microsomal proteins. By further evaluation of autoantibodies using ELISA and immunoblotting LKM1 and LKM3 autoantibodies could be revealed. The target antigen of LKM3 autoantibodies proved to be UGT-1.1 isoenzyme. In the absence of chronic hepatitis D infection or autoimmune hepatitis type 2, this is the first case that reports the occurrence of LKM3 autoantibodies in HCV-induced chronic liver disease.

Expression of human hyaluronan synthases in response to external stimuli

In the present study we have investigated the expression of mRNAs for hyaluronan synthase isoforms (HAS1, HAS2 and HAS3) in different cells in response to various stimuli. Human mesothelial cells, which synthesize large amounts of hyaluronan, express mRNAs encoding all three HAS isoforms, whereas their transformed counterparts, mesothelioma cells, which produce only minute amounts of hyaluronan, express only HAS3 mRNA. Human lung fibroblasts and the glioma cell line U-118 MG express only the HAS2 and HAS3 genes. The expression of the transcripts was higher in subconfluent than in confluent cultures and was well correlated with the production of hyaluronan by the cells. Stimulation of mesothelial cells with platelet-derived growth factor-BB induced an up-regulation of mRNA for HAS2 to a maximum after 6 h of stimulation; HAS1 and HAS3 genes were only induced slightly. Transforming growth factor-beta1 reduced HAS2 mRNA slightly, and hydrocortisone reduced it strongly, within 6 h of stimulation in mesothelial cell cultures but did not significantly affect the expression of mRNAs for HAS1 and HAS3. Induction of HAS1 and HAS2 protein levels in response to the stimuli above correlated with HAS transcript levels. Thus the expression of the three HAS isoforms is more prominent in growing cells than in resting cells and is differentially regulated by various stimuli suggesting distinct functional roles of the three proteins.

Target proteins in human autoimmunity: cytochromes P450 and UDP- glucuronosyltransferases

Cytochromes P450 (CYPs) and UDP-glucuronosyltransferases (UGTs) are targets of autoantibodies in several hepatic and extrahepatic autoimmune diseases. Autoantibodies directed against hepatic CYPs and UGTs were first detected by indirect immunofluorescence as antiliver and/or kidney microsomal antibodies. In autoimmune hepatitis (AIH) type 2, liver and/or kidney microsomal (LKM) type 1 autoantibodies are detected and are directed against CYP2D6. About 10% of AIH-2 sera further contain LKM-3 autoantibodies directed against family 1 UGTs. Chronic infections by hepatitis C virus and hepatitis delta virus may induce several autoimmune phenomena, and multiple autoantibodies are detected. Anti-CYP2D6 autoantibodies are detected in up to 4% of patients with chronic hepatitis C, and anti-CYP2A6 autoantibodies are detected in about 2% of these patients. In contrast, 14% of patients with chronic hepatitis delta virus infections generate anti-UGT autoantibodies. In a small minority of patients, certain drugs are known to induce immune-mediated, idiosyncratic drug reactions, also known as 'druginduced hepatitis'. Drug-induced hepatitis is often associated with autoantibodies directed against hepatic CYPs or other hepatic proteins. Typical examples are tienilic acid-induced hepatitis with anti-CYP2C9, dihydralazine hepatitis with anti-CYP1A2, halothane hepatitis with anti-CYP2E1 and anticonvulsant hepatitis with anti-CYP3A. Recent data suggest that alcoholic liver disease may be induced by mechanisms similar to those that are active in drug-induced hepatitis. Autoantibodies directed against several CYPs are further detected in sera from patients with the autoimmune polyglandular syndrome type 1. Patients with autoimmune polyglandular syndrome type 1 with hepatitis often develop anti-CYP1A2; patients with adrenal failure develop anti-CYP21, anti- CYP11A1 or CYP17; and patients with gonadal failure develop anti-CYP11A1 or CYP17. In idiopathic Addison disease, CYP21 is the major autoantigen.

Expression and inducibility of the human bilirubin UDP-glucuronosyltransferase UGT1A1 in liver and cultured primary hepatocytes: evidence for both genetic and environmental influences

In Crigler-Najjar type II patients and, recently, in Crigler-Najjar type I patients treated with human hepatocyte cell therapy, phenobarbital has been used for reducing the serum bilirubin load. Its effect is attributed to induction of the enzyme required for hepatic bilirubin elimination, UDP-glucuronosyltransferase, UGT1A1. This study investigated the expression and inducibility of UGT1A1 in human donor livers and their corresponding primary hepatocyte cultures. Immunoblot analysis using a specific antibody directed against the amino terminal of the human UGT1A1 isoform showed that 5 hepatocyte donors exhibited a >50-fold difference in UGT1A1 level. UGT1A1 protein level correlated strongly with both liver microsomal bilirubin UGT activity and liver UGT1A1 mRNA level (r(2) =.82 and.72, respectively). Of the 4 patients with the lowest UGT1A1 levels, 3 were homozygotes for the UGT1A1 promoter variant sequence associated with Gilbert's syndrome, and the fourth was a heterozygote. The 3 donors with the highest levels had a history of phenytoin exposure. Hepatocytes isolated from the phenytoin-exposed donors exhibited marked declines in UGT1A1 mRNA levels during culturing. Induction studies using hepatocytes treated for 48 hours with phenobarbital (2 mmol/L), oltipraz (50 micromol/L), or 3-methylcholanthrene (2.5 micromol/L) revealed UGT1A1-inducing effects of phenobarbital, oltipraz, and, in particular, 3-methylcholanthrene. Our data suggest that both genetic and environmental factors play an important role in the marked interindividual variability in UGT1A1 expression. An understanding of these mechanisms could lead to advances in the pharmacological therapy of life-threatening unconjugated hyperbilirubinemia.

UDP-glucuronosyltransferase activity in human liver and colon

BACKGROUND & AIMS

The contribution of glucuronidation toward human drug metabolism is carried out by the Super gene family of UDP-glucuronosyltransferases (UGTs). Regulation of the human UGT1A locus is tissue specific, resulting in the unique expression of multiple hepatic and extrahepatic gene products. Studies were undertaken to examine UGT1A expression in human hepatic and colonic tissues.

METHODS

UGT1A messenger RNA, protein, catalytic activity, and substrate kinetics were studied in 5 samples of normal hepatic and sigmoid colon tissue using duplex reverse-transcription polymerase chain reaction (RT-PCR), enzymatic and Western blot analysis, and indirect immunofluorescence analysis.

RESULTS

Specific patterns of UGT1A gene expression occur in the liver and colon, which were consistent with different banding patterns as detected by Western blot analysis using a UGT1A-specific antibody. However, microsomal UGT activities in colon were up to 96-fold lower for many phenolic substrates, a finding that was not concordant with RT-PCR and Western blot analysis. Interestingly, UGT activity toward tertiary amines and some steroid hormones was equal.

CONCLUSIONS

Differences of glucuronidation activity between human liver and colon suggest that UGT1A activity may be regulated as a result of the relative presence of individual isoforms with differing catalytic activities or by tissue-specific modulators after gene expression.

Characterization of hyaluronan synthase from a human glioma cell line

In the present study we describe a method to prepare membranes with high hyaluronan synthase activity from human glioma cells by pretreatment of the cells with both testicular hyaluronidase and 4-phorbol 12-myristate 13-acetate (PMA). A 23-fold increase in hyaluronan synthase activity was detected in comparison to untreated cells. Using isolated membranes as a source of hyaluronan synthase activity we demonstrate that chain elongation occurs at the reducing end of the hyaluronan molecule. We also present a method to solubilize hyaluronan synthase in active form with 1% digitonin. The solubilized synthase synthesized shorter hyaluronan chains than the membrane bound enzyme. Partial purification of the solubilized enzyme on a Superdex-200 column revealed a 12-fold increase in specific activity. Affinity purified polyclonal antibodies, raised against a synthetic peptide corresponding to the carboxy-terminus of the deduced protein sequence of human hyaluronan synthase recognized a 66 kDa component in the purified preparations. The elution position of the solubilized hyaluronan synthesizing activity immediately after V0 corresponding to a molecular mass of about 600 kDa, suggested that the 66 kDa enzyme forms a complex with other components which may have accessory or regulatory roles during hyaluronan synthesis.

Cytochromes P450 and uridine triphosphate-glucuronosyltransferases: model autoantigens to study drug-induced, virus-induced, and autoimmune liver disease

Enzymes of phase I (cytochromes P450) and phase II (UDP [uridine diphosphate]-glucuronosyltransferases) of drug metabolism are targets of autoimmunity in the following chronic liver diseases of different etiology: 1)autoimmune hepatitis (AIH); 2) hepatitis associated with the autoimmune polyendocrine syndrome type 1 (APS-1); 3) virus-induced autoimmunity; and 4) drug-induced hepatitis. AIH is diagnosed by the following: the absence of infection with hepatitis viruses; the presence of a threshold of relevant factors, including circulating autoantibodies, hypergammaglobulinemia, female sex (female/male ratio 4:1), human leukocyte antigen (HLA) B8, DR3, or DR4; and benefit from immunosuppression. Patients with autoimmune hepatitis type 2 (AIH-2) are characterized by antibodies directed against liver and kidney microsomes, by an early onset of autoimmune hepatitis, which is a more aggressive course of the disease, and by a higher prevalence of autoimmunity directed against other organs. The major target of autoimmunity in patients with AIH-2 is cytochrome P450 2D6. Epitope mapping experiments revealed four short linear epitopes on cytochrome P450 2D6, recognized by liver/kidney microsomal autoantibodies type 1 (LKM-1) in patients with AIH-2. In addition, about 10% of the patient sera contain autoantibodies that detect a conformational epitope on UDP-glucuronosyltransferases (UGTs) of family 1. Presently, LKM-1 autoantibodies are used as diagnostic markers for AIH-2. It is unclear whether these autoantibodies have a pathogenetic role. Hepatitis is found in some patients with APS-1. Presumably this also is an autoimmune liver disease. APS-1 patients with hepatitis may develop autoantibodies directed against microsomal P450 enzymes of the liver; however, these autoantibodies do not recognize cytochrome P450 2D6, but they do recognize cytochrome P450 1A2. Autoimmunity in patients with APS-1 usually is directed against several organs simultaneously, and several organ specific autoantibodies may exist. Interestingly, APS-1 patients may produce various anti-cytochrome P450 antibodies. In addition to the hepatic anti-cytochrome P450, 1A2 autoantibodies are directed against steroidogenic cytochromes P450, namely P450 c21, P450 scc, and P450 c17. These autoantibodies correlate with adrenal and ovarian failure and often these steroidal cell autoantibodies precede the manifestation of adrenal or ovarian dysfunction. Whether anti-P450 1A2 autoantibodies have a similar predictive value is not yet known. LKM autoantibodies are further found in association with chronic hepatitis C and D. In chronic hepatitis C, the major target of LKM autoantibodies is cytochrome P450 2D6. Predominantly, conformational epitopes are recognized by LKM-1 sera of patients with chronic hepatitis C. In 13% of patients with chronic hepatitis D, LKM-3 autoantibody is detectable. The target proteins are UGTs of family 1 and in a minority of sera UGTs of family 2. The epitopes are conformational. All hepatic diseases discussed earlier have in common that autoimmunity, which is directed against enzymes of drug metabolizing multigene families. Each disease is characterized by a specific pattern of autoantibodies, with apparently little overlap. For example, LKM-1 autoantibodies, which are directed against P450 2D6, seem to overlap between AIH and chronic hepatitis C. However, a close examination of these autoantibodies shows differences between LKM-1 autoantibodies from patients with chronic hepatitis C and with AIH. In AIH, LKM autoantibodies are more homogenous, titers are higher, and major autoepitopes on cytochrome P450 2D6 are small and linear. LKM autoantibodies in viral hepatitis C are more heterogeneous and there are multiple epitopes, many of which are conformational. These differences indicate the different mechanisms that are involved in the generation of autoimmunity. (ABSTRACT TRUNCATED)

Induction of two UDP-glucuronosyltransferase isoforms sensitive to phenobarbital that are involved in morphine glucuronidation: production of isoform-selective antipeptide antibodies toward UGT1.1r and UGT2B1

We document here in that two UDP-glucuronosyltransferase (UGT) isoforms sensitive to phenobarbital are involved in morphine glucuronidation in Wistar and Sprague-Dawley rats. The hepatic microsomal morphine UGT activity in untreated Gunn rats was significantly less than that of untreated Wistar rats. Although the morphine UGT activity in the liver of Gunn rats was increased by phenobarbital (PB) treatment, this was significantly less than that in the liver of PB-treated Wistar rats. UGT1.1r is an isoform of morphine UGT in rat, and UGT2B1 is also considered an isoform of morphine UGT, because UGT2B1 (stably expressed in V79 cells) exhibited morphine UGT activity. We prepared specific antipeptide antibodies against UGT1.1r and UGT2B1. Using isoform-specific antipeptide antibodies, both UGT1.1r and UGT2B1 in Wistar and Sprague-Dawley rats were inducible by PB treatment. However, UGT1.1r is not present in the liver from Gunn rats. This study is the first demonstration that protein levels of two morphine UGT isoforms, UGT1.1r and UGT2B1, in the liver of Wistar and Sprague-Dawley rats are inducible by PB treatment.

Autoantibodies against glucuronosyltransferases differ between viral hepatitis and autoimmune hepatitis

BACKGROUND & AIMS

Approximately 13% of patients with chronic hepatitis D virus (HDV) infection have liver-kidney microsomal antibodies type 3 (LKM-3) directed against family 1 uridine 5'-diphosphate-glucuronosyl-transferases (UGT-1). The aim of this study was to characterize the prevalence and specificity of LKM-3 by recombinant antigen testing systems.

METHODS

Enzyme-linked immunosorbent assay (ELISA) and Western blot were performed using baculovirus-generated human UGT-1.1 and -1.6 and rabbit UGT-1.6. Sera from patients with HDV (n = 50), autoimmune hepatitis (AIH) type 2 (n = 50), hepatitis B virus (n = 26), hepatitis C virus (HCV) (n = 25), and LKM-1 autoantibody-positive HCV (n = 14) and sera from normal controls (n = 50) and italian patients with HDV and known LKM-3 autoantibodies were studied.

RESULTS

Six percent of patients with HDV from Germany and 8% of patients with type 2 AIH had LKM-3. Sera from italian patients with HDV and patients with AIH type 2 recognized all three recombinant UGT-1. HDV sera from Germany selectively recognized human UGT-1. LKM-3 titers were lower in HDV than in AIH. One patient with AIH had LKM-3 as the only marker of AIH.

CONCLUSIONS

This study indicates a molecular target and titer difference of LKM-3 autoantibodies in German subjects with HDV and AIH. It also suggests a geographic target and titer difference of LKM-3 in HDV. LKM-3 are identified as a rare and previously undescribed independent marker of AIH.

Cytochromes P450 and UDP-glucuronosyl-transferases as hepatocellular autoantigens

Autoantibodies directed against cytochromes P450 or UDP-glucuronosyl-transferases (UGTs) are detected in hepatitis of different aetiology: drug-induced hepatitis autoimmune hepatitis type 2, hepatitis associated with the autoimmune polyglandular syndrome type 1 (APS1) and virus-induced autoimmunity. Autoantibodies directed against cytochrome P450 2C9 are induced by tienilic acid, and anti-P450 1A2 autoantibodies by dihydralazine. Potential mechanisms involved may be metabolic activation of the drugs by cytochromes P450, adduct formation and circumvention of T cell tolerance. In contrast, little is known about the aetiology of autoimmune hepatitis type 2. This disease is characterized by marked female predominance, hypergammaglobulinaemia, circulating autoantibodies and benefit from immunosuppression. Patients with HLA B8, DR3 or DR4 are over-represented. The major target of autoimmunity in this disease is cytochrome P450 2D6. The autoantibodies were shown to be directed against at four short linear epitopes. In addition, about 10% of the patient sera form an additional autoantibody that detects a conformational epitope on UGTs of family 1. The phenomenon of virus-associated autoimmunity is found in chronic infections with hepatitis C and D. In chronic hepatitis C the major target of the autoantibodies again is cytochrome P450 2D6. Some linear and a high proportion of conformational epitopes are recognized. The LKM3 autoantibody is found in 13% of patients with chronic hepatitis D. The target proteins are UGTs of family 1 and, in some sera also, low titres of anto-antibodies directed against UGTs of family 2 are found. The epitopes detected are conformational. In contrast to the patients suffering from autoimmune hepatitis, patients with hepatitis as part of the autoimmune polyglandular syndrome type 1 recognize cytochrome P450 1A2. Interestingly, in APS1 patients also, autoantibodies directed against cytochromes P450 c21, P450 scc and P450 c17a may be detected; these autoantibodies are associated with adrenal and ovarian failure.

Cytochrome P450 enzymes and UDP-glucuronosyltransferases as hepatocellular autoantigens

Cytochromes P450 and UDP-Glucuronosyltransferases (UGT) are targets of microsomal autoantibodies in liver and kidney (LKM). LKM autoantibodies are observed in autoimmune hepatitis, in some patients with viral hepatitis, drug-induced hepatitis and autoimmune hepatitis as disease component of the autoimmune polyglandular syndrome type 1 (APS-1). In autoimmune hepatitis LKM antibodies are markers of autoimmune hepatitis type 2. The major target of LKM-1 antibodies is cytochrome P450 2D6; a second less frequent target was the described UGTs of family 1. In autoimmune hepatitis LKM-1 autoantibodies are usually directed against small linear epitopes. LKM autoantibodies are also associated with infection with hepatitis viruses C and D. In hepatitis C about 1-2% of patients develop LKM-1 autoantibodies. About 60% of these autoantibodies are conformation dependent. The presence of LKM autoantibodies in hepatitis C may be associated with an increased risk in interferon treatment. LKM-3 autoantibodies are found in about 8% of patients with hepatitis D and are directed against conformational epitopes. Patients treated with certain drugs may develop drug induced hepatitis. In hepatitis induced by tienilic acid, tienilic acid is activated by and covalently bound to cytochrome P450 2C9. Activation of the immune system results in the formation of autoantibodies against cytochrome P450 2C9 (LKM-2) and infiltration of the liver with immune cells. A similar mechanism has been described for dihydralazine induced hepatitis, where autoantibodies are directed against P450 1A2 (LM). Autoantibodies directed against cytochrome P450 1A2 also are found in patients suffering from hepatitis as a disease component of APS-1.

Identification and analysis of drug-responsive expression of UDP-glucuronosyltransferase family 1 (UGT1) isozyme in rat hepatic microsomes using anti-peptide antibodies

Expression of rat hepatic UDP-glucuronosyltransferase family 1 (UGT1) isozymes has been examined using anti-peptide antibodies raised against a conserved carboxyl-terminal portion of all isozymes and variable amino-terminal portions of each isozyme of the phenol cluster (UGT1A) and bilirubin cluster (UGT1B). Among the isozymes expressed in rat hepatic microsomes, UGT1B1 (54 kDa) of bilirubin cluster was found to be a major form and minor forms were identified as UGT1A1 (53 kDa), UGT1B2 (56 kDa), and UGT1B5 (57 kDa). Using a combination of 2D sodium dodecyl sulfate gel electrophoresis and immunoblotting, all the isozymes were found to be simultaneously lacked in Gunn rat hepatic microsomes. The effects of various drugs as inducer on the expression of each UGT1 isozyme were analyzed. The UGT1A1 and UGT1A2 of the phenol cluster isozymes were significantly induced in 3-methylcholanthrene-treated rats. The expression of UGT1B1 and the glucuronidation activity toward bilirubin in rat hepatic microsomes were induced two- to threefold by clofibrate and dexamethasone administration. On the other hand, the regulation of UGT1B2 and UGT1B5 expression was different from that of UGT1B1. These results clearly show the drug-responsive expression of each UGT1 isozyme using isozyme-specific antibodies for the first time.

Antibodies against proteins of streptococcal hyaluronate synthase bind to human fibroblasts and are present in patients with rheumatic fever

Antibodies directed against the streptococcal 42 kDa hyaluronate synthase and a 56 kDa auxiliary protein bound to the surface of intact human fibroblasts in vitro. Staining was most prominent during the detachment phase of mitosis. In eukaryotic plasma membranes a 52 kDa protein was recognized by the antiserum against the 56 kDa streptococcal protein. Since the cross-reacting proteins could be involved in immunological mimicry between streptococcal and human antigens leading to heart cell necrosis, the reactivity of sera from patients with rheumatic fever was compared with that of sera from healthy or streptococcal infected persons. The sera from patients with rheumatic fever showed a higher reactivity against the 56 kDa protein than those from healthy persons or from patients with an antibiotic treated streptococcal infection. This difference was not observed for the 42 kDa protein. These sera were able to lead to cell lysis in the presence of complement.

Immunoaffinity purification and reconstitution of the human bilirubin/phenol UDP-glucuronosyltransferase family

When membrane proteins are solubilized and subjected to purification procedures, the loss of lipids surrounding the protein often results in irreversible inactivation. We describe a procedure for the immunoaffinity purification of the membrane protein UDP-glucuronosyltransferase from human liver. This procedure reduces exposure of the protein to detergent, thereby reducing lipid loss. Triton X-100 was used to solubilize human liver microsomes. The solubilized proteins were applied to a sephacryl 300 (S-300) gel filtration column equilibrated with detergent-free buffer. UDP-glucuronosyltransferase activity eluted in turbid fractions in the void volume. During passage through the column Triton X-100 can partition in the buffer, while lipids are reconstituted into vesicular structures. Proteins with a high affinity for phospholipids remain associated with the lipid and elute in the void volume. The active fractions from the S-300 column were resolubilized with Triton X-100 and applied to a column with immobilized antibody. Washing this column with buffer containing phosphatidylcholine liposomes and no detergent removed unbound proteins and minimized loss of lipid from bound UDP-glucuronosyltransferase. Raising the pH of the washing buffer to 11.5 in the presence of liposomes resulted in elution and simultaneous reconstitution of active UDP-glucuronosyltransferase. Antibodies against membrane proteins are often available but immunoaffinitypurification of active enzyme is difficult. The approach described here could be useful for the isolation of other membrane proteins.

Discrimination between Crigler-Najjar type I and II by expression of mutant bilirubin uridine diphosphate-glucuronosyltransferase

Crigler-Najjar (CN) disease is classified into two subtypes, type I and II. The molecular basis for the difference between these types is not well understood. Several mutations in the bilirubin UDP-glucuronosyl-transferase (B-UGT) gene of six CN type I and two CN type II patients were identified. Recombinant cDNAs containing these mutations were expressed in COS cells. B-UGT activity was measured using HPLC and the amount of expressed protein was quantitated using a sandwich ELISA. This enabled us to determine the specific activities of the expressed enzymes. All type I patients examined had mutations in the B-UGT1 gene that lead to completely inactive enzymes. The mutations in the B-UGT1 gene of patients with CN type II only partially inactivated the enzyme. At saturating concentrations of bilirubin (75 microM) CN type II patient A had 4.4 +/- 2% residual activity and CN type II patient B had 38 +/- 2% residual activity. Kinetic constants for the glucuronidation of bilirubin were determined. The affinities for bilirubin of B-UGT1 expressed in COS cells and B-UGT from human liver microsomes were similar with Km of 5.1 +/- 0.9 microM and 7.9 +/- 5.3 microM, respectively. B-UGT1 from patient B had a tenfold decreased affinity for bilirubin, Km = 56 +/- 23 microM. At physiological concentrations of bilirubin both type II patients will have a strongly reduced conjugation capacity, whereas type I patients have no B-UGT activity. We conclude that CN type I is caused by a complete absence of functional B-UGT and that in CN type II B-UGT activity is reduced.

Recognition of uridine diphosphate glucuronosyl transferases by LKM-3 antibodies in chronic hepatitis D

Patients with chronic hepatitis D often have liver-kidney microsomal antibodies type 3 (LKM-3). These antibodies react with several microsomal antigens that have a molecular weight of 55 KDa and an isoelectric point of about 8. We studied the molecular nature of the antigen and, by immunoscreening a human liver cDNA expression library with KM-3 sera, found that uridine diphosphate glucuronosyl transferases (UGT) appeared as candidate antigens. We confirmed the identity of UGT as an antigen by reacting the sera with recombinant rabbit liver UGT proteins. Some sera reacted with rabbit UGT-2 proteins, but UGT-1 proteins were more sensitive and specific in detecting LKM-3 autoantibodies in patient sera. Anti-UGT-1 antibodies were detected in all LKM-3 positive sera from patients with hepatitis D and 1 out of 11 patients with autoimmune hepatitis type 2. Sera from patients who had hepatitis B only did not react with UGT proteins. The UGT proteins are part of the phase II enzymes of drug metabolism and are the first such enzymes to be identified as human autoantigens.

Immunochemical confirmation of the primary structure of streptococcal hyaluronan synthase and synthesis of high molecular weight product by the recombinant enzyme

We have recently identified and cloned the gene for hyaluronan (HA) synthase, hasA, from group A Streptococci [DeAngelis, P.L., Papaconstantinou, J., & Weigel, P.H. (1993) J. Biol. Chem. 268, 19181-19184]. We have now generated two polyclonal monospecific antibodies against synthetic peptides corresponding to portions of the deduced protein. Both antibodies recognize a protein with an apparent molecular weight of 42,000 either from wild-type Streptococcus pyogenes or from Escherichia coli containing the cloned gene on a plasmid. Immobilized affinity-purified antibody depleted HA synthase activity from functional detergent extracts of streptococcal membranes in a specific fashion. The immobilized protein displayed HA synthase activity, and HasA was the major bound polypeptide. The recombinant HA synthase behaves identically to that from Streptococci, with respect to sugar nucleotide specificity and polysaccharide production. Only the authentic sugar nucleotides UDP-glucuronic acid and UDP-N-acetylglucosamine support HA polymerization. The recombinant enzyme elongates HA in a processive manner and rapidly produces polymers on the order of > or = 5 x 10(6) Da at rates of about 10-30 monosaccharides/s at three times the apparent Km of substrates.

Expression and role of the human liver UDP-glucuronosyltransferase UGT1*6 analyzed by specific antibodies raised against a hybrid protein produced in Escherichia coli

Characterization of human UDP-glucuronyltransferases (UGTs) has been limited by the unavailability of probes selective for each of several highly related isoforms. To better understand the role of this superfamily in the metabolism of drugs and xenobiotics, we describe a molecular/immunological strategy for discriminating the implication of each human isoenzyme in this process. Specific polyclonal antibodies were generated against the divergent amino-terminal domain of the UGT isoform UGT1*6 which is involved in the detoxification of nucleophilic compounds related to phenols and naphthols in human liver. The novel approach consists of the expression of a N-terminal UGT polypeptide fused to Staphylococcus aureus protein A in Escherichia coli and a single step purification of the fusion protein by immunoaffinity chromatography. Immunoblot and immunoinhibition analysis showed that the antibodies raised against the fusion protein selectively recognized both the denaturated and the native forms of UGT1*6, when expressed in V79 cell lines, but not three other recombinant UGT isoenzymes. In human liver microsomes, specific immunoinhibition analysis demonstrated that glucuronidation by UGT1*6 represented 20 to 50% of the total 1-naphthol UGT activity with a good correlation with the amount of protein selectively quantified on immunoblot. The specific expression of UGT1*6 was found to be significantly reduced in tumoral tissues but enhanced in cholestatic livers, when compared with healthy hepatic tissues. Interestingly, in human kidney microsomes, antibodies revealed a high level of UGT1*6 expression on immunoblot and inhibited 1-naphthol glucuronidation up to 55%, indicating that this isoform is also expressed in kidney and extensively contributes to phenol glucuronidation in this tissue.

Monoclonal antibodies against 4-hydroxybiphenyl-UDP-glucuronosyltransferase

Monoclonal antibodies against purified rat liver 4-hydroxybiphenyl UDP-glucuronosyltransferase were developed using the hybridoma technology. In immunoblot analysis the antibodies specifically reacted with purified 4-hydroxybiphenyl-UDPGT but not with other purified UDPGT enzyme fractions. One single band was detected with microsomes of rat liver and small intestine but not with microsomes of kidney and lung. The reactive protein was also found in dog and human liver microsomes. It could be shown that there was no increase of immunoreactive protein after pretreatment with phenobarbital or 5,6-benzoflavone. This supports the hypothesis that more than one 4-hydroxybiphenyl-UDPGT exist in rat liver which are differently inducible.

Topological disposition of UDP-glucuronyltransferase in rat liver microsomes

The topological disposition of a form of UDP-glucuronyltransferase (called GT-1) in rat liver microsomes was examined. Concanavalin A-Sepharose failed to bind microsomal vesicles even though GT-1 has sugar chains of "high mannose" type, indicating that mannose-containing sugar chains of microsomal glycoproteins including GT-1 are not exposed to the outer surface of microsomal vesicles. Polyclonal antibodies raised against purified GT-1 could bind to microsomal vesicles, indicating that at least part of the GT-1 polypeptide chain is extruded to the outside of the microsomal membrane. Intact microsomal vesicles were digested with carboxypeptidase Y and then subjected to immunoblot analysis using the anti-GT-1 antibodies. It was thus found that the digestion resulted in cleavage of a C-terminal, 2-kDa fragment, leaving a 52-kDa fragment of GT-1 still tightly bound to the membrane. From these results, it is concluded that GT-1 is a transmembrane protein, which extrudes its C-terminal end (at least 2 kDa) to the outside of the membrane, whereas most of its polypeptide chain together with the sugar chains are located on the luminal side of the membrane.

Purification and properties of a rat liver phenobarbital-inducible 4-hydroxybiphenyl UDP-glucuronosyltransferase

A phenobarbital-inducible rat hepatic microsomal UDP-glucuronosyltransferase (UDPGT) that catalyzes the glucuronidation of 4-hydroxybiphenyl (4-HBP) has been purified to homogeneity. This UDPGT has an apparent subunit molecular weight of 52,500, as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The 4-HBP UDPGT was shown to catalyze the glucuronidation of 4-HBP, 4-methylumbelliferone, and p-nitrophenol but did not react with testosterone, androsterone, morphine, chloramphenicol, 4-hydroxycoumarin, or 7-methoxycoumarin. The apparent Km of 4-HBP UDPGT for 4-HBP was determined to be 0.26 mM and for UDPGA was 1.0 mM. Upon treatment with endoglycosidase H, the 4-HBP UDPGT underwent about a 2000-dalton decrease in subunit molecular weight, suggesting that this protein is N-glycosylated. Additionally, this protein demonstrated immunoreactivity with antibodies raised in rabbit against rat 17 beta-hydroxysteroid and 3 alpha-hydroxysteroid UDPGTs. This work describes the purification and characterization of a 4-HBP UDPGT from rat liver microsomes and, furthermore, provides evidence that suggests that this UDPGT is different from another UDPGT previously shown to react with 4-HBP and chloramphenicol.

Differential effects of phospholipids on two similar forms of UDP-glucuronyltransferase purified from rat liver and kidney microsomes

Two isoforms of UDP-glucuronyltransferase purified from rat liver (named GT-1) and kidney (named GT-2) have various properties in common but differ in their NH2-terminal sequences. In this study, the two forms were further found to have common immunochemical properties, i.e., they could not be distinguished by Ouchterlony double diffusion and immunoblotting analyses. These isoforms also had the same inducibility as shown by immunoblotting analysis: GT-2 protein in rat was increased by treatment with beta-naphthoflavone and 3-methylcholanthrene, whereas GT-1 was inducible by 3-methylcholanthrene. However, the effects of phospholipids on these enzymes were extremely different. 1-Naphthol glucuronizing activity of GT-1 was increased 7.5-8-fold by lysophosphatidylcholine, but the activity of GT-2 was increased only 3-3.6-fold. The transferase activity of GT-1 toward 4-methylumbelliferone was increased 2-2.5-fold by dilauroylphosphatidylcholine, but that of GT-2 was reduced, while its 4-nitrophenol glucuronidation activity was increased 1.5-fold by the phospholipid. These results indicate that the two similar UDP-glucuronyltransferases from rat liver and kidney interact differently with phospholipids and that the activation level of UDP-glucuronyltransferase activity with phospholipids depends on the aglycone substrates.

Persistently increased expression of a 3-methylcholanthrene-inducible phenol uridine diphosphate-glucuronosyltransferase in rat hepatocyte nodules and hepatocellular carcinomas

Increased UDP-glucuronosyltransferase in rat hepatocyte nodules and hepatocellular carcinomas produced by feeding 2-acetylaminofluorene or N-nitrosomorpholine was studied using isozyme-selective substrates, antibodies, and DNA probes. UDP-glucuronosyltransferase (UDP-GT) activities toward 4-methylumbelliferone, 1-naphthol, and benzo[a]pyrene-3,6-quinol were reversibly increased by short term feeding of 2-acetylaminofluorene but were persistently increased in hepatocyte nodules and differentiated hepatocellular carcinomas. Immunoblot analysis revealed that short term feeding of 2-acetylaminofluorene increased a Mr 55,000 polypeptide corresponding to the previously characterized UDP-GTI or phenol UDP-GT. However, in some hepatocyte nodules and hepatocellular carcinomas either the Mr 55,000 or a new Mr 53,000 polypeptide was preferentially increased, suggesting heterogeneous UDP-GT forms in liver nodules and carcinomas. Northern blot hybridization with a synthetic DNA probe to phenol UDP-GT demonstrated increased levels of mRNA in liver nodules. The results suggest persistently increased expression of at least two phenol UDP-GT enzyme forms in hepatocyte nodules, which may contribute to the toxin-resistance phenotype frequently observed at cancer prestages.

Immunochemical analysis of uridine diphosphate-glucuronosyltransferase in four patients with the Crigler-Najjar syndrome type I

The functional heterogeneity of uridine diphosphate-glucuronosyltransferase (UDPGT) and its deficiency in human liver were investigated. The monoclonal antibody (MAb) WP1, which inhibits bilirubin and phenol-glucuronidating activity, was used to immunopurify UDPGTs from human liver. Purified UDPGTs were injected into mice to obtain new MAbs. Immunoblotting of microsomes with MAb HEB7 revealed at least three polypeptides in liver (56, 54, and 53 kD) and one in kidney (54 kD). In liver microsomes from four patients (A, B, C, and D) with Crigler-Najjar syndrome type I (CN type I), UDPGT activity towards bilirubin was undetectable (A, B, C, and D) and activity towards phenolic compounds and 5-hydroxytryptamine either reduced (A and B) or normal (C and D). UDPGT activity toward steroids was normal. Immunoblot studies revealed that the monoclonal antibody WP1 recognized two polypeptides (56 and 54 kD) in liver microsomes from patient A and none in patient B. With HEB7 no immunoreactive polypeptides were seen in these two patients. Patient C showed a normal banding pattern and in patient D only the 53-kD band showed decreased intensity. These findings suggest considerable heterogeneity with regard to the expression of UDPGT isoenzymes among CN type I patients.

Heterogeneous alterations of UDP-glucuronosyltransferases in mouse hepatic foci

UDP-glucuronosyltransferase (UDPGT) was studied immunohistochemically in hepatic foci and nodules of N-nitrosomorpholine-treated mice. Serial sections were stained for glucose-6-phosphatase (G6Pase). It was found that a high percentage of G6Pase-negative liver foci and nodules were also UDPGT-negative (34%). In addition, G6Pase-negative foci without altered UDPGT phenotype (30%) and UDPGT-negative foci without altered G6Pase phenotype (8%) were detected. G6Pase-positive foci were also present (24%). Interestingly, most G6Pase-positive foci were UDPGT-positive (16%). Some G6Pase-positive lesions without altered UDPGT phenotype were also found (8%). The major phenotype observed in rat hepatocarcinogenesis models (UDPGT-positive/G6Pase-negative foci) was not detectable in the mouse model. These results demonstrate heterogeneous alterations of UDPGTs in mouse hepatic foci. They furthermore suggest marked differences between the mouse and the rat in the regulation of UDPGTs in similarly induced rat hepatic foci.

Development of human liver UDP-glucuronosyltransferases

The development of multiple UDPGT activities towards eight substrates has been studied in fetal term and adult post-mortem (less than 5 h after death) liver samples. Most fetal and term liver activities were less than 14% of adult values, except that towards 5-hydroxytryptamine which was present in fetal and term liver at adult levels. The majority of UDPGT activities develop to adult levels within 10-20 weeks postnatally, and even premature (30 weeks) which survive for up to 10 weeks will develop these enzyme activities. Immunoblot analysis of human liver microsomes and cDNA cloning of human UDPGT shows the existence of the family of isoenzymes in man, and it is important to determine the developmental pattern of individual drug glucuronidating enzymes in liver. Immunoblot analysis of developing liver shows the presence of two major UDPGT polypeptides in fetal liver, whereas more than five are observed in adult liver. The investigation of substrate specificity of individual UDPGTs by expression of cloned genes in COS-7 cells and the use of antibodies will facilitate the identification of enzymes present in perinatal liver.

Characterization of antibodies to a rabbit hepatic UDP-glucuronosyltransferase and the identification of an immunologically similar enzyme in human liver

An antibody to a UDP-glucuronosyltransferase (UDPGT) isoenzyme which catalyzes the glucuronidation of p-nitrophenol (PNP) in rabbit liver was raised in sheep and used to identify immunologically similar UDPGTs in rabbit and human livers. Immunoblotting experiments showed that the antisera specifically recognized PNP UDPGT but not estrone UDPGT purified from rabbit liver. Sheep anti-rabbit liver PNP UDPGT IgG immunoprecipitated PNP, 1-naphthol, and 4-methylumbelliferone glucuronidation activities in rabbit and human liver microsomal preparations. In rabbit liver microsomes the antibody did not immunoprecipitate estrone or estradiol glucuronidation activities. In human liver microsomes, 4-aminobiphenyl but not estriol glucuronidation activities were immunoprecipitated, suggesting that the antibody recognizes a specific UDPGT (pI 6.2) in human liver microsomes.

Characterization and tissue specificity of a monoclonal antibody against human uridine 5'-diphosphate-glucuronosyltransferase

A monoclonal antibody against human liver uridine 5'-diphosphate-glucuronosyltransferase (UDPGTase) was developed. Enzyme inhibition studies with this monoclonal antibody showed inhibition of human liver UDPGTase activity with bilirubin, 4-methylumbelliferone, and 4-nitrophenol as substrates. Testosterone, estrone, and phenolphthalein UDPGTase activity was not inhibited. The monoclonal antibody probably recognizes the uridine 5'-diphosphate-glucuronic acid binding site at 4-nitrophenol UDPGTase. Proteins with a molecular mass of 54,000 daltons were immunopurified from solubilized human liver using the monoclonal antibody as ligand coupled to Sepharose 4B beads. The distribution of UDPGTase isoforms in various human tissues was studied by immunofluorescence. The enzyme could be detected in liver, kidney, stomach, small intestine, colon, and skin. In liver, only hepatocytes contain UDPGTase. In kidney, the enzyme was localized exclusively in proximal tubuli and in stomach in epithelial mucous cells. In small intestinal epithelium, maximal fluorescence was seen at the villous tip. In colon, all lining epithelial cells were stained. In colon polyps, staining for UDPGTase was clearly decreased, and in colon carcinoma it was undetectable. In skin, the stratum corneum was intensely stained, whereas the stratum basale showed no fluorescence.

Cloning of a human liver microsomal UDP-glucuronosyltransferase cDNA

A cDNA clone (HLUG 25) encoding the complete sequence of a human liver UDP-glucuronosyltransferase was isolated from a lambda gt11 human liver cDNA library. The library was screened by hybridization to a partial-length human UDP-glucuronosyltransferase cDNA (pHUDPGT1) identified from a human liver pEX cDNA expression library by using anti-UDP-glucuronosyltransferase antibodies. The authenticity of the cDNA clone was confirmed by hybrid-select translation and extensive sequence homology to rat liver UDP-glucuronosyltransferase cDNAs. The sequence of HLUG 25 cDNA was determined to be 2104 base-pairs long, including a poly(A) tail, and contains a long open reading frame. The possible site of translation initiation of this sequence is discussed with reference to a rat UDP-glucuronosyltransferase cDNA clone (RLUG 38).

Immunochemical and functional characterization of UDP-glucuronosyltransferases from rat liver, intestine and kidney

Glucuronidation of various substrates in hepatic, intestinal and renal microsomes of control, phenobarbital (PB), 3-methylcholanthrene (3MC) and Aroclor-1254 (A1254) pretreated rats was investigated. UDPGT activities tested could be divided in four groups on the basis of their tissue distribution and induction by PB or 3MC in liver microsomes. GT1 activities (1-naphthol, benzo(a)pyrene-3,6-quinol) are induced by 3MC in liver microsomes and are present in all tissues investigated. GT2 activities (morphine, 4-hydroxybipheynl) are induced by PB in liver microsomes and appear to be restricted to the liver and the intestine. UDPGT activity towards bilirubin, although induced by PB, can be detected in hepatic, intestinal and renal microsomes. UDPGT activity towards fenoterol is restricted to the liver and intestine and is not induced by PB, 3MC or A1254. The presence of inducible immunoreactive UDPGT isoenzymes in microsomes of liver, intestine and kidney of control and induced rats was demonstrated by immunoblot analysis using rabbit anti-rat liver-GT1 antibodies. Induction of both 54 and 56 kDa polypeptides in hepatitis, intestinal and renal microsomes by 3MC or A1254 was observed. Purification of UDPGT (1-naphthol as substrate) from intestinal microsomes to apparent homogeneity yielded a polypeptide with an apparent molecular weight of 54-56 kDa. The results indicate that 54 and 56 kDa UDPGT polypeptides are the major A1254 inducible isoenzymes in intestinal and renal microsomes. An increase in immunoreactive protein is correlated with a biochemically measurable increase in glucuronidation capacity for GT1 substrates.