![[Feedback]](/icons/banner/feedbackACT.gif){kind=icon}
![[For Subscribers]](/icons/banner/subscriberACT.gif){kind=icon}
![[Archive]](/icons/banner/archiveACT.gif){kind=icon}
![[Search]](/icons/banner/searchACT.gif){kind=icon}
![[Contents]](/icons/banner/tocACT.gif){kind=icon}
|
|
|
|
|
||
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
CELLULAR AND MOLECULAR
Viikki Drug Discovery and Development Technologies Center, Faculty of Pharmacy, University of Helsinki, Helsinki, Finland (M.F.); Department of Biochemistry and Molecular Biology, University of Arkansas for Medical Sciences, Little Rock, Arkansas (X.L., S.B., A.R.-P.); and Department of Clinical Pharmacology, Flinders University, Flinders Medical Centre, Bedford Park, South Australia, Australia (D.G.-S., P.I.M.)
Received July 1, 2005; accepted August 19, 2005.
 |
Abstract |
|---|
 Top Abstract Materials and MethodsResultsDiscussionReferences |
|---|
; Ouzzine et al., 2003; Wells et al., 2004). The human genome contains many UGT-encoding genes, which have been divided into two subfamilies, UGT1 and UGT2. The UGT1A isoforms are encoded by a single large gene cluster on chromosome 2, and the expression of individual UGTs of this subfamily is governed by exon sharing (Ritter et al., 1992; Mackenzie et al., 1997). Hence, exon 1, encoding the N-terminal portion of each UGT1A, is unique, whereas exons 2 to 5, together encoding the C-terminal portion of these proteins, are shared by all the UGT1A isoforms (Ritter et al., 1992).
The expression of the UGTs is tissue-specific, and there are large differences in their expression levels in different tissues. Several UGT1A isoforms, including 1A1, 1A3, 1A4, 1A6, and 1A9, are rather highly expressed in the liver, whereas UGT1A7, 1A8, and 1A10 are mainly expressed in extrahepatic tissues, particularly the intestine (Strassburg et al., 1997; Tukey and Strassburg, 2001; Mackenzie et al., 2003; Gregory et al., 2004). The tissue-specific expression of UGT1As has been studied extensively, but thus far, there are no reports about the expression of human UGT1A5 in any tissue. Therefore, there was the question of whether the gene encoding this "missing UGT" was functional (see legend to Fig. 5 of Tukey and Strassburg, 2001). Recombinant human UGT1A5 was previously synthesized and assayed for activity toward several different substrates (Ciotti et al., 1999; Basu et al., 2004). The only detectable activity of UGT1A5 reported in these studies was glucuronidation of 7-ethyl-10-hydroxycamptothecin (SN-38) at very low rates (Ciotti et al., 1999). In the absence of more significant activity, one might wonder about the function of UGT1A5, even if it is shown to be expressed. However, the expression of xenobiotic metabolizing enzymes, including the UGTs, is often induced by different compounds via nuclear receptors and promoter elements that are specific for certain xenobiotics (Mackenzie et al., 2003; Bock and Kohle, 2004). Hence, the absence of detectable expression of a given UGT in human tissues may not be sufficient to indicate that the gene in question is not functional.
Most human UGTs glucuronidate multiple substrates, and there is extensive overlap in their substrate specificities. Little is currently known about the structural elements that determine substrate binding to UGTs or the detailed location of the substrate binding site(s) within these enzymes. The most studied enzyme in this respect is UGT2B7, for which the interaction of morphine with several different peptides from the N-terminal region of the enzyme has been studied by nuclear magnetic resonance (Coffman et al., 2001, 2003). These experiments suggested that the binding site for the opioid is between residues 84 and 118 of UGT2B7, within which residues 96 to 101 are directly involved in substrate binding (Coffman et al., 2003). Human UGT1A3–1A5 are highly homologous to each other, and sequence alignment of UGT1A4 and 1A5 (Fig. 1) reveals that the majority of the 35 nonidentical residues in these isoforms are located among the N-terminal 110 residues. This observation, together with the above-mentioned results from UGT2B7, suggests that any differences in activity between UGT1A5 and UGT1A4 could originate from one or more of these nonidentical amino acids within this N-terminal region.
|
In the present study, we have investigated both the mRNA expression and the activity of human recombinant UGT1A5. The results indicate that this is a functional member of the UGT1A subfamily, and its close examination could yield important new findings about both the regulation of and structure-function relationships within the UGTs.
|
Materials and Methods |
|---|
|
TopAbstractMaterials and MethodsResultsDiscussionReferences |
|---|
|
|
Human Intestinal Tissue. Human gastrointestinal tissue was obtained from organ donors (details are given in the appropriate figure legend) by transplant surgeons at the University of Arkansas for Medical Sciences under a protocol approved by the Human Research Advisory Committee. Working at 4°C, the tissue was divided into the following segments: stomach; duodenum, four segments of the remaining small intestine (S-1 to S-4); and colon. Each segment was opened and cleaned, and mucosa was recovered by scraping with a glass slide. RNA from H1 and H2 was prepared from mucosa that had been stored at –80°C, whereas the mucosa from H3 and H4 was collected and used immediately for RNA isolation, as described below.
Human Hepatic Tissue. The two human livers used in these studies were also obtained from the transplantation program at the University of Arkansas for Medical Sciences. Donor information is given in the legend to Fig. 2.
RNA Isolation and cDNA Synthesis. Total RNA was isolated from cultured cells or mucosa using a phenol and guanidine isothiocyanate RNA extraction method following the instructions of the supplier (TRIzol; Invitrogen). To avoid any contamination of the RNA by genomic DNA, DNase treatment was performed using RQ1 RNase-Free DNase (Promega, Madison, WI). cDNA was synthesized by mixing 1 µg of total RNA from each sample with 100 pmol of random hexamers in 50 mM Tris-HCl, pH 8.3, 75 mM KCl, 3 mM MgCl2, 10 mM dithiothreitol, 100 U of Moloney murine leukemia virus reverse transcriptase, 20 U of RNase inhibitor, and 1 mM of each dNTP (all from Promega) in a total volume of 20 µl. The samples were incubated at 37°C for 60 min and heated at 95°C for 5 min to inactivate the reverse transcriptase. The reaction mixture was diluted to 100 µl with sterile diethylpyrocarbonate-treated H2O. For semiquantitative RT-PCR, the primers for GAPDH and UGT1A5 are described in Table 2. The specificity of all primer pairs was confirmed through sequencing or restriction analysis of the PCR products. The PCR reactions were performed as follows. A 10-µl cDNA aliquot was added to a reaction mixture containing 10 mM Tris-HCl buffer, pH 8, 20 mM KCl, 0.1% Triton X-100, 1.5 mM MgCl2, 0.2 mM each dNTP, 50 pmol of each primer, and 2 units of TaqDNA polymerase (Promega) in a total volume of 50 µl. The mixture was subjected to 34 cycles (26 for GAPDH), each consisting of a 45-s denaturing step at 94°C, a 45-s annealing step at 59°C, and a 45-s elongation step at 72°C in a thermal cycler (PTC100; MJ Research, Watertown, MA). Amplification of the ubiquitously expressed GAPDH cDNA was performed under the same conditions in separate experiments. Primer pairs were designed to specifically amplify across exon boundaries in mRNA from UGT1A5 and GAPDH, and Table 1 details the annealing temperature and cycle number required for each template. For each primer pair, PCR was performed with different cycle numbers, and these data were plotted to form a standard curve. The cycle that was found to be within the nonsaturable range of amplification was chosen for use in further experiments. All other conditions were kept consistent unless significant changes in mRNA level were observed. The PCR products were resolved by electrophoresis on 2% agarose gels and detected by ethidium bromide. The bands were visualized under UV light and photographed with a computed-assisted camera. Quantification of each band was performed by densitometric analysis by using NIH Image software (National Institutes of Health, Bethesda, MD). The RT-PCR products for UGT1A5 generated from mRNA from hepatocyte donor HH1117 were extracted from the gel and, after purification, were sequenced by the University of Arkansas for Medical Sciences sequencing core. The sequences were then compared with corresponding known sequences from GenBank.
|
Cloning. The preparation of cDNA from Caco-2 cells after transfection with PXR and treatment by Rif has been described recently (Gardner-Stephen et al., 2004). The coding region of the human UGT1A5 was amplified from such cDNA by nested PCR. The initial PCR reaction consisted of 4 µl of Caco-2 cDNA, 20 mM Tris-HCl, pH 8.8, 10 mM KCl, 2 mM MgSO4, 10 mM (NH4)2SO4, 0.1% Triton X-100, 0.1 mg/ml bovine serum albumin, 0.2 mM dNTPs, 2.5 ng/µl each of the oligonucleotide primers UGT1A 3'-SpeI and 1A5cDNAUTR (Table 1), and 2.5 units of Pfu Turbo DNA polymerase (Stratagene, La Jolla, CA) in 50 µl. The PCR cycling conditions were as follows: 4-min denaturation at 95°C followed by 30 cycles of 30 s at 95°C, 30 s at 50°C, and 5 min at 72°C and a final step of 72°C for 5 min. The product from the first PCR (1 µl) was used as a template in the second PCR, which was done similarly, with the exception that the primers were UGT1A3'-SpeI and 1A5cDNAATG, the annealing temperature was 55°C, and the reaction was extended to include an extra 10 PCR cycles. The resulting PCR product was subjected to restriction digestion and cloned into the XhoI and SpeI sites of pBluescript II SK (Stratagene), facilitated by sites engineered into the 1A5cDNAATG and UGT1A3'-SpeI oligonucleotides, respectively. The cloned UGT1A5 (GenBank accession no. NM_019078
[GenBank]
) was sequenced and found to have a single silent nucleotide difference (T792C) with respect to the published genomic sequence (GenBank accession no. AF297093
[GenBank]
).
Production of Recombinant UGT1A5 and Enzymatic Assays. The cloned UGT1A5 was transferred in two steps from the original pBluescript into pFBXHC, a derivative of pFastBac1 (Invitrogen) designed to add a C-terminal enterokinase cleavage site followed by a His tag (Kurkela et al., 2003). The XhoI-SpeI fragment from the pBluescript construct was first subcloned into Litmus 29 (New England Biolabs, Beverly, MA) that was digested with the same enzymes. Subsequently, the BssH2-BstE2 fragment from the latter construct, together with the BstE2-HindIII fragment from the previously cloned UGT1A6 in pFB-XHC (Kurkela et al., 2003), was subcloned into pFastBac1 that was digested with BssH2 and HindIII. The preparation of recombinant baculoviruses, insect cell infection, and membrane isolation were done as described previously (Kurkela et al., 2003). The glucuronidation activity of the recombinant UGTs was assayed in the presence of 5 mM UDP-glucuronic acid, 0.5 mM appropriate substrate, and 15 µg/ml membrane protein. The samples were incubated at 37°C for 60 min in the cases of scopoletin, 4-methylumbelliferon (4-MU), and 4-aminobiphenyl (4-ABP) or 45 min when 1-hydroxypyrene (1-HP) glucuronidation was assayed. These incubation conditions were within the linear range of the reactions with respect to both time of incubation and time of protein concentration. The glucuronides were analyzed and quantified by high-performance liquid chromatography with sensitive fluorescence detection, using authenticated (scopoletin, 1-HP, and 4-MU) or radiolabeled (4-ABP) standards, as detailed previously (Luukkanen et al., 2005).
Preparation of the Chimeric Enzymes UGT1A4/5 and UGT1A5/4. The pFastbac derivatives containing the subcloned UGTs 1A4 and 1A5 were each digested with the restriction enzymes XbaI and HindIII. The fragment from the digestion of UGT1A5 containing the gene segment from the internal XbaI site to the HindIII site immediately downstream of the stop codon was subsequently ligated into the digested vector from UGT1A4 (that also contained the 5' segment of UGT1A4, from the first ATG to the internal XbaI site), giving rise to 1A4/5. The construction of 1A5/4 was performed in a similar manner, with the exception that the XbaI-HindIII fragment was from 1A4 and the digested vector from 1A5. Expression in baculovirus-infected insect cells and the preparation of membranes were done as for UGT1A5. Protein concentrations were measured by the bicinchoninic acid system (Pierce Chemical, Rockford, IL) using bovine serum albumin as a standard.
|
Results |
|---|
|
TopAbstractMaterials and MethodsResultsDiscussionReferences |
|---|
|
|
In addition to the induction of UGT1A5 mRNA levels in hepatocytes in response to inducers, the levels of mRNA for other UGT1A isoforms were also elevated (data not shown). It would be impossible to demonstrate an increase in UGT1A5 protein level by Western blot or an increase in UGT1A5-specific catalytic activity because of the fact that an anti-UGT1A5-specific antibody is not available and specific UGT1A5 substrates have not been identified.
Expression of UGT1A5 mRNA in the GI Tract. mRNA was isolated from the mucosa of the available segments of the GI tracts of four human donors. The expression level of UGT1A5 mRNA in each segment from each donor was determined by parallel RT-PCR, using the ubiquitous GAPDH mRNA for normalization (Fig. 5). The expected product for UGT1A5 was identified in all four donors; however, expression levels varied widely along the length of the GI tract and between donors. Mucosa from some segments contained no measurable UGT1A5 mRNA, whereas others contained relatively high levels of mRNA for this isoform (Fig. 5).
|
); therefore, we examined its suitability as a substrate for recombinant UGT1A5. The results indicated that 1-HP was a much better substrate for UGT1A5 than any of the other substrates reported thus far. Glucuronidation of 1-HP by recombinant UGT1A5 was approximately 100-fold higher than its activity toward either 4-MU or scopoletin (Table 2).
The Chimeric UGTs 1A4/5 and 1A5/4. At the level of amino acid sequence, UGT1A5 is highly homologous to UGT1A4 (and UGT1A3) (Fig. 1). Because of this similarity and the efficiency of both UGT1A4 and 1A3 in N-glucuronidation of 4-ABP (Green et al., 1998), it was anticipated that UGT1A5 would also catalyze this activity. The results, however, showed that recombinant UGT1A5 did not glucuronidate 4-ABP (Table 2). Consequently, two chimeric enzymes, UGT1A4/5 and UGT1A5/4, were prepared, taking advantage of a suitably located internal XbaI restriction site, and expressed in baculovirus-infected insect cells. The activities of the chimeric enzymes were determined, and the results were somewhat surprising (Table 2). UGT1A4/5, like UGT1A5, did not glucuronidate 4-ABP, whereas UGT1A5/4 did exhibit low levels of activity toward this substrate. Although the rate of 4-ABP glucuronidation by UGT1A5/4 was very low in comparison with UGT1A4 (Table 2), it is significant that this activity was detectable in only UGT1A5/4 but not in UGT1A5 or UGT1A4/5.
|
Discussion |
|---|
|
TopAbstractMaterials and MethodsResultsDiscussionReferences |
|---|
). Nonetheless, we have investigated its expression in induced Caco-2 cells, because it seemed feasible that this gene, like several other xenobiotic metabolizing enzymes, would be induced by certain treatments. Once the cDNA for UGT1A5 had been detected in induced Caco-2 cells, we have examined the expression of this gene in several different tissues and cultured cell systems. The detection of UGT1A5 mRNA in human hepatocytes and HepG2 cells (Figs. 2, 3, 4) indicated that its expression was not restricted to induced Caco-2 cells. Moreover, the effects of 3-MC and Rif on the expression level in hepatocytes (Fig. 4) suggest that UGT1A5 expression is regulated, at least in part, through PXR.
The RT-PCR experiments with intestinal segments from four donors (Fig. 5) yielded two interesting results. The first is the clear demonstration that this gene is expressed in the human intestine. The second result is that, as has been shown for UGT protein expression and enzymatic activity (Radominska-Pandya et al., 1998; Little et al., 1999; Czernik et al., 2000), there is an extensive interindividual variation in the expression level of UGT1A5 among donors and along the length of the intestine (Fig. 5). For example, in donors 1 and 2, the level of UGT1A5 mRNA in the duodenum was very close to or even below the detection limit, whereas in donors 3 and 4, it was clearly detectable in this intestinal segment. These findings might partly explain why, in some previous studies, no expression of UGT1A5 in the duodenum was detected (Strassburg et al., 2000), whereas in another case, it seemed to be expressed (see Fig. 7 of Tukey and Strassburg, 2001). It may be added here that a very recent abstract has described the identification of UGT1A5 mRNA in small intestine and colon of a transgenic mice that express the human UGT1A locus (Buser et al., 2005).
Having demonstrated that UGT1A5 is expressed in certain human tissues and cell cultures, we have investigated the physiological significance of this expression by examining the activity of the recombinant protein. UGT1A5 has been reported previously to glucuronidate SN-38 at a very low rate (Ciotti et al., 1999). However, unlike results with all other UGT1A isoforms, we found no report of high glucuronidation activity of UGT1A5 toward any substrate. This corresponded to the results of the initial activity assays in our laboratory. Using sensitive high-performance liquid chromatography methods and using 4-MU and scopoletin, substrates that can be glucuronidated by many human UGTs, we have shown that recombinant UGT1A5 could glucuronidate these substrates, although at very low levels, in the range of 1 pmol/min/mg membrane protein (Table 2). However, the activity rate was approximately 100 times higher when the recombinant UGT1A5 was assayed for 1-HP glucuronidation (Table 2). The latter results with 1-HP, a compound that was recently shown to be a very good substrate for other UGT1A isoforms (Luukkanen et al., 2005), have demonstrated that UGT1A5 is a fully functional enzyme (Table 2).
It has been reported previously that the morphine binding site of UGT2B7 is within the N-terminal 120 residues and that amino acids 96 to 101 are probably directly involved in the binding (Coffman et al., 2003). Inspection of the alignment of UGT1A4 and UGT1A5 (Fig. 1) indicates that the few differences in amino acids between them are concentrated within the first 120 residues. Therefore, it was possible that replacing the N-terminal region of UGT1A5 with the equivalent segment from UGT1A4 would yield a chimeric enzyme with activity toward 4-ABP, an activity that the recombinant UGT1A5 failed to catalyze (Table 2). The presence of an internal XbaI restriction site at a suitable location in both UGT1A4 and 1A5 (Fig. 1) prompted the selection of UGT1A4 rather than UGT1A3 for the first round of chimera construction as well as the position in which to exchange the segments between them. It was anticipated that UGT1A4/5, the hybrid containing residues 1 to 110 from 1A4, would be more active in 4-ABP glucuronidation than UGT1A5. However, the results showed that only UGT1A5/4, the hybrid that carried residues 1 to 110 from UGT1A5 exhibited any 4-ABP glucuronidation activity (Table 2). Nevertheless, because the activity of UGT1A5/4 toward 4-ABP was very low, it may be premature to conclude from these results that residues 29 to 110 (the first 28 residues at the N-terminal are a signal sequence) do not participate in substrate binding. Further experiments to determine substrate binding directly are needed to answer this question, an undertaking that is beyond the scope of this study. In summary, the results of this work show that UGT1A5 is a functional enzyme that is expressed at relatively low levels and high interindividual variability in human liver and intestine.
|
Acknowledgements |
|---|
|
Footnotes |
|---|
ABBREVIATIONS: UGT, UDP-glucuronosyltransferase; HMM, hepatocyte maintenance medium; Dex, dexamethasone; Rif, rifampicin; 3-MC, 3-methylcholanthrene; RT-PCR, reverse transcription-polymerase chain reaction; GAPDH, glyceraldehyde-3-phosphate dehydrogenase; PCR, polymerase chain reaction; PXR, pregnane X receptor; 4-MU, 4-methylumbelliferone; 4-ABP, 4-aminobiphenyl; 1-HP, 1-hydroxypyrene; GI, gastrointestinal.
Address correspondence to: Dr. Moshe Finel, Viikki DDTC, Faculty of Pharmacy, University of Helsinki, P.O. Box 56 (Viikinkaari 5E), 00014 University of Helsinki, Finland. E-mail: moshe.finel{at}helsinki.fi
|
References |
|---|
|
TopAbstractMaterials and MethodsResultsDiscussionReferences |
|---|
Basu NK, Ciotti M, Hwang MS, Kole L, Mitra PS, Cho JW, and Owens IS (2004) Differential and special properties of the major human UGT1-encoded gastrointestinal UDP-glucuronosyltransferases enhance potential to control chemical uptake. J Biol Chem 279: 1429–1441.
Bock KW and Kohle C (2004) Coordinate regulation of drug metabolism by xenobiotic nuclear receptors: UGTs acting together with CYPs and glucuronide transporters. Drug Metab Rev 36: 595–615.[CrossRef][Medline]
Buser K, Beaton D, Tukey RH, and Nguyen N (2005) Identification of human UGT1A5 in transgenic mice that express the UGT1A locus. FASEB J 19: A1109.
Ciotti M, Basu N, Brangi M, and Owens IS (1999) Glucuronidation of 7-ethyl-10-hydroxycamptothecin (SN-38) by the human UDP-glucuronosyltransferases encoded at the UGT1 locus. Biochem Biophys Res Commun 260: 199–202.[CrossRef][Medline]
Coffman BL, Kearney WR, Green MD, Lowery RG, and Tephly TR (2001) Analysis of opioid binding to UDP-glucuronosyltransferase 2B7 fusion proteins using nuclear magnetic resonance spectroscopy. Mol Pharmacol 59: 1464–1469.
Coffman BL, Kearney WR, Goldsmith S, Knosp BM, and Tephly TR (2003) Opioids bind to the amino acids 84 to 118 of UDP-glucuronosyltransferase UGT2B7. Mol Pharmacol 63: 283–288.
Czernik PJ, Little JM, Barone GW, Raufman J-P, and Radominska-Pandya A (2000) Glucuronidation of estrogens and retinoic acid and expression of UDP-glucuronosyltransferase 2B7 in human intestinal mucosa. Drug Metab Dispos 28: 1210–1216.
Gardner-Stephen D, Heydel JM, Goyal A, Lu Y, Xie W, Lindblom T, Mackenzie P, and Radominska-Pandya A (2004) Human PXR variants and their differential effects on the regulation of human UDP-glucuronosyltransferase gene expression. Drug Metab Dispos 32: 340–347.
Green MD, King CD, Mojarrabi B, Mackenzie PI, and Tephly TR (1998) Glucuronidation of amines and other xenobiotics catalyzed by expressed human UDP-glucuronosyltransferase 1A3. Drug Metab Dispos 26: 507–512.
Gregory PA, Lewinsky RH, Gardner-Stephen DA, and Mackenzie PI (2004) Regulation of UDP glucuronosyltransferases in the gastrointestinal tract. Toxicol Appl Pharmacol 199: 354–363.[CrossRef][Medline]
Kurkela M, Garcia-Horsman JA, Luukkanen L, Morsky S, Taskinen J, Baumann M, Kostiainen R, Hirvonen J, and Finel M (2003) Expression and characterization of recombinant human UDP-glucuronosyltransferases (UGTs). UGT1A9 is more resistant to detergent inhibition than other UGTs and was purified as an active dimeric enzyme. J Biol Chem 278: 3536–3544.
Little JM, Lester R, Kuipers F, Vonk R, Mackenzie PI, Drake RR, Frame L, and Radominska-Pandya A (1999) Variability of human hepatic UDP-glucuronosyltransferase activity. Acta Biochim Pol 46: 351–363.[Medline]
Luukkanen L, Taskinen J, Kurkela M, Kostiainen R, Hirvonen J, and Finel M (2005) Kinetic characterization of the 1A subfamily of recombinant human UDP-glucuronosyltransferases. Drug Metab Dispos 33: 1017–1026.
Mackenzie PI, Owens IS, Burchell B, Bock KW, Bairoch A, Belanger A, Fournel-Gigleux S, Green M, Hum DW, Iyanagi T, et al. (1997) The UDP glycosyltransferase gene superfamily: recommended nomenclature update based on evolutionary divergence. Pharmacogenetics 7: 255–269.[Medline]
Mackenzie PI, Gregory PA, Gardner-Stephen DA, Lewinsky RH, Jorgensen BR, Nishiyama T, Xie W, and Radominska-Pandya A (2003) Regulation of UDP glucuronosyltransferase genes. Curr Drug Metab 4: 249–257.[CrossRef][Medline]
Ouzzine M, Barre L, Netter P, Magdalou J, and Fournel-Gigleux S (2003) The human UDP-glucuronosyltransferases: structural aspects and drug glucuronidation. Drug Metab Rev 35: 287–303.[CrossRef][Medline]
Radominska-Pandya A, Little JM, Pandya JT, Tephly TR, King CD, Barone GW, and Raufman J-P (1998) UDP-Glucuronosyltransferases in human intestinal mucosa. Biochim Biophys Acta 1394: 199–208.[Medline]
Radominska-Pandya A, Czernik PJ, Little JM, Battaglia E, and Mackenzie PI (1999) Structural and functional studies of UDP-glucuronosyltransferases. Drug Metab Rev 31: 817–899.[CrossRef][Medline]
Ritter JK, Chen F, Sheen YY, Tran HM, Kimura S, Yeatman MT, and Owens IS (1992) A novel complex locus UGT1 encodes human bilirubin, phenol and other UDP-glucuronosyltransferase isozymes with identical carboxyl termini. J Biol Chem 267: 3257–3261.
Strassburg CP, Oldhafer K, Manns MP, and Tukey RH (1997) Differential expression of the UGT1A locus in human liver, biliary and gastric tissue: identification of UGT1A7 and UGT1A10 transcripts in extrahepatic tissue. Mol Pharmacol 52: 212–220.
Strassburg CP, Kneip S, Topp J, Obermayer-Straub P, Barut A, Tukey RH, and Manns MP (2000) Polymorphic gene regulation and interindividual variation of UDP-glucuronosyltransferase activity in human small intestine. J Biol Chem 275: 36164–36171.
Tukey RH and Strassburg CP (2001) Genetic multiplicity of the human UDP-glucuronosyltransferases and regulation in the gastrointestinal tract. Mol Pharmacol 59: 405–414.
Wells PG, Mackenzie PI, Chowdhury JR, Guillemette C, Gregory PA, Ishii Y, Hansen AJ, Kessler FK, Kim PM, Chowdhury NR, et al. (2004) Glucuronidation and the UDP-glucuronosyltransferases in health and disease. Drug Metab Dispos 32: 281–290.
This article has been cited by other articles:
|
|
 |
|
  H. Yamanaka, M. Nakajima, M. Katoh, and T. Yokoi Glucuronidation of Thyroxine in Human Liver, Jejunum, and Kidney Microsomes Drug Metab. Dispos., September 1, 2007; 35(9): 1642 - 1648. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 S. Kaivosaari, P. Toivonen, L. M. Hesse, M. Koskinen, M. H. Court, and M. Finel Nicotine Glucuronidation and the Human UDP-Glucuronosyltransferase UGT2B10 Mol. Pharmacol., September 1, 2007; 72(3): 761 - 768. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
Z. Wen, M. N. Tallman, S. Y. Ali, and P. C. Smith UDP-Glucuronosyltransferase 1A1 Is the Principal Enzyme Responsible for Etoposide Glucuronidation in Human Liver and Intestinal Microsomes: Structural Characterization of Phenolic and Alcoholic Glucuronides of Etoposide and Estimation of Enzyme Kinetics Drug Metab. Dispos., March 1, 2007; 35(3): 371 - 380. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
D. A. Gardner-Stephen and P. I. Mackenzie Isolation of the UDP-Glucuronosyltransferase 1A3 and 1A4 Proximal Promoters and Characterization of Their Dependence on the Transcription Factor Hepatocyte Nuclear Factor 1{alpha} Drug Metab. Dispos., January 1, 2007; 35(1): 116 - 120. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
T. Sten, S. Qvisen, P. Uutela, L. Luukkanen, R. Kostiainen, and M. Finel Prominent but Reverse Stereoselectivity in Propranolol Glucuronidation by Human UDP-Glucuronosyltransferases 1A9 and 1A10 Drug Metab. Dispos., September 1, 2006; 34(9): 1488 - 1494. [Abstract] [Full Text] [PDF]
|
|
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
 |
 |
 |
|
 |
 |
 |
