Glucuronidation of the Dietary Fatty Acids, Phytanic Acid and Docosahexaenoic Acid, by Human UDP-Glucuronosyltransferases

Little, Joanna M.; Williams, Lisa L.; Xu, Jing; Radominska‐Pandya, Anna

doi:10.1124/dmd.30.5.531

Cited by 28 publications

(18 citation statements)

References 23 publications

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“…Depending on the substrate, variations in UGT activity of 6-to 15-fold in liver microsomes and 10-to 100-fold in intestinal microsomes have been found. Similar variations in UGT protein content have been demonstrated by Western blot in liver and intestinal microsomes (Burchell and Coughtrie, 1997;Little et al, 1999Little et al, , 2002Strassburg et al, 1999;Court et al, 2001;Antonio et al, 2003). A similar degree of variability in hepatic UGT mRNA levels has also been reported (Congiu et al, 2002).…”

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confidence: 51%

Human PXR Variants and Their Differential Effects on the Regulation of Human Udp-Glucuronosyltransferase Gene Expression

et al. 2004

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This article is available online at http://dmd.aspetjournals.org ABSTRACT:The pregnane X receptor (PXR) has three known major transcript variants resulting from alternative splicing. The less well characterized variants T2 and T3 are identical to the well described variant T1 except for a 39-amino acid N-terminal extension in T2 and an internal 37-amino acid deletion in T3. We have developed reverse transcription-polymerase chain reaction (RT-PCR) methods to detect and quantify each human PXR (hPXR) in human liver and intestinal tissues and HepG2 and Caco-2 cell lines. All three isoforms were expressed in hepatic cells, whereas only T1 transcripts were found in Caco-2 cells. In general, most normal human liver and intestinal mucosa contained all three hPXR variants, but considerable interindividual variation in expression levels was found. The effect of each hPXR variant on expression of UDPglucuronosyltransferase (UGT) UGT1A and UGT2B family isoforms was investigated in transiently transfected HepG2 and Caco-2 cells. As a family, UGT1A transcripts were up-regulated by T1 and T2 but not T3. Isoform-specific RT-PCR revealed that UGT1A1, 1A3, and 1A4 were the major isoforms induced in both cell lines. The levels of several UGT1A isoforms were also examined in human liver samples from a number of donors with characterized PXR expression. The data suggest that individual variation in PXR expression may account for differential expression of some UGT isoforms between subjects.

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confidence: 51%

Human PXR Variants and Their Differential Effects on the Regulation of Human Udp-Glucuronosyltransferase Gene Expression

et al. 2004

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“…Glucuronides present on silica gel were identified by autoradiography of the TLC plates for 3-5 days at −80 °C. Silica gel containing labeled glucuronides or in corresponding areas in control lanes was transferred to scintillation vials, and radioactivity was quantified by liquid scintillation counting (Packard TRI-CARB 2100TR, Perkin-Elmer) as previously described [33]. The position of glucuronidation (i.e., which hydroxyl group was glucuronidated) was not determined.…”

Section: Glucuronidation Activity Assaysmentioning

confidence: 99%

Identification of UDP-glucuronosyltransferase 1A10 in non-malignant and malignant human breast tissues

2008

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UGT1A10 was recently identified as the major isoform that conjugates estrogens. In this study, realtime PCR revealed high levels of UGT1A10 and UGT2B7 in human breast tissues. The expression of UGT1A10 in breast was a novel finding. UGT1A10 and UGT2B7 mRNAs were differentially expressed among normal and malignant specimens. Their overall expression was significantly decreased in breast carcinomas as compared to normal breast specimens (UGT1A10: 68 ± 26 vs. 252 ± 86, respectively; p < 0.05) and (UGT2B7: 1.4 ± 0.7 vs. 12 ± 4, respectively; p < 0.05). Interestingly, in African American women, UGT1A10 expression was significantly decreased in breast carcinomas in comparison to normals (57 ± 35 vs. 397 ± 152, respectively; p < 0.05). Among Caucasian women, UGT2B7 was significantly decreased in breast carcinomas in comparison to normals (1.1 ± 0.5 vs. 13.5 ± 6, respectively; p < 0.05). Glucuronidation of 4-OHE 1 was significantly reduced in breast carcinomas compared to normals (30 ± 15 vs. 106 ± 31, respectively; p < 0.05). Differential downregulation of UGT1A10 and UGT2B7 mRNA, protein, and activity in breast carcinomas compared to the adjacent normal breast specimens from the same donor were also found. These data illustrate the novel finding of UGT1A10 in human breast and confirm the expression of UGT2B7. Significant individual variation and down-regulation of expression in breast carcinomas of both isoforms was also demonstrated. These findings provide evidence that decreased UGT expression and activity could result in the promotion of carcinogenesis.

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“…Glucuronides present on silica gel were identified by autoradiography of the TLC plates for 3-5 days at −80 ºC. Silica gel containing labeled glucuronides or in corresponding areas in control lanes was transferred to scintillation vials, and radioactivity was quantified by liquid scintillation counting (Packard TRI-CARB 2100TR, Perkin-Elmer) as previously described [26].…”

Section: Activity Assaysmentioning

confidence: 99%

Phenylalanine90 and phenylalanine93 are crucial amino acids within the estrogen binding site of the human UDP-glucuronosyltransferase 1A10

et al. 2007

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Human UDP-glucuronosyltransferase 1A10 has been identified as the major isoform involved in the biotransformation of a wide range of phenolic substrates, including native estrogens and their oxidized metabolites. Our recent studies point to the F 90 -M 91 -V 92 -F 93 amino acid motif of UGT1A10, which was identified using photoaffinity labeling followed by LC-MS/MS analysis, as a key determinant of the binding of phenolic substrates. In this report, we have evaluated the role of F 90 , V 92 , and F 93 in the recognition of estrogens by UGT1A10 using site-directed mutagenesis. Kinetic studies using 5 mutants revealed that F 90 and F 93 are critical residues for the recognition of all estrogen substrates. The substitution of F 90 with alanine totally abolished the activity of this enzyme toward all the estrogens investigated. Overall, sequential removal for the aromatic (FtoL) and of the hydrophobic chain (FtoA and VtoA) from amino acids 90, 92, and 93 position effectively alters estrogen recognition. This demonstrates that individual features of the native and hydroxylated estrogens determine the specific binding properties of the compound within the binding site of the human UGT1A10 and the mutants. The resulting activities are completely abolished, unchanged, increased or decreased depending on the structures of both the mutant and the substrate. The novel identification of UGT1A10 as the major isoform involved in the glucuronidation of all estrogens and the discovery of the importance of the FMVF motif in the binding of steroids will help to elucidate the molecular mechanism of glucuronidation, resulting in the design of more effective estrogen-based therapies.

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Glucuronidation of the Dietary Fatty Acids, Phytanic Acid and Docosahexaenoic Acid, by Human UDP-Glucuronosyltransferases

Cited by 28 publications

References 23 publications

Human PXR Variants and Their Differential Effects on the Regulation of Human Udp-Glucuronosyltransferase Gene Expression

Human PXR Variants and Their Differential Effects on the Regulation of Human Udp-Glucuronosyltransferase Gene Expression

Identification of UDP-glucuronosyltransferase 1A10 in non-malignant and malignant human breast tissues

Phenylalanine90 and phenylalanine93 are crucial amino acids within the estrogen binding site of the human UDP-glucuronosyltransferase 1A10

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