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J Biol Chem. 1991 Jan 15;266(2):1043-7.

Cloning of two human liver bilirubin UDP-glucuronosyltransferase cDNAs with expression in COS-1 cells.

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Section on Genetic Disorders of Drug Metabolism, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892.


We report the isolation and characterization of two human liver cDNA clones, HUG-Br1 and HUG-Br2; each encodes a UDP-glucuronosyltransferase enzyme which glucuronidates bilirubin IX alpha to form both the IX alpha C8 and IX alpha C12 monoconjugates and a diconjugate. HUG-Br1 cDNA (2351 base pairs) and HUG-Br2 cDNA (2368 base pairs) encode proteins with 533 and 534 amino acid residues, respectively, with a typical membrane-insertion signal peptide, membrane-spanning domain, and 3 or 5 potential asparagine-linked glycosylation sites. At the nucleic acid and deduced amino acid sequence levels the two clones are 82% similar overall, 66% similar in the amino termini, and identical after codon 287, thus encoding proteins with the same carboxyl terminus. The mRNA encoding HUG-Br1 is of high abundance, and the one encoding HUG-Br2 is of low abundance; both are 2.6 kilobases in length. Both messages (2.6 kilobases) were present in the explanted liver of a Type I Crigler-Najjar patient, although the level for that of HUG-Br1 was reduced 4.5-fold. Northern blot analysis of poly(A)+ RNA isolated from the liver of an untreated and a phenobarbital-treated Erythrocebus patas monkey with 5'-specific probes for each clone indicated that the HUG-Br2-encoded message is induced two fold, but that for HUG-Br1 is not. These data indicate that bilirubin is glucuronidated by at least two different proteins, most likely present in very different amounts. These cDNAs which encode functional bilirubin UDP-glucuronosyltransferases will allow the isolation of an appropriate gene to develop a gene therapy model for patients which have the totally deficient trait.

[Indexed for MEDLINE]

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