GLUCURONIDATION OF HYODEOXYCHOLIC ACID IN HUMAN LIVER - EVIDENCE FOR A SELECTIVE ROLE OF UDP-GLUCURONOSYLTRANSFERASE-2B4

Citation
T. Pillot et al., GLUCURONIDATION OF HYODEOXYCHOLIC ACID IN HUMAN LIVER - EVIDENCE FOR A SELECTIVE ROLE OF UDP-GLUCURONOSYLTRANSFERASE-2B4, The Journal of biological chemistry, 268(34), 1993, pp. 25636-25642
Citations number
43
Categorie Soggetti
Biology
ISSN journal
00219258
Volume
268
Issue
34
Year of publication
1993
Pages
25636 - 25642
Database
ISI
SICI code
0021-9258(1993)268:34<25636:GOHAIH>2.0.ZU;2-2
Abstract
Monospecific polyclonal antibodies were raised against a variable amin o-terminal domain (amino acids 14-150) of a human liver form of UDP-gl ucuronosyltransferase conjugating bile acids, UGT2B4 (Jackson, M. R., McCarthy, L. R., Harding, D., Wilson, S., Coughtrie, M. W., and Burche ll, B. (1987) Biochem. J. 242, 581-588), expressed as a fusion protein in Escherichia coli. The antibodies were able to recognize the protei n, stably expressed in a genetically engineered eukaryotic V79 cell li ne, against which they were directed. The specificity of these antibod ies allowed their use for analyzing the substrate specificity of this isoform in human liver, as well as for determining its contribution to the total hepatic and extra-hepatic glucuronidation of hyodeoxycholic acid. Western blot analysis of microsomal proteins demonstrated the p resence of UGT2B4 exclusively in human liver and not in human kidney. In human liver microsomes, the antibodies were able to inhibit and pre cipitate up to 90% of the total hyodeoxycholic acid 6-O-glucuronidatio n activity, but had no effect on activities toward several other subst rates, such as phenols, bilirubin, or other bile acids, especially hyo cholic acid and the steroids 4-hydroxyestrone and estriol. Moreover, W estern blot analysis and immunoinhibition studies of human liver micro somes from healthy patients and from patients presenting liver disease s revealed a good correlation between the glucuronidation rate of hyod eoxycholic acid and the UGT2B4 expression level. The absence of immuno inhibition of hyodeoxycholic acid conjugation with UDP sugars other th an UDP-glucuronic acid suggests the involvement of different enzymatic systems in the glucosidation and xylosylation of hyodeoxycholic acid. Altogether, the results provided strong evidence for the specific and predominant involvement of UGT2B4 in the 6-O-glucuronidation of this bile acid via a UDP-glucuronic acid-dependent mechanism.