Isolation and Characterization of the UGT2B28 cDNA Encoding a Novel Human Steroid Conjugating UDP-Glucuronosyltransferase

Abstract

UDP-glucuronosyltransferase (UGT) enzymes belonging to the UGT2B subfamily catalyze the transfer of glucuronic acid to a large number of endogenous compounds, particularly steroids, to facilitate their elimination from target cells. A novel human UGT2B cDNA of 1666 bp was isolated and encodes a 529-amino acid protein named UGT2B28 type I. Glucuronidation assays demonstrated that UGT2B28 type I catalyzes the conjugation of endogenous and exogenous compounds. The tissue distribution of UGT2B28 revealed the expression of the type I transcript in the liver, breast, and LNCaP cells. Two other UGT2B cDNAs were isolated, and sequence analysis led to the identification of two truncated UGT2B28 species. UGT2B28 type II differs from type I by a deletion of 308 bp in the cofactor binding domain, whereas UGT2B28 type III lacks 351 bp in the putative substrate binding domain. All UGT2B28 isoforms are encoded by a single UGT2B28 gene which has a genomic organization similar to that of the other UGT2B genes characterized thus far. Although no substrates could be identified for the shorter isoforms, the three subtypes were shown to be located in the endoplasmic reticulum and the perinuclear membrane, demonstrating that the missing domains are not required for the subcellular localization of these UGT2B proteins. However, all the domains remain necessary for observing glucuronidation activity. The expression of UGT2B28 type I in the breast and liver suggests a role of this enzyme in the androgen and estrogen metabolism in these tissues.

Unravelling the transcriptomic landscape of the major phase II UDP-glucuronosyltransferase drug metabolizing pathway using targeted RNA sequencing

“…However, we cannot exclude that some of the less frequent exon-exon junctions arise from mapping errors. Consistent with findings of previous laborious targeted approaches, 9,10,14,15,18,27,28 all reported alternative UGT exons and transcripts were identified, validating the robustness of our approach. Overall, this study reports nearly 300 transcribed variants encoded by the ten human genes, well beyond the suspected complexity already hinted by previous studies.…”

Identification of molecular apocrine breast tumours by microarray analysis

“…The GO analysis revealed the presence of many genes involved in steroid metabolism in the apocrine group. Some, like HSD17B2 and UGT2B28, are involved in the catabolism of oestrogens and androgens (Wu et al, 1993;Levesque et al, 2001). Increased expression of catabolic as well as synthetic enzymes is a feature of steroid responsive tissues (Labrie et al, 2003).…”

Pharmacogenomics of human UDP-glucuronosyltransferase enzymes

“…Several UGT2Bs were isolated from liver as well from extrahepatic tissues. 76,[81][82][83][84][96][97][98][99][100][101] In addition, numerous homologous pseudogenes have been found, 83 all of which are clustered with UGT2B genes encoding functional proteins on chromosome 4 (4q13). Similar to the UGT1 family, members of the UGT2B subfamily share a high degree of similarity in the C-terminal portion of the protein and the highest degree of divergence in sequences encoded by exons 1.…”

“…128 These results suggest that the UGT1A1 genotype is a predictor of breast density within groups of different menopausal status and would predict that interindividual differences in 101 (e) Polymorphic expression of two truncated UGT2B28 variants (types II and III) has been reported. 99 UGT2B28 type II differs from type I by a deletion of 308 bp in the cofactor-binding domain, whereas UGT2B28 type III lacks 351 bp in the putative substrate-binding domain. (f) An additional cDNA clone isolated from human liver corresponds to the UGT2B4 Phe 109 Leu, Phe 396 Leu allele but appears to be very rare as it was not found in two independent population studies.…”