Immunohistochemical expression of conjugating UGT1A-derived splice proteins in normal and tumoral drug-metabolising tissues in humans

Authors: Bellemare, JudithRouleau, MélanieHarvey, MarioPopa, IonPelletier, Georges-H.Têtu, BernardGuillemette, Chantal
Abstract: Glucuronidation by UDP-glucuronyltransferase (UGT) enzymes is the prevailing conjugative pathway for the metabolism of both xenobiotics and endogenous compounds. Alterations in this pathway, such as those generated by common genetic polymorphisms, have been shown to significantly impact on the health of individuals, influencing cancer susceptibility, responsiveness to drugs and drug-induced toxicity. Alternative usage of terminal exons leads to UGT1A-derived splice variants, namely the classical and enzymatically active isoforms 1 (i1) and the novel enzymatically inactive isoforms 2 (i2). In vitro functional data from heterologous expression and RNA interference experiments indicate that these i2 isoforms act as negative modulators of glucuronidation, likely by forming inactive complexes with active isoform 1. We used specific antibodies against either active i1 or inactive i2 proteins to examine their distribution in major drug-metabolizing tissues. Data revealed that UGT1A_i1 and inactive UGT1A_i2 are co-produced in the same tissue structures, including liver, kidney, stomach, intestine and colon. Examination of the cellular distribution and semi-quantitative level of expression of UGT1As revealed heterogeneous expression of i1 and i2 proteins, with increased expression of i2 in liver tumours and decreased levels of i1 and i2 in colon cancer specimens, compared to normal tissues. These differences in expression may be relevant to human colon and liver cancer tumorigenesis. Our data clearly demonstrate the similar immunolocalization of active and inactive UGT1A isoforms in most UGT1A-expressing cell types of major tissues involved in drug metabolism. These expression patterns are consistent with a dominant-negative function for the i2 encoded by the UGT1A gene.
Document Type: Article de recherche
Issue Date: 29 October 2010
Open Access Date: 1 September 2016
Document version: AM
Permalink: http://hdl.handle.net/20.500.11794/9608
This document was published in: The Journal of pathology, Vol. 223 (3), 425-435 (2011)
http://dx.doi.org/10.1002/path.2805
Wiley
Alternative version: 10.1002/path.2805
21171088
Collection:Articles publiés dans des revues avec comité de lecture

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