The Role of Nuclear Receptors in the Regulation of Bilirubin Conjugation by UDP-glucuronosyltransferase 1A1.

Schoor, L.W.E. van der (Lori) (2014) The Role of Nuclear Receptors in the Regulation of Bilirubin Conjugation by UDP-glucuronosyltransferase 1A1. thesis, Medicine.

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Abstract

Background: Severe unconjugated hyperbilirubinemia is associated with the development of kernicterus, resulting in permanent neurological damage or even death. UGT1A1 is the rate limiting enzyme in bilirubin secretion and plays a pivotal role in the genesis of unconjugated hyperbilirubinemia, as occurs in Crigler Najjar syndrome or neonatal hyperbilirubinemia. The expression level of UGT1A1 is partially determined by the transcriptional activity of the UGT1A1 gene. The transcription of many metabolic genes has shown to be partially modulated by nuclear receptors (NR), which are ligand-activated transcription factors. We aimed to identify NRs that play a role in the regulation of UGT1A1 expression. Methods: A dual luciferase-based promoter activity screen was performed on 2.3kb rat UGT1A1 promoter (rUGT1A1) together with all known NRs (49 members) to identify NRs-rUGT1A1 interactions. In silico analysis was performed to identify the response element of the identified NRs in the rUGT1A1 promoter. The identified response element was mutated by overlap extension PCR followed by dual-luciferase assay to assess the change on NRs-rUGT1A1 interactions. Results: The Glucocorticoid Receptor (GR) and the Progesterone Receptor (PR) were shown to induce rUGT1A1 expression when stimulated with their ligands, dexamethasone (DEX) and progesterone (PRG), respectively. In subsequent experiments, GR with DEX significantly induced rUGT1A1 10-17-fold in CV1 cells, and 26-fold in HepG2 cells. PR with PRG significantly induced rUGT1A1 10-13 fold in CV-1 cells and 10-fold in HepG2 cells. We identified a GR response element at -77/-95 bp from the rUGT1A1 gene. Mutation of this binding site completely abolished both the GR- and PR-mediated rUGT1A1 induction. Conclusion: Our data clearly demonstrate that GR and PR strongly induce rUGT1A1 expression in hepatoctyes by direct binding to the proximal UGT1A1 promoter at -77/-95 bp upstream the transcription starting site. Thus, regulation of GR and PR by their ligands could serve as a potential therapy for hyperbilirubinemia by inducing UGT1A1 expression.

Item Type:	Thesis (Thesis)
Supervisor name:	Jonker, Prof. dr. Johan W. and Weilin Liu
Faculty:	Medical Sciences
Date Deposited:	25 Jun 2020 11:01
Last Modified:	25 Jun 2020 11:01
URI:	https://umcg.studenttheses.ub.rug.nl/id/eprint/2110

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