The phenobarbital response enhancer module in the human bilirubin UDP-glucuronosyltransferase UGT1A1 gene and regulation by the nuclear receptor CAR

Junko Sugatani, Hiroyuki Kojima, Akiko Ueda, Satoru Kakizaki, Kouichi Yoshinari, Qi Hui Gong, Ida S. Owens, Masahiko Negishi, Tatsuya Sueyoshi

Research output: Contribution to journalArticlepeer-review

320 Citations (Scopus)

Abstract

The UDP-glucuronosyltransferase, UGT1A1, is the critical enzyme responsible for detoxification of the potentially neurotoxic bilirubin by conjugating it with glucuronic acid. For decades, phenobarbital (PB) treatment for hyperbilirubinemia has been known to increase expression of the UGT1A1 gene in liver. We have now delineated the PB response activity to a 290-bp distal enhancer sequence (-3483/-3194) of the UGT1A1 gene. The enhancer contains 3 putative nuclear receptor motifs, and it was activated by the nuclear orphan receptor, human constitutive active receptor (hCAR), in cotransfected HepG2 cells. Bacterially expressed hCAR, acting as a heterodimer with in vitro-translated retinoid X receptor (RXRα), only bound to 1 of the 3 NR motifs, named gtNR1 in a gel-shift assay. Consistently, mutations of the gtNR1 site significantly decreased the activation by hCAR of the 290-bp DNA in transfection assays. Moreover, the 290-bp DNA was effectively activated in mouse primary hepatocytes in response to PB, offering an excellent clinical test for the examination of the responsiveness of the UGT1A1 to PB in the human population, particularly individuals with hyperbilirubinemia.

Original languageEnglish
Pages (from-to)1232-1238
Number of pages7
JournalHepatology
Volume33
Issue number5
DOIs
Publication statusPublished - 2001 Jan 1

ASJC Scopus subject areas

  • Hepatology

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