Hepatocyte Nuclear Factor-1α Is a Causal Factor Responsible for Interindividual Differences in the Expression of UDP-Glucuronosyltransferase 2B7 mRNA in Human Livers

Abstract

This article is available online at http://dmd.aspetjournals.org ABSTRACT:UDP-glucuronosyltransferase (UGT) 2B7 is one of the most important UGT isozymes expressed in human livers. This enzyme is reported to show more than 10-fold interindividual differences in its enzyme activities. Thus, the amounts of UGT2B7 mRNA in 12 human livers were quantified by quantitative reverse transcriptionpolymerase chain reaction. The amounts of UGT2B7 mRNA in the subjects ranged from 0.22 to 2.63 copies/10 3 copies of ␤-actin. A novel point mutation (؊253G to A) found in this study did not affect the level of UGT2B7 mRNA in the subjects. To clarify a causal factor(s) determining the expression level of UGT2B7 mRNA, we examined the correlation between the amounts of mRNAs for UGT2B7 and hepatocyte nuclear factor (HNF)-1␣, which regulates the expression of UGT2B7 gene. HNF-1␣ mRNA was expressed at a level ranging from 2.99 to 24.76 copies/10 6 copies of ␤-actin in the subjects. The amounts of mRNAs for UGT2B7 expressed in these individual liver samples were highly associated with the amount of mRNA for HNF-1␣ (r ‫؍‬ 0.786, p ‫؍‬ 0.002), suggesting that HNF-1␣ is a factor limiting the expression of UGT2B7 mRNA and a causal factor responsible for an interindividual difference in human livers.

Sequence variations in the UDP-glucuronosyltransferase 2B7 (UGT2B7) gene: identification of 10 novel single nucleotide polymorphisms (SNPs) and analysis of their relevance to morphine glucuronidation in cancer patients

“…This implies that factors other than UGT2B7 polymorphism may be more deciding for the variability in morphine metabolite to morphine serum ratios. Interestingly, Toide et al 25 recently presented evidence suggesting that hepatocyte nuclear factor-1 alpha (HNF-1a) may be a limiting factor in hepatic UGT2B7 mRNA expression. Therefore, interindividual variation in HNF-1a expression may contribute to variability in morphine metabolite to morphine serum ratios.…”

Identification of a Novel Polymorphic Enhancer of the HumanCYP3A4Gene

“…A part of hepatic CYP3A4 variation, which cannot be fully explainable by genetic polymorphisms in the CYP3A4 gene itself, may also be attributable to the variation of HNF-1 and/or HNF-4 levels. Recently, we demonstrated that the interindividual variation of hepatic dihydrodiol dehydrogenase 4 and UDP-glucuronosyltransferase 2B7 mRNA levels correlated highly with the variation of HNF-1 plus HNF-4 and HNF-1 mRNA levels, respectively (Toide et al, 2002;Ozeki et al, 2002). Because CLEM4 contained both functional HNF-1 and HNF-4 recognition sites, amounts of these transcription factors may also modulate the CYP3A4 expression level.…”

Quantitation of CYP2B6, Constitutive Androstane Receptor, and Pregnane X Receptor mRNA levels

“…In particular, collection conditions for human tissues tend to be suboptimal. Consequently, it has become standard practice for these types of studies to normalize the data to the mRNA content of a quality control gene such as glyceraldehyde-3-phosphate dehydrogenase, hypoxanthine-guanine phosphoribosyl transferase, TATA box-binding protein, ␤-glucuronidase, ␤-actin, or 18S rRNA (Sumida et al, 1999;Rodriguez-Antona et al, 2001;Koch et al, 2002;Lin et al, 2002;Toide et al, 2002). With this approach the effect of mRNA degradation on the gene of interest should affect the normalization gene to a similar extent thereby substantially reducing associated variability.…”