title: Development of humanized steroid and xenobiotic receptor mouse by homologous knock-in of the human steroid and xenobiotic receptor ligand binding domain sequence.
abstract: The human steroid and xenobiotic receptor (SXR), (also known as pregnane X receptor PXR, and NR1I2) is a low affinity sensor that responds to a variety of endobiotic, nutritional and xenobiotic ligands. SXR activates transcription of Cytochrome P450, family 3, subfamily A (CYP3A) and other important metabolic enzymes to up-regulate catabolic pathways mediating xenobiotic elimination. One key feature that demarcates SXR from other nuclear receptors is that the human and rodent orthologues exhibit different ligand preference for a subset of toxicologically important chemicals. This difference leads to a profound problem for rodent studies to predict toxicity in humans. The objective of this study is to generate a new humanized mouse line, which responds systemically to human-specific ligands in order to better predict systemic toxicity in humans. For this purpose, the ligand binding domain (LBD) of the human SXR was homologously knocked-in to the murine gene replacing the endogenous LBD. The LBD-humanized chimeric gene was expressed in all ten organs examined, including liver, small intestine, stomach, kidney and lung in a pattern similar to the endogenous gene expressed in the wild-type (WT) mouse. Quantitative reverse transcription-polymerase chain reaction (RT-PCR) analysis showed that the human-selective ligand, rifampicin induced Cyp3a11 and Carboxylesterase 6 (Ces6) mRNA expression in liver and intestine, whereas the murine-selective ligand, pregnenolone-16-carbonitrile did not. This new humanized mouse line should provide a useful tool for assessing whole body toxicity, whether acute, chronic or developmental, induced by human selective ligands themselves and subsequently generated metabolites that can trigger further toxic responses mediated secondarily by other receptors distributed body-wide.
authors.affiliation: Division of Cellular and Molecular Toxicology, Biological Safety Research Center, National Institute of Health Sciences, Tokyo, Japan.
authors.forename: Katsuhide
authors.initials: K
authors.lastname: Igarashi
authors.forename: Satoshi
authors.initials: S
authors.lastname: Kitajima
authors.forename: Ken-ichi
authors.initials: K
authors.lastname: Aisaki
authors.forename: Kentaro
authors.initials: K
authors.lastname: Tanemura
authors.forename: Yuhji
authors.initials: Y
authors.lastname: Taquahashi
authors.forename: Noriko
authors.initials: N
authors.lastname: Moriyama
authors.forename: Eriko
authors.initials: E
authors.lastname: Ikeno
authors.forename: Nae
authors.initials: N
authors.lastname: Matsuda
authors.forename: Yumiko
authors.initials: Y
authors.lastname: Saga
authors.forename: Bruce
authors.initials: B
authors.lastname: Blumberg
authors.forename: Jun
authors.initials: J
authors.lastname: Kanno
mesh_terms: D000818:Animals; D030801:Animals, Genetically Modified / Q000235:genetics*; D002265:Carboxylic Ester Hydrolases / Q000235:genetics; D051544:Cytochrome P-450 CYP3A / Q000235:genetics; D005260:Female; D006801:Humans; D007421:Intestine, Small / Q000378:metabolism; D008024:Ligands; D008099:Liver / Q000378:metabolism; D008297:Male; D008565:Membrane Proteins / Q000235:genetics; D051379:Mice / Q000235:genetics*; D008813:Mice, Inbred ICR; D000077297:Pregnane X Receptor; D011285:Pregnenolone Carbonitrile / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D011987:Receptors, Steroid / Q000235:genetics* / Q000378:metabolism; D012293:Rifampin / Q000378:metabolism
chemical_list: D008024:Ligands; D008565:Membrane Proteins; C000625852:NR1I2 protein, human; C000625853:Nr1i2 protein, mouse; D000077297:Pregnane X Receptor; D012333:RNA, Messenger; D011987:Receptors, Steroid; D011285:Pregnenolone Carbonitrile; C496508:Cyp3a11 protein, mouse; D051544:Cytochrome P-450 CYP3A; D002265:Carboxylic Ester Hydrolases; D012293:Rifampin