title: A comprehensive analysis and functional characterization of naturally occurring non-synonymous variants of nuclear receptor PXR.
abstract: Pregnane & Xenobiotic Receptor (PXR) acts as a xenosensing transcriptional regulator of many drug metabolizing enzymes and transporters of the 'detoxification machinery' that coordinate in elimination of xenobiotics and endobiotics from the cellular milieu. It is an accepted view that some individuals or specific populations display considerable differences in their ability to metabolize different drugs, dietary constituents, herbals etc. In this context we speculated that polymorphisms in PXR gene might contribute to variability in cytochrome P450 (CYP450) metabolizing enzymes of phase I, drug metabolizing components of phase II and efflux components of the detoxification machinery. Therefore, in this study, we have undertaken a comprehensive functional analysis of seventeen naturally occurring non-synonymous variants of human PXR. When compared, we observed that some of the PXR SNP variants exhibit distinct functional and dynamic responses on parameters which included transcriptional function, sub-cellular localization, mitotic chromatin binding, DNA-binding properties and other molecular interactions. One of the unique SNP located within the DNA-binding domain of PXR was found to be functionally null and distinct on other parameters. Similarly, some of the non-synonymous SNPs in PXR imparted reduced transactivation function as compared to wild type PXR. Interestingly, PXR is reported to be a mitotic chromatin binding protein and such an association has been correlated to an emerging concept of 'transcription memory' and altered transcription output. In view of the observations made herein our data suggest that some of the natural PXR variants may have adverse physiological consequences owing to its influence on the expression levels and functional output of drug-metabolizing enzymes and transporters. The present study is expected to explain not only the observed inter-individual responses to different drugs but may also highlight the mechanistic details and importance of PXR in drug clearance, drug-drug interactions and diverse metabolic disorders. This article is part of a Special Issue entitled: Xenobiotic nuclear receptors: New Tricks for An Old Dog, edited by Dr. Wen Xie.
authors.affiliation: Special Centre for Molecular Medicine, Jawaharlal Nehru University, New Delhi 110067, India.
authors.forename: Manjul
authors.initials: M
authors.lastname: Rana
authors.affiliation: School of Life-Sciences, Jawaharlal Nehru University, New Delhi 110067, India.
authors.forename: Suneeta
authors.initials: S
authors.lastname: Devi
authors.affiliation: School of Life-Sciences, Jawaharlal Nehru University, New Delhi 110067, India.
authors.forename: Samudrala
authors.initials: S
authors.lastname: Gourinath
authors.affiliation: Department of Endocrinology and Metabolism, All India Institute of Medical Sciences, New Delhi 110029, India.
authors.forename: Ravinder
authors.initials: R
authors.lastname: Goswami
authors.affiliation: Special Centre for Molecular Medicine, Jawaharlal Nehru University, New Delhi 110067, India. Electronic address: rktyagi@yahoo.com.
authors.forename: Rakesh K
authors.initials: RK
authors.lastname: Tyagi
mesh_terms: D000483:Alleles; D019943:Amino Acid Substitution; D000818:Animals; D019556:COS Cells; D002522:Chlorocebus aethiops; D002843:Chromatin / Q000737:chemistry* / Q000378:metabolism; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics* / Q000378:metabolism; D004247:DNA / Q000737:chemistry* / Q000378:metabolism; D005091:Exons; D005786:Gene Expression Regulation; D005787:Gene Frequency; D056945:Hep G2 Cells; D006801:Humans; D008658:Inactivation, Metabolic / Q000235:genetics; D008938:Mitosis; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D020641:Polymorphism, Single Nucleotide; D000077297:Pregnane X Receptor; D011485:Protein Binding; D000072417:Protein Domains; D017433:Protein Structure, Secondary; D011987:Receptors, Steroid / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D040681:Structural Homology, Protein; D013329:Structure-Activity Relationship
chemical_list: D002843:Chromatin; D000077297:Pregnane X Receptor; D011987:Receptors, Steroid; D004247:DNA; D003577:Cytochrome P-450 Enzyme System
keywords: Homology modelling; Mitotic chromatin; Pregnane & Xenobiotic Receptor (PXR); Promoter–reporter assays; SNPs; Site-directed mutagenesis