TY - JOUR T1 - FUNCTIONAL CHARACTERIZATION OF FOUR NATURALLY OCCURRING VARIANTS OF HUMAN PREGNANE X RECEPTOR (PXR): ONE VARIANT CAUSES DRAMATIC LOSS OF BOTH DNA BINDING ACTIVITY AND THE TRANSACTIVATION OF THE <em>CYP3A4</em> PROMOTER/ENHANCER REGION JF - Drug Metabolism and Disposition JO - Drug Metab Dispos SP - 149 LP - 154 DO - 10.1124/dmd.32.1.149 VL - 32 IS - 1 AU - Satoru Koyano AU - Kouichi Kurose AU - Yoshiro Saito AU - Shogo Ozawa AU - Ryuichi Hasegawa AU - Kazuo Komamura AU - Kazuyuki Ueno AU - Shiro Kamakura AU - Masafumi Kitakaze AU - Toshiharu Nakajima AU - Kenji Matsumoto AU - Akira Akasawa AU - Hirohisa Saito AU - Jun-Ichi Sawada Y1 - 2004/01/01 UR - http://dmd.aspetjournals.org/content/32/1/149.abstract N2 - Metabolism of administered drugs is determined by expression and activity of many drug-metabolizing enzymes, such as the cytochrome P450 (P450s) family members. Pregnane X receptor (PXR) is a master transcriptional regulator of many drug/xenobiotic-metabolizing enzymes, including P450s and drug transporters. In this study, we describe the functional analysis of four naturally occurring human PXR (hPXR) variants (R98C, R148Q, R381W, and I403V) that we have recently identified. By a reporter gene assay using the CYP3A4 promoter/enhancer reporter in COS-7 or HepG2 cells, it was found that the R98C variant failed to transactivate the CYP3A4 reporter. The R381W and I403V variants also showed varying degrees of reduction in transactivation, depending on the dose of PXR activators, rifampicin, clotrimazole, and paclitaxel. The transcriptional activities of the R148Q variant were not significantly different from that of the wild-type hPXR. The electrophoretic mobility shift assay revealed that only the R98C variant lacked DNA binding. Furthermore, the cellular localization of the hPXR proteins was analyzed. All four variants as well as the wild-type hPXR localized exclusively to the nucleus, regardless of the presence or absence of rifampicin. These data suggest that the R98C, R381W, and I403V hPXR variants, especially R98C, may influence the expression of drug-metabolizing enzymes and transporters, which are transactivated by PXR. The American Society for Pharmacology and Experimental Therapeutics ER -