Abstract:
The pregnane X receptor (PXR) plays a crucial role in drug metabolism. It acts as the major transcriptional regulator of cytochrome P-450 monooxygenase 3A4, which metabolizes 60% of all drugs. Recent pharmacodynamic studies have shown that the mouse is an inappropriate model for human clinical drug studies. Therefore, we characterized the swine PXR gene as an alternate model. Gene-specific BACs were isolated from the porcine CHORI 242 library using an in silicone cloning strategy, and primers were designed to identify PXR exons 2 to 9. Amplified BAC-derived products were then sequenced. The genomic sequence from exon 2 to 9 was determined using sequential primer analysis and cloning. A complete swine mRNA sequence was obtained using 3’ and 5’ RACE with extracted liver and brain mRNA. The swine protein showed 83% identity and 87% similarity with the human PXR protein. Like the human, the swine PXR gene contained a number of predicted splicing variants. Thus, swine liver and brain tissues were then analyzed and two unique splicing variants were detected. One spliced out exon 6 and the second variant completely excised both Exon 6 and 7. Northern blot analysis indicated that PXR was expressed in tissues including the liver, small intestine, heart, kidney, and colon. In addition, a group of pigs representing eight breeds were analyzed for SNPs to permit comparison between human and porcine variants. This characterization of the swine PXR gene will contribute to the development of a swine metabolic medical model.