| The human nuclear pregnane X receptor (PXR) activates cytochrome P450-3A expression in response to a wide variety of xenobiotics and plays a critical role in mediating dangerous drug-drug interactions. The human PXR is related to the mouse Pxr1, which they had cloned and shown to be activated by dexamethasone, pregnenolone 16-alpha-carbonitrile (PCN), and other compounds known to induce expression of the CYP3A1 gene, the predominant form of CYP3A in rat liver and intestine. Northern blot analysis detected most abundant expression in liver, colon, and small intestine; transcripts of 2.6, 4.3, and 5 kb were present in each of these tissues. |
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