Cell Signaling, PXR Phosphorylation & Drug Disposition

描述（由申请人提供）：在哺乳动物中，药物处置是一个高度监管的过程。例如，编码药物转运和药物代谢蛋白的基因的表达是由它们在肝脏和肠道中的底物诱导的。最近的研究对这一现象的分子机制有了新的认识。妊娠X受体（PXR）是一种配体激活的转录因子，在肝脏和肠道中表达。PXR协调调节肝脏和肠道中药物诱导的药物转运和药物代谢蛋白的表达。PXR与靶基因启动子中的异种反应元件（XREs）结合，与9-顺式维甲酸受体（RXR）形成异源二聚体。一个极其重要的pxr靶基因是细胞色素P450 3A4 （CYP3A4）基因。CYP3A4主要表达于肝脏和肠道，催化近60%临床处方药物的氧化代谢。肝脏中CYP3A4和其他pxr靶基因的表达在炎症细胞因子的作用下被迅速抑制，尽管这种抑制的分子基础目前尚不清楚。pxr靶基因表达的抑制发生在接受有创手术以应对炎症的人群中，从而使这些患者药物的药代动力学特性发生改变。PXR被大量结构多样的分子激活，包括药物、类固醇、胆汁酸和异种生物。因此，抑制pxr靶基因表达可能会产生潜在的危及生命的药物-药物相互作用。因此，了解pxr靶基因抑制的分子基础对于预测和预防术后患者药物相互作用的发生具有重要意义。转录调节蛋白磷酸化状态的改变可能是介导炎症后pxr靶基因表达抑制的机制。这些研究的目的是：(1)确定特定细胞信号通路激活后PXR磷酸化的位点，(2)确定PXR磷酸化增加对其(a)反激活，(b)结合DNA， (c)从细胞质转运到细胞核以及(d)与蛋白质辅助因子相互作用的能力的影响。这些研究的成功完成将使我们能够确定炎症反应过程中关键药物代谢基因抑制的分子基础，并为了解外源反应提供更多机会。这些研究将为药物处置和药物-药物相互作用的调节提供额外的见解。

DESCRIPTION (PROVIDED BY APPLICANT): Drug disposition is a highly regulated process in mammals. For example, the expression of genes encoding drug-transporting and drug-metabolizing proteins is induced by their substrates in liver and intestine. Recent research has shed new light on the molecular mechanism of this phenomenon. The pregnane X receptor (PXR) is a ligand-activated transcription factor that is expressed in liver and intestine. PXR coordinately regulates the drug-inducible expression of drug-transporting and drug-metabolizing proteins in liver and intestine. PXR binds to xenobiotic-response elements (XREs) in the promoters of its target genes as a heterodimer with the 9-cis-retinoic acid receptor (RXR). One extremely important PXR-target gene is the cytochrome P450 3A4 (CYP3A4) gene. CYP3A4 is primarily expressed in liver and intestine where it catalyzes the oxidative metabolism of nearly 60% of all clinically prescribed drugs. The hepatic expression of CYP3A4 and other PXR-target genes is rapidly suppressed in response to inflammatory cytokines, though the molecular basis of this repression is currently unknown. Repression of PXR-target gene expression occurs in people that undergo invasive surgery in response to inflammation, thereby producing altered pharmacokinetic properties of drugs in these patients. PXR is activated by a plethora of structurally diverse molecules including drugs, steroids, bile acids, and xenobiotics. Therefore, repression of PXR-target gene expression can produce potentially life-threatening drug-drug interactions. Thus, it is important to understand the molecular basis of the repression of PXR-target genes in order to predict and prevent the occurrence of drug interactions in post-operative patients. An alteration in the phosphorylation status of transcriptional regulatory proteins is a likely mechanism that mediates the repression of PXR-target gene expression following inflammation. The goals of these investigations are to (1) identify the sites of PXR phosphorylation following activation of specific cell signaling pathways, and (2) determine the effect of increased PXR phosphorylation on it's ability to (a) transactivate, (b) bind DNA, (c) translocate from the cytoplasm to the nucleus, and (d) interact with protein co-factors. Successful completion of these studies will allow us to determine the molecular basis of the repression of key drug metabolizing genes during the inflammatory response and provide increased opportunities to understand the xenobiotic response. These studies will provide additional insight into the regulation of drug disposition and drug-drug interaction.