Nuclear Receptor Response Elements Mediate Induction of Intestinal MDR1 by Rifampin

Abstract

Intestinal P-glycoprotein, which is encoded by the MDR1 gene, plays an important role in the absorption and presystemic elimination of many xenobiotics. Hence, an understanding of the factors regulating its expression and function is of substantial interest. In addition to genetic factors, exposure to drugs such as rifampin can profoundly affect its expression. So far, the mechanisms by which rifampin induces MDR1 expression are poorly understood. Recent studies demonstrate that the nuclear receptor PXR (pregnane X receptor) is involved in xenobiotic induction of CYP3A4. Because CYP3A4 and MDR1 are often co-induced, we investigated whether a similar mechanism is also involved in MDR1 induction. The human colon carcinoma cell line LS174T was used as an intestinal model to study induction because in these cells the endogenous MDR1 gene is highly inducible by rifampin. The 5-upstream region of human MDR1 was examined for the presence of potential PXR response elements. Several binding sites were identified that form a complex regulatory cluster at about ؊8 kilobase pairs. Only one DR4 motif within this cluster is necessary for induction by rifampin. We conclude that induction of MDR1 is mediated by a DR4 motif in the upstream enhancer at about ؊8 kilobase pairs, to which PXR binds. The MDR11 gene product P-glycoprotein (P-gp) plays an important role in the transport of hydrophobic xenobiotics and peptides from the inside to the outside of cells. Initially discovered in cancer cells as a mechanism responsible for resistance against certain cytostatic drugs (reviewed in Ref. 1), it was later shown that P-gp is also expressed in different nonmalignant cells of various organs. In agreement with its assumed physiologic role as a defense mechanism against potential toxic substances present in the diet and from environmental exposure, it is expressed in the brush border membrane of the mature enterocytes, the canalicular membrane of hepatocytes, the brush border of proximal renal tubular cells, and the luminal side of endothelial cells of brain capillaries (2, 3).In the gut P-gp functions as an efflux pump, actively transporting substances back into the intestinal lumen (4) and, hence, has an important role for the absorption and presystemic elimination of many chemicals including drugs. The level of intestinal P-gp expression shows wide interindividual differences (5) controlled by both genetic and environmental factors. Recently a genetic polymorphism of the MDR1 gene has been reported that affects the P-gp expression in the epithelial cell lining of the small intestine (6). In addition to this genetic polymorphism, environmental factors can affect the expression of P-gp. A number of drugs and steroid hormones have been shown to induce P-gp expression (7-11). For instance, the antibiotic rifampin not only induces intestinal cytochrome P 450 3A4 enzyme but also elicits a significant increase of intestinal P-gp (11). As a consequence, the plasma concentrations of orally administered digoxin are dramatically reduced. So fa...

Non-coplanar polychlorinated biphenyls (PCBs) are direct agonists for the human pregnane-X receptor and constitutive androstane receptor, and activate target gene expression in a tissue-specific manner

“…We used reporter gene constructs for CYP3A4 and MDR1, which are classical target genes for PXR (Geick et al, 2001;Bombail et al, 2004;Plant, 2007), and can also be activated by CAR (Xie et al, 2000). Cells were exposed to the classical PXR agonist rifampicin (10µM), the mixed CAR/PXR agonist phenobarbital (500µM), or each PCB (10µM).…”

Membrane microparticles mediate transfer of P-glycoprotein to drug sensitive cancer cells

“…MDR1 transcriptional induction typically shows a time and concentration dependence, peaking anywhere between 8-72 h after xenobiotic exposure in most cells, including the CCRF-CEM cells. [37][38][39][40] For these cells, long-term drug exposure is required to overcome translational block and to express P-gp on their surface. 41 Consequently, considering the time frames used in this manuscript (2-4 h co-culture periods), it is more likely that we are observing exogenous P-gp being transferred to the parental cells through MPs rather than induction of transcription, translation and subsequent trafficking to the plasma membrane from intracellular compartments.…”

Effect of the ATP-binding cassette drug transporters ABCB1, ABCG2, and ABCC2 on erlotinib hydrochloride (Tarceva) disposition inin vitroandin vivopharmacokinetic studies employing Bcrp1−/−/Mdr1a/1b−/− (triple-knockout) and wild-type mice

“…Considering that erlotinib is metabolized primarily by the CYP3A4 enzyme system (22) and that rifampicin and ketoconazole are wellknown CYP3A4 inducer and inhibitor, respectively, these drug-drug interactions have been considered as primarily CYP3A4 mediated. However, given that rifampicin has been shown to induce also intestinal P-gp (23,24) and that ketoconazole is a P-gp inhibitor (25,26), although the effects of these two drugs on CYP3A expression/activity are expected to be greater and therefore more clinically relevant compared with the modulation of P-gp, a potential contribution of ATP-binding cassette drug efflux transporters to these interactions cannot completely be excluded.…”