Expression and transcriptional activities of nuclear receptors involved in regulation of drug-metabolizing enzymes are not altered by colchicine: Focus on PXR, CAR, and GR in primary human hepatocytes

Abstract

Recent findings show that colchicine (COL) in submicromolar concentrations downregulates the expression of major drug-metabolizing P450 enzymes in human hepatocytes. Concomitantly, the expression of pregnane X receptor (PXR) and constitutive androstane receptor (CAR) was diminished by COL, whereas expression of glucocorticoid receptor (GR) remained unaltered. A tentative mechanism is perturbation of the GR-PXR/CAR-CYP2/3 signaling cascade, resulting in restricted transcriptional activity of GR receptor by colchicine. In this work we focused on 10-demethylcolchicine (colchiceine; EIN), a structural analogue and a putative metabolite of COL that lacks tubulin-binding activity. We investigated the effects of EIN on the expression of PXR, CAR, and GR receptors in primary cultures of human hepatocytes. In contrast with the effects of COL, EIN does not alter the expression of PXR, CAR, and/or GR receptors mRNAs. In addition, EIN had no effects on transcriptional activities of PXR, CAR, and GR receptors in reporter gene assays using transfected cell lines. Considering that COL and EIN are structurally very close and differ only in their tubulin-binding activity, the data presented imply that the deleterious effects of COL on the GR-PXR/CAR-CYP2/3 cascade are primarily due to perturbation of the microtubule network. Our data support the idea of replacing COL by EIN, which is less toxic and does not interact with xenoreceptors.

Dependence on the Microtubule Network and 90-kDa Heat Shock Protein of Phenobarbital-Induced Nuclear Translocation of the Rat Constitutive Androstane Receptor

“…Because disruption of the microtubule network was found to repress human CAR mRNA expression via inhibition of the GRmediated pathway (Dvorak et al, 2003;Dvorá k et al, 2007), we measured the CAR protein and mRNA expression levels with NCZ or COL in rat primary hepatocytes. Rat primary hepatocytes were incubated for 6 or 24 h with either NCZ or Fig.…”

“…At the nuclear membrane, the NLS of GR are recognized by transport proteins called importins and undergo facilitated diffusion through nuclear pores. Dvorak et al (2003) and Dvorá k et al (2007) showed that the microtubule disrupting reagent colchicine (COL) inhibited PB-inducible CYP2B6 mRNA expression in human primary hepatocytes. Because human CAR is known to be a target gene of GR (Pascussi et al, 2000, COL might repress GR-mediated mRNA expression of CAR by blocking GR nuclear translocation, affecting the GR-CAR-CYP2B cascade.…”

Induction of xenobiotic-metabolizing enzymes in hepatocytes by beta-naphthoflavone: Time-dependent changes in activities, protein and mRNA levels

“…In the present in vitro study, primary cultures of rat hepatocytes served as the model considered to be the most relevant for predicting in vivo induction (4,18,19).…”