Correlation between apical localization of Abcc2/Mrp2 and phosphorylation status of ezrin in rat intestine

Oxidative stress promotes post-translational down-regulation of MRP2 in Caco-2 cells: Involvement of proteasomal degradation and toxicological implications

The intestinal tract is highly susceptible to oxidative stress (OS), which impairs gut barrier function. Multidrug Resistance-Associated Protein 2 (MRP2) is a key efflux pump in the intestinal transcellular barrier, regulating toxicant and drug disposition. We here evaluated the effects of OS on MRP2 in Caco-2 cells treated with tert-butyl hydroperoxide (TBH). After 24 h, TBH 250 μM increased ROS production and lipid peroxidation while decreasing GSH content and SOD activity, confirming OS induction. Under these conditions, total MRP2 protein levels decreased, while P-gp levels remained unchanged. Correspondingly, MRP2 efflux activity decreased, impairing barrier function against ochratoxin A (OTA), a substrate of MRP2, and exacerbating OTA toxicity. Localization analysis revealed reduced apical MRP2 signal in TBH 250 group, with unchanged mRNA levels, indicating post-transcriptional regulation. Mechanistically, TBH induced rapid MRP2 internalization (30 min), mediated by cPKC and clathrin, without microtubule involvement, followed by proteasomal degradation at 24 h. Both processes were dependent on GSH depletion, as treatment with N-Acetyl-l-Cysteine (NAC) restored GSH levels, MRP2 localization, and activity. We provide here the first evidence that human intestinal MRP2 is post-translationally downregulated under specific OS conditions, highlighting its potential role in exacerbating xenobiotic absorption and toxicity in OS-related human diseases.

Mechanism of Lysoforte in Improving Jejuna Morphology and Health in Broiler Chickens

Lysoforte (LFT) plays a vital role in maintaining broilers' health and intestinal morphology. However, the mechanism behind the effects of LFT improving intestinal morphology and health is still unclear. Therefore, this study was implemented to explore the central genes linked to the regulatory effect of LFT. Seventy-five newly hatched Cobb 500 male broilers were randomly divided into three groups: control, LFT500, and LFT1000 groups, with 25 chicks per group. The control chicks were provided with the basal diet, and the birds in LFT500 and LFT1000 groups were offered the same basal diet with 500 g/ton and 1,000 g/ton LFT, respectively. GSE94622 dataset consisted of the control and two LFT-treated groups (LFT500 and LFT1000). Jejuna samples were obtained from Gene Expression Omnibus (GEO). Totally 106–344 DEGs were obtained by comparing LFT500 and LFT1000 vs. control and LFT1000 vs. LFT500. Gene ontology (GO) enrichment suggested that the DEGs are mainly related to the phosphatidylethanolamine biosynthetic process and neuron projection extension. KEGG analysis suggested the DEGs were enriched in AGE-RAGE, fatty acid elongation, ECM-receptor interaction (ECMRI), glycerophospholipid metabolism, focal adhesion, unsaturated fatty acids biosynthesis, and ABC transporters. Moreover, 29 genes, such as REG4, GJB1, KAT2A, APOA5, SERPINE2, ELOVL1, ABCC2, ANKRD9, CYP4V2, and PISD, might be closely related to promoting jejuna morphology in broilers. Taken together, our observation enhances the understanding of LFT in maintaining intestinal architecture and the general health of broiler chickens.

Multidrug resistance-associated protein 2 is negatively regulated by oxidative stress in rat intestine via a posttranslational mechanism. Impact on its membrane barrier function

Oxidative stress (OS) is a key factor in the development of gastrointestinal disorders, in which the intestinal barrier is altered. However, the Multidrug resistance-associated protein 2 (Mrp2) status, an essential component of the intestinal transcellular barrier exhibiting pharmaco-toxicological relevance by limiting the orally ingested toxicants and drugs absorption, has not been investigated. We here evaluated the short-term effect of OS on Mrp2 by treatment of isolated rat intestinal sacs with tert-butyl hydroperoxide (TBH) for 30 min. OS induction by TBH (250 and 500 μM) was confirmed by increased lipid peroxidation end products, decreased reduced glutathione (GSH) content and altered antioxidant enzyme activities. Under this condition, assessment of Mrp2 distribution between brush border (BBM) and intracellular (IM) membrane fractions, showed that Mrp2 protein decreased in BBM and increased in IM, consistent with an internalization process. This was associated with decreased efflux activity and, consequently, impaired barrier function. Subsequent incubation with N-Acetyl-L-Cysteine (NAC, 1 mM) reestablished GSH content and reverted concomitantly the alteration in Mrp2 localization and function induced by TBH. Cotreatment with a specific inhibitor of classic calcium-dependent Protein Kinase C (cPKC) implicated this kinase in TBH-effects. In conclusion, we demonstrated a negative posttranslational regulation of rat intestinal Mrp2 after short-term exposition to OS, a process likely mediated by cPKC and dependent on intracellular GSH content. The concomitant impairment of the Mrp2 barrier function may have implications in xenobiotic absorption and toxicity in a variety of human diseases linked to OS, with notable consequences on the toxicity/safety of therapeutic agents.

Physiological Roles of ERM Proteins and Transcriptional Regulators in Supporting Membrane Expression of Efflux Transporters as Factors of Drug Resistance in Cancer

One factor contributing to the malignancy of cancer cells is the acquisition of drug resistance during chemotherapy via increased expression of efflux transporters, such as P-glycoprotein (P-gp), multidrug resistance-associated proteins (MRPs), and breast cancer resistance protein (BCRP). These transporters operate at the cell membrane, and are anchored in place by the scaffold proteins ezrin (Ezr), radixin (Rdx), and moesin (Msn) (ERM proteins), which regulate their functional activity. The identity of the regulatory scaffold protein(s) differs depending upon the transporter, and also upon the tissue in which it is expressed, even for the same transporter. Another factor contributing to malignancy is metastatic ability. Epithelial-mesenchymal transition (EMT) is the first step in the conversion of primary epithelial cells into mesenchymal cells that can be transported to other organs via the blood. The SNAI family of transcriptional regulators triggers EMT, and SNAI expression is used is an indicator of malignancy. Furthermore, EMT has been suggested to be involved in drug resistance, since drug excretion from cancer cells is promoted during EMT. We showed recently that ERM proteins are induced by a member of the SNAI family, Snail. Here, we first review recent progress in research on the relationship between efflux transporters and scaffold proteins, including the question of tissue specificity. In the second part, we review the relationship between ERM scaffold proteins and the transcriptional regulatory factors that induce their expression.

Acute regulation of apical ABC transporters in the gut. Potential influence on drug bioavailability

The extensive intestinal surface offers an advantage regarding nutrient, ion and water absorptive capacity but also brings along a high exposition to xenobiotics, including drugs of therapeutic use and food contaminants. After absorption of these compounds by the enterocytes, apical ABC transporters play a key role in secreting them back to the intestinal lumen, hence acting as a transcellular barrier. Rapid and reversible modulation of their activity is a subject of increasing interest for pharmacologists. On the one hand, a decrease in transporter activity may result in increased absorption of therapeutic agents given orally. On the other hand, an increase in transporter activity would decrease their absorption and therapeutic efficacy. Although of less relevance, apical ABC transporters also contribute to disposition of drugs systemically administered. This review article summarizes the present knowledge on the mechanisms aimed to rapidly regulate the activity of the main apical ABC transporters of the gut: multidrug resistance protein 1 (MDR1), multidrug resistance-associated protein 2 (MRP2) and breast cancer resistance protein (BCRP). Regulation of these mechanisms by drugs, drug delivery systems, drug excipients and nutritional components are particularly considered. This information could provide the basis for controlled regulation of bioavailability of therapeutic agents and at the same time would help to prevent potential drug-drug interactions.

Role of interleukin 1 beta in the regulation of rat intestinal multidrug resistance-associated protein 2 under conditions of experimental endotoxemia

Multidrug resistance-associated protein 2 (Mrp2), expressed at the brush border membrane (BBM) of the enterocyte, is an ABC transporter with relevant intestinal barrier function. Its toxicological relevance lies in preventing absorption and tissue accumulation of dietary contaminants, drugs, and potentially harmful endogenous metabolites. Expression and activity of intestinal Mrp2 is downregulated in LPS-induced endotoxemia. In addition, confocal microscopy studies demonstrated internalization of the transporter to endocytic vesicles. Since IL-1β plays an important role as early mediator of LPS-inflammatory responses, we evaluated whether IL-1β mediates LPS-induced impairment of Mrp2 function. Two protocols were used: I) In vivo administration of LPS (5 mg/kg b.wt., i.p., single dose) to rats in simultaneous with administration of anti-IL-1β (25 μg/kg b.wt., i.p., 4 doses), followed by studies of Mrp2 expression, localization and activity, 24 h after LPS administration; II) In vitro incubation of isolated intestinal sacs with IL-1β (10 ng/mL) for 30 min, followed by analysis of Mrp2 activity and localization. We found that in vivo immunoneutralization of IL-1β partially prevented the decrease of Mrp2 protein expression and activity as well as its internalization to intracellular domains induced by LPS. Involvement of IL-1β in the alteration of Mrp2 localization and activity was more directly demonstrated in isolated intestinal sacs, as incubation with IL-1β resulted in detection of Mrp2 in intracellular regions of the enterocyte in simultaneous with alteration of transport activity. In conclusion, IL-1β induces early internalization of intestinal Mrp2, which could partially explain loss of expression at the BBM under conditions of experimental endotoxemia. Concomitant impairment of Mrp2-dependent barrier function may have pathophysiological relevance since IL-1β mediates the effect of many local and systemic inflammatory processes.

Acute regulation of multidrug resistance-associated protein 2 localization and activity by cAMP and estradiol-17β-D-glucuronide in rat intestine and Caco-2 cells

Multidrug resistance-associated protein 2 (MRP2) is an ATP-dependent transporter expressed at the brush border membrane of the enterocyte that confers protection against absorption of toxicants from foods or bile. Acute, short-term regulation of intestinal MRP2 activity involving changes in its apical membrane localization was poorly explored. We evaluated the effects of dibutyryl-cAMP (db-cAMP), a permeable analog of cAMP, and estradiol-17β-D-glucuronide (E₂17G), an endogenous derivative of estradiol, on MRP2 localization and activity using isolated rat intestinal sacs and Caco-2 cells, a model of human intestinal epithelium. Changes in MRP2 localization were studied by Western blotting of plasma membrane (PM) vs. intracellular membrane (IM) fractions in both experimental models, and additionally, by confocal microscopy in Caco-2 cells. After 30 min of exposure, db-cAMP-stimulated sorting of MRP2 from IM to PM both in rat jejunum and Caco-2 cells at 10 and 100 µM concentrations, respectively, with increased excretion of the model substrate 2,4-dinitrophenyl-S-glutathione. In contrast, E₂17G (400 µM) induced internalization of MRP2 together with impairment of transport activity. Confocal microscopy analysis performed in Caco-2 cells confirmed Western blot results. In the particular case of E₂17G, MRP2 exhibited an unusual pattern of staining compatible with endocytic vesiculation. Use of selective inhibitors demonstrated the participation of cAMP-dependent protein kinase and classic calcium-dependent protein kinase C in db-cAMP and E₂17G effects, respectively. We conclude that localization of MRP2 in intestine may be subjected to a dynamic equilibrium between plasma membrane and intracellular domains, thus allowing for rapid regulation of MRP2 function.

Protein Kinases C-Mediated Regulations of Drug Transporter Activity, Localization and Expression

Drug transporters are now recognized as major actors in pharmacokinetics, involved notably in drug–drug interactions and drug adverse effects. Factors that govern their activity, localization and expression are therefore important to consider. In the present review, the implications of protein kinases C (PKCs) in transporter regulations are summarized and discussed. Both solute carrier (SLC) and ATP-binding cassette (ABC) drug transporters can be regulated by PKCs-related signaling pathways. PKCs thus target activity, membrane localization and/or expression level of major influx and efflux drug transporters, in various normal and pathological types of cells and tissues, often in a PKC isoform-specific manner. PKCs are notably implicated in membrane insertion of bile acid transporters in liver and, in this way, are thought to contribute to cholestatic or choleretic effects of endogenous compounds or drugs. The exact clinical relevance of PKCs-related regulation of drug transporters in terms of drug resistance, pharmacokinetics, drug–drug interactions and drug toxicity remains however to be precisely determined. This issue is likely important to consider in the context of the development of new drugs targeting PKCs-mediated signaling pathways, for treating notably cancers, diabetes or psychiatric disorders.

Role of Passive Diffusion, Transporters, and Membrane Trafficking-Mediated Processes in Cellular Drug Transport

Intracellular drug accumulation is thought to be dictated by two major processes, passive diffusion through the lipid membrane or membrane transporters. The relative role played by these distinct processes remains actively debated. Moreover, the role of membrane-trafficking in drug transport remains underappreciated and unexplored. Here we discuss the distinct processes involved in cellular drug distribution and propose that better experimental models are required to elucidate the differential contributions of various processes in intracellular drug accumulation.

Canalicular membrane MRP2/ABCC2 internalization is determined by Ezrin Thr567 phosphorylation in human obstructive cholestasis

BACKGROUND & AIMS

Multidrug resistance-associated protein 2 (MRP2) excretes conjugated organic anions including bilirubin and bile acids. Malfunction of MRP2 leads to jaundice in patients. Studies in rodents indicate that Radixin plays a critical role in determining Mrp2 canalicular membrane expression. However, it is not known how human hepatic MRP2 expression is regulated in cholestasis.

METHODS

We assessed liver MRP2 expression in patients with obstructive cholestasis caused by gallstone blockage of bile ducts, and investigated the regulatory mechanism in HepG2 cells.

RESULTS

Western blot detected that liver MRP2 protein expression in obstructive cholestatic patients (n=30) was significantly reduced to 25% of the non-cholestatic controls (n=23). Immunoprecipitation identified Ezrin but not Radixin associating with MRP2 in human livers, and the increased amount of phospho-Ezrin Thr567 was positively correlated with the amount of co-precipitated MRP2 in cholestatic livers, whereas Ezrin and Radixin total protein levels were unchanged in cholestasis. Further detailed studies indicate that Ezrin Thr567 phosphorylation plays an important role in MRP2 internalization in HepG2 cells. Since increased expression of PKCα, δ and ε were detected in these cholestatic livers, we further confirmed that these PKCs stimulated Ezrin phosphorylation and reduced MRP2 membrane expression in HepG2 cells. Finally, we identified GP78 as the key ubiquitin ligase E3 involved in MRP2 proteasome degradation.

CONCLUSIONS

Activation of liver PKCs during cholestasis leads to Ezrin Thr567 phosphorylation resulting in MRP2 internalization and degradation where ubiquitin ligase E3 GP78 is involved. This process provides a mechanistic explanation for jaundice seen in patients with obstructive cholestasis.

[Effect of repeated oral treatment with etoposide on the expression of intestinal P-glycoprotein and oral morphine analgesia]

Currently, the World Health Organization recommends oral administration of opioid analgesics for patients with cancer to treat cancer-related pain from the initial stage of treatment. Furthermore, many anticancer drugs have been newly-developed and approved as oral form. Because of this trend, the chances of drug-drug interactions between anticancer drugs and opioid analgesics during absorption process from the intestine are likely to increase. To investigate these possible drug-drug interactions, we have focused on intestinal P-glycoprotein (P-gp) which regulates the absorption of various substrate drugs administered orally. Previously, we have found that repeated oral treatment with etoposide (ETP), an anticancer drug, attenuates analgesia of oral morphine, a substrate drug for P-gp, by increasing the expression and activity of intestinal P-gp. However, the mechanism by which ETP treatment increases the intestinal P-gp expression and decreases oral morphine analgesia remains unclear. RhoA, a small G-protein, and ROCK, an effector of RhoA, pathway has been attracted attention with regard to their involvement in the regulatory mechanism of the expression and activity of P-gp. Interestingly, this pathway is activated in response to various signaling induced by some anticancer drugs. Furthermore, it has been reported that ezrin/radixin/moesin (ERM) play a key role in the plasma membrane localization of P-gp, and that RhoA/ROCK pathway regulates the activation process of ERM. This review article introduces the result of our previous research as well as recent findings on the involvement of ERM via activation of RhoA/ROCK in the increased expression of intestinal P-gp and decreased oral morphine analgesia induced by repeated oral treatment with ETP.

Involvement of moesin in the development of morphine analgesic tolerance through P-glycoprotein at the blood-brain barrier

Altered expression of P-glycoprotein (P-gp), a drug efflux transporter expressed by brain capillary endothelial cells (BCECs), may contribute to the development of opioid analgesic tolerance, as demonstrated by cumulative evidence from research. However, the detailed mechanism by which chronic morphine treatment increases P-gp expression remains unexplained. Ezrin/radixin/moesin (ERM) are scaffold proteins that are known to regulate the plasma membrane localization of some drug transporters such as P-gp in peripheral tissues, although a few reports suggest its role in the central nervous system as well. In this study, we investigated the involvement of ERM in the development of morphine analgesic tolerance through altered P-gp expression in BCECs. Repeated treatment with morphine (10 mg/kg/day, s.c. for 5 days) decreased its analgesic effect in the tail-flick test and increased P-gp protein expression in BCECs, as determined by Western blotting. Furthermore, moesin protein expression increased in the same fraction whereas that of ezrin decreased; no change was observed in the radixin expression. Furthermore, immunoprecipitation and immunofluorescence assays revealed interaction between moesin and P-gp molecules, along with co-localization, in BCECs. In conclusion, an increase in moesin expression may contribute to the increased expression of P-gp in BCECs, leading to the development of morphine analgesic tolerance.

Ezrin regulates the expression of Mrp2/Abcc2 and Mdr1/Abcb1 along the rat small intestinal tract

Multidrug resistance-associated protein 2 (MRP2)/ATP-binding cassette protein C2 (ABCC2) and multidrug resistance protein 1 (MDR1)/ABCB1 are well-known efflux transporters located on the brush border membrane of the small intestinal epithelia, where they limit the absorption of a broad range of substrates. The expression patterns of MRP2/ABCC2 and MDR1/ABCB1 along the small intestinal tract are tightly regulated. Several reports have demonstrated the participation of ERM (ezrin/radixin/moesin) proteins in the posttranslational modulation of MRP2/ABCC2 and MDR1/ABCB1, especially with regard to their membrane localization. The present study focused on the in vivo expression profiles of MRP2/ABCC2, MDR1/ABCB1, ezrin, and phosphorylated ezrin to further elucidate the relationship between the efflux transporters and the ERM proteins. The current results showed good correlation between the phosphorylation status of ezrin and Mrp2/Abcc2 expression along the gastrointestinal tract of rats and between the expression profiles of both ezrin and Mdr1/Abcb1 in the small intestine. We also demonstrated the involvement of conventional protein kinase C isoforms in the regulation of ezrin phosphorylation. Furthermore, experiments conducted with wild-type (WT) ezrin and a T567A (Ala substituted Thr) dephosphorylated mutant showed a decrease in membrane surface-localized and total expressed MRP2/ABCC2 in T567A-expressing vs. WT ezrin-expressing Caco-2 cells. In contrast, T567A- and WT-expressing cells both showed an increase in membrane surface-localized and total expressed MDR1/ABCB1. These findings suggest that the phosphorylation status and the expression profile of ezrin differentially direct MRP2/ABCC2 and MDR1/ABCB1 expression, respectively, along the small intestinal tract.

Linkage disequilibrium between polymorphisms of ABCB1 and ABCC2 to predict the treatment outcome of Malaysians with complex partial seizures on treatment with carbamazepine mono-therapy at the Kuala Lumpur Hospital

PURPOSE

Carbamazepine (CBZ) is used as the first line of treatment of Complex Partial Seizures (CPS) in the Epilepsy Clinic, Neurology Department of Kuala Lumpur Hospital (KLH). More than 30% of the patients remain drug resistant to CBZ mono-therapy. CBZ is transported by the P-glycoprotein (P-gp). The P-gp encoded by the ABCB1 and ABCC2 genes are expressed in drug resistant patients with epilepsy. A few studies have shown significant association between CBZ resistant epilepsy and Linkage Disequilibrium (LD) with adjacent polymorphisms of these genes. Our study is aimed at determining the correlation between patients' response to CBZ mono-therapy to Single Nucleotide Polymorphisms G2677T and C3435T of the ABCB1 gene as well as G1249A and -24C>T of the ABCC2 gene.

METHOD

314 patients with CPS were recruited from the Neurology Department of the KLH based on stringent inclusion and exclusion criteria, of whom 152 were responders and the other 162 were non-responders. DNA was extracted from their blood samples and Taqman technology for allelic discrimination was performed. Results were described as genotype frequencies. The SHEsis analysis platform was used to calculate linkage disequilibrium index and infer haplotype frequencies. Haploview was used to do permutation test to obtain a corrected p-value.

RESULTS

Resistance to treatment with CBZ mono-therapy was significantly associated with the 2677TT and the 3435TT genotypes while it was not significantly associated with the G1249A and -24C>T polymorphisms. The GCGC haplotype combination of the 2677G>T, 3435C>T, 1249G>A and -24C>T respectively was found to be extremely significant (p = 1.10e-20) with good drug response to CBZ mono-therapy.

CONCLUSION

Linkage disequilibrium between the 2677G>T, 3435C>T, 1249G>A and -24C>T SNPs may be used as a reliable screening marker to determine the treatment outcome of CBZ mono-therapy with CPS irrespective of race or gender.

The ERM protein, ezrin, regulates neutrophil transmigration by modulating the apical localization of MRP2 in response to the SipA effector protein during Salmonella Typhimurium infection

In human disease induced by Salmonella enterica serovar Typhimurium (S. Typhimurium), transepithelial migration of neutrophils rapidly follows attachment of the bacteria to the epithelial apical membrane. We have previously shown that during S. Typhimurium infection the multidrug resistance-associated protein 2 (MRP2) is highly expressed at the apical surface of the intestinal epithelia, and that it functions as an efflux pump for the potent neutrophil chemoattractant hepoxilin A(3) . However, the molecular mechanisms regulating its apical localization during active states of inflammation remain unknown. Thus, our objective was to determine the mechanistic basis for the translocation of MRP2 to the apical surface of intestinal epithelial cells during S. Typhimurium infection. We show that suppression of ezrin, through either RNAi or truncation of the C-terminus, results not only in a decrease in S. Typhimurium-induced neutrophil transmigration but also significantly attenuates the apical membrane expression of MRP2 during Salmonella infection. In addition, we determined that S. Typhimurium induces the activation of ezrin via a PKC-α-dependent pathway and that ezrin activation is coupled to apical localization of MRP2. Based on these results we propose that activation of ezrin is required for the apical localization of MRP2 during S. Typhimurium infection.

PDZ adaptors: their regulation of epithelial transporters and involvement in human diseases

Homeostasis in the body is at least partially maintained by mechanisms that control membrane permeability, and thereby serve to control the uptake of essential substances (e.g., nutrients) and the efflux of unwanted substances (e.g., xenobiotics and metabolites) in epithelial cells. Various transporters play fundamental roles in such bidirectional transport, but little is known about how they are organized on plasma membranes. Protein-protein interactions may play a key role: several transporters in epithelial cells interact with the so-called adaptor proteins, which are membrane anchored and interact with both transporters and other membranous proteins. Although most of the evidences for transporter-adaptor interaction has been obtained in vitro, recent studies suggest that adaptor-mediated transporter regulation does occur in vivo and could be relevant to human diseases. Thus, protein-protein interaction is not only associated with the formation of macromolecular complexes but is also involved in various cellular events, and may provide transporters with additional functionality by forming transporter networks on plasma membranes. Interactions between xenobiotic transporters and PSD95/Dlg/ZO1 (PDZ) adaptors were previously reviewed by Kato and Tsuji (2006. Eur J Pharm Sci 27:487-500); the present review focuses on the latest findings about PDZ adaptors as regulators of transporter networks and their potential role in human diseases.