Contribution of Radixin to P-Glycoprotein Expression and Transport Activity in Mouse Small Intestine In Vivo

Slug Mediates MRP2 Expression in Non-Small Cell Lung Cancer Cells

Transcriptional factors, such as Snail, Slug, and Smuc, that cause epithelial-mesenchymal transition are thought to regulate the expression of Ezrin, Radixin, and Moesin (ERM proteins), which serve as anchors for efflux transporters on the plasma membrane surface. Our previous results using lung cancer clinical samples indicated a correlation between Slug and efflux transporter MRP2. In the current study, we aimed to evaluate the relationships between MRP2, ERM proteins, and Slug in lung cancer cells. HCC827 cells were transfected by Mock and Slug plasmid. Both mRNA expression levels and protein expression levels were measured. Then, the activity of MRP2 was evaluated using CDCF and SN-38 (MRP2 substrates). HCC827 cells transfected with the Slug plasmid showed significantly higher mRNA expression levels of MRP2 than the Mock-transfected cells. However, the mRNA expression levels of ERM proteins did not show a significant difference between Slug-transfected cells and Mock-transfected cells. Protein expression of MRP2 was increased in Slug-transfected cells. The uptake of both CDCF and SN-38 was significantly decreased after transfection with Slug. This change was abrogated by treatment with MK571, an MRP2 inhibitor. The viability of Slug-transfected cells, compared to Mock cells, significantly increased after incubation with SN-38. Thus, Slug may increase the mRNA and protein expression of MRP2 without regulation by ERM proteins in HCC827 cells, thereby enhancing MRP2 activity. Inhibition of Slug may reduce the efficacy of multidrug resistance in lung cancer.

Bile duct ligation causes opposite impacts on the expression and function of BCRP and P-gp in rat brain partly via affecting membrane expression of ezrin/radixin/moesin proteins

Breast cancer resistance protein (BCRP) and P-glycoprotein (P-gp) are co-located at blood-brain barrier (BBB) cells, preventing their substrates from entering brain. Accumulating evidence demonstrates that liver failure impairs P-gp and BCRP expression and function in the brain. In the current study, we investigated how liver failure influenced the expression and function of brain BCRP and P-gp in rats subjected to bile duct ligation (BDL). The function of BCRP, P-gp and BBB integrity was assessed using distribution of prazosin, rhodamine 123 and fluorescein, respectively. We showed that BDL significantly decreased BCRP function, but increased P-gp function without affecting BBB integrity. Furthermore, we found that BDL significantly downregulated the expression of membrane BCRP and upregulated the expression of membrane P-gp protein in the cortex and hippocampus. In human cerebral microvascular endothelial cells, NH₄Cl plus unconjugated bilirubin significantly decreased BCRP function and expression of membrane BCRP protein, but upregulated P-gp function and expression of membrane P-gp protein. The decreased expression of membrane BCRP protein was linked to the decreased expression of membrane radixin protein, while the increased expression of membrane P-gp protein was related to the increased location of membrane ezrin protein. Silencing ezrin impaired membrane location of P-gp, whereas silencing radixin impaired membrane location of BCRP protein. BDL rats showed the increased expression of membrane ezrin protein and decreased expression of membrane radixin protein in the brain. We conclude that BDL causes opposite effects on the expression and function of brain BCRP and P-gp, attributing to the altered expression of membrane radixin and ezrin protein, respectively, due to hyperbilirubinemia and hyperammonemia.

Drug resistance via radixin-mediated increase of P-glycoprotein membrane expression during SNAI1-induced epithelial-mesenchymal transition in HepG2 cells

OBJECTIVES

Epithelial-mesenchymal transition (EMT) plays a role in cancer metastasis as well as in drug resistance through various mechanisms, including increased drug efflux mediated by P-glycoprotein (P-gp). In this study, we investigated the activation mechanism of P-gp, including its regulatory factors, during EMT in hepatoblastoma-derived HepG2 cells.

METHODS

HepG2 cells were transfected with SNAI1 using human adenovirus serotype 5 vector. We quantified mRNA and protein expression levels using qRT-PCR and western blot analysis, respectively. P-gp activity was evaluated by uptake assay, and cell viability was assessed by an MTT assay.

KEY FINDINGS

P-gp protein expression on plasma membrane was higher in SNAI1-transfected cells than in Mock cells, although there was no difference in P-gp protein level in whole cells. Among the scaffold proteins such as ezrin, radixin and moesin (ERM), only radixin was increased in SNAI1-transfected cells. Uptake of both Rho123 and paclitaxel was decreased in SNAI1-transfected cells, and this decrease was blocked by verapamil, a P-gp inhibitor. The reduced susceptibility of SNAI1-transfected cells to paclitaxel was reversed by elacridar, another P-gp inhibitor.

CONCLUSIONS

Increased expression of radixin during SNAI1-induced EMT leads to increased P-gp membrane expression in HepG2 cells, enhancing P-gp function and thereby increasing drug resistance.

Subcellular distribution of ezrin/radixin/moesin and their roles in the cell surface localization and transport function of P-glycoprotein in human colon adenocarcinoma LS180 cells

The ezrin/radixin/moesin (ERM) family proteins act as linkers between the actin cytoskeleton and P-glycoprotein (P-gp) and regulate the plasma membrane localization and functionality of the latter in various cancer cells. Notably, P-gp overexpression in the plasma membrane of cancer cells is a principal factor responsible for multidrug resistance and drug-induced mutagenesis. However, it remains unknown whether the ERM proteins contribute to the plasma membrane localization and transport function of P-gp in human colorectal cancer cells in which the subcellular localization of ERM has yet to be determined. This study aimed to determine the gene expression patterns and subcellular localization of ERM and P-gp and investigate the role of ERM proteins in the plasma membrane localization and transport function of P-gp using the human colon adenocarcinoma cell line LS180. Using real-time reverse transcription polymerase chain reaction and immunofluorescence analyses, we showed higher levels of ezrin and moesin mRNAs than those of radixin mRNA in these cells and preferential distribution of all three ERM proteins on the plasma membrane. The ERM proteins were highly colocalized with P-gp. Additionally, we show that the knockdown of ezrin, but not of radixin and moesin, by RNA interference significantly decreased the cell surface expression of P-gp in LS180 cells without affecting the mRNA expression of P-gp. Furthermore, gene silencing of ezrin substantially increased the intracellular accumulation of rhodamine123, a typical P-gp substrate, with no alterations in the plasma membrane permeability of Evans blue, a passive transport marker. In conclusion, ezrin may primarily regulate the cell surface localization and transport function of P-gp as a scaffold protein without influencing the transcriptional activity of P-gp in LS180 cells. These findings should be relevant for treating colorectal cancer, which is the second leading cause of cancer-related deaths in males and females combined.

Rapid Increase of Gastrointestinal P-Glycoprotein Functional Activity in Response to Etoposide Stimulation

We previously reported that exposure of human colon adenocarcinoma (Caco-2) cells to the bitter substance phenylthiocarbamide (PTC) rapidly enhanced the transport function of P-glycoprotein (P-gp). In this study, we investigated the short-term effect of etoposide, another bitter-tasting P-gp substrate, on P-gp transport function in the same cell line. We found that etoposide exposure significantly increased both the P-gp protein level in the plasma membrane fraction and the efflux rate of rhodamine123 (Rho123) in Caco-2 cells within 10 min. The efflux ratio (ratio of the apparent permeability coefficient in the basal-to-apical direction to that in the apical-to-basal direction) of Rho123 in etoposide-treated cells was also significantly increased compared with the control. These results indicated that etoposide rapidly enhances P-gp function in Caco-2 cells. In contrast, P-gp expression in whole cells at both the mRNA and protein level was unchanged by etoposide exposure, compared with the levels in non-treated cells. Furthermore, etoposide increased the level of phosphorylated ezrin, radixin and moesin (P-ERM) proteins in the plasma membrane fraction of Caco-2 cells within 10 min. P-gp functional changes were blocked by YM022, an inhibitor of cholecystokinin (CCK) receptor. These results suggest that etoposide induces release of CCK, causing activation of the CCK receptor followed by phosphorylation of ERM proteins, which recruit intracellular P-gp for trafficking to the gastrointestinal membrane, thereby increasing the functional activity of P-gp.

Functional Alterations of Multidrug Resistance-Associated Proteins 2 and 5, and Breast Cancer Resistance Protein upon Snail-Induced Epithelial-Mesenchymal Transition in HCC827 Cells

Our previous report indicated that Snail-induced epithelial-mesenchymal transition (EMT) enhanced P-glycoprotein (P-gp) function and drug resistance to P-gp substrate anticancer drug in a human non-small cell lung cancer (NSCLC) cell line, HCC827. Our objective is to evaluate the changes in the mRNA and protein expression levels and the functions of multidrug resistance-associated protein (MRP) 2, MRP5 and breast cancer resistance protein (BCRP). Snail-expressing HCC827 cells showed increased mRNA levels of Snail and a mesenchymal marker vimentin, and decreased mRNA levels of an epithelial marker E-cadherin after transduction, indicating that Snail had induced EMT consistent with our previous reports. The mRNA level of MRP2 was significantly decreased, while that of MRP5 remained unchanged, in Snail-expressing cells. The expression levels of MRP2 and MRP5 proteins in whole-cell homogenate were unchanged in Snail-expressing cells, but MRP5 protein showed significantly increased membrane localization. Snail-transduction increased the efflux transport of 5-(and-6)-carboxy-2',7'-dichlorofluorescein (CDCF), a substrate of MRP2, 3 and 5. This increase was blocked by MK571, which inhibits MRP1, 2, and 5. Toxicity of cisplatin, a substrate of MRP2 and 5, was significantly decreased in Snail-expressing cells. BCRP mRNA and protein levels were both decreased in Snail-expressing cells, which showed an increase in the intracellular accumulation of 7-ethyl-10-hydroxycamptothecin (SN-38), a BCRP substrate, resulting in reduced viability. These results suggested that MRP5 function appears to be increased via an increase in membrane localization, whereas the BCRP function is decreased via a decrease in the expression level in HCC827 cells with Snail-induced EMT.

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.

Distinct roles of ezrin, radixin and moesin in maintaining the plasma membrane localizations and functions of human blood-brain barrier transporters

The purpose of this study was to clarify the roles of ERM proteins (ezrin/radixin/moesin) in the regulation of membrane localization and transport activity of transporters at the human blood-brain barrier (BBB). Ezrin or moesin knockdown in a human in vitro BBB model cell line (hCMEC/D3) reduced both BCRP and GLUT1 protein expression levels on the plasma membrane. Radixin knockdown reduced not only BCRP and GLUT1, but also P-gp membrane expression. These results indicate that P-gp, BCRP and GLUT1 proteins are maintained on the plasma membrane via different ERM proteins. Furthermore, moesin knockdown caused the largest decrease of P-gp and BCRP efflux activity among the ERM proteins, whereas GLUT1 influx activity was similarly reduced by knockdown of each ERM protein. To investigate how moesin knockdown reduced P-gp efflux activity without loss of P-gp from the plasma membrane, we examined the role of PKCβI. PKCβI increased P-gp phosphorylation and reduced P-gp efflux activity. Radixin and moesin proteins were detected in isolated human brain capillaries, and their protein abundances were within a 3-fold range, compared with those in hCMEC/D3 cell line. These findings may mean that ezrin, radixin and moesin maintain the functions of different transporters in different ways at the human BBB.

Moesin-Mediated P-Glycoprotein Activation During Snail-Induced Epithelial-Mesenchymal Transition in Lung Cancer Cells

Epithelial-mesenchymal transition (EMT) plays a role in not only cancer metastasis, but also drug resistance, which is associated with increased levels of efflux transporters such as P-glycoprotein (P-gp). Here, we examined whether P-gp activation during Snail-induced EMT of lung cancer cells is mediated by ezrin, radixin, and moesin (ERM), which regulate transporter localization. HCC827 lung cancer cells overexpressing the transcription factor Snail showed increased Rhodamine123 efflux and increased paclitaxel resistance, reflecting increased P-gp activity. Concomitantly, the expression level of moesin, but not ezrin or radixin, was significantly increased. The increase of P-gp activity was suppressed by knockdown of moesin. Thus, the increase of P-gp activity associated with Snail-induced EMT may be mediated mainly by moesin in HCC827 cells. On the other hand, the Snail mRNA expression level was correlated with the expression level of each ERM in 4 non-small-cell lung cancer cell lines (HCC827, A549, H441, H1975) and in tumor tissues, but not normal tissues, of patients with lung cancer. These results suggest that P-gp activation during EMT is at least partially due to increased expression of moesin. Coadministration of moesin inhibitors with anticancer drugs might block P-gp-mediated drug efflux organ-specifically, improving treatment efficacy and minimizing side effects on other organs.

Regulation of breast cancer resistance protein and P-glycoprotein by ezrin, radixin and moesin in lung, intestinal and renal cancer cell lines

Objectives

Ezrin (Ezr), radixin (Rdx) and moesin (Msn) (ERM) proteins anchor other proteins to the cell membrane, serving to regulate their localization and function. Here, we examined whether ERM proteins functionally regulate breast cancer resistance protein (BCRP) and P-glycoprotein in cell lines derived from lung, intestinal and renal cancers.

Methods

ERM proteins were each silenced with appropriate siRNA. BCRP and P-gp functions were evaluated by means of efflux and uptake assays using 7-ethyl-10-hydroxycamptothecin (SN-38) and rhodamine123 (Rho123) as specific substrates, respectively, in non-small cell lung cancer HCC827 cells, intestinal cancer Caco-2 cells and renal cancer Caki-1 cells.

Key findings

In HCC827 cells, the efflux rates of SN-38 and Rho123 were significantly decreased by knockdown of Ezr or Msn, but not Rdx. However, BCRP function was unaffected by Ezr or Rdx knockdown in Caco-2 cells, which do not express Msn. In Caki-1 cells, Rdx knockdown increased the intracellular SN-38 concentration, while knockdown of Ezr or Msn had no effect.

Conclusions

Our findings indicate that regulation of BCRP and P-gp functions by ERM proteins is organ-specific. Thus, if the appropriate ERM protein(s) are functionally suppressed, accumulation of BCRP or P-gp substrates in lung, intestine or kidney cancer tissue might be specifically increased.

Changes in Radixin Expression and Interaction with Efflux Transporters in the Liver of Adjuvant-Induced Arthritic Rats

Scaffold proteins such as radixin help to modulate the plasma membrane localization and transport activity of the multidrug resistance-associated protein 2 (MRP2/ABCC2) and P-glycoprotein (P-gp/ABCB1) efflux transporters in the liver. We examined changes in radixin expression and interaction with efflux transporters in adjuvant-induced arthritic (AA) rats, an animal model of rheumatoid arthritis, as well as in human liver cancer (HepG2) cells because inflammation affects drug pharmacokinetics via the efflux transporters. The expression levels of radixin and phosphorylated radixin (p-radixin) were measured 24 h after treatment with inflammatory cytokines comprising tumor necrosis factor (TNF)-α, interleukin (IL)-1β, IL-6 or sodium nitroprusside (SNP; a nitric oxide donor). The protein levels of radixin, MRP2, and P-gp in the rat liver were next examined. We also investigated whether inflammation affected the formation of complexes between radixin and MRP2 or P-gp. The mRNA and protein levels of radixin in HepG2 cells were significantly decreased by TNF-α treatment, while minimal changes were observed after treatment with IL-1β, IL-6 or SNP. TNF-α also significantly decreased the protein levels of p-radixin, suggesting that TNF-α inhibited the activation of radixin and thereby reduced the activity of the efflux transporters. Complex formation of radixin with MRP2 and P-gp was significantly decreased in AA rats but this was reversed by prednisolone and dexamethasone treatment, indicating that decreased interactions of radixin with MRP2 and P-gp likely occur during liver inflammation. These data suggest that liver inflammation reduces radixin function by decreasing its interactions with MRP2 and P-gp.

Advances in Studies of P-Glycoprotein and Its Expression Regulators

This review deals with recent advances in studies on P-glycoprotein (P-gp) and its expression regulators, focusing especially on our own research. Firstly, we describe findings demonstrating that the distribution of P-gp along the small intestine is heterogeneous, which explains why orally administered P-gp substrate drugs often show bimodal changes of plasma concentration. Secondly, we discuss the post-translational regulation of P-gp localization and function by the scaffold proteins ezrin, radixin and moesin (ERM proteins), together with recent reports indicating that tissue-specific differences in regulation by ERM proteins in normal tissues might be retained in corresponding cancerous tissues. Thirdly, we review evidence that P-gp activity is enhanced in the process of epithelial-to-mesenchymal transition (EMT), which is associated with cancer progression, without any increase in expression of P-gp mRNA. Finally, we describe two examples in which P-gp critically influences the brain distribution of drugs, i.e., oseltamivir, where low levels of P-gp associated with early development allow oseltamivir to enter the brain, potentially resulting in neuropsychiatric side effects in children, and cilnidipine, where impairment of P-gp function in ischemia allows cilnidipine to enter the ischemic brain, where it exerts a neuroprotective action.

Beyond Competitive Inhibition: Regulation of ABC Transporters by Kinases and Protein-Protein Interactions as Potential Mechanisms of Drug-Drug Interactions

ATP-binding cassette (ABC) transporters are transmembrane efflux transporters mediating the extrusion of an array of substrates ranging from amino acids and lipids to xenobiotics, and many therapeutic compounds, including anticancer drugs. The ABC transporters are also recognized as important contributors to pharmacokinetics, especially in drug-drug interactions and adverse drug effects. Drugs and xenobiotics, as well as pathologic conditions, can influence the transcription of ABC transporters, or modify their activity or intracellular localization. Kinases can affect the aforementioned processes for ABC transporters as do protein interactions. In this review, we focus on the ABC transporters ABCB1, ABCB11, ABCC1, ABCC4, and ABCG2 and illustrate how kinases and protein-protein interactions affect these transporters. The clinical relevance of these factors is currently unknown; however, these examples suggest that our understanding of drug-drug interactions will benefit from further knowledge of how kinases and protein-protein interactions affect ABC transporters.

Different regulation of P-glycoprotein function between Caco-2 and Caki-1 cells by ezrin, radixin and moesin proteins

Objectives

P-glycoprotein (P-gp) mediates efflux of many xenobiotics, including therapeutic drugs, from normal and tumour tissues, and its functional localization on the plasma membrane of cells is regulated by scaffold proteins, such as ezrin, radixin and moesin (ERM proteins). We previously reported that radixin is involved in post-translational regulation of P-gp in hepatocellular carcinoma HepG2 cells and mouse small intestine, but not in mouse kidney.

Methods

Here, we investigated whether the role of ERM proteins in regulation of P-gp transport activity in cancers is the same as that in the corresponding normal tissues, using human colon adenocarcinoma (Caco-2) cells and renal carcinoma (Caki-1) cells.

Key findings

In Caco-2 cells, radixin silencing alone reduced the P-gp-mediated intracellular accumulation of rhodamine123 (Rho123), while the mRNA level of P-gp was unchanged. Thus, it appears that only radixin among the ERMs regulates P-gp activity in Caco-2 cells. On the other hand, none of the ERM proteins influenced P-gp activity in Caki-1 cells.

Conclusions

The regulation of P-gp by ERM proteins is different between Caco-2 and Caki-1 cells. Moreover, these regulatory properties are the same as those of the corresponding normal tissues, and suggest that tissue-specific differences in the regulation of P-gp by ERM proteins are retained in cancerous tissues.

Drug Transporters and Na+/H+ Exchange Regulatory Factor PSD-95/Drosophila Discs Large/ZO-1 Proteins

Drug transporters govern the absorption, distribution, and elimination of pharmacologically active compounds. Members of the solute carrier and ATP binding-cassette drug transporter family mediate cellular drug uptake and efflux processes, thereby coordinating the vectorial movement of drugs across epithelial barriers. To exert their physiologic and pharmacological function in polarized epithelia, drug transporters must be targeted and stabilized to appropriate regions of the cell membrane (i.e., apical versus basolateral). Despite the critical importance of drug transporter membrane targeting, the mechanisms that underlie these processes are largely unknown. Several clinically significant drug transporters possess a recognition sequence that binds to PSD-95/Drosophila discs large/ZO-1 (PDZ) proteins. PDZ proteins, such as the Na(+)/H(+) exchanger regulatory factor (NHERF) family, act to stabilize and organize membrane targeting of multiple transmembrane proteins, including many clinically relevant drug transporters. These PDZ proteins are normally abundant at apical membranes, where they tether membrane-delimited transporters. NHERF expression is particularly high at the apical membrane in polarized tissue such as intestinal, hepatic, and renal epithelia, tissues important to drug disposition. Several recent studies have highlighted NHERF proteins as determinants of drug transporter function secondary to their role in controlling membrane abundance and localization. Mounting evidence strongly suggests that NHERF proteins may have clinically significant roles in pharmacokinetics and pharmacodynamics of several pharmacologically active compounds and may affect drug action in cancer and chronic kidney disease. For these reasons, NHERF proteins represent a novel class of post-translational mediators of drug transport and novel targets for new drug development.

[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.

Decreased radixin function for ATP-binding cassette transporters in liver in adjuvant-induced arthritis rats

Pathophysiological changes are associated with alterations in the expression and function of numerous ADME-related proteins. We have previously demonstrated that the membrane localization of ATP-binding cassette (ABC) transporters in liver was decreased without change of total expression levels in adjuvant-induced arthritis (AA) in rats. Ezrin/radixin/moesin (ERM) proteins are involved in localization of some ABC transporters in canalicular membrane. The mRNA levels of radixin decreased significantly in liver but not kidney, small intestine, and brain. The mRNA levels of ezrin and moesin did not change in AA. The membrane localization of radixin was reduced in liver of AA and the ratios of activated radixin (p-radixin) to total radixin were decreased in AA, although the protein levels of radixin did not change in homogenate and membrane protein. To clarify whether AA affects the linker functions of ERM proteins, we examined the interactions between ERM proteins and ABC transporters. The interactions between radixin and ABC transporters were decreased in AA. In vitro studies using human hepatoma HepG2 cells showed that interleukin-1β decreased the mRNA levels of radixin and colocalization of radixin and Mrp2. Our results show that the decreased radixin functions affect the interaction between radixin and ABC transporters in inflammation.

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.

Involvement of PtdIns(4,5)P2 in the regulatory mechanism of small intestinal P-glycoprotein expression

Previously, we reported that repeated oral administration of etoposide (ETP) activates the ezrin/radixin/moesin (ERM) scaffold proteins for P-glycoprotein (P-gp) via Ras homolog gene family member A (RhoA)/Rho-associated coiled-coil containing protein kinase (ROCK) signaling, leading to increased ileal P-gp expression. Recent studies indicate that phosphatidyl inositol 4,5-bisphosphate [PtdIns(4,5)P2] regulates the plasma-membrane localization of certain proteins, and its synthase, the type I phosphatidyl inositol 4-phosphate 5-kinase (PI4P5K), is largely controlled by RhoA/ROCK. Here, we examined whether PtdIns(4,5)P2 and PI4P5K are involved in the increased expression of ileal P-gp following the ERM activation by ETP treatment. Male ddY mice (4-week-old) were treated with ETP (10 mg/kg/day, per os, p.o.) for 5 days. Protein-expression levels were measured by either western blot or dot blot analysis and molecular interactions were assessed using immunoprecipitation assays. ETP treatment significantly increased PI4P5K, ERM, and P-gp expression in the ileal membrane. This effect was suppressed following the coadministration of ETP with rosuvastatin (a RhoA inhibitor) or fasudil (a ROCK inhibitor). Notably, the PtdIns(4,5)P2 expression in the ileal membrane, as well as both P-gp and ERM levels coimmunoprecipitated with anti-PtdIns(4,5)P2 antibody, were increased by ETP treatment. PtdIns(4,5)P2 and PI4P5K may contribute to the increase in ileal P-gp expression observed following the ETP treatment, possibly through ERM activation via the RhoA/ROCK pathway.

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.