Contribution of radixin and ezrin to the maintenance of hepatocytes' excretory function in health and disease

Background & aims

Excretory liver failure is frequently associated with poor prognosis in critically ill patients. It is characterized by the loss of canalicular membrane export pumps at the hepatocyte membrane. The membrane export pump Multidrug resistant-associated protein (MRP) 2 is pivotal in hepatocytes for brushed membrane morphology and transport of various metabolites. In addition, MRP2 anchoring proteins of the Ezrin/Radixin/Moesin (ERM) family are crucial for the correct MRP2 location, integration, and function in different tissues. In hepatocytes, altered ERM signaling is elementary for developing excretory liver failure.

Methods

Polarized human HepaRG cells, primary human hepatocytes, and hepatocyte-specific Ezrin knockout mice are employed to investigate ERM expression and function in health and the bile duct ligation model of obstructive cholestasis.

Results

ERM-scaffolding protein Ezrin has no relevant function in maintaining the canalicular structure in hepatocytes during health and disease.

Conclusions

Homeostasis of the canalicular pole in hepatocytes is maintained exclusively by Radixin but not Ezrin, and Radixin dysfunction promotes cholestasis.

Cellular Membrane Localization of Innate Immune Checkpoint Molecule CD47 Is Regulated by Radixin in Human Pancreatic Ductal Adenocarcinoma Cells

In the past decade, immune checkpoint inhibitors have exhibited potent antitumor efficacy against multiple solid malignancies but limited efficacy against pancreatic ductal adenocarcinoma (PDAC). Cluster of differentiation (CD) 47, a member of the immunoglobulin G superfamily, is overexpressed in the surface membrane of PDAC and independently correlates with a worse clinical prognosis. Furthermore, CD47 functions as a dominant macrophage checkpoint, providing a potent "do not eat me" signal to enable cancer cells to evade the innate immune system. Thus, the blockade of CD47 is a promising immunotherapeutic strategy for PDAC. In this study, we determined whether ezrin/radixin/moesin (ERM) family members, which post-translationally modulate the cellular membrane localization of numerous transmembrane proteins by crosslinking with the actin cytoskeleton, contribute to the cellular membrane localization of CD47 in KP-2 cells derived from human PDAC. Immunofluorescence analysis showed that CD47 and ezrin/radixin were highly co-localized in the plasma membrane. Interestingly, gene silencing of radixin but not ezrin dramatically decreased the cell surface expression of CD47 but had little effects on its mRNA level. Furthermore, CD47 and radixin interacted with each other, as determined by a co-immunoprecipitation assay. In conclusion, radixin regulates the cellular membrane localization of CD47 as a scaffold protein in KP-2 cells.

Ezrin and Its Phosphorylated Thr567 Form Are Key Regulators of Human Extravillous Trophoblast Motility and Invasion

The protein ezrin has been shown to enhance cancer cell motility and invasion leading to malignant behaviours in solid tumours, but a similar regulatory function in the early physiological reproduction state is, however, much less clear. We speculated that ezrin may play a key role in promoting first-trimester extravillous trophoblast (EVT) migration/invasion. Ezrin, as well as its Thr567 phosphorylation, were found in all trophoblasts studied, whether primary cells or lines. Interestingly, the proteins were seen in a distinct cellular localisation in long, extended protrusions in specific regions of cells. Loss-of-function experiments were carried out in EVT HTR8/SVneo and Swan71, as well as primary cells, using either ezrin siRNAs or the phosphorylation Thr567 inhibitor NSC668394, resulting in significant reductions in both cell motility and cellular invasion, albeit with differences between the cells used. Our analysis further demonstrated that an increase in focal adhesion was, in part, able to explain some of the molecular mechanisms involved. Data collected using human placental sections and protein lysates further showed that ezrin expression was significantly higher during the early stage of placentation and, importantly, clearly seen in the EVT anchoring columns, further supporting the potential role of ezrin in regulating migration and invasion in vivo.

Special AT-rich sequence binding protein 1 promotes multidrug resistance in gastric cancer by regulation of Ezrin to alter subcellular localization of ATP-binding cassette transporters

Multidrug resistance is a primary factor in the poor response to chemotherapy and subsequent death in gastric cancer patients. However, the molecular mechanisms involved remain unclear. In this study, the high expression of special AT-rich sequence binding protein 1 (SATB1) in gastric cancer was found to be associated with reduced sensitivity to various chemotherapy drugs. Our results demonstrate that SATB1 can promote chemotherapy resistance in gastric cancer in vitro and in vivo. SATB1 exerts its effect by enhancing the activity of multiple ATP-binding cassette (ABC) transporters (P-glycoprotein, multidrug resistance-associated protein, and breast cancer resistance protein) in gastric cancer cell lines. We also found that SATB1 affects ABC transporters by altering the subcellular localization of the ABC transporter rather than its expression. Subsequently, we confirmed that Ezrin binds to various ABC transporters and affects their subcellular localization. In addition, we found that SATB1 can also bind to the Ezrin promoter and regulate its expression. In the present study, we elucidate the mechanism of SATB1-mediated multidrug resistance in gastric cancer, providing a basis for SATB1 as a potential target for reversal of resistance.

The relationship among amyloid-β deposition, sphingomyelin level, and the expression and function of P-glycoprotein in Alzheimer's disease pathological process

In Alzheimer's disease, the transporter P-glycoprotein is responsible for the clearance of amyloid-β in the brain. Amyloid-β correlates with the sphingomyelin metabolism, and sphingomyelin participates in the regulation of P-glycoprotein. The amyloid cascade hypothesis describes amyloid-β as the central cause of Alzheimer's disease neuropathology. Better understanding of the change of P-glycoprotein and sphingomyelin along with amyloid-β and their potential association in the pathological process of Alzheimer's disease is critical. Herein, we found that the expression of P-glycoprotein in APP/PS1 mice tended to increase with age and was significantly higher at 9 and 12 months of age than that in wild-type mice at comparable age. The functionality of P-glycoprotein of APP/PS1 mice did not change with age but was significantly lower than that of wild-type mice at 12 months of age. Decreased sphingomyelin levels, increased ceramide levels, and the increased expression and activity of neutral sphingomyelinase 1 were observed in APP/PS1 mice at 9 and 12 months of age compared with the levels in wild-type mice. Similar results were observed in the Alzheimer's disease mouse model induced by intracerebroventricular injection of amyloid-β1-42 and human cerebral microvascular endothelial cells treated with amyloid-β1-42. In human cerebral microvascular endothelial cells, neutral sphingomyelinase 1 inhibitor interfered with the changes of sphingomyelin metabolism and P-glycoprotein expression and functionality caused by amyloid-β1-42 treatment. Neutral sphingomyelinase 1 regulated the expression and functionality of P-glycoprotein and the levels of sphingomyelin and ceramide. Together, these findings indicate that neutral sphingomyelinase 1 regulates the expression and function of P-glycoprotein via the sphingomyelin/ceramide pathway. These studies may serve as new pursuits for the development of anti-Alzheimer's disease drugs.

Moesin Serves as Scaffold Protein for PD-L1 in Human Uterine Cervical Squamous Carcinoma Cells

Immune checkpoint blockade (ICB) therapy targeting the programmed death ligand-1 (PD-L1)/PD-1 axis has emerged as a promising treatment for uterine cervical cancer; however, only a small subset of patients with uterine cervical squamous cell carcinoma (SCC) derives clinical benefit from ICB therapies. Thus, there is an urgent unmet medical need for novel therapeutic strategies to block the PD-L1/PD-1 axis in patients with uterine cervical SCC. Here, we investigated the involvement of ezrin/radixin/moesin (ERM) family scaffold proteins, which crosslink several plasma membrane proteins with the actin cytoskeleton, on the plasma membrane localization of PD-L1 in BOKU and HCS-2 cells derived from human uterine cervical SCC. Immunofluorescence analysis showed that PD-L1 colocalized with all three ERM proteins in the plasma membrane. Gene knockdown of moesin, but not ezrin and radixin, substantially reduced the plasma membrane expression of PD-L1, with limited effect on mRNA expression. An immunoprecipitation assay demonstrated the molecular interaction between PD-L1 and moesin. Moreover, phosphorylated, i.e., activated, moesin was highly colocalized with PD-L1 in the plasma membrane. In conclusion, moesin may be a scaffold protein responsible for the plasma membrane expression of PD-L1 in human uterine cervical SCC.

Ezrin gone rogue in cancer progression and metastasis: An enticing therapeutic target

Cancer metastasis is the primary cause of morbidity and mortality in cancer as it remains the most complicated, devastating, and enigmatic aspect of cancer. Several decades of extensive research have identified several key players closely associated with metastasis. Among these players, cytoskeletal linker Ezrin (the founding member of the ERM (Ezrin-Radixin-Moesin) family) was identified as a critical promoter of metastasis in pediatric cancers in the early 21st century. Ezrin was discovered 40 years ago as a aminor component of intestinal epithelial microvillus core protein, which is enriched in actin-containing cell surface structures. It controls gastric acid secretion and plays diverse physiological roles including maintaining cell polarity, regulating cell adhesion, cell motility and morphogenesis. Extensive research for more than two decades evinces that Ezrin is frequently dysregulated in several human cancers. Overexpression, altered subcellular localization and/or aberrant activation of Ezrin are closely associated with higher metastatic incidence and patient mortality, thereby justifying Ezrin as a valuable prognostic biomarker in cancer. Ezrin plays multifaceted role in multiple aspects of cancer, with its significant contribution in the complex metastatic cascade, through reorganizing the cytoskeleton and deregulating various cellular signaling pathways. Current preclinical studies using genetic and/or pharmacological approaches reveal that inactivation of Ezrin results in significant inhibition of Ezrin-mediated tumor growth and metastasis as well as increase in the sensitivity of cancer cells to various chemotherapeutic drugs. In this review, we discuss the recent advances illuminating the molecular mechanisms responsible for Ezrin dysregulation in cancer and its pleiotropic role in cancer progression and metastasis. We also highlight its potential as a prognostic biomarker and therapeutic target in various cancers. More importantly, we put forward some potential questions, which we strongly believe, will stimulate both basic and translational research to better understand Ezrin-mediated malignancy, ultimately leading to the development of Ezrin-targeted cancer therapy for the betterment of human life.

Functional role and regulation of permeability-glycoprotein (P-gp) in the fetal membrane during drug transportation

OBJECTIVE

Na⁺ /H⁺ exchange regulatory factor-1 (NHERF-1) is a class I PDZ (PSD95/Discs-large/ZO-1) binding protein involved in cell-surface expression and stabilization of transporter proteins, including permeability-glycoprotein (P-gp) in various cell types. P-gp, expressed in placental trophoblasts, is an efflux transporter protein that influences the pharmacokinetics of various drugs used during pregnancy. Previously we have reported that NHERF-1 regulates fetal membrane inflammation. However, the role of NHERF-1 in regulating P-gp in the fetal membrane during drug transportation remains unclear. This study determined the interplay between NHERF-1 and P-gp in human fetal membrane cells.

METHODS

Fetal membranes from normal, term cesareans were screened for P-gp by immunohistochemistry (IHC). Chorionic trophoblast (CTC), with the highest expression of P-gp among fetal membrane cells, was further used to test interactive properties between NHERF-1 and P-gp. BeWo (placental trophoblast cell line) cells were used as a control. Immunoprecipitation (IP) of CTC lysates using the P-gp antibody followed by western blot determined co-precipitation of NHERF-1. Silencing NHERF-1 using small interfering RNA further tested the relevance of NHERF-1 in P-gp expression and function in CTC and BeWo cells. NHERF-1 regulation of P-gp's efflux function (drug resistance) was further tested using the ENZO^TM efflux dye kit.

RESULTS

Immunohistochemistry localized, and western blot confirmed P-gp in human fetal membranes, primarily in the CTC with limited expression in the amnion epithelial layer. P-gp expression in the membranes was similar to that seen in the placenta. IP data showed P-gp co-precipitating with NHERF1. Silencing of NHERF-1 resulted in significant drug resistance suggesting P-gp function mediated through NHERF1 in CTCs.

CONCLUSION

Proinflammatory mediator NHERF-1 regulates P-gp and control drug transportation across the fetal membranes. Our data suggest a novel functional role for fetal membranes during pregnancy. Besides the placenta, fetal membranes may also regulate efflux of materials at the feto-maternal interface and control drug transport during pregnancy.

Ezrin and Radixin Differentially Modulate Cell Surface Expression of Programmed Death Ligand-1 in Human Pancreatic Ductal Adenocarcinoma KP-2 Cells

Immune checkpoint blockade (ICB) therapies, such as immune checkpoint inhibitors against programmed death ligand-1 (PD-L1), have not been successful in treating patients with pancreatic ductal adenocarcinoma (PDAC). Despite the critical role of PD-L1 in various types of cancers, the regulatory mechanism of PD-L1 expression on the cell surface of PDAC is poorly understood. Therefore, uncovering potential modulators of cell surface localisation of PD-L1 may provide a new strategy to improve ICB therapy in patients with PDAC. Here, we examined the role of ezrin/radixin/moesin (ERM) family scaffold proteins that crosslink transmembrane proteins with the actin cytoskeleton in the surface localisation of PD-L1 in KP-2 cells, a human PDAC cell line. Our results demonstrated the abundant protein expression of PD-L1, ezrin, and radixin, but not moesin, as well as their colocalisation in the plasma membrane. Interestingly, immunoprecipitation analysis detected the molecular interaction of PD-L1 with ezrin and radixin. Moreover, gene silencing of ezrin moderately decreased the mRNA and cell surface expression of PD-L1, while that of radixin greatly decreased the surface expression of PD-L1 without altering the mRNA levels. Thus, radixin and ezrin differentially modulate the cell surface localisation of PD-L1 in KP-2 cells, highlighting a potential therapeutic target to improve the current ICB therapy in PDAC.

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.

NHERF1/EBP50 as a Target for Modulation of MRP Function in HepG2 Cells

As increased expression and activities of efflux transporters (ETs) often cause drug resistance in cancers, we tried modulating ET activity in cancer cells, using scaffold proteins such as ezrin/radixin/moesin (ERM) proteins, and Na⁺/H⁺ exchanger regulatory factor-1 (NHERF1)/ERM-binding phosphoprotein of 50 kDa (EBP50). To see whether EBP50 modulated ET activities in human liver cancer HepG2 cells, we used EBP50 siRNA and a designed TAT-PDZ1 peptide. The EBP50 knockdown (EBP50^KD) cells had significantly higher intracellular accumulations of Rho123 and carboxy-dichlorofluorescein (CDF), but not H33342 (i.e., the respective substrates of P-glycoprotein (P-gp), multidrug resistance-associated protein (MRP), and breast cancer resistance protein (BCRP)), compared with control HepG2, suggesting that EBP50 knockdown in HepG2 cells decreased activity of P-gp and MRP but not BCRP. Treatment with TAT-PDZ1 peptide (>1 pM) resulted in significantly higher CDF accumulation in HepG2 cells, which persisted for ≥180 min after TAT-PDZ1 peptide treatment. These results imply that EBP50 can modulate ET activities. To our knowledge, this is the first report on using a competitive peptide to modulate interactions between MRP and EBP50.

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.

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.

Proteins Regulating Microvesicle Biogenesis and Multidrug Resistance in Cancer

Microvesicles (MV) are emerging as important mediators of intercellular communication. While MVs are important signaling vectors for many physiological processes, they are also implicated in cancer pathology and progression. Cellular activation is perhaps the most widely reported initiator of MV biogenesis, however, the precise mechanism remains undefined. Uncovering the proteins involved in regulating MV biogenesis is of interest given their role in the dissemination of deleterious cancer traits. MVs shed from drug-resistant cancer cells transfer multidrug resistance (MDR) proteins to drug-sensitive cells and confer the MDR phenotype in a matter of hours. MDR is attributed to the overexpression of ABC transporters, primarily P-glycoprotein and MRP1. Their expression and functionality is dependent on a number of proteins. In particular, FERM domain proteins have been implicated in supporting the functionality of efflux transporters in drug-resistant cells and in recipient cells during intercellular transfer by vesicles. Herein, the most recent research on the proteins involved in MV biogenesis and in the dissemination of MV-mediated MDR are discussed. Attention is drawn to unanswered questions in the literature that may prove to be of benefit in ongoing efforts to improve clinical response to chemotherapy and circumventing MDR.

Recent Advances in the Studies of Molecular Mechanisms Regulating Multidrug Resistance in Cancer Cells

Here we present new approaches to better understanding multidrug resistance (MDR) development in cancer cells, such as identification of components of a complex process of MDR evolution. Recent advances in the studies of MDR are discussed: 1) chemotherapy agents might be involved in the selection of cancer stem cells resulting in the elevated drug resistance and enhanced tumorigenicity; 2) cell-cell interactions have a great effect on the MDR emergence and evolution; 3) mechanotransduction is an important signaling mechanism in cell-cell interactions; 4) proteins of the ABC transporter family which are often involved in MDR might be transferred between cells via microvesicles (epigenetic MDR regulation); 5) proteins providing cell-to-cell transfer of functional P-glycoprotein (MDR1 protein) via microvesicles have been investigated; 6) P-glycoprotein may serve to regulate apoptosis, as well as transcription and translation of target genes/proteins. Although proving once again that MDR is a complex multi-faceted process, these data open new approaches to overcoming it.

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.

Proteins regulating the intercellular transfer and function of P-glycoprotein in multidrug-resistant cancer

Chemotherapy is an essential part of anticancer treatment. However, the overexpression of P-glycoprotein (P-gp) and the subsequent emergence of multidrug resistance (MDR) hampers successful treatment clinically. P-gp is a multidrug efflux transporter that functions to protect cells from xenobiotics by exporting them out from the plasma membrane to the extracellular space. P-gp inhibitors have been developed in an attempt to overcome P-gp-mediated MDR; however, lack of specificity and dose limiting toxicity have limited their effectiveness clinically. Recent studies report on accessory proteins that either directly or indirectly regulate P-gp expression and function and which are necessary for the establishment of the functional phenotype in cancer cells. This review discusses the role of these proteins, some of which have been recently proposed to comprise an interactive complex, and discusses their contribution towards MDR. We also discuss the role of other pathways and proteins in regulating P-gp expression in cells. The potential for these proteins as novel therapeutic targets provides new opportunities to circumvent MDR clinically.

The Effects of Fentanyl on Hepatic Mitochondrial Function

BACKGROUND

Remifentanil interferes with hepatic mitochondrial function. The aim of the present study was to evaluate whether hepatic mitochondrial function is affected by fentanyl, a more widely used opioid than remifentanil.

METHODS

Human hepatoma HepG2 cells were exposed to fentanyl or pretreated with naloxone (an opioid receptor antagonist) or 5-hydroxydecanoate (5-HD, an inhibitor of mitochondrial adenosine triphosphate (ATP)-sensitive potassium [mitoKATP] channels), followed by incubation with fentanyl. Mitochondrial function and metabolism were then analyzed.

RESULTS

Fentanyl marginally reduced maximal mitochondrial complex-specific respiration rates using exogenous substrates (decrease in medians: 11%-18%; P = 0.003-0.001) but did not affect basal cellular respiration rates (P = 0.834). The effect on stimulated respiration was prevented by preincubation with naloxone or 5-HD. Fentanyl reduced cellular ATP content in a dose-dependent manner (P < 0.001), an effect that was not significantly prevented by 5-HD and not explained by increased total ATPase concentration. However, in vitro ATPase activity of recombinant human permeability glycoprotein (an ATP-dependent drug efflux transporter) was significantly stimulated by fentanyl (P = 0.004).

CONCLUSIONS

Our data suggest that fentanyl reduces stimulated mitochondrial respiration of cultured human hepatocytes by a mechanism that is blocked by a mitoKATP channel antagonist. Increased energy requirements for fentanyl efflux transport may offer an explanation for the substantial decrease in cellular ATP concentration.

The Role of CD44 and ERM Proteins in Expression and Functionality of P-glycoprotein in Breast Cancer Cells

Multidrug resistance (MDR) is often attributed to the over-expression of P-glycoprotein (P-gp), which prevents the accumulation of anticancer drugs within cells by virtue of its active drug efflux capacity. We have previously described the intercellular transfer of P-gp via extracellular vesicles (EVs) and proposed the involvement of a unique protein complex in regulating this process. In this paper, we investigate the role of these mediators in the regulation of P-gp functionality and hence the acquisition of MDR following cell to cell transfer. By sequentially silencing the FERM domain-binding proteins, Ezrin, Radixin and Moesin (ERM), as well as CD44, which we also report a selective packaging in breast cancer derived EVs, we have established a role for these proteins, in particular Radixin and CD44, in influencing the P-gp-mediated MDR in whole cells. We also report for the first time the role of ERM proteins in the vesicular transfer of functional P-gp. Specifically, we demonstrate that intercellular membrane insertion is dependent on Ezrin and Moesin, whilst P-gp functionality is governed by the integrity of all ERM proteins in the recipient cell. This study identifies these candidate proteins as potential new therapeutic targets in circumventing MDR clinically.

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.

[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.

Vps11, a subunit of the tethering complexes HOPS and CORVET, is involved in regulation of glycolipid degradation and retrograde toxin transport

We recently reported that ERM (ezrin, radixin, moesin) proteins are involved in intracellular sorting of Shiga toxin (Stx) and its receptor globotriaosylceramide (Gb3), and that depletion of ezrin and moesin reduced retrograde Golgi transport of Stx. In the same study, we found that knockdown of Vps11, a core subunit of both the homotypic fusion and protein sorting (HOPS) complex and the class C core vacuole/endosome tethering factor (CORVET), increased retrograde transport of Stx and could counteract the inhibiting effect of moesin and ezrin knockdown. In this study we demonstrate that Vps11 knockdown also leads to increased Stx toxicity as well as increased retrograde transport and toxicity of ricin. Additionally, we show that knockdown of Vps11 restores the reduced Gb3 level observed after moesin depletion.

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.

Silence of ezrin modifies migration and actin cytoskeleton rearrangements and enhances chemosensitivity of lung cancer cells in vitro

Ezrin, primarily acts as a linker between the plasma membrane and the cytoskeleton, is involved in many cellular functions, including regulation of actin cytoskeleton, control of cell shape, adhesion, motility, and modulation of signaling pathways. Although ezrin is now recognized as a key component in tumor metastasis, its roles and the underlying mechanisms remain unclear. In the present study, we chose highly metastatic human lung carcinoma 95D cells, which highly express the ezrin proteins, as a model to examine the functional roles of ezrin in tumor suppression. An ezrin-silenced 95D cell line was established using lentivirus-mediated short hairpin RNA method. CCK-8 assay and soft agar assay analysis showed that downregulation of ezrin significantly suppressed the tumorigenicity and proliferation of 95D cells in vitro. cell migration and invasion studies showed that ezrin-specific deficiency in the cells caused the substantial reduction of the cell migration and invasion. In parallel, it also induced rearrangements of the actin cytoskeleton. Flow cytometry assay showed that changes in the ezrin protein level significantly affected the cell cycle distribution and eventual apoptosis. Furthermore, further studies showed that ezrin regulated the expression level of E-cadherin and CD44, which are key molecules involved in cell growth, migration, and invasion. Meanwhile, the suppression of ezrin expression also sensitized cells to antitumor drugs. Altogether, our results demonstrated that ezrin played an important role in the tumorigenicity and metastasis of lung cancer cells, which will benefit the development of therapeutic strategy for lung cancer.