Contribution of multidrug resistance-associated proteins (MRPs) to the release of prostanoids from A549 cells

Probenecid ameliorates testosterone-induced benign prostatic hyperplasia: Implications of PGE-2 on ADAM-17/EGFR/ERK1/2 signaling cascade

Benign prostatic hyperplasia (BPH) is one of the most prevalent clinical disorders in the elderly. Probenecid (Prob) is a well-known FDA-approved therapy for gout owing to its uricosuric effect. The present study evaluated the use of Prob for BPH as a COX-2 inhibitor. Prob (100 and 200 mg/kg) was intraperitoneally injected into male Wistar rats daily for 3 weeks. In the second week, testosterone (3 mg/kg) was subcutaneously injected to induce BPH. Compared with BPH-induced rats, Prob treatment reduced prostate weight and index and improved histopathological architecture. The protease activity of ADAM-17/TACE and its ligands (TGF-α and TNF-α) were regulated by prob, which in turn abolished EGFR phosphorylation, and several inflammatory mediators (COX-2, PGE2, NF-κB (p65), and IL-6) were suppressed. By reducing the nuclear import of extracellular regulated kinase protein 1/2 (ERK1/2), Prob helped re-establish the usual equilibrium between antiapoptotic proteins like Bcl-2 and cyclin D1 and proapoptotic proteins like Bax. All of these data point to Prob as a promising treatment for BPH because of its ability to inhibit COX-2-syntheiszed PGE2 and control the ADAM-17/TGF-α-induced EGFR/ERK1/2 signaling cascade. These findings might help to repurpose Prob for the treatment of BPH.

ABCC4 is a PGE2 efflux transporter in the ovarian follicle: A mediator of ovulation and a potential non-hormonal contraceptive target

The role of prostaglandins (PGs) in the ovulatory process is known. However, the role of the ATP binding cassette subfamily C member 4 (ABCC4), transmembrane PG carrier protein, in ovulation remains unknown. We report herein that ABCC4 expression is significantly upregulated in preovulatory human granulosa cells (GCs). We found that PGE2 efflux in cultured human GCs is mediated by ABCC4 thus regulating its extracellular concentration. The ABCC4 inhibitor probenecid demonstrated effective blocking of ovulation and affects key ovulatory genes in female mice in vivo. We postulate that the reduction in PGE2 efflux caused by the inhibition of ABCC4 activity in GCs decreases the extracellular concentration of PGE2 and its ovulatory effect. Treatment of female mice with low dose of probenecid as well as with the PTGS inhibitor indomethacin or Meloxicam synergistically blocks ovulation. These results support the hypothesis that ABCC4 has an important role in ovulation and might be a potential target for non-hormonal contraception, especially in combination with PGE2 synthesis inhibitors. These findings may fill the gap in understanding the role of ABCC4 in PGE2 signaling, enhance the understanding of ovulatory disorders, and facilitate the treatment and control of fertility.

Inside-out extracellular vesicles-like biomimetic magnetic nanoparticles for efficient screening P-Glycoprotein inhibitors to overcome cancer multidrug resistance

The discovery of P-Glycoprotein (P-gp) inhibitors to block chemotherapy drugs efflux is considered an attractive treatment strategy for overcoming cancer multidrug resistance (MDR). Cell membrane biomimetic platform has emerged as a promising candidate method for screening small molecule P-gp inhibitors from natural products. However, randomly oriented cell membrane coating does not guarantee the inward-opening conformation of P-gp, limiting the precise screening of P-gp inhibitors. Herein, inside-out orientation extracellular vesicles camouflaged magnetic nanoparticles (IOVMNPs) were prepared to discover P-gp inhibitors with low toxicity and high efficiency from natural products. The orientation of extracellular vesicles on the surface of IOVMNPs was rigorously confirmed by immunogold electron microscopy and sialic acid quantification assay. Finally, two potential P-gp inhibitors, honokiol and magnolol, were captured by obtained IOVMNPs. The effect of MDR reversal in combination with chemotherapy drugs was further verified by pharmacological activity experiments. The inside-out orientation extracellular vesicles encapsulation strategy provides an effective tool for the discovery of novel P-gp inhibitors from nature products, thus further extending the application field of orientation assembly cell membrane biomimetic magnetic nanoparticles. This inside-out extracellular vesicles coating also proposes a new concept for the assembly of cell membrane biomimetic platform.

[Transfer Mechanisms of Compounds between Mother and Fetus/Infant Aimed for Optimized Medication during Pregnancy and Breastfeeding]

Potential risks to the fetus or infant should be considered prior to medication during pregnancy and lactation. It is essential to evaluate the exposure levels of drugs and their related factors in addition to toxicological effects. Epilepsy is one of the most common neurological complications in pregnancy; some women continue to use antiepileptic drugs (AEDs) to control seizures. Benzodiazepines (BZDs) are widely prescribed for several women who experience symptoms such as anxiety and insomnia during the postpartum period. In this review, we describe the 1) transport mechanisms of AEDs across the placenta and the effects of these drugs on placental transporters, and 2) the transfer of BZDs into breast milk. Our findings indicated that carrier systems were involved in the uptake of gabapentin (GBP) and lamotrigine (LTG) in placental trophoblast cell lines. SLC7A5 was the main contributor to GBP transport in placental cells. LTG was transported by a carrier that was sensitive to chloroquine, imipramine, quinidine, and verapamil. Short-term exposure to 16 AEDs had no effect on folic acid uptake in placental cells. However, long-term exposure to valproic acid (VPA) affected the expression of folate carriers (FOLR1, SLC46A1). Furthermore, VPA administration changed the expression levels of various transporters in rat placenta, suggesting that sensitivity to VPA differed across gestational stages. Lastly, we developed a method for quantifying eight BZDs in human breast milk and plasma using LC/MS/MS, and successfully applied it to quantify alprazolam in breast milk and plasma donated by a lactating woman.

ATP-Binding Cassette Transporter C4 is a Prostaglandin D2 Exporter in HMC-1 cells

ATP-binding cassette transporter C4 (ABCC4) is associated with multidrug resistance and the regulation of cell signalling. Some prostaglandins (PGs), including: PGE₂, PGF_2α, PGE₃, and PGF_3α are known substrates of ABCC4, and are released from some types of cells to exert their biological effects. In the present study, we demonstrate that PGD₂ is a novel substrate of ABCC4 using a transport assay based on inside-out membrane vesicles prepared from ABCC4-overexpressing cells. Then, we used two types of cell lines with confirmed ABCC4 mRNA and PGD₂ release capacity (human mast cell lines HMC-1 cells and human rhabdomyosarcoma cell lines TE671 cells) to evaluate the contribution of ABCC4. The extracellular levels of PGD₂ were unchanged following addition of a selective ABCC4 inhibitor in TE671 cells. Pharmacological inhibition and knockdown of ABCC4 significantly reduced the extracellular levels of PGD₂ by at least 53% in HMC-1 cells. Moreover, the extracellular levels of PGD₂ decreased by at least 20% using the selective ABCC4 inhibitor in the other mast cell line RBL-2H3 cells. Therefore, our results suggest that ABCC4 functions as a PGD₂ exporter in HMC-1 cells.

Involvement of H+-gradient dependent transporter in PGE2 release from A549 cells

The purpose of this study was to identify the transporter involved in the release of prostaglandin E₂ (PGE₂). In the present study, transport assays were conducted using membrane vesicles prepared from human lung adenocarcinoma A549 cells, thus enabling identification of the novel exporter present in A549 cells. PGE₂ transport into A549 vesicles was higher in the presence of a proton (H⁺)-gradient, thus suggesting the involvement of PGE₂H⁺ symporter in PGE₂ transport. Results from our experiments showed enhanced PGE₂ release in A549 cells in the presence of H⁺-gradient ([H⁺]_{extracellular} < [H⁺]_{intracellular}). Moreover, in vesicular transport assays, H⁺-gradient-dependent transport of PGE₂ did not show saturation up to 500 μM PGE_2, and 10 mM aromatic monocarboxylic acids (acetylsalicylic acid, salicylic acid, and p-nitrobenzoic acid) significantly inhibited PGE₂ transport by 62-70%. These results suggest, the involvement of monocarboxylate transporters in the H⁺-gradient-dependent PGE₂ export.

MRP4/ABCC4 As a New Therapeutic Target: Meta-Analysis to Determine cAMP Binding Sites as a Tool for Drug Design

MRP4 transports multiple endogenous and exogenous substances and is critical not only for detoxification but also in the homeostasis of several signaling molecules. Its dysregulation has been reported in numerous pathological disorders, thus MRP4 appears as an attractive therapeutic target. However, the efficacy of MRP4 inhibitors is still controversial. The design of specific pharmacological agents with the ability to selectively modulate the activity of this transporter or modify its affinity to certain substrates represents a challenge in current medicine and chemical biology. The first step in the long process of drug rational design is to identify the therapeutic target and characterize the mechanism by which it affects the given pathology. In order to develop a pharmacological agent with high specific activity, the second step is to systematically study the structure of the target and identify all the possible binding sites. Using available homology models and mutagenesis assays, in this review we recapitulate the up-to-date knowledge about MRP structure and aligned amino acid sequences to identify the candidate MRP4 residues where cyclic nucleotides bind. We have also listed the most relevant MRP inhibitors studied to date, considering drug safety and specificity for MRP4 in particular. This meta-analysis platform may serve as a basis for the future development of inhibitors of MRP4 cAMP specific transport.

Analysis of membrane transport mechanisms of endogenous substrates using chromatographic techniques

Membrane transporters are expressed in various bodily tissues and play essential roles in the homeostasis of endogenous substances and the absortion, distribution and/or excretion of xenobiotics. For transporter assays, radioisotope-labeled compounds have been mainly used. However, commercially available radioisotope-labeled compounds are limited in number and relatively expensive. Chromatographic analyses such as high-performance liquid chromatography with ultraviolet absorptiometry and liquid chromatography with tandem mass spectrometry have also been applied for transport assays. To elucidate the transport properties of endogenous substrates, although there is no difficulty in performing assays using radioisotope-labeled probes, the endogenous background and the metabolism of the compound after its translocation across cell membranes must be considered when the intact compound is assayed. In this review, the current state of knowledge about the transport of endogenous substrates via membrane transporters as determined by chromatographic techniques is summarized. Chromatographic techniques have contributed to our understanding of the transport of endogenous substances including amino acids, catecholamines, bile acids, prostanoids and uremic toxins via membrane transporters.

Transporters MRP1 and MRP2 Regulate Opposing Inflammatory Signals To Control Transepithelial Neutrophil Migration during Streptococcus pneumoniae Lung Infection

Streptococcus pneumoniae is a Gram-positive bacterium that normally inhabits the human nasopharynx asymptomatically. However, it is also a major cause of pneumonia, bacteremia, and meningitis. The transition from pneumonia to bacteremia is critical, as patients that develop septicemia have ~20% mortality rates. Previous studies have shown that while neutrophils, a major bacterium-induced leukocyte, aid in S. pneumoniae elimination, they also contribute to pathology and may mediate the lung-to-blood passage of the bacteria. Herein, we show that epithelium-derived MRP1 and MRP2 efflux immunomodulatory agents that assist in controlling passage of neutrophils during infection and that limiting neutrophil infiltration produced less bacteremia and better survival during murine infection. The importance of our work is twofold: ours is the first to identify an MRP1/MRP2 axis of neutrophil control in the lung. The second is to provide possible therapeutic targets to reduce excess inflammation, thus reducing the chances of developing bacteremia during pneumococcal pneumonia.

Streptococcus pneumoniae remains a source of morbidity and mortality in both developed and underdeveloped nations of the world. Disease can manifest as pneumonia, bacteremia, and meningitis, depending on the localization of infection. Interestingly, there is a correlation in experimental murine infections between the development of bacteremia and influx of neutrophils into the pulmonary lumen. Reduction of this neutrophil influx has been shown to improve survivability during infection. In this study, we use in vitro biotinylation and neutrophil transmigration and in vivo murine infection to identify a system in which two epithelium-localized ATP-binding cassette transporters, MRP1 and MRP2, have inverse activities dictating neutrophil transmigration into the lumen of infected mouse lungs. MRP1 effluxes an anti-inflammatory molecule that maintains homeostasis in uninfected contexts, thus reducing neutrophil infiltration. During inflammatory events, however, MRP1 decreases and MRP2 both increases and effluxes the proinflammatory eicosanoid hepoxilin A3. If we then decrease MRP2 activity during experimental murine infection with S. pneumoniae, we reduce both neutrophil infiltration and bacteremia, showing that MRP2 coordinates this activity in the lung. We conclude that MRP1 assists in depression of polymorphonuclear cell (PMN) migration by effluxing a molecule that inhibits the proinflammatory effects of MRP2 activity.

IMPORTANCEStreptococcus pneumoniae is a Gram-positive bacterium that normally inhabits the human nasopharynx asymptomatically. However, it is also a major cause of pneumonia, bacteremia, and meningitis. The transition from pneumonia to bacteremia is critical, as patients that develop septicemia have ~20% mortality rates. Previous studies have shown that while neutrophils, a major bacterium-induced leukocyte, aid in S. pneumoniae elimination, they also contribute to pathology and may mediate the lung-to-blood passage of the bacteria. Herein, we show that epithelium-derived MRP1 and MRP2 efflux immunomodulatory agents that assist in controlling passage of neutrophils during infection and that limiting neutrophil infiltration produced less bacteremia and better survival during murine infection. The importance of our work is twofold: ours is the first to identify an MRP1/MRP2 axis of neutrophil control in the lung. The second is to provide possible therapeutic targets to reduce excess inflammation, thus reducing the chances of developing bacteremia during pneumococcal pneumonia.

Multiple drug resistance-associated protein (MRP4) exports prostaglandin E2 (PGE2) and contributes to metastasis in basal/triple negative breast cancer

Cyclooxygenase-2 (COX-2) and its primary enzymatic product, prostaglandin E2 (PGE2), are associated with a poor prognosis in breast cancer. In order to elucidate the factors contributing to intratumoral PGE₂ levels, we evaluated the expression of COX-2/PGE₂ pathway members MRP4, the prostaglandin transporter PGT, 15-PGDH (PGE₂ metabolism), the prostaglandin E receptor EP4, COX-1, and COX-2 in normal, luminal, and basal breast cancer cell lines. The pattern of protein expression varied by cell line reflecting breast cancer heterogeneity. Overall, basal cell lines expressed higher COX-2, higher MRP4, lower PGT, and lower 15-PGDH than luminal cell lines resulting in higher PGE₂ in the extracellular environment. Genetic or pharmacologic suppression of MRP4 expression or activity in basal cell lines led to less extracellular PGE₂. The key finding is that xenografts derived from a basal breast cancer cell line with stably suppressed MRP4 expression showed a marked decrease in spontaneous metastasis compared to cells with unaltered MRP4 expression. Growth properties of primary tumors were not altered by MRP4 manipulation. In addition to the well-established role of high COX-2 in promoting metastasis, these data identify an additional mechanism to achieve high PGE₂ in the tumor microenvironment; high MRP4, low PGT, and low 15-PGDH. MRP4 should be examined further as a potential therapeutic target in basal breast cancer.

Metabolomics analysis of multidrug-resistant breast cancer cellsin vitrousing methyl-tert-butyl ether method

MTBE-based cellular lipidomics to investigate the mechanisms of multidrug resistance of breast cancer.

The Pharmacological and Physiological Role of Multidrug-Resistant Protein 4

Multidrug-resistant protein 4 (MRP4), a member of the C subfamily of ATP-binding cassette transporters, is distributed in a variety of tissues and a number of cancers. As a drug transporter, MRP4 is responsible for the pharmacokinetics and pharmacodynamics of numerous drugs, especially antiviral drugs, antitumor drugs, and diuretics. In this regard, the functional role of MRP4 is affected by a number of factors, such as genetic mutations; tissue-specific transcriptional regulations; post-transcriptional regulations, including miRNAs and membrane internalization; and substrate competition. Unlike other C family members, MRP4 is in a pivotal position to transport cellular signaling molecules, through which it is tightly connected to the living activity and physiologic processes of cells and bodies. In the context of several cancers in which MRP4 is overexpressed, MRP4 inhibition shows striking effects against cancer progression and drug resistance. In this review, we describe the role of MRP4 more specifically in both healthy conditions and disease states, with an emphasis on its potential as a drug target.

Pannexin‑1 silencing inhibits the proliferation of U87‑MG cells

Pannexin‑1 (Panx‑1) is abundantly expressed in vertebrates and has been shown to assemble into high‑conductance single‑membrane channels, which are permeable to large molecules and regulate cellular function. However, the association between Panx‑1 and astrocyte proliferation is poorly understood. This study provides evidence for a difference in cell proliferation between wild‑type and Panx‑1‑knockdown cells. Proliferation of the U87‑MG malignant glioma cell line was reduced following transfection with Panx‑1‑short interfering RNA. In addition, treatment with the Panx‑1 activator, adenosine triphosphate, significantly reduced cell proliferation at 48 h in Panx‑1‑knockdown cells compared with wild type cells. In conclusion, on the basis of the present findings, Panx‑1 is likely to be important in the regulation of U87‑MG cell proliferation. This provides further support for the hypothesis that there is a correlation between Panx‑1 expression and U87‑MG cell proliferation.

Multiple drug resistance-associated protein 4 (MRP4), prostaglandin transporter (PGT), and 15-hydroxyprostaglandin dehydrogenase (15-PGDH) as determinants of PGE2 levels in cancer

The cyclooxygenase-2 (COX-2) enzyme and major lipid product, prostaglandin E2 (PGE2) are elevated in many solid tumors including those of the breast and are associated with a poor prognosis. Targeting this enzyme is somewhat effective in preventing tumor progression, but is associated with cardiotoxic secondary effects when used chronically. PGE2 functions by signaling through four EP receptors (EP1-4), resulting in several different cellular responses, many of which are pro-tumorigenic, and there is growing interest in the therapeutic potential of targeting EP4 and EP2. Other members in this signaling pathway are gaining more attention. PGE2 is transported out of and into cells by two unique transport proteins. Multiple Drug Resistance-Associated Protein 4 (MRP4) and Prostaglandin Transporter (PGT) modulate PGE2 signaling by increasing or decreasing the levels of PGE2 available to cells. 15-hydroxyprostaglandin dehydrogenase (15-PGDH) metabolizes PGE2 and silences the pathway in this manner. The purpose of this review is to summarize the extensive data supporting the importance of the COX-2 pathway in tumor biology with a focus on more recently described pathway members and their role in modulating PGE2 signaling. This review describes evidence supporting roles for MRP4, PGT and 15-PGDH in several tumor types with an emphasis on the roles of these proteins in breast cancer. Defining the importance of these latter pathway members will be key to developing new therapeutic approaches that exploit the tumor-promoting COX-2 pathway.

Transport of eicosapentaenoic acid-derived PGE₃, PGF(3α), and TXB₃ by ABCC4

Background

Eicosapentaenoic acid-derived prostaglandin (PG) E₃, PGF_3α, and thromboxane (TX) B₃ are bioactive lipid mediators which have anti-cancer and anti-inflammatory effects. To exert their effects, PGE₃, PGF_3α, and TXB₃ must be released to the extracellular space from cells, but the release mechanism has been unclear. We therefore investigated the contribution of ATP-binding cassette transporter C4 (ABCC4), which has been known as a prostanoids efflux transporter, to the release of PGE₃, PGF_3α, and TXB₃.

Materials and Methods

ATP-dependent transport of PGE₃, PGF_3α, and TXB₃ via ABCC4 was investigated by using inside-out membrane vesicles prepared from ABCC4-overexpressing HEK293 cells. To evaluate the contribution of ABCC4 to the release of PGE₃, PGF_3α, and TXB₃, we measured the extracellular and intracellular levels of PGE₃, PGF_3α, and TXB₃ in A549 cells when we used ABCC4 inhibitors (dipyridamole, MK571, and probenecid) or ABCC4 siRNAs. The quantification of PGE₃, PGF_3α, and TXB₃ was performed by using liquid chromatography-tandem mass spectrometry.

Results

The apparent K_m values for ABCC4-mediated transport were 2.9±0.1 µM for PGE₃, 12.1±1.3 µM for PGF_3α, and 11.9±1.4 µM for TXB₃ and the ATP-dependent accumulation of PGE₃, PGF_3α, and TXB₃ into vesicles was decreased by using typical substrates and inhibitors of ABCC4. ABCC4 inhibitors and ABCC4 knockdown showed the reduction of extracellular/intracellular ratio of PGE₃ (40–60% of control) and PGF_3α (60–80% of control) in A549 cells.

Conclusions

Our results suggest that PGE₃, PGF_3α, and TXB₃ are substrates of ABCC4 and ABCC4 partially contributes to the release of PGE₃ and PGF_3α.

Quantification of intracellular and extracellular eicosapentaenoic acid-derived 3-series prostanoids by liquid chromatography/electrospray ionization tandem mass spectrometry

3-Series prostanoids are bioactive lipid mediators synthesized from eicosapentaenoic acid (EPA). Determination of intracellular and extracellular levels of prostanoids is needed to elucidate the mechanism of action, and we therefore developed a method for quantification of intracellular and extracellular levels of 3-series prostanoids (including prostaglandin E3 (PGE3), PGD3, PGF3α, thromboxane B3 (TXB3), and Δ(17)-6-keto PGF1α) by using liquid chromatography/electrospray ionization tandem mass spectrometry. The separation of prostanoids was performed with a CAPCELL PAK C18 MG II column (2.0mm×150mm, 3µm) with an isocratic flow of acetonitrile/water/acetic acid (40:60:0.1, v/v/v). This method was validated for measurement of both extracellular and intracellular samples with high levels of precision and accuracy. We applied this method to human lung epithelial A549 cells stimulated with calcium ionophore A23187 under the condition of arachidonic acid or EPA treatment and we could measure PGE3 in both intracellular and extracellular samples.