Multidrug resistance protein 5 affects cell proliferation, migration and gemcitabine sensitivity in pancreatic cancer MIA Paca‑2 and PANC‑1 cells

Gemcitabine‑based chemotherapy has been widely adopted as the standard and preferred chemotherapy regimen for treating advanced pancreatic cancer. However, the contribution of multidrug resistance protein 5 (MRP5) to gemcitabine resistance and pancreatic cancer progression remains controversial. In the present study, the effect of silencing MRP5 on gemcitabine resistance and cell proliferation and migration of human pancreatic cancer MIA Paca‑2 and PANC‑1 cells was investigated by using short‑hairpin RNA delivered by lentiviral vector transduction. The knockdown of MRP5 was confirmed on both mRNA and protein levels using qPCR and surface staining assays, respectively. MRP5‑regulated gemcitabine sensitivity was assessed by MTT, PrestoBlue and apoptosis assays. The effect of MRP5 on pancreatic cancer cell proliferation and migration was determined using colony‑formation, wound‑healing and Transwell migration assays. The interaction of gemcitabine and cyclic guanosine monophosphate (cGMP) with MRP5 protein was explored using molecular docking. The results indicated that the MRP5 mRNA and protein levels were significantly reduced in all the MIA Paca‑2 and PANC‑1 clones. MRP5 affected gemcitabine cytotoxicity and the rate of gemcitabine‑induced apoptosis. Silencing MRP5 decreased cell proliferation and migration in both MIA Paca‑2 and PANC‑1 cells. Docking studies showed high binding affinity of cGMP towards MRP5, indicating the potential of MRP5‑mediated cGMP accumulation in the microenvironment. In conclusion, MRP5 has an important role in cancer proliferation and migration in addition to its drug efflux functions in two widely available pancreatic tumour cell lines (MIA Paca‑2 and PANC‑1).

Inhibition of multidrug resistance proteins by MK571 restored the erectile function in obese mice through cGMP accumulation

BACKGROUND

Intracellular levels of cyclic nucleotides can also be controlled by the action of multidrug resistance protein types 4 (MRP4) and 5 (MRP5). To date, no studies evaluated the role of their inhibition in an animal model of erectile dysfunction (ED).

OBJECTIVES

To evaluate the effect of a 2-week treatment with MK571, an inhibitor of the efflux of cyclic nucleotides in the ED of obese mice.

MATERIALS AND METHODS

Mice were divided in three groups: (i) lean, (ii) obese, and (iii) obese + MK571. The corpus cavernosum (CC) were isolated, and concentration-response curves to acetylcholine (ACh), sodium nitroprusside (SNP), and tadalafil in addition to electrical field stimulation (EFS) were carried out in phenylephrine pre-contracted tissues. Expression of ABCC4 and ABCC5, intracellular levels of cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP), the protein levels for pVASP^Ser157 and pVASP^Ser239 , and the intracavernous pressure (ICP) were also determined. The intracellular and extracellular (supernatant) ratios in CC from obese and lean stimulated with a cGMP-increasing substance (BAY 58-2667) in the absence and presence of MK571 (20 μM, 30 min) were also assessed.

RESULTS

The treatment with MK571 completely reversed the lower relaxing responses induced by EFS, ACh, SNP, and tadalafil observed in obese mice CC in comparison with untreated obese mice. Cyclic GMP and p-VASP^Ser239 expression were significantly reduced in CC from obese groups. MK571 promoted a sixfold increase in cGMP without interfering in the protein expression of p-VASP^Ser239 . Neither the cAMP levels nor p-VASP^Ser157 were altered in MK571-treated animals. The ICP was ∼50% lower in obese than in the lean mice; however, the treatment with MK571 fully reversed this response. Expressions of ABCC4 and ABCC5 were not different between groups. The intra/extracellular ratio of cGMP was similar in CC from obese and lean mice stimulated with BAY 58-2667.

CONCLUSIONS

The MRPs inhibition by MK571 favored the accumulation of cGMP in the smooth muscle cells, thus improving the smooth muscle relaxation and the erectile function in obese mice.

The potential involvement of MRP5 pump in urethral dysfunction in streptozotocin-induced diabetic rats

PURPOSE

To examine the effects of i.v. administration of MK-571, a MRP4/5 pump inhibitor, on urethral function in the urethane-anesthetized rat, and the changes of urethral multidrug resistance protein 5 (MRP5) pump in streptozotocin (STZ)-induced diabetes mellitus (DM) rats.

METHODS

Isovolumetric cystometry and urethral perfusion pressure (UPP) measurements were carried out in normal control (NC) group and 8week DM groups under urethane anesthesia. When stable rhythmic bladder contractions were showed, UPP parameters were recorded after successive administration of various dose of MK-571. Additionally, urethral cyclic guanosine monophosphate (cGMP) protein level was evaluated by ELISA, and changes of MRP5 pump and neurogenic nitric oxide synthase (nNOs) in the urethra were examined with immunohistochemical staining and Western blot analysis.

RESULTS

In NC group, UPP_nadir was significantly decreased but UPP change increased after administration of MK-571, while no significant differences in UPP parameters were observed in 8-week DM group. Furthermore, urethral MRP5 protein level was up-regulated, whereas urethral cGMP and nNOS protein levels were down-regulated in 8-week DM group.

CONCLUSIONS

MK-571 could not restore NO-mediated urethral relaxation dysfunction in DM rats, which may be attributed to the up-regulation of urethral MRP5 pump, and thus decrease of intracellular cGMP concentration in the urethra. These novel results would be useful for a better understanding of DM-related lower urinary tract dysfunction LUT (LUTD). Also, they could be helpful to study the importance of MRP pumps in the control of urethral relaxation mechanisms under physiological and pathological states.

Inhibition of ABCC5-mediated cGMP transport by progesterone, testosterone and their analogues

The biodynamics and biokinetics of sex hormones are complex. In addition to the classical steroid receptors (nuclear receptors), these hormones act through several non-genomic mechanisms. Modulation of ABC-transporters by progesterone represents a non-genomic mechanism. In the present study, we employed inside out vesicles from human erythrocytes to characterize high affinity cGMP transport by ABCC5 (member 5 of the ATP-Binding Cassette subfamily C). Progesterone and testosterone inhibited the transport with respective K_i of 1.2 ± 0.3 and 2.0 ± 0.6 μmol/L. We used virtual ligand screening (VLS) to identify analogues to progesterone and testosterone. A large number of substances were screened in silico and the 19 most promising candidates were screened in vitro. Each substance was tested for a concentration of 10 μmol/L. The range of cGMP transport reduction was 21.5% to 86.2% for progesterone analogues and 8.6% to 93.8 % for testosterone analogues. Three of the most potent test compounds (TC) of each analogue class, in addition to progesterone and testosterone, were characterized for concentrations from 1 nanomol/L to 1 mmol/L. The progesterone analogues showed following K_i-values (μmol/L): TC-08: 0.61, TC-16: 0.66 and TC-15: 9.3. The K_i-values (μmol/L) for the testosterone analogues were: TC-18: 0.10, TC-07: 0.67 andTC-05: 2.0. The present study shows that VLS may be a versatile tool in the development of membrane transport modulating agents (MTMAs).

Phosphodiesterase 5 (PDE5) restricts intracellular cGMP accumulation during enterotoxigenic Escherichia coli infection

Diarrhea caused by enterotoxigenic Escherichia coli (ETEC) has a continuing impact on residents and travelers in underdeveloped countries. Both heat-labile (LT) and heat-stable (ST) enterotoxins contribute to pathophysiology via induction of cyclic nucleotide synthesis, and previous investigations focused on intracellular signal transduction rather than possible intercellular second messenger signaling. We modeled ETEC infection in human jejunal enteroid/organoid monolayers (HEM) and evaluated cyclic nucleotide pools, finding that intracellular cAMP was significantly increased but also underwent apical export, whereas cGMP was minimally retained intracellularly and predominantly effluxed into the basolateral space. LT and virulence factors including EatA, EtpA, and CfaE promoted ST release and enhanced ST-stimulated cGMP production. Intracellular cGMP was regulated by MK-571-sensitive export in addition to degradation by phosphodiesterase 5. HEMs had limited ST-induced intracellular cGMP accumulation compared to T84 or Caco-2 models. Cyclic nucleotide export/degradation demonstrates additional complexity in the mechanism of ETEC infection and may redirect understanding of diarrheal onset.

Identification and experimental confirmation of novel cGMP efflux inhibitors by virtual ligand screening of vardenafil-analogues

BACKGROUND

Clinical studies have reported overexpression of PDE5 and elevation of intracellular cyclic GMP in various types of cancer cells. ABCC5 transports cGMP out of the cells with high affinity. PDE5 inhibitors prevent both cellular metabolism and cGMP efflux by inhibiting ABCC5 as well as PDE5. Increasing intracellular cGMP is hypothesized to promote apoptosis and growth restriction in tumor cells and also has potential for clinical use in treatment of cardiovascular disease and erectile dysfunction. Vardenafil is a potent inhibitor of both PDE5 and ABCC5-mediated cGMP cellular efflux. Nineteen novel vardenafil analogs that have been predicted as potent inhibitors by VLS were chosen for tests of their ability to inhibit ATP- dependent transport of cGMP by measuring the accumulation of cyclic GMP in inside-out vesicles.

AIM

In this study, we investigated the ability of nineteen new compounds to inhibit ABCC5- mediated cGMP transport. We also determined the Ki values of the six most potent compounds.

METHODS

Preparation of human erythrocyte inside out vesicles and transport assay.

RESULTS

Ki values for six of nineteen compounds that showed more than 50 % inhibition of cGMP transport in the screening test were determined and ranged from 1.1 to 23.1 μM. One compound was significantly more potent than the positive control, sildenafil.

CONCLUSION

Our findings show that computational screening correctly identified vardenafil-analogues that potently inhibit cGMP efflux-pumps from cytosol and could have substantial clinical potential in treatment of patients with diverse disorders.

Suppression of pancreatic adenocarcinoma upregulated factor (PAUF) increases the sensitivity of pancreatic cancer to gemcitabine and 5FU, and inhibits the formation of pancreatic cancer stem like cells

Pancreatic cancer stem cells (CSCs) play a crucial role in tumorigenesis and chemoresistance of pancreatic ductal adenocarcinoma. Pancreatic adenocarcinoma up-regulated factor (PAUF), a novel secretory protein, has been shown to contribute to cancer progression and metastasis. Because the clinical relationship between PAUF and pancreatic CSCs is largely unknown, we investigated the associations between the functional role of PAUF and pancreatic CSCs. Pancreatic cancer sphere cultured from the CFPAC-1 cells showed elevated expression of PAUF and pluripotent stemness genes (Oct4, Nanog, Stat3, and Sox2), and the mRNA of PAUF were increased in CD44⁺CD24⁺ESA⁺ pancreatic CSCs. PAUF knockdown (shPAUF) CFPAC-1 diminished the number of spheres and decreased stemness genes and CSC surface markers (CD133, c-MET and ALDH1). In addition, siPAUF CFPAC-1 decreased the mRNA expression of multidrug resistant protein 5 (MRP5) and ribonucleotide reductase M2 (RRM2) and were more vulnerable to gemcitabine and 5-FU than negative control (p<0.05). In conclusion, PAUF was increased in pancreatic CSCs and the suppression of PAUF enhances chemotherapeutic response to gemcitabine and 5FU by decreasing MRP5 and RRM2 in pancreatic cancer cells.

ATP-binding Cassette Subfamily C Member 5 (ABCC5) Functions as an Efflux Transporter of Glutamate Conjugates and Analogs

The ubiquitous efflux transporter ABCC5 (ATP-binding cassette subfamily C member 5) is present at high levels in the blood-brain barrier, neurons, and glia, but its in vivo substrates and function are not known. Using untargeted metabolomic screens, we show that Abcc5(-/-) mice accumulate endogenous glutamate conjugates in several tissues, but brain in particular. The abundant neurotransmitter N-acetylaspartylglutamate was 2.4-fold higher in Abcc5(-/-) brain. The metabolites that accumulated in Abcc5(-/-) tissues were depleted in cultured cells that overexpressed human ABCC5. In a vesicular membrane transport assay, ABCC5 also transported exogenous glutamate analogs, like the classic excitotoxic neurotoxins kainic acid, domoic acid, and NMDA; the therapeutic glutamate analog ZJ43; and, as previously shown, the anti-cancer drug methotrexate. Glutamate conjugates and analogs are of physiological relevance because they can affect the function of glutamate, the principal excitatory neurotransmitter in the brain. After CO2 asphyxiation, several immediate early genes were expressed at lower levels in Abcc5(-/-) brains than in wild type brains, suggesting altered glutamate signaling. Our results show that ABCC5 is a general glutamate conjugate and analog transporter that affects the disposition of endogenous metabolites, toxins, and drugs.

ABCC5 is required for cAMP-mediated hindgut invagination in sea urchin embryos

ATP-binding cassette (ABC) transporters are evolutionarily conserved proteins that pump diverse substrates across membranes. Many are known to efflux signaling molecules and are extensively expressed during development. However, the role of transporters in moving extracellular signals that regulate embryogenesis is largely unexplored. Here, we show that a mesodermal ABCC (MRP) transporter is necessary for endodermal gut morphogenesis in sea urchin embryos. This transporter, Sp-ABCC5a (C5a), is expressed in pigment cells and their precursors, which are a subset of the non-skeletogenic mesoderm (NSM) cells. C5a expression depends on Delta/Notch signaling from skeletogenic mesoderm and is downstream of Gcm in the aboral NSM gene regulatory network. Long-term imaging of development reveals that C5a knockdown embryos gastrulate, but ∼90% develop a prolapse of the hindgut by the late prism stage (∼8 h after C5a protein expression normally peaks). Since C5a orthologs efflux cyclic nucleotides, and cAMP-dependent protein kinase (Sp-CAPK/PKA) is expressed in pigment cells, we examined whether C5a could be involved in gastrulation through cAMP transport. Consistent with this hypothesis, membrane-permeable pCPT-cAMP rescues the prolapse phenotype in C5a knockdown embryos, and causes archenteron hyper-invagination in control embryos. In addition, the cAMP-producing enzyme soluble adenylyl cyclase (sAC) is expressed in pigment cells, and its inhibition impairs gastrulation. Together, our data support a model in which C5a transports sAC-derived cAMP from pigment cells to control late invagination of the hindgut. Little is known about the ancestral functions of ABCC5/MRP5 transporters, and this study reveals a novel role for these proteins in mesoderm-endoderm signaling during embryogenesis.

N-lactoyl-amino acids are ubiquitous metabolites that originate from CNDP2-mediated reverse proteolysis of lactate and amino acids

Despite technological advances in metabolomics, large parts of the human metabolome are still unexplored. In an untargeted metabolomics screen aiming to identify substrates of the orphan transporter ATP-binding cassette subfamily C member 5 (ABCC5), we identified a class of mammalian metabolites, N-lactoyl-amino acids. Using parallel protein fractionation in conjunction with shotgun proteomics on fractions containing N-lactoyl-Phe-forming activity, we unexpectedly found that a protease, cytosolic nonspecific dipeptidase 2 (CNDP2), catalyzes their formation. N-lactoyl-amino acids are ubiquitous pseudodipeptides of lactic acid and amino acids that are rapidly formed by reverse proteolysis, a process previously considered to be negligible in vivo. The plasma levels of these metabolites strongly correlate with plasma levels of lactate and amino acid, as shown by increased levels after physical exercise and in patients with phenylketonuria who suffer from elevated Phe levels. Our approach to identify unknown metabolites and their biosynthesis has general applicability in the further exploration of the human metabolome.

Chrysin enhances sensitivity of BEL-7402/ADM cells to doxorubicin by suppressing PI3K/Akt/Nrf2 and ERK/Nrf2 pathway

Nuclear factor-E2-related factor 2 (Nrf2) is an important cytoprotective transcription factor which plays a key role in antioxidant and detoxification processes. Recent studies have reported that development of chemoresistance is associated with the constitutive activation of the Nrf2-mediated signaling pathway in many types of cancer cells. Here, we investigated whether Nrf2 was associated with drug resistant in doxorubicin resistant BEL-7402 (BEL-7402/ADM) cells, and if chrysin could reverse drug resistance in BEL-7402/ADM cells. We found that remarkable higher level of Nrf2 and its target proteins in BEL-7402/ADM cells compared to BEL-7402 cells. Similarly, intracellular Nrf2 protein level was significantly decreased and ADM resistance was partially reversed by Nrf2 siRNA in BEL-7402/ADM cells. chrysin is a potent Nrf2 inhibitor which sensitizes BEL-7402/ADM cells to ADM and increases intracellular concentration of ADM. Mechanistically, chrysin significantly reduced Nrf2 expression at both the mRNA and protein levels through down-regulating PI3K-Akt and ERK pathway. Consequently, expression of Nrf2-downstream genes HO-1, AKR1B10, and MRP5 were reduced and the Nrf2-dependent chemoresistance was suppressed. In conclusion, these results clearly indicate that activation of Nrf2 is associated with drug resistance in BEL-7402/ADM cells and chrysin may be an effective adjuvant sensitizer to reduce anticancer drug resistance by down-regulating Nrf2 signaling pathway.

Curcumin analogue identified as hyaluronan export inhibitor by virtual docking to the ABC transporter MRP5

Hyaluronan is overproduced in many diseases including metastasis, inflammation or ischemia, but there is no drug to attenuate hyaluronan production. Hyaluronan is exported from fibroblasts by the multidrug resistance associated protein 5 (MRP5) which is inhibited by the plant phenols curcumin or xanthohumol. We performed virtual docking and chemical synthesis of analogues to optimize the inhibitors. The AutoDock software was used to identify the binding cavity within the open conformation of MRP5. Inhibitory plant phenols bound to the ATP binding site between the two nucleotide binding domains NBD1 and NBD2. This binding cavity was chosen to screen about 120 derivatives and analogues. The superior hyaluronan export inhibitor was 1,5-bis(4-hydroxy-3-methoxyphenyl)-1,4-pentadien-3-one (hylin). It inhibited hyaluronan export from fibroblasts with an IC50 of 4.9 μM. Hylin is a minor component in natural curcumin preparations and has previously been described as anti-metastatic and anti-inflammatory. Since curcumin itself is unstable under physiological conditions, the active component for many cell biological and pharmaceutical effects of natural curcumin preparations could be hylin that acts by hyaluronan export inhibition.

Differential expression of multidrug resistance protein 5 and phosphodiesterase 5 and regulation of cGMP levels in phasic and tonic smooth muscle

Previous studies have identified differences in the expression of proteins that regulate myosin light chain phosphorylation and contraction in tonic and phasic smooth muscle. cGMP plays a critical role in smooth muscle relaxation and is important for optimal function of phasic and tonic smooth muscle. The intracellular cGMP levels are regulated by its hydrolysis via phosphodiesterase 5 (PDE5) and efflux via novel multidrug resistance protein 5 (MRP5). In the present study we tested the hypothesis that the differences in the phasic and tonic behavior of smooth muscles may be related to differences in mechanisms that terminate cGMP signaling. Expression of PDE5 and MRP5 was significantly (more than 2-fold) higher in fundus compared with antrum. The NO donor S-nitrosoglutathione (GSNO) caused an increase in PDE5 activity and intra- and extracellular cGMP levels in both fundus and antrum. Stimulation of PDE5 activity and increase in extracellular cGMP were significantly higher in fundus, whereas increase in intracellular cGMP was significantly higher in antrum. GSNO-induced increase in extracellular cGMP was blocked in dispersed cells by the cyclic nucleotide export blocker probenecid and in cultured muscle cells by depletion of ATP or suppression of MRP5 by siRNA, providing evidence that cGMP efflux was mediated by ATP-dependent export via MRP5. Consistent with the higher expression and activity levels of PDE5 and MRP5, GSNO-induced PKG activity and muscle relaxation were significantly lower in muscle cells from fundus compared with antrum. Thus higher expression of PDE5 and MRP5 in muscle cells from fundus correlates with tonic phenotype of muscle.