Partial enrichment of a population of human limbal epithelial cells with putative stem cell properties based on collagen type IV adhesiveness

The concept that corneal epithelium stem cells reside in limbus has been recognized for more than a decade, but isolation of these stem cells has not been accomplished. This study was an initial attempt to isolate a population of human limbal epithelial cells enriched for certain putative stem cell properties based on their phenotype. Epithelial cells harvested from fresh human limbal rings and their primary cultures were allowed to adhere to collagen IV-coated dishes for 20 min and 2 hr, sequentially. The rapidly adherent cells (RAC), slowly adherent cells and non-adherent cells were evaluated for certain stem cell properties: (a) BrdU-label retention, (b) expression of basal cell (integrin beta1, p63, ABCG2) and differentiation (involucrin, keratin 12) markers, and (c) colony forming efficiency (CFE) and growth capacity on a 3T3 fibroblast feeder layer. Among unfractionated cells and the three selected populations, the RAC, accounting for about 10% of whole population, were enriched 5-fold in BrdU label-retaining cells, displayed the highest number of integrin beta1 and p63 positive and involucrin negative cells, expressed high levels of DeltaNp63 and ABCG2 mRNA, and lacked involucrin and K12 expression, and possessed the greatest CFE and growth capacity. These findings demonstrated for the first time that human limbal epithelial cells with stem cell properties can be partially enriched by their adhesiveness to collagen IV. The RAC population enriched for certain putative stem cell properties may prove useful in the future for transplantation to diseased and damaged corneas with limbal stem cell deficiency.

K ATP channels of primary human coronary artery endothelial cells consist of a heteromultimeric complex of Kir6.1, Kir6.2, and SUR2B subunits

Functional ATP-sensitive potassium (K(ATP)) channels can be reconstituted by expression of various combinations of different pore-forming subunits (Kir6.1 and Kir6.2) and sulfonylurea receptor (SUR) subunits. Using dominant negative and gene knockout approaches, Kir6.2 subunits have been identified as required pore-forming components of plasmalemmal K(ATP) channels in ventricular myocytes. Previous data obtained in heterologous expression systems suggest that Kir6.1 and Kir6.2 subunits are capable of forming a functional heteromultimeric channel complex. However, until now the existence of such heteromultimeric Kir6.1/Kir6.2 complexes has not been demonstrated for native K(ATP) channels. The primary aim of this study was to identify the molecular composition of native K(ATP) channels in primary human coronary artery endothelial cells (HCAEC) and smooth muscle cells (HCASMC) from human origin. We specifically investigated the potential that heteromultimeric Kir6.1/Kir6.2 channels exist in these cells. Using reverse transcriptase-polymerase chain reaction, we detected the expression of Kir6.1, Kir6.2, and SUR2B in both cell types. Western blotting and immunoprecipitation assays demonstrated the presence of Kir6.1 protein in both HCAEC and HCASMC; however, Kir6.2 protein was only expressed in HCAEC. Interaction between Kir6.1 and Kir6.2 subunits was demonstrated by reciprocal co-immunoprecipitation of these two subunits in HCAEC. Furthermore, Kir6.1 and Kir6.2 were detected in the immunoprecipitate when using an anti-SUR2 antibody. Confocal microscopy imaging demonstrated Kir6.1 and Kir6.2 subunits to co-localize at the cell surface membrane in HCAEC. In conclusion, our data characterize the molecular composition of primary human coronary smooth muscle and endothelial cells. We demonstrate that human coronary endothelial K(ATP) channels consist of a heteromultimeric complex of Kir6.1, Kir6.2, and SUR2B subunits.

Predictive Markers in Breast and Other Cancers: A Review

Background: Unpredictable efficacy and toxicity are hallmarks of most anticancer therapies. Predictive markers are factors that are associated with response or resistance to a particular therapy.

Methods: The English literature relating to predictive markers in oncology was reviewed. Particular attention was paid to metaanalyses, systematic reviews, prospective trials, and guidelines issued by expert panels.

Results: The prototype predictive tests in oncology are the estrogen receptor (ER) and progesterone receptor (PR), which are used to select patients with breast cancer likely to respond to hormone therapy. A more recently introduced predictive marker is HER-2 for selecting patients with advanced breast cancer for treatment with the therapeutic antibody trastuzumab (Herceptin). In adjuvant breast cancer, overproduction of HER-2 may also indicate an enhanced sensitivity to high-dose anthracycline-based regimens. On the other hand, in both early and advanced breast cancer, high concentrations of HER-2 appear to correlate with a lower probability of response to hormone therapy. Although many different anticancer drugs appear to mediate tumor regression by inducing apoptosis, there is currently no consistent evidence that any of the molecules implicated in this process can be used as predictive markers.

Conclusions: Currently, the only recommended predictive markers in oncology are ER and PR for selecting endocrine-sensitive breast cancers and HER-2 for identifying breast cancer patients with metastatic disease who may benefit from trastuzumab. For malignancies other than breast cancers, validated predictive markers do not exist at present.

ABC Transporters of Pathogenic Fungi: Recent Advances in Functional Analyses

ABC (ATP binding cassette) transporters consist of transmembrane domains which confer specificity, and structurally conserved nucleotide binding domains that contain highly conserved amino acid motifs. They act not only as transporters but also as receptors or channels that use energy generated by ATP hydrolysis. ABC transporters are widely dispersed in nature. They are found in cells ranging from prokaryotes (bacteria) to eukaryotes (including humans) and several are considered to play crucial roles in cellular homeostasis. Defects in ABC transporters in humans are associated with severe diseases such as type 2 diabetes and cystic fibrosis. Some ABC transporters extrude xenobiotics and confer resistance to chemotherapeutics on microbial pathogens and cancer cells. Thus ABC transporters are of considerable medical importance. Structure-function analysis of ABC transporters has begun to elucidate their mechanisms of substrate recognition, the functional regulation of ATP-binding and hydrolysis and to identify intrinsic physiological functions. In pathogenic fungi, ABC transporters contribute to the clinical problem of drug resistance. The application of new technologies to the examination of fungal ABC transporter function is providing new insights into the use of antifungal drugs in medical mycology and contributing to a better understanding of these important membrane proteins.

Distribution, lateral mobility and function of membrane proteins incorporated into giant unilamellar vesicles

GUVs have been widely used for studies on lipid mobility, membrane dynamics and lipid domain (raft) formation, using single molecule techniques like fluorescence correlation spectroscopy. Reports on membrane protein dynamics in these types of model membranes are by far less advanced due to the difficulty of incorporating proteins into GUVs in a functional state. We have used sucrose to prevent four distinct membrane protein(s) (complexes) from inactivating during the dehydration step of the GUV-formation process. The amount of sucrose was optimized such that the proteins retained 100% biological activity, and many proteo-GUVs were obtained. Although GUVs could be formed by hydration of lipid mixtures composed of neutral and anionic lipids, an alternate current electric field was required for GUV formation from neutral lipids. Distribution, lateral mobility, and function of an ATP-binding cassette transport system, an ion-linked transporter, and a mechanosensitive channel in GUVs were determined by confocal imaging, fluorescence correlation spectroscopy, patch-clamp measurements, and biochemical techniques. In addition, we show that sucrose slows down the lateral mobility of fluorescent lipid analogs, possibly due to hydrogen-bonding with the lipid headgroups, leading to larger complexes with reduced mobility.

Ethacrynic-acid-induced glutathione depletion and oxidative stress in normal and Mrp2-deficient rat liver

Oxidative stress in the liver is sometimes accompanied by cholestasis. We investigated the localization and role of multidrug-resistance-associated protein (Mrp) 2, a biliary transporter involved in bile-salt-independent bile flow, under ethacrynic acid (EA)-induced acute oxidative stress. Normal Sprague-Dawley rat (SDR) and Mrp2-deficient Eisai hyperbilirubinemic rat (EHBR) livers were perfused with 500 microM EA. The release of glutamic pyruvic transaminase (GPT) and thiobarbituric-acid-reactive substances (TBARS) from EHBR liver was markedly delayed compared with that from SDR liver. This is mainly due to the higher basal level of glutathione (GSH) in EHBR liver (59.1 +/- 0.3 nmol/mg protein) compared with SDR liver (39.7 +/- 1.5 nmol/mg protein). EA similarly induced a rapid reduction in GSH followed by mitochondrial permeability transition in the isolated mitochondria from both SDR and EHBR. Internalization of Mrp2 was detected before nonspecific disruption of the canalicular membrane and GPT release in SDR liver perfused with 100 microM EA. SDR liver preperfused with hyperosmolar buffer (405 mosmol/L) for 30 min induced internalization of Mrp2 without changing the basal GSH level, while elimination of hepatic GSH by 300 microM EA perfusion was significantly delayed thereafter. Concomitantly, hepatotoxicity assessed by the release of GPT and TBARS was also significantly attenuated under hyperosmolar conditions. In conclusion, preserved cytosolic and intramitochondrial GSH is the key factor involved in the acute hepatotoxicity induced by EA and its susceptibility could be altered by the presence of Mrp2.

The distribution of drug-efflux pumps, P-gp, BCRP, MRP1 and MRP2, in the normal blood-testis barrier and in primary testicular tumours

The drug-efflux pumps P-glycoprotein (P-gp) and multidrug resistance-associated protein 1 (MRP1) are present in the blood-testis barrier (BTB) and may hamper the delivery of cytotoxic drugs to the testis. The precise localisation of P-gp and MRP1 in testicular tissue and the presence of the efflux pumps MRP2 and breast cancer resistance protein (BCRP) in the BTB are unknown. We therefore studied the localisation of these pumps in the BTB in normal testis (n = 12), in non-seminoma (n = 10) seminoma (n = 10), and testicular lymphoma (n = 9). Slides were scored semi-quantitatively for P-gp, MRP1, MRP2 and BCRP and blood vessels with factor VIII antibody. In normal testis, P-gp and BCRP were strongly expressed by myoid cells and luminal capillary endothelial wall and P-gp also by Leydig cells. MRP1 was observed at the basal side of Sertoli cells and on Leydig cells. MRP2 was only weakly expressed by myoid cells. Seminomas and non-seminomas expressed P-gp and/or BCRP and/or MRP1, lymphomas strongly expressed P-gp, weakly expressed BCRP and did not or showed weak expression of MRP1. There was very little staining for MRP2 in the tumours. Newly formed vessels in all tumours only expressed P-gp and BCRP. P-gp, BCRP and MRP1 are present in different cell layers of the normal testis, suggesting the optimal protection of spermatogenesis. In germ cell tumours, this expression pattern may explain the chemoresistance observed to P-gp, BCRP and MRP1 substrates. In germ cell tumours and testicular lymphomas, P-gp and BCRP expression by tumour cells and by newly formed vessels may also contribute to chemoresistance. These findings underscore the importance of removing the affected testis in cases of primary germ cell tumours and testicular lymphomas, irrespective of whether the patient has already undergone chemotherapy.

On the hepatic mechanism of HDL assembly by the ABCA1/apoA-I pathway

The mechanism for the assembly of HDL with cellular lipid by ABCA1 and helical apolipoprotein was investigated in hepatocytes. Both HepG2 cells and mouse primary culture hepatocytes produced HDL with apolipoprotein A-I (apoA-I) whether endogenously synthesized or exogenously provided. Probucol, an ABCA1 inactivator, inhibited these reactions, as well as the reversible binding of apoA-I to HepG2. Primary cultured hepatocytes of ABCA1-deficient mice also lacked HDL production regardless of the presence of exogenous apoA-I. HepG2 cells secreted apoA-I into the medium even when ABCA1 was inactivated by probucol, but it was all in a free form as HDL production was inhibited. When a lipid-free apoA-I-specific monoclonal antibody, 725-1E2, was present in the culture medium, production of HDL was suppressed, whether with endogenous or exogenously added apoA-I, and the antibody did not influence HDL already produced by HepG2 cells. We conclude that the main mechanism for HDL assembly by endogenous apoA-I in HepG2 cells is an autocrine-like reaction in which apoA-I is secreted and then interacts with cellular ABCA1 to generate HDL.

Expression of Multiple Drug Resistance Conferring Proteins in Normal Chinese and Caucasian Small and Large Intestinal Tissue Samples

Multidrug resistance conferring proteins (MDRCP) are ATP-binding cassette (ABC) transporters known to significantly influence the absorption, distribution, metabolism, and elimination (ADME) and toxic behavior of many therapeutic agents. Research in the pharmacogenomics area has suggested that mutations and variable expression patterns of these MDCRPs may exist in tissue samples from different ethnic groups. The goal of this study was to examine the expression of P-glycoprotein (PGP), sister of PGP (S-PGP), multidrug resistance protein 3 (Mdr3), multidrug resistance like proteins 1-5 (MRP 1-5), and lung resistance associated protein (LRP) in tissue slides and protein lysates derived from normal adult small or large intestines of Caucasian or Chinese origin. Our results demonstrated ubiquitous expression of PGP, MRP 1, MRP 4, and LRP in the small and large intestinal epitheliums originating from both Caucasian and Chinese origin. S-PGP, Mdr3, MRP 2, and MRP 3 exhibited variable expression in the tissue slides and protein lysates derived from the Chinese and Caucasian small and large intestines. MRP 5 was not observed in any of the samples studied. The results suggest that MDCRPs may have distinct expression profiles in the small and large intestines that potentially vary with genetic background. These studies provide a foundation for further investigations to verify these findings across a wider number of patients of different ethnic backgrounds.

Breast cancer resistance protein impacts clinical outcome in platinum-based chemotherapy for advanced non-small cell lung cancer

PURPOSE

The purpose of this study was to investigate the relationship between the level of expression of ATP-binding cassette (ABC) transporter proteins, and response to chemotherapy and prognosis in advanced non-small cell lung cancer (NSCLC).

EXPERIMENTAL DESIGN

Expression of ABC transporter proteins, including P-glycoprotein, multidrug resistance protein (MRP) 1, MRP2, MRP3, and breast cancer resistance protein (BCRP), was examined immunohistochemically in 72 formalin-fixed tumor samples from untreated stage IIIB or IV NSCLC patients. All of the patients received platinum-based chemotherapy. Response to chemotherapy, progression-free survival (PFS), and overall survival were compared in relation to expression of each of the ABC transporter proteins and clinicopathological factors.

RESULTS

Expression of P-glycoprotein, MRP1, and MRP3 was not significantly associated with response to chemotherapy or survival. MRP2 expression was associated with overall survival (P = 0.002) but not with response to chemotherapy and PFS. By contrast, the response rate to chemotherapy of patients with BCRP-negative tumors was 44%, as opposed to 24% in patients with BCRP-positive tumors. Response rate was lower in BCRP-positive tumors, although this difference was not statistically significant (P = 0.08). BCRP-positive patients had also shorter PFS (P = 0.0003) and overall survival (P = 0.004) than BCRP-negative patients. Multivariate analysis confirmed BCRP status as an independent variable related to PFS (P = 0.001).

CONCLUSIONS

Positive immunostaining for BCRP appears to be a predictor of survival in patients with advanced NSCLC. These findings indicate that BCRP may serve as a molecular target for reducing drug resistance to chemotherapy in advanced NSCLC patients.

Plasma pharmacokinetics and tissue distribution of the breast cancer resistance protein (BCRP/ABCG2) inhibitor fumitremorgin C in SCID mice bearing T8 tumors

Multidrug resistance (MDR) remains a major obstacle in the treatment of human cancers. The recently discovered breast cancer resistance protein (BCRP/ABCG2) has been found to be an important mediator of chemotherapeutic MDR. Fumitremorgin C (FTC) is a selective and potent inhibitor of BCRP that completely inhibits and reverses BCRP-mediated resistance at micromolar concentrations. We report a study of the pharmacokinetics and tissue distribution of FTC when administered intravenously (IV) at a dose of 25 mg/kg to female SCID mice bearing the BCRP-overexpressing human ovarian xenograft Igrov1/T8 tumors. Plasma pharmacokinetics and tissue distribution of FTC in various organs and tissues were studied. In addition, the effect of FTC administration on the expression of BCRP in T8 tumors was also assessed by RT-PCR. Administration of a single FTC IV dose did not appear to cause any major toxicities. The resulting pharmacokinetic data were fit to a two-compartment model using NONMEM and the FTC clearance was determined to be 0.55 ml/min (25.0 ml/min/kg) with a 56% inter-animal variability. Area under the plasma concentration time curve was determined by Bailer's method and was calculated to be 1128+/-111 microg min/ml. FTC was widely distributed in all tissues assayed with highest concentrations found in lungs, liver and kidney in decreasing order, respectively. FTC did not appear to have any effect on the expression of BCRP in T8 tumors. Less than 2% of the administered dose was recovered in the urine and feces after 24 h, suggesting hepatic metabolism as a primary mechanism of elimination. The current study can be used as a basis for future animal or in vivo studies with FTC designed to further understand the impact of BCRP on drug resistance.

Profiling and comprehensive expression analysis of ABC transporter solute-binding proteins of Bacillus subtilis membrane based on a proteomic approach

We analyzed ABC transporter solute-binding proteins (SBPs) of the Bacillus subtilis membrane using a proteomic approach. We prepared a washed cell membrane fraction that was insoluble in 134 mM nondetergent sulfobetaine and then extracted proteins using mixtures of detergents in a stepwise manner. The membrane proteins were resolved by three two-dimensional polyacrylamide gel electrophoresis (2-D PAGE) or two one-dimensional (1-D) PAGE procedures, electroblotted, and digested in the presence of 5% or 80% acetonitrile. Thereafter, matrix-assisted laser desorption/ionization-time of flight-mass spectrometry (MALDI-TOF MS) identified 637 proteins corresponding to 15.9% of the total cellular proteins. We predicted that among these, 256 were membrane proteins, 101 were lipoproteins or secretory proteins and 280 were soluble proteins containing peripheral proteins that function in both the cytoplasm and the cell membrane such as SecA and FtsY. Among the 637 proteins, we identified 30 SBPs among 38 importers predicted by a bioinformatic search of the genome. We confirmed expression of the genes for the 30 SBPs using DNA microarray analysis. We compared the 2-D gel separation profiles of submembrane fractions solubilized by 1% n-dodecyl-beta-D-maltoside from cells cultured on Luria Bertani (LB), S7, and S7 medium without glutamate as well as DNA microarray data on LB and S7. The results suggested that YcdH, YtmK and YurO are binding proteins for Mn(++), glutamate and glucose, respectively, and that YqiX and YxeM are binding proteins for amino acids (tryptophan in S7 medium).

Enhanced efflux of cholesterol from ABCA1-expressing macrophages to serum from type IV hypertriglyceridemic subjects

Since elevated plasma triglycerides (TGs) are an independent cardiovascular risk factor, we have compared the cholesterol efflux potential of sera from asymptomatic hypertriglyceridemic (HTG) type IIb, type IV or normolipidemic (NLP) individuals using two different cell systems. In both type IIb and IV HTG, the efflux of cholesterol from SR-BI-rich Fu5AH cells was similar to that obtained with NLP. The maintenance of efflux efficiency in spite of reduced HDL-cholesterol levels can be mainly attributed to the relative enrichment of HDL with phospholipid. In the J774 macrophage cell system, pretreatment with cAMP, which upregulates ABCA1, induced a markedly higher increase in efflux to type IV sera compared with type IIb or NLP. In addition, type IV sera exhibited two-fold higher pre-beta HDL relative concentration (percentage of total apo AI) compared with NLP. Moreover, positive correlations were established between ABCA1-mediated efflux and the serum pre-beta HDL levels or TG concentrations. Thus, the hyperTGemia is associated with a higher fraction of apo AI recovered as pre-beta HDL which appear to be partly responsible for enhanced efflux obtained upon the cAMP stimulation of J774 cells. In conclusion, we demonstrated for the first time that the ABCA1-expressing J774 cell system is responsive to the percent of apo AI present in human serum as pre-beta HDL. Our results suggest that high-plasma TG, accompanied by low HDL may not result in an impaired cholesterol efflux capacity.

Reduced hepatic expression of farnesoid X receptor in hereditary cholestasis associated to mutation in ATP8B1

Farnesoid X receptor (FXR) is a transcription factor that controls bile acid homeostasis. The phenotype of Fxr null mice is characterized by hypercholanaemia, impaired secretion of bile acids and failure to thrive. Human disorders with these characteristics include FIC1 disease (caused by mutations in ATP8B1, which encodes a putative aminophospholipid translocase, FIC1, whose function in bile handling is unknown) and bile salt export pump (BSEP) disease (caused by mutation in ABCB11, which encodes BSEP, the primary canalicular bile salt export pump). We investigated the possibility of hepatic down-regulation of FXR in FIC1 disease and BSEP disease. Three siblings with this phenotype, born to consanguine parents, were initially studied. The children were demonstrated to be compound heterozygotes for missense and nonsense mutations in ATP8B1. Expression of specific genes in liver was analysed, comparing one of these siblings with a child homozygous for missense mutation in ABCB11, as well as with a child having idiopathic cholestatic liver disease, a child with extrahepatic biliary atresia and a normal organ donor. The expression of two main FXR isoforms was specifically decreased in the liver of the FIC1 disease patient. A consistent and concomitant reduction in messenger RNA levels of FXR targets, such as BSEP and small heterodimer partner, was also found. Gene-profiling experiments identified 163 transcripts whose expression changed significantly in FIC1-disease liver. Of note was that several genes involved in synthesis, conjugation and transport of bile acids were down-regulated. A cluster of genes involved in lipid metabolism was also differentially expressed. Our findings suggest that hepatic down-regulation of FXR contributes to the severe cholestasis of FIC1 disease.

Characterization of oligomeric human ATP binding cassette transporter A1. Potential implications for determining the structure of nascent high density lipoprotein particles

The oligomeric structure of ABCA1 transporter and its function related to the biogenesis of nascent apoA-I-containing particles (LpA-I) were investigated. Using n-dodecylmaltoside and perfluoro-octanoic acid combined with non-denaturing gel, the majority of ABCA1 was found as a tetramer in ABCA1-induced human fibroblasts. Furthermore, using chemical cross-linking and SDS-PAGE, ABCA1 dimers but not the tetramers were found covalently linked. Oligomeric ABCA1 was present in isolated plasma membranes as well as in intracellular compartments. Interestingly, apoA-I was found to be associated with both dimeric and tetrameric, but not monomeric, forms of ABCA1. Neither apoA-I nor lipid molecules did affect ABCA1 oligomerization. Immunoprecipitation analysis showed that oligomeric ABCA1 did not contain other associated proteins. We next investigated the relationship between the oligomeric ABCA1 complex and the structure of LpA-I. Lipid-free apoA-I incubated with normal cells generated LpA-I with diameters between 9.5 and 20 nm. Subsequent isolation of LpA-I followed by cross-linking revealed the presence of four and eight apoA-I molecules per particle, whereas apoA-I incubated with ABCA1 mutant (Q597R) cells was unable to form such particles and remained in the monomeric form. These results demonstrate that: 1) ABCA1 exists as an oligomeric complex; and 2) ABCA1 oligomerization was independent of apoA-I binding and lipid molecules. The findings that the majority of ABCA1 exists as a tetramer that binds apoA-I, together with the observation that LpA-I contains at least four molecules of apoA-I per particle, support the concept that the homotetrameric ABCA1 complex constitutes the minimum functional unit required for the biogenesis of high density lipoprotein particles.

Breast cancer resistance protein (BCRP/MXR/ABCG2) in acute myeloid leukemia: discordance between expression and function

Data on breast cancer resistance protein (BCRP, MXR, ABCG2) expression in acute myeloid leukemia (AML) have been inconsistent, possibly due to use of different assays in different studies. BCRP mRNA was studied by the reverse-transcription polymerase chain reaction and BCRP protein expression (BXP-21, BXP-34 or anti-ABCG2 antibody, with anti-CD34 and anti-CD33) and function (fumitremorgin C modulation of mitoxantrone retention) by flow cytometry in eight cell lines and in pretreatment blasts from 31 AML patients. BCRP mRNA levels, antibody staining and function correlated strongly in cell lines (Pearson r values, 0.73-0.97), but not in AML samples. AML sample BCRP mRNA levels were between those in parental 8226 and 35-fold mitoxantrone-resistant 8226/MR20 cells in all but one case, and BCRP mRNA had the wild-type sequence at codon 482 in all. In AML, unlike in cell lines, BCRP protein expression or function, when present, was only detected in small subpopulations. BCRP mRNA and protein expression did not correlate, nor did staining with different BCRP antibodies, and function did not correlate with mRNA nor protein expression. Presence of BCRP only in subpopulations and discordance among BCRP measurements suggest complex biology of BCRP in AML and incomplete modeling by cell lines.

Transporter associated protein expression in uveal melanoma

BACKGROUND/AIM

Transporter associated protein (TAP) is important for presenting peptides to major histocompatibility complex (MHC) class I molecules. Defects in TAP lead to decreased MHC class I expression. The immunoexpression of human leucocyte antigen (HLA) class I molecules and the TAP1 subunit were studied in primary uveal melanomas and correlated with the cell types and extrascleral extension.

METHODS

The HLA class I antigen and TAP1 subunit were analysed by immunoperoxidase staining with monoclonal antibodies on 45 primary uveal melanoma archival specimens. The tumours were divided into two groups-group A: tumours with no extrascleral extension; group B tumours with extrascleral extension/liver metastasis. Immunoanalysis was done by a semiquantitative method.

RESULTS

HLA class I antigen and TAP1 were decreased in 35 of 35 tumours with no extrascleral extension and positive in six of 10 tumours with liver metastasis. Decreased immunoexpression of HLA class I antigen and TAP1 in uveal melanomas with no extrascleral extension was significant (p<0.001). HLA class I antigen and TAP1 were negative in spindle cell melanomas (p<0.001).

CONCLUSIONS

HLA class I antigen and TAP1 expression were decreased in uveal melanomas with no extrascleral extension and in spindle cell melanomas. Decreased expression of TAP1 may lead to decreased expression of HLA class I antigen in uveal melanomas. This preliminary observation deserves further investigation, which may shed more light on the immune escape mechanisms of this tumour and thus enable novel therapeutic strategies.

Arabidopsis immunophilin-like TWD1 functionally interacts with vacuolar ABC transporters

Previously, the immunophilin-like protein TWD1 from Arabidopsis has been demonstrated to interact with the ABC transporters AtPGP1 and its closest homologue, AtPGP19. Physiological and biochemical investigation of pgp1/pgp19 and of twd1 plants suggested a regulatory role of TWD1 on AtPGP1/AtPGP19 transport activities. To further understand the dramatic pleiotropic phenotype that is caused by loss-of-function mutation of the TWD1 gene, we were interested in other TWD1 interacting proteins. AtMRP1, a multidrug resistance-associated (MRP/ABCC)-like ABC transporter, has been isolated in a yeast two-hybrid screen. We demonstrate molecular interaction between TWD1 and ABC transporters AtMRP1 and its closest homologue, AtMRP2. Unlike AtPGP1, AtMRP1 binds to the C-terminal tetratricopeptide repeat domain of TWD1, which is well known to mediate protein-protein interactions. Domain mapping proved that TWD1 binds to a motif of AtMRP1 that resembles calmodulin-binding motifs; and calmodulin binding to the C-terminus of MRP1 was verified. By membrane fractionation and GFP-tagging, we localized AtMRP1 to the central vacuolar membrane and the TWD1-AtMRP1 complex was verified in vivo by coimmunoprecipitation. We were able to demonstrate that TWD1 binds to isolated vacuoles and has a significant impact on the uptake of metolachlor-GS and estradiol-beta-glucuronide, well-known substrates of vacuolar transporters AtMRP1 and AtMRP2.

Folate Deprivation Results in the Loss of Breast Cancer Resistance Protein (BCRP/ABCG2) Expression

Breast cancer resistance protein (BCRP/ABCG2) is currently the only ABC transporter that exports mono- and polyglutamates of folates and methotrexate (MTX). Here we explored the relationship between cellular folate status and BCRP expression. Toward this end, MCF-7 breast cancer cells, with low BCRP and moderate multidrug resistance protein 1 (MRP1/ABCC1) levels, and their mitoxantrone (MR)-resistant MCF-7/MR subline, with BCRP overexpression and low MRP1 levels, were gradually deprived of folic acid from 2.3 microm to 3 nm resulting in the sublines MCF-7/LF and MCF-7/MR-LF. These cell lines expressed only residual BCRP mRNA and protein levels and retained a poor MRP2 (ABCC2) through MRP5 (ABCC5) expression. Furthermore, MCF-7/MR-LF cells also displayed 5-fold decreased MRP1 levels relative to MCF-7/MR cells. In contrast, BCRP overexpression was largely retained in MCF-7/MR cells grown in MR-free medium containing 2.3 microm folic acid. Loss of BCRP expression in MCF-7/LF and MCF-7/MR-LF cells resulted in the following: (a) a prominent decrease in the efflux of Hoechst 33342, a BCRP substrate; (b) an approximately 2-fold increase in MR accumulation as revealed by flow cytometry; this was accompanied by a 2.5- and approximately 84-fold increased MR sensitivity in these cell lines, respectively. Consistently, Ko143, a specific BCRP inhibitor, rendered MCF-7 and MCF-7/MR cells 2.1- and approximately 16.4-fold more sensitive to MR, respectively. Loss of BCRP expression also resulted in the following: (c) an identical MTX sensitivity in these cell lines thereby losing the approximately 28-fold MTX resistance of the MCF-7/MR cells; (d) an approximately 2-fold increase in the 4- and 24-h accumulation of [(3)H]folic acid. Furthermore, MCF-7/MR-LF cells displayed a significant increase in folylpoly-gamma-glutamate synthetase activity. Hence, consistent with the mono- and polyglutamate folate exporter function of BCRP, down-regulation of BCRP and increased folylpoly-gamma-glutamate synthetase activity appear to be crucial components of cellular adaptation to folate deficiency conditions. This is the first evidence for the possible role of BCRP in the maintenance of cellular folate homeostasis.

Intracellular trafficking of bile salt export pump (ABCB11) in polarized hepatic cells: constitutive cycling between the canalicular membrane and rab11-positive endosomes

The bile salt export pump (BSEP, ABCB11) couples ATP hydrolysis with transport of bile acids into the bile canaliculus of hepatocytes. Its localization in the apical canalicular membrane is physiologically regulated by the demand to secrete biliary components. To gain insight into how such localization is regulated, we studied the intracellular trafficking of BSEP tagged with yellow fluorescent protein (YFP) in polarized WIF-B9 cells. Confocal imaging revealed that BSEP-YFP was localized at the canalicular membrane and in tubulo-vesicular structures either adjacent to the microtubule-organizing center or widely distributed in the cytoplasm. In the latter two locations, BSEP-YFP colocalized with rab11, an endosomal marker. Selective photobleaching experiments revealed that single BSEP-YFP molecules resided in canalicular membranes only transiently before exchanging with intracellular BSEP-YFP pools. Such exchange was inhibited by microtubule and actin inhibitors and was unaffected by brefeldin A, dibutyryl cyclic AMP, taurocholate, or PI 3-kinase inhibitors. Intracellular carriers enriched in BSEP-YFP elongated and dissociated as tubular elements from a globular structure adjacent to the microtubule-organizing center. They displayed oscillatory movement toward either canalicular or basolateral membranes, but only fused with the canalicular membrane. The pathway between canalicular and intracellular membranes that BSEP constitutively cycles within could serve to regulate apical pools of BSEP as well as other apical membrane transporters.

Proteome analysis reveals disease-associated marker proteins to differentiate RA patients from other inflammatory joint diseases with the potential to monitor anti-TNFα therapy

New experimental approaches of molecular medicine such as transcriptome and proteome analysis have been implemented in rheumatology research. Two-dimensional gel electrophoresis in combination with mass spectrometry was used to visualize and to identify proteins in synovial fluid (SF) and plasma samples from patients with rheumatoid arthritis (RA) and osteoarthritis (OA). The small calcium binding protein S100A9 (MRP14) was identified as a discriminatory marker protein in SF by global proteomic analysis. To confirm these results and to examine the reproducibility and the applicability as a diagnostic marker, levels of the S100A8 (MRP8)/A9 (MRP14) heterocomplex in plasma and in synovial fluid were validated from patients with RA, OA, and other inflammatory joint diseases using enzyme immunoassay techniques. It was found that plasma levels of the S100A8/A9 heterocomplex correlate well with levels in SF, and hence, determination of plasma levels can be used to distinguish RA patients from patients with other inflammatory joint diseases, as well as from OA patients and controls. Initial studies on RA patients also indicate that plasma levels of the S100A8/A9 heterocomplex are a useful marker in monitoring anti TNFalpha therapy.

Development of sulfasalazine resistance in human T cells induces expression of the multidrug resistance transporter ABCG2 (BCRP) and augmented production of TNFalpha

OBJECTIVE

To determine whether overexpression of cell membrane associated drug efflux pumps belonging to the family of ATP binding cassette (ABC) proteins contributes to a diminished efficacy of sulfasalazine (SSZ) after prolonged cellular exposure to this disease modifying antirheumatic drug (DMARD).

METHODS

A model system of human T cells (CEM) was used to expose cells in vitro to increasing concentrations of SSZ for a period of six months. Cells were then characterised for the expression of drug efflux pumps: P-glycoprotein (Pgp, ABCB1), multidrug resistance protein 1 (MRP1, ABCC1), and breast cancer resistance protein (BCRP, ABCG2).

RESULTS

Prolonged exposure of CEM cells to SSZ provoked resistance to SSZ as manifested by a 6.4-fold diminished antiproliferative effect of SSZ compared with parental CEM cells. CEM cells resistant to SSZ (CEM/SSZ) showed a marked induction of ABCG2/BCRP, Pgp expression was not detectable, while MRP1 expression was even down regulated. A functional role of ABCG2 in SSZ resistance was demonstrated by 60% reversal of SSZ resistance by the ABCG2 blocker Ko143. Release of the proinflammatory cytokine tumour necrosis factor alpha (TNFalpha) was threefold higher in CEM/SSZ cells than in CEM cells. Moreover, twofold higher concentrations of SSZ were required to inhibit TNFalpha release from CEM/SSZ cells compared with CEM cells.

CONCLUSION

Collectively, ABCG2 induction, augmented TNFalpha release, and less efficient inhibition of TNFalpha production by SSZ may contribute to diminished efficacy after prolonged exposure to SSZ. These results warrant further clinical studies to verify whether drug efflux pumps, originally identified for their roles in cytostatic drug resistance, can also be induced by SSZ or other DMARDs.

A predicted ABC transporter, FtsEX, is needed for cell division in Escherichia coli

FtsE and FtsX have homology to the ABC transporter superfamily of proteins and appear to be widely conserved among bacteria. Early work implicated FtsEX in cell division in Escherichia coli, but this was subsequently challenged, in part because the division defects in ftsEX mutants are often salt remedial. Strain RG60 has an ftsE::kan null mutation that is polar onto ftsX. RG60 is mildly filamentous when grown in standard Luria-Bertani medium (LB), which contains 1% NaCl, but upon shift to LB with no NaCl growth and division stop. We found that FtsN localizes to potential division sites, albeit poorly, in RG60 grown in LB with 1% NaCl. We also found that in wild-type E. coli both FtsE and FtsX localize to the division site. Localization of FtsX was studied in detail and appeared to require FtsZ, FtsA, and ZipA, but not the downstream division proteins FtsK, FtsQ, FtsL, and FtsI. Consistent with this, in media lacking salt, FtsA and ZipA localized independently of FtsEX, but the downstream proteins did not. Finally, in the absence of salt, cells depleted of FtsEX stopped dividing before any change in growth rate (mass increase) was apparent. We conclude that FtsEX participates directly in the process of cell division and is important for assembly or stability of the septal ring, especially in salt-free media.

Antigen presentation and immune regulatory capacity of immature and mature-enriched antigen presenting (dendritic) cells derived from human bone marrow

Several reports including those from this laboratory have demonstrated that bone marrow cells (BMC) downregulate in vitro both mixed leukocyte reaction and cytotoxic T lymphocyte reactions. We consequently hypothesized that a general property of immature cells of hematopoietic organs is their ability to suppress immune reactivity. As one of these suppressive activities, the lack of costimulatory molecules was proposed as a mechanism by which immature antigen presenting cells of the bone marrow might be involved. In the present report, we used two culture environments, each of which would regulate a different maturation pattern of human bone marrow-derived enriched dendritic antigen presenting cells (DC or APC) to determine the respective effects on in vitro immune regulatory function. Human BMC depleted of CD3+ cells were cultured with either: interleukin-4 (IL-4) and granulocyte macrophage-colony stimulating factor (GM-CSF), to maintain DC-enriched populations in an immature state (iAPC); or an interferon-gamma (IFNgamma), tumor necrosis factor alpha (TNF-alpha), GM-CSF, LPS, and IL-6 cocktail to promote the maturation of DC-enriched APC (mAPC). These iAPC and mAPC were, respectively, phenotypically characterized and also tested in vitro for the following: (1) both direct and indirect-antigen presentation functions; (2) immune regulatory functions on the response of autologous and allogeneic peripheral blood lymphocytes (PBL); and (3) Western blot analysis determining the levels of both major histocompatibility complex (MHC) class I related cytoplasmic transporter molecules associated with antigen processing (TAP1) and as well as proteasome activator molecules (PA28alpha). The iAPC population expressed fewer dendritic cell markers (CD83 and DCsign), and costimulator molecules (CD86 and CD40) than the mAPC, such that there was an approximate threefold increase in expression of CD83, 2.5-fold increase in DCsign, and a threefold increase in CD40 and CD86 on mAPC than on iAPC (p=0.005 for CD83; p=0.001 for DCsign; p=0.001 for CD86; and p=0.001 for CD40). In lymphoproliferative assays, indirect and direct alloantigen presentation by iAPC was weaker than by mAPC (p=0.05 and 0.04). In addition, iAPC were able to downregulate allogeneic CTL responses. Also, after pulsing with Epstein-Barr virus (EBV) protein antigens, the iAPC were less efficient in their presentation to autologous EBV-specific T-cell lines, and caused an inhibition of EBV-CTL generation. The expression of TAP1 and PA28alpha was reduced in iAPC in comparison to mAPC. These findings support the notion that a maturation state of BMC-derived APC correlates with their capacity to present antigen. The observed in vitro deficiency of this function by immature bone marrow cells may therefore contribute to the immune downregulatory capacity seen in the BMC compartment.

Effect of mutated transporters associated with antigen-processing 2 on characteristic major histocompatibility complex binding peptides: analysis using electrospray ionization tandem mass spectrometry

A novel allele of transporters associated with the antigen-processing (TAP) 2 gene, TAP2*Bky2 (Val(577)), is significantly increased in Japanese patients with Sjögren's syndrome (SS), and has a strong association with SS-A/Ro autoantibody production in SS and autoantibody including anti-SS-A/Ro and anti-U1 RNP antibody in systemic lupus erythematosus (SLE). To determine the influence of this natural mutated TAP on peptides loaded onto MHC class I, we analyzed the repertoire of peptides loaded onto MHC class I on transfectants with TAP1 and TAP2 or mutated TAP2 by electrospray ionization tandem mass spectrometry (ESI-MS/MS). After comparison of the peptide profiles we identified three peptides from only mutated TAP transfectants. Moreover, one of these peptides is derived from snRNP A, which is a target for anti-U1 RNP antibody. To our knowledge this is the first report to show that the natural mutation of TAP2 changes the peptide profile loaded onto MHC class I molecules.