Identification of stem-like cells in head and neck cancer cell lines

This study investigated the existence of stem-like cells in established head and neck squamous cell carcinoma (HNSCC) lines, HSC3 and HSC4. Flow cytometric analysis confirmed the presence of side population (SP) cells excluding Hoechst 33342 in HSC4 cells (0.37+/-0.06%) but not HSC3 cells in a reserpine-sensitive manner. After sorting, the SP cells generated both SP and main population (MP) cells in culture while MP cells generated MP cells only. Higher expression of stem cell markers was detected in SP than in MP cells. These results suggest that cancer stem-like cells exist in head and neck squamous cell carcinoma.

A novel ABC transporter: the first insight into zebrafish (Danio rerio) ABCH1

Abch1 is a novel ATP binding cassette (ABC) transporter found in fish. This study represents an initial characterisation of this transporter using phylogenetic analyses, membrane topology prediction and determination of its tissue expression pattern in adult zebrafish (Danio rerio). Blast search showed that Abch1 orthologs are not present in genomes of other vertebrate taxa and similar genes are found only in invertebrate genomes. Abch1 is most closely related to the ABCG subfamily, although it shares only 12-14% of amino acid sequence identity with ABCG subfamily members. Topology analysis indicated that Abch1 is a half transporter that consists of six transmembrane domains with reverse domain arrangement (NBD-TMD), like ABCG subfamily members, but with differences in loop organization. Tissue distribution pattern revealed the highest Abch1 expression in brain, gills and kidney, followed by lower expression in intestine, gonads, skeletal muscle and liver. Considering moderate similarity in topology and tissue distribution pattern between Abch1 and ABCG subfamily members, we speculate that Abch1 is either involved in sterol transport similar to ABCG1, or is a part of the multidrug/multixenobiotic defence like ABCG2. These hypotheses remain to be addressed in further research.

Recurrence of bile salt export pump deficiency after liver transplantation

Severe bile salt export pump (BSEP) deficiency is a hereditary cholestatic condition that starts in infancy and leads to end-stage liver disease. Three children who underwent orthotopic liver transplantation for severe BSEP deficiency had post-transplantation episodes of cholestatic dysfunction that mimicked the original disease. Remission of all episodes was achieved by intensifying the immunosuppressive regimen. The phenotypic recurrence of the disease correlated with the presence of circulating high-titer antibodies against BSEP that inhibit transport by BSEP in vitro. When administered to rats, these antibodies targeted the bile canaliculi and impaired bile acid secretion.

Breast Cancer Resistance Protein (BCRP) in Acute Leukaemia

Multidrug resistance, cross-resistance to structurally and functionally unrelated drugs, is an important cause of treatment failure in acute leukemia. Multidrug resistance can result from the overexpression of ATP-dependent efflux pumps, such as P-glycoprotein and members of the multidrug resistance associated protein (MRP) family. Recently a novel transporter has been identified, which is called breast cancer resistance protein (BCRP), ABCG2 or mitoxantrone resistance protein. BCRP confers resistance to chemotherapeutic agents, such as mitoxantrone, doxorubicin and daunorubicin. This review describes BCRP detection techniques and the normal physiology of BCRP. The role of BCRP in the physiology of hematopoietic stem cells is addressed as well as the involvement of BCRP in multidrug resistance in acute leukemia. In AML and ALL, several studies showed that BCRP is expressed and functionally active at low, but variable levels. However, further studies are warranted to investigate its effect on clinical outcome, and explore whether patients could benefit from the combination of BCRP inhibitors and chemotherapy.

Characterisation of the hepatic progenitor cell compartment in normal liver and in hepatitis: an immunohistochemical comparison between dog and man

The liver progenitor cell compartment in the normal canine liver and in spontaneous canine acute (AH) and chronic hepatitis (CH) was morphologically characterised and compared to its human equivalents. Immunohistochemistry was performed for cytokeratin-7 (CK7), human hepatocyte marker (Hep Par 1), multidrug resistance-associated protein-2 (MRP2), and breast cancer resistance protein (BCRP) on paraffin and frozen sections from canine and human tissues. Normal liver showed similar morphology and immunohistochemical reaction of the progenitor cell compartment/canal of Hering in man and dog. In addition, a ductular reaction, comparable in terms of severity, location and immunohistochemical characteristics, was observed in canine and human AH and CH. CK7 was a good marker for canine progenitor cells, including intermediate cells, which were positively identified in cases of AH and CH. In both species, BCRP was expressed in both hepatocytes and bile ducts of the normal liver, and in ductular reaction in AH and CH. MRP2 detected bile canalicular membranes in man and dog. These findings underline the similarities between canine and human liver reaction patterns and may offer mutual advantage for comparative research in human and canine spontaneous liver diseases.

Proteomic analysis in the lichen Physcia adscendens exposed to cadmium stress

This work was undertaken to explore the potential of proteomics to dissect parallel and consecutive events of cadmium stress response in the lichen Physcia adscendens (Fr.) H. Olivier. Thalli were exposed to 0 (control) and 36 microM Cd for 6, 18, 24 and 48 h. Two-dimensional electrophoresis and mass spectrometry analyses showed an 80-85% spot identity between 6 and 18 h vs. 24 and 48 h of Cd exposure. Putative heat-shock proteins and glutathione S-transferase generally increased their expression all over the Cd treatments. By contrast, ABC transporters were underexpressed after 6-18 h, but in some cases induced after 24-48 h of Cd exposure. The cytochrome P450 appeared to have a variable expression pattern over time. Overall these data suggest that a considerable importance in the response of P. adscendens thalli to Cd stress can be assumed by differential expression of various protein families.

Influence of feeder layer on the expression of stem cell markers in cultured limbal corneal epithelial cells

BACKGROUND & OBJECTIVE

The limbus is enriched with the stem cells of corneal epithelium. Auto- and allograft limbal transplantations are effective in restoring the corneal epithelium and inhibiting inflammation and neovascularization. Preserved human amniotic membrane (AM) is now widely used as a substrate for ocular surface reconstruction. The combination of limbal and AM transplantation has been shown to improve the surgical outcome in patients with total limbal stem cell deficiency (LSCD). The purpose of this study was to compare the expression of putative stem cell markers ATP binding cassette protein (ABCG2) and keratinocyte stem cell marker: p63 and differentiation markers. (connexin 43 and keratin 3 / keratin 12) on the limbal epithelial cells cultured over the denuded AM with and without the 3T3 murine fibroblast cells as feeder layer.

METHODS

Human limbal tissues obtained from the cadaveric donor eyes were cultured over the denuded human amniotic membrane in the presence of mitomycin C treated 3T3 fibroblasts and the cultured cells studied for the expression of ABCG2 and p63 by immunohistochemistry and Western blot. Semi-quantitative reverse transcriptase polymerase chain reaction (RT-PCR) was done on the cultured cells at varying intervals of time for expression of ABCG2, p63, connexin43 (Cnx43), and keratin 3 (K3) and keratin 12 (K12).

RESULTS

The growth rates were similar in both denuded AM and denuded AM + 3T3. The cells cultured over AM + 3T3 showed the expression of p63 and ABCG2 till 21 days of incubation by immunohistochemistry and Western blot. The expression of p63 and ABCG2 were retained till 21 days of incubation on the cells cultured over denuded AM + 3T3, whereas it was expressed only till day 8 on the cells cultured over the denuded membrane by semi quantitative RT-PCR. Cnx43 and K3/K12 were observed in both the conditions.

INTERPRETATION & CONCLUSION

The limbal epithelial cells cultured in the presence of mitomycin C treated 3T3 feeder layer were able to maintain the expression of putative stem cell markers. Further in vitro studies using feeder layer will enable us to understand the factors, which play a role in maintaining the limbal stem cell niche.

Detection and characterization of CD133+ cancer stem cells in human solid tumours

BACKGROUND

Osteosarcoma is the most common primary tumour of bone. Solid tumours are made of heterogeneous cell populations, which display different goals and roles in tumour economy. A rather small cell subset can hold or acquire stem potentials, gaining aggressiveness and increasing expectancy of recurrence. The CD133 antigen is a pentaspan membrane glycoprotein, which has been proposed as a cancer stem cell marker, since it has been previously demonstrated to be capable of identifying a cancer initiating subpopulation in brain, colon, melanoma and other solid tumours. Therefore, our aim was to observe the possible presence of cells expressing the CD133 antigen within solid tumour cell lines of osteosarcoma and, then, understand their biological characteristics and performances.

METHODOLOGY AND PRINCIPAL FINDINGS

In this study, using SAOS2, MG63 and U2OS, three human sarcoma cell lines isolated from young Caucasian subjects, we were able to identify and characterize, among them, CD133+ cells showing the following features: high proliferation rate, cell cycle detection in a G2\M phase, positivity for Ki-67, and expression of ABCG2 transporters. In addition, at the FACS, we were able to observe the CD133+ cell fraction showing side population profile and forming sphere-clusters in serum-free medium with a high clonogenic efficiency.

CONCLUSIONS

Taken together, our findings lead to the thought that we can assume that we have identified, for the first time, CD133+ cells within osteosarcoma cell lines, showing many features of cancer stem cells. This can be of rather interest in order to design new therapies against the bone cancer.

Effects of combined PPARgamma and PPARalpha agonist therapy on reverse cholesterol transport in the Zucker diabetic fatty rat

AIM

We investigated the effects of the combined therapy of PPARgamma and PPARalpha agonists on HDL metabolism, especially concerning reverse cholesterol transport (RCT), using Zucker diabetic fatty rats (ZDF/Crl-Lepr fa rats) that are the rodent model for type 2 diabetes with obesity, hyperlipidaemia and insulin resistance.

METHODS

The ZDF rats were divided into four medicated groups as follows: pioglitazone as a PPARgamma agonist (5 mg/kg/day; P group, n = 6), fenofibrate as a PPARalpha agonist (30 mg/kg/day; F group, n = 6), both these medications (P + F group, n = 6) and no treatment (UNT group, n = 6). Non-diabetic rats (ZDF/GmiCrl-lean, CON group, n = 6) served as controls. We evaluated HDL particle size and messenger RNA (mRNA) levels of the following factors: liver X receptor alpha (L x R alpha), ATP-binding cassette A1 (ABCA1) and ABCG1 which are regulated by PPARs and are related to early stage RCT.

RESULTS

The significant increase in HDL particle size was demonstrated in rats of the F and P + F groups, although changes in plasma HDL-cholesterol levels were not significant. In accordance with this finding, mRNA levels of ABCG1 in the liver increased significantly.

CONCLUSIONS

These findings suggest the efficacy of combined therapy with PPARgamma and PPARalpha in improving lipid metabolism, partly through the enhanced RCT, and insulin resistance in type 2 diabetes mellitus.

Up-regulation of MRP4 and down-regulation of influx transporters in human leukemic cells with acquired resistance to 6-mercaptopurine

To investigate the mechanism of cellular resistance to 6-MP, we established a 6-MP resistant cell line (CEM-MP5) by stepwise selection of the human T-lymphoblastic leukemia cell line (CEM). CEM-MP5 cells were about 100-fold resistant to 6-MP compared with parental CEM cells. Western blot analysis demonstrated that multidrug resistant protein 4 (MRP4) was increased in CEM-MP5 cells, whereas the levels of the nucleoside transporters hENT1, hCNT2 and hCNT3 were decreased compared with those of parental CEM cells. Consistent with the operation of an efflux pump, accumulation of [14C]6-MP and/or its metabolites was reduced, and ATP-dependent efflux was increased in CEM-MP5 cells. Taken together these results showed that up-regulation of MRP4 and down-regulation of influx transporters played a major role in 6-MP resistance of CEM-MP5 cells.

ME3738 protects against lithocholic acid-induced hepatotoxicity, which is associated with enhancement of biliary bile acid and cholesterol output

ME3738 (22beta-methoxyolean-12-ene-3beta, 24(4beta)-diol), a derivative of soyasapogenol, attenuates liver disease in several models of chronic liver inflammation. In the present study, we have investigated a protective effect of ME3738 in a typical bile acid-induced cholestatic liver model, lithocholate (LCA) feeding mouse. Co-administration of ME3738 resulted in decreases in plasma alanine aminotransferase (ALT) and alkaline phosphatase (ALP) activities and hepatic bile acid level, and increases in biliary outputs of bile acid and cholesterol, as compared with the results in mice treated with LCA alone. LCA sulfation by hydroxysteroid sulfotransferase 2a and hydroxylation have been reported to be involved in protection against LCA-induced hepatotoxicity. ME3738-treatment, however, had no clear influence on the hydroxysteroid sulfotransferase 2a protein level and LCA 6alpha-, 6beta- and 7alpha-hydroxylase activities, but increased biliary cholesterol output. Cholate (CA)-treatment has been shown to induce hepatotoxicity in farnesoid X receptor-null mice, which is scarcely dependent on bile acid sulfation and hydroxylation but associated with decreased biliary bile acid output. Co-administration of ME3738 decreased the ALT and ALP activities and hepatic bile acid level, and increased biliary outputs of bile acid and cholesterol in farnesoid X receptor-null mice, as compared with the results in the mice treated with CA. Moreover, a clear correlation between biliary outputs of cholesterol and bile acid was observed in these two bile acid-induced hepatotoxicity mouse models. These results suggest that ME3738 protects against bile acid-induced hepatotoxicity through increased biliary bile acid output that is not related to bile acid metabolism but associated with cholesterol output.

Use of arrays to investigate the contribution of ATP-binding cassette transporters to drug resistance in cancer chemotherapy and prediction of chemosensitivity

Multidrug resistance (MDR) is a major problem in cancer chemotherapy. One of the best known mechanisms of MDR is the elevated expression of ATP-binding cassette (ABC) transporters. While some members of human ABC transporters have been shown to cause drug resistance with elevated expression, it is not yet known whether the over-expression of other members could also contribute to drug resistance in many model cancer cell lines and clinics. The recent development of microarrays and quantitative PCR arrays for expression profiling analysis of ABC transporters has helped address these issues. In this article, various arrays with limited or full list of ABC transporter genes and their use in identifying ABC transporter genes in drug resistance and chemo-sensitivity prediction will be reviewed.

Molecular interaction between caveolin-1 and ABCA1 on high-density lipoprotein-mediated cholesterol efflux in aortic endothelial cells

OBJECTIVE

Caveolin-1 and ATP-binding cassette transporter A1 (ABCA1) are proteins that are involved in cellular cholesterol efflux. In this study, we analyzed the relationships between caveolin-1 and ABCA1 on high-density lipoprotein (HDL)-mediated cholesterol efflux in rat aortic endothelial cells.

METHODS AND RESULTS

Overexpression of caveolin-1 by transfection with caveolin-1 cDNA in aortic endothelial cells up-regulated ABCA1 expression and enhanced cholesterol efflux. Suppression of caveolin-1 by siRNA decreased ABCA1 expression and reduced cholesterol efflux. The number of caveolae increased after transfection with caveolin-1 into cells. Immunoprecipitation assays revealed a molecular interaction between caveolin-1 and ABCA1 in the plasma membrane and in the cytoplasm after HDL incubation. Immunoelectron microscopy demonstrated that caveolin-1 colocalized with ABCA1 in the caveolae and in the cytoplasmic vesicles; it was also found that caveolin-1 and ABCA1 colocalized with cellular cholesterol by immunofluorescence microscopy. Blocking of intracellular lipid transport by inhibitors disrupted the interaction between caveolin-1 and ABCA1 and reduced cholesterol to methyl-beta-cyclodextrin and HDL.

CONCLUSIONS

The molecular interaction between caveolin-1 and ABCA1 is associated with the HDL-mediated cholesterol efflux pathway in aortic endothelial cells.

Human ABCB6 Localizes to Both the Outer Mitochondrial Membrane and the Plasma Membrane

Expression of the ATP-binding cassette transporter ABCB6 has been associated with multiple cellular functions, including resistance to several cytotoxic agents, iron homeostasis, and porphyrin transport. To further elucidate its physiological function and/or role in drug resistance, we determined the subcellular location of ABCB6. Using three novel ABCB6-specific antibodies, Western blot analysis of cells expressing cDNA-derived or endogenous ABCB6 revealed two distinct molecular weight forms. Confocal microscopy indicates that the protein localizes to both mitochondria and the plasma membrane. Differential centrifugation revealed that the lower molecular weight form predominantly resides in the mitochondria, while the larger protein form is more abundant in the plasma membrane. Preliminary studies indicate that ABCB6 is functionally relevant in the plasma membrane, where its expression prevents the accumulation of specific porphyrins in the cell. Digitonin solubilization of mitochondria demonstrated that ABCB6 is present in the outer mitochondrial membrane, while back-titration assays with the ABCB6-specific antibodies reveal that the nucleotide binding domain of ABCB6 is cytoplasmic. These studies are the first to demonstrate that ABCB6 exists in two molecular weight forms, is localized to both the outer mitochondrial membrane and the plasma membrane, and plays a functional role in the plasma membrane.

Placental ABCA1 Expression is Reduced in Primary Antiphospholipid Syndrome Compared to Pre-eclampsia and Controls

The ATP binding cassette transporter A1 (ABCA1) mediates cellular cholesterol and phospholipid efflux, and is implicated in phosphatidylserine translocation and apoptosis. Loss of functional ABCA1 in null mice results in severe placental malformation. This study aimed to establish the placental localisation of ABCA1 and to investigate whether ABCA1 expression is altered in placentas from pregnancies complicated by pre-eclampsia and antiphospholipid syndrome. ABCA1 mRNA and protein localisation studies were carried out using in situ hybridization and immunohistochemistry. Comparisons of gene expression were performed using real-time PCR and immunoblotting. ABCA1 mRNA and protein was localised to the apical syncytium of placental villi and endothelia of fetal blood vessels within the villi. ABCA1 mRNA expression was reduced in placentas from women with APS when compared to controls (p<0.001), and this was paralleled by reductions in ABCA1 protein expression. There were no differences in ABCA1 expression between placentas from pre-eclamptic pregnancies and controls. The localisation of ABCA1 in human placenta is consistent with a role in cholesterol and phospholipid transport. The decrease in ABCA1 protein in APS may reflect reduced cholesterol transport to the fetus affecting the formation of cell membranes and decreasing the level of substrate available for steroidogenesis.

Gene expression profiles of ATP-binding cassette transporter A and C subfamilies in mouse retinal vascular endothelial cells

The purpose of this study was to quantify gene expression levels of the ATP-binding cassette (ABC) transporter A and C subfamilies ABCA1-A9, and ABCC1-6/Mrp1-6, C10/Mrp7 in mouse retinal vascular endothelial cells (RVEC) using a combination of a magnetic isolation method for mouse RVEC and real-time quantitative PCR analysis. The transcript level of endothelial cell markers, such as CD31, Tie-2, claudin-5, occludin, ABCB1a/mdr1a, and ABCG2, were more than 20-fold higher than those in the non-RVEC fraction, suggesting that RVEC in the RVEC fraction are concentrated at least 20-fold compared with those of the non-RVEC fraction. In the ABCA1 to A9 families, the transcript level of ABCA3 and A9 in the RVEC fraction was 1.2- and 32-fold higher than that in the non-RVEC fraction. Although ABCA3 was expressed in both the RVEC and non-RVEC fractions, A9 is predominantly expressed in the RVEC fraction. In the ABCC1 to C6 and C10 families, the transcript level of ABCC3, C4, and C6 in the RVEC fraction was 27-, 251-, and 242-fold higher, respectively, than that in the non-RVEC fraction, suggesting that ABCC3, C4, and C6 are predominantly expressed in the RVEC. In conclusion, ABCA3, ABCA9, ABCC3, ABCC4, and ABCC6 mRNAs are predominantly expressed at the inner blood-retina barrier (inner BRB) and appear to play a major role in the efflux transport of their substrates at the inner BRB.

The challenges of targeting chronic myeloid leukemia stem cells

Chronic myeloid leukemia (CML) is sustained by a clonally amplified population of Bcr Abl-positive pluripotent stem cells. Persistence of a large, functionally intact yet suppressed residual normal hematopoietic stem cell population in most patients with CML has made it possible to aim at the development of curative therapies. However, achieving this goal requires the identification of agents that will eradicate the leukemic stem cell population. Several potent Bcr-Abl-targeted drugs have now been introduced into clinical practice with remarkable effects. Nevertheless, accumulating data indicate that the leukemic CML stem cells in patients with chronic phase CML are less responsive to these agents than the bulk of the neoplastic cells. In this article, we review emerging evidence that CML stem cells have a number of unusual properties that underlie their relative insensitivity to treatment, including those that specifically target the Bcr-Abl oncoprotein. The biology of the neoplastic stem cells in patients with CML is clearly important to the future attainment of cures and might also prove a paradigm relevant to other types of malignancies that are sustained by transformed stem cell populations.

Physiologically regulated transgenic ABCA1 does not reduce amyloid burden or amyloid-β peptide levels in vivo

ABCA1-deficient mice have low levels of poorly lipidated apolipoprotein E (apoE) and exhibit increased amyloid load. To test whether excess ABCA1 protects from amyloid deposition, we crossed APP/PS1 mice to ABCA1 bacterial artificial chromosome (BAC) transgenic mice. Compared with wild-type animals, the ABCA1 BAC led to a 50% increase in cortical ABCA1 protein and a 15% increase in apoE abundance, demonstrating that this BAC supports modest ABCA1 overexpression in brain. However, this was observed only in animals that do not deposit amyloid. Comparison of ABCA1/APP/PS1 mice with APP/PS1 controls revealed no differences in levels of brain ABCA1 protein, amyloid, Abeta, or apoE, despite clear retention of ABCA1 overexpression in the livers of these animals. To further investigate ABCA1 expression in the amyloid-containing brain, we then compared ABCA1 mRNA and protein levels in young and aged cortex and cerebellum of APP/PS1 and ABCA1/APP/PS1 animals. Compared with APP/PS1 controls, aged ABCA1/APP/PS1 mice exhibited increased ABCA1 mRNA, but not protein, selectively in cortex. Additionally, ABCA1 mRNA levels were not increased before amyloid deposition but were induced only in the presence of extensive Abeta and amyloid levels. These data suggest that an induction of ABCA1 expression may be associated with late-stage Alzheimer's neuropathology.

Decreased expression of breast cancer resistance protein in the duodenum in patients with obstructive cholestasis

BACKGROUND/AIMS

The expression of transporters involved in bile acid homeostasis is differentially regulated during obstructive cholestasis. Since the drug efflux transporter breast cancer resistance protein (BCRP) is known to transport bile acids, we investigated whether duodenal BCRP expression could be altered during cholestasis.

METHODS

Using real-time RT-PCR analysis we determined mRNA expression levels in duodenal tissue of 19 cholestatic patients. Expression levels were compared to 14 healthy subjects. BCRP protein staining was determined in biopsies of 6 cholestatic and 6 healthy subjects by immunohistochemistry.

RESULTS

We found that in patients with obstructive cholestasis mean duodenal BCRP mRNA levels were significantly reduced to 53% and mean protein staining was reduced to 57%.

CONCLUSIONS

BCRP, a transporter for bile acids and numerous drugs, appears to be down-regulated in the human duodenum during cholestasis. The clinical impact of these results has to be investigated in further studies.

Ethanol consumption alters expression and colocalization of bile salt export pump and multidrug resistance protein 2 in the rat

Chronic ethanol consumption elicits detrimental changes of liver metabolism. By employing a 12-week-long feeding regimen, we investigated the effects of chronic ethanol consumption on the expression and localization of bile salt export pump (Bsep), a major canalicular exporter of bile salts, and multidrug resistance protein 2 (Mrp2), a canalicular organic anion transporter, in the rat liver. RT-PCR, confocal immunofluorescence microscopy, immunoblotting, and quantitative colocalization analysis were used to examine their gene and protein expression, and changes in the distribution of antigenic sites. Bsep mRNA was upregulated, while Mrp2 mRNA responded by downregulation. In agreement with mRNA, the expression of Bsep protein increased, while the expression of Mrp2 protein responded with a decrease, suggesting that the expression of both of them is transcriptionally regulated. Confocal immunofluorescence microscopy showed disruption of the colocalization of Bsep and Mrp2 proteins at the hepatocyte canalicular membrane and their relocation intracellularly. Quantitative colocalization analysis of Bsep and Mrp2 proteins revealed a steady decrease in the degree of colocalization and Mrp2 expression, indicating that although the properties of both transporters are affected, Mrp2 is altered more. These findings provide evidence that ethanol alters Bsep and Mrp2 canalicular transporters in the rat liver, at both the mRNA and protein levels. Mrp2 shows deeper involvement. Eight weeks appears to be a critical time point in this process.

Imatinib mesylate potentiates topotecan antitumor activity in rhabdomyosarcoma preclinical models

High levels of PDGFR expression in primary rhabdomyosarcoma (RMS) have been associated with disease progression. To date however, there are no reports on the activity of imatinib mesylate, a selective PDGFR inhibitor, in RMS preclinical models. A panel of 5 RMS cell lines was used to investigate the expression of PDGFRalpha and PDGFRbeta, c-Kit and the multidrug transporter ABCG2 (also inhibited by imatinib). In vitro and in vivo experiments were performed using RD (embryonal) and RH30 (alveolar) cell lines to determine the efficacy of imatinib as single agent and in combination with topotecan (TPT). PDGFRbeta was significantly expressed in all cell lines, with the highest levels in RD, while PDGFR alpha and ABCG2 were significantly expressed only in RH30 and RMZ-RC2. c-Kit was not detected. PDGFRbeta signaling was active in RD but not in RH30, whilst PDGFRalpha signaling was not active in either cell lines. Significant ABCG2-mediated extrusion of Hoechst 33342 was demonstrated in RH30 but not in RD, and was inhibited by imatinib and the specific ABCG2 inhibitor Ko143. In vitro, imatinib was not active as a single agent at therapeutic concentrations, but significantly potentiated TPT antitumor activity in both cell lines. In vivo experiments using tumor xenografts confirmed the synergistic interaction in both cell lines. These results suggest that at least 2 different mechanisms--inhibition of ABCG2 and/or PDGFRbeta--are involved in the synergistic interaction between imatinib and TPT, and support the use of this combination for the treatment of high-risk RMS patients.

Phytosterol-mediated inhibition of intestinal cholesterol absorption is independent of ATP-binding cassette transporter A1

An increased activity of ATP-binding cassette transporter (ABC) A1 has been proposed as a mechanism underlying the hypocholesterolaemic effect of phytosterols. In the present study, ABCA1-deficient mice (ABCA1−/− mice) were used to examine the involvement of the ABCA1 in the reduction of intestinal cholesterol absorption in response to a phytosterol-enriched diet. A decrease in intestinal cholesterol absorption of 39 and 35% was observed after phytosterol treatment in ABCA1+/+ mice and in ABCA1−/− mice, respectively. No statistically significant changes in plasma lipoprotein profile or in intestinal ABCG5, ABCG8 and Niemann-Pick C1-Like 1 gene expression levels were found when phytosterol-treated ABCA1−/− mice and untreated ABCA1−/− mice were compared. We conclude that phytosterol inhibition of cholesterol absorption in mice is independent of ABCA1

Fluctuation of the SP/non-SP phenotype in the C6 glioma cell line

Using the C6 glioma cell as a paradigm, we found that (i) the clonogenicity of C6 cells is several orders of magnitude higher than the percentage of SP cells; (ii) non-SP cells are able to generate SP cells, and conversely SP cells generate non-SP cells; (iii) non-SP sorted cells behave as tumorigenic cells. Hence, in C6 cells cultured in serum-containing medium, SP cells can be generated from non-SP cells. This dynamic equilibrium explains in C6 cells the maintenance of the SP phenotype with cell passaging and demonstrates the existence of tumorigenic non-SP cells.

Effects of genetic backgrounds on hyperbilirubinemia in radixin-deficient mice due to different expression levels of Mrp3

ERM (ezrin/radixin/moesin) proteins are organizers of apical actin cortical layer in general. We previously reported that the knockout of radixin resulted in Rdx(-/-) mice with displacement/loss of the canalicular transporter Mrp2, giving rise to Dubin-Johnson syndrome-like conjugated hyperbilirubinemia in the mixed genetic background (C57BL/6-129/Sv) (Kikuchi, et al. (2002) Nature Genetics 31, 320-325). However, when these mice were kept under mixed genetic background for years (late mixed backgrounds; LMB), the conjugated hyperbilirubinemia gradually became inconspicuous, while evidence of liver injury increased. We examined the effect of genetic background by backcrossing LMB Rdx(-/-) mice to C57BL/6 and 129/Sv wild type mice with the result that the Rdx(-/-) congenic mice regained hyperbilirubinemia with reduced hepatocellular damage. As revealed by immunofluorescence and western blots, the localization/expression of apical transporters, Mrp2, CD26, P-gps, and Bsep were not influenced by backcrossing, though those of a basolateral transporter, Mrp3, were strikingly increased by backcrossing.

ΔF508 Mutation Results in Impaired Gastric Acid Secretion

The cystic fibrosis transmembrane conductance regulator (CFTR) is recognized as a multifunctional protein that is involved in Cl(-) secretion, as well as acting as a regulatory protein. In order for acid secretion to take place a complex interaction of transport proteins and channels must occur at the apical pole of the parietal cell. Included in this process is at least one K(+) and Cl(-) channel, allowing for both recycling of K(+) for the H,K-ATPase, and Cl(-) secretion, necessary for the generation of concentrated HCl in the gastric gland lumen. We have previously shown that an ATP-sensitive potassium channel (K(ATP)) is expressed in parietal cells. In the present study we measured secretagogue-induced acid secretion from wild-type and DeltaF508-deficient mice in isolated gastric glands and whole stomach preparations. Secretagogue-induced acid secretion in wild-type mouse gastric glands could be significantly reduced with either glibenclamide or the specific inhibitor CFTR-inh172. In DeltaF508-deficient mice, however, histamine-induced acid secretion was significantly less than in wild-type mice. Furthermore, immunofluorescent localization of sulfonylurea 1 and 2 failed to show expression of a sulfonylurea receptor in the parietal cell, thus further implicating CFTR as the ATP-binding cassette transporter associated with the K(ATP) channels. These results demonstrate a regulatory role for the CFTR protein in normal gastric acid secretion.