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Results for “Vault Ribonucleoprotein Particles”

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PubMed2004

[Predictive value of drug resistance-related genes expression in neoadjuvant chemotherapy in patients with non-small cell lung cancer of stage III].

BACKGROUND & OBJECTIVE: P-glycoprotein (P-gp), multidrug resistance-associated protein (MRP), and lung resistant protein (LRP) play important roles in multidrug resistance (MDR). This study was to determine P-gp, MRP, and LRP expression in patients with non-small cell lung cancer (NSCLC) of stage III, and evaluate their predictive value in neoadjuvant chemotherapy. METHODS: Immunohistochemical analyses were performed on 31 patients with NSCLC of stage III before, and after neoadjuvant chemotherapy. RESULTS: The frequency of P-gp, MRP, and LRP expression were 29.0% (9/31), 45.2% (14/31), and 38.7% (12/31) before chemotherapy, and were 61.3% (19/31), 51.6% (16/31), and 41.9% (13/31) after chemotherapy. Of 31 patients, 10 (10/31, 32.3%) expressed both MRP and LRP before chemotherapy, which indicated significant positive correlation between MRP and LRP expression (r=0.061, P< 0.001). In patients with P-gp, MRP, or LRP expression before chemotherapy, the response rates towards chemotherapy were 44.4% (4/9), 28.6% (4/14), and 16.7% (2/12). Of 10 patients with both MRP and LRP expression, only 1 (1/10, 10.0%) responded to chemotherapy. The median survival time of patients who responded to chemotherapy was 31 months, while that of patients who did not responded to chemotherapy was 15 months, that of patients who didn't receive neoadjuvant chemotherapy before surgery was 18 months. CONCLUSION: Patients with both MRP and LRP expression are probably resistant to chemotherapy, the value of neoadjuvant chemotherapy is limit in such patients.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed2005

[The interference in correlated molecular mechanism obtained multi-drug resistance of mouse S180's tumour cell for different alkaloid].

OBJECTIVE: To observe the base of the interference in correlated biotic active matter obtained multi-drug resistance induced by chemotherapy for different alkaloid, and to supervise the use in clinic to restrain the multi-drug resistant of chemotherapy, and thereby to improve the curative effect. METHOD: After bestowing subter-dosage unite chemotherapeutant to ascites S180 mouse to set up the mouse models of multi-drug resistance of S180 tumour cell, and giving the mouse matrine, terandrine, oxymatrine and berberine hydrooh loride for 4 weeks, the P170, LRP, TOPOII, Fas and apoposis were determined by flow cytometry. RESULT: Matrine and terandrine could obviously reduce the express of P170, LRP and the activation of TOPOII, and increase the ratio of the express of Fas and the apoposis of drug resistant tumour cell. And at the same time it could obviously reduce the express of intercellular adhesion molecule(CD54). CONCLUSION: Matrine and terandrine can interfere in MDR which results from chemotherapeutics by the adjustment of correlated biotic active matter, besides, the different degree of alkaloid effect with different configuration.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed2001

Multiple human vault RNAs. Expression and association with the vault complex.

Human vaults are intracellular ribonucleoprotein particles believed to be involved in multidrug resistance. The complex consists of a major vault protein (MVP), two minor vault proteins (VPARP and TEP1), and several small untranslated RNA molecules. Three human vault RNA genes (HVG1-3) have been described, and a fourth was found in a homology search (HVG4). In the literature only the association of hvg1 with vaults was shown in vivo. However, in a yeast three-hybrid screen the association of hvg1, hvg2, and hvg4 with TEP1 was demonstrated. In this study we investigated the expression and vault association of different vault RNAs in a variety of cell lines, including pairs of drug-sensitive and drug-resistant cells. HVG1-3 are expressed in all cell lines examined, however, none of the cell lines expressed HVG4. This probably is a consequence of the absence of essential external polymerase III promoter elements. The bulk of the vault RNA associated with vaults was hvg1. Interestingly, an increased amount of hvg3 was bound to vaults isolated from multidrug-resistant cell lines. Our findings suggest that vaults bind the RNA molecules with different affinities in different situations. The ratio in which the vault RNAs are associated with vaults might be of functional importance.

Base Sequence↗

PubMed1998

Interaction of vault particles with estrogen receptor in the MCF-7 breast cancer cell.

A 104-kD protein was coimmunoprecipitated with the estrogen receptor from the flowtrough of a phosphocellulose chromatography of MCF-7 cell nuclear extract. mAbs to this protein identified several cDNA clones coding for the human 104-kD major vault protein. Vaults are large ribonucleoprotein particles of unknown function present in all eukaryotic cells. They have a complex morphology, including several small molecules of RNA, but a single protein species, the major vault protein, accounts for >70% of their mass. Their shape is reminiscent of the nucleopore central plug, but no proteins of known function have been described to interact with them. Western blot analysis of vaults purified on sucrose gradient showed the presence of estrogen receptor co-migrating with the vault peak. The AER317 antibody to estrogen receptor coimmunoprecipitated the major vault protein and the vault RNA also in the 20,000 g supernatant fraction. Reconstitution experiments of estrogen receptor fragments with the major vault protein mapped the site of the interaction between amino acids 241 and 280 of human estrogen receptor, where the nuclear localization signal sequences are located. Estradiol treatment of cells increased the amount of major vault protein present in the nuclear extract and coimmunoprecipitated with estrogen receptor, whereas the anti-estrogen ICI182,780 had no effect. The hormone-dependent interaction of vaults with estrogen receptor was reproducible in vitro and was prevented by sodium molybdate. Antibodies to progesterone and glucocorticoid receptors were able to coimmunoprecipitate the major vault protein. The association of nuclear receptors with vaults could be related to their intracellular traffic.

Animals↗

PubMed2002

The activity profile of the hexacyclic camptothecin derivative DX-8951f in experimental human colon cancer and ovarian cancer.

DX-8951f or exatecan mesylate ((1S,9S)-1-amino-9-ethyl-5-fluoro-2,3-dihydro-9-hydroxy-4-methyl-1H,12H-benzo[de]pyrano[3',4':6,7]indolizino[1,2-b]quinoline-10-13(9H,15H)-dione methanesulfonate dihydrate), is a new water-soluble derivative of camptothecin. We determined the activity of DX-8951f in experimental human colon cancer and ovarian cancer, being tumor types sensitive to camptothecins. With the use of the MTT assay, DX-8951f was more potent than SN-38 in four out of five human colon cancer cell lines and three out of four human ovarian cancer cell lines (P<0.05). DX-8951f was considerably more potent than topotecan in all cell lines tested (P<0.05). Prolonged exposure to DX-8951f resulted in a greater increase in inhibition of cell proliferation as compared to that obtained with SN-38 or topotecan (P<0.05). Overexpression of Pgp, MRP1, and LRP did not affect the in vitro activity of DX-8951f. DX-8951f administered daily x 5 or weekly x 2 resulted in growth inhibition <50% in two human colon cancer xenografts grown s.c. in nude mice. In three human ovarian cancer xenografts, however, >50% growth inhibition was observed at both schedules. In the OVCAR-3 human ovarian cancer model, DX-8951f showed considerably greater activity than topotecan (P<0.01). DX-8951f combined with cisplatin or paclitaxel did not indicate the presence of a pharmacological interaction. In OVCAR-3 xenografts the combination was clearly more effective than DX-8951f alone, as the number of complete remissions increased substantially. In conclusion, this study shows that DX-8951f is highly potent in vitro and highly effective in experimental human ovarian cancer in vivo. Prolonged exposure to DX-8951f in vitro greatly increased the antiproliferative effects, which may be a rationale for testing a continuous infusion schedule in the clinic. Addition of cisplatin or paclitaxel improved the in vivo antitumor effects of DX-8951f.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMedDate not supplied

Chemo- and radiation sensitivity of xenografted acute lymphoblastic leukemias--correlation to the expression of multidrug resistance proteins.

The aim of our study was to characterise, for the first time, the chemo- and radiation sensitivity of seven pediatric acute lymphoblastic leukemias xenotransplanted into immunodeficient NOD/SCID mice and to correlate the findings with the expression of three drug resistance proteins, P-glycoprotein (P-gp), multidrug resistance-associated protein (MRP1) and lung resistance protein (LRP). Mice were treated with single drugs used in clinical protocols: daunorubicin, doxorubicin, cyclophosphamide, vincristine, cytarabine, asparaginase and methotrexate. Two ALL samples, established from primarily diagnosed patients, responded to 5 or 6 of the tested cytostatics, respectively, while 3 out of 5 ALLs from relapse patients were only sensitive towards 2-4 drugs tested. Daunorubicin was more efficient than doxorubicin. The response of xenografted ALL toward vincristine and cyclophosphamide was inversely correlated with the expression of P-gp, LRP and MRP1 (R2 = 0.71, 0.70 and 0.64 for vincristine and 0.44, 0.70 and 0.60 for cyclophosphamide). A good correlation could be detected between the expression of P-gp and LRP (R2 = 0.88), P-gp and MRP1 (R2 = 0.75) and LRP and MRP1 (R2 = 0.90). The highest co-expression of the drug resistance proteins in the leukemia ALL-SCID 6 coincided with a high resistance to radiation and chemotherapy. Prediction of the individual drug resistance profile of a patient on the basis of results from the ALL-SCID xenograft studies was not possible because of the relatively long time necessary and because of the changes in the expression of P-gp, LRP and MRP1 during the murine generations. We conclude that in the drug resistance phenotype of ALL not only the above mentioned proteins but a variety of different molecules are involved.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed1993

cDNA cloning and disruption of the major vault protein alpha gene (mvpA) in Dictyostelium discoideum.

Vaults are large cytoplasmic ribonucleoprotein particles found in nearly all eukaryotic cells. Dictyostelium vaults contain two major proteins, MVP alpha (94.2 kDa) and MVP beta (approximately 92 kDa). Using an anti-rat vault antibody, we screened a Dictyostelium cDNA expression library and isolated a 2.8-kilobase pair clone that contained a single full-length reading frame. The identity of the clone was established by the presence of a predicted 20-amino acid sequence identical to that found in a peptide sequenced from purified MVP alpha. We have disrupted the single copy gene using homologous recombination and have demonstrated a loss of MVP alpha. Although the cells still produce MVP beta, they do not contain characteristic vault particles, suggesting that MVP alpha is required for normal vault structure. These cells should be a valuable tool for elucidating the function of vaults.

Amino Acid Sequence↗

PubMed2005

Multidrug resistance-related phenotype and apoptosis-related protein expression in ovarian serous carcinomas.

OBJECTIVE: Multidrug resistance (MDR) to chemotherapy is a major obstacle in attempts to improve the clinical outcome of ovarian carcinoma patients. The MDR-related phenotype is associated with over-expression of certain drug transporters, such as P-glycoprotein (P-gp), multidrug resistance protein 1 (MRP1), and lung resistance protein (LRP). The aim of this study was to evaluate the extent and prognostic significance of MDR-related protein expression in ovarian serous carcinomas. In addition, we correlated expression of these proteins with the apoptosis-related proteins p53, bcl-2, and bax. METHODS: Consecutive sections from 60 cases of ovarian serous carcinoma were assessed immunohistochemically for expression of P-gp, MRP1, LRP, p53, bcl-2, and bax. The level of protein expression was scored based on staining intensity and extent. RESULTS: Strong P-gp expression was observed in 12 (20%), MRP1 in 39 (65%), LRP in 27 (45%), p53 in 45 (75%), bcl-2 in 25 (41.7%), and bax in 30 (50%) of the 60 tumors. MRP1 expression was associated with both p53 and bcl-2 expressions (P = 0.01 and P = 0.03, respectively). Univariate analysis of survival revealed a significant inverse correlation between P-gp expression and patient survival (P = 0.015). Moreover, P-gp expression was significantly increased in tumors of patients unresponsive to chemotherapy (P = 0.009). Multivariate analysis revealed that only FIGO stage and P-gp expression were useful negative independent predictors of survival (P = 0.035 and P = 0.045, respectively). CONCLUSIONS: Our pilot study demonstrates that P-gp expression may be a reliable independent prognostic factor of survival in patients with ovarian serous carcinoma. Moreover, P-gp immunostaining may be useful for dividing ovarian carcinoma patients into chemoresponsive and chemoresistant groups.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed2004

CD34+ cells from acute myeloid leukemia, myelodysplastic syndromes, and normal bone marrow display different apoptosis and drug resistance-associated phenotypes.

Myelodysplastic syndromes and acute myeloid leukemia (AML) are heterogeneous disorders in which conflicting results in apoptosis and multidrug resistance (MDR) have been reported. We have evaluated by multiparameter flow cytometry the expression of apoptosis- (APO2.7, bcl-2, and bax) and MDR-related proteins [P-glycoprotein (P-gp), multidrug resistance protein (MRP), and lung resistance protein (LRP)] specifically on bone marrow (BM) CD34+ cells, and their major CD32-/dim and CD32+ subsets, in de novo AML (n=90), high-risk myelodysplastic syndrome (n=9), and low-risk myelodysplastic syndrome (n=21) patients at diagnosis, and compared with normal BM CD34+ cells (n=6). CD34+ myeloid cells from AML and high-risk myelodysplastic syndrome patients displayed higher expression of bcl-2 (P <0.0001) and lower reactivity for APO2.7 (P=0.002) compared with low-risk myelodysplastic syndrome and normal controls. Similar results applied to the two predefined CD34+ myeloid cell subsets. No significant differences were found in the expression of P-gp, MRP, and LRP between low-risk myelodysplastic syndrome patients and normal BM, but decreased expression of MRP (P <0.03) in AML and high-risk myelodysplastic syndromes and P-gp (P=0.008) in high-risk myelodysplastic syndromes were detected. Hierarchical clustering analysis showed that low-risk myelodysplastic syndrome patients were clustered next to normal BM samples, whereas high-risk myelodysplastic syndromes were clustered together and mixed with the de novo AML patients. In summary, increased resistance to chemotherapy of CD34+ cells from both AML and high-risk myelodysplastic syndromes would be explained more appropriately in terms of an increased antiapoptotic phenotype rather than a MDR phenotype. In low-risk myelodysplastic syndromes abnormally high apoptotic rates would be restricted to the CD34- cell compartments.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed2005

YB-1 facilitates basal and 5-fluorouracil-inducible expression of the human major vault protein (MVP) gene.

Vaults have been suggested to play a direct role in multidrug resistance (MDR) to anticancer drugs. The human major vault protein (MVP) also known as lung resistance-related protein (LRP) represents the predominant component of vaults that may be involved in the defense against xenobiotics. Here, we demonstrate that besides MDR-related cytostatics, also the non-MDR-related drug 5-fluorouracil (5-FU) was able to induce MVP mRNA and protein expression. Treatment with 5-FU amplified the binding activity and interaction of the transcription factor Y-box binding protein-1 (YB-1) with the Y-box of the human MVP gene promoter in a time-dependent manner. 5-FU also induced reporter expressions driven by a panel of newly generated MVP promoter deletion mutants. Interestingly, stably YB-1 overexpressing cell clones showed enhanced binding of YB-1 to the Y-box motif, associated with enhanced basal as well as 5-FU-inducible MVP promoter-driven reporter expressions. Moreover, transduction of YB-1 cDNA led to increased expression of endogenous MVP protein. Under physiological conditions, we observed a strong coexpression of MVP and YB-1 in human colon carcinoma specimen. In summary, our data demonstrate a direct involvement of YB-1 in controlling basal and 5-FU-induced MVP promoter activity. Therefore, YB-1 is directly linked to MVP-mediated drug resistance.

Antimetabolites, Antineoplastic↗

PubMed2004

The major vault protein is a novel substrate for the tyrosine phosphatase SHP-2 and scaffold protein in epidermal growth factor signaling.

The catalytic activity of the Src homology 2 (SH2) domain-containing tyrosine phosphatase, SHP-2, is required for virtually all of its signaling effects. Elucidating the molecular mechanisms of SHP-2 signaling, therefore, rests upon the identification of its target substrates. In this report, we have used SHP-2 substrate-trapping mutants to identify the major vault protein (MVP) as a putative SHP-2 substrate. MVP is the predominant component of vaults that are cytoplasmic ribonucleoprotein complexes of unknown function. We show that MVP is dephosphorylated by SHP-2 in vitro and it forms an enzyme-substrate complex with SHP-2 in vivo. In response to epidermal growth factor (EGF), SHP-2 associates via its SH2 domains with tyrosyl-phosphorylated MVP. MVP also interacts with the activated form of the extracellular-regulated kinases (Erks) in response to EGF and a constitutive complex between tyrosyl-phosphorylated MVP, SHP-2, and the Erks was detected in MCF-7 breast cancer cells. Using MVP-deficient fibroblasts, we demonstrate that MVP cooperates with Ras for optimal EGF-induced Elk-1 activation and is required for cell survival. We propose that MVP functions as a novel scaffold protein for both SHP-2 and Erk. The regulation of MVP tyrosyl phosphorylation by SHP-2 may play an important role in cell survival signaling.

Amino Acid Sequence↗

PubMed2006

Intracellular localization and content of YB-1 protein in multidrug resistant tumor cells.

The multifunctional mammalian protein YB-1 is a member of the large DNA- and RNA-binding protein family with an evolutionarily ancient cold-shock domain. YB-1 is involved in multiple DNA- and mRNA-dependent events and regulates gene expression at various levels. It can be found both in the nucleus and the cytoplasm. Bound to DNA in the cell nucleus, YB-1 functions as a transcription factor interacting with inverted CCAAT-box (Y-box) in promoters and enhancers of multiple genes. In particular, YB-1 regulates activity of the multidrug resistance (MDR) genes MDR1 and LRP. In tumors, YB-1 has been suggested to be an early and global marker of MDR. In this study, we compared amounts of YB-1 mRNAs and intracellular localization of YB-1 protein in six pairs of drug sensitive and drug resistant sublines of diverse tumors. We have shown that neither great increase in the level of YB-1 mRNA nor substantial increase in the number of cells with nuclear localization of YB-1 are obligatory traits of drug resistant tumor cell populations. However, the cells with highest amounts of YB-1 mRNA also demonstrated increased quantities of MDR1, MRP1, BCRP, and LRP mRNAs encoding different MDR proteins. Transfection of two different populations of drug-sensitive cells with YB-1 cDNA led to increase in the amount of YB-1 mRNA. The quantities of MRP1 and LRP mRNAs increased in both populations. Introduction of YB-1 small hairpin RNA (shRNA) resulted in decreased amounts of YB-1 mRNA, as well as MRP1, LRP, and MDR1 mRNAs (in three different cell lines). Our data suggest that although YB-1 regulates several MDR genes, it could not be regarded as a global marker of already formed drug resistant tumor cell populations. It is most likely that at the first steps of MDR development YB-1 activity is necessary for propagation of resistant cell populations rather than for maintenance of drug resistance.

Amino Acid Sequence↗

PubMed2001

Differential expression of the lung resistance-related protein/major vault protein in the histological compartments of nephroblastomas.

Nephroblastomas (Wilms' tumors) are curable with survival rates above 80%. Some tumors, however, fail to respond to therapy and those patients have a poor prognosis. In a search for molecular markers of drug resistance, we investigated the expression of lung resistance protein (LRP) in tissue samples from 32 children with nephroblastoma by means of immunohistochemistry. LRP is a human major vault protein (MVP) and is associated with multidrug resistance of tumors. LRP/MVP expression was found in the blastemal and epithelial compartments but to a significantly lesser extent in the stromal compartment of Wilms' tumors. Expression was generally heterogeneous with respect to staining intensity and percentage of positive cells. We found significant relationships between LRP/MVP expression and chemotherapeutic pre-treatment of tumors and tumor stage. The immunohistochemical results were validated with a real-time RT-PCR technique and a significant association between protein and mRNA expression was observed.

Antibiotics, Antineoplastic↗

PubMed1997

Analysis of a cDNA encoding the major vault protein from the electric ray Discopyge ommata.

The major vault protein is the predominant constituent of vaults ubiquitous large cytosolic ribonucleoprotein particles. A cDNA clone encoding the 100-kDa major vault protein (MVP100) was isolated from an electric lobe library of Discopyge ommata. The complete nucleotide sequence was determined. Northern blot analysis revealed a 2.8-kb transcript with a high expression in neural tissue. Southern blot analysis indicates that the electric ray MVP100 is a single copy-gene with at least two introns. The primary structure of major vault proteins characterized in slime mold, ray, rat and human is evolutionary highly conserved.

Amino Acid Sequence↗

PubMedDate not supplied

Expression of apoptosis, cell proliferation, and drug resistance genes in pediatric Wilms' tumors.

The expression of genes associated with apoptosis, cell proliferation and drug resistance in tumor cells was investigated in two pediatric Wilms' tumor patients (MCH-WT-1 and MCH-WT-3) for their association with cell cycle, daunorubicin accumulation and clinical data. DNA content, cell cycle and drug accumulation were analyzed immediately after surgery by flow cytometry and mRNA expression by reverse transcriptase-polymerase chain reaction (RT-PCR) assay. Primary cell cultures were established from tumor specimens and tumor cells in both cases showed epithelial morphology. Although cell proliferation markers (Ki67 and PCNA) were expressed in both cases, MCH-WT-3 showed higher levels of mRNA expression, which corresponded, with metastatic behavior of the tumor in the patient. While p53 and p21 mRNAs were expressed at low levels in MCH-WT1, MCH-WT-3 showed high levels of p21 mRNA only. The increased expression of cyclin kinase inhibitor (p21) in MCH-WT-3 compared to MCH-WT-1 correlated with a higher percentage of G0/G1 cell population in the tumor specimen. Despite the expression of multidrug resistance markers (MDR1 and LRP) in MCH-WT-1, flow cytometric analysis showed tumor cell populations with very low and high daunorubicin accumulation and with the absence of any effect for verapamil and dipyridamole on daunorubicin accumulation of tumor cells.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed1999

Vaults and telomerase share a common subunit, TEP1.

Vaults are large cytoplasmic ribonucleoprotein complexes of undetermined function. Mammalian vaults have two high molecular mass proteins of 193 and 240 kDa. We have identified a partial cDNA encoding the 240-kDa vault protein and determined it is identical to the mammalian telomerase-associated component, TEP1. TEP1 is the mammalian homolog of the Tetrahymena p80 telomerase protein and has been shown to interact specifically with mammalian telomerase RNA and the catalytic protein subunit hTERT. We show that while TEP1 is a component of the vault particle, vaults have no detectable telomerase activity. Using a yeast three-hybrid assay we demonstrate that several of the human vRNAs interact in a sequence-specific manner with TEP1. The presence of 16 WD40 repeats in the carboxyl terminus of the TEP1 protein is a convenient number for this protein to serve a structural or organizing role in the vault, a particle with eight-fold symmetry. The sharing of the TEP1 protein between vaults and telomerase suggests that TEP1 may play a common role in some aspect of ribonucleoprotein structure, function, or assembly.

Animals↗

PubMed1998

Vaults are up-regulated in multidrug-resistant cancer cell lines.

Vaults are 13-MDa ribonucleoprotein particles composed largely of a 104-kDa protein, termed major vault protein or MVP, and a small vault RNA, vRNA. While MVP levels have been found to increase up to 15-fold in non-P-glycoprotein multidrug-resistant cell lines, the levels of vault particles have not been investigated. As both the function of vault particles and the mechanism of drug resistance in non-P-glycoprotein cells are unknown, we decided to determine whether vault synthesis was coupled to MDR. By cloning the human gene for vRNA and careful quantitation of the MVP and vRNA levels in MDR cells, we find that vRNA is in considerable excess to MVP. Sedimentation measurements of vault particles in multidrug resistance cells have indeed revealed up to a 15-fold increase in vault synthesis, coupled with a comparable shift of associated vRNA, demonstrating that vault formation is limited by expression of MVP or the minor vault proteins. The observation that vault synthesis is linked directly to multidrug resistance supports a direct role for vaults in drug resistance.

Base Sequence↗

PubMed1999

Bcl-2, bax and bcl-xL expression in human sensitive and resistant leukemia cell lines.

With the growing understanding of cytostatic drug-induced programmed cell death new drug-resistance mechanisms based on the altered ability of cells to die by apoptosis have been defined. At first, the sensitive and P-glycoprotein (P-gp)-related resistant cell lines were tested to induce apoptosis by a non-P-gp transported drug, such as cytosine arabinoside (ara-C). It was demonstrated that ara-C induces apoptosis in sensitive as well as in P-gp-related resistant cell lines, as expected. Furthermore, the role of bcl-2 and bcl-xL apoptosis inhibitors as well as bax expression (apoptosis inducer) in human sensitive leukemic cell lines (CCRF-CEM and HL-60) as compared to their resistant variants such as CCRF-CEM/ACT400, CCRF-CEM/VCR1000, HL-60/IDA40, HL-60/DNR250 was evaluated. In addition to the P-gp-related resistance, a possible multidrug resistance-associated protein (MRP) and the lung resistance protein (LRP)-related resistance were assessed by flow cytometry using the monoclonal antibodies 4E3.16, MRPr1 and LRP56. Furthermore, the function of P-gp was determined with the rhodamine-123 (R-123) accumulation test. Bcl-2 and bax were analyzed by both flow cytometry and ECL Western blot, bcl-xL by ECL-Western blot alone. Comparison of the two sensitive cell lines demonstrated different bcl-2, bax and bcl-xL patterns. The common characteristic was the increased expression of one of the apoptosis inhibitor proteins, such as bcl-2 or bcl-xL. The sensitive CCRF-CEM showed a high bax level, where a decrease of about 75% in resistant variants was measured. Compared to their sensitive counterpart HL-60, a low bax expression was analyzed, which increased in the resistant variant. The common characteristic of all resistant cell lines was the decreased expression of bax compared to bcl-2 or bcl-xL. In the P-gp-related resistant HL-60/DNR250 only an increase in bcl-xL was seen, whereas in the LRP-expressing as well as P-gp and MRP negative resistant HL-60/IDA40 both apoptotic inhibitor proteins bcl-2 and bcL-xL showed maximum increase, compared to the other resistant cell lines. The P-gp-related resistant cell lines CCRF-CEM/ACT400 and CCRF-CEM/VCR1000 also showed an increased expression of both bcl-2 and bcl-xL. Summarizing these results, it was shown that the examined sensitive human leukemic cell lines and their resistant variants demonstrated a different pattern of markers for preventing and promoting apoptosis. An association between P-gp and possible LRP-expressing leukemic cells as well as apoptosis-preventing markers (bcl-2, bcl-xL) seems to exist. The clinical relevance of the coexpression of various resistance mechanisms remains to be confirmed in large leukemia patient groups.

ATP Binding Cassette Transporter, Subfamily B↗