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N Kartner

Publications and source records attributed to N Kartner.

36 records · Page 2Linked to original sources
PubMed1991

Expression of the cystic fibrosis gene in non-epithelial invertebrate cells produces a regulated anion conductance.

The nature of involvement of the cystic fibrosis gene product (CFTR) in epithelial anion transport is not yet understood. We have expressed CFTR in Sf9 insect cells using the baculovirus expression vector system. Reactivity with antibodies against 12 different epitopes spanning the entire sequence suggested that the complete polypeptide chain was synthesized. Immunogold labeling showed localization to both cell-surface and intracellular membranes. Concomitant with CFTR expression, these cells exhibited a new cAMP-stimulated anion permeability. This conductance, monitored both by radioiodide efflux and patch clamping, strongly resembled that present in several CFTR-expressing human epithelial cells. These findings demonstrate that CFTR can function in heterologous nonepithelial cells and lend support to the possibility that CFTR may itself be a regulated anion channel.

Animals↗
PubMed1989

Multidrug resistance in cancer.

Chemotherapy often fails because a tumor develops resistance to an array of different drugs. A single glycoprotein turns out to be responsible: it proliferates in some cells and pumps out the drugs. Now that the protein pump has been identified it may be possible to interfere with its action or to make it the target for drugs that destroy the cancer cell.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1988

Altered plasma membrane ultrastructure in multidrug-resistant cells.

Multidrug resistance is mediated by P-glycoprotein, an integral plasma membrane component which is thought to function as a drug export pump. This model can explain drug resistance, but fails to account for the broader pleiotropy of the multidrug resistance phenotype. We report here a freeze-fracture study revealing increases in the densities of protoplasmic face intramembrane particles in multidrug-resistant Chinese hamster ovary (CHO) and human leukemic cells. The intramembrane particle density in a CHO cell revertant which had lost the characteristics of the multidrug resistance phenotype was indistinguishable from that of the drug-sensitive parental cell line. This demonstration of a global multidrug resistance-linked change in plasma membrane architecture may have significant implications for understanding the variety of concurrent membrane-related changes which are not easily explained by the current model for multidrug resistance.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1987

Expression of hamster P-glycoprotein and multidrug resistance in DNA-mediated transformants of mouse LTA cells.

The overexpression of a plasma membrane glycoprotein, P-glycoprotein, is strongly correlated with the expression of multidrug resistance. This phenotype (frequently observed in cell lines selected for resistance to a single drug) is characterized by cross resistance to many drugs, some of which are used in cancer chemotherapy. In the present study we showed that DNA-mediated transformants of mouse LTA cells with DNA from multidrug-resistant hamster cells acquired the multidrug resistance phenotype, that the transformants contained hamster P-glycoprotein DNA sequences, that these sequences were amplified whereas the recipient mouse P-glycoprotein sequences remained at wild-type levels, and that the overexpressed P-glycoprotein in these cells was of hamster origin. Furthermore, we showed that the hamster P-glycoprotein sequences were transfected independently of a group of genes that were originally coamplified and linked within a 1-megabase-pair region in the donor hamster genome. These data indicate that the high expression of P-glycoprotein is the only alteration required to mediate multidrug resistance.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1987

P-glycoprotein in human sarcoma: evidence for multidrug resistance.

Overexpression of an immunologically conserved, cell-surface glycoprotein (P-glycoprotein) is consistently associated with multidrug resistance in cell lines in vitro. A preliminary survey of specimens from 12 solid tumor types in our laboratories indicates significant overexpression of P-glycoprotein in some sarcomas. When tested by immunoblotting with monoclonal antibodies directed against P-glycoprotein; tumors from six of 25 sarcoma patients displayed elevated levels of P-glycoprotein. Three of the sarcoma patients exhibiting P-glycoprotein had not previously been exposed to chemotherapy, implying that overexpression of this marker and possible concomitant multidrug resistance may not depend only on selection during prior drug treatments. The P-glycoprotein overexpression in the sarcoma specimens is evidence for the presence of multidrug resistant cells in these tumors; thus, our data suggest that this mode of resistance may have clinical significance in sarcoma patients.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1986

Multidrug resistance.

Multidrug resistance describes a complex phenotype whose predominant feature is resistance to a wide range of structurally unrelated cytotoxic compounds, many of which are anticancer agents. This phenotype occurs frequently in mammalian cell lines and transplantable tumours selected for resistance to a single drug. Reduced cellular accumulation of the drugs involved appears to account for the resistance. This may be a consequence of reduced drug influx, increased drug efflux, or both. A wide variety of biochemical changes have been identified in multidrug resistant cell lines, the most consistent of which is the increased expression of P-glycoprotein, a conserved, high molecular weight, plasma membrane glycoprotein. The level of P-glycoprotein expression correlates with the degree of drug resistance in a variety of different cell types. In a number of multidrug resistant cell lines, overexpression of P-glycoprotein results from gene amplification. While the function of P-glycoprotein is unknown, independent lines of evidence support the notion that P-glycoprotein is the causative molecule mediating the multidrug resistance phenotype. Significant levels of P-glycoprotein expression have been detected in some biopsy specimens from patients with ovarian and sarcoma tumours. These findings suggest that multidrug resistant tumour cells can occur in human malignancies. The presence of such cells may affect the outcome of chemotherapy.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1985

Detection of P-glycoprotein in ovarian cancer: a molecular marker associated with multidrug resistance.

A multidrug resistance phenotype is frequently observed in animal and human cell lines selected for in vitro resistance to a single chemotherapeutic agent. Overexpression of a highly conserved cell-surface glycoprotein (P-glycoprotein) is consistently associated with this phenotype in these mutant lines. A monoclonal antibody against P-glycoprotein was used to examine tumor samples from five patients with advanced ovarian cancer for evidence of P-glycoprotein overexpression. High levels of P-glycoprotein were detected in samples from two patients suggesting that a multidrug resistance mutation may also occur in ovarian cancer. This finding has broad implications for the understanding of nonresponse to chemotherapy in a variety of human neoplasms, and may provide a rational explanation for failure of chemotherapy in treatment of advanced ovarian cancer.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1984

Expression of cell surface P-glycoprotein by an adriamycin-resistant murine fibrosarcoma.

Analysis of the cell membrane of Adriamycin (doxorubicin)-resistant UV-2237 ADMR murine fibrosarcoma cells revealed a 170,000-dalton component that is not found in the drug-sensitive parent or revertant cells. Immunoblot (Western blot) analysis showed that this component is similar to the 170,000-dalton P-glycoprotein found on the surface of Chinese hamster ovary cells that exhibit multidrug resistance. Thus, multidrug resistance and P-glycoprotein expression apparently can occur in a wide variety of cells, including the metastatic murine solid tumor cell line described here.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1984

Multidrug resistance.

Mutations resulting in a complex phenotype of cross-resistance and collateral-sensitivity are frequently observed in mammalian cell lines. A cell surface 170 000 dalton glycoprotein (P-glycoprotein) has been identified to be intimately associated with this multidrug resistance phenotype. We speculate that such mutations also occur in advanced cancers and play a major role in contributing to the non-response to combination chemotherapy. In this context, P-glycoprotein may be a useful molecular marker for diagnostic and therapeutic applications.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1983

Cell surface P-glycoprotein associated with multidrug resistance in mammalian cell lines.

The plasma membranes of hamster, mouse, and human tumor cell lines that display multiple resistance to drugs were examined by gel electrophoresis and immunoblotting. In every case, increased expression of a 170,000-dalton surface antigen was found to be correlated with multidrug resistance. This membrane component is of identical molecular size and shares some immunogenic homology with the previously characterized P-glycoprotein of colchicine-resistant Chinese hamster ovary cells. This finding may have application to cancer therapy.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1983

Daunorubicin-resistant Chinese hamster ovary cells expressing multidrug resistance and a cell-surface P-glycoprotein.

Independent lines of Chinese hamster ovary cells resistant to the antineoplastic drug, daunorubicin, were obtained by clonal isolation in increasing drug concentrations. A single daunorubicin-resistant phenotype typified by reduced cellular drug accumulation was observed. These mutants displayed a complex phenotype of resistance to a variety of unrelated drugs. Such properties are similar to those of membrane-altered colchicine-resistant lines (V. Ling and L.H. Thompson, J. Cell. Physiol., 83: 103-116, 1974). Analysis of the plasma membrane components of the daunorubicin-resistant clones by gel electrophoresis revealed a prominent cell surface glycoprotein with a molecular weight of about 170,000. This component was immunologically cross-reactive with the cell surface P-glycoprotein of about the same molecular weight, previously identified in colchicine-resistant cells. Thus, it appears that the mechanism of resistance characterized by P-glycoprotein expression could be the basis of many drug-resistant phenotypes.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1983

Multidrug-resistance phenotype in Chinese hamster ovary cells.

Multidrug resistance is a complex pleiotropic phenotype of cross-resistance and collateral sensitivity to unrelated compounds observed in many mammalian cell mutants selected for resistance to single agents. In Chinese hamster ovary cells, colchicine-resistant mutants expressing this phenotype have been characterized extensively. Such mutants arise apparently from a single genetic event, and the basis of this phenotype appears to be localized at the membrane level, resulting in altered drug permeability. Expression of a 170,000-dalton surface glycoprotein (P-glycoprotein) has been identified to correlate with the multidrug-resistance phenotype. Selection of a second mutation in colchicine-resistant mutants, for resistance to phytohemagglutinin, results in an alteration of the carbohydrate moiety in P-glycoprotein and other surface components. This mutation does not noticeably affect the multi-drug-resistance phenotype. The altered permeability of mutant cells to drugs, however, can be modulated by nonionic detergents or metabolic inhibitors. These findings are consistent with a molecular mechanism of multidrug resistance whereby the pleiotropic response of the cell is mediated by an overexpression of a cell-surface protein, the P-glycoprotein.

Animals↗
PubMed1982

DNA-mediated transfer of multiple drug resistance and plasma membrane glycoprotein expression.

Colchicine-resistant Chinese hamster ovary (CHO) cell mutants whose resistance results from reduced drug permeability have been isolated previously in our laboratories. This reduced permeability affects a wide range of unrelated drugs, resulting in the mutants displaying a multiple drug resistance phenotype. A 170,000-dalton cell surface glycoprotein (P-glycoprotein) was identified, and its expression appears to correlate with the degree of resistance. In this study we were able to confer the multiple drug resistance phenotype on sensitive mouse L cells by DNA-mediated gene transfer of DNA obtained from the colchicine-resistant mutants. P-glycoprotein was detected in plasma membranes of these DNA transformants by staining with an antiserum raised against membranes of mutant CHO cells. These results are consistent with a causal relationship between P-glycoprotein expression and the multiple drug resistance phenotype.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1977

Nature of the lectin-induced activation of plasma membrane Mg2+ATPase.

The Mg2+ATPase activity of liver plasma membranes decreases markedly with increasing temperature above 30 degrees. This negative temperature dependency is counteracted by the binding of wheat germ agglutinin, concanavalin A, or Ricinus communis agglutinin (at concentrations greater than or equal 0.5 mg/ml) to membranes prior to assay of the enzyme. With one of these lectins bound, the enzyme has a single energy of activation between 20 degrees and 45 degrees. The binding of dimeric succinyl concanavalin A, soybean agglutinin, fucose-binding lectin from Lotus tetragonolobus, or the leucoagglutinin from Phaseolus vulgaris does not alter the temperature dependency of the enzyme. The latter two lectins, however, do prevent the concanavalin A-induced activation of the enzyme at 37 degrees. At saturating substrate concentrations, the enzyme is not inhibited by any of the lectins tested over a wide range of concentrations. Cytochalasin B and colchicine separately or in combination have little influence on the lectin-induced enhancement of enzyme activity. Chlorpromazine and vinblastine sulfate each partially prevent the activation and in combination do so completely. Treatment of the membranes with the detergent Lubrol-PX or phospholipase A prevents activation of the enzyme by concanavalin A. The results are consistent with a restriction by the lectin of an environment which is normally too disordered for maximal enzyme activity above 30 degrees.

Adenosine Triphosphatases↗
PubMedDate not supplied

Amplification of P-glycoprotein genes in multidrug-resistant mammalian cell lines.

The multidrug-resistance phenotype expressed in mammalian cell lines is complex. Cells selected with a single agent can acquire cross-resistance to a remarkably wide range of compounds which have no obvious structural or functional similarities. The basis for cross-resistance seems to be a decreased net cellular accumulation of the drug involved, and has been attributed to alterations in the plasma membrane. An over-expressed plasma membrane glycoprotein of relative molecular mass (Mr) 170,000 (P-glycoprotein) is consistently found in different multidrug-resistant human and animal cell lines, and in transplantable tumours. Consequently, it has been postulated that P-glycoprotein directly or indirectly mediates multidrug resistance. Here we report the cloning of a complementary DNA encoding P-glycoprotein. Southern blot analysis of hamster, mouse and human DNA using this cDNA as a probe showed that P-glycoprotein is conserved and is probably encoded by a gene family, and that members of this putative family are amplified in multidrug-resistant cells.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMedDate not supplied

Detection of P-glycoprotein in multidrug-resistant cell lines by monoclonal antibodies.

One reason for the failure of chemotherapy in the treatment of advanced cancers may be the outgrowth of multidrug-resistant tumour cells. Multidrug resistance has been modelled in numerous mammalian cell lines in which the phenotype is characterized by a pleiotropic cross-resistance to unrelated drugs. In the study reported here, we have produced monoclonal antibodies whose binding to plasma membranes of different multidrug-resistant mammalian cells correlates with the degree of drug resistance. All these antibodies are specific for P-glycoprotein, a cell surface component of relative molecular mass (Mr) 170,000 (170K) that has been described previously, and are directed against three spatially distinct epitopes which define a conserved cytoplasmic domain in the C-terminal region of the P-glycoprotein polypeptide. The conserved nature of P-glycoprotein and its low-level expression is drug-sensitive cells suggest that it has an important function at the cell surface. The monoclonal antibodies against P-glycoprotein described here might serve as diagnostic reagents for clinically unresponsive tumours.

ATP Binding Cassette Transporter, Subfamily B, Mem↗