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Biomedical subjects

V Ling

Publications and source records attributed to V Ling.

At least 181 records · Page 10Linked to original sources
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

Metastatic variants are generated spontaneously at a high rate in mouse KHT tumor.

Using the Luria-Delbrück fluctuation analysis, we have examined the lung tumor-forming ability of a series of parallel clones derived from the KHT tumor, grown to small defined sizes. From these studies, we conclude that metastatic variants arise spontaneously in the clonal lines during their growth, at an apparent rate of approximately 10(-5) per cell per generation. This rapid rate has implications for our understanding of tumor heterogeneity and the process of tumor progression. Previous results have suggested that heterogeneity observed in cloning experiments reflects stable subpopulations of cells in the original tumor. We propose here an alternative "dynamic heterogeneity" model, in which metastatic variants arise at a high rate (as detected in the cloning experiments) but need not be stable mutations in order to effectively produce metastases.

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↗
PubMed1982

A model system for studying metastasis using the embryonic chick.

An assay capable of recovering individual viable rodent cells localized in various organs of the chick embryo is described. This assay is based on the differential sensitivity of chick and rodent cells to the cytotoxic drug ouabain. Utilizing this assay, the potential of the chick embryo as a model system for studying metastasis was examined. Several cell lines were characterized in three ways: (a) ability to form local tumors after cell application onto the chorioallantoic membrane; (b) ability to form macro- or microscopic metastasis in the embryo from chorioallantoic membrane tumors; (c) experimental metastatic ability following i.v. injection into chorioallantoic membrane veins. These results were compared with the results obtained from the ouabain-plating assay. We conclude that this assay permits detection of viable metastatic cells even when tumors cannot be detected and helps to overcome the time constraints that have, in the past, limited the usefulness of the chick embryo in modeling metastasis.

Allantoin↗
PubMed1981

Hoechst 33342 dye uptake as a probe of membrane permeability changes in mammalian cells.

Flow cytometric analysis of the uptake of the DNA-specific and fluorescent probe Hoechst 33342 (HO342) offers a simple and rapid method for measuring membrane transport rates in mammalian cells and identifying cellular subpopulations that differ in their membrane transport rates. In a Chinese hamster ovary wild-type cell line and in three colchicine-resistant lines derived from it, the rate of uptake of HO342 dye decreases as the stepwise resistance to colchicine increases. A colchicine-sensitive revertant cell line shows an increased rate of dye uptake. Drug resistance in these lines has previously been shown to be related to changes in transport rate. In a manner similar to colchicine, the rate of uptake of HO342 dye shows nonsaturation kinetics. The effects of KCN, a metabolic inhibitor, on HO342 dye uptake, both in the presence and in the absence of glucose, is similar to that previously observed for colchicine uptake. When murine spleen cells are stained with HO342 under appropriate conditions, one sees two populations of lymphocytes differing in HO342 fluorescence intensity, a difference not related to DNA content. The two subpopulations show the same relative difference in both colchicine and HO342 uptake. HO342 dye appears, therefore, to enter mammalian cells by the same mechanism as colchicine--i.e., by unmediated diffusion--and can be used as a probe of cytoplasmic membrane permeability. Potential applications of the dye in studies of drug resistance, detection of activated T cells, and recognition of lymphocyte subpopulations are discussed.

Animals↗
PubMed1981

Structural and functional alterations in microtubule protein from Chinese hamster ovary cell mutants.

We have examined mutant lines of Chinese hamster ovary cells that have increased resistance to the antimicrotubule drug Colcemid. Analysis of the functional properties of purified microtubule protein indicates that increased tolerance to the drug in vivo is reflected in altered properties of microtubules and tubulin in vitro. In this study, we have examined one series of related mutants and have found different microtubule alterations associated with each selection step. These changes include decreased Colcemid-binding affinity, an altered electrophoretic pattern of tubulin subcomponents, increased resistance to Colcemid inhibition of polymerization in vitro and, in one case, a decreased critical concentration for microtubule assembly. Characterized mutants of the class described here will be useful for probing the regulation of microtubule assembly in vivo.

Animals↗
PubMed1981

Tumor heterogeneity and stability of the metastatic phenotype of mouse KHT sarcoma cells.

Heterogeneity in metastatic ability has been demonstrated in model systems for in vitro-cloned cell lines for a number of different tumors. We have examined the clonal diversity of mouse KHT sarcoma cells cloned either in vitro or in vivo by determining their ability to form lung colonies following i.v. injection into syngeneic mice. A wide range of metastatic ability was found in both the in vitro- and in vivo-isolated clones, suggesting that the diversity observed is not due to any selection occurring during in vitro growth. The stability of four in vitro-isolated clones, two of high metastatic and two of low metastatic ability, was then studied over a period of 3 to 4 months of growth in vitro. The phenotype of the highly metastatic cells remained relatively stable, declining only slightly over time. The clones with low metastatic ability, however, demonstrated a significant increase in ability to form lung colonies over the first 30 days in culture before becoming stable at levels approximately 10-fold higher than their original values. Even after this increase, however, there remained a difference of about a factor of 10 in the metastatic ability of the high and low pairs of clones. It was found that the number of lung colonies formed by all four cell lines was significantly increased when plastic microspheres were injected with the cell suspension. The cells with low metastatic ability were affected to a greater degree by the microspheres, resulting in the elimination of the difference between the four clones after 30 days in culture. This result suggests that the use of microspheres may provide a means to distinguish different cellular properties which affect the ability of cells to form lung metastases.

Animals↗
PubMed1981

Selection and characterization of Chinese hamster ovary cell mutants resistant to melphalan (L-phenylalanine mustard).

Melphalan (Alkeran) is an alkylating agent commonly used in the treatment of multiple myeloma and other neoplasia. We have isolated melphalan-resistant (MelR) Chinese hamster ovary cells in vitro. Stably resistant clones were observed with a frequency of about 10(-7) after a single drug exposure. Two clones, MelR1 and MelR6, were studied in detail, and their phenotypes were compared to a colchicine-resistant membrane permeability mutant (CHRC5) isolated previously by Ling and Thompson (J. Cell Physiol., 83: 103-116, 1974), which was cross-resistant to melphalan. The MelR cones were cross-resistant to the nitrogen mustard class of alkylating agents, such as melphalan, nitrogen mustard, and chlorambucil, but not to alkylating agents, such as methanesulfonic acid:ethyl ester or mitomycin C. The MelR clones differed from CHRC5 in their lack of cross-resistance to puromycin and Adriamycin. Studies with [14C]melphalan showed CHRC5, but not the MelR clones, to be defective in drug accumulation into whole cells. The mechanism of melphalan resistance in CHRC5 is attributed to reduced drug accumulation due to a plasma membrane alteration. In the MelR clones, investigation of drug distribution into cell subfractions revealed reduced accumulation into the nucleus compared to the parental cell line. We therefore propose that the mechanism of resistance in the MelR cells results from a nuclear alteration(s) specific to a subclass of alkylating agents.

Animals↗
PubMed1980

Small intestinal and colonic changes induced by a chemically defined diet.

Three groups of rats were fed, respectively, a chemically defined diet intragastrically (IG), an equivalent diet intravenously (IV) and solid food orally (CH) for 8 days, and their small intestines and colons compared. All received equal calories. The small intestine was divided into equal proximal (A), middle (B), and distal (C) segments for measurements. Mucosal weight per cm in segments A and B of IG were, respectively, 65 and 38% higher than in IV (P less than 0.01), but 27 and 33% lower than in CH (P less than 0.01). However, in the distal segment, C, mucosal weight in IG was similar to IV and CH was 79% higher (P less than 0.01). DNA and protein followed the same pattern. Segment A sucrase activities were similar in CH and IG and were much higher than in IV (P less than 0.01). Sucrase in IG dropped very rapidly distally so that it became much lower than in CH (P less than 0.05) and similar to IV. Mucosal weight, DNA, and protein in the colon were not significantly different in IG and IV, which were both significantly lower than in CH (P less than 0.01). The results indicate that a chemically defined diet maintains intestinal mass well in the proximal small intestine, but the effect diminishes rapidly in a distal direction so that distal small intestine and colon become atrophied and similar to those in intravenous feeding.

Animals↗
PubMed1979

Mutants of Chinese hamster ovary (CHO) cells with altered colcemid-binding affinity.

Clones of CHO cells stably resistant to colcemid have been isolated in the presence of the nonionic detergent Tween 80 after mutagen treatment. Successive single-step selections for increasing resistance were performed resulting in lines after three selection steps about 10 fold more resistant to colcemid than the parental cells. Three observations indicate that these colcemid-resistant (CMR) mutants are different from the colchicine-resistant permeability mutants isolated previously. First, their relative resistance to colcemid was not diminished in the presence of detergent which promoted increased drug permeability. Second, the CMR clones displayed limited cross-resistances only to tubulin-binding compounds. Third, the binding affinity of labeled colcemid by cytoplasmic extracts from CMR clones was reduced, and the reduction was greater in the more resistant clones. No reduction in binding of labeled colcemid was observed in the membrane-altered colchicine-resistant mutants. All these observations are consistent with the CMR clones being tubulin-altered mutants. In further support of this conclusion, we observed that tubulin purified from a CMR mutant still possessed reduced colcemid-binding affinity compared with that from parental cells.

Animals↗
PubMed1978

Dominance of colchicine resistance in hybrid CHO cells.

Intraspecific hybrids of colchicine-sensitive with colchicine-resistant (CHR) Chinese hamster ovary cells were constructed, using six different colchicine-resistant clones from two independent series. In each instance, colchicine resistance was expressed in an incompletely dominant manner. Some hybrid clones were examined further for the expression of the pleiotropic CHR phenotype and for the cell surface P glycoprotein. These features of the colchicine-resistant phenotype were also expressed coordinately.

Animals↗
PubMed1978

Influence of biliary stasis on enterokinase activity in the rat.

After 48 h of bile duct ligation, enterokinase activity in rat mucosa was significantly lowered in comparison with controls or rats with bile fistula. Rats with bile fistula were similar to controls. Sucrase levels were similar in all groups. Without endogenous trypsinogen, duodenal perfusion with a trypsinogen-containing solution led to more conversion to trypsin by controls. When their own pancreatic secretion was the source of trypsinogen, trypsin was much higher in perfusate from bile-ligated rats. Solubilized enterokinase was also higher in this group. These results indicate that bile stasis leads to decreased mucosal enterokinase activity and increased pancreatic function. The latter may have caused accelerated loss of enterokinase into the lumen, leading to lower mucosal levels.

Animals↗