PMID(sorted ascending)
in vitro study of a novel atypical beta-adrenoceptor agonist, (l-threo-3-(3,4-dihydroxyphenyl)-n-[3-(4-fluorophenyl) propyl] serine pyrrolidine amide hydrobromide) stimulated the relaxation of guinea pig ileum (ec50: 3.0 x 10(-8) m), trachea (ec50: 1.3 x 10(-7) m), lung parenchyma (ec50: 2.1 x 10(-6) m) and the increase in right atrial rate (ec50: 6.9 x 10(-6) m). it also induced lipolysis of rat white adipocytes (ec50: 1.2 x 10(-6) m). both the relaxant response of ileum and the lipolytic response of adipocytes to sm-11044 were resistant to inhib ...19921356795
modelling the formation of polycentric chromosome chromosome aberrations produced by ionizing radiation or restriction enzymes are believed to result from pairwise interaction of dna double-strand breaks (dsb). in addition to dicentrics, such aberrations may include higher-order polycentrics (tricentrics, tetracentrics, etc.). we have developed computer programs that calculate the probability of the various polycentrics for a given average number of pairwise interactions. two models are used. model i incorporates kinetic competiti ...19921357058
intrinsic activity determinations at the dopamine d2 guanine nucleotide-binding protein-coupled receptor: utilization of receptor state binding affinities.guanine nucleotide-binding protein-coupled receptors have been shown to exist in both a high affinity agonist (hiag) and a low affinity agonist (lowag) state. the formation of the hiag state is promoted by agonists, and the formation of this state of the receptor appears to be a critical factor in the generation of the effector-activating complex g alpha.gtp.mg2+ and in the production of a stimulus. the magnitude of the difference in the affinity a compound has for the hiag versus the lowag stat ...19921357542
homology of a vesicular amine transporter to a gene conferring resistance to 1-methyl-4-phenylpyridinium.the vesicular amine transporter (vat) catalyzes transport and storage of catechol and indolamines into subcellular organelles in a wide variety of cells. it plays a central role in neurotransmission and is the primary target for several pharmacological agents. one of the drugs, reserpine, binds very tightly to the transporter and remains bound even after solubilization, a finding that has proven useful for purification of the transporter from bovine adrenal medulla in a fully functional state. t ...19921357668
disposition of metabolically labeled recombinant soluble cd4 (st4) in male sprague-dawley rats following intravenous and subcutaneous administration.soluble cd4 (st4) has been metabolically labeled with [3h]leucine in chinese hamster ovary cells and purified by s sepharose chromatography. over 250 microci of high specific radioactivity [3h]st4 (42 ci/mmol) was prepared. the radiolabeled molecule was chemically and biologically representative of the unlabeled molecule and thus appropriate for in vivo metabolic investigations. to explore the biotransformation and disposition of a recombinant protein, this uniformly labeled [3h]st4 was administ ...19921358574
involvement of sequences near both amino and carboxyl termini in the rapid intracellular degradation of tyrosine aminotransferase.the degradation of rat liver tyrosine aminotransferase has been studied after transfection of suitable expression vectors into mammalian cells in culture. a normal rapid rate of degradation (half-life about 6 h) was observed in cells under stable transfection conditions. however, the higher enzyme levels produced during transient transfections or after amplification with methotrexate caused the apparent half-life of degradation to increase substantially. analysis of expression in chinese hamster ...19921358885
chinese hamster ovary mrna-dependent, na(+)-independent l-leucine transport in xenopus laevis freshly prepared uninjected folliculated oocytes, na(+)-independent leucine uptake is mediated predominantly by a system l-like transport system. removal of follicular cells, however, results in an irreversible loss of this transport activity. when total poly(a)+ mrna derived from chinese hamster ovary (cho) cells was injected into prophase-arrested stage v or vi xenopus laevis oocytes, enhanced expression of na(+)-independent leucine transport was observed. the injected mrnas associated with ...19921360143
characterization of adriamycin-resistant and radiation-sensitive chinese hamster cell lines.a series of cell lines derived from chinese hamster v79 cells by selection in increasing concentrations of adriamycin (adrm) was developed to study the mechanisms of drug resistance and its relationship to radiation response. survival studies revealed that selection in increasingly higher concentrations of adrm positively correlated with increased cellular drug resistance. increased cellular resistance correlated positively with amplification of the hamster multidrug-resistance gene (pgp 1) as d ...19921360213
liposome-mediated modulation of multidrug resistance in human hl-60 leukemia cells.multidrug resistance (mdr) is a major obstacle in cancer treatment. resistance of cultured tumor cells to major classes of cytotoxic drugs is frequently due to expression of a plasma membrane p-glycoprotein encoded by mdr genes. we have demonstrated that liposome-encapsulated doxorubicin is more toxic than the free drug and that it modulates mdr in chinese hamster lz cells and human colon cancer cells.19921361008
thyroid stimulatory autoantibodies in different patients with autoimmune thyroid disease do not all recognize the same components of the human thyrotropin receptor: selective role of receptor amino acids study the interaction between tsh, autoantibodies and the amino-terminal half of the tsh receptor extracellular region (amino acids 1-260; domains abc), we constructed 20 lh/cg chimeric receptor cdnas. the prototypic receptor for modification contained domains abc of the tsh receptor and domains de of the lh/cg receptor. segments (6-13 amino acids) within the abc domains were replaced with the corresponding amino acids of the rat lh/cg receptor. fifteen of the 20 chimeric receptors could be e ...19921361193
binding assay for thyrotropin receptor autoantibodies using the recombinant receptor protein.we have characterized a transfected chinese hamster ovary cell line, jp09, which expresses high levels of the human tsh receptor (tsh-r). based on a theoretical biological activity for tsh of 40 iu/mg, jp09 has approximately 90,000 receptors per cell, having a dissociation constant of 1.64 x 10(3) mu/l or 1.47 x 10(-9) mol/l. we have used jp09 to prepare solubilized tsh-rs which have formed the basis of a binding assay for thyroid-binding inhibiting immunoglobulins in unfractionated sera. we hav ...19921361194
factors influencing the dna content of radiation-induced micronuclei.the distribution of the dna content of radiation-induced micronuclei was analysed in several cell lines (chinese hamster, syrian hamster and mouse nih-3t3 cells) by flow cytometry. frequency and dna content of micronuclei were measured simultaneously using fluorescence and forward scatter signals of micronuclei and nuclei in suspension stained with ethidium bromide. computerized random breakage of chromosomes and random combination of fragments was performed to compare the measured micronucleus ...19921361516
cytotoxicity of 125i decay in the dna double strand break repair deficient mutant cell line, xrs-5.the survival of parental chinese hamster ovary (cho) k1 cells and the dna double strand break (dsb) repair deficient mutant, xrs-5 was determined after accumulation of 125i decays. both cho and xrs-5 cells were extremely sensitive to accumulated 125i decays. the d0 values for cho and xrs-5 cells were 40 and approximately 7 decays per cell, respectively. the difference in cell survival between cho and xrs-5 cells was not due to differences in overall 125iudr incorporation, differences in labellin ...19921361518
identification of kinetochores and dna synthesis in micronuclei induced by mitomycin c and colchicine in chinese hamster ovary cells.the presence of kinetochore and dna synthesis in micronuclei (mn) induced in chinese hamster ovary (cho) cells by clastogenic and aneuploidogenic substances such as mitomycin c (mmc) and colchicine was determined by immunofluorescence technique using crest antikinetochore antibodies and anti-bromodeoxyuridine (brdurd) antibodies. a cytofluorimetric analysis was also performed. colchicine significantly increased micronucleated cells at least up to 96 h from the end of treatment. as expected, amon ...19921363157
mammalian origins of has been almost twenty-five years since huberman and riggs first showed that there are multiple bidirectional origins of replication scattered at approximately 100 kb intervals along mammalian chromosomal fibers. since that time, every conceivable physical property unique to replicating dna has been taken advantage of to determine whether origins of replication are defined sequence elements, as they are in microorganisms. the most thoroughly studied mammalian locus to date is the dihydrofolat ...19921365877
growth behavior of chinese hamster ovary cells in a compact loop bioreactor: 1. effects of physical and chemical environments.chinese hamster ovary (cho) cells were cultivated in a compact loop bioreactor using mem-alpha medium supplemented with 10% fetal calf serum. effects of physical and chemical environments, i.e., ph in the medium, stirring speed of impellers, temperature and partial pressure of oxygen (po2) upon growth of suspended cells in the bioreactor were determined in batch cultures. growth behavior was characterized by specific rates of growth (mu), glucose consumption (qg) and lactate production (ql), and ...19901366683
growth behavior of chinese hamster ovary cells in a compact loop bioreactor. 2. effects of medium components and waste products.effects of biochemical factors, i.e., medium components and metabolic byproducts, on growth of chinese hamster ovary (cho) cells were investigated. glucose and ammonia were found to inhibit the growth. kinetic analysis gave the inhibition constants, 0.14 g l-1 for ammonia and 5.0 g l-1 for glucose. since glutamine was unstable and was a main source of ammonia, precise studies on glutamine degradation and ammonia formation process were done. by evaluating the spontaneous reactions, net glutamine ...20051366684
growth kinetics of chinese hamster ovary cells in a compact loop bioreactor. 3. selection and characterization of an anchorage-independent subline and medium improvement.four sublines of chinese hamster ovary (cho) cells were selected or cloned on a 10% fetal calf serum supplemented mem-alpha medium. three of them were monolayer cultures and could proliferate by 2000 times a week (mu = 1.1 d 1) in t-flasks. the other subline, s1, could grow in suspension even in static t-flask cultures. the stability in chromosome number of these cell lines was investigated. by evaluating the kinetic growth parameters, i.e. the specific rates of growth, glucose consumption and l ...19901366937
effect of free fatty acids and phospholipids on growth of and product formation by recombinant baby hamster kidney (rbhk) and chinese hamster ovary (rcho) cells in culture.recombinant bhk and cho cells producing human antithrombin iii (rh atiii) were used to investigate the utilization of phospholipids and free fatty acids from low-serum (0.1% fbs) culture medium. both cell lines show distinctly different patterns of fatty acid utilization. for rbhk atiii cells it is shown that under low serum conditions several different combinations of free fatty acids (bound to bovine albumin) elicit an identical growth stimulatory effect although individual consumption and pro ...19911366984
cultivation of anchorage-dependent animal cells in microsphere-induced aggregate culture.diethylaminoethyl-derivatized dextran microspheres were used to cultivate chinese hamster ovary, 293, vero and swine testicular cells. cells became attached to the microspheres but did not spread out. instead, they grew in a more spherical shape and eventually formed multiple-cell-layer aggregates. viability in these aggregates remained high after the cultures reached high cell concentrations. this cultivation method allows a high cell density to be achieved with a low microsphere concentration.19911367199
high level expression of the humanized monoclonal antibody campath-1h in chinese hamster ovary cells.we have cloned the light and heavy chain cdnas for the humanized monoclonal antibody campath-1h and expressed them in chinese hamster ovary (cho) cells using a dihydrofolate reductase (dhfr) amplification procedure. each cdna was positioned under control of the strong human beta-actin promoter/polyadenylation signals and used to evaluate alternative vector design and amplification procedures. by employing a dual selection co-transfection strategy, initial transformants accumulated antibody level ...19911367214
high density culture of anchorage-dependent animal cells by polyurethane foam packed-bed culture systems.monkey kidney cells (vero) and chinese hamster ovary cells (cho-k1) attached to the internal surface of polyurethane foam (puf) and grew to a high cell density (1.1 x 10(8) cells/cm3 puf and 4.2 x 10(7) cells/cm3 puf, respectively) in a puf-plates packed-bed culture system. this density of vero cells was twice that obtained previously with a puf-particles packed-bed culture system. a maximum cell density of 6.7 x 10(7) cells/cm3 culture vessel volume was obtained in a puf-disc packed-bed culture ...19911367366
suppression of the degradation of recombinant human apolipoprotein e by a protease inhibitor obtained from fetal bovine serum in serum-free culture.the recombinant human apolipoprotein e (apo-e) produced by chinese hamster ovary cells (cho-322 cells) in serum free culture was degraded to 24k and 23k fragments that contained n-terminal amino acid. the degradation site of apo-e to 24k fragment was between arg180 and leu181 and the c-terminal amino acid of 23k fragment was gly169. in fetal bovine serum (fbs)-containing culture, the degradation was inhibited. however, in calf serum (cs) the inhibitory activity was not detected. thus, we attempt ...19911367397
spin filter perfusion system for high density cell culture: production of recombinant urinary type plasminogen activator in cho cells.we have used a 20 liter stirred tank fermentor, equipped with a 127 mesh ethylene-tetrafluoroethylene rotating screen for cell recycle, for the continuous production of recombinant single chain urokinase-type plasminogen activator (rscu-pa) from chinese hamster ovary (cho) cells. viable cell densities between 60 and 74 million per ml were maintained at medium perfusion rates of 3.0 to 4.0 fermentor volumes per day. cells were retained by the 120 micron nominal opening filter through the formatio ...19901367426
anchorage-dependent mammalian cell culture using polyurethane foam as a new substratum for cell attachment.anchorage-dependent mammalian cells were cultivated at high cell density in a novel culture system using polyurethane foam (puf) as a substratum for cell attachment. puf has a macroporous structure giving a high surface area to volume ratio. monkey kidney cells (vero) and chinese hamster ovary cells (cho-k1) attached to the internal surface of puf and grew to a high cell density (1.04 x 10(8) cells/cm3 puf and 3.5 x 10(7) cells/cm3 puf, respectively) in puf stationary cultures. in addition, we h ...19901367457
chinese hamster ovary cell growth and interferon production kinetics in stirred batch culture.recombinant human interferon-gamma production by chinese hamster ovary cells was restricted to the growth phase of batch cultures in serum-free medium. the specific interferon production rate was highest during the initial period of exponential growth but declined subsequently in parallel with specific growth rate. this decline in specific growth rate and interferon productivity was associated with a decline in specific metabolic activity as determined by the rate of glucose uptake and the rates ...19911367524
"differentiation induction" culture of human leukemic myeloid cells stimulates high production of macrophage differentiation inducing factor.a suitable procedure for the production of human monokines was defined as 'differentiation-induction' culture. human monocytic leukemia thp-1 cells were well-differentiated from nonfunctional promonocytes into macrophage-like cells by the induction with a combination of mezerein, retinoic acid, and a mycoplasma fermentans extract. the differentiated thp-1 cells secreted a high amount of macrophage differentiation-inducing factor (dif) activity and concomitantly produced other known monokines, su ...19911367527
a cho strain producing high-level human il-6 with the 3' deletion construct.a chinese hamster ovary (cho) strain producing high-level human interleukin 6 (il-6) was obtained, by introduction of the il-6 cdna from which the 3' au-rich region was deleted. the il-6 mrna of this strain was stable. the productivity was more than 15 times higher than the previously obtained clone, which has intact il-6 cdna in the same expression vector. this strain produced il-6 at a high level of 30 micrograms ml-1 in batch culture, or a continuous 20 micrograms per 10(6) cells per day in m ...19921367984
production of human antithrombin-iii in a serum-free culture of cho cells.a simple method was developed to establish serum-independent chinese hamster ovary (cho) cells that grew and secreted high level of human antithrombin-iii (at-iii). first, human at-iii and mouse dihydrofolate reductase (dhfr) cdnas were transfected into dhfr-deficient cho cells. transfected cells were treated with increasing concentrations of methotrexate (mtx) and clones secreting high levels of at-iii (10-20 micrograms/ml/3 day) in a serum-containing medium were obtained. serum-independent clo ...19921368211
inhibition by lactoferrin and kappa-casein glycomacropeptide of binding of cholera toxin to its receptor.inhibition from binding of cholera toxin (ct) to chinese hamster ovary (cho)-k1 cells and ganglioside gm1 by lactoferrin (lf) and kappa-casein glycomacropeptide (gmp) from cow's milk was examined. both lf and gmp effectively reduced the ct-derived morphological changes in cho-k1 cells. the competitive binding assay demonstrated that both lf and gmp inhibited the binding of ct to gm1, although their affinity for ct was lower than that of gm1. the inhibitory effect of lf and gmp seemed to be attri ...19921368296
utilization and stability of vitamins in serum-containing and serum-free media in cho cell culture.the concentrations of four vitamins, ascorbic acid, nicotinamide, choline and thiamine were evaluated in the culture supernatant of chinese hamster ovary (cho) cells. the media used were alpha-modified eagle's minimum essential medium (mem-alpha) supplemented with 10% fetal calf serum, and a 1:1 mixture of ham's f12 and dulbecco's modified eagle's medium (dme/f12), containing neither serum nor protein. the reference experiment without cells revealed instability of ascorbic acid and thiamine. mor ...19901368624
effect of glycosylation on properties of soluble interferon gamma receptors produced in prokaryotic and eukaryotic expression systems.we investigated the influence of glycosylation on solubility, chromatographic behavior and resistance to heat- and chaotrope-dependent denaturation and proteolytic digestion of three recombinant human interferon gamma receptors produced in escherichia coli, spodoptera frugiperda and chinese hamster ovary cells. the proteins produced in the eukaryotic expression systems were glycosylated, carrying different, heterogeneous carbohydrate moieties. they were assayed fully glycosylated and after remov ...19921368793
two-dimensional electrophoresis as a tool for control of quality and consistency in production systems using animal cells. two-dimensional electrophoresis in animal cell culture technology.a nonrecombinant human melanoma cell line and recombinant chinese hamster ovary (cho) cells were used as examples for long-term in vitro cultivation in protein-free media. the method used to monitor the consistency of protein release by these mammalian cells was two-dimensional electrophoresis with immobilized ph gradient. secreted proteins from a melanoma cell line cultivated in a continuous fermentation system over a period of 22 months were monitored. two-dimensional patterns of secreted prot ...19921368812
a novel protease obtained from fbs-containing culture supernatant, that processes single chain form hepatocyte growth factor to two chain form in serum-free culture.the recombinant human hepatocyte growth factor (r-hhgf) produced by chinese hamster ovary cells transfected with hhgf cdna (cho bd-24 cells) was the two chain form in fetal bovine serum (fbs) containing culture. however, in serum-free culture the non-processed r-hhgf, single chain form, was detected with two chain form r-hhgf. we purified the protease that proteolytically processed single chain r-hhgf to two chain form r-hhgf. a protease was purified to give a single peak from the culture supern ...19921368819
gene transfer to tumor-infiltrating lymphocytes and other mammalian somatic cells by microprojectile bombardment.we demonstrate the application of particle delivery to the transformation of mammalian somatic cells. two mouse t-lymphocyte cell lines and chinese hamster ovary (cho) cells were transformed transiently with the rsv-adh (alcohol dehydrogenase) gene. stable gene transfer was also demonstrated in cho cells at a frequency of 6 x 10(-4) and in t-cells at a frequency of 1 x 10(-4), using beta-gal/neomycin-resistance gene constructs. the helium gas acceleration mechanism (pds 1000/he) and particle del ...19921369001
application of a statistical design to the optimization of culture medium for recombinant interferon-gamma production by chinese hamster ovary cells.the importance of serum-free medium components on the growth of chinese hamster ovary (cho) cells and production of recombinant human interferon(ifn)-gamma was investigated. the complexity of the medium led to the adoption of a statistical optimization approach based on a plackett-burman design. from this analysis a set of nutritional components was identified as important for cell growth and recombinant protein production. glycine was identified as an important determinant of specific growth ra ...19921369013
effect of amplification of dhfr and lac z genes on growth and beta-galactosidase expression in suspension cultures of recombinant cho cells.studies were conducted to characterize the effect of gene amplification and foreign gene expression on recombinant cho cell growth. chinese hamster ovary (cho) cells were transfected with an expression vector containing the gene for dihydrofolate reductase (dhfr) and the gene for human beta-interferon (beta-ifn) or the lac z gene which codes for beta-galactosidase (beta-gal). the recombinant genes in these cho cells were amplified stepwise by growth in 0, 10(-7), and 10(-6) m methotrexate (mtx), ...19921369176
construction of a toxic insulin molecule: selection and partial characterization of cells resistant to its killing effects.we have constructed an insulin-diphtheria hormono-toxin which migrates as a single 29 kd band on 10% sds polyacrylamide gel electrophoresis. this corresponds to a one to one molar ratio of the diphtheria a-chain (23 kda) and insulin (6 kda) molecules. the diphtheria a-chain: insulin (dtai) hormono-toxin demonstrates cytotoxicity in v-79 chinese hamster cells exhibiting an ld50 of 1.1 x 10(-8) m, which is 22 x more potent than whole diphtheria toxin. also, dtai can competitively displace [125i]-i ...19921369208
production of analytical quantities of recombinant proteins in chinese hamster ovary cells using sodium butyrate to elevate gene expression.sodium butyrate was used to enhance expression levels and thereby facilitate the generation of analytical quantities of nine different tissue plasminogen activator (tpa) analogues expressed under the control of the cytomegalovirus immediate early (cmv ie) promoter by the chinese hamster ovary (cho) mammalian expression system. production involved growth in roller bottles, using serum free or low serum media formulations, together with repetitive, sodium butyrate inductions. average inductions in ...19911369310
constitutive high-level production of human lymphotoxin by cho-k1 cells transformed with the human lymphotoxin gene controlled by a human beta-actin achieve high-level production of human lymphotoxin (hlt), a plasmid (p beta lt-ldhfr) containing the hlt genomic dna, a mouse dihydrofolate reductase (dhfr) cdna, and a bacterial ecogpt gene was cotransfected with a plasmid (p beta ltml) encoding only the hlt genomic dna into chinese hamster ovary (cho-k1) cells at a 1:7 molar ratio. subsequently one of the ecogpt-positive clones (clone a31) was grown in stepwise increasing concentrations of methotrexate (mtx). a large amount of the hlt was s ...19911369325
high level expression of tissue inhibitor of metalloproteinases in chinese hamster ovary cells using glutamine synthetase gene amplification.we have used a glutamine synthetase (gs) gene as an amplifiable marker in chinese hamster ovary (cho) cells. gs was combined with an efficient transcription unit to produce tissue inhibitor of metalloproteinases (timp). initial transfectant cell-lines selected using a gs gene secreted up to 9 micrograms timp/10(6) cells/24h. after one round of gs gene amplification expression levels of 110 micrograms timp/10(6) cells/24h were achieved. these gs gene amplified cho cells, when adapted to grow in s ...20001369995
production of recombinant von willebrand factor by cho cells cultured in macroporous microcarriers.recombinant chinese hamster ovary cells producing von willebrand factor have been successfully grown in gelatin macroporous microcarriers (cultispher-g). serum-free cultures were maintained in 1, 4, and 10 liter fermentors for more than two months. comparative studies with cytodex-3 microcarriers have been performed in 1 liter fermentors. the lower specific von willebrand factor productivity of cho cells cultivated on cultispher-g were offset by higher cell densities (10(7) - 2 x 10(7) cells/ml) ...19901370026
comparison of human lymphotoxin gene expression in cho cells directed by genomic dna or cdna sequences.four recombinant plasmids coding for human lymphotoxin (lt) were constructed with genomic dna (gdna) or cdna sequences. the simian virus 40 (sv40) early region, which contains the early promoter, an intron of the small-t-antigen-encoding gene, and polyadenylation signal sequences, was used for transcriptional and post-transcriptional regulatory elements in the construction of these plasmids. two of them contained gdna and the other two contained cdna. one of the gdna plasmids and one of the cdna ...19901370034
tunicamycin treatment of cho cells abrogates multiple blocks to retrovirus infection, one of which is due to a secreted inhibitor.chinese hamster ovary (cho) cells are resistant to infection by all of the major classes of murine retroviruses and are partially resistant to infection by gibbon ape leukemia virus. treatment of cho cells with the glycosylation inhibitor tunicamycin rendered these cells susceptible to infection by retroviral vectors with ecotropic, xenotropic, and amphotropic host ranges and increased the titer of gibbon ape leukemia virus pseudotyped vectors 10-fold. vectors having a polytropic host range did ...19921370096
clastogenicity of lead chromate particles in hamster and human cells.several insoluble compounds of chromium, such as lead chromate, are respiratory carcinogens in experimental animals and suspected to be so in humans. lead chromate induces neoplastic transformation in cultured cells but the mechanism of genotoxicity is unknown. we examined the effect of lead chromate on the integrity of chromosomes of chinese hamster ovary (cho) and human foreskin fibroblasts (hff) after a 24-h exposure. at 0.4 microgram/cm2, 0.8 microgram/cm2, 2 microgram/cm2 and 8 microgram/cm ...19921370121
stable expression of monkey cytochrome p-450ia1 cdna in chinese hamster chl cells and its application for detection of mutagenicity of aflatoxin b1.a monkey cytochrome p-450ia1 cdna (mkah1) was transfected into chinese hamster chl cells using a vector containing the sr alpha promoter, and sublines stably expressing p-450ia1 were established. the cells showed 25-fold higher sensitivity to the cytotoxic effect of aflatoxin b1 than the parental chl cells. this hypersensitivity was almost completely suppressed by alpha-naphthoflavone, which is a known specific inhibitor of p-450ia. the cells expressing p-450ia1, but not chl cells, showed a posi ...19921370240
effect of sampling time on chromosome aberration yield for 7 chemicals in chinese hamster ovary cells.choice of harvest time is one of the most important variables in the assessment of whether a compound is clastogenic and in establishing a dose relation. we examined the effects of sampling time on aberration yield for 7 diverse chemicals in cho-wbl cells by harvesting at intervals from 9 to 30 h after treatment for 3 h with or without s9 metabolic activation. we observed both the percentage of aberrant cells and the total number of aberrations. our data suggest that for most compounds a single ...19921370241
a quantitative assessment of the cytotoxicity associated with chromosomal aberration detection in chinese hamster ovary cells.regulatory guidelines suggest testing chemicals up to cytotoxic doses in chromosomal-aberration assays. to investigate the utility and limitations of various cytotoxicity indicators we used chinese hamster ovary (cho) cells to test 8 chemicals with differing ratios of cytotoxicity to clastogenicity. we measured immediate or delayed cell killing and growth inhibition (atp levels, cell counts, colony-forming efficiency, cfe) and cell-cycle perturbations (mitotic index, mi; average generation time, ...20021370242
chromosome rearrangements associated with cad gene amplification. experiments with cell hybrids.resistance to phosphonacetyl-l-aspartate (pala) is caused by cad gene amplification. the marker chromosome of a pala-resistant cell line containing a homogeneously staining region with amplified cad gene was introduced into pala-sensitive chinese hamster cells by microcell-mediated chromosome transfer. two monochromosomal hybrids containing the marker chromosome in addition to the normal chromosome complement of sensitive cells and 1 tetraploid hybrid containing the complete genomes of donor (re ...19921370246
murine b7 antigen provides an efficient costimulatory signal for activation of murine t lymphocytes via the t-cell receptor/cd3 complex.we demonstrate that the murine b7 (mb7) protein is a potent costimulatory molecule for the activation of resting murine cd4+ t cells through the t-cell receptor (tcr)/cd3 complex. stable mb7-transfected chinese hamster ovary cells, but not vector-transfected controls, synergize with anti-cd3 monoclonal antibody and con a-induced t-cell activation, resulting ultimately in proliferation. mb7 exerted its effect by inducing production of interleukin 2 and expression of the interleukin 2 receptor. th ...19921370349
cd58 and cd59 molecules exhibit potentializing effects in t cell adhesion and activation.we have generated stable chinese hamster ovary (cho) cell transfectants expressing either cd58 or cd59 or both molecules to compare their respective parts played in t cell adhesion and activation. using a rosetting assay, we have shown the following: 1) the cd59 molecule was directly responsible for adhesive interaction between human t cells and cd59+ cho transfectants. cd59-mediated adhesion induced 12 +/- 2% (mean +/- sem, n = 25) of rosettes. 2) the cd58 molecule expressed on cd58+ cho transf ...19921370512
chromosomal aberrations and sister-chromatid exchanges induced by n-nitroso-2-acetylaminofluorene and their modifications by arsenite and selenite in chinese hamster ovary cells.the frequencies of chromosomal aberrations (ca) and sister-chromatid exchanges (sce) in chinese hamster cells were significantly increased by the direct-acting mutagen n-nitroso-2-acetylaminofluorene (n-no-aaf) at the concentration of 0.1 mm. n-no-aaf was prepared by nitrosation of the protohepatocarcinogen 2-acetylaminofluorene. the induced ca, which included chromatid breaks, chromatid exchanges, chromosome breaks, and chromosome ring formation were significantly potentiated by the presence of ...20051370719
direct linkage of three tachykinin receptors to stimulation of both phosphatidylinositol hydrolysis and cyclic amp cascades in transfected chinese hamster ovary cells.the mammalian tachykinin system consists of three distinct peptides, substance p, substance k, and neuromedin k, and possesses three corresponding receptors. in this investigation we examined intracellular signal transduction of the individual tachykinin receptors by transfection and stable expression of these receptor cdnas in chinese hamster ovary cells. the three receptors commonly showed a rapid and marked stimulation in both phosphatidylinositol (pi) hydrolysis and cyclic amp formation in r ...19921370820
the protective role of polyphenols in cytotoxicity of hydrogen peroxide.a variety of synthetic and natural polyphenols protect mammalian cells from hydrogen peroxide (h2o2). cytotoxicity of h2o2 on chinese hamster v79 cells was assessed with a colony formation assay, and several polyphenols prevented the decrease in the number of colonies caused by h2o2. a study of the structure-activity relationship revealed that affinity of the polyphenols for the cell membrane and the presence of an ortho-dihydroxy moiety in their structure proved essential to this protection.19921370984
a spontaneous mutation of integrin alpha iib beta 3 (platelet glycoprotein iib-iiia) helps define a ligand binding site.this work characterizes a mutant integrin alpha iib beta 3 (glycoprotein (gp) iib-iiia) from a thrombasthenic patient, et, whose platelets fail to aggregate in response to stimuli. the nature of defect was defined by the reduced ability of synthetic peptide ligands, corresponding to the carboxyl terminus of the fibrinogen gamma chain (gamma 402-411) and arg-gly-asp (rgd), to increase the binding of the occupancy-dependent anti-libs1 antibody to mutant alpha iib beta 3 and the reduced binding of ...19921371279
plant extracts induce chromosome aberrations and sister-chromatid exchanges in chinese hamster ovary cells and human lymphocytes.effects of extracts from vicia faba were compared with those of zea mays for the induction of sister-chromatid exchanges (sces) and of chromosome aberrations (cas) in chinese hamster ovary (cho) cells. ca induction by the maize extract was also tested in human lymphocytes. the extracts from roots and leaves of vicia faba induced cas and sces in cho cells. the extracts from maize leaves also induced sces and cas in cho cells, and cas in human lymphocytes. maize extracts were more potent in induci ...19921371591
antibodies against the cystic fibrosis transmembrane regulator.rabbit polyclonal antibodies have been raised against high-performance liquid chromatography purified synthetic peptides corresponding to two discrete regions of the cystic fibrosis transmembrane regulator (cftr) protein: the r-domain (residues 785-796) and the extreme cooh-terminus (residues 1467-1480). antibodies (ab) to each of these peptides were affinity purified either by passage over a peptide-derivatized agarose matrix (ab 785) to produce monospecific polyclonal antibodies or by protein ...19921371641
a flow cytometric study of the effect of heat on the kinetics of cell proliferation of chinese hamster v-79 cells.two methods involving labelling cells with bromodeoxyuridine (brdurd) have been used to study by flow cytometry the effect of hyperthermia (43 degrees c for up to 1 h) on chinese hamster v79 cells. one method involved the use of an antibody to brdurd after pulse-labelling the cells either before or at time intervals after treatment. in the second method, the cells were incubated continuously in brdurd after heat treatment, and the components of the cell cycle were then visualized by staining wit ...19921371702
cloning and expression of a human atp-citrate lyase cdna.a full-length cdna clone of 4.3 kb encoding the human atp-citrate lyase enzyme has been isolated by screening a human cdna library with the recently isolated rat atp-citrate lyase cdna clone [elshourbagy et al. (1990) j. biol. chem. 265, 1430]. nucleic-acid sequence data indicate that the cdna contains the complete coding region for the enzyme, which is 1105 amino acids in length with a calculated molecular mass of 121,419 da. comparison of the human and rat atp-citrate lyase cdna sequences reve ...19921371749
epitope mapping of the carcinoembryonic antigen with various related recombinant proteins expressed in chinese hamster ovary cells and 25 distinct monoclonal antibodies.antigenic epitopes of carcinoembryonic antigen (cea) and non-specific cross-reacting antigen (nca) were analysed in relation to their domain structures [domains n, i (a1-b1), ii (a2-b2), iii (a3-b3) and m for cea and domains n, i (a1-b1), and m for nca]. we reconstructed cdnas for cea-n, cea-n-i, cea-n-i-ii, cea-n-i-ii-iii-m (cea-whole), nca-n, nca-n-i and nca-n-i-m (nca-whole), which were expressed in chinese hamster ovary (cho) cells. the recombinant proteins were purified by immunoadsorption ...19921371822
application of an epithelial liver cell line, metabolically competent, for mutation studies of promutagens.recently numerous attempts have been made to reduce the use of vertebrate animals in laboratory experiments to evaluate general and acute toxicity, mutagenesis and teratogenesis of new drugs or chemicals. one common approach is to use established, proliferating cell lines that preserve differentiated functions such as the competence to metabolize xenobiotics. to this end a continuous chinese hamster epithelial liver cell line (chel cells) was established, cultured as used for mutagenesis studies ...19921371832
biphenyl and fluorinated derivatives: liver enzyme-mediated mutagenicity detected in salmonella typhimurium and chinese hamster v79 cells.hepatocarcinogenic polychlorinated and polybrominated biphenyls usually show negative results in in vitro mutagenicity assays. problems in their testing result from their low water solubility and their slow rate of metabolism. we therefore investigated better soluble model compounds, namely biphenyl and its 3 possible monofluorinated derivatives. in the direct test, these compounds proved to be nonmutagenic in salmonella typhimurium ta98 and ta100 (reversion to histidine prototrophy) and in chin ...19921371835
differential effect of the amino acid cystine in cultured mammalian and bacterial cells exposed to oxidative stress.the effect of cystine in the cytotoxic response of cultured chinese hamster ovary and escherichia coli cells to challenge with hydrogen peroxide has been investigated. it was found that this amino acid could either protect or sensitize cells, depending on the cellular system. in fact, although a reduction in the growth-inhibitory effect of hydrogen peroxide was observed in mammalian cells, a marked increase in the susceptibility to oxidative stress was induced by cystine in bacteria. none of the ...19921371836
n-methyl-n'-nitro-n-nitrosoguanidine-induced light emission in chinese hamster cell cultures: correlation with enhancement of chromosomal aberrations.n-methyl-n'-nitro-n-nitrosoguanidine (mnng) was found to induce an ultraweak photon emission in cultures of chinese hamster fibroblasts (chl). measurements suggest that the light emission is due to a reaction between mnng and cellular metabolites. the light emission depended on the concentration of mnng and was oxygen-dependent, disappearing in a nitrogen atmosphere. superoxide dismutase (sod) or sodium azide decreased the emission intensity. the production of chromosomal aberrations in chl by m ...19921371845
tyrosine phosphorylation of biliary glycoprotein, a cell adhesion molecule related to carcinoembryonic antigen.biliary-glycoprotein (bgp), a cell adhesion molecule related to carcinoembryonic antigen (cea), has been shown to exist as several alternatively spliced isoforms. here we show that bgpa and bgpb are phosphorylated in the chronic myelogenous leukaemia cell line kg-1, which constitutively expresses several bgp isoforms, and chinese hamster lr-73 cells transfected with the cdnas encoding bgpa and bgpb. the phosphorylation can be augmented with the protein tyrosine phosphatase inhibitor ammonium van ...19921371937
cultivation of mammalian cells on macroporous microcarriers.adherent cells can be cultivated in a stirred-tank bioreactor by attaching to microcarriers. macroporous microcarriers, with their intraparticle space and surface area for cell growth, can potentially support a higher cell concentration than conventional microcarriers, which support cell growth only on the external surface. chinese hamster ovary (cho) cells and green monkey kidney (vero) cells were cultivated on macroporous microcarriers, cultispher-g. cells attached to the microcarriers at a sl ...19921372509
functional expression and growth factor activation of an epitope-tagged p44 mitogen-activated protein kinase, p44mapk.mitogen-activated protein kinases (mapks) or extracellular signal-regulated kinases (erks) are serine/threonine kinases of apparent mr 42-44 kda that are rapidly activated by a variety of extracellular signals in many cell types. this activation coincides with their phosphorylation on tyrosine and threonine residues, and these covalent modifications are required for full activity of the enzymes. they are thought to play a pivotal role in integrating and transmitting transmembrane signals for gro ...19921372523
cloning and expression of a cdna for mouse prostaglandin e receptor ep3 subtype.a functional cdna clone for mouse ep3 subtype of prostaglandin (pg) e receptor was isolated from a mouse cdna library using polymerase chain reaction based on the sequence of the human thromboxane a2 receptor and cross-hybridization screening. the mouse ep3 receptor consists of 365 amino acid residues with putative seven-transmembrane domains. the sequence revealed significant homology to the human thromboxane a2 receptor. ligand binding studies using membranes of cos cells transfected with the ...19921372606
antibody and b7/bb1-mediated ligation of the cd28 receptor induces tyrosine phosphorylation in human t cells.cd28 is an adhesion receptor expressed as a 44-kd dimer on the surface of a major subset of human t cells. the cd28 receptor regulates the production of multiple lymphokines, including interleukin 2 (il-2), by activation of a signal transduction pathway that is poorly understood. here we show that ligation of cd28 by a monoclonal antibody (mab) or by a natural ligand, b7/bb1, induces protein tyrosine phosphorylation that is distinct from t cell receptor (tcr)-induced tyrosine phosphorylation. cd ...19921372649
effect of iron chelators on the cytotoxic and genotoxic action of hyperoxia in chinese hamster ovary cells.the iron chelators o-phenanthroline and desferrioxamine were tested for their ability to protect chinese hamster ovary cells against the cytotoxic and genotoxic effects of normobaric hyperoxia. desferrioxamine added at sub-toxic concentrations (up to 2.5 microm) over a period of several days had no protective effect on hyperoxia-induced clonogenic cell killing and growth inhibition. the clastogenic effect of hyperoxia was strongly potentiated by desferrioxamine, while the induction of sister-chr ...19921372685
characterization of the coexisting multiple mechanisms of methotrexate resistance in mouse 3t6 r50 fibroblasts.we have studied the discrepancy in the degree of methotrexate (mtx) resistance that exists between two clonal cell lines, mouse 3t6 r50 cells and chinese hamster ovary b11 0.5 cells that overexpress comparable levels of dihydrofolate reductase, yet exhibit a 100-fold difference in mtx resistance while maintaining similar sensitivity to the lipophilic antifolates trimetrexate and piritrexim. these data suggested that r50 cells may possess additional mechanism(s) of antifolate resistance, such as ...19921372892
antagonists to cholinergic receptors increase the frequency of binuclear v79 chinese hamster cells. a mechanism for induction of aneuploidy.v79 chinese hamster cells were found to produce significant amounts of acetylcholine. asynchronously growing v79 cells were treated with five different antagonists to cholinergic receptors: atropine and scopolamine, which are inhibitors of muscarinic receptors, and mecamylamine, d-tubocurarine and alpha-bungarotoxin, which are inhibitors of nicotinic receptors. all compounds caused a slight but significant increase of the frequency of binuclear interphase cells and also of the frequency of cells ...19921373221
effects of benzyladenine on prokaryotic and eukaryotic cells.comparative studies of the effect of benzyladenine (ba) on the yeast saccharomyces cerevisiae, the bacterium salmonella typhimurium, the shallot allium ascalonicum and chinese hamster fibroblast cells were performed. the tested substance had no mutagenic activity on yeast, bacteria and cultured fibroblast cells. changes in mitotic activity and cell division abnormalities were observed after ba treatment in shallot root-tip cells.19921373222
overexpression of grp78 mitigates stress induction of glucose regulated proteins and blocks secretion of selective proteins in chinese hamster ovary cells.grp78 is a resident protein of the endoplasmic reticulum (er) and a member of the glucose regulated protein (grp) family. many secretion incompetent proteins are found in stable association with grp78 and are retained in the er. some proteins which are destined for secretion transiently associate with grp78. to further increase our understanding of the role of grp78 in secretion, we have stably overexpressed grp78 in chinese hamster ovary (cho) cells and examined the effect on protein secretion ...19921373378
characterization of the murine bek fibroblast growth factor (fgf) receptor: activation by three members of the fgf family and requirement for heparin.the bek gene encodes a member of the high-affinity fibroblast growth factor receptor family. the bek/fgfr-2 receptor is a membrane-spanning tyrosine kinase with the typical features of fgf receptors. we have cloned a murine bek cdna and expressed it in receptor-negative chinese hamster ovary cells and in 32d myeloid cells. the bek receptor expressed in chinese hamster ovary cells binds acidic fgf, basic fgf, and kaposi fgf equally well but does not bind keratinocyte growth factor or fgf-5 apprec ...19921373495
contribution of the n-linked carbohydrate of erythrocyte antigen cd59 to its complement-inhibitory activity.the contribution of n-linked carbohydrate to the complement-inhibitory function of the human erythrocyte membrane glycoprotein, cd59, was investigated. amino acid sequence analysis of tryptic peptides labeled with [3h]borohydride revealed an n-linked carbohydrate moiety at the asn18 residue. no o-linked carbohydrate was detected, as judged by the failure of asialo-cd59 to bind peanut agglutinin and by its resistance to digestion by o-glycanase. the apparent molecular mass of cd59 was reduced fro ...19921373727
combined mutagenicity of methyl methanesulfonate and ethyl methanesulfonate in chinese hamster v79 cells.the combined effects of methyl methanesulfonate (mms) and ethyl methanesulfonate (ems) on the induction of 6-thioguanine (6tg)-resistant mutants and chromosome aberrations were examined in chinese hamster v79 cells. cells were simultaneously treated with ems at a concentration of d20 and mms at various concentrations for 3, 6 or 9 h. in other experiments cells were simultaneously treated with mms at a concentration of d20 and ems at various concentrations for 3, 6 or 9 h. the mathematical analys ...19921373826
a mutational hotspot in the aprt gene of chinese hamster cells.early work with adenine phosphoribosyltransferase-deficient mutants of cho cells suggested that a site existed in the third exon of this gene which was preferentially susceptible to mutation by ethyl methanesulphonate. to determine whether this was real we analysed a large collection of induced mutants, and generated a high-density mutational spectrum for this exon. in addition, 4 sites outside exon 3 were analysed by blot. 37 mutations were found in 19 available sites, six of which were at nucl ...19921373832
chromosomal changes in chinese hamster aa8 cells caused by podophyllin, a common treatment for genital warts.podophyllin, a plant derivative of variable composition, is used widely within new zealand as a treatment for genital warts. one local source of podophyllin has been tested for ability to cause mutagenic effects in salmonella typhimurium as well as for effects on chromosomes of chinese hamster aa8 cells. although only weakly mutagenic in one strain of salmonella, podophyllin caused structural aberrations as well as changes in chromosome number in the chinese hamster cells. the range of aberratio ...19921373833
predictive assay for rodent carcinogenicity using in vivo biochemical parameters: operational characteristics and complementarity.111 chemicals of known rodent carcinogenicity (49 carcinogens, 62 noncarcinogens), including many promoters of carcinogenesis, nongenotoxic carcinogens, hepatocarcinogens, and halogenated hydrocarbons, were selected for study. the chemicals were administered by gavage in two dose levels to female sprague-dawley rats. the effects of these 111 chemicals on 4 biochemical assays (hepatic dna damage by alkaline elution (dd), hepatic ornithine decarboxylase activity (odc), serum alanine aminotransfera ...19921373835
responsiveness of tumorigenic and non-tumorigenic chef18 chinese hamster cells to 1-beta-d-arabinofuranosylcytosine cultured mammalian cells, sister chromatid exchanges are easily induced by agents that perturb the scheduled timing of dna replication. in this work a blockage of dna synthesis induced by 1-beta-d-arabinofuranosylcytosine was applied to non-tumorigenic and tumorigenic chef18 chinese hamster cells, and their responsiveness was compared. the data show that both the induction of sister chromatid exchanges and the reduction of the colony-forming ability were less extensive in non-tumorigenic than ...19921373836
effects of l-ascorbic acid on the mutagenicity of ethyl methanesulfonate in cultured mammalian cells.the effects of l-ascorbic acid (asa) on the mutations induced by ethyl methanesulfonate (ems) were examined by means of the 6-thioguanine (6tg)-resistant mutation assay and chromosome aberration assay in cultured chinese hamster v79 cells. when cells were treated with ems at various concentrations in the presence of 100 micrograms/ml asa, ems-induced 6tg-resistant mutations were reduced about one third or one fourth. ems-induced chromosome aberrations were also reduced by asa. these reductions i ...19921373842
structure-activity relationships of epoxides: induction of sister-chromatid exchanges in v79 cells by enantiomeric epoxides.analysis of sce frequencies in chinese hamster v79 cells was used to investigate the influence of the stereoisomeric forms of epoxides in mammalian genotoxicity tests. the sce-inducing potency of 12 pairs of (r)- and (s)-enantiomeric epoxides which differed in the degree of substitution of the oxirane ring was determined. of these, 2 pairs of epoxides failed to induce sce. different sce-inducing potencies between the (r)- and (s)-enantiomers were shown for 5 epoxides. this study demonstrates tha ...19921373866
expression and function of the murine b7 antigen, the major costimulatory molecule expressed by peritoneal exudate cells.the murine b7 (mb7) protein is a potent costimulatory molecule for the t-cell receptor (tcr)-mediated activation of murine cd4+ t cells. we have previously shown that stable mb7-transfected chinese hamster ovary (cho) cells but not vector-transfected controls synergize with either anti-cd3 monoclonal antibody-induced or concanavalin a-induced t-cell activation, resulting ultimately in lymphokine production and proliferation. we now have generated a hamster anti-mb7 monoclonal antibody. this reag ...19921373896
the shape of dna elution dose-response curves under non-denaturing conditions: the contribution of the degree of chromatin condensation.we have re-examined the effect of detergent type, ph and temperature of lysis on the shape of the dna elution dose response under non-denaturing conditions using plateau-phase cho cells. results practically identical to those previously published (okayasu and iliakis, 1989) were obtained, with a 1 h incubation at 60 degrees c during lysis with sodium-n-laurylsarcosine (nls) resulting in almost linear dose-response curves. we also examined chromatin decondensation as a contributing factor in the ...19921374110
faster rates of dna unwinding under alkaline conditions in xrs-5 cells may reflect chromatin structure alterations.the chinese hamster ovary (cho) cell line xrs-5 is a radiation-sensitive mutant isolated from cho-k1 cells. the radiation sensitivity is associated with a defect in dna double-strand break rejoining. the dna alkaline unwinding technique was used to measure the dna single-strand breakage caused by gamma-rays in xrs-5 and cho-k1 cells. greater rates of dna unwinding were found in xrs-5 cells as compared to cho-k1. independent measurement of dna strand breakage by dna filter elution or pulsed-field ...19921374151
application of the standard mutagenesis assay results in underestimation of ethyl methanesulphonate-induced mutations to ouabain-resistance in chinese hamster cells.chinese hamster v79 cells were exposed to ethyl methanesulphonate (ems) and the incidence of mutant cells resistant to 8-azaguanine (8azg), 6-thioguanine (6tg) or ouabain (oua) was determined both by the respreading and the in situ techniques. in the former assay, the mutagen-treated cultures were grown for several days to permit the expression of mutations after which the cells were trypsinized, replated (10(5) cells/100-mm dish), and grown in medium supplemented with a selective agent. in the ...19921374155
purification and characterization of soluble forms of human and rat stem cell factor recombinantly expressed by escherichia coli and by chinese hamster ovary cells.stem cell factor (scf) is a novel, early-acting hematopoietic factor. it was isolated from the medium of a rat cell line in a soluble, processed form (zsebo et al., 1990, cell 63, 195). the cloned human and rat genes encode the soluble form plus additional c-terminal amino acids including a hydrophobic transmembrane domain (martin et al., 1990, cell 63, 203). we have recombinantly expressed forms of human and rat scf corresponding to the soluble, processed form in escherichia coli and in chinese ...19921374224
beta 1,4-galactosyltransferase: a short nh2-terminal fragment that includes the cytoplasmic and transmembrane domain is sufficient for golgi retention.beta 1,4-galactosyltransferase (beta 1,4-gt) is a golgi-resident, type ii membrane-bound glycoprotein that functions in the coordinate biosynthesis of complex oligosaccharides. additionally, beta 1,4-gt has been localized to the cell surface of a variety of cell types and tissues where it is proposed to function in intercellular recognition and/or adhesion. thus beta 1,4-gt is an appropriate molecule to be used in analyzing the molecular basis for retention of a membrane-bound enzyme in the golg ...19921374389
cyclic amp-dependent protein kinase activation of cystic fibrosis transmembrane conductance regulator chloride channels in planar lipid bilayers.membrane vesicles, prepared from mouse nih-3t3 fibroblasts and chinese hamster ovary cells expressing high levels of cystic fibrosis transmembrane conductance regulator (cftr), were fused with mueller-rudin planar lipid bilayers. upon addition of the catalytic subunit of camp-dependent protein kinase and atp, low conductance cl(-)-selective ion channels were observed in 10 of 16 experiments. the channels had a linear current-voltage relationship and a unitary conductance of approximately 6.5 ps. ...19921374403
amplification of the dihydrofolate reductase gene in methotrexate-resistant chinese hamster cells. 19921374513
the evolution of the amplified adenylate deaminase 2 domains in chinese hamster cells suggests the sequential operation of different mechanisms of dna amplification.fluorescent in situ hybridization was used to localize the adenylate deaminase 2 (ampd2) genes and flanking sequences on the chromosomes of the chinese hamster line gma32 and to study the distribution of additional copies of these genetic sequences in amplified mutants selected at several early stages of the amplification process. the synteny of ampd2 genes and mdr1 genes, located on chromosomes 1, was demonstrated; in gma32 the existence of a rearrangement positioning the two ampd2 genes at dif ...19921374518
gene amplification in the murine sewa system.considerable work with dna amplification has been carried out in the murine sewa ascites tumor cell system. in sewa cells there is 'spontaneous' amplification of the c-myc oncogene, and transitions between different cytogenetic expressions of gene amplification such as dm (double minutes), cm (c-bandless chromosomes) and hsr (homogeneously staining regions) of the amplified dna have been recorded during serial in vivo transplantations. in sewa cells it has also been shown that the c-myc-containi ...19921374520
the mechanism of carcinogen-induced dna amplification: in vivo and in vitro studies.exposure to chemical carcinogens provides a means for the enhancement of the frequency of gene amplification and for the facilitation of research into its mechanism(s). using carcinogen-induced sv40 amplification as a model system it was shown that amplification of the viral sequences occurs via a replication-dependent mode. this process involves overactivation of the origin region and the generation of inverted repeats. carcinogen-induced enhancement of gene amplification is triggered by cellul ...19921374526
epitope mapping of the nonspecific cross-reacting antigen using various related recombinant proteins expressed in chinese hamster ovary cells and eight distinct monoclonal antibodies.antigenic epitopes of nonspecific cross-reacting antigen (nca) recognized by 8 different monoclonal antibodies (mabs) were analyzed in relation to the domain structures of nca [domains n, i (a1-b1) and m] and cea [domains n, i (a1-b1), ii (a2-b2), iii (a3-b3) and m]. we reconstructed cdnas for nca-n, nca-n-i-m, cea-n, cea-n-i, cea-n-i-ii, cea-n-i-ii-iii-m in a eukaryotic expression vector, pdkcr-dhfr, and expressed them in chinese hamster ovary (cho) cells. the recombinant proteins were purified ...19921374735
sensitivity and single-strand dna break repair in chinese hamster mutants exposed to the carcinogen aflatoxin b1 epoxide and its dichloride model.aflatoxin b1 (afb1) is a potent carcinogen and mutagen. it requires metabolic activation to be converted to the dna-binding product aflatoxin b1 epoxide (afb1-epoxide). a model of this epoxide is aflatoxin b1 dichloride (afb1cl2). both react at the n7 position of guanine to form large adducts. the major adduct formed can either be rapidly removed to leave an apurinic site or can undergo ring opening of the imidazole ring to form a chemically stable adduct. a number of chinese hamster dna repair- ...19921374845
immunoreactivity of recombinant carcinoembryonic antigen proteins expressed in escherichia coli.immunoreactivities of recombinant carcinoembryonic antigen (cea) proteins expressed in escherichia coli (e. coli) were analyzed in relation to the cea domain structure [domains n, i (a1-b1), ii (a2-b2), iii (a3-b3) and m]. we reconstructed in a prokaryotic expression vector, pucpl-ci, the cdnas fro cea-n, cea-i, cea-ii, and cea-iii-m. the latter three were expressed as fusion products with bacterial beta-galactosidase. the recombinant proteins were solubilized by sonication in 1% sodium dodecyl ...19921375188
a recombinant ectodomain of the receptor for the stem cell factor (scf) retains ligand-induced receptor dimerization and antagonizes scf-stimulated cellular responses.the stem cell factor (scf) is a polypeptide ligand that is essential for the development of germ cells, hematopoietic progenitor cells, and melanocyte precursors. it binds to a tyrosine kinase membrane receptor that is encoded by the c-kit proto-oncogene. we have constructed an expression vector that directs the synthesis of the entire extracellular ligand-binding domain of the kit/scf receptor. when expressed and amplified in chinese hamster ovary cells, a secreted 90-kda glycoprotein could be ...19921375232
nuclease modification in chinese hamster cells hypersensitive to dna cross-linking agents--a model for fanconi anemia.fanconi anemia is a human inherited disease that is characterized by cellular hypersensitivity to dna cross-linking agents. a number of potential experimental models for that disorder have been developed by selecting mutants that are hypersensitive to bifunctional mutagens. the six mutants of that class in drosophila, all of which map to the mus308 locus, express an alteration in a mitochondrial nuclease. a recent extension of that observation to cell lines from complementation group a of fancon ...19921375328
cytotoxicity and genotoxicity testing of sodium fluoride on chinese hamster v79 cells and human eue cells.the cytotoxic effects of sodium fluoride (naf) on hamster v79 cells and human eue cells were studied by measuring the cloning efficiency and dna, rna and protein synthesis in cells cultured in the presence of naf. potential mutagenicity of naf was followed on the basis of induced 6-thioguanine-resistant mutants in treated chinese hamster v79 cells. the results showed that the addition of 10-150 micrograms of naf per ml of culture medium induced 10-75% cytotoxic effect on hamster v79 cells but ha ...19921375335
Displaying items 1601 - 1700 of 26566