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PubMed1994

Effects of transient expression of spermidine/spermine N1-acetyltransferase in COS cells.

Mammalian spermidine/spermine N1-acetyltransferase (SSAT) was transiently expressed in COS cells. As compared to COS cells transfected with control vector alone, cells transfected with the expression vector containing SSAT cDNA contained lower concentrations of spermidine and spermine. The putrescine content, on the other hand, was markedly increased in the COS cells expressing large amounts of SSAT. These changes in polyamine content were most likely caused by an interconversion of spermine and spermidine into putrescine. The SSAT-induced changes in cellular polyamine content resulted in a compensatory increase in the activities of ornithine decarboxylase and S-adenosylmethionine decarboxylase, i.e. the enzymes catalyzing the rate-limiting steps in polyamine biosynthesis. This is the first demonstration that a primary increase in SSAT activity will induce an interconversion-like change in the polyamine levels and the physiological role of SSAT is most likely to protect cells against too high concentrations of spermidine and spermine.

Acetyltransferases↗

PubMed1996

High level expression of the NMDAR1 glutamate receptor subunit in electroporated COS cells.

The rat N-methyl-D-aspartate (NMDA) glutamate receptor subunit NR1-1a was transiently expressed in COS cells using the technique of electroporation, which was fivefold more efficient than the calcium phosphate precipitation method of transfection. The glycine site antagonist 5,7-[3H]dichlorokynurenic acid labeled a single high-affinity site (KD = 29.6 +/- 6 nM; Bmax = 19.4 +/- 1.6 pmol/mg of protein) in membranes derived from COS cells electroporated with NR1-1a. In contrast to previous reports using transiently transfected human embryonic kidney 293 cells, binding of the noncompetitive antagonist (+)-5-[3H]methyl-10,11-dihydro-5H-dibenzo[a,d]-cyclohepten-5, 10-imine ([3H]MK-801) was not detected in NR1-1a-transfected COS cells. Although immunofluorescent labeling of electroporated COS cells demonstrated that the NR1-1a protein appears to be associated with the cell membrane, neither NMDA nor glutamate effected an increase in intracellular calcium concentration in fura-2-loaded cells, suggesting that homomeric NR1-1a receptors do not act as functional ligand-gated ion channels. Therefore, COS cells appear to differ from Xenopus oocytes with respect to the transient expression of functional homomeric NR1 receptors. Although expression of NR1-1a is sufficient to reconstitute a glycine binding site with wild-type affinity for antagonists in COS cells, recombinant homomeric NR1-1a receptors do not display properties that are characteristic of native NMDA receptors, such as permeability to Ca2+ and channel occupancy by MK-801, when expressed in this mammalian cell line.

Animals↗

PubMed1992

The gene for human eosinophil Charcot-Leyden crystal protein directs expression of lysophospholipase activity and spontaneous crystallization in transiently transfected COS cells.

Expression of the gene encoding human eosinophil lysophospholipase, the Charcot-Leyden crystal (CLC) protein, was studied in transiently transfected COS cells. Recombinant CLC (rCLC) protein expression was demonstrated both by Western blot and radioimmunoassay inhibition analyses of transfected COS cell extracts and by immunofluorescent staining and ultrastructural immunogold analyses of intact cells. The rCLC protein was immunochemically indistinguishable from native eosinophil-derived CLC protein, and each transfected COS cell expressed approximately 11 pg of rCLC protein as determined by radioimmunoassay and assessment of transfection efficiency. Immunofluorescent microscopy and ultrastructural immunogold analyses localized rCLC protein to the nucleus, cytoplasm, and plasma membrane of COS cells. Lysates from transfected COS cells producing CLC protein expressed significant lysophospholipase activity. Furthermore, rCLC protein expressed in COS cells spontaneously formed the distinctive intracytoplasmic and intranuclear hexagonal bipyramidal crystals characteristic of the native eosinophil and basophil-derived protein. Expression of the CLC gene confirms the authenticity of the CLC cDNA, the expression of lysophospholipase activity by this unique eosinophil and basophil constituent, and will facilitate the routine purification of the active enzyme for in vitro and animal model studies of its role (or roles) in eosinophil and basophil associated allergic inflammation and eosinophil-parasite interactions.

Animals↗

PubMed1993

Maximal expression of recombinant cDNAs in COS cells for use in expression cloning.

In the process of establishing an expression cloning system for cell surface receptors we examined parameters which influence the expression of foreign genes in COS cells. The bacterial beta-galactosidase gene was chosen as a reporter gene, since it permits the determination of (i) the fraction of cells transfected as well as (ii) the total activity of the synthesized enzyme in parallel experiments. This renders it possible to calculate the enzyme activity per individual cell. In transfected COS cells, the plasmid pXMgal directed a 20- and 10-fold higher beta-galactosidase activity than pCH110 and pCDLgal, respectively. DEAE-dextran-mediated DNA uptake and protoplast fusion were found to result in higher expression rates than lipofection and electroporation. A coincubation of the cells with chloroquine during the DEAE-dextran transfection protocol caused, as reported, an increase of beta-galactosidase positive cells but considerably reduced the total beta-galactosidase activity. However, a 10% DMSO shock at the end of the transfection procedure simultaneously increased the number of transfected cells and the total beta-galactosidase activity, thus maintaining the high expression per single cell. Using these optimized conditions, COS-1 cells expressed higher amounts of recombinant protein than COS-7 cells.

Animals↗

PubMed1990

Ligand autoradiographic receptor screening: receptor cDNA expression in replicas of transfected COS cells.

In this paper we validate a methodology, ligand autoradiographic receptor screening (LARS), for detecting expression of full length receptor cDNAs in COS cells. The method involves transfection of COS cells with receptor cDNAs by spheroplast fusion, production of filter replicas of the cell fragments, ligand binding to the receptors expressed in the membranes, and autoradiographic detection of bound ligand. A beta-adrenergic receptor cDNA cloned into a eukaryotic expression vector reliably induces high levels of beta-adrenergic receptor expression in 2-12% of COS cell colonies transfected with this plasmid after experimental conditions are optimized. Receptor expression is monitored by autoradiographic detection of 125iodocyanopindolol binding to COS cell fragments immobilized on polyester filter replicas. Binding displays appropriate pharmacological properties. The number of high-density binding spots per filter depends on the fraction of the spheroplasts in the fusion mixture that contain the beta-adrenergic receptor cDNA. A 100-plate LARS experiment can assess receptor expression in more than 10(4) transfected colonies. Thus detection of receptor-encoding sequences present in libraries in proportions as low as 1 in 10(4) should be possible. This technique may therefore be useful in detecting expression of other receptor cDNAs for which selective radioligands are available.

Animals↗

PubMed1991

Transient expression of wild type and mutant human apolipoprotein AI in COS cells.

A human apolipoprotein AI (apo AI) minigene and two mutants were cloned into the vector pUHD10-1 for expression studies in COS cells under the control of the strong CMV (cytomegalovirus) enhancer and the own apo AI promoter. In the mutated apo AI minigene (mutant M1) the positions of the triplets of Gln(-2)-Gln-1 at the C-terminus of the prosequence were exchanged against Gln(-8)-Ala-7, the recognition site of the signal peptidase of the wild type human apo AI. The prosequence has been deleted in mutant M2 and the presequence linked directly to the N-terminus of the mature apo AI form. We report here on expression studies in COS cells, a cell line, which does not express apo AI. They were transfected by electroporation with pUHD10-1 constructs, which contain a) the wild type apo AI minigene and b) the two mutant apo AI minigenes with mutations described above. The following results were obtained: a) the wild type and mutant apo AI constructs were efficiently transcribed and translated in COS cells, b) the expression of the wild type preproapo AI minigene in COS cells led to the secretion of proapo AI (29 kDa), that of the mutant (M2) gene, devoid of the prosequence of mature apo AI (28.4 kDa), whereas the product of mutant gene M1 (31 kDa) with the recognition site of the signal peptides transposed to the C-terminus of the prosequence remained uncleaved within the COS cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗

PubMed1994

Human high-affinity Fc IgG receptor (Fc gamma RI)-mediated phagocytosis and pinocytosis in COS cells.

The high-affinity receptor (Fc gamma RI) for the constant (Fc) portion of immunoglobulin G (IgG) is one of three Fc IgG receptor classes (Fc gamma Rs) found on mononuclear phagocytes. The functional specialization of each of the Fc gamma R classes is not well understood. Previous studies utilizing anti-Fc gamma R monoclonal antibodies (mAbs) as opsonins suggest that Fc gamma RI, like the other Fc gamma Rs expressed by macrophages, is able to mediate phagocytosis. The ability of Fc gamma RI to mediate pinocytosis, however, had not been certain, since it binds, but does not mediate, internalization of monomeric IgG in the monocytoid U937 cells. We studied Fc gamma RI-mediated internalization by introducing it into the Fc gamma R-negative fibroblastic COS cells. We found, using electron microscopy and fluorescence microscopy, that COS cells expressing Fc gamma RI are able to phagocytose IgG-coated zymosan particles and sheep red blood cells (SRBC), as well as pinocytose cross-linked IgG. There was no intracellular accumulation of monomeric IgG. Chimeric receptors which retain the extracellular domains of Fc gamma RI but lack the entire wild-type transmembrane and intracellular regions of the receptor mediated both phagocytosis and pinocytosis with equal or increased efficiency when compared to the wild-type receptor. Control COS cells transfected with CD2 rosetted, but did not phagocytose, SRBC. Attachment of phagocytic targets to COS cells is therefore not sufficient for phagocytosis. Taken together, this suggests that the extracellular domain of Fc gamma RI is sufficient for it to mediate phagocytosis and pinocytosis in this system.

Amino Acid Sequence↗

PubMed1988

Rat liver beta-glucuronidase. cDNA cloning, sequence comparisons and expression of a chimeric protein in COS cells.

A cDNA for rat liver beta-glucuronidase was isolated, its sequence determined and its expression after transfection into COS cells studied. The deduced amino acid sequence of the rat liver clone showed 77% homology with that from the cDNA for human placental beta-glucuronidase and 47% homology with that deduced from the cDNA for Escherichia coli beta-glucuronidase. Several differences were found between the cDNA from rat liver and that previously reported from rat preputial gland. Only one change leads to an amino acid difference in the mature enzyme. A chimeric clone was constructed by using a fragment encoding the first 18 amino acid residues of the signal sequence from the human placental cDNA clone and a fragment from the rat clone encoding four amino acid residues of the signal sequence, all 626 amino acid residues of the mature rat enzyme, and all of the 3' untranslated region. After transfection into COS cells the chimeric clone expressed beta-glucuronidase activity that was specifically immunoprecipitated by antibody to rat beta-glucuronidase. The Mr value of 76,000 of the expressed gene product was characteristic of the glycosylated rat enzyme. It was proteolytically processed in COS cells to Mr 75,000 6 h after metabolic labelling. At least 50% of the expressed enzyme was secreted at 60 h post-transfection, but the secreted enzyme did not undergo proteolytic processing. These results provide evidence that the partial cDNA isolated from a rat liver library contains the complete coding sequence for the mature rat liver enzyme and that the chimeric signal sequence allows normal biosynthesis and processing of the transfected rat liver enzyme in COS cells.

Amino Acid Sequence↗

PubMed1996

Rate-determining steps in the biosynthesis of glycogen in COS cells.

Consistent with previous results, overexpression of rabbit skeletal muscle glycogen synthase in COS cells did not lead to overaccumulation of glycogen unless activating Ser-->Ala mutations were present at key regulatory phosphorylation sites 2 (Ser7) and 3a (Ser644) in the enzyme. In addition, we found that expression of glycogenin, glycogen branching enzyme, or UDP-glucose pyrophosphorylase alone in COS cells had no effect on the glycogen level. However, coexpression of the hyperactive 2,3a glycogen synthase mutant with either glycogenin or UDP-glucose pyrophosphorylase led to higher glycogen accumulation than that obtained from the expression of glycogen synthase alone. Coexpression of glycogenin with the 2,3a mutant of glycogen synthase led to the appearance of glycogenin with a lower molecular weight suggestive of reduced glucosylation. Increased glycogen synthesis may lead to competition between glycogenin and glycogen synthase for their common substrate UDP-glucose. In summary, we conclude that (i) glycogen synthase is a primary rate-limiting enzyme of glycogen biosynthesis in COS cells, (ii) that phosphorylation of glycogen synthase is regulatory for glycogen accumulation, and (iii) once glycogen synthase is activated, the reaction mediated by UDP-glucose pyrophosphorylase can become rate-determining.

1,4-alpha-Glucan Branching Enzyme↗

PubMed2002

Pharmacological characterisation of (E)-N-(3-iodoprop-2-enyl)-2beta-carbomethoxy-3beta-(4'-methylphenyl)nortropane (PE2I) binding to the rat neuronal dopamine transporter expressed in COS cells.

The interaction of (E)-N-(3-iodoprop-2-enyl)-2beta-Carbomethoxy-3beta-(4'-methylphenyl) nortropane (PE2I) with the rat neuronal dopamine transporter (DAT) was studied in transfected COS cells by measuring its ability to inhibit DA uptake and by measuring its affinity in radioligand binding experiments. Saturable [3H]DA uptake was measured in COS cells transiently transfected with the cDNA sequence encoding the rat DAT. Pharmacological characterisation of this uptake revealed functional properties with a V(max) value of 45.05+/-2.62 pmol/mg protein per min and a K(m) value of 2.86+/-0.28 microM. The specific [3H]DA uptake was fully inhibited by 1 microM PE2I. Concentration response curves revealed the high potency of PE2I in inhibiting DA uptake (pEC(50) value of 8.70+/-0.33), 25 times higher than that observed for the reference DAT inhibitor, GBR 12935. On crude homogenates from transfected COS cells, PE2I displaced the specific binding of [3H]GBR 12935 with a pK(i) value of 7.73+/-0.13. Accordingly, [125I]PE2I was found to specifically recognise a single binding site population which is almost completely displaced by GBR 12935 and nomifensine. Saturation experiments revealed the high affinity of [125I]PE2I (K(D) value of 3.8+/-0.63 nM) that correlates with the high potency of PE2I in inhibiting the [3H]DA uptake. This contrasts with the results obtained with GBR 12935 for which a discrepancy was found between its high affinity in binding assays (K(D) value of 0.43+/-0.04 nM) and its rather low potency in functional assays (pEC(50) value of 7.30+/-0.05). A relatively high level of [3H]GBR 12935 binding was detected in non transfected COS cells. Such nomifensine resistant binding is attributed to the interaction of GBR 12935 with cytochrome P-450 as it was displaced by cis-(Z)-flupentixol (an inhibitor of cytochrome P-450). Such interaction was not observed using PE2I. Taken together, these data demonstrate that PE2I was a highly potent inhibitor of cloned DAT compared with GBR 12935 and provided a useful tool for further investigations in cells transfected with cDNA encoding the DAT.

Animals↗

PubMed2000

Dilution enhancement of COS cell expression cloning.

To search for an efficient expression cloning method, we mixed plasmid pmDATsv, which contains the mouse dopamine transporter (mDAT) cDNA, with a large amount of another plasmid prGlyTsv to mimic the situation of a cDNA library and examined COS cell expression. Both plasmids have an SV40 replication origin and thus will be replicated to high copy numbers in COS cells. After transfecting COS-7 cells with pmDATsv/prGlyTsv mixture at 1/1000 ratio, we could not detect any cells expressing strong mDAT activity. In contrast, when prGlyTsv was replaced by prSERTsk (no SV40 origin) in the transfection mixture, we observed hundreds of cells expressing strong mDAT activity. The results suggested that in many cells low mDAT expression was not due to the lack of pmDATsv plasmid but due to the presence of large numbers of replicable prGlyTsv. Analysis with a mathematical model suggests that diluting cDNA libraries with other plasmids without the SV40 origin should improve the detection of COS cells expressing target cDNAs. We tested this conclusion with pmDATsv/prGlyTsv mixture. When the mixture at 1/1000 ratio was diluted with prSERTsk and used for transfection, we could now easily detect cells expressing strong mDAT activity.

Animals↗

PubMed1996

[35S]GTP gamma S binding: a tool to evaluate functional activity of a cloned opioid receptor transiently expressed in COS cells.

In this paper we propose a powerful procedure to measure functional activation of the mouse delta-opioid receptor transiently expressed in mammalian cells. Receptor stimulation was assessed using a population of electroporated COS cells, transfected at a 50% efficiency. Under those conditions, agonist-promoted activation of the receptor was measured by [35S]GTP gamma S binding. Both BW373U86, an alkaloid compound, and DADLE, a peptide agonist, elicited increase of specific [35S]GTP gamma S binding representing 300% of basal level. Maximal activation was compared to that obtained for the cloned receptor stably expressed in CHO cells. Agonist efficacy was similar in both expressions systems, demonstrating the high sensitivity of the proposed method applied to transient expression. Finally dose-response curves were found highly reproducible across transfection experiments, opening the possibility for a direct comparison of distinct recombinant receptor preparations. This method represents a powerful tool for the study of opioid signal transduction at the receptor level. It may also be extended to investigate signalling properties of other Gi/Go coupled receptors.

Animals↗

PubMed1986

Mechanism of interferon action. Expression of vesicular stomatitis virus G gene in transfected COS cells is inhibited by interferon at the level of protein synthesis.

The effect of interferon on the expression of the vesicular stomatitis virus glycoprotein G gene was examined in simian COS cells transfected with the expression vector pSVGL containing the G gene under the control of the SV40 late promoter. When COS cells were treated with interferon 24 h after transfection, the synthesis of vesicular stomatitis virus G protein was inhibited by about 80% as compared to that in untreated controls. By contrast, under the same conditions, neither the plasmid copy number nor the G gene mRNA levels were detectably affected by interferon treatment. Likewise, the synthesis of simian virus 40 large T-antigen was not inhibited by interferon treatment of transfected COS cells even though the synthesis of vesicular stomatitis virus G protein was markedly inhibited. The residual G protein synthesized in transfected, interferon-treated COS cells appeared to be normally glycosylated.

Animals↗

PubMed1997

Effect of energy shortage and oxidative stress on amyloid precursor protein metabolism in COS cells.

The present study investigates the influence of energy related metabolic stress on amyloid precursor protein (APP) non-amyloidogenic secretory processing in COS cells. The effect of glucose deprivation on soluble APP (sAPP) secretion has been evaluated: incubation of COS cells with 50 mM 2-deoxy-D-glucose (2-DG) in glucose free medium was able to reduce sAPP secretion (-26%). Sodium azide (NaN3), an inhibitor of cytochrome c oxidase (complex IV of the mitochondrial electron transfer chain) decreased sAPP release in a concentration dependent way (maximum -75%). Treatment of COS cells with the antioxidant glutathione (GSH) fully antagonized the inhibitory effect of azide (1 mM) and elicited sAPP release over basal level. These results suggest that the inhibition of energy metabolism can influence APP processing leading to a decreased secretion of non-amyloidogenic fragments of APP.

Amyloid beta-Protein Precursor↗

PubMed1994

Characterization of a COS cell line deficient in polyamine transport.

In the present study, we describe the isolation and characterization of a COS cell line deficient in polyamine uptake that may provide an important tool for the molecular cloning of polyamine transporter(s). The cells were selected by isolation for resistance against the cytotoxic agent, methylglyoxal bis(guanylhydrazone) (MGBG), which is entering the cells using the same transport system as the polyamines. The isolated cell line was capable of growing in the presence of 100 microM MGBG, which totally inhibited the growth of the wild-type cells. The transport of putrescine and spermidine was markedly decreased in the COS-MGBGr cells. The decrease in putrescine transport was mainly a result of a 14-fold decrease in Vmax, whereas the reduced spermidine uptake was due to a 3-4-fold decrease in Vmax as well as 12-fold increase in Km, indicating the existence of at least two separate transport systems. No major difference in polyamine content was seen between the parental and the COS-MGBGr cells when grown without MGBG. In the presence of MGBG, both cell lines exhibited an increase in putrescine content. Treatment with MGBG also resulted in a decrease in spermidine and spermine contents in the wild-type cells. In the COS-MGBGr cells, on the other hand, there were no statistically significant effects on the spermidine and spermine contents by MGBG treatment. In the wild-type cells, depletion of polyamines, e.g., by treatment with the ornithine decarboxylase inhibitor 2-difluoromethylornithine (DFMO), stimulated the uptake of polyamines (3-7-fold), whereas in the COS-MGBGr cells the effect of DFMO treatment on polyamine transport was only minor. In contrast to the growth-medium of the wild-type cells, large amounts of polyamines accumulated in the medium of the COS-MGBGr cells, presumably indicating that COS cells normally excrete polyamines and then salvage them using the polyamine transport system.

Animals↗

PubMed1993

Processing of the small GTP-binding protein SpYPT1p in Schizosaccharomyces pombe and in mammalian COS cells.

SpYPT1p belongs to a family of ras-like GTP-binding proteins which is believed to be involved in the regulation of intracellular vesicular trafficking. We have analyzed the processing of this protein in its natural environment, the fission yeast Schizosaccharomyces pombe, and when expressed in transfected mammalian COS cells. In COS cells SpYPT1p exists in two forms: a cytosolic 24 kDa protein which represents the unprocessed precursor form and a prenylated 23.5 kDa protein which is equally distributed between membranes and cytosol. In contrast, in S.pombe we have been unable to detect any prenylation of the protein, despite the presence of a potential C-terminal CysCys prenylation site. In addition a 23.5 kDa form was localized exclusively in the cytosol and a third membrane-bound 23 kDa form was also detected. Pulse-chase experiments revealed that in S.pombe SpYPT1p is co-translationally or immediately after translation converted to the 23.5 kDa form which is then rapidly processed to the 23 kDa membrane bound form. We have been unable to detect any significant soluble pool of the protein.

Animals↗

PubMed2004

Intracellular expression patterns of the human papillomavirus type 59 E1/E4 protein in COS cells, keratinocytes, and genital epithelium.

OBJECTIVE: To compare and contrast the intracellular distribution pattern of the human papillomavirus type 59 (HPV 59) E1/E4 protein in COS cells, human keratinocytes, and naturally infected genital epithelium. METHODS: The HPV 59 E1/E4 protein was expressed in COS cells and NIKS cells (immortalized human keratinocytes). A subset of NIKS cells was induced to differentiate. The intracellular distribution pattern of E1/E4 and the effects of E1/E4 expression on the cytoskeleton network were compared for COS and NIKS cells. Expression of E1/E4 was examined in HPV 59-infected foreskin xenografts grown in athymic mice and in a natural HPV 59-infected genital lesion. RESULTS: The HPV 59 E1/E4 protein formed dense perinuclear inclusions in COS cells, similar to those reported for the HPV 16 E1/E4 protein. In contrast, the E1/E4 protein was diffusely cytoplasmic in undifferentiated NIKS cells, co-localizing with an intact cytokeratin filament network. The E1/E4 protein was concentrated in the region of the cornified cell envelope (CCE) of differentiated NIKS cells, co-localizing with involucrin, a CCE component. A similar distribution in the region of the CCE was observed for E1/E4 protein in HPV 59-infected human epithelial tissues. CONCLUSIONS: The HPV 59 E1/E4 protein is cytoplasmic and co-localizes with an intact cytokeratin filament network in undifferentiated keratinocytes. The E1/E4 protein is distributed in the region of the CCE and co-localizes with involucrin in differentiated human keratinocytes, consistent with the intracellular distribution pattern observed in HPV 59-infected epithelium.

Animals↗

PubMed1990

Intracellular fate of fibrinogen B beta chain expressed in COS cells.

Full-length fibrinogen B beta cDNA was subcloned into an expression vector, pBC12BI, and transfected into COS cells. B beta chain expression was measured by pulse-labelling cells with L-[35S]methionine, immunoprecipitating the B beta chain with antibody to fibrinogen and separating the nascent radioactive protein by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). B beta chain was expressed in transfected COS cells but was not secreted into the medium. Treatment with endoglycosidase H showed that non-secreted B beta chain contains mannose-rich carbohydrates rather than the complex form of carbohydrate which occurs in plasma fibrinogen and indicates that B beta chain is not transported to the Golgi apparatus. In transfected COS cells, antibody to fibrinogen co-immunoprecipitated B beta chain and 78 kDa immunoglobulin-binding protein (BiP) and antibody to BiP immunoprecipitated BiP and nascent B beta chains. Non-secreted B beta chain was degraded intracellularly with a half-life of 5 h by enzymes which were not affected by incubating transfected cells with NH4Cl, which indicates a non-lysosomal pathway of degradation. These studies indicate that B beta chain by itself does not contain the signal for fibrinogen secretion and that non-secreted B beta chain is associated with BiP and degraded in the rough endoplasmic reticulum.

Animals↗