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At least 19 recordsLinked to original sources
PubMed1977

Expression of differentiated functions in hepatoma cell hybrids: selection in glucose-free media of segregated hybrid cells which reexpress gluconeogenic enzymes.

Selective glucose-free media have been used to study the reexpression of liver-specific gluconeogenic enzymes in rat hepatoma X mouse lymphoblastoma somatic hybrids. The utilization for gluconeogenesis of dihydroxyacetone or oxaloacetate requires two enzymes: fructose diphosphatase as well as either triokinase for the former or phosphoenolpyruvate carboxykinase for the latter. By sequential selection with these substrates, the reexpression of the three gluconeogenic enzymes has been dissociated. The reexpression of these enzymes is correlated with the loss of mouse chromosomes. In addition, the characterization of the parental forms of aldolase B, another liver-specific enzyme, shows that reexpression corresponds to the simultaneous production of the rat and mouse enzymes. These results demonstrate the chromosomal origin of extinction and suggest that activation of mouse silent genes which accompanies reexpression can occur without loss of the parental determinations. The hypothesis that determination involves regulatory rather than structural genes is discussed.

Alcohol Oxidoreductases↗
PubMedDate not supplied

Persistence of the Fc cytophilic antibody receptor in macrophage hybrid cells.

Hybrid cell clones were obtained from mouse macrophase/Ehrlich ascites cell fusions which showed the 'Fc' cytophilic antibody receptor site, phagocytosis and motility typical of macrophages. With continued growth of the clones for 11 weeks, the receptor became undetectable but could be unmasked by dilute trypsin treatment; subsequent remasking of the receptor could be prevented with cycloheximide treatment of the hybrid cells. These hybrids produced cystic anaplastic tumours in neonatal irradiated mice. Chinese hamster/mouse interspecific macrophage hybrid cells did not show macrophage markers. This was probably due to rapid loss of macrophage chromosomes from the hybrid cells.

Animals↗
PubMed1979

Induction of secretion of IgM from cells of the B cell line 38c-13 by somatic cell hybridization.

Cells of the murine B cell line 38C-13 possess immunoglobulins of the IgM class on their surface but do not secrete them. Upon hybridization of 38C-13 cells with murine myeloma cells, hybridoma clones were obtained that secreted both pentameric IgM of 38C-13 origin and the myeloma protein. All hybridoma clones synthesized and secreted large amounts of homogeneous IgM with a half disappearance time of about 2 hr, typical of mature plasma cells. Concomitantly with the induction of IgM secretion, the hybridoma cells lost their surface IgM. The possibility of separate pathways for the synthesis of membrane and secreted IgM is discussed.

Animals↗
PubMed1979

Genetic and adaptive differences in the expression of drug resistance in hybrid cells.

Hybrids between Chinese hamster cells were isolated and maintained in media that were selective or nonselective for markers present in the parent cells (HGPRT and TK deficiencies, respectively). Segregation frequencies for resistance to azaguanine (AZG), thioguanine (THG), or bromodeoxyuridine (BrdU) could be enhanced for some groups of hybrids if the stock cells were maintained under nonselective conditions rather than in HAT medium. In these populations the expression of resistance was dominant or codominant even though marker patterns were recessive for the same cells in HAT. Clonal analysis showed that enhancement took place by adaptive shifts rather than by variation and selection. Segregation frequencies in hybrids were also found to differ significantly between clones isolated by replicate fusions of any two parental cell types. The basis for this heterogeneity is unknown and deserves further study.

Animals↗
PubMed1979

Adenylate cyclase and acetylcholine release regulated by separate serotonin receptors of somatic cell hybrids.

Serotonin activates adenylate cyclase [ATP pyrophosphate-lyase (cyclizing), EC 4.6.1.1] of NCB-20 neuroblastoma--brain hybrid cells with an activation constant of 530 nM, but has little or no effect on cellular cyclic AMP or cyclic GMP content of NIE-115 neuroblastoma or NG108-15 hybrid cells. In homogenates of NCB-20 hybrid cells, lysergic acid diethylamide stimulates adenylate cyclase activity (Kact = 12 nM) and partially inhibits (Ki = 10 nM) the stimulation of adenylate cyclase activity by serotonin. No desensitization was detected of serotonin receptors coupled to adenylate cyclase. Serotonin also depolarizes NCB-20, NG108-15, and NIE-115 cells and increases acetylcholine release. Serotonin receptors mediating depolarizing responses desensitize rapidly and reversibly, and the depolarizing effects of serotonin are neither mimicked nor inhibited by lysergic acid diethylamide. These results indicate that (i) NCB-20 cells possess at least two species of serotonin receptors, which independently regulate cellular functions, (ii) activation of adenylate cyclase does not directly affect membrane potential or acetylcholine release, and (iii) serotonin-dependent cell depolarization does not affect cyclic AMP or cyclic GMP synthesis in the cell lines tested.

Acetylcholine↗
PubMed1979

Suppression of malignancy in human lung cancer (A549/8) times mouse fibroblast (3T3-4E) somatic cell hybrids.

Interspecies hybrid cells were formed by the fusion of two parent cells: 1) the human lung cancer (bronchioloalveolar) line A549/8, which is not contact inhibited, rapidly produces tumors in athymic nude (nu/nu) mice, and forms colonies in agarose, and 2) the mouse fibroblast line 3T3-4E, which is contact inhibited, is nontumorgenic in nuce mice, and does not form colonies in agarose. These hybrid cells were tested 40-50 generations after fusion. The presence of 20 of the 23 different human chromosomes was tested by isoenzyme analysis, and examples of expression of each isoenzyme marker were found in at least some hybrid clones. All 14 independent hybrid clones tested were nontumorigenic in nude mice. Testing of hybrid clones for their ability to form colonies in agarose revealed two distinct phenotypes: agarose (clones forming colonies at 1-4% of the plated cells) and agarose (no colonies formed/10(5) cells tested). These phenotypes were discordant with all human isoenzymes tested. Malignant human lung cancer A549/8 times non-malignant mouse 3T3-4E cell hybrids were nontumorigenic in nude mice; thus malignancy of the bronchioloalveolar lung cancer behaved as a recessive trait. This nontumorigenicity was not accounted for by an absolute loss of the human chromosomes tested, but gene dosage may play a role. In contrast, the ability to clone in agarose was expressed in some hybrids (and thus behaved as a dominant trait); at present, agarose clonability cannot be related to specific human chromosomes.

Animals↗
PubMed1977

Characterization of residual hexosaminidase activity in Sandhoff's disease using man-Chinese hamster cell hybrids.

To obtain information about the nature of the residual hexosaminidase activity in Sandhoff's disease, hybrid cell lines between fibroblasts from a patient with Sandhoff's disease and Chinese hamster cells were isolated. In these hybrid cell lines, a heteropolymeric isoenzyme was detected that is composed of human alpha- and Chinese hamster hexosaminidase subunits. Due to the electrophoretic and immunological behavior of the heteropolymeric molecules in interspecies hybrids with normal fibroblasts and with cells from a patient with Sandhoff's disease, we conclude that Sandhoff cells contain an alpha-subunit of hexosaminidase with normal characteristics.

Animals↗
PubMed1979

Structure of tumor antigen on hybrid cells between mouse mammary ascites tumor and mouse fibroblast L cells.

Somatic cell hybrids between mouse fibroblast L cells and MM2 mouse mammary ascites tumor grown in BALB/c mice were isolated and the structures of tumor-associated surface antigen of the hybrid cells, and parental MM2 and mouse L cells were investigated by the methods of radioiodination of membrane proteins, immunoprecipitation with a specific antiserum against tumor-associated surface antigens of MM2 tumor (anti-MM2 serum), and sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Two molecules of 105,000 and 76,000 daltons were detected on the MM2 cell surface, but no MM2 tumor antigen was detected on the mouse L cells. On the hybrids between these two kinds of cells, in addition to the two MM2 tumor antigens, molecules of 48,000-51,000 and 12,000 daltons were observed. On Sendai-virus-infected mouse L cells only a molecule of 68,000 daltons was detected by the anti-MM2 serum, and furthermore this molecule was also detected by normal mouse serum, indicating that antibodies against Sendai virus were contaminating in both the anti-MM2 and normal mouse sera used, and thus the molecules detected on the hybrid cells were distinguishable from possible viral components of Sendai virus on the hybrid cells. The results indicate that somatic cell hybrids between mouse L cells and MM2 tumor grown in BALB/c mice expressed on their cell surface the molecules that were not exposed on either parent cell. The experiments comparing newly detected molecules with the H-2 antigen suggested that they were similar to H-2 in their electrophoretic pattern.

Animals↗
PubMed1976

Genetic homology between man and the chimpanzee: syntenic relationships of genes for galactokinase and thymidine kinase and adenovirus-12-induced gaps using chimpanzee-mouse somatic cell hybrids.

The induction by adenovirus-12 of a site-specific gap and assignment of the chimpanzee genes for thymidine kinase and galactokinase were studied by utilizing chimpanzee-mouse hybrid cells. It has been shown that adenovirus-12 induces a specific gap in the long arm of human chromosome 17 (HS 17); with chimpanzee-mouse hybrid cells the specific gap appears on the short arm of the chimpanzee homolog [PTR 19 (HS 17)] of HS 17. This result supports the proposed relationship of HS 17 to PTR 19 (HS 17) by means of a pericentric inversion. The chimpanzee thymidine kinase and galactokinase genes were assigned to PTR 19 (HS 17), further confirming the homology to HS 17. Other syntenic relationships and gene assignments were consistent with proposed homologies between chimpanzee and human chromosomes.

Adenoviridae↗
PubMed1978

A new immunochemical method for the quantitative measurement of specific gene products in man-rodent somatic cell hybrids.

An immunochemical method has been developed for the quantitative determination of species-specific gene products, for instance alpha-galactosidase and N-acetyl-alpha-galactosaminidase, in man-rodent hybrid cells and in the parental cell lines. Antisera raised against the purified enzymes are covalently coupled to Sepharose 4B. The gene products are specifically removed from a cell lysate by incubating with the appropriate Sepharose-coupled antiserum. After centrifugation followed by washing of the precipitated Sepharose, the enzymic activity can be quantitatively measured on the Sepharose beads. With this technique it has been demonstrated that the ability of human N-acetyl-alpha-galactosaminidase (also known as alpha-galactosidase B) to hydrolyze alpha-galactosidic linkages is lost when the enzyme is expressed in man-Chinese hamster hybrid cells.

Animals↗
PubMed1978

Presence of human chromosome 21 alone is sufficient for hybrid cell sensitivity to human interferon.

Human/mouse somatic cell hybrids with chromosome 21 as the only detectable human genetic material were sensitive to both human leukocyte and fibroblast interferons. The presence of additional human chromosomes decreased the amount of interferon needed to attain a given level of virus resistance. Decreased cytopathic effects, decreased virus yields, and the appearance of a specific phosphorylated protein associated with interferon treatment were all observed in hybrids maintaining only human chromosome 21. The phosphorylated protein found in extracts of these human interferon-treated hybrid cells was of mouse origin.

Animals↗
PubMed1978

Activation of teratocarcinoma-derived hemoglobin genes in teratocarcinoma-Friend cell hybrids.

Hybrid cells formed by the fusion of murine teratocarcinoma and Friend erythroleukemia cells synthesize hemoglobin in the presence of chemical inducers such as dimethylsulfoxide (DMSO). By making use of the fact that the parental teratocarcinoma and Friend cells carried different alleles at the locus coding for the alpha chain of hemoglobin, it was possible to demonstrate that the teratocarcinoma-derived genes for the globin alpha chains are genetically active in hemoglobin-synthesizing hybrid cells. In addition, evidence is presented suggesting that the teratocarcinoma-derived genes for the beta-globin chains may also be expressed in the hybrids. Apparently the teratocarcinoma-derived genome has become reprogrammed to express erythroid functions following fusion of the teratocarcinoma cell to the Friend cell.

Alleles↗
PubMed1979

Segregation of rat chromosomes in somatic cell hybrids between rat cells and HT 1080 human fibrosarcoma cells.

We produced somatic cell hybrids between HT 1080-6TG human fibrosarcoma cells and either rat white blood cells (WBC) or cells directly derived from rat spleen. Karyologic and isozyme analyses of hybrid cells indicated that they preferentially lose rat chromosomes. Hypoxanthine-aminopterine thymidine-selected hybrid clones expressing rat hypoxanthine phosphoribosyltransferase (HPRT), glucose-6-phosphate dehydrogenase (G6PD), and phosphoglycerate kinase (PGK) and containing the rat X chromosome were counterselected in a medium containing 30 micrograms/ml of 6-thioguanine. Concordant loss of the rat X chromosome and of the expression of rat HPRT and G6PD was observed in the hybrid clones.

Animals↗
PubMed1979

Mouse hybrid cell lines produce antibodies to herpes simplex virus type 1.

A solid-phase radioimmunoassay procedure has been devised for the assay of antibodies produced in the mouse to herpes simplex virus type 1 (HSV-1). It is based on the adsorption of virus to flexible micro-well plates and uses radio-iodine-labelled rabbit antibody against mouse immunoglobulin to assess antibody binding. Using this assay for screening, cell hybrids have been obtained which yield monoclonal antibody to HSV-1. The hybrids are between spleen cells from hyperimmune mice and an immunoglobulin-non-secreting, azaquanine resistant myeloma cell line (NS-1). From 480 hybrid cell lines initially examined, five stable cell lines were obtained which released HSV-1-specific antibody in vitro and in vivo. Mice carrying transplants of these cell lines yield binding titres in serum of up to 1/25000. Both IgG and IgM antibodies were obtained in this way.

Animals↗
PubMed1978

Expression of latent Epstein-Barr virus genomes in human epithelial/Burkitt's lymphoblastoid hybrid cells.

Expression of latent Epstein-Barr virus genomes in somatic-cell hybrids of Burkitt's lymphoblastoid cells has been studied. Treatment of the hybrid cells, D98/Raji and D98/HR-1, with IUDR induced the formation of EA and VCA and replication of virus DNA, whereas the same treatment of Raji cells induced only the formation of EA. The patterns of transcription of virus genomes in these three cell lines were, however, very similar: 25% without treatment with IUDR, 30% immediately after the treatment and 50% (entire genome transcription) three days after being transferred to fresh medium. The amount of virus RNA in the cells, calculated from DNA-RNA hybridization kinetics, was proportional to the number of virus genomes per cell, suggesting that every copy of virus DNA in these cells is actively transcribed.

Antigens, Viral↗
PubMed1979

Cytogenetics of somatic cell hybrids. I. Progression of stemlines in continuous uncloned cultures of man-mouse cell hybrids.

Karyotypes of hybrid cells were studied in continuous uncloned cultures by Q- and C-bandings. Cultures were initiated by virus-mediated or spontaneous cell fusions from normal human diploid fibroblasts and mouse heteroploid RAG cells. Heterokaryons containing complete genomes of both parental cells randomly lost chromosomes from both species. The majority of cells in early growth stages, however, still possessed a nearly complete human genome. The rate of human chromosome loss in subsequent growth periods was not uniform, being gradual in some and rapid in others. The initially predominant 2n human-1s mouse (1h:1m) type was soon replaced by a less frequent 2n human-2s mouse (1h:2m) type. Over an increased period of time in mass culture, the number of stemlines decreased. One stemline, often a (1h:2m) type with a greatly reduced human complement, outgrew the others and occupied the entire culture. Therefore, the usual process of clonal isolation may confer a negative selection bias against cell hybrids retaining a large number of human chromosomes. Hybrid stemlines with stable karyotypes were established in the present HAT-agar selection system before 36 days after fusion had elapsed.

Animals↗