Genetic analysis of tumorigenesis: IV. Chromosome reduction and marker segregation in progeny clones from Chinese hamster cell hybrids.

Hybrid cells produced by the fusion of pairs of cells, one a tumorigenic derivative of CHEF/16 and the other a nontumorigenic derivative of CHEF/18, give rise to clones which are largely tetraploid, but rare reduced hybrids with chromosome counts in the diploid range have been recovered from tumors of hybrid origin. This paper describes the recovery in cell culture of reduced hybrids in the diploid range by selection with 5-bromodeoxyuridine (BrdU) or methylcellulose as well as by growth in culture of cells from excised tumors. All selected subclones were tumorigenic and resistant to BrdU, but they segregated for resistance to 6-thioguanine. Unselected subclones were tetraploid, nontumorigenic, and sensitive to both drugs. These data show that chromosome reassortment as well as extensive chromosome reduction both occur in a small fraction of the population during growth of each hybrid clone.     

Genetic analysis of metabolic cooperation in mammalian cell lines

Metabolites can be exchanged between cells in culture by direct transfer from the cytoplasm of one cell to that of another in a process known as metabolic cooperation. Most mammalian cell lines are able to transfer small molecules directly between adjacent cells in this way and are consequently mec+; however, a small number are defective in this ability (mec-). Results obtained from somatic cell hybrids formed between combinations of these cells have shown that the four different cell lines examined in this study can be divided into at least two different complementation groups on the basis of their ability to transfer 3H-labeled nucleotides to adjacent cells. Two of the cell lines clearly fall into a single complementation group.     

Genetic analysis of tumorigenesis. VIII. Suppression of SV40 transformation in cell hybrids and cytoplasmic transferants

Intraspecies somatic cell hybrids of BALB/c mouse 3T3 and SV40-transformed embryonic fibroblast (SVT2) cells were analyzed for transformation-associated properties and their tumorigenic potential in nude mice. In confirmation of our earlier findings, hybrids expressing the viral T-antigen were not suppressed for the ability to clone in medium with 1% serum. In contrast, division rate in medium with 1% or 10% serum, anchorage independence, cytochalasin-sensitive growth control, and tumorigenicity were suppressed noncoordinately, and the extent of suppression varied from one hybrid to another. Suppression was not simply determined by the increased chromosome content of the hybrid cells, nor was suppression correlated with rearrangements of the integrated viral sequence (SAGER et al., 1981a, b). Similar results were found in cytoplasmic transferants expressing T-antigen. Four independent transferants and subclones derived from them varied in the extent of suppression of anchorage independence and tumorigenicity. In both hybrids and transferants, a low serum requirement for clonal growth apparently was determined solely by expression of SV40 T-antigen, but other transformation properties, as well as tumorigenicity, appeared to require multiple changes in the cellular genome for their expression. These changes must occur during or after viral integration, since they are not expressed in uninfected 3T3 cells.     

Rapid analysis of mouse-hamster hybrid cell lines by in situ hybridization

In situ hybridization techniques for analyzing the murine DNA complement of mouse-hamster hybrid cells are described. Total genomic mouse DNA is labeled with biotin and hybridized without suppression to metaphase spreads from a mouse-hamster hybrid line containing the mouse fusion chromosome X12. Detection via fluorochrome-conjugated avidin reveals mouse chromosomal DNA with high sensitivity and permits the identification of both normal and aberrant murine chromosomes. Conversely, biotinylated total genomic DNA from a hybrid line can be used as a probe on normal mouse metaphase spreads if suppression techniques are employed, facilitating the analysis of mouse chromosomes present in the hybrid line.     

Expression and function of a putative cell surface receptor for fibronectin in hamster and human cell lines

We have previously reported the use of monoclonal antibodies to identify a 140-kD cell surface glycoprotein in mammalian cells that is specifically involved in fibronectin-mediated cell adhesion. We now report the purification of this molecule using immunoaffinity chromatography and the subsequent generation of polyclonal antibodies that selectively immunoprecipitate 140-kD putative fibronectin receptor glycoprotein (gp140) extracted from rodent or human cells; these antibodies also specifically block fibronectin-mediated cell adhesion but not adhesion mediated by other factors in serum. Expression of gp140-like molecules was detected on the surfaces of several adherent human cell lines (HDF, WISH, and EFC) but not on erythrocytes; however, gp140 was also detected on a nonadherent human lymphoid line (DAUDI). Analysis of gp140 on nonreducing SDS gels revealed two closely migrating bands. Protease digestion and peptide mapping suggests that the two bands are closely related polypeptides.     

Expression of galactose genes in mammalian cells. I. Galactose enzymes in Chinese hamster ovary cell hybrids

Galactokinase and galactose 1-phosphate uridyl transferase activities have been studied in several Chinese hamster ovary clonal lines following hybridization of two glycine-requiring mutants. Initially, the hybrids have about twice the parental activity of both enzymes. However, with time, there is a further increase beyond this activity, especially for the transferase enzyme, followed by a decline and a leveling off. The final average kinase activity in the hybrids is about 1.2 times the parental kinase, while the final average transferase is about 1.9 times the parental amount. The cultures lose about 10% of their chromosomes during the period under study; however, there is no obvious correlation between gross chromosome loss and enzyme activity. Protein calculated on a per chromosome basis (to correct for chromosome loss) behaves in a manner similar to the enzyme activities. One possible interpretation of the results is that, following hybridization, there is a derepression of some activities followed by repression during which time new levels of cellular parameters become established. This investigation was aided in part by U.S. Public Health Service Grant 1RO1 GM18481-01. Paper no. 476 from the Department of Biophysics and Genetics, University of Colorado, Denver, Colorado.     

Mutagenesis by simian virus 40. I. detection of mutations in Chinese hamster cell lines using different resistance markers.

The mutagenic action of SV40 in permanent lines of Chinese hamster cells (CHO-K1 and V79) was investigated with the aid of different resistance markers. The markers studied had resistance to 8-azaguanine (25 and 30 mug/ml), aminopterin (3.3--5.5X10(-3) mug/ml), colchicine (6.5 and 7.0X10(-2) mug/ml) and 5-bromodeoxyuridine (50--120 mug/ml), respectively. After virus infection the mutation frequencies were increased by one (azaguanine, aminopterin) and two (colchicine) orders of magnitude as compared with spontaneous mutation frequencies. In contrast, it was not possible to enhance the frequency of mutation to BUdR resistance. On the other hand, the ability to proliferate in HAT medium was induced in three of five BUdR-resistant cell clones by infection with SV40. The resistance induced by SV40 was stable when isolated clones were cultured under non-selective conditions. Mechanisms are proposed that may be responsible for the mutagenic action of SV40.     

Specific staining of human chromosomes in Chinese hamster x man hybrid cell lines demonstrates interphase chromosome territories

Summary In spite of Carl Rabl's (1885) and Theodor Boveri's (1909) early hypothesis that chromosomes occupy discrete territories or domains within the interphase nucleus, evidence in favor pf this hypothesis has been limited and indirect so far in higher plants and animals. The alternative possibility that the chromatin fiber of single chromosomes might be extended throughout the major part of even the whole interphase nucleus has been considered for many years. In the latter case, chromosomes would only exist as discrete chromatin bodies during mitosis but not during interphase. Both possibilities are compatible with Boveri's well established paradigm of chromosome individuality. Here we show that an active human X chromosome contained as the only human chromosome in a Chinese hamster x man hybrid cell line can be visualized both in metaphse plates and in interphase nuclei after in situ hybridization with either ³H- or biotin-labeled human genomic DNA. We demonstrate that this chromosome is organized as a distinct chromatin body throughout interphase. In addition, evidence for the territorial organization of human chromosomes is also presented for another hybrid cell line containing several autosomes and the human X chromosome. These findings are discussed in the context of our present knowledge of the organization and topography of interphase chromosomes. General applications of a strategy aimed at specific staining of individual chromosomes in experimental and clinical cytogenetics are briefly considered.     

Isolation and characterization of lectin-resistant mouse cell lines defective in their ability to yield hybrid cells

Lectin-resistant variants of the mouse mammary tumor cell line FM3A in suspension were isolated after multiple-step selection using toxic concentrations of phytohemagglutinin (PHA) and concanavalin A (Con A). In fusion experiments, both PHA- and Con A-resistant lines were found to have lost the ability to yield hybrids with suspension-grown cells, although they were capable of yielding hybrids with monolayer-grown cells. This phenotype of PHA-resistant lines was stable during a long period of culture in the absence of PHA.     

Genetic complementation in hybrid cells derived from two metabolic co-operative defective mammalian cell lines

A series of hybrid clones have been isolated following the somatic cell fusion of two mammalian cell lines, each defective in junctional transfer of metabolites. One of these parental lines is a variant isolated by selection from the metabolic co-operation competent embryonal carcinoma line PC13TG8. The other parent is LMTK^? in which inability to transfer was found to be a pre-existing property. Hybrids between these two cell lines are restored in their ability to co-operate, indicating the existence of at least two genetically distinct lesions affecting metabolic co-operation, each of which is recessive. This is the first demonstration that more than one locus is involved in junctional communication.     

Genetic complementation in hybrid cells derived from two metabolic co-operation defective mammalian cell lines

A series of hybrid clones have been isolated following the somatic cell fusion of two mammalian cell lines, each defective in junctional transfer of metabolites. One of these parental lines is a variant isolated by selection from the metabolic co-operation competent embryonal carcinoma line PC13TG8. The other parent is LMTK⁻ in which inability to transfer was found to be a pre-existing property. Hybrids between these two cell lines are restored in their ability to co-operate, indicating the existence of at least two genetically distinct lesions affecting metabolic co-operation, each of which is recessive. This is the first demonstration that more than one locus is involved in junctional communication.     

Expression analysis of a modified factor X in stably transformed insect cell lines.

A modified Factor X protein was combined with a cellulose-binding domain tag and expressed in insect cell lines. The protein, CBDFX, was expressed and secreted into the medium. Stable, transformed Hi5 and Sf9 insect cell lines were generated and tested for production of secreted CBDFX. The highest Sf9 and Hi5 CBDFX-producing cell lines were scaled up to 2-liter fermentors to evaluate production of this recombinant protein. Secreted protein production levels reached 4 mg/liter for the stable, transformed Hi5 cell line and 18 mg/liter for the stable, transformed Sf9 cell line. The protein was properly processed as determined by amino terminal sequencing and bound well to the cellulose substrate Avicel. In addition the activated recombinant CBDFX(a) was capable of recognizing and efficiently processing a Factor X cleavage site.     

Genetic analysis of mitomycin-C-sensitive mutants of a Chinese hamster ovary cell line

5 mutants of a Chinese hamster ovary (CHO) cell line, which exhibit similar levels of sensitivity to killing by mitomycin C, have been analysed genetically to determine whether they represent one or more genetic complementation groups. Hybrids were constructed by fusing cells carrying either the neo or the Ecogpt marker and selecting in medium containing G418 and mycophenolic acid. Selectable markers were introduced into the cells by DNA transfection using pSV5-neo or pSV5-gpt, which represents a quick and convenient method for generating resistant derivatives. Hybrids generated by crosses between any one mutant and the parental cell line exhibited near wild-type resistance to mitomycin C, indicating that the mutants are phenotypically recessive. Self-cross hybrids for all 5 mutants had D37 values for killing by mitomycin C of between 20 and 30 ng/ml. The values obtained for crosses between different mutants were 60-105 ng/ml, with the exception of 1 pairing which gave a value of 33 ng/ml. These results indicate that that the mutants represent at least 4 different genetic complementation groups, suggesting that cellular resistance to mitomycin C is mediated via a number of different mechanisms.     

Facilitating haplotype analysis by fully automated analysis of all chromosomes in human-mouse hybrid cell lines

Recent evidence suggests that haplotype analysis is essential in recognizing genetic factors involved in the tendency toward a particular disease or pharmacogenetic phenotype, as well as to identify genes involved in multigenic disorders. Because of the increasing need for efficient haplotype tests, a new hybrid system, called conversion technology, was developed. Conversion technology aims at converting the diploid chromosome content into a haploid state so that hybrids contain a single copy of any desired chromosome. A number of mutations can now be identified easily, as they are no longer obscured by the normal sequence present on the other copy of the chromosome. However, the efficient use of this hybrid system depends on a complete analysis of both human and mouse chromosome complements in order to assess the stability of the hybrid cells and to accurately determine their human chromosome content. We describe a new multicolor FISH-based method capable of analyzing both genomes simultaneously in a single hybridization. This new technique should become an instrumental part of inexpensive, reliable haplotype tests.     

Comparative study of rabies virus persistence in human and hamster cell lines.

Persistent infections by rabies virus in BHK-21/13S and HEp-2 cells were studied comparatively. No evidence of interferon production, selection of virus-resistant cells, or integration of the viral genome could be found. Persisting viruses replicated efficiently at 34, 36, and 40 degrees C. Both persistently infected cultures released defective interfering virus particles. A cyclical pattern of infection, which was not characteristic of the persistently infected HEp-2 system, was observed in persistently infected BHK cultures. The virus from persistently infected BHK cultures lost its virulence for mice, whereas the virus from persistently infected HEp-2 cultures retained mouse-killing capacity for more than 3 years.     

Herpes simplex virus DNA in transformed cells: sequence complexity in five hamster cell lines and one derived hamster tumor.

Analyses of the hybridization kinetics of labeled herpes simplex virus 2 (HSV-2) DNA with DNA from five hamster cell lines transformed by UV light-irradiated HSV-2 revealed the following. (i) Viral DNA sequences were detected in all five cell lines tested. (ii) None of the cell lines contained the full complement of HSV-2 DNA. (iii) The amount of viral DNA present in the cells varied in different transformed cell lines and ranged from 8 to 32% of the HSV-2 DNA genome in 1 to 3 copies/cell. (iv) Two parallel passages of the same cell line (333-2-29) differed in the amount of viral DNA they contained. We also compared the viral DNA sequences present in (i) one transformed cell line (333-8-9) propagated serially in culture for 80 passages, (ii) a tumor produced by inoculation of a newborn hamster with the 333-8-9 cells, and (iii) a cell line derived from a hamster tumor as above and propagated in culture for 32 passages. The results show that viral DNA present in the hamster tumor and in the cells derived from the tumor had a lower sequence complexity than that present in the original serially passaged 333-8-9 cell line.     

Purine mutants of mammalian cell lines. I. Accumulation of formylglycinamide ribotide by purine mutants of Chinese hamster ovary cells

Mutants unable to perform de novo biosynthesis of purines have been isolated from cultures of mutagen-treated Chinese hamster ovary cells using bromodeoxyuridine selection techniques. Accumulation of C ¹⁴ -labeled formylglycinamide ribotide by suspension cultures of mutant cells incubated with glycine-C ¹⁴ suggested that the defect leading to auxotrophy most probably involves the gene coding for formylglycinamide amidotransferase, (E.C. 6.3, 5.3), the fourth enzyme in the de novo purine biosynthetic pathway. Direct assay of formylglycinamide amidotransferase activity in cell-free extracts prepared from mutant and parental cells has demonstrated the absence of amidotransferase activity in mutant derived extracts.