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  • 1
    Electronic Resource
    Electronic Resource
    Three new complementation groups of temperature-sensitive Chinese hamster ovary cell mutants defective in the endocytic pathway (1988)
    Springer
    Somatic cell and molecular genetics 14 (1988), S. 499-507 
    Details
    ISSN: 1572-9931
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract We describe here the results of complementation studies with six mutant Chinese hamster ovary cells expressing temperature-sensitive lesions affecting the endocytic pathway. The mutants were crossed with representatives of the End1 and End2 complementation groups identified previously by Robbins et al. (J. Cell Biol. 99:1296–1308, 1984). Two mutants, G.8.1 and 31.1, were members of the End1 complementation group. One mutant, 25.2, was a member of the End2 complementation group. The other three mutants each defined new complementation groups, which we have designated End3 (mutant G.7.1), End4 (mutant V.24.1), and End5 (mutant 42.2). Previous work on mutants of the Endl, End2, and End3 classes had shown that these mutants were defective in endosomal acidification. We prepared postnuclear supernatants from mutants harvested at the nonpermissive temperature and compared their acidification activities, assessed by ATP-stimulated quenching of acridine orange. Members of the End1, End2, and End2 groups had reduced acidification activity, correlating with the acidification defects known to be expressed by these mutants. Strain V.24.1 (End4) also expressed a 40% reduction in acidification activity, while strain 42.2 (End5) had no reduction of acidification activity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01534715
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  • 2
    Electronic Resource
    Electronic Resource
    Two pathways of transferrin recycling evident in a variant of mouse LMTK− cells (1988)
    Springer
    Somatic cell and molecular genetics 14 (1988), S. 473-487 
    Details
    ISSN: 1572-9931
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract We describe here the properties of a variant cell line, termed AF192, selected by exposing mouse LMTK}-cells to a cytotoxic form of transferrin prepared by conjugating transferrin to diphtheria toxin. AF192 cells were mildly resistant to the transferrindiphtheria toxin conjugate and were cross-resistant to the protein toxins modeccin, abrin, ricin, and Pseudomonas aeruginosa exotoxin A. AF192 cells had an aberrant transferrin cycle characterized by an ∼50% reduction in the rate of iron uptake from diferric transferrin, an ∼25% reduction in the number of surface transferrin receptors, and a time course for transferrin recycling that resolved into two apparent first-order rate processes. The aberrant transferrin cycle was not the result of a failure of endocytosed transferrin to discharge iron; rather, part, but not all, of the transferrin taken up by AF192 cells was diverted to an intracellular site from which it was recycled very slowly.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01534713
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  • 3
    Electronic Resource
    Electronic Resource
    Novel method for isolating mammalian cells defective in fluid-phase endocytosis (1992)
    Springer
    Somatic cell and molecular genetics 18 (1992), S. 543-551 
    Details
    ISSN: 1572-9931
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract A new method for isolating mutants defective in fluid-phase endocytosis has been developed based on the observation that endocytosed horseradish peroxidase can be made lethal to cells. The method was used to isolate a mutant from Chinese hamster ovary cells, termed HRP-1, that was temperature-sensitive for viability and had a 70% reduction in the rate of horseradish peroxidase endocytosis at the restrictive temperature. At high temperature, HRP-1 cells were also defective in the secretory path and their Golgi complex disappeared at the resolution of fluorescence microscopy. These properties are similar to two previously described mutants of CHO cells, DS28-6 and V.24.1. In complementation tests, mutants HRP-1, DS28-6, and V.24.1 all appeared to be in the same complementation group.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01232650
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  • 4
    Electronic Resource
    Electronic Resource
    Biosynthesis of lysosomal enzymes in cells of the End3 complementation group conditionally defective in endosomal acidification (1991)
    Springer
    Somatic cell and molecular genetics 17 (1991), S. 137-150 
    Details
    ISSN: 1572-9931
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Various aspects of lysosome biogenesis have been studied in Chinese hamster ovary (CHO) cells of the End3 complementation group (designated G.7.1 cells), which display a temperature-sensitive defect in the acidification of endosomes, but not lysosomes. In G.7.1 and normal wild-type cells grown at the permissive temperature (34°C), the lysosomal enzymes α-glucosidase and cathepsin D were synthesized as high-molecular-weight precursors that subsequently underwent intracellular proteolytic processing to yield lower molecular weight mature forms. The mature forms of the enzymes were retained in cells, and small amounts of each precursor were secreted. However, in G.7.1 cells grown at the restrictive temperature (41°C), there was a massive and inappropriate oversecretion of lysosomal enzyme precursors, which resulted in very little of the mature forms being processed and retained by the cells. This mistargeting of lysosomal enzymes was not due to an absence of phosphorylated oligosaccharides on the enzymes, nor to a defect in mannose 6-phosphate (Man6P) receptors. However, it was found that whereas G.7.1 cells had the same number of cell surface Man6P receptors at 34°C and 41°C, the rate of accumulation and degradation of Man6P-containing ligands was about two to three times more rapid in cells maintained at the permissive temperature. There did not appear to be any gross changes in Golgi function as the oligosaccharides of α-glucosidase and the Man6P receptor were processed in a similar fashion at both 34°C and 41°C. In addition to these studies, electron microscopic observations revealed that at 41°C, G.7.1 cells accumulated inclusion-type bodies reminiscent of those found in I-cell disease fibroblasts. Thus, the biochemical and electron microscopic results on G.7.1 cells provide further evidence that acidified endosomes are important for the biogenesis of lysosomes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01232971
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  • 5
    Electronic Resource
    Electronic Resource
    Studies of the diphtheria toxin receptor on chinese hamster cells (1978)
    New York, N.Y. : Wiley-Blackwell
    Journal of Supramolecular Structure 9 (1978), S. 47-55 
    Details
    ISSN: 0091-7419
    Keywords: diphtheria toxin ; lectins ; cell surface receptors ; diphtheria toxin resistance ; somatic cell mutants ; Life Sciences ; Molecular Cell Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Concanavalin A, wheat germ agglutinin and the ovalbumin glycopeptide are all inhibitors of the cytotoxic effect of diphtheria toxin on Chinese hamster cells. Ovalbumin glycopeptide loses its inhibitory property after treatment with β-N-acetylglucosaminidase. This demonstrates the importance of the glycopeptide structure for the mechanism of inhibition. The glycopeptide may be a toxin cell-surface receptor analogue.Diphtheria toxin-resistant mutants were isolated in order to search for cells that might have an altered toxin receptor. One mutant was 10-to 15-fold more resistant to diphtheria toxin than wild-type cells when protein synthesis was measured as a function of toxin concentration. However, when protein synthesis was measured as a function of time at a high toxin concentration, the time before onset of inhibition was identical in the mutant and wild-type cells. We present evidence indicating that the resistance of this mutant can be accounted for by a decreased affinity of toxin for a cell-surface receptor.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jss.400090106
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