Abstract
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 β-interferon (β-IFN) or thelac Z gene which codes for β-galactosidase (β-gal). The recombinant genes in these CHO cells were amplified stepwise by growth in 0, 10−7, and 10−6 M methotrexate (MTX), and the β-gal expressing cells were adapted to suspension culture. Flow cytometric methods (FCM) were used to measure the distribution of amplifieddhfr gene content and foreign β-gal gene expression in the cell populations. A biochemical assay for β-gal was also used. Beta-gal expression was found to increase with increasing gene amplification. The growth rate of recombinant CHO cells at 10−7 M MTX was found to be 20% lower than that of recombinant CHO cells in MTX-free medium, and the cell growth rate at 10−6 M MTX was 20% lower than that of recombinant CHO cells at 10−7 M MTX. There was no effect of 10−5 M MTX on the growth of CHO-DG44 (dhfr-) cells. The reduction of growth rate in recombinant CHO cells is therefore thought to be mainly due to the effect ofdhfr and foreign gene amplification and increased β-galactosidase expression.
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Abbreviations
- Ampr :
-
ampicillin resitance gene
- CDβG:
-
plasmid bearingdhfr andlac Z genes
- CMV:
-
cytomegalovirus promoter
- CHO:
-
Chinese hamster ovary
- dhfr :
-
dihydrofolate reductase gene
- DHFR:
-
dihydrofolate reductase enzyme
- dFBS:
-
dialyzed fetal bovine serum
- FBS:
-
fetal bovine serum
- FCM:
-
flow cytometric method
- FITC-MTX:
-
fluorescein-methotrexate
- β-gal:
-
β-galactosidase (E.C. 3.2.1.23)
- β-IFN:
-
human β-interferon
- Met IIA :
-
metallothionein IIA promoter
- MTX:
-
methotrexate (4-amino-10-methylfolic acid)
- pSVdMIF:
-
plasmid bearingdhfr and β-IFN genes
References
Alt FW, Kellems RE, Bertino JR and Schimke RT (1978) Selective multiplication of dihydrofolate reductase genes in methotrexate-resistant variants of cultured murine cells. J Biol Chem 253: 1357–1370.
Bentley WE, Mirjalili N, Andersen DC, Davis RH and Kompala DS (1990) Plasmid-encoded protein: The principal factor in the “metabolic-burden” associated with recombinant bacteria. Biotech Bioeng 35: 668–681.
Biedler JL, Chang T, Peterson RHF, Melera PW, Meyer MB and Spengler BA (1983) Gene amplification and phenotypic instability in drug-resistant revertant cells. In: Chabner BA (ed) Rational Basis for Chemotherapy. New York, USA, pp. 71–92.
Cockett MI, Bebbington CR and Yarrantin GT (1990) High level expression of tissue inhibitor of metalloproteinase in Chinese hamster ovary cells using glutamine synthetase gene amplification. Bio/Technology 8: 662–667.
Hall CV, Jacob PE, Ringold GM and Lee F (1983) Expression and regulation ofEscherichia coli lac Z gene fusions in mammalian cells. J Mol Appl Gen 2: 101–109.
Hamlin JL, Milbrandt JD, Heintz NH and Azizkhan JC (1984) DNA sequence amplification in mammalian cells. Intl Rev Cytol 90: 31–82.
Karin M, Haslinger A, Holtgreve H, Cathala G, Slater E and Baxter JD (1984) Activation of a heterologous promoter in response to dexamethasone and cadmium by methallothionein gene 5′-flanking DNA. Cell 36: 371–379.
Kaufman RJ, Brown PC and Schimke RT (1979) Amplified dihydrofolate reductase genes in unstably methotrexate-resistant cells are associated with double minute chromosomes. Proc Natl Acad Sci 76: 5669–5673.
Kaufman RJ and Schimke RT (1981) Amplification and loss of dihydrofolate reductase genes in a Chinese hamster ovary cell line. Mol Cell Biol 1: 1069–1076.
Kern JA (1990) Overexpression in recombinant mammalian cells: Effect of growth rate and genetic stability. MS Thesis, University of Colorado, Boulder, USA.
Miller JH (1972) Experiments in Molecular Genetics. Cold Spring Harbor Laboratory. Cold Spring Harbor, USA.
Page MJ (1985) Expression of amplified human beta interferon genes using heavy metal induction in Chinese hamster ovary cells. Gene 37: 139–144.
Sambrook J and Gething MJ (1988) Vectors for high level expression of proteins in mammalian cells. Focus 10: 41–48.
Sanes JR, Rubenstein JLR and Nicolas JF (1986) Use of a recombinant retrovirus to study post-implantation cell lineage in mouse embryos. EMBO 5: 3133–3142.
Schimke RT, Kaufman RJ, Alt FW and Kellems RE (1978) Gene amplification and drug resistance in cultured murine cells. Science 202: 1051–1055.
Seed B (1987) An LFA-3 cDNA encodes a phospholipid-linked membrane protein homologous to its receptor CD2. Nature 329:840–842.
Subramani S, Mulligan R and Berg P (1981) Expression of the mouse dihydrofolate reductase complementary deoxyribonucleic acid in simian virus 40 vectors. Mol Cell Biol 2: 854–864.
Weidle UH, Buckel P and Wienberg J (1988) Amplified expression constructs for human tissue-type plasminogen activator in Chinese hamster ovary cells: Instability in the absence of selective pressure. Gene 66: 193–203.
Weymouth LA and Barsoum J (1986) Genetic engineering in mammalian cells. In: Thilly WG (ed) Mammalian Cell Technology. Butterworth Publishers, MA, USA, pp. 9–62.
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Gu, M.B., Kern, J.A., Todd, P. et al. Effect of amplification ofdhfr andlac Z genes on growth and β-galactosidase expression in suspension cultures of recombinant CHO cells. Cytotechnology 9, 237–245 (1992). https://doi.org/10.1007/BF02521751
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DOI: https://doi.org/10.1007/BF02521751