Amplification and expression of recombinant genes in serum-independent Chinese hamster ovary cells.
CHO SSF3 cells grow as a suspension culture in unmodified commercial medium with only low-molecular weight ingredients. Continuous serum-free culture unexpectedly induced expression of a low dihydrofolate reductase activity in the originally dhfr- CHO cells. Nevertheless, it was possible with methotrexate to induce amplification of a gene coding for the hybrid plasminogen activator K2tu-PA cotransfected with a dhfr gene. Expression of K2tu-PA expression was proportionally increased to that of dhfr, which was measured with fluorescent methotrexate. Because no serum proteases were present, secreted K2tu-PA was not converted to the enzymatically active form, but was exclusively recovered in proenzyme form.
Department of Biotechnology, Swiss Federal Institute of Technology, Zürich, Switzerland.
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Gandor
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Leist
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Fiechter
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Asselbergs
D000220:Adaptation, Biological; D000818:Animals; D016466:CHO Cells / Q000502:physiology*; D006224:Cricetinae; D016895:Culture Media, Serum-Free; D004274:DNA, Recombinant; D004351:Drug Resistance; D005784:Gene Amplification; D005786:Gene Expression Regulation; D008727:Methotrexate / Q000494:pharmacology; D010960:Plasminogen Activators / Q000096:biosynthesis* / Q000235:genetics; D012641:Selection, Genetic; D013762:Tetrahydrofolate Dehydrogenase / Q000096:biosynthesis / Q000235:genetics*; D014162:Transfection
D016895:Culture Media, Serum-Free; D004274:DNA, Recombinant; D013762:Tetrahydrofolate Dehydrogenase; D010960:Plasminogen Activators; D008727:Methotrexate