Gandor C, Leist C, Fiechter A, Asselbergs F A
Department of Biotechnology, Swiss Federal Institute of Technology, Zürich, Switzerland.
FEBS Lett. 1995 Dec 27;377(3):290-4. doi: 10.1016/0014-5793(95)01328-8.
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.
CHO SSF3细胞在仅含有低分子量成分的未改良商业培养基中以悬浮培养的方式生长。连续无血清培养意外地在原本二氢叶酸还原酶缺陷（dhfr-）的CHO细胞中诱导出低水平的二氢叶酸还原酶活性。然而，使用甲氨蝶呤有可能诱导与二氢叶酸还原酶基因共转染的编码杂合纤溶酶原激活剂K2tu-PA的基因扩增。K2tu-PA的表达与用荧光甲氨蝶呤测量的二氢叶酸还原酶的表达成比例增加。由于不存在血清蛋白酶，分泌的K2tu-PA不会转化为酶活性形式，而是仅以酶原形式回收。
