A regulatable selective system facilitates isolation of heterologous protein hyper-producing mammalian cells without gene amplification

In this article, we describe a new method that facilitates to isolate mammalian cells inducible hyper-producing heterologous proteins. This method uses the tetracycline-inducible system to express both the selection marker and the heterologous gene, therefore, allows to increase the selection pressure by reducing the transcription of the selection maker gene. Using this method, we were able to isolate recombinant Chinese hamster ovary cells with a high efficiency. One of established clones produced the recombinant bovine β-lactoglobulin as heterologous protein at a peak rate of 12 μg 10^-6 cells/day with an inducibility of about 100-fold. This clone was over expressed the mRNA of β-lactoglobulin and the drug resistant gene but did not amplify their genes. When cultured in a hollow fiber bioreactor, the cells were able to secrete β-lactoglobulin over 300 μg ml^-1. This method is applicable to a broad range of eukaryotic systems and is of general value to technology for recombinant protein production.