Productivity enhancement of recombinant protein in CHO cells via specific promoter activation by oncogenes

To construct a recombinant protein highly producing cell lines, we have previously developed the Oncogene Activated Production (OAP) system by using BHK-21 cells. Here we verified the availability of the OAP system in CHO cells. We firstly generated 'primed' ras amplified CHO cells, ras clone I, by introducing human c-Ha-ras oncogene into CHO cells. This ras clone I enables quick and easy establishment of recombinant protein hyper producing cell lines by introduction reporter gene of interest. Then we generated I13 by introducing human interleukin 6 (hIL-6) gene as a reporter gene, which showed enhanced productivity rate as compared to A7 established by conventional method. Furthermore, we found that hIL-6 production level of I13 was slightly improved by raising the CO₂ concentration from 5 to 8% possibly because of the enhanced growth rate. We further introduced the E1A oncogene, which has been shown to have a synergistic effect on the recombinant protein production of the ras-amplified BHK21 cells, then evaluated the productivity. When culture in 5% CO₂ condition, only the slight effect can be seen. However when cultured in 8% CO₂ condition, not only cell number, but also productivity increased significantly, resulted in great augmentation of hIL-6 production, maximum production being 88.6 μg/ml/3 days. This study demonstrates that recombinant protein production level reached commercially desirable level by utilizing our OAP system in CHO cells and optimizing the culture condition.