Availability of oncogene activated production system for mass production of light chain of human antibody in CHO cells

We previously established a ras-oncogene amplified Chinese hamster ovary (CHO) cell line, named ras clone I, as an universal host cell line for oncogene activated production (OAP) system to mass-produce recombinant protein by activation of the cytomegalovirus immediate early (CMV) promoter with ras protein. The λ light chain (C5λ) of human monoclonal antibody HB4C5 is expected to be potentially useful for lung cancer targeting. We generated a C5λ hyper-producing cell line by transfecting ras clone I with the C5λ gene expression plasmid regulated by the CMV promoter, of which productivity was 5.3 times greater than the hyper productive CHO cell line generated by using conventional CHO cells. Introduction of the adenovirus E1A gene into the hyper-producing cell line derived from ras clone I resulted in further 9.5 times enhancement of the productivity, suggesting the synergistic effect of E1A and ras oncogenes on the recombinant protein production driven by the CMV promoter. In addition, intracellular accumulation of C5λ and upregulation of BiP was found in hyper-producing cell lines which were introduced E1A and ras oncogene. This result suggests that excessive intracellular accumulation of C5λ protein, which might be caused by that the amount of produced C5λ in ER is beyond the ability of CHO cells to secrete, might signal the BiP promoter. Our data imply that ras clone I is available as a general host cell for establishing the recombinant protein hyper-producing CHO cells by the OAP system, and suggest that further mass production of recombinant proteins in the OAP system can be possible by clarifying the accurate role of upregulated BiP protein.