Efficient and inducible production of human interleukin 6 in Chinese hamster ovary cells using a novel expression system

High level and inducible production of human interleukin 6 (hIL-6) was achieved using a novel expression system in Chinese hamster ovary (CHO) cells. In this system, the transcription of hIL-6 gene under the control of PhCMV*-1 promoter composed of tetracycline operator sequences and a minimal promoter is activated by a chimeric transactivator (tTA) composed of tetracycline repressor and transactivating domain of VP16 protein of herpes simplex virus. The transcription of tTA gene, which is also under the control of PhCMV*-1 promoter, is activated by itself via a positive feedback cycle. The expression of both genes is further enhanced by potentiating the VP16 transactivating domain of tTA transactivator with pX protein of hepatitis B virus. In the presence of tetracycline, the tTA transactivators can not bind to PhCMV*-1 promoter, therefore, the expression of hIL-6 and tTA gene is suppressed, and the pX will not activate basal transcription. In the absence of tetracycline, tTA transactivators bind to PhCMV*-1 promoter and activate efficient transcription of hIL-6 and tTA gene, and the transcription is further enhanced by pX via VP16 transactivating domain. Using this strategy, we isolated a clone (UX1) producing hIL-6 at a rate about 1425 ng/10⁶ cells/day. Furthermore, the hIL-6 production is stringently regulated by tetracycline. This results suggested a novel strategy to establish highly efficient, inducible and cell type independent recombinant protein production system by using an artificial promoter to recruit transactivators and coactivators which can synergistically activate transcription.