Human T-lymphotropic virus tax activates human cytomegalovirus major-immediate early promoter and improves production of recombinant proteins in HEK293 cells.

The human cytomegalovirus (CMV) major immediate-early (MIE) promoter is widely used in mammalian cells for production of recombinant proteins. It is of great interest to further enhance protein production driven by the CMV promoter. Here, we report that the Tax protein of human T-lymphotropic virus stimulates the transgene expression under the control of CMV MIE promoter in HEK293 cells. At least threefold increases in transient production of recombinant proteins, including luciferase and two biopharmaceutical proteins (erythropoietin and interferon-γ), were detected. Furthermore, cyclic adenosine monophosphate (AMP)-response element binding protein 2 (CREB2) was identified as a cellular cofactor, which might be responsible for Tax transactivation of the CMV MIE promoter. Our results not only demonstrate the potential use of this novel expression strategy for improvement of recombinant protein production in HEK293 cells but also provide the molecular mechanism for Tax-mediated activation of CMV MIE promoter.

Identification of cellular genes critical to recombinant protein production using a Gaussia luciferase-based siRNA screening system.

Development of high-throughput functional genomic screening, including siRNA screening, provides a novel approach for quick identification of critical factors involved in biological processes. Here, we apply this strategy to search for cellular genes involved in recombinant protein production. Since most of biopharmaceutical proteins are secreted proteins, we develop a cell-based reporter assay using a secreted luciferase, Gaussia luciferase (Gluc), as the reporter. Human embryonic kidney 293 (HEK293) cells transiently transfected with the Gluc reporter plasmid are used to screen our siRNA panel. Three cellular genes, CCAAT/enhancer binding protein gamma (CEBPG), potassium channel tetramerisation domain containing 2 (KCTD2), transmembrane protein 183A (TMEM183A), were isolated from the screening. Production of erythropoietin (EPO) was significantly inhibited when CEBPG, KCTD2, and TMEM183A were knocked down. Furthermore, overexpression of CEBPG is shown to significantly improve production of recombinant EPO, interferon gamma, and monoclonal antibody in HEK293 and Chinese hamster ovary cells. Collectively, this novel Gluc-based siRNA screening system is proven to be a useful tool for investigation of secreted protein production in mammalian cells.

Identification of HUGT1 as a potential BiP activator and a cellular target for improvement of recombinant protein production using a cDNA screening system.

The development of a high-throughput functional genomic screening provides a novel and expeditious approach in identifying critical genes involved in specific biological processes. Here we describe a cell-based cDNA screening system to identify the transcription activators of BiP, an endoplasmic reticulum (ER) chaperone protein. BiP promoter contains the ER stress element which is commonly present in the genes involved in unfolded protein response (UPR) that regulates protein secretion in cells. Therefore, the positive regulators of BiP may also be utilized to improve the recombinant protein production through modulation of UPR. Four BiP activators, including human UDP-glucose:glycoprotein glucosyltransferase 1 (HUGT1), are identified by the cDNA screening. Overexpression of HUGT1 leads to a significant increase in the production of recombinant erythropoietin, interferon gamma, and monoclonal antibody in HEK293 cells. Our results demonstrate that the cDNA screening for BiP activators may be effective to identify the novel BiP regulators and HUGT1 may serve as an ideal target gene for improving the recombinant protein production in mammalian cells.