Effects of pCIneo and pCEP4 expression vectors on transient and stable protein production in human and simian cell lines

Abstract

To support and meet the demand for recombinant proteins early in the drug discovery process, much work has been directed toward improving the methods used for transient gene transfection and expression. A factor which could potentially affect the outcome of experiments is the choice of the expression vector. Conventional vectors such as pCIneo and pcDNA3 have been used frequently. Each of these places the gene of interest under the control of the CMV promoter. An interesting alternative is provided by episomal vectors. For example, the pCEP4 vector contains the gene coding for the Epstein Barr nuclear antigen as well as the EBNA ori P sequence. This combination allows for the episomal replication of the plasmid. In preliminary experiments, we compared transient secreted placental alkaline phosphatase production in 8 cell lines from 3 different species using the pCIneo vs. pCEP4 vectors and found the utility of the pCEP4 vector to be limited to the human 293 EBNA cell line. In this paper, we have compared the two vectors in six cell lines of simian and human origin, measuring the transient production of secreted placental alkaline phosphatase and human hepatocyte growth factor. In general, the pCEP4 vector produced higher amounts of both proteins in transient transfections. Results were particularly pronounced in the HEK 293 and 293 EBNA cell lines. Stable pools of cells (uncloned) expressing human hepatocyte growth factor were isolated using pCIneo and pCEP4 and protein production levels were compared to those seen in transient transfections. Stable expression with pCEP4 was found to produce the highest levels of human hepatocyte growth factor in 3 of 4 cell lines. Finally, electroporation and FuGENE(TM)6(Roche, Indianapolis IN) as transfection methods were compared measuring transient production of secreted placental alkaline phosphatase, human hepatocyte growth factor, and green fluorescent protein. FuGENE produced higher protein concentrations in less time than electroporation for all 3 proteins.