Impact of using different promoters and matrix attachment regions on recombinant protein expression level and stability in stably transfected CHO cells.

High expression level and long-term expression stability are required for therapeutic protein production in mammalian cells. Three commonly used promoters from the simian virus 40 (SV40), the CHO elongation factor 1α gene (EF1α), and the human cytomegalovirus major immediate early gene (CMV) and two matrix attachment regions from the chicken lysozyme gene (cMAR) and the human interferon β (iMAR) were evaluated for enhancing recombinant gene expression level and stability in stably transfected CHO cells. In the absence of MAR elements, the SV40 promoter gave lower expression level but higher stability than the EF1α promoter and the CMV promoter. The inclusion of MAR elements did not increase the integrated gene copies for all promoters but did enhance expression level for only the SV40 promoter. The enhanced gene expression was due to an increase in mRNA levels. Neither MAR elements enhance gene expression stability during long-term culture. The combinations of SV40 promoter and MAR elements are the best for obtaining both high expression level and stability. The information presented here would be valuable to those developing vectors for generation of CHO cell lines with stable and high productivity.