Transient Expression of Foreign Genes in Insect Cells (sf9) for Protein Functional Assay

The transient gene expression system is one of the most important technologies for performing protein functional analysis in the baculovirus in vitro cell culture system. This system was developed to express foreign genes under the control of the baculoviral promoter in transient expression plasmids. Furthermore, this system can be applied to a functional assay of either the baculovirus itself or foreign proteins. The most widely and commercially available transient gene expression system is developed based on the immediate-early gene (IE) promoter of Orgyia pseudotsugata multicapsid nucleopolyhedrovirus (OpMNPV). However, a low expression level of foreign genes in insect cells was observed. Therefore, a transient gene expression system was constructed for improving protein expression. In this system, recombinant plasmids were constructed to contain the target sequence under the control of the Drosophila heat shock 70 (Dhsp70) promoter. This protocol presents the application of this heat shock-based pDHsp/V5-His (V5 epitope with 6 histidine)/Spodoptera frugiperda cell (sf9 cell) system; this system is available not only for gene expression but also for evaluating the anti-apoptotic activity of candidate proteins in insect cells. Furthermore, this system can be either transfected with one recombinant plasmid or co-transfected two potentially functionally antagonistic recombinant plasmids in insect cells. The protocol demonstrates the efficiency of this system and provides a practical case of this technique.