Transfected insect cells in suspension culture rapidly yield moderate quantities of recombinant proteins in protein-free culture medium

Screening of Membrane Protein Production by Comparison of Transient Expression in Insect and Mammalian Cells

Membrane proteins are difficult biomolecules to express and purify. In this paper, we compare the small-scale production of six selected eukaryotic integral membrane proteins in insect and mammalian cell expression systems using different techniques for gene delivery. The target proteins were C terminally fused to the green fluorescent marker protein GFP to enable sensitive monitoring. We show that the choice of expression systems makes a considerable difference to the yield and quality of the six selected membrane proteins. Virus-free transient gene expression (TGE) in insect High Five cells combined with solubilization in dodecylmaltoside plus cholesteryl hemisuccinate generated the most homogeneous samples for all six targets. Further, the affinity purification of the solubilized proteins using the Twin-Strep^® tag improved protein quality in terms of yield and homogeneity compared to His-tag purification. TGE in High Five insect cells offers a fast and economically attractive alternative to the established methods that require either baculovirus construction and the infection of the insect cells or relatively expensive transient gene expression in mammalian cells for the production of integral membrane proteins.

The mechanistic insight of a specific interaction between 15d-Prostaglandin-J2 and eIF4A suggests an evolutionary conserved role across species

15-deoxy-delta 12,14-prostaglandin J2 (15d-PGJ2) is an anti-inflammatory/anti-neoplastic prostaglandin that functions through covalent binding to cysteine residues of various target proteins. We previously showed that 15d-PGJ2 mediated anti-inflammatory responses are dependent on the translational inhibition through its interaction with eIF4A (Kim et al., 2007). Binding of 15d-PGJ2 to eIF4A specifically blocks the interaction between eIF4G and eIF4A, which leads to the formation of stress granules (SGs), which then cluster mRNAs with inhibited translation. Here, we show that the binding between 15d-PGJ2 and eIF4A specifically blocks the interaction between the MIF4G domain of eIF4G and eIF4A. To reveal the mechanism of this interaction, we used computational simulation-based docking studies and identified that the carboxyl tail of 15d-PGJ2 could stabilize the binding of 15d-PGJ2 to eIF4A through arginine 295 of eIF4A, which is the first suggestion that the 15d-PGJ2 tail plays a physiological role. Interestingly, the putative 15d-PGJ2 binding site on eiF4A is conserved across many species, suggesting a biological role. Our data propose that studying 15d-PGJ2 and its targets may uncover new therapeutic approaches in anti-inflammatory drug discovery.

Efficient production of antibody Fab fragment by transient gene expression in insect cells

Transient gene expression allows a rapid production of diverse recombinant proteins in early-stage preclinical and clinical developments of biologics. Insect cells have proven to be an excellent platform for the production of functional recombinant proteins. In the present study, the production of an antibody Fab fragment by transient gene expression in lepidopteran insect cells was investigated. The DNA fragments encoding heavy-chain (Hc; Fd fragment) and light-chain (Lc) genes of an Fab fragment were individually cloned into the plasmid vector pIHAneo, which contained the Bombyx mori actin promoter downstream of the B. mori nucleopolyhedrovirus (BmNPV) IE-1 transactivator and the BmNPV HR3 enhancer for high-level expression. Trichoplusia ni BTI-TN-5B1-4 (High Five) cells were co-transfected with the resultant plasmid vectors using linear polyethyleneimine. When the transfection efficiency was evaluated, a plasmid vector encoding an enhanced green fluorescent protein (EGFP) gene was also co-transfected. Transfection and culture conditions were optimized based on both the flow cytometry of the EGFP expression in transfected cells and the yield of the secreted Fab fragments determined by enzyme-linked immunosorbent assay (ELISA). Under optimal conditions, a yield of approximately 120 mg/L of Fab fragments was achieved in 5 days in a shake-flask culture. Transient gene expression in insect cells may offer a promising approach to the high-throughput production of recombinant proteins.

Transfection of insect cell in suspension for efficient baculovirus generation

Baculovirus (BV) mediated insect cell expression system utilizes transfection as a first step to introduce recombinant baculovirus DNA into insect cells. Many labs are still relying on the conventional liposome based transfection method in adherent culture. Here we describe a more efficient method that can replace the existing method. This method is economical and does not require any special adjustment in existing labs. •An innovative method of transfecting insect cells in suspension using polyethyleneimine (PEI) is described here.•The beauty of this method is minimal intermediate manipulation of culture during transfection and virus generation.•The method significantly reduces the chances of cross contamination of viruses while handling multiple targets and constructs as well as the other microbial contamination.

Introduction of cationic virosome derived from vesicular stomatitis virus as a novel gene delivery system for sf9 cells

Insect-derived cell lines are used extensively to produce recombinant proteins because they are capable of performing a range of post-translational modifications. Due to their significance in biotechnological applications, various methods have been developed to transfect them. In this study, we introduce a virosome constructed from vesicular stomatitis virus (VSV) as a new delivery system for sf9 cells. We labeled these VSV virosomes by fluorescent probe Rhodamine B chloride (R18). By fluorescence microscope observation and conducting a fusion assay, we confirmed the uptake of VSV virosomes via endocytosis by sf9 cells and their fusion with the endosomal membrane. Moreover, we incubated cationic VSV virosomes with a GFP-expressing bacmid and transfected sf9 cells, after 24 h some cells expressed GFP indicating the ability of VSV virosomes to deliver heterologous DNA to these cells. This is the first report of a virosome-based delivery system introduced for an insect cell line.

High-throughput insect cell protein expression applications

The Baculovirus Expression Vector System (BEVS) is one of the most efficient systems for production of recombinant proteins and consequently its application is wide-spread in industry as well as in academia. Since the early 1970s, when the first stable insect cell lines were established and the infectivity of bacu-lovirus in an in vitro culture system was demonstrated (1, 2), virtually thousands of reports have been published on the successful expression of proteins using this system as well as on method improvement. However, despite its popularity the system is labor intensive and time consuming. Moreover, adaptation of the system to multi-parallel (high-throughput) expression is much more difficult to achieve than with E. coli due to its far more complex nature. However, recent years have seen the development of strategies that have greatly enhanced the stream-lining and speed of baculovirus protein expression for increased throughput via use of automation and miniaturization. This chapter therefore tries to collate these developments in a series of protocols (which are modifications to standard procedure plus several new approaches) that will allow the user to expedite the speed and throughput of baculovirus-mediated protein expression and facilitate true multi-parallel, high-throughput protein expression profiling in insect cells. In addition we also provide a series of optimized protocols for small and large-scale transient insect cell expression that allow for both the rapid analysis of multiple constructs and the concomitant scale-up of those selected for on-going analysis. Since this approach is independent of viral propagation, the timelines for this approach are markedly shorter and offer a significant advantage over standard bacu-lovirus expression approach strategies in the context of HT applications.

Production of recombinant proteins in clonal root cultures using episomal expression vectors

We have developed a fully contained system for expressing recombinant proteins that is based on clonal root cultures and episomal expression vectors. Clonal root lines expressing green fluorescent protein (GFP) or human growth hormone were generated from Nicotiana benthamiana leaves infected with the tobacco mosaic virus-based vector 30B after exposure to Agrobacterium rhizogenes. These lines accumulated GFP at over 50 mg per kg fresh tissue, a level that is comparable with other plant production systems in early stage development. Accumulation of both hGH and GFP in the clonal root lines was sustained over a 3-year period, and in the absence of antibiotic selection. This technology shows promise for commercial production of vaccine antigens and therapeutic proteins in contained facilities.

Potential ligands of DmP29, a putative juvenile hormone esterase binding protein of Drosophila melanogaster

We previously reported the identification of a putative juvenile hormone esterase (JHE) binding protein DmP29 in Drosophila melanogaster and its primary localization to the mitochondria [Liu, Z., Ho, L., Bonning, B.C., 2007. Localization of a Drosophila melanogaster homolog of the putative juvenile hormone esterase binding protein of Manduca sexta. Insect Biochem. Mol. Biol. 37(2), 155-163]. To further characterize DmP29, we identified potential ligands of this protein. Recombinant DmP29 was shown by ligand blot and co-immunoprecipitation analyses to bind recombinant JHE as well as to larval serum proteins (LSP). The possible biological relevance of the in vitro DmP29-JHE interaction is provided by detection of JHE activity in D. melanogaster mitochondrial fractions; 0.48 nmol JH hydrolyzed/min/mg mitochondrial protein, 97% of which was inhibited by the JHE-specific inhibitor OTFP. However, the DmP29-LSP interactions may not be biologically relevant. Given the high abundance, and "sticky" nature of these proteins, interaction of DmP29 with LSP may result from non-specific associations. No DmP29 interactions with non-specific esterases were detected by co-immunoprecipitation analyses. The potential role of DmP29 as a chaperone of JHE is discussed.

Large-scale transfection of mammalian cells for the fast production of recombinant protein

Recombinant proteins (r-proteins) are increasingly important in fundamental research and for clinical applications. As many of these r-proteins are of human or animal origin, cultivated mammalian cells are the host of choice to ensure their functional folding and proper posttranslational modifications. Large-scale transfection of human embryonic kidney 293 or Chinese hamster ovary cells is now an established technology that can be used in the production of hundreds of milligram to gram quantities of a r-protein in less than 1 mo from cloning of its cDNA. This chapter aims to provide an overview of large-scale transfection technology with a particular emphasis on calcium phosphate and polyethylenimine-mediated gene transfer.

High cell density fed batch and perfusion processes for stable non-viral expression of secreted alkaline phosphatase (SEAP) using insect cells: Comparison to a batch Sf-9-BEV system

The development of insect cells expressing recombinant proteins in a stable continuous manner is an attractive alternative to the BEV system for recombinant protein production. High cell density fed batch and continuous perfusion processes can be designed to maximize the productivity of stably transformed cells. A cell line (Sf-9SEAP) expressing high levels of the reporter protein SEAP stably was obtained by lipid-mediated transfection of Sf-9 insect cells and further selection and screening. The expression of the Sf-9SEAP cells was compared with the BEVS system. It was observed that, the yield obtained in BEVS was similar to the batch Sf-9SEAP at 8 and 7 IU/mL, respectively. The productivity of this foreign gene product with the stable cells was enhanced by bioprocess intensification employing the fed-batch and perfusion modes of culture to increase the cell density in culture. The fed batch process yielded a maximum cell density of 28 x 10(6) cells/mL and 12 IU/mL of SEAP. Further improvements in the productivity could be made using the perfusion process, which demonstrated a stable production rate for extended periods of time. The process was maintained for 43 days, with a steady-state cell density of 17-20 x 10(6) cells/mL and 7 IU/mL SEAP. The total yield obtained in the perfusion process (394 IU) was approximately 22 and 8 times higher than that obtained in a batch (17.6 IU) and fed batch (46.1 IU) process, respectively.

Baculovirus-mediated gene delivery into Mammalian cells does not alter their transcriptional and differentiating potential but is accompanied by early viral gene expression

Gene delivery to neural cells is central to the development of transplantation therapies for neurological diseases. In this study, we used a baculovirus derived from the domesticated silk moth, Bombyx mori, as vector for transducing a human cell line (HEK293) and primary cultures of rat Schwann cells. Under optimal conditions of infection with a recombinant baculovirus containing the reporter green fluorescent protein gene under mammalian promoter control, the infected cells express the transgene with high efficiency. Toxicity assays and transcriptome analyses suggest that baculovirus infection is not cytotoxic and does not induce differential transcriptional responses in HEK293 cells. Infected Schwann cells retain their characteristic morphological and molecular phenotype as determined by immunocytochemistry for the marker proteins S-100, glial fibrillary acidic protein, and p75 nerve growth factor receptor. Moreover, baculovirus-infected Schwann cells are capable of differentiating in vitro and express the P0 myelination marker. However, transcripts for several immediate-early viral genes also accumulate in readily detectable levels in the transduced cells. This transcriptional activity raises concerns regarding the long-term safety of baculovirus vectors for gene therapy applications. Potential approaches for overcoming the identified problem are discussed.

Stably Transformed Insect Cell Lines: Tools for Expression of Secreted and Membrane‐anchored Proteins and High‐throughput Screening Platforms for Drug and Insecticide Discovery

Insect cell-based expression systems are prominent amongst current expression platforms for their ability to express virtually all types of heterologous recombinant proteins. Stably transformed insect cell lines represent an attractive alternative to the baculovirus expression system, particularly for the production of secreted and membrane-anchored proteins. For this reason, transformed insect cell systems are receiving increased attention from the research community and the biotechnology industry. In this article, we review recent developments in the field of insect cell-based expression from two main perspectives, the production of secreted and membrane-anchored proteins and the establishment of novel methodological tools for the identification of bioactive compounds that can be used as research reagents and leads for new pharmaceuticals and insecticides.

From gene to protein: a review of new and enabling technologies for multi-parallel protein expression

In the post-genomic era, increasingly greater demands and expectations are being placed on protein production laboratories to produce more proteins and in faster timelines. This has been coupled with an exponential increase in the number of requests for the production of proteins which lack structural and functional information. No longer can groups use literature available in the public domain solely to drive their expression strategy, and moreover current expression and concomitant purification strategies clearly do not meet modern-day demands for protein production. This review will therefore attempt to provide a definitive review of current 'best in class' cloning, expression and purification systems, and the adaptations and developments that have been made by laboratories, both academic and industrial, to enhance protein production throughput.