Comparative analysis of GFPUV-β1,3-N-acetylglucosaminyltransferase 2 production in two insect-cell-based expression systems

Transforming Lepidopteran Insect Cells for Continuous Recombinant Protein Expression

The baculovirus expression vector system (BEVS) is widely used to produce large quantities of recombinant proteins. However, the yields of extracellular and membrane-bound proteins obtained with this system are often very low, possibly due to the adverse effects of baculovirus infection on the host insect cell secretory pathway. An alternative approach to producing poorly expressed proteins is to transform lepidopteran insect cells with the gene of interest under the control of promoters that are constitutively active in uninfected cells, thereby making cell lines that continuously express recombinant protein. This chapter provides an overview of the methods and considerations for making stably transformed lepidopteran insect cells. Techniques for the insertion of genes into continuous expression vectors, transfection of cells, and the selection and isolation of stably transformed Sf-9 clones by either colony formation or end-point dilution are described in detail.

Optimization of canine interleukin-12 production using a baculovirus insect cell expression system

Background

Interleukin-12 is an important cytokine in mediating cellular immune responses.

Results

Recombinant single-chain canine IL-12 was produced in a baculovirus-insect cell system with the aim of conducting further studies on modulation of immune responses in dogs. To optimize the production of recombinant canine IL-12, a classical baculovirus and a modified vector (chitinase A and v-cathepsin knockout) were used containing a native or an optimized insert of canine IL-12. The optimized IL-12 construct contained the GP64 signal peptide and was synthesized with optimized codons for expression in Trichoplusia ni cells. Dot-blot and Western blot analysis showed the highest production levels of recombinant IL-12 protein by the use of the modified baculovirus vector containing the optimized insert, at a multiplicity of infection of five and at 48 h after infection. The recombinant cytokine was successfully purified and showed a good degree of purity, integrity, folding, and yield, with very little endotoxin contamination. Recombinant canine IL-12 induced IFN-γ in canine lymphocytes, indicating that it was biologically active.

Conclusion

Therefore, this study describes an efficient method to produce adequate amounts of biologically active canine IL-12, useful for immunomodulation studies in dogs.

Chemokine receptor interactions with virus-like particles

Virus-like particles (VLPs) presenting conformational envelope proteins on their surface represent an invaluable tool to study molecular interactions between viruses and cellular receptors/co-receptors, eliminating biological risks associated with working with live native viruses. The availability of target cells expressing specific chemokine receptors facilitates the dissection of specific interactions between human immunodeficiency virus (HIV) viral envelope proteins and these receptors in the laboratory. Here, we describe a method to evaluate HIV-VLP binding to cellular chemokine co-receptors, by carboxyfluorescein succinimidyl ester labeling and cellular uptake.

Development of a stable insect cell line constitutively expressing rotavirus VP2

An insect High-Five cell line was generated constitutively and stably expressing the VP2 protein of rotavirus RF strain leading to the formation of core-like particles. The integration of the VP2 gene was confirmed by PCR, Real-time PCR and Southern blot, and the protein expression was confirmed by Western blot and immunofluorescence microscopy. Integrity and self assembly of VP2 as core-like particles was demonstrated by electron microscopy. The High-Five cell system stably expressing rotavirus core-like particles can be applied to the study of viral protein structure and functions; it may be useful for vaccine development, gene therapy and drug delivery.

HIV-Gag VLPs presenting trimeric HIV-1 gp140 spikes constitutively expressed in stable double transfected insect cell line

We have previously described the establishment and characterization of a stably transfected insect cell line for the constitutive and efficient expression of Pr55 HIV Gag proteins, which auto-assemble into enveloped Virus-Like Particles (VLPs) released into the cell culture supernatant. Such HIV-Gag VLPs have been shown to elicit a specific systemic humoral response in vivo, proving the appropriate antigenic presentation of the HIV Gag protein to the immune system. Here we describe the establishment of a stable double transfected insect cell line for the constitutive and reproducible production of Pr55Gag-VLPs expressing on their surface trimeric forms of HIV-1 envelope glycoproteins. The persistence of HIV coding genes has been verified in clonal resistant insect cells, the protein expression and conformation has been verified by Western blot analysis. The resulting HIV-VLPs have been visualized by standard transmission electron microscopy and their immunogenicity has been evaluated in vivo. This represents, to our knowledge, the first example of stable double transfected insect cell line for the constitutive production of enveloped HIV-Gag VLPs presenting trimeric HIV-gp140 on their surface.

Enhanced gene expression in insect cells and silkworm larva by modified polyhedrin promoter using repeated Burst sequence and very late transcriptional factor-1

The Burst of expression from polyhedrin (polh) promoter during very late phase of baculovirus infection requires a sequence located between TAAG and the translation initiation site, typically referred to as burst sequence (BS). The expression of polh promoter is stimulated by specifically binding of very late transcriptional factor 1 (VLF-1) to BS. In order to enhance the production of recombinant proteins the polh promoter was modified via a multiple BS bacmid system in which the number of BSs was increased. Compared to an expression from a normal polh promoter, β-glucuronidase (GUS) activity in High Five insect cells was three times higher with a modified polh promoter containing two BSs. Using a modified polh promoter that contains nine BSs in silkworm expression system, β1-3-N-acetylglucosaminyltransferase 2 (β3GnT2) activity per larva was 6.8-fold higher than control. Furthermore, the co-expression of modified promoters along with VLF-1-enhanced β3GnT activity. Thus, an increased optimal number of BS and its co-expression with VLF-1 leads to the production of higher level of gene expression in insect cells and silkworm larvae. This new modified promoter engineered in the current study is the strongest promoter for overexpressing foreign proteins in an eukaryotic cell and system, thus leading a progress in baculovirus-insect cell and silkworm biotechnology.

Constitutive expression of HIV-VLPs in stably transfected insect cell line for efficient delivery system

We have previously developed HIV-1 Pr55gag-based virus-like particles (HIV-VLPs) as presentation and delivery model using a transient Baculovirus expression system. Here we describe the establishment and characterization of stably transfected insect cell line for the constitutive and reproducible production of HIV-VLPs. The persistence of HIV gag coding gene has been verified in clonal resistant insect cells and the protein expression has been confirmed by Western blot analysis. The resulting HIV-VLPs have been evaluated by standard transmission electron microscopy and their immunogenicity has been evaluated in vivo. Our results demonstrate that this strategy is highly efficient for constitutive expression of conformational enveloped VLPs which can be employed as presentation and delivery system for pathogen as well as tumor-associated antigens. This represents, to our knowledge, the first example of stably transfected insect cell line for the constitutive production of VLPs.

Efficient production of an antibody Fab fragment using the baculovirus-insect cell system

The production of an Fab fragment of the catalytic antibody 6D9 in lepidopteran insect cells infected with a recombinant baculovirus that contained both the heavy chain (Hc) and light chain (Lc) genes of the Fab fragment was investigated. Western blotting and enzyme-linked immunosorbent assay (ELISA) of culture supernatant showed that baculovirus-infected Trichoplusia ni BTI-TN-5B1-4 (High Five) cells secreted an Fab fragment that retained antigen-binding activity. Infection of High Five cells with a recombinant baculovirus, in which the Lc and Hc genes were located downstream of the baculovirus p10 and polyhedrin promoters, respectively, produced a higher Fab fragment yield than that obtained with a baculovirus in which the Hc and Lc genes were downstream of the p10 and polyhedrin promoters, respectively. Baculovirus-infected High Five cells secreted more of the Fab fragment than Spodoptera frugiperda Sf9 cells. Moreover, use of the baculovirus gp64 signal sequence upstream of the Lc and Hc genes resulted in greater yield of the secreted Fab fragment than use of the insect-derived BiP and melittin signal sequences. Consequently, the Fab fragment was obtained in a high yield (>600 μg/ml) in a shake-flask culture of High Five cells infected at a multiplicity of infection (MOI) of 10 plaque-forming units (pfu)/cell with the recombinant baculovirus in which the Lc and Hc genes with the gp64 signal sequence were expressed under the control of the p10 and polyhedrin promoters, respectively. These results indicate that the baculovirus-insect cell system may allow efficient production of antibody Fab fragments.

Comparison of the N-linked glycosylation of human beta1,3-N-acetylglucosaminyltransferase 2 expressed in insect cells and silkworm larvae

N-Glycosylation of human beta1,3N-acetylglucosaminyltransferase 2 (beta3GnT2) is essential for its biological function. beta3GnT2 fused to GFP(uv) (GFP(uv)-beta3GnT2) was produced by non-virus expression systems in stably transformed insect cells and silkworm larvae using a recombinant BmNPV bacmid, and purified for analysis of N-glycosylation. The N-glycan structure of beta3GnT2 was identified by glycoamidase A digestion, labeling with 2-aminopyridine (PA), and HPLC mapping. The paucimannosidic N-glycan structure (73.2%) was predominant in stably transformed Trichoplusia ni cells. In contrast, N-glycan with Gal (21.3%) and GlcNAc (16.2%) terminal residues linked to Manalpha(1,3) branch were detected on beta3GnT2 expressed in silkworm larvae. The presence of terminal Gal and bisecting GlcNAc residues such as Galbeta1, 4GlcNAcbeta1, 2Manalpha1,3(GlcNAcbeta1,4)(Manalpha1,6)Manbeta1, 4GlcNAc is not typical structure for lepidopteran insect N-glycosylation. Although allergenic alpha1,3-fucose residues have been found in T. ni cells, only alpha1,6-fucose residues were attached to the beta3GnT2 glycan in silkworm larvae. Therefore, silkworm larvae might be a useful host for producing human glycoproteins.

Molecular chaperone-assisted production of human alpha-1,4-N-acetylglucosaminyltransferase in silkworm larvae using recombinant BmNPV bacmids

In this study, human alpha-1,4-N-acetylglucosaminyltransferase (alpha4GnT) fused with GFP(uv) (GFP(uv)-alpha4GnT) was expressed using both a transformed cell system and silkworm larvae. A Tn-pXgp-GFP(uv)-alpha4GnT cell line, isolated after expression vector transfection, produced 106 mU/ml of alpha4GnT activity in suspension culture. When Bombyx mori nucleopolyhedrovirus containing a GFP(uv)-alpha4GnT fusion gene (BmNPV-CP (-)/GFP(uv)-alpha4GnT) bacmid was injected into silkworm larvae, alpha4GnT activity in larval hemolymph was 352 mU/ml, which was 3.3-fold higher than that of the Tn-pXgp-GFP(uv)-alpha4GnT cell line. With human calnexin (CNX) or human immunoglobulin heavy chain-binding protein (BiP, GRP78) coexpressed under the control of the ie-2 promoter, alpha4GnT activity in larval hemolymph increased by 1.4-2.0-fold. Moreover, when BmNPV-CP (-)/GFP(uv)-alpha4GnT bacmid injection was delayed for 3 h after BmNPV-CP (-)/CNX injection, the alpha4GnT activity increased significantly to 922 mU/ml, which was 8.7-fold higher than that of the Tn-pXgp-GFP(uv)-alpha4GnT cell line. Molecular chaperone assisted-expression in silkworm larvae using the BmNPV bacmid is a promising tool for recombinant protein production. This system could lead to large-scale production of more complex recombinant proteins.

Estrogen receptor beta yield from baculovirus lytic infection is higher than from stably transformed Sf21 cells

The production of estrogen receptors (ER) in cultured insect cells is advantageous because these cells are relatively easy to culture and they perform post-translation modifications necessary for protein stability and function. There are three options for protein expression in insect cells: transient transfection, lytic baculovirus infection, or transfection followed by selection to create stable cell lines. Stable transfection has been promoted to be advantageous for the production of recombinant proteins because no re-infection is required, which might provide better lot-to-lot reproducibility in protein production. In this paper, we demonstrate that lytic baculovirus infection of Sf21 cells yields approximately tenfold more bioactive ERbeta than cells stably transformed with pIZ/V5-His plasmid under OpIE2 promoter. We provide the first evidence that stable expression of recombinant human ERbeta decreases the proliferation of Sf21 cells by inhibition of cell replication in a ligand-independent manner. These results mirror findings in breast cancer cells showing that an increase in ERbeta expression decreases cell proliferation. We conclude that baculovirus infection of Sf21 cells is better for human ERbeta production than stable-transformation of Sf21 cells.

Enhanced production of secretory beta1,3-N-acetylglucosaminyltransferase 2 fusion protein into hemolymph of Bombyx mori larvae using recombinant BmNPV bacmid integrated signal sequence

The enhanced secretion of beta1,3-N-acetylglucosaminyltransferase 2 (beta3GnT2) fusion protein into the hemolymph of Bombyx mori larvae was studied using a recombinant B. mori nucleopolyhedrovirus (BmNPV) bacmid integrating seven signal sequences. When the BmNPV bacmid encoding the signal sequences from the silkworm B. mori bombyxin (bx) and B. mori prophenoloxidase-activating enzyme (ppae) was injected into silkworm larvae, 56.1 and 51.5mU/ml beta3GnT, respectively, were secreted into the hemolymph of silkworm larvae. For bx, 97.3% of the total beta3GnT activity was secreted into hemolymph, and only 1.1% remained in the intestines of silkworm larvae. For ppae, 90.8% of the total beta3GnT activity was secreted to the hemolymph, but 7.8% remained in the intestines of silkworm larvae. Using the BmNPV bacmid encoding bx, the amount of secreted beta3GnT was 91mug per larva, which was 2.5% of the total amount of protein in the hemolymph.

Transforming lepidopteran insect cells for continuous recombinant protein expression

The baculovirus expression vector system is widely used to produce large quantities of recombinant proteins. However, yields of extracellular and membrane-bound proteins obtained with this system often are very low, possibly because of the adverse effects of baculovirus infection on the host insect cell secretory pathway. An alternative approach to producing poorly expressed proteins is to transform insect cells with the gene of interest under the control of promoters that are constitutively active in uninfected cells, thereby making cell lines that continuously express recombinant protein. This chapter provides an overview of the methods and considerations for making stably transformed lepidopteran cells. Techniques for the insertion of genes into continuous expression vectors, transfection of cells, and the selection and isolation of stably transformed Sf-9 clones by either colony formation or end-point dilution are described in detail.

Comparison of different signal peptides for protein secretion in nonlytic insect cell system

Protein expression and secretion in insect cells have been widely studied in the baculovirus-infected insect cell system. In directly transfected insect cells only intracellular expression and purification of recombinant proteins have been studied in detail. To examine multiple recombinant protein variants, easy and fast expression and a purification screening system are required. The aim of this study was to establish an effective and rapid secretion system for human azurocidin using directly transfected insect cells. We also constructed and tested expression vectors possessing heterologous signal peptides derived from human azurocidin, yellow lupin diphosphonucleotide phosphatase/phosphodiesterase (PPD1), and papaya papain IV to secrete yellow lupin and red kidney bean purple acid phosphatases, PPD1, and papain IV. Our results demonstrate that the secretion vectors used here can direct recombinant proteins to the culture medium very effectively, allowing their simple purification on a small/medium scale. Based on secretion and activity analyses it seems that the azurocidin signal peptide is one of the most potent secretion signals.

Improvement of the production of GFPuv-?1,3-N-acetylglucosaminyltransferase 2 fusion protein using a molecular chaperone-assisted insect-cell-based expression system

A stable Tn-5B1-4 insect cell line co-expressing the recombinant GFPuv-beta1,3-N-acetylglucosaminyltransferase 2 (GFPuv-beta3GnT2) protein fused to a melittin signal sequence with a lectin-like molecular chaperone, human calnexin (hCNX) or human calreticulin (hCRT), was constructed. The expression of either of these molecular chaperones is under the control of a weak promoter, OpMNPV IE2, while that of GFPuv-beta3GnT2 is under the control of Bombyx mori actin promoter. This co-expression system was compared between two different insect cell-baculovirus expression systems: (1) co-infection of the recombinant baculovirus containing a molecular chaperone (AcNPV-hCNX or -hCRT) with a recombinant baculovirus containing GFPuv-beta3GnT2 fused with the melittin signal sequence (AcNPV-me-GGT); (2) infection of AcNPV-me-GGT to a stably expressing cell line for either hCNX or hCRT. In the co-infection system, the intracellular GFPuv-beta3GnT2 expression level was low because of the improved secretion level ratio of the fusion protein, due to the chaperone expression. In the case of infection to the stably expressing cell line for a chaperone, the extracellular GFPuv-beta3GnT2 expression level was similar to the intracellular expression level. This suggests that the amount of expressed chaperone is not sufficient to process beta3GnT2. On the other hand, the co-expression system produced an extracellular beta3GnT activity of 22-23 mU/mL, which was approximately 3.5- and 11-fold higher than those of the stable expression of the fusion gene without the chaperone and the conventional BES with the addition of protease, respectively. The secretion level ratio of the fusion protein of this system increased to 82%, which was approximately 1.5-fold that of any other expression system investigated thus far. These results indicate that the ratio of the expression level of the target gene to that of the chaperone gene may be an important factor in maximizing the production of a target protein. The molecular-chaperone-assisted expression system using a stably transformed insect cell line offers promising prospects for the efficient production of recombinant secretory proteins in insect cells.

Expression and purification of active plant diphosphonucleotide phosphatase/phosphodiesterase from baculovirus-infected insect cells

We have previously purified and characterized a diphosphonucleotide phosphatase/phosphodiesterase (PPD1) from yellow lupin seeds. This report describes an efficient strategy for overexpression in baculovirus-infected Spodoptera frugiperda Sf9 cells and purification of a functional PPD1 enzyme. We tested six variants of recombinant PPD1, differing in secretion peptides, fusion tags, and promoters. The highest expression level of the active PPD1 was achieved when the native signal peptide and the C-terminal V5-6His tag were attached. This recombinant protein was secreted at very high level (18.4 mg/L) to serum-free medium. Single-step purification procedure using metal affinity chromatography resulted in the homogeneous PPD1. The overexpressed protein showed enzymatic activity comparable to the native enzyme isolated previously from plant material. We showed that PPD1, which belongs to purple acid phosphatase family, formed tetrameric structure, which is non-typical for this group of enzymes.