Optimization of transfection conditions for expression of green fluorescent protein in Drosophila melanogaster S2 cells

Single-cell cloning enables the selection of more productive Drosophila melanogaster S2 cells for recombinant protein expression

The generation of monoclonal cell lines is an important early process development step for recombinant protein production. Although single-cell cloning is an established method in mammalian cell lines, straightforward protocols are not yet available for insect cells. We describe a new method for the generation of monoclonal insect cells without using fetal bovine serum and/or feeder cells pretreated by irradiation or exposure to mitomycin. Highly productive clones of Drosophila melanogaster S2 cells were prepared in a two-step procedure, comprising the establishment of a polyclonal population and subsequent single cell isolation by limiting dilution. Necessary growth factors were provided by co-cultivation of single transformants with untransfected feeder cells, which were later removed by antibiotic selection. Enhanced expression of EGFP and two target peptides was confirmed by flow cytometry and dot/western blotting. Highly productive clones were stable, showed a uniform expression profile and typically a sixfold to tenfold increase in cell-specific productivity.

Drosophila melanogaster S2 cells for expression of heterologous genes: From gene cloning to bioprocess development

In the present review we discuss strategies that have been used for heterologous gene expression in Drosophila melanogaster Schneider 2 (S2) cells using plasmid vectors. Since the growth of S2 cells is not dependent on anchorage to solid substrates, these cells can be easily cultured in suspension in large volumes. The factors that most affect the growth and gene expression of S2 cells, namely cell line, cell passage, inoculum concentration, culture medium, temperature, dissolved oxygen concentration, pH, hydrodynamic forces and toxic metabolites, are discussed by comparison with other insect and mammalian cells. Gene expression, cell metabolism, culture medium formulation and parameters involved in cellular respiration are particularly emphasized. The experience of the authors with the successful expression of a biologically functional protein, the rabies virus glycoprotein (RVGP), by recombinant S2 cells is presented in the topics covered.

Expression of membrane proteins in Drosophila Melanogaster S2 cells: Production and analysis of a EGFP-fused G protein-coupled receptor as a model

In the process of selecting an appropriate host for the heterologous expression of functional eukaryotic membrane proteins, Drosophila S2 cells, although not yet fully explored, appear as a valuable alternative to mammalian cell lines or other virus-infected insect cell systems. This nonlytic, plasmid-based system actually combines several major physiological and bioprocess advantages that make it a highly potential and scalable cellular tool for the production of membrane proteins in a variety of applications, including functional characterization, pharmacological profiling, molecular simulations, structural analyses, or generation of vaccines. We present here a series of protocols and hints that would serve the successful expression of membrane proteins in S2 cells, using an enhanced green fluorescent protein (EGFP)/G protein-coupled receptor (EGFP-GPCR) as a model.

Culture of transgenic Drosophila melanogaster Schneider 2 cells in serum-free media based on TC100 basal medium

Requirements of eliminating animal proteins from cell culture have intensified in recent years, with the pressure of regulatory agencies related to biopharmaceuticals production. In this work, the substitution of fetal bovine serum by yeastolate and a soy hydrolysate (Hy Soy) for the culture of Drosophila melanogaster Schneider 2 cells transfected for the production of rabies virus G glycoprotein was evaluated. TC100 supplemented with glucose, glutamine, lipid emulsion and Pluronic F68 was employed as basal medium. Results show that yeastolate was more efficient on cell growth stimulation than Hy Soy. Cells adapted in medium formulation supplemented with 3 g/L yeastolate, 1% lipid emulsion, 10 g/L glucose, 3.5 g/L glutamine and 0.1% Pluronic F68 attained a maximum concentration of 10.7 x 10(6) cells/mL, with the expression of 9.4 ng/mL G glycoprotein.

Improving heterologous protein expression in transfected Drosophila S2 cells as assessed by EGFP expression

Drosophila melanogaster S2 cells were co-transfected with plasmid vectors containing the enhanced green fluorescent protein gene (EGFP), under the control of metallothionein promoter (pMt), and the hygromycin selection gene, in view of establishing parameters for optimized gene expression. A protocol of transfection was worked out, leading after hygromycin selection, to approximately 90% of S2MtEGFP fluorescent cells at day 5 after copper sulfate (CuSO(4)) induction. As analyzed by confocal microscopy, S2MtEGFP cell cultures were shown to be quite heterogeneous regarding the intensity and cell localization of fluorescence among the EGFP expressing cells. Spectrofluorimetry kinetic studies of CuSO(4) induced S2MtEGFP cells showed the EGFP expression at 510 nm as soon as 5 h after induction, the fluorescence increasing progressively from this time to attain values of 4.6 x 10(5) counts/s after 72 h of induction. Induction with 700 muM of CuSO(4) performed at the exponential phase of the S2MtEGFP culture (10(6) cells/mL) led to a better performance in terms of cell growth, percent of fluorescent cells and culture intensity of fluorescence. Sodium butyrate (NaBu) treatment of CuSO(4) induced S2MtEGFP cell cultures, although leading to a loss of cell culture viability, increased the percent of EGFP expressing cells and sharply enhanced the cell culture fluorescence intensity. The present study established parameters for improving heterologous protein expression in stably transfected Drosophila S2 cells, as assessed by the EGFP expression.

Optimal production and in vitro activity of recombinant endostatin from stably transformed Drosophila melanogaster S2 cells

Recombinant plasmids containing a complementary deoxyribonucleic acid coding mouse endostatin were transfected and stably expressed in Drosophila melanogaster Schneider 2 (S2) cells. Stably transformed polyclonal cell populations expressing recombinant endostatin were isolated after 4 wk of selection with hygromycin B. Recombinant endostatin expressed in the stably transformed S2 cells under the influence of the Drosophila BiP protein signal sequence was secreted into the medium. Recombinant endostatin was also purified to homogeneity using a simple one-step Ni2+ affinity fractionation method. Purified recombinant endostatin inhibited endothelial cell proliferation in a dose-dependent manner. The concentration at maximum inhibition for recombinant endostatin was approximately 1.8 microg/ml. The stably transformed S2 cells produced 18 mg recombinant endostatin/L 7 d after induction with 5 microM CdCl2. Sodium butyrate supplementation (2.5 mM) increased recombinant endostatin production by 17%. These findings demonstrate optimal production and in vitro activity of recombinant endostatin from stably transformed D. melanogaster S2 cells.