Production of a recombinant mouse monoclonal antibody in transgenic silkworm cocoons

Production of scFv-conjugated affinity silk film and its application to a novel enzyme-linked immunosorbent assay

Bombyx mori (silkworm) silk proteins have been utilized as unique biomaterials for various medical applications. To develop a novel affinity silk material, we generated a transgenic silkworm that spins silk protein containing the fibroin L-chain linked with the single-chain variable fragment (scFv) as a fusion protein. Previously, the scFv-conjugated “affinity” silk powder specifically immunoprecipitated its target protein, Wiskott-Aldrich syndrome protein. To expand the applicability of affinity silk materials, we processed the scFv-conjugated silk protein into a thin film by dissolving it in lithium bromide, then drying it in the wells of 96-well plates. Enzyme-linked immunosorbent assay demonstrated specific detection of Wiskott-Aldrich syndrome protein, both as a recombinant protein and in its native form extracted from mouse macrophages. These findings suggest that this scFv-conjugated silk film serves as the basis for an alternative immunodetection system.

Advances in silkworm studies accelerated by the genome sequencing of Bombyx mori

Significant progress has been achieved in silkworm (Bombyx mori) research since the last review on this insect was published in this journal in 2005. In this article, we review the new and exciting progress and discoveries that have been made in B. mori during the past 10 years, which include the construction of a fine genome sequence and a genetic variation map, the evolution of genomes, the advent of functional genomics, the genetic basis of silk production, metamorphic development, immune response, and the advances in genetic manipulation. These advances, which were accelerated by the genome sequencing project, have promoted B. mori as a model organism not only for lepidopterans but also for general biology.

An optimized sericin-1 expression system for mass-producing recombinant proteins in the middle silk glands of transgenic silkworms

The middle silk gland (MSG) of silkworm is thought to be a potential host for mass-producing valuable recombinant proteins. Transgenic MSG expression systems based on the usage of promoter of sericin1 gene (sericin-1 expression system) have been established to produce various recombinant proteins in MSG. However, further modifying the activity of the sericin-1 expression system to yield higher amounts of recombinant proteins is still necessary. In this study, we provide an alternative modification strategy to construct an efficient sericin-1 expression system by using the hr3 enhancer (hr3 CQ) from a Chongqing strain of the Bombyx mori nuclear polyhedrosis virus (BmNPV) and the 3'UTRs of the fibroin heavy chain (Fib-HPA), the fibroin light chain (Fib-LPA), and Sericin1 (Ser1PA) genes. We first analyzed the effects of these DNA elements on expression of luciferase, and found that the combination of hr3 CQ and Ser1PA was most effective to increase the activity of luciferase. Then, hr3 CQ and Ser1PA were used to modify the sericin1 expression system. Transgenic silkworms bearing these modified sericin1 expression vectors were generated by a piggyBac transposon mediated genetic transformation method. Our results showed that mRNA level of DsRed reporter gene in transgenic silkworms containing hr3 CQ and Ser1PA significantly increased by 9 fold to approximately 83 % of that of endogenous sericin1. As the results of that, the production of recombinant RFP increased by 16 fold to 9.5 % (w/w) of cocoon shell weight. We conclude that this modified sericin-1 expression system is efficient and will contribute to the MSG as host to mass produce valuable recombinant proteins.

Spatial immobilization of bone morphogenetic protein-4 in a collagen-PLGA hybrid scaffold for enhanced osteoinductivity

The introduction of bioactive molecules into three-dimensional porous scaffolds to mimic the in vivo microenvironment is a promising strategy for tissue engineering and stem cell research. In this study, bone morphogenetic protein-4 (BMP4) was spatially immobilized in a collagen-PLGA hybrid scaffold with a fusion BMP4 composed of an additional collagen-binding domain derived from fibronectin (CBD-BMP4). CBD-BMP4 bound to the collagen-PLGA hybrid scaffold and the BMP4-immobilized hybrid scaffold supported cell adhesion and proliferation. The osteogenic induction effect of the immobilized CBD-BMP4 was investigated with three-dimensional culture of human bone marrow-derived mesenchymal stem cells in the BMP4-immobilized collagen-PLGA hybrid scaffold. The in vivo implantation experiment demonstrated that the immobilized CBD-BMP4 maintained its osteoinductive activity, being capable of up-regulating osteogenic gene expression and biomineralization. The strong osteoinductivity of the BMP4-immobilized scaffold suggests it should be useful for bone tissue engineering, stem cell function manipulation and bone substitutes.

Lepidopteran cells, an alternative for the production of recombinant antibodies?

Monoclonal antibodies are used with great success in many different therapeutic domains. In order to satisfy the growing demand and to lower the production cost of these molecules, many alternative systems have been explored. Among them, the baculovirus/insect cells system is a good candidate. This system is very safe, given that the baculoviruses have a highly restricted host range and they are not pathogenic to vertebrates or plants. But the major asset is the speed with which it is possible to obtain very stable recombinant viruses capable of producing fully active proteins whose glycosylation pattern can be modulated to make it similar to the human one. These features could ultimately make the difference by enabling the production of antibodies with very low costs. However, efforts are still needed, in particular to increase production rates and thus make this system commercially viable for the production of these therapeutic agents.

Production of scFv-conjugated affinity silk powder by transgenic silkworm technology

Bombyx mori (silkworm) silk proteins are being utilized as unique biomaterials for medical applications. Chemical modification or post-conjugation of bioactive ligands expand the applicability of silk proteins; however, the processes are elaborate and costly. In this study, we used transgenic silkworm technology to develop single-chain variable fragment (scFv)-conjugated silk fibroin. The cocoons of the transgenic silkworm contain fibroin L-chain linked with scFv as a fusion protein. After dissolving the cocoons in lithium bromide, the silk solution was dialyzed, concentrated, freeze-dried, and crushed into powder. Immunoprecipitation analyses demonstrate that the scFv domain retains its specific binding activity to the target molecule after multiple processing steps. These results strongly suggest the promise of scFv-conjugated silk fibroin as an alternative affinity reagent, which can be manufactured using transgenic silkworm technology at lower cost than traditional affinity carriers.

A cell free assay system estimating the neutralizing capacity of GM-CSF antibody using recombinant soluble GM-CSF receptor

BACKGROUNDS

Previously, we demonstrated that neutralizing capacity but not the concentration of GM-CSF autoantibody was correlated with the disease severity in patients with autoimmune pulmonary alveolar proteinosis (PAP)¹⁻³. As abrogation of GM-CSF bioactivity in the lung is the likely cause for autoimmune PAP⁴⁻⁵, it is promising to measure the neutralizing capacity of GM-CSF autoantibodies for evaluating the disease severity in each patient with PAP. Until now, neutralizing capacity of GM-CSF autoantibodies has been assessed by evaluating the growth inhibition of human bone marrow cells or TF-1 cells stimulated with GM-CSF⁶⁻⁸. In the bioassay system, however, it is often problematic to obtain reliable data as well as to compare the data from different laboratories, due to the technical difficulties in maintaining the cells in a constant condition.

OBJECTIVE

To mimic GM-CSF binding to GM-CSF receptor on the cell surface using cell-free receptor-binding-assay.

METHODS

Transgenic silkworm technology was applied for obtaining a large amount for recombinant soluble GM-CSF receptor alpha (sGMRα) with high purity⁹⁻¹³. The recombinant sGMRα was contained in the hydrophilic sericin layers of silk threads without being fused to the silk proteins, and thus, we can easily extract from the cocoons in good purity with neutral aqueous solutions¹⁴(,)¹⁵. Fortunately, the oligosaccharide structures, which are critical for binding with GM-CSF, are more similar to the structures of human sGMRα than those produced by other insects or yeasts.

RESULTS

The cell-free assay system using sGMRα yielded the data with high plasticity and reliability. GM-CSF binding to sGMRα was dose-dependently inhibited by polyclonal GM-CSF autoantibody in a similar manner to the bioassay using TF-1 cells, indicating that our new cell-free assay system using sGMRα is more useful for the measurement of neutralizing activity of GM-CSF autoantibodies than the bioassay system using TF-1 cell or human bone marrow cells.

CONCLUSIONS

We established a cell-free assay quantifying the neutralizing capacity of GM-CSF autoantibody.

Expression profiling and regulation of genes related to silkworm posterior silk gland development and fibroin synthesis

The posterior silk gland (PSG) is the most important suborgan responsible for the synthesis and secretion of silk core fibroin proteins in silkworm. Here, we performed genome-scale expression profiling analysis of silkworm PSG at the fourth molting (M4) and at day 1 (V1), day 3 (V3), day 5 (V5), and wandering stage (W) of the fifth instar by microarray analysis with 22 987 probes. We found that the five genes of silk proteins secreted from PSG including fibroin heavy (H) and light (L) chains, P25, seroin 1, and seroin 2 basically showed obvious up-regulation at V3 which lasted to V5, while slight down-regulation at W. The expression of translation-related genes including ribosomal proteins and translation initiation factors generally remained stable from M4 to V5, whereas it showed clear down-regulation at W. Clustering analysis of the 643 significantly differentially expressed transcripts revealed that 43 of the important genes including seroin 1 and sugar transporter protein had co-expression patterns which were consistent with the rate changes of fibroin synthesis and PSG growth. Pathway analysis disclosed that the genes in different clusters might have co-regulations and direct interactions. These genes were supposed to be involved in the fibroin synthesis and secretion. The differential expression of several hormone-related genes also suggested their functions on the regulation of PSG development and fibroin synthesis. 2D gel-based proteomics and phosphoproteomics profiling revealed that the phosphorylated proteins accounted for no more than one-sixth of the total proteins at each stage, which was much lower than the level in normal eukaryotic cells. Changes in the phosphorylation status and levels of several proteins such as actin-depolymerizing factor 1 and enolase might be deeply involved in fibroin secretion and tissue development. Shotgun proteomic profiling combined with label-free quantification analysis on the PSG at V3, V5, and W revealed that many small heat shock proteins (sHSP) were specially expressed at W, which was substantially consistent with the results from 2-DE analysis, and implied the close correlations of sHSP with the physiological states of PSG at W. A majority of significantly up-regulated proteins at V5 were related to ribosome pathway, which was different from the microarray results, implying that the translation-level regulation of ribosomal proteins might be critical for fibroin synthesis. In contrast, the ubiquitin-proteasome pathway related proteins appeared obviously up-regulated at W, suggesting that the programmed cell death process of PSG cells might be started before cocooning.

Production of a non-triple helical collagen alpha chain in transgenic silkworms and its evaluation as a gelatin substitute for cell culture

We generated transgenic silkworms that synthesized human type I collagen alpha1 chain [alpha1(I) chain] in the middle silk glands and secreted it into cocoons. The initial content of the recombinant alpha1(I) chain in the cocoons of the transgenic silkworms was 0.8%. The IE1 gene, a trans-activator from the baculovirus, was introduced into the transgenic silkworm to increase the content of the chain. We also generated silkworms homozygous for the transgenes. These manipulations increased the alpha1(I) chain content to 8.0% (4.24 mg per cocoon). The alpha1(I) chain was extracted and purified from the cocoons using a very simple method. The alpha1(I) chain contained no hydroxyprolines due to the absence of prolyl-hydroxylase activity in the silk glands. Circular dichroism analysis showed that the secondary structure of the alpha1(I) chain is similar to that of denatured type I collagen, demonstrating the absence of the triple helical structure. Human skin fibroblasts were seeded on the alpha1(I) chain-coated dishes. The cells attached and spread, although at decreased chain concentrations the spreading rate was lower than that of the collagen and gelatin. Cynomolgus monkey embryonic stem cells cultured on the alpha1(I) chain-coated dishes maintained an undifferentiated state after 30 passages, and their pluripotency was confirmed by teratoma formation in severe combined immunodeficient mice. These results show that the recombinant human alpha1(I) chain is a promising candidate biomaterial as a high-quality and safe gelatin substitute for cell culture.

New opportunities for an ancient material

Spiders and silkworms generate silk protein fibers that embody strength and beauty. Orb webs are fascinating feats of bioengineering in nature, displaying magnificent architectures while providing essential survival utility for spiders. The unusual combination of high strength and extensibility is a characteristic unavailable to date in synthetic materials yet is attained in nature with a relatively simple protein processed from water. This biological template suggests new directions to emulate in the pursuit of new high-performance, multifunctional materials generated with a green chemistry and processing approach. These bio-inspired and high-technology materials can lead to multifunctional material platforms that integrate with living systems for medical materials and a host of other applications.

The silkworm-an attractive BioResource supplied by Japan

Silkworms have played an important agricultural role in supporting Japan's modernization, and traditionally, Japan has led the world as a repository of silkworm bioresources. The silkworm is a small and highly domesticated insect, which is ideal as a laboratory tool, although it is a bioresource that is relatively infrequently used in experiments at present. In this review, we describe the potential for silkworm resources to contribute to life sciences.