Expression of the extracellular region of the human interleukin-4 receptor α chain and interleukin-13 receptor α1 chain by a silkworm–baculovirus system

Efficient preparation of human and mouse CD1d proteins using silkworm baculovirus expression system

CD1d is a major histocompatibility complex (MHC) class I-like glycoprotein and binds to glycolipid antigens that are recognized by natural killer T (NKT) cells. To date, our understanding of the structural basis for glycolipid binding and receptor recognition of CD1d is still limited. Here, we established a preparation method for the ectodomain of human and mouse CD1d using a silkworm-baculovirus expression system. The co-expression of human and mouse CD1d and β2-microglobulin (β2m) in the silkworm-baculovirus system was successful, but the yield of human CD1d was low. A construct of human CD1d fused with β2m via a flexible GS linker as a single polypeptide was prepared to improve protein yield. The production of this single-chained complex was higher (50 μg/larva) than that of the co-expression complex. Furthermore, differential scanning calorimetry revealed that the linker made the CD1d complex more stable and homogenous. These results suggest that the silkworm-baculovirus expression system is useful for structural and biophysical studies of CD1d in several aspects including low cost, easy handling, biohazard-free, rapid, and high yielding.

A real-time PCR-based quantitative assay for 3-methylcytosine demethylase activity of ALKBH3

Human AlkB homolog 3 (ALKBH3), a homolog of the Escherichia coli protein AlkB, demethylates 1-methyladenine and 3-methylcytosine (3-meC) in single-stranded DNA and RNA by oxidative demethylation. Immunohistochemical analyses on clinical cancer specimens and knockdown experiments using RNA interference in vitro and in vivo indicate that ALKBH3 is a promising molecular target for the treatment of prostate, pancreatic, and non-small cell lung cancer. Therefore, an inhibitor for ALKBH3 demethylase is expected to be a first-in-class molecular-targeted drug for cancer treatment. Here, we report the development of a novel, quantitative real-time PCR-based assay for ALKBH3 demethylase activity against 3-meC by highly active recombinant ALKBH3 protein using a silkworm expression system. This assay enables us to screen for inhibitors of ALKBH3 demethylase, which may result in the development of a novel molecular-targeted drug for cancer therapy.

Efficient and cost effective production of active-form human PKB using silkworm larvae

Protein kinase B (PKB) also known as Akt is involved in many signal transduction pathways. As alterations of the PKB pathway are found in a number of human malignancies, PKB is considered an important drug target for cancer therapy. However, production of sufficient amounts of active PKB for biochemical and structural studies is very costly because of the necessity of using a higher organism expression system to obtain phosphorylated PKB. Here, we report efficient production of active PKBα using the BmNPV bacmid expression system with silkworm larvae. Following direct injection of bacmid DNA, recombinant PKBα protein was highly expressed in the fat bodies of larvae, and could be purified using a GST-tag and then cleaved. A final yield of approximately 1 mg PKBα/20 larvae was recorded. Kinase assays showed that the recombinant PKBα possessed high phosphorylation activity. We further confirmed phosphorylation on the activation loop by mass spectrometric analysis. Our results indicate that the silkworm expression system is of value for preparation of active-form PKBα with phosphorylation on the activation loop. This efficient production of the active protein will facilitate further biochemical and structural studies and stimulate subsequent drug development.

The potential for genetically altered microglia to influence glioma treatment

Diffuse and unstoppable infiltration of brain and spinal cord tissue by neoplastic glial cells is the single most important therapeutic problem posed by the common glioma group of tumors: astrocytoma, oligoastrocytoma, oligodendroglioma, their malignant variants and glioblastoma. These neoplasms account for more than two thirds of all malignant central nervous system tumors. However, most glioma research focuses on an examination of the tumor cells rather than on host-specific, tumor micro-environmental cells and factors. This can explain why existing diffuse glioma therapies fail and why these tumors have remained incurable. Thus, there is a great need for innovation. We describe a novel strategy for the development of a more effective treatment of diffuse glioma. Our approach centers on gaining control over the behavior of the microglia, the defense cells of the CNS, which are manipulated by malignant glioma and support its growth. Armoring microglia against the influences from glioma is one of our research goals. We further discuss how microglia precursors may be genetically enhanced to track down infiltrating glioma cells.

A novel ligand delivery system to non-invasively visualize and therapeutically exploit the IL13Rα2 tumor-restricted biomarker

Our objective was to exploit a novel ligand-based delivery system for targeting diagnostic and therapeutic agents to cancers that express interleukin 13 receptor alpha 2 (IL13Rα2), a tumor-restricted plasma membrane receptor overexpressed in glioblastoma multiforme (GBM), meningiomas, peripheral nerve sheath tumors, and other peripheral tumors. On the basis of our prior work, we designed a novel IL13Rα2-targeted quadruple mutant of IL13 (TQM13) to selectively bind the tumor-restricted IL13Rα2 with high affinity but not significantly interact with the physiologically abundant IL13Rα1/IL4Rα heterodimer that is also expressed in normal brain. We then assessed the in vitro binding profile of TQM13 and its potential to deliver diagnostic and therapeutic radioactivity in vivo. Surface plasmon resonance (SPR; Biacore) binding experiments demonstrated that TQM13 bound strongly to recombinant IL13Rα2 (Kd∼5 nM). In addition, radiolabeled TQM13 specifically bound IL13Rα2-expressing GBM cells and specimens but not normal brain. Of importance, TQM13 did not functionally activate IL13Rα1/IL4Rα in cells or bind to it in SPR binding assays, in contrast to wtIL13. Furthermore, in vivo targeting of systemically delivered radiolabeled TQM13 to IL13Rα2-expressing subcutaneous tumors was demonstrated and confirmed non-invasively for the first time with 124I-TQM13 positron emission tomography imaging. In addition, 131I-TQM13 demonstrated in vivo efficacy against subcutaneous IL13Rα2-expressing GBM tumors and in an orthotopic synergeic IL13Rα2-positive murine glioma model, as evidenced by statistically significant survival advantage. Our results demonstrate that we have successfully generated an optimized biomarker-targeted scaffolding that exhibited specific binding activity toward the tumor-associated IL13Rα2 in vitro and potential to deliver diagnostic and therapeutic payloads in vivo.

Improved isolation and purification of functional human Fas receptor extracellular domain using baculovirus-silkworm expression system

To achieve an efficient isolation of human Fas receptor extracellular domain (hFasRECD), a fusion protein of hFasRECD with human IgG1 heavy chain Fc domain containing thrombin cleavage sequence at the junction site was overexpressed using baculovirus-silkworm larvae expression system. The hFasRECD part was separated from the fusion protein by the effective cleavage of the recognition site with bovine thrombin. Protein G column treatment of the reaction mixture and the subsequent cation-exchange chromatography provided purified hFasRECD with a final yield of 13.5mg from 25.0 ml silkworm hemolymph. The functional activity of the product was examined by size-exclusion chromatography analysis. The isolated hFasRECD less strongly interacted with human Fas ligand extracellular domain (hFasLECD) than the Fc domain-bridged counterpart, showing the contribution of antibody-like avidity in the latter case. The purified glycosylated hFasRECD presented several discrete bands in the disulphide-bridge non-reducing SDS-PAGE analysis, and virtually all of the components were considered to participate in the binding to hFasLECD. The attached glycans were susceptible to PNGase F digestion, but mostly resistant to Endo Hf digestion under denaturing conditions. One of the components exhibited a higher susceptibility to PNGase F digestion under non-denaturing conditions.

Efficient production of human Fas receptor extracellular domain-human IgG1 heavy chain Fc domain fusion protein using baculovirus/silkworm expression system

The fusion protein consisting of human Fas receptor extracellular domain and human IgG1 heavy chain Fc domain (hFasRECD-Fc) is a medically important protein that potentially has therapeutic uses. The fusion gene composed of a synthetic human Fas receptor extracellular domain gene and the cDNA encoding human IgG1 heavy chain Fc domain was investigated on the secretory expression using two baculovirus systems which employed either Spodoptera frugiperda 9 (Sf9) cell line or Bombyx mori (silkworm) larvae as the host organism. Both expression systems produced the functional hFasRECD-Fc as a dimer molecule linked by disulfide bridges. The secretion level per unit volume was much higher in the case of silkworm larvae as compared to Sf9 cell line, and was estimated to be more than 150 times. A substantially pure hFasRECD-Fc sample from silkworm larvae was obtained by single step Protein G-agarose affinity column chromatography. The affinity purified sample was further fractionated by anion-exchange chromatography with the final purification yield of 22.5 mg from 26 ml hemolymph. The hFasRECD-Fc from silkworm larvae and the tag-free human Fas ligand extracellular domain derivative from Pichia pastoris formed a stable complex in solution, which was verified by size-exclusion chromatography. This study demonstrated that the baculovirus/silkworm expression system provided the means for efficient production of highly pure hFasRECD-Fc with functional activity.

Silkworm expression system as a platform technology in life science

Many recombinant proteins have been successfully produced in silkworm larvae or pupae and used for academic and industrial purposes. Several recombinant proteins produced by silkworms have already been commercialized. However, construction of a recombinant baculovirus containing a gene of interest requires tedious and troublesome steps and takes a long time (3-6 months). The recent development of a bacmid, Escherichia coli and Bombyx mori shuttle vector, has eliminated the conventional tedious procedures required to identify and isolate recombinant viruses. Several technical improvements, including a cysteine protease or chitinase deletion bacmid and chaperone-assisted expression and coexpression, have led to significantly increased protein yields and reduced costs for large-scale production. Terminal N-acetyl glucosamine and galactose residues were found in the N-glycan structures produced by silkworms, which are different from those generated by insect cells. Genomic elucidation of silkworm has opened a new chapter in utilization of silkworm. Transgenic silkworm technology provides a stable production of recombinant protein. Baculovirus surface display expression is one of the low-cost approaches toward silkworm larvae-derived recombinant subunit vaccines. The expression of pharmaceutically relevant proteins, including cell/viral surface proteins, membrane proteins, and guanine nucleotide-binding protein (G protein) coupled receptors, using silkworm larvae or cocoons has become very attractive. Silkworm biotechnology is an innovative and easy approach to achieve high protein expression levels and is a very promising platform technology in the field of life science. Like the "Silkroad," we expect that the "Bioroad" from Asia to Europe will be established by the silkworm expression system.

Grading the commercial optical biosensor literature-Class of 2008: 'The Mighty Binders'

Optical biosensor technology continues to be the method of choice for label-free, real-time interaction analysis. But when it comes to improving the quality of the biosensor literature, education should be fundamental. Of the 1413 articles published in 2008, less than 30% would pass the requirements for high-school chemistry. To teach by example, we spotlight 10 papers that illustrate how to implement the technology properly. Then we grade every paper published in 2008 on a scale from A to F and outline what features make a biosensor article fabulous, middling or abysmal. To help improve the quality of published data, we focus on a few experimental, analysis and presentation mistakes that are alarmingly common. With the literature as a guide, we want to ensure that no user is left behind.

Distinct structural requirements for interleukin-4 (IL-4) and IL-13 binding to the shared IL-13 receptor facilitate cellular tuning of cytokine responsiveness

Both interleukin-4 (IL-4) and IL-13 can bind to the shared receptor composed of the IL-4 receptor alpha chain and the IL-13 receptor alpha1 chain (IL-13Ralpha1); however, the mechanisms by which these ligands bind to the receptor chains are different, enabling the principal functions of these ligands to be different. We have previously shown that the N-terminal Ig-like domain in IL-13Ralpha1, called the D1 domain, is the specific and critical binding unit for IL-13. However, it has still remained obscure which amino acid has specific binding capacity to IL-13 and why the D1 domain acts as the binding site for IL-13, but not IL-4. To address these questions, in this study we performed mutational analyses for the D1 domain, combining the structural data to identify the amino acids critical for binding to IL-13. Mutations of Lys-76, Lys-77, or Ile-78 in c' strand in which the crystal structure showed interaction with IL-13, and those of Trp-65 and Ala-79 adjacent to the interacting site, resulted in significant impairment of IL-13 binding, demonstrating that these amino acids generate the binding site. Furthermore, mutations of Val-35, Leu-38, or Val-42 at the N-terminal beta-strand also resulted in loss of IL-13 binding, probably from decreased structural stability. None of the mutations employed here affected IL-4 binding. These results demonstrate that the D1 domain of IL-13Ralpha1 acts as an affinity converter, through direct cytokine interactions, that allows the shared receptor to respond differentially to IL-4 and IL-13.

Silkworm expression and sugar profiling of human immune cell surface receptor, KIR2DL1

Immune cell surface receptors are directly involved in human diseases, and thus represent major drug targets. However, it is generally difficult to obtain sufficient amounts of these receptors for biochemical and structural studies because they often require posttranslational modifications, especially sugar modification. Recently, we have established a bacmid expression system for the baculovirus BmNPV, which directly infects silkworms, an attractive host for the large-scale production of recombinant sugar-modified proteins. Here we produced the human immune cell surface receptor, killer cell Ig-like receptor 2DL1 (KIR2DL1), by using the BmNPV bacmid expression system, in silkworms. By the direct injection of the bacmid DNA, the recombinant KIR2DL1 protein was efficiently expressed, secreted into body fluids, and purified by Ni(2+) affinity column chromatography. We further optimized the expression conditions, and the final yield was 0.2mg/larva. The sugar profiling revealed that the N-linked sugars of the purified protein comprised very few components, two paucimannose-type oligosaccharides, Manalpha1-6Manbeta1-4GlcNAcbeta1-4GlcNAc and Manalpha1-6Manbeta1-4GlcNAcbeta1-4(Fucalpha1-6)GlcNAc. This revealed that the protein product was much more homogeneous than the complex-sugar type product obtained by mammalian cell expression. The surface plasmon resonance analysis demonstrated that the purified KIR2DL1 protein exhibited specific binding to the HLA-Cw4 ligand. Moreover, the CD spectrum showed the proper secondary structure. These results clearly suggested that the silkworm expression system is quite useful for the expression of cell surface receptors that require posttranslational modifications, as well as for their structural and binding studies, due to the relatively homogeneous N-linked sugar modifications.

Nonviral production of human interleukin-7 in spodoptera frugiperda insect cells as a soluble recombinant protein

Human interleukin-7 (hIL-7) is a cytokine secreted by the stromal cells of the red marrow. It is important for proliferation during certain stages of B-cell maturation and for T and NK cell survival, development, and homeostasis. It is a critical growth factor for enhancement and recovery of the immune T-cell. Because of its strong immunomodulatory effects, hIL-7 may become a valuable supplementary agent for immunotherapeutical treatments in patients with HIV infection or immunodeficiency. Human IL-7 has previously been produced in various protein expression systems. In this paper, we present an alternative expression system, in Spodoptera frugiperda cells, for the production of hIL-7 using nonlytic vector systems. This system allows generation of correctly translated and accurately processed heterologous proteins as soluble recombinant proteins. Here we report plasmid construction, transfection, and consequent expression of hIL-7 using this nonlytic insect cell expression system. The levels of secreted hIL-7 in a small scale experiment reached a level of 1.7 μg·1⁻¹ under serum-free cell culture conditions.