Tatsunari Nishi

Mutagenesis of human granulocyte colony stimulating factor

To define the structure-function relationship, we have made a number of mutants of human granulocyte colony-stimulating factor (hG-CSF) by in vitro mutagenesis. The results indicate that most of the mutations located in the internal and C-terminal regions of the molecule abolished the activity, whereas the mutants without N-terminal 4, 5, 7, or 11 amino acids retained the activity. N-terminal amino acids were also altered by cassette mutagenesis using a synthetic oligonucleotide mixture. Among them, KW2228, in which Thr-1, Leu-3, Gly-4, Pro-5 and Cys-17 were respectively substituted with Ala, Thr, Tyr, Arg and Ser, showed more potent granulopoietic activity than that of intact hG-CSF both in vitro and in vivo.

Enzymatic Characterization of Human α1,3-Fucosyltransferase Fuc-TVII Synthesized in a B Cell Lymphoma Cell Line

The human α1,3-fucosyltransferase, Fuc-TVII, a key enzyme in the biosynthesis of selectin ligands, was expressed as a soluble protein-A chimeric form in a human B cell lymphoma cell line, Namalwa KJM-1, and purified using IgG-Sepharose. The enzymatic properties of recombinant soluble Fuc-TVII were then examined. Its enzyme activity was highest at pH 7.5, and the presence of 25 mm Mn2+ was required for full activity. Fuc-TVII exhibits an acceptor specificity restricted to α2,3-sialylated type 2 oligosaccharides, and the apparentK m values for α2,3-sialyl lacto-N-neotetraose and GDP-fucose were 3.08 mmand 16.4 μm, respectively. The inhibitory effects of various nucleotides on the activity of Fuc-TVII reflected its donor specificity for the nucleotide portion of GDP. Fuc-TVII was demonstrated to be useful for the synthesis of a sialyl Lewis x hexasaccharide from lacto-N-neotetraose in combination with an α2,3-sialyltransferase, ST3Gal IV. Polyethylene glycols enhanced the thermal stability of Fuc-TVII, leading to increased formation of the reaction product.

Enhancement of transcriptional activity of the Escherichia coli trp promoter by upstream A+T-rich regions

The Escherichia coli trp promoter has two A + T-rich blocks in the upstream region. The deletion of the segments containing these blocks resulted in a decrease in promoter strength. By replacing the upstream region of trp promoter with one or two large A + T-rich blocks of the major leftward lambda promoter (pL), modified trp promoters (designated let) were constructed, and the transcriptional activities of these promoters towards the expression of the human interferon-gamma gene were measured. The let promoters which contain one (designated letI) or two (designated letII) A + T-rich blocks were about 6 times (at the levels of interferon activity produced) or about 3 times (at the levels of mRNA synthesized de novo) stronger than the wild-type trp promoter. The transcription from the letI promoter was controlled both by the trpR-coded repressor and the cI-coded repressor of phage lambda.

High level production of a peptide hormone analogue [Leu13]motilin inE. coli

SummaryA peptide hormone analogue [Leu13]motilin has been produced in high yield by recombinant DNA techniques. The peptide was expressed from a multicopied [Leu13]motilin gene fused to a salmon growth hormone gene fragment. The monomeric [Leu13]motilin was obtained by treatment of the fusion protein with cyanogen bromide, carboxypeptidase A and B. [Leu13]motilin showed the equivalent biological activity to that of the natural form.

Recognition of cell surface GD3 by monoclonal antibody anti-6C2 in rheumatoid arthritis synovial fluid: Expression on human T cells with transendothelial migratory activity

OBJECTIVE We have previously reported that the anti-6C2 monoclonal antibody (mAb) defines a subset of human CD4+ memory T cells. The present study sought to determine the nature of the 6C2 molecule and the function associated with 6C2+ T cells, and to examine whether this T cell subset is involved in the pathophysiology of rheumatoid arthritis (RA). METHODS Cytofluorographic analysis was performed for identification of T cell surface molecules displaying a distribution similar to that of the 6C2 molecule. T cells in the synovial fluid of RA patients were examined for expression of the 6C2 molecule. Transendothelial migratory activity was assessed by assay using monolayers of human endothelial cells. Specific reactivity of the anti-6C2 mAb was determined by immunoblotting on gangliosides separated by thin-layer chromatography, and flow cytometric analysis of the cells transfected with complementary DNA (cDNA) was performed for determination of the glycosyltransferases involved in biosynthesis of the gangliosides. RESULTS On human peripheral T cells, the 6C2 molecule was distributed, by and large, in a pattern similar to that of CDw60, or O-acetyl-GD3. The majority (>70%) of synovial fluid T cells from patients with RA were found to be 6C2 positive, and those 6C2+ T cells exhibited a transendothelial migratory capacity that was inhibited by pretreatment of T cells with anti-6C2 mAb. Moreover, treatment of T cells with neuraminidase resulted in a loss of 6C2 expression as well as a reduction in the transendothelial migratory activity. Anti-6C2 mAb reacted specifically with GD3, but not with O-acetyl-GD3. The reactivity of anti-6C2 mAb was induced on the cell surface only by transfection with cDNA for GD3 synthase. CONCLUSION The 6C2 molecule is a disialoganglioside, GD3, and is present on a subset of T cells with transendothelial migratory capacity. The 6C2/GD3 molecules, as well as 6C2/GD3+ T cells, appear to play a role in T cell migration and in the inflammation of RA.

Stabile production of a thrombin resistant pro-urokinase derivative (PRO-UKS1) by Namalwa KJM-1 cells adapted to serum-free medium

Pro-UKS1 was designed as a thrombin-resistant derivative of pro-urokinase (pro-UK) by introducing a glycosylation site using site-directed mutagenesis. An expression plasmid for pro-UKS1, pMo1UKS1SEd1-5, was constructed and introduced into Namalwa KJM-1 cells (Hosoiet al., 1988), and cells resistant to G418 and Methotrexate (MTX) were obtained. Amongst them, the highest pro-UKS1 producer (resistant to 500 nM of MTX), clone 41-8, was selected and further characterized. Clone 41-8 was cultured in serum-free ITPSGF medium (Hosoiet al., 1988). Under the conventional conditions, the concentration of pro-UKS1 reached 26 μg ml−1. Addition of glucose and tri-iodothyronine (T3) improved productivity, and the maximal productivity of pro-UKS1 was 67 μg ml−1 day−1. In this conditioned medium, content of pro-UKS1 was above 80% of total proteins.

A reporter assay for G-protein-coupled receptors using a B-cell line suitable for stable episomal expression.

We have established a cAMP response element (CRE)-mediated reporter assay system for G-protein-coupled receptors (GPCRs) using an oriP-based estrogen-inducible expression vector and the B-cell line (GBC53 or GBCC71) that expresses EBNA-1 and is adapted to serum-free culture. GBC53 harbors a GAL4-ER expression unit and a CRE-luciferase gene in the genome, and GBCC71 also harbors expression units for two chimeric Galphas proteins (Gs/q and Gs/i). Introduction of a GPCR expression plasmid into GBC53 or GBCC71 creates polyclonal stable transformants in 2 weeks, and these are easily expanded and used for assays after induction of the GPCR expression. Using GBC53, we detected ligand-dependent signals of Gs-coupled GPCRs such as glucagon-like peptide 1 receptor (GLP1R) and beta2 adrenergic receptor (beta2AR) with high sensitivity. Interestingly, we also detected constitutive activity of beta2AR. Using GBCC71, we detected ligand-dependent signals of Gq- or Gi-coupled GPCRs such as H1 histamine receptor and CXCR1 chemokine receptor in addition to Gs-coupled GPCRs. An agonist, antagonist, or inverse agonist was successfully evaluated in this system. We succeeded in constructing a 384-well high-throughput screening (HTS) system for GLP1R. This system enabled us to easily and rapidly make a large number of efficient GPCR assay systems suitable for HTS as well as ligand hunting of orphan GPCRs.

Efficient expression of pro-urokinase by human lymphoblastoid Namalwa KJM-1 cells using Moloney retroviral promoter

We have compared the level of expression of several enhancer/promoters in human lymphoblastoid Namalwa KJM-1 cells when fused to a common reporter gene. A cassette containing the pro-urokinase (pro-UK) coding sequence followed by the rabbit β-globin and simian virus 40 (SV40) 3′ nontranslated region was used for evaluation of the enhancer activity. Cells containing Moloney murine leukemia virus (Mo-MuLV) promoter had an average of 10–20 fold higher expression levels of pro-UK than those containing other promoters, such as SV40 early gene promoter, human cytomegalovirus (hCMV) major immediate-early gene promoter, Rous sarcoma virus (RSV) promoter and chicken β-actin gene promoter. The expression level of pro-UK under the control of Mo-MuLV promoter was 2–3 μg/106 cells/day and was constant for more than 6 months. Furthermore, the production of a high producer clone, obtained by using dhfr gene coamplification, reached 30–40 μg/106 cells/day. Thus, Mo-MuLV promoter showed the desired characteristics for efficient expression of foreign genes in Namalwa KJM-1 cells.

Stable Production of Pro-urokinase and its Derivative by Namalwa KJM-1 Cells Adapted to a Serum-free Medium

We have previously reported that Namalwa KJM-1 cells adapted to a serum-free medium and derived from Namalwa (B lymphoblastoid) cells were more useful than CHO (Chinese hamster ovary) cells as the host cell line for producing various recombinant proteins with a dhfr gene coamplification method, because CHO cells secrete a cysteine endopeptidase (Satoh, 1990).