The establishment of IL-2 producing cells by genetic engineering

Construction and characterization of functional anti-epiregulin humanized monoclonal antibodies

Growth factors are implicated in several processes essential for cancer progression. Specifically, epidermal growth factor (EGF) family members, including epiregulin (EREG), are important prognostic factors in many epithelial cancers, and treatments targeting these molecules have recently become available. Here, we constructed and expressed humanized anti-EREG antibodies by variable domain resurfacing based on the three-dimensional (3D) structure of the Fv fragment. However, the initial humanized antibody (HM0) had significantly decreased antigen-binding affinity. Molecular modeling results suggested that framework region (FR) residues latently important to antigen binding included residue 49 of the light chain variable region (VL). Back mutation of the VL49 residue (tyrosine to histidine) generated the humanized version HM1, which completely restored the binding affinity of its murine counterpart. Importantly, only one mutation in the framework may be necessary to recover the binding capability of a humanized antibody. Our data support that HM1 exerts potent antibody-dependent cellular cytotoxicity (ADCC). Hence, this antibody may have potential for further development as a candidate therapeutic agent and research tool.

The level of synthesis and secretion of Gaussia princeps luciferase in transfected CHO cells is heavily dependent on the choice of signal peptide

There is a great demand for the improvement of mammalian cell production systems such that they can compete economically with their prokaryotic counterparts. Of a number of parameters that need to be explored to accomplish this we have tested the effects of different signal peptides on the synthesis and secretion of Gaussia princeps luciferase in mammalian cells. A series of plasmids were transfected into CHO cells where the coding region for the marine luciferase was fused to the signal peptide coding regions derived from different sources. Both cell extracts and medium samples were analysed for luciferase activity. When the native Gaussia luciferase signal sequence in the vector was substituted by that from human interleukin-2 or albumin then the amount of active recombinant protein produced was substantially reduced, both in transiently and stably transfected cells. Western blotting showed that enzyme activity and protein levels mirrored one another. The major decrease in luciferase activity was shown not to be a result of decreased mRNA levels, indicating the involvement of a post-transcriptional event. When the coding region of human endostatin was fused to that of the Gaussia luciferase signal peptide then an elevated level of secreted endostatin was observed compared to when that of the albumin signal peptide was used. Stable transfection of HepG2 cells with the different signal peptide constructs gave essentially the same results as seen in CHO cells. The overall results indicate that the choice of signal peptide can be imperative to ensure an optimal synthesis and secretion of a recombinant protein in a mammalian cell culture system.

Vectors Encoding Seven Oikosin Signal Peptides Transfected into CHO Cells Differ Greatly in Mediating Gaussia luciferase and Human Endostatin Production although mRNA Levels are Largely Unaffected

The signal peptide of the luciferase secreted by the marine copepod Gaussia princeps has been shown to promote high-level protein synthesis/secretion of recombinant proteins, being far superior to mammalian counterparts. The main aim of the present study was to investigate the effects of seven selected signal peptides derived from oikosins, house proteins of the marine organism Oikopleura dioica, on synthesis/secretion of recombinant proteins. Vector constructs were made in which the coding regions of two naturally secreted proteins, Gaussia luciferase and human endostatin (hEndostatin), were “seamlessly” fused to the signal peptide coding sequences of interest. CHO cells were transfected with the plasmids and populations of stably transfected cells established. The amounts of reporter proteins in cell extract and medium samples were determined and the results compared to those obtained from cells stably transfected with a reference vector construct. In addition, the amounts of luciferase or hEndostatin encoding mRNAs in the cells were determined and related to the protein levels obtained. The levels of reporter protein produced varied greatly among the seven oikosin signal peptides tested. Whereas the oikosin 1 signal peptide resulted in about 40% production of Gaussia luciferase compared to the reference construct, oikosins 2–7 were extremely ineffective (<1%). mRNA levels were not dramatically affected such that inadequate availability of transcript for translation was not the underlying reason for the observations. The oikosin 1 signal peptide was also the most effective regarding synthesis/secretion of hEndostatin. No secreted product was observed using the oikosin 3 signal peptide. Interestingly, the molecular weight of hEndostatin in cell extracts prepared from cells transfected with oikosin 2 and 3 constructs was higher than that using the oikosin 1 signal peptide. The overall findings indicate that the signal peptide affects the efficiency of protein synthesis and secretion through a mechanism operating at the post-transcriptional level. The results described here provide substantial support to our previous observations which suggested that the choice of the signal peptide is imperative when aiming to achieve optimal synthesis and secretion of a recombinant protein using transfected mammalian cells.

Alteration in the IL-2 signal peptide affects secretion of proteinsin vitro andin vivo

BACKGROUND

Although hundreds of different signal peptides have now been identified, few studies have examined the factors enabling signal peptides to augment secretion of mature proteins. Signal peptides, located at the N-terminus of nascent secreted proteins, characteristically have three domains: (1) a basic domain at the N-terminus, (2) a central hydrophobic core, and (3) a carboxy-terminal cleavage region. In this study, we investigated whether alterations in the basic and/or the hydrophobic domains of a commonly used signal peptide from interleukin-2 (IL-2) affected secretion of two proteins: placental alkaline phosphatase (AP) and endostatin.

METHODS

A series of modifications in the basic and/or hydrophobic domains of the IL-2 signal peptide were made by polymerase chain reaction with endostatin or AP plasmids as templates. Transfection of wild-type or modified IL-2 signal peptides fused in-frame with endostatin or AP were done with Superfect in vitro or by the hydrodynamic method in vivo.

RESULTS

Increasing both the basicity and hydrophobicity of the signal peptide augmented the secretion of AP and endostatin by approximately 2.5- and 3.5-fold, respectively, from MDA-MB-435 cells in vitro. Over a range of DNA concentrations and times, the most effective IL-2 signal peptide increased AP levels in the medium compared to the wild-type IL-2 signal peptide. Comparable results from these modified IL-2 signal peptides were found to increase AP levels in the medium from bovine aortic endothelial cells. Moreover, the combined changes in basic and hydrophobic domains of the IL-2 signal peptide augmented serum levels of endostatin and placental AP by 3-fold when the optimal plasmid constructs were injected in vivo.

CONCLUSIONS

Modification of the IL-2 signal peptide augments protein secretion both in vitro and in vivo. As a result, optimizing the signal peptide should be considered for increasing the therapeutic levels of secreted proteins.

Autocrine transformation by fibroblast growth factor 9 (FGF-9) and its possible participation in human oncogenesis

Transfection of human fibroblast growth factor 9 (FGF-9) cDNA into mouse BALB/c 3T3 clone A31 cells led to morphological transformation of the cells and foci formation 4 weeks later. Isolated transformants had a higher saturation density than parental A31 cells, could grow in soft agar, and secreted FGF-9 into the culture supernatant. The introduction of FGF-9 N33 cDNA, which encodes a truncated protein that has 33 N-terminal amino acids deleted and has the same mitogenic potency as FGF-9, failed to lead to foci formation. Although FGF-9 is a secretory protein, it does not have a typical secretory signal sequence, and the secreted protein retains the full sequence coded in the cDNA except for the initiating methionine. The produced FGF-9 N33 was not secreted and remained within the cell. It is possible that FGF-9 has an uncleavable signal sequence within the first 33 N-terminal amino acids. All of the phenotypes acquired by transformation could be arrested by treatment with a neutralizing anti-human FGF-9 monoclonal antibody (MAb) 150-59. Additionally, transformants formed tumors in nude mice. Injection of MAb 150-59 suppressed tumor formation in nude mice and caused existing tumors to regress. Our results suggest that the cellular transformation mediated by FG F-9 is produced by autocrine stimulation. We have detected FGF-9 production in the human tumor cell lines glioma NMC-G1, from which FGF-9 was originally purified, and stomach carcinoma AZ-521. The growth of NMC-G1 was not affected by MAb 150-59, but that of AZ-521 was arrested by MAb 150-59 in the presence of heparin. Moreover, the growth of the AZ-521 cell tumor in nude mice could be partially arrested by antibody treatment. The possibility of a participation of FGF-9 in the formation of human tumors is suggested.

Molecular cloning and functional expression of a human thyrotropin-releasing hormone (TRH) receptor gene

In this study, we isolated genomic DNA fragments coding for the human thyrotropin-releasing hormone (TRH) receptor. Analysis of the nucleotide sequence revealed that the human TRH receptor gene had an exon-intron structure comprising at least two exons. A polypeptide encoded by the gene consisted of 398 amino acid residues with putative seven transmembrane domains. It showed high homology as a whole amino acid sequence with the rat and mouse TRH receptors except for considerable variation in the C-terminal region. Chromosomal mapping study indicated that the human TRH receptor gene was assigned to chromosome 8. Chinese hamster ovary (CHO) cells transfected with a DNA fragment containing the coding regions of the human TRH receptor bound with [3H]TRH. This binding was inhibited by adding unlabeled TRH in a dose-dependent fashion. Scatchard analysis indicated that the transfected CHO cells expressed a single class of high affinity binding sites at a dissociation constant (Kd) of approximately 1 nM. These results demonstrated that the isolated gene encoded a specific TRH receptor with high affinity.

Purification and characterization of biologically active recombinant human neurotrophin-3 produced by expression of a chimera gene in Chinese hamster ovary cells

In order to obtain high-level expression of recombinant human neurotrophin-3 (NT-3), we constructed several types of expression plasmids and examined several cell lines for expression of the human NT-3 gene. The highest level production of the recombinant protein was attained in Chinese hamster ovary cells transfected with an expression plasmid that contains a chimera gene encoding the human nerve growth factor (NGF) prepro-region and human NT-3 mature-region under control of a murine leukemia virus-derived long terminal repeat (MuLV-LTR). This cell line can produce more than 1 mg recombinant human NT-3/1 conditioned medium. The recombinant protein was purified to apparent homogeneity with a cation exchange column, a gel filtration column and a reversed-phase HPLC column with a recovery of about 30%. The purified NT-3, at a concentration as low as 0.2 ng/ml, induced neurite out-growth in neurons prepared from 8-day-old chick embryonic dorsal root ganglia; however, it showed little neurotrophic effect on rat PC12 pheochromocytoma cells, which are known to be NGF-responding cells. In addition, this protein promoted colony formation by human peripheral blood lymphocytes in soft agar culture.

Expression and characterization of a chimeric bispecific antibody against fibrin and against urokinase-type plasminogen activator

We have produced a chimeric bispecific antibody that has dual specificity of human fibrin and urokinase-type plasminogen activator (u-PA). Complementary DNAs for variable regions of both anti-fibrin and anti-u-PA antibodies were cloned from two murine hybridomas secreting respective antibodies using polymerase chain reaction (PCR) techniques, and joined to cDNAs for human constant regions to form chimeric antibody genes. Both of two expression vectors for chimeric anti-fibrin and chimeric anti-u-PA antibodies were sequentially introduced into Chinese hamster ovary cells, and stable transfectants secreting the chimeric bispecific antibody were obtained. The highest producer transfectant (SULF/C2-30) secreted high level (about 40 micrograms ml-1) of total chimeric IgG and about 2% of the IgG had the bispecific activity of binding with both antigens. The chimeric bispecific antibody was purified by a combination of affinity chromatographies employing antigen-coupled columns and hydroxyapatite high-performance liquid chromatography. The purified chimeric bispecific antibody significantly enhanced the thrombolytic potency of single chain u-PA in an in vitro clot lysis assay as well as the original murine bispecific antibody.

Molecular cloning of a novel cytokine cDNA encoding the ninth member of the fibroblast growth factor family, which has a unique secretion property

Glia-activating factor (GAF) is a novel heparin-binding growth factor purified from the culture supernatant of a human glioma cell line. It shows a spectrum of activity slightly different from those of other known growth factors. We have isolated the cDNA which encodes human GAF. A homology search revealed that GAF would be the ninth member of the FGF family, and we therefore call it FGF-9. The human FGF-9 cDNA cloned by using oligonucleotide probes encoded a polypeptide consisting of 208 amino acids. Sequence similarity to other members of the FGF family was estimated to be around 30%. Two cysteine residues and other consensus sequences in family members were also well conserved in the FGF-9 sequence. FGF-9 was found to have no typical signal sequence in its N terminus like those in acidic FGF and basic FGF. Acidic FGF and basic FGF are known not to be secreted from cells in a conventional manner. However, FGF-9 was found to be secreted from cells after synthesis despite its lack of a typical signal sequence. It could be detected exclusively in the culture medium of cDNA-transfected COS cells. The amino acid sequence of proteins purified from culture supernatant of the CHO cell line, which was cDNA transfected and selected as a high producer of FGF-9, showed that no peptides were cleaved from the N terminus except the initiation methionine. The rat FGF-9 cDNA was also cloned, and the structural analysis indicated that the PGF-9 gene is highly conserved. Expression of the FGF-9 gene could be detected in the brain and kidney of the adult rat. Restricted gene expression in organs and the unique secretion nature of the protein suggest that FGF-9 plays a physiological role which differs from those of well-characterized acidic FGF and basic FGF.

Molecular cloning of a novel cytokine cDNA encoding the ninth member of the fibroblast growth factor family, which has a unique secretion property

Glia-activating factor (GAF) is a novel heparin-binding growth factor purified from the culture supernatant of a human glioma cell line. It shows a spectrum of activity slightly different from those of other known growth factors. We have isolated the cDNA which encodes human GAF. A homology search revealed that GAF would be the ninth member of the FGF family, and we therefore call it FGF-9. The human FGF-9 cDNA cloned by using oligonucleotide probes encoded a polypeptide consisting of 208 amino acids. Sequence similarity to other members of the FGF family was estimated to be around 30%. Two cysteine residues and other consensus sequences in family members were also well conserved in the FGF-9 sequence. FGF-9 was found to have no typical signal sequence in its N terminus like those in acidic FGF and basic FGF. Acidic FGF and basic FGF are known not to be secreted from cells in a conventional manner. However, FGF-9 was found to be secreted from cells after synthesis despite its lack of a typical signal sequence. It could be detected exclusively in the culture medium of cDNA-transfected COS cells. The amino acid sequence of proteins purified from culture supernatant of the CHO cell line, which was cDNA transfected and selected as a high producer of FGF-9, showed that no peptides were cleaved from the N terminus except the initiation methionine. The rat FGF-9 cDNA was also cloned, and the structural analysis indicated that the PGF-9 gene is highly conserved. Expression of the FGF-9 gene could be detected in the brain and kidney of the adult rat. Restricted gene expression in organs and the unique secretion nature of the protein suggest that FGF-9 plays a physiological role which differs from those of well-characterized acidic FGF and basic FGF.

Mitochondrial transport of mitoribosomal proteins, YmL8 and YmL20, in Saccharomyces cerevisiae

Two mitochondrial ribosomal (mitoribosomal) proteins, YmL8 and YmL20, of the yeast Saccharomyces cerevisiae and their derivatives were synthesized in vitro and their transport into isolated yeast mitochondria was examined. Of the two proteins, YmL20 possesses an N-terminal presequence of 18 amino acid residues, while YmL8 has no such presequence. Both proteins were found to be transported into isolated mitochondria in an energy-dependent manner. Furthermore, YmL20 protein without its N-terminal presequence was also transported, despite the fact that the presequence alone was capable of transporting a fused passenger protein, Chinese hamster dihydrofolate reductase (DHFR). Therefore, YmL20 protein appears to possess redundant transport signals in its structure. Similarly, YmL8 derivatives lacking either 40 or 86 amino acid residues from the N-terminus and/or 52 amino acid residues from the C-terminus were transported. In addition, the N-terminal segment of this protein was capable of transporting Chinese hamster DHFR into mitochondria, while its C-terminal segment was not. Thus, YmL8 protein also appears to possess two or more transport signals in its structure. Perhaps the presence of many basic amino acid residues in these proteins might, at least partly, contribute to their mitochondrial transport.

Suppression of cell motility and metastasis by transfection with human motility-related protein (MRP-1/CD9) DNA

Previously we showed that motility-related protein (MRP-1) is an antigen recognized by monoclonal antibody (mAb) M31-15 inhibiting cell motility and that the sequence of MRP-1 coincides with that of CD9. In the present study, plasmid was constructed in which human MRP-1/CD9 cDNA is expressed under the control of the Abelson murine leukemia virus promoter sequence. The expression plasmid for MRP-1/CD9 was introduced into Chinese hamster ovary cells, human lung adenocarcinoma cell line MAC10 (MRP-1 positive), and human myeloma cell line ARH77 (MRP-1 negative). All of the MRP-1/CD9 (over)expressing clones obtained from these transfected cells showed suppressed cell motility (penetration and phagokinetic track assays) depending on the degree of expression of MRP-1/CD9. Overexpression of MRP-1/CD9 by MAC10 cells resulted in the suppression of cell motility (maximally 73%) associated with considerable inhibition of the cell growth (maximally 48%). However, the inhibition of the growth of MAC10 cells by mAb M31-15 was < 17% at an antibody concentration of 1-5 micrograms/ml, which inhibits cell motility by > 90%. These results suggest that MRP-1/CD9 directly regulates cell motility and may also affect cell growth. Effects on metastasis by the expression of MRP-1 CD9 were investigated with mouse melanoma BL6 cells-BALB/c nu/nu mouse system. Metastatic potential of all transformants expressing MRP-1/CD9 was lower than that of parent BL6 cells.

Adjuvant-independent enhanced immune responses to recombinant herpes simplex virus type 1 glycoprotein D by fusion with biologically active interleukin-2

A truncated herpes simplex virus (HSV) type 1 glycoprotein D (t-gD) gene was fused to the human interleukin-2 (IL-2) gene (t-gD-IL-2 gene) and introduced into mouse myeloma Sp2/0 cells. The gene product, t-gD-IL-2, secreted from the cells was immunoprecipitated with five monoclonal antibodies specific for native gD. Purified t-gD-IL-2 supported the growth of IL-2-dependent cells, with a specific activity almost comparable to that of recombinant human IL-2. Mice immunized with t-gD-IL-2 in an adjuvant-free form showed superior anti-HSV antibody responses, and were completely protected against HSV challenge, whereas immunization with t-gD adsorbed onto aluminum hydroxide (alum) partially failed to prevent the virus infection. The high immunogenicity of t-gD-IL-2 was due to the biological activity of the fused IL-2 rather than to a hapten-carrier effect of the IL-2 moiety, because mice primed with t-gD-IL-2 showed delayed-type hypersensitivity against stimulation with gD, but not against that with IL-2 antigen, and because a booster immunization with t-gD-IL-2 extensively augmented the response of anti-gD antibody, but not that of the anti-human IL-2 antibody. The serological half-life of IL-2 activity in mice injected with t-gD-IL-2 was prolonged to about four times that of rIL-2. However, when t-gD-IL-2 was co-administered with human albumin (HSA), the mouse anti-HSA antibody response was slightly enhanced.(ABSTRACT TRUNCATED AT 250 WORDS)

Cell division arrest induced by phorbol ester in CHO cells overexpressing protein kinase C-delta subspecies

Several lines of CHO cells stably overexpressing protein kinase C (PKC) subspecies to various extents were established by the DNA-mediated transfer. Upon treatment with phorbol 12-myristate 13-acetate, the growth of the cells expressing the PKC-delta subspecies was markedly inhibited, whereas cell lines expressing PKC-alpha, PKC-beta II, and PKC-zeta subspecies were not significantly affected. Flow cytometric analysis indicated that all cell lines overexpressing PKC-delta subspecies accumulated in G2/M phase in response to phorbol 12-myristate 13-acetate. In these arrested cells, dikaryons were predominant, implying that phorbol ester-induced inhibition of cell division is specific to telophase. These results suggest PKC-delta subspecies may play a role in the normal cell cycle progression.

A novel strategy for converting recombinant viral protein into high immunogenic antigen

Interleukin 2 (IL-2) is a lymphokine promoting immune response and therefore has been investigated as an immunological adjuvant. In order to enhance the immunogenicity of recombinant viral protein, herpes simplex virus type 1 (HSV-1) glycoprotein D (gD), we genetically created a fusion protein consisting of gD and human IL-2. The fusion protein, without any other adjuvants, induced high antibody responses and cell-mediated immunity to HSV-1 in mice. Mice immunized with the fusion protein were protected against HSV-1 infection. The results indicate that IL-2-fusing can provide a means for converting a weak immunogenic protein into a high immunogenic antigen, and the strategy would be widely applicable to the other antigens for pathogens.

Two cDNAs encoding novel human FGF receptor

Two types of cDNAs encoding novel human FGF receptors were isolated. These two cDNAs were found to be closely related to the oncogene bek. Products from these genes were membrane-bound when their cDNAs were transiently expressed in COS cells, whereas products from the regions coding extracellular domains were free of membrane attachment and found in the culture medium.

Production, purification and characterization of biologically active recombinant human nerve growth factor

The human NGF gene was isolated and inserted downstream from murine leukemia virus LTR in a plasmid having dihydrofolate reductase cDNA. The expression plasmid was introduced into CHO cells. Selection of the transformants for the resistance to methotrexate gave a CHO cell line which produced human NGF at a level of 4 mg/L in the culture medium. The recombinant human NGF was purified to near homogeneity from the culture supernatant. The NH2-terminal amino acid sequence, the COOH-terminal amino acid (Ala), and the amino acid composition of the human NGF were identical to those deduced from the nucleotide sequence of the human NGF gene. The recombinant human NGF was composed of 120 amino acid residues. Three disulfide linkages were determined to be Cys15-Cys80, Cys-58-Cys108, and Cys68-Cys110; the locations were identical to those in the mouse 2.5S NGF molecule. The specific biological activity of the recombinant human NGF was comparable with that of authentic mouse 2.5S NGF as determined by stimulation of neurite outgrowth from PC12 cells.

Transformation of mouse BALB/c 3T3 cells with human basic fibroblast growth factor cDNA

The expression of human basic fibroblast growth factor (bFGF) cDNA in mouse BALB/c 3T3 clone A31 cells induced morphological transformation. These transformed cells grew well and reached more than a sixfold-higher saturation density than parental A31 cells even in serum-free medium. They were able to form colonies in soft agar. The phenotypic alteration in the transformed cells was reversed by the addition of anti-human bFGF antibodies to the medium. These results suggest that the cellular transformation mediated by bFGF is caused by autocrine stimulation with secreted bFGF molecules.

Transformation of mouse BALB/c 3T3 cells with human basic fibroblast growth factor cDNA

The expression of human basic fibroblast growth factor (bFGF) cDNA in mouse BALB/c 3T3 clone A31 cells induced morphological transformation. These transformed cells grew well and reached more than a sixfold-higher saturation density than parental A31 cells even in serum-free medium. They were able to form colonies in soft agar. The phenotypic alteration in the transformed cells was reversed by the addition of anti-human bFGF antibodies to the medium. These results suggest that the cellular transformation mediated by bFGF is caused by autocrine stimulation with secreted bFGF molecules.