Novel betacellulin derivatives. Separation of the differentiation activity from the mitogenic activity

Betacellulin (BTC) is a member of the epidermal growth factor family. It has two biological activities: mitogenic activity in fibroblasts and vascular smooth muscle cells, and differentiation activity for the differentiation of pancreatic acinar AR42J cells into insulin-secreting cells. The previous finding that recombinant BTC promotes the neogenesis of beta-cells in a mouse model supports the possibility that BTC is a therapeutic protein. However, the mitogenic activity of BTC may not be needed for differentiation into beta-cells and may cause a side effect in clinical use. We prepared several derivatives of BTC to segregate the two activities, to decrease the mitogenic activity, and to maintain the differentiation activity. We succeeded in obtaining BTC derivatives segregated by the two biological activities by preparing truncated-type derivatives. A derivative of BTC, BTC24-76, with a truncated N-terminal 23 amino acids and C-terminal 4 amino acids, was 2.5-fold more active in differentiation and had one-tenth of the mitogenic activity. The derivatives described in the present study should be helpful in future applications as therapeutic proteins and in basic research for discovery of a BTC-specific receptor.

Immunohistochemical localization of Betacellulin, a member of epidermal growth factor family, in atherosclerotic plaques of human aorta

Betacellulin (BTC), a new member of the EGF family, has been reported to be a potent mitogen for rat vascular smooth muscle cells (SMCs). BTC mRNA is known to be expressed in several human organs. However, the localization of BTC in human vascular tissues has not yet been clarified. We investigated whether or not BTC protein is involved in the pathogenesis of human atherosclerosis. Recombinant human BTC showed a mitogenic activity on cultured human aortic SMCs by measuring [3H]thymidine incorporation. The immunohistochemical localization of BTC, SMCs, macrophages, EGF receptors and ErbB4 was examined in autopsied human aortas. BTC was detected in both intimal and medial SMCs of the aortic wall. The percentage of BTC-positive medial SMCs in early types of atherosclerotic lesions decreased with age, but in adult, it was significantly higher in advanced types than in early types of atherosclerotic lesions. BTC-positive SMCs were predominantly localized in the medial side of the intima. Furthermore, numerous BTC-positive SMCs and macrophages were observed around the core lesion of atherosclerotic plaques. Receptors for BTC, EGF receptor and ErbB4, were expressed on SMCs, suggesting that BTC is associated with EGF receptor family-mediated signaling. BTC is produced in human aortic tissue and might play important roles in atherogenesis.

Recombinant human betacellulin promotes the neogenesis of beta-cells and ameliorates glucose intolerance in mice with diabetes induced by selective alloxan perfusion

Betacellulin (BTC), a member of the epidermal growth factor family, is expressed predominantly in the human pancreas and induces the differentiation of a pancreatic acinar cell line (AR42J) into insulin-secreting cells, suggesting that BTC has a physiologically important role in the endocrine pancreas. In this study, we examined the in vivo effect of recombinant human BTC (rhBTC) on glucose intolerance and pancreatic morphology using a new mouse model with glucose intolerance induced by selective alloxan perfusion. RhBTC (1 microg/g body wt) or saline was injected subcutaneously every day from the day after alloxan treatment. The intraperitoneal glucose tolerance test revealed no difference between rhBTC-treated and rhBTC-untreated glucose-intolerant mice at 2-4 weeks. However, glucose tolerance was significantly improved and body weight was significantly increased in rhBTC-treated mice compared with untreated mice at 8 weeks. Islet-like cell clusters, consisting mainly of beta-cells, were increased in the pancreas and were localized in contact with the ductal lining cells and sometimes with acinar cells. In conclusion, administration of rhBTC improved glucose tolerance in this mouse model by increasing beta-cell volume, primarily through accelerated neogenesis from ductal lining cells.

Molecular cloning and expression of rat betacellulin cDNA

The cDNA encoding an entire open reading frame of rat betacellulin has been cloned from rat kidney. Expression of this cDNA in COS7 cells showed a significant amount of mitogenic activity in the culture media. Western blotting of the cell lysates suggested that the membrane-anchored precursor was cleaved to release its ectodomain very efficiently.

Immunohistochemical localization of betacellulin, a new member of the EGF family, in normal human pancreas and islet tumor cells

Betacellulin (BTC) purified from mouse beta cell tumor (betaTC-3) is a new member of the epidermal growth factor (EGF) family which can bind receptor tyrosine kinase, EGF receptor (erbB1) and erbB4. It has been demonstrated that proBTC mRNA was abundantly expressed in human pancreas tissue, and that BTC converted amylase-secreting rat acinar cell line (AR42J) into insulin-secreting cells, suggesting that BTC might be important for the growth and/or differentiation of islet cells. However, the cell type producing BTC in the pancreas has not been clarified. In this study, we examined the localization of BTC in human pancreas and islet cell tumors. Immunohistochemistry using specific antibodies to human BTC revealed that this protein was produced in alpha cells and duct cells, and probably in beta cells in normal adult pancreas. Furthermore, strong immunoreactivity to BTC was detected in primitive duct cells of the fetal pancreas, and both insulinoma and glucagonoma cells also showed positive immunoreactivity to BTC. EGF receptor (erbB1) and erbB4 were expressed mainly in islet and duct cells, and duct cells, respectively. These results demonstrate the localization of BTC and its receptors, and suggest that BTC may be one of the factors that have physiologically important roles such as growth and differentiation of islet cells in the human pancreas.

Processing and juxtacrine activity of membrane-anchored betacellulin

Betacellulin (BTC) was originally isolated as a secreted growth factor from a mouse pancreatic beta-tumor cell line, whereas the cDNA sequence predicts that BTC is synthesized as a larger transmembrane protein. In the present study, we have characterized the membrane-anchored forms of BTC, using Chinese hamster ovary (CHO) cells, mouse fibroblast A9 cells, and a human breast cancer cell line MCF-7, all of which were stably transfected with human BTC cDNA. A9 and MCF-7 transfectants produced membrane-anchored BTC isoforms of 21, 25, 29, and 40 kDa on the cell surface, as well as a secreted BTC isoform. CHO transfectants secreted little BTC but accumulated the membrane-anchored isoforms. The cleavage of the membrane-anchored forms to release a secreted from of BTC was not enhanced by biological mediators such as a phorbol ester, which stimulates the cleavage of other membrane-anchored growth factors. The membrane-anchored forms of BTC expressed on the transfected cells induced the insulin production and/or promoted the growth in subclones of AR42J rat pancreatic cells. These results suggest that the membrane-anchored BTC can function as a juxtacrine factor in regulating the growth and differentiation of pancreatic endocrine cells.

BALB/c 3T3 cells co-expressing FGF-2 and soluble FGF receptor acquire tumorigenicity

The physiological significance of the soluble fibroblast growth factor (FGF) receptors is not clear yet although they are present in blood, vitreous fluid and in the extracellular matrix of vascular endothelial cells. A hypothesis that they might help FGF-2 release from cells is very interesting because FGF-2 does not have clear secretion signal and the mechanism of the secretion of FGF-2 is still unclear. Single overexpression of FGF-2 is related neither to the secretion potential of the molecule nor to the tumorigenicity of the cells. In this report, BALB/c 3T3 cells transformed with the full length of human FGF-2 cDNA are further transformed with the cDNA coding the extracellular domain of human FGF receptor 1. The obtained transformants co-expressing FGF-2 and soluble FGF receptor are highly tumorigenic in nude mice, while the parental cells do not show any tumorigenicity. In the conditioned medium of the double-transformants, FGF-2 is immunologically detected. These results suggest that naturally produced soluble form of FGF receptor supports the release of FGF-2 from the cells and that over-expression of these two molecules leads to induce the malignant tumours in vivo.

Protective effect of transfection with secretable superoxide dismutase (SOD) (a signal sequence-SOD fusion protein coding cDNA) expression vector on superoxide anion-induced cytotoxicity in vitro

For ex vivo gene therapy, superoxide dismutase (SOD) must be secreted into the extracellular space and delivered to damaged cells. Recombinant DNA technique can be used to produce a secretory protein that is fused to a non-secretory protein and a signal peptide of another secretory protein gene. We constructed a secretable SOD eukaryotic expression vector which expresses human SOD cDNA by fusing it to the signal peptide DNA sequence of the human interleukin-2 (IL-2) gene. The ILSOD cDNA constructed by PCR-based gene expression was ligated into the multicloning site of the pRc/CMV plasmid (pRc/CMV-ILSOD). Rat lung epithelial like cells (L2 cells) were transfected with pRc/CMV-ILSOD by lipofection. The extracellular SOD activity of ILSOD-L2 cells (transfected cells with pRc/CMV-ILSOD) was 3 times as high as that of host cells. We used the xanthin (X)/xanthin oxidase (XO) system to produce superoxide anions at the extracellular space. We initially investigated the direct cytotoxicity of superoxide anions upon cells. Host and ILSOD-L2 cells were killed by using X/XO, although the sensitivity of the ILSOD-L2 cells to X/XO induced cytotoxicity was significantly decreased compared with that of host cells. The production of lipid peroxidated substances in the host in the presence of X/XO increased to about twice the control (absence of X/XO) level. However, that of ILSOD-L2 cells did not change in the presence of X/XO. Therefore, ILSOD-L2 cells were resistant to X/XO induced lipid peroxidation. These findings indicated that ILSOD gene transfection protected against direct oxidant stress by X/XO. We then investigated the effect of extracellular SOD secreted from ILSOD-L2 cells on extracellular superoxide anion induced cytotoxicity in normal cells. The conditioned media of host cells had no significant effect upon X/XO induced cytotoxicity. However, the conditioned media of ILSOD-L2 cells protected against X/XO induced cytotoxicity. Furthermore, the conditioned medium of ILSOD-L2 cells was more effective than that of host cells against the production of lipid peroxidated substances by normal cells under conditions of oxidative stress. These results indicated that non-secretable protein could be delivered to target cells by means of DNA engineering. This strategy could thus provide an ex vivo means of applying gene therapy using non-secretable proteins.

Human betacellulin, a member of the EGF family dominantly expressed in pancreas and small intestine, is fully active in a monomeric form

Betacellulin (BTC) was found to be expressed mainly in human pancreas and small intestine. This finding suggests that BTC possesses some specific function distinguished from the other members of epidermal growth factor (EGF) family. To clarify this function, the released form of human BTC has been expressed in E.coli, purified, and characterized. The recombinant human BTC was produced as an inclusion body. This material was dissolved in guanidine-HCl under reducing conditions, refolded, and purified through sequential liquid chromatography. Purified BTC was electrophoresed under reducing conditions and a molecular size of 18 kDa was determined, which is the supposed size of a dimer of the peptide. However, chemical analysis failed to show a covalently linked dimer. The molecular mass of BTC analyzed by mass spectrometry revealed it to be 9 kDa, which is consistent with theoretical value for a monomer. Recombinant BTC showed growth promoting activity for mouse fibroblasts and rat aortic smooth muscle cells which was equivalent to EGF On the other hand, BTC was found to exhibit a growth inhibitory effect on the cells overexpressing EGF receptor.

A human monoclonal antibody to a human self-antigen, CD2 derived from human peripheral blood lymphocytes engrafted in SCID mice

To establish human hybridoma lines, production of human immunoglobulin (Ig) and behavior of the implanted human peripheral blood lymphocytes (PBL) were characterized in severe combined immunodeficiency (SCID) mice. Human PBL from healthy donors were injected into the peritoneal cavity of SCID mice, and they were immunized with self-antigen, CD2. CD45+ cells (human PBL) migrated to lymphoid tissues in the mice as early as 4 days, accounting for more than half the lymph node cells and thymocytes. The number of cells releasing human IgG specific to the antigen increased 3.5 weeks after immunization without the usual constraint that production of the IgG, an autoantibody, is prohibited by immunological tolerance in humans. Therefore, we established several human hybridomas secreting human IgG to CD2, since splenocytes and lymph node cells from the implanted SCID mice at 3.5 weeks were fused with a human B lymphoblastoid cell line. A human anti-CD2 monoclonal antibody (MAb) was confirmed to bind to natural CD2 on human T cells by flow cytometric analysis. The epitope for the MAb was identical with a portion that the ligand LFA-3 binded, so that the MAb might reduce the inflammatory reaction caused by preventing activation of human T cells. Here, we report that the human immune system could be reconstituted in SCID mice to develop human hybridomas producing human MAb to a human self-antigen.

Nitric oxide mediates cytotoxicity and basic fibroblast growth factor release in cultured vascular smooth muscle cells. A possible mechanism of neovascularization in atherosclerotic plaques

To define the pathophysiological role of nitric oxide (NO) released from vascular smooth muscle cells (VSMC), we examined whether NO released from VSMC induces cytotoxicity in VSMC themselves and adjacent endothelial cells (EC) using a coculture system. Prolonged incubation with interleukin-1 (IL-1) induced large amounts of NO release and cytotoxicity in VSMC. NG-Monomethyl-L-arginine, an inhibitor of NO synthesis, inhibited both NO release and cytotoxicity induced by IL-1. In contrast, DNA synthesis in cocultured EC was not inhibited but rather stimulated by prolonged incubation with IL-1 or sodium nitroprusside (SNP), a NO donor. However, IL-1 and SNP did not stimulate but inhibited DNA synthesis in EC alone. On the other hand, conditioned medium from VSMC incubated for a long period with IL-1 or SNP stimulated DNA synthesis in EC alone. Furthermore, the concentration of basic fibroblast growth factor in the conditioned medium was increased and correlated with the degree of cytotoxicity in VSMC. These results indicate that NO released from VSMC induces VSMC death, which results in release of basic fibroblast growth factor, which then stimulates adjacent EC proliferation. Thus, NO released from VSMC may participate in the mechanism of neovascularization in atherosclerotic plaques.

Recombinant human betacellulin. Molecular structure, biological activities, and receptor interaction

Soluble forms of human betacellulin (BTC) were purified to homogeneity from the conditioned medium of mouse A9 cells transfected with the BTC precursor cDNA. Three types of soluble BTC, designated BTC-1a, BTC-1b and BTC-2, were resolved by cation-exchange and size-exclusion column chromatography. Physicochemical analysis has revealed that BTC-1a represents the glycosylated, intact molecule composed of 80 amino acid residues (Asp32 to Tyr111 of the precursor molecule). BTC-1b appears to be a truncated molecule lacking 12 amino acid residues from the amino terminus of BTC-1a. BTC-2 was found to be a 50-amino acid molecule (Arg62 to Tyr111) that corresponds to the epidermal growth factor (EGF) structural unit. The biological activities of these BTC molecules were essentially identical as judged by their mitogenicity on Balb/c 3T3 fibroblasts. BTC and EGF were equipotent in stimulating Balb/c 3T3 cell proliferation and rat mesangial cell Ca2+ mobilization as well as in inhibiting the growth of human epidermoid carcinoma A431 cells. BTC and EGF antagonized each other with similar dose dependence for binding to A431 cells, indicating that these factors bind the same receptor molecules with equivalent avidity. The Kd value of EGF receptor (EGFR) and BTC is 0.5 nM as determined on Balb/c 3T3 cells. In addition, human mammary carcinoma MDA-MB-453 cells, which express multiple members of the EGFR family, were found to possess 2.7 x 10(3) BTC binding sites/cell, and the binding was readily quenched by EGF. These results suggest that the primary receptor for BTC is EGFR.

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.

Antagonism of the human thromboxane A2 receptor by an anti-asthmatic agent AA-2414

The human thromboxane A2 receptor (TXA2-R)-coding gene was introduced into Chinese hamster ovary cells and a cell line (TCHO-25) stably expressing TXA2-R, at a level of 3 x 10(5)/cell, was obtained. An anti-asthmatic agent AA-2414 [(+-)-7-(3,5,6-trimethyl-1,4-benzoquinon-2-yl)-7- phenylheptanoic acid] competitively inhibited the specific binding of a TXA2 mimic ([3H]U-46619) to the TCHO-25 cells, with an IC50 of 6.0 x 10(-8) M, indicating that the drug is an antagonist of human TXA2-R. The TCHO-25 cells offer a tool for the screening and characterization of human TXA2-R antagonists.

Monoclonal antibodies against hst-1 gene product

Four monoclonal antibodies (MAbs) against the hst-1 gene product (hst-1 protein) were obtained by a somatic cell hybridization technique. The recognition sites of these MAbs designated HS-131, HS-210, HS-233 and HS-276 on the hst-1 protein were evaluated by competitive binding assay with synthetic polypeptides. HS-131 MAb and HS-276 MAb recognize the epitope located within the 59-73 and the 197-206 amino acid sequences, respectively. The epitopes recognized by HS-210 and HS-233 MAbs could not be determined, but these MAbs showed neutralizing activity against hst-1 protein. Using HS-131 and HS-233 MAbs, a sensitive sandwich enzyme immunoassay (sandwich EIA) has been developed. The assay sensitivity was 1.2-2.5 pg/well of hst-1 protein. Acidic and basic fibroblast growth factors were not cross-reactive up to a concentration of 1 microgram/ml.

[Betacellulin: a new growth factor for vascular smooth muscle cells]

Betacellulin, a new member of the epidermal growth factor family, has been purified from the conditioned media of mouse pancreatic beta tumor cells. Purified betacellulin is a single chain glycoprotein with a molecular weight of approximately 32K. This factor is a potent mitogen for retinal pigment epithelial cells and vascular smooth muscle cells. Molecular cloning of the mouse and human cDNAs reveals that the mature form of this factor, composed of 80 amino acid residues, appears to be processed from a larger transmembrane precursor by proteolytic cleavage. Seventy nine % amino acid similarity is present between mouse and human precursor proteins. The carboxyl-terminal domains of both mouse and human betacellulins have a 50% sequence similarity with that of rat transforming growth factor alpha. The betacellulin gene is found to be expressed in several mouse tissues, including kidney, liver and pancreatic beta cells.

Monoclonal antibodies against human neurotrophin-3

Hybridomas producing monoclonal antibodies (MoAbs) against human neurotrophin-3 (hNT-3) were established using recombinant hNT-3 produced in CHO cells and E. coli as immunogens. Of the five MoAbs obtained, MoAb 3w3 showed the highest antibody titer and also best neutralized NT-3 activity as measured by the survival of chick embryonic day-8 dorsal root ganglia neurons. A sandwich enzyme immunoassay (EIA) for NT-3 was established with solid phase MoAb 3W3 and the Fab' fragment of MoAb 3W3 conjugated to horseradish peroxidase. The detection limit was 2.7 pg/well of NT-3 and no cross-reactivity with nerve growth factor up to 100 ng/well was observed. Using this EIA system we have screened a variety of cell lines for NT-3 production. Among these tested, only human Burkitt's lymphoma Namalwa cells were found to be producing NT-3.

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.

Betacellulin: a mitogen from pancreatic beta cell tumors

Betacellulin, a member of the epidermal growth factor family, has been identified in the conditioned medium of cell lines derived from mouse pancreatic beta cell tumors. Betacellulin is a 32-kilodalton glycoprotein that appears to be processed from a larger transmembrane precursor by proteolytic cleavage. The carboxyl-terminal domain of betacellulin has 50 percent sequence similarity with that of rat transforming growth factor alpha. Betacellulin is a potent mitogen for retinal pigment epithelial cells and vascular smooth muscle cells.

Cloning and expression of cDNA encoding human betacellulin, a new member of the EGF family

Betacellulin (BTC) is a novel growth factor purified from the conditioned media of mouse pancreatic beta tumor cells and has been found to be a new member of the epidermal growth factor (EGF) family. The cDNA encoding human BTC has been cloned from a cDNA library prepared from human breast adenocarcinoma cell line MCF-7. The nucleotide sequence encodes a polypeptide which consists of 178 amino acid residues including a putative signal sequence, indicating that the structural organization of human BTC is similar to that of mouse BTC. The amino acid sequence of the human BTC precursor protein exhibits 79% similarity with that of the mouse precursor protein. The BTC gene was found to be expressed in several mouse tissues including kidney and liver as well as in a mouse beta tumor cell line and MCF-7 cells, suggesting that BTC might play a physiological role in normal tissues.

Novel secretory heparin-binding factors from human glioma cells (glia-activating factors) involved in glial cell growth. Purification and biological properties

Growth factors for rat primary glial cells were identified in conditioned medium of a human glioma-derived cell line. The factors, designated glia-activating factors (GAFs), were purified to homogeneity by a combination of heparin affinity chromatography, gel filtration, and high performance liquid chromatography on a heparin affinity column and a C4 reversed-phase column. GAFs could be resolved into three peaks by C4 column chromatography. The M(r) values of these three proteins were estimated to be 30,000, 29,000, and 25,000 on sodium dodecyl sulfate-polyacrylamide gel electrophoresis under reducing conditions. These M(r) values were in good agreement with the value of 26,000 +/- 3,000 estimated from the elution volume upon gel filtration chromatography under nondenaturing conditions. These data suggested that each of the GAFs consists of a single polypeptide chain and has no subunit structures. These three purified GAFs had almost the same growth-stimulating effect on glial cells in vitro, and the half-maximal dose was around 10(-11) M. Concanavalin A staining and glycopeptide N-glycosidase treatment of GAFs indicated that an asparagine-linked oligosaccharide chain(s) was attached to these three kinds of GAFs. Microsequencing of each GAF revealed a single amino-terminal sequence with no significant homology to any known protein, and the amino-terminal sequence of the 30-kDa GAF included that of the 29-kDa GAF. GAFs also stimulated the cell growth of oligodendrocyte type 2 astrocyte progenitor cells, BALB/c3T3 fibroblasts, and PC-12 cells but not that of human umbilical vein endothelial cells.

Identification of the functional regulatory region of the neurotrophin-3 gene promoter

The 5'-flanking region of the human neurotrophin-3 (NT-3) gene was isolated from a human placental genomic library using the oligonucleotide corresponding to the 5'-noncoding region of the NT-3 cDNA as a probe. A 3.8 kbp genomic fragment containing the 5'-flanking region, the first exon and a portion of the first intron was isolated and sequenced. The transcriptional initiation site, identified by S1 nuclease mapping, was located 27 bp downstream from the TATA-like sequence. Several plasmids, in which the NT-3 promoter regions were fused to the chloramphenicol acetyltransferase (CAT) gene, were constructed. Transient expression in human glioma Hs683 cells demonstrated that a fragment of about 0.1 kbp from the transcriptional initiation site was sufficient for promoter activity. While, in human plasma cell leukemia ARH77 cells, in which NT-3 mRNA was not detected, the region upstream from -65 functioned to silence CAT activity. It is suggested that this region contains the transcriptional regulatory element for the specific expression of the NT-3 gene.

Suppression of solid tumor growth by immunoneutralizing monoclonal antibody against human basic fibroblast growth factor

Basic fibroblast growth factor (bFGF) is a potent angiogenic mitogen. To elucidate the effect of bFGF inhibitors in vivo, anti-bFGF immunoneutralizing monoclonal antibody was prepared. One monoclonal antibody against human bFGF, obtained by cell fusion and designated 3H3, completely inhibited bFGF-induced proliferation of human umbilical vein endothelial cells at a concentration of 100 ng/ml. 3H3 did not bind to acidic fibroblast growth factor or HST1 protein, indicating high specificity for bFGF. Furthermore, the immunoneutralizing activity of 3H3 was examined in vivo. K1000 cells (a BALB/c 3T3 transformant in which the leader sequence-fused bFGF gene was transfected) were transplanted s.c. into BALB/c nude mice. Growth of the tumor cells was inhibited by i.v. treatment with 3H3 at a concentration of 200 micrograms/mouse. Histological observation showed that the antitumor effect of 3H3 was due to the inhibition of bFGF-induced angiogenesis. This experiment provides direct causal evidence for the hypothesis that tumor growth is angiogenesis dependent. This finding could also have implications for the development of novel therapeutic approaches to angiogenic solid tumors.

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.

Improvement in the antibody productivity of human-human hybridomas by transfection with Tac gene

The presence of a highly purified recombinant interleukin-2 (rIL-2) increased the production of immunoglobulin (IgM or IgG) by human-human hybridomas to 1.5-2.0 times the production by untreated cells. However, these cells did not react with anti-Tac (IL-2 receptor alpha) antibody. To enhance the response of the hybridoma cells to rIL-2, Tac gene was introduced by co-transfection with Tac gene expression plasmid pTB459 and G418 resistant gene expression plasmid pRSVneo. Tac cDNA transfected hybridoma (HBW-4.16.459-6-126) was induced to produce 6 times as much IgG by rIL-2 as was the control. This antibody production promoting phenomenon mediated by rIL-2 was depressed by anti-Tac antibody.

Molecular characterization of recombinant human acidic fibroblast growth factor produced in E. coli: comparative studies with human basic fibroblast growth factor

Synthetic cDNA coding for human acidic fibroblast growth factor (haFGF) was expressed in E. coli under the control of the T7 promoter. The haFGF produced was purified extensively using heparin-Sepharose and phenyl-Sepharose columns. The mitogenic activity of haFGF on 3T3 and endothelial cells was significantly potentiated in the presence of heparin (10-50 micrograms/ml), while angiogenic activity was observed on chick embryo chorioallantoic membrane without exogenously added heparin. This significant potentiation of mitogenic activity was observed specifically with haFGF, not human basic fibroblast growth factor (hbFGF). Circular dichroism spectra of haFGF was not affected by the presence of heparin. The affinity of haFGF for heparin was examined using heparin affinity HPLC and was precisely confirmed to be relatively lower than that of hbFGF. These results implied that haFGF was potentiated by heparin and that this potentiation did not involve a significant change in the conformation of the haFGF molecule. The affinity of haFGF for copper was also confirmed to be higher than that of hbFGF using a copper affinity HPLC column. In addition, under acidic conditions, haFGF appeared more stable than hbFGF and was further stabilized in the presence of heparin.

Carboxyl-terminal structure of basic fibroblast growth factor significantly contributes to its affinity for heparin

The carboxyl-terminal sequence of basic fibroblast growth factor (bFGF) is rich in basic amino acid residues, a common characteristic amongst fibroblast growth factors, and is considered to contribute greatly to the binding to negatively charged extracellular matrixes such as heparin. To study the relationship between the affinity for heparin and the carboxyl-terminal structure of bFGF, amino- or carboxyl-terminal truncated molecules were produced in Escherichia coli using recombinant DNA techniques. These terminally truncated bFGFs were applied to a heparin-affinity HPLC column. Truncation of more than six amino acid residues from the carboxyl-terminal made the bFGF produced in E. coli markedly difficult to solubilize and weakened its affinity for heparin, though bFGF having up to 46 amino acids removed showed significant stimulation of the DNA synthesis of BALB/c3T3 cells. This stimulation of the DNA synthesis was also recognized by the bFGF having 40 amino acids removed from its amino-terminal, while the affinity of this peptide for heparin has been shown to be equal to that of the mature bFGF (146 amino acids). These results show that the affinity of bFGF for heparin depends significantly on its carboxyl-terminal structure and that the essential part for receptor binding is present between Asp41 and Ser100. Moreover, it suggests that the Phe139Leu140Pro141, present in all members of the FGF family, contributes greatly to the stable structure of the intact molecule.

Monoclonal antibodies against human basic fibroblast growth factor

Recombinant human basic fibroblast growth factor (hbFGF) was used as an antigen to develop, by a somatic cell fusion technique, four monoclonal antibodies (MAbs), that recognize the complete and amino-terminal truncated form of hbFGF. Isotype identification showed that MAbs designated MAb12 and MAb98 were IgG1; and those designated MAb52 and MAb78 were IgG2b. All these MAbs bound the complete form of hbFGF produced in E.coli. Competition with synthetic polypeptides, a replication of 1-9 aa and of 141-146 aa of hbFGF, and truncated forms of hbFGF by 13 and 40 amino acid residues in its amino-terminal produced in E. coli by recombinant technique, revealed at least two epitopes recognized by the four IgG type MAbs. MAb12 and MAb78 recognized the epitope located within the first 9 amino acid residues at the amino terminal of the complete hbFGF. MAb52 and MAb98 recognized the one located between the amino acid residue no. 14 and 40. None of MAbs bound bovine acidic FGF (aFGF). Using MAb52 or MAb98 and MAb78, a two-site EIA has been developed. This EIA is sensitive enough to detect 0.5 ng/ml of hbFGF. Furthermore, MAb78 was used as a ligand for affinity chromatography to purify hbFGF mutein CS4, which binds weakly to a heparin affinity column.

Secretion of human EGF and IgE in mammalian cells by recombinant DNA techniques; use of a IL-2 leader sequence

Expression plasmids were constructed containing chemically synthesized human epidermal growth factor (EGF) gene fused in a frame to a leader sequence of human interleukin-2 (IL-2) gene under the control of a viral promoter. COS7 cells transfected with the plasmids synthesized and secreted EGF. Transfection of mouse A9 cells or BALB/3T3 clone A31 cells with the plasmids permitted the isolation of cell lines secreting the product which showed EGF activity. In particular, A31 transformed cells secreting human EGF grew well even in a medium containing a minimal level of serum. Using similar vectors having IgE cDNA (C2-C4) in place of EGF gene, a human IgE Fc fragment was also produced and secreted in mouse cells. These results show that heterologous leader sequences are useful for the expression and secretion of proteins whose genes lack leader sequences.

Stabilizing basic fibroblast growth factor using protein engineering

Using site directed mutagenesis, each of the four cysteines present at amino acid residues 26, 70, 88, and 93 of the mature protein of human basic fibroblast growth factor (bFGF) was individually changed to serine. The biological activity and heparin binding ability was retained when the serine was substituted for the cysteine residue at either 70 or 88 of the bFGF protein. This finding indicates that the cysteines at these positions are not essential for expressing biological activity. The substitution of the residues at these positions, especially at position 88, reduced the heterogeneity recognized as several peaks of bFGF eluted from a heparin affinity column, even after oxidation with hydrogen peroxide, suggesting that the cysteines at these positions are exposed to the surface of the molecule to form disulfide bonds that induce heterologous conformations. Furthermore, under acidic conditions, these modified bFGFs are revealed to be more stable in maintaining their activity. These facts suggest that this protein has been successfully modified by protein engineering.

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.

Expression of cDNA encoding human basic fibroblast growth factor in E. coli

The cDNA encoding human basic fibroblast growth factor was expressed in E. coli under the control of trp promoter. Bacterially synthesized hbFGF was highly purified using a heparin affinity HPLC column. By this chromatography, hbFGF was eluted as four distinct forms, which were indistinguishable by SDS polyacrylamide gel electrophoresis, amino acid composition, and partial terminal sequence analysis. These molecules stimulated the growth of fibroblasts and endothelial cells although their specific activities varied. The angiogenesis activity of these molecules was also confirmed.

The establishment of IL-2 producing cells by genetic engineering

Expression plasmids containing human interleukin-2(IL-2) cDNA under the control of viral promoters (SV40 early region, MuLV LTR, HTLV-I LTR, and ASV (Y73) LTR) were introduced into TK- mouse L cells and human FL cells to establish IL-2 producing cells. The highest levels of IL-2 producing clones were obtained in TK+ mouse L cells transformed with a recombinant plasmid having MuLV LTR as a promoter, whereas transformed cells of human FL cells (G418r) were revealed to produce IL-2 at the highest level when the cells were transfected with a plasmid containing HTLV LTR as a promoter. These results suggest that these promoter/enhancer regions possess different cell specificities in gene expression. To obtain higher levels of IL-2 production using gene amplification, the hybrid plasmids containing the hamster DHFR and human IL-2 genes were constructed and transfected into DHFR- CHO cells. DHFR+ colonies produced IL-2 at about the same level as that produced by TK+ L cells transformed with the recombinants containing MuLV LTR. Selection of methotrexate-resistant cells resulted in a 5- to 30-fold increase of IL-2 production. These cells produced IL-2 stably for at least 3 months, even in the absence of methotrexate.

Cloning and expression of cDNA encoding human basic fibroblast growth factor

A cDNA encoding human basic fibroblast growth factor (bFGF) was isolated from a human foreskin fibroblast cDNA library. The cDNA, 4 kilobases in size, had a coding sequence, 5' and 3' untranslated regions, and a poly(A) chain. Isolation of additional cDNA clones that had a short 3' untranslated region suggested the presence of multiple mRNA forms. By Northern blot analysis, at least five bFGF mRNA species were detected in cultured fibroblast cells. Transfection of the cDNA to COS cells resulted in the detection of mitogenic activity in the culture medium of the transfected cells, suggesting that a part of the synthesized protein might be secreted from cells despite its unusual short signal sequence.

Establishment of hybridomas secreting monoclonal antibodies against C epsilon 2 and C epsilon 4 domains of human IgE

Three kinds of hybridomas secreting monoclonal antibodies (MAbs) against the epsilon chain of human IgE were constructed by somatic cell hybridization between mouse myeloma P3U1 cells and spleen cells from BALB/c mice immunized with human IgE purified from the culture supernatant of U-266 cells. These MAbs were used effectively for the purification and determination of human IgE. The recognition site in the IgE molecule of each antibody was examined by using various epsilon chain fragment peptides produced in Escherichia coli. From these experiments, it was suggested that one recognized C epsilon 2 and the second C epsilon 4. The third did not recognize the C epsilon 1-C epsilon 4 domains of the recombinant epsilon chain from E. coli, although it bound to the epsilon chain of natural human IgE.

Direct expression of hepatitis B surface antigen gene in E. coli

A 809 bp Sau 3A - Hpa I fragment containing a complete HBsAg gene and fragments 744 bp Hinc II - Hpa I and 712 bp Xba I - Hpa I containing a truncated HBsAg gene lacking the sequence encoding the NH2-terminal hydrophobic domain were prepared from a composite plasmid pHBV933 containing the 3.2 kb Eco RI DNA fragment of the entire HBV/adw genome and inserted into an expression vector pTRP801 to give plasmids pTRP SS-6, pTRP SS-39, and pTRP SS-50, respectively. The growth of a recombinant having pTRP SS-6 was greatly inhibited and the transformant expressed a low level of HBsAg, which is reactive to human anti-HBsAg antibody. Interestingly, the growth of transformants harbouring pTRP SS-39 and pTRP SS-50 was not inhibited and these transformants expressed a considerable level of the HBsAg. Minicells harbouring pTRP SS-6, pTRP SS-39, and pTRP SS-50 formed specific polypeptides of about 24 K, 23 K, and 22 K daltons, respectively.

Expression of human immunoglobulin E epsilon chain cDNA in E. coli

Using the cDNA of human epsilon chain, three expression plasmids that code directly the constant portion of the epsilon chain (C epsilon 1-C epsilon 4, C epsilon 2-C epsilon 4 and C epsilon 3-C epsilon 4 domains) were constructed. These epsilon chain peptides were synthesized in E. coli under the control of the trp promoter-operator. The bacterially produced peptides have the antigenicity of human epsilon chain and gave the molecular weights equal to the values calculated from the amino acid sequence of the constructed plasmids.

The complete nucleotide sequences of the cloned hepatitis B virus DNA; subtype adr and adw

The complete nucleotide sequences of two different subtypes (adr and adw) of hepatitis B virus (HBV) DNA cloned in E. coli were determined. The sequence of the viral genome of the adr clone was 3188 nucleotides long, and that of the adw clone was 3200 nucleotides long. The adr and adw clones differed from the reported cloned ayw HBV DNA (3182 nucleotides long) in 11.2% and 10.0% of nucleotides, respectively. Heterogeneity of the HBV genome in the clones with the same subtype was observed.

Molecular cloning and nucleotide sequencing of human immunoglobulin epsilon chain cDNA

DNA complementary to mRNA of human immunoglobulin E heavy chain (epsilon chain) isolated and purified from U266 cells has been synthesized and inserted into the PstI site of pBR322 by G-C tailing. This recombinant plasmid was used to transform E. coli chi 1776 to screen 1445 tetracycline resistant colonies. Nine clones (pGETI - 9) containing cDNA coding for the human epsilon chain were recognized by colony hybridization and Southern blotting analysis with a nick-translated human IgE genome fragment. The nucleotide sequence of the longest cDNA contained in pGET2 was determined. The results indicate that the sequence of 1657 nucleotides codes for 494 amino acids covering a part of the variable region and all of the constant region of the human epsilon chain. Most of the amino acid sequence deduced from the nucleotide sequence is in substantial agreement with that reported. Furthermore a termination codon after the -COOH terminal amino acid marks the beginning of a 3' untranslated region of 125 nucleotides with a poly A tail. Taking this into account, the structure of the human epsilon chain mRNA, except a part of the 5' end, is conserved fairly well in the cDNA insert in pGET2.

Spontaneous production of a C-type RNA virus in a cell line derived from rat glioma

The spontaneous production of a rat C-type RNA virus (ACV) in a cultured cell line (AC cells) established from a chemically induced rat glioma was studied. The characteristics of ACV were: morphology typical of C-type RNA virus; buoyant density of 1.15 g/ml in a sucrose density gradient; RNA directed DNA polymerase activity; viral core with a density of 1.28 to 1.30 g/ml; 70S RNA with dimer structure; and structural protein composed of mainly four polypeptides. Kinetical analysis of DNA-DNA hybridization revealed that DNA sequences homologous to DNA transcripts of RNA of ACV were present in rat cells. RNA directed DNA polymerase of ACV partially cross-reacted with antiserum to the polymerase of Rauscher murine leukemia virus. These data suggest that ACV is an endogenous C-type RNA virus of rat origin.

Biochemical studies on bovine adenovirus type 3. IV. Transformation by viral DNA and DNA fragments

By the calcium technique, intact DNA of bovine adenovirus type 3 (BAV3) was found to transform A31 cells, a clone of BALB/3T3. Transforming activity was resistant to RNase and Pronase but sensitive to DNase. The efficiency of transformation was approximately 5 to 10 foci per mug of DNA. Attempts were also made to test for transforming activity of BAV3 DNA fragments prepared with restriction endonucleases EcoRI and HindIII. The activity was found to associate exclusively with the EcoRI D fragment mapped in the region of 3.6 and 19.7 units (molecular weight, 3.9 x 10(6)). No transformation could be obtained with three HindIII fragments, J, E, and B, located at the left-hand end of the BAV3 genome. However, the enzymatic joining of J and E fragments (0 to 11.9 map units) with a ligase restored the transforming activity. These results suggest that all the genetic information of BAV3 required for transformation is located in the region between 3.6 and 11.9 units on the viral genome. Some properties of A31 cells transformed by BAV3 DNA EcoRI D fragment (TrD) and the ligated DNA of HindIII J and E fragments (TrJE), as well as those transformed by whole BAV3 DNA (Tr), were examined. As compared to untransformed A31 cells, all the transformed cell lines tested showed rapid growth, high saturation densities, and anchorage-independent growth. Moreover, they contained BAV3-specific T antigen and induced tumors in adult nude and BALB/c mice. These properties of Tr, TrD, and TrJE lines were similar to those of BAV3-transformed cells.