K Weindel

Clinic for Tumor Biology Freiburg, Freiburg, Baden-Württemberg, Germany

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Publications (19)88.38 Total impact

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    ABSTRACT: Vascular endothelial growth factor (VEGF) is an angiogenic growth factor with a target-cell specificity highly restricted to vascular endothelial cells. Recombinant baculovirus were constructed for the production of two different forms of the human VEGF protein in insect cells. VEGF165 and VEGF121 proteins produced by Sf158 cells underwent a similar processing compared with mammalian cells, including efficient glycosylation, formation of a disulfide-linked dimer and secretion into the media. Only one of these forms, VEGF165 had a high affinity for heparin and this characteristic was used to purify this form to homogenicity by a two-step heparin-affinity chromatcgraphy. The biological activity of the purified 43-kDa homodimer was demonstrated by high-affinity binding to VEGF receptors, and by the induction of DNA synthesis in vascular endothelial cells. A positive angiogenic activity in vivo was demonstrated by the day-13 chorioallantoic-membrane assay. The mitogenic potency of VEGF121 for human umbilical vein endothelial cells was very similar compared to VEGF165. These results demonstrate that an angiogenic growth factor whose normal processing requires glycosylation and disulfide-bridge formation can be efficiently expressed in high concentration (up to 5 μg/ml) in insects cells.
    European Journal of Biochemistry. 03/2005; 211(1‐2):19 - 26.
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    ABSTRACT: Angiopoietin-2 (Ang-2) is a non-signal transducing ligand of the endothelial receptor tyrosine kinase Tie-2. Ang-2 is produced by endothelial cells and acts as an autocrine regulator mediating vascular destabilization by inhibiting Angiopoietin-1-mediated Tie-2 activation. To examine the transcriptional regulation of Ang-2, we studied the Ang-2 promoter in endothelial cells and nonendothelial cells. The human Ang-2 promoter contains a 585-bp region around the transcriptional start site (-109 to +476) that is sufficient to control endothelial cell-specific and cytokine-dependent Ang-2 expression. Strong repressor elements of Ang-2-promoter activity are located in the 5'-region of the promoter and in the first intron. The Ets family transcription factors Ets-1 and Elf-1 act as strong enhancers of endothelial cell Ang-2-promoter activity. Ets-binding sites -4 and -7 act as positive regulators, whereas Ets-binding site -3 acts as negative regulator. Demethylation experiments revealed that the Ang-2 gene (in contrast to the Tie-2 gene) is not controlled by imprinting. The data determine unique positive and negative regulatory mechanisms of endothelial cell Ang-2 expression and provide further evidence for the critical role of Ang-2 as a key autocrine regulator of vascular stability and responsiveness.
    Arteriosclerosis Thrombosis and Vascular Biology 11/2004; 24(10):1803-9. · 6.34 Impact Factor
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    ABSTRACT: The neu (c- erbB-2 or HER2 ) proto-oncogene which encodes a receptor protein homologous to the epidermal growth factor receptor is overexpressed in 20%-30% of human breast and ovarian cancers. Oncogenic activation of Neu can also occur through multiple molecular mechanisms, including a point mutation in the transmembrane domain, deletion of the extracellular domain and short in-frame deletions of 7-12 amino acids in the extracellular region proximal to the transmembrane domain. Because of the highly vascularized phenotype of breast and ovarian cancers and the contribution of the Neu receptor to the development and progression of these tumors, we investigated the effect of Neu on the expression of the tumor angiogenesis factor VEGF. Expression of various activated Neu receptors but not wild-type Neu in Rat-1 cells, leads to increased VEGF expression on mRNA as well as on protein level. This effect is mediated by transcriptional activation of the VEGF promoter via a cluster of Sp 1 binding sites. Molecular analysis of the activation mechanism of Sp 1 revealed that neither the VEGF promoter binding activity of Sp 1 nor the expression of Sp 1 is affected by Neu transformation of the cells. Instead, functional Neu-induced transactivation of Sp 1 was observed by using a GAL4-based transactivation assay. These results demonstrate that functional changes of the transcription factor Sp 1 mediates a Neu-signaling cascade leading to VEGF promoter activation.
    Angiogenesis 02/2004; 7(1):59-68. · 4.41 Impact Factor
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    ABSTRACT: The transmembrane tyrosine kinase TIE-2, the receptor for the angiopoietins-1 and -2, has been shown to be involved in angiogenic processes. Investigating the regulation of TIE-2 expression on endothelial cells, we found that stimulators such as PMA induce a decrease of TIE-2 protein from the cell surface without affecting TIE-2 mRNA. In conditioned media of PMA stimulated endothelial cells, a soluble form of this receptor comprising parts of the extracellular domain can be detected. Using a sandwich ELISA, we were able to detect and quantify TIE-2 receptors in cell lysates (representing the whole transmembrane receptor) and in cell culture supernatants (representing a soluble form of this receptor, sTIE-2). Several factors influencing the shedding process e.g. basic FGF could be identified. Finally, the soluble form of TIE-2 could also be detected in human biological fluids such as sera and plasma from healthy controls.
    Angiogenesis 02/2001; 4(2):123-31. · 4.41 Impact Factor
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    ABSTRACT: We have used the avian chorioallantoic membrane (CAM) to study the interaction of tumor cells with the lymphatics in vivo. The vascular endothelial growth factor-C (VEGF-C) has been shown to be lymphangiogenic. We have therefore grown VEGF-C-expressing human A375 melanoma cells on the CAM. These tumors induced numerous lymphatics at the invasive front, and compressed or destroyed VEGF receptor (R)-3-positive lymphatics were observed within the solid tumors. The lymphatics in the CAM and in the A375 melanomas could also be demonstrated with an antibody against Prox 1, a highly specific marker of lymphatic endothelial cells. Proliferation studies revealed a BrdU labeling index of 11.6% of the lymphatic endothelial cells in the tumors and at their margins. A great number of melanoma cells invaded the lymphatics. Such interactions were not observed with VEGF-C-negative Malme 3 M melanoma cells. Lymphangiogenesis was inhibited to some extent when A375 melanoma cells were transfected with cDNA encoding soluble VEGFR-3 (sflt4), and the BrdU labeling index of the lymphatics in these tumors was 3.9%. Invasion of lymphatics and growth of blood vascular capillaries were not inhibited by the transfection. Therefore, tumor-induced lymphangiogenesis seems to be dependent to some extent on VEGF-C/flt4 interactions, but invasion of lymphatics seems to be a distinct mechanism.
    Histochemie 12/2000; 114(5):373-85. · 2.61 Impact Factor
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    ABSTRACT: BACKGROUND Clinical data clearly indicate a correlation between tumor neovascularization, aggressiveness of tumor growth, and metastatic spread. One of the key factors capable of stimulating tumor angiogenesis is vascular endothelial growth factor (VEGF). Using an immunoassay for VEGF, we assessed the levels of soluble VEGF in the sera and effusions of patients with malignant and nonmalignant disease as well as in the sera of healthy controls.METHODS Using a sandwich enzyme-linked immunoadsorbent assay, the concentration of VEGF was measured in serum specimens (n = 445) and effusions (n = 56) collected from a total of 212 patients with various types of cancer, 88 patients with nonmalignant disease, and 145 healthy individuals.RESULTSLow and rather stable levels of VEGF were detected in the serum of healthy individuals (median, 294 pg/mL; range, 30–1752 pg/mL; 95th percentile, 883 pg/mL). Compared with healthy individuals, serum levels in patients with acute infections were elevated (P = 0.03), whereas patients with chronic cirrhosis had lower serum VEGF levels. Among patients with various types of neoplasia, VEGF serum levels in patients with ovarian or gastrointestinal carcinoma were significantly higher than in healthy individuals. Moreover, VEGF concentrations in sera from patients with metastatic disease were higher than in sera from patients with localized tumors. Maximum serum concentrations of VEGF (median, 1022 pg/mL; range, 349–7821 pg/mL) were found in patients with metastatic ovarian carcinoma. Median VEGF levels (and ranges) in malignant effusions were up to 10-fold higher than in matched serum samples: 5528 pg/mL (468–49269 pg/mL) in ovarian carcinoma, 885 pg/mL (77–14,337 pg/mL) in breast carcinoma, and 813 pg/mL (372–18,331 pg/mL) in gastrointestinal carcinoma. In contrast, ascitic fluid from patients with cirrhosis contained only 303 pg/mL (median, range 116–676 pg/mL) of VEGF, corresponding to the low serum levels in this patient group.CONCLUSIONS Depending on the tumor type, elevated levels of VEGF are detectable in the serum of only 0–20% of patients with localized cancer but in 11–65% of patients with metastatic cancer. Of cytology-proven malignant ascites or peritoneal exudates from various malignancies, 46–96% show VEGF levels above the upper limit (95th percentile, 676 pg/mL) of nonmalignant ascites. Maximum VEGF concentrations in malignant effusions indicate abundant local release of VEGF within the pleural or peritoneal cavity. These results suggest that VEGF might play an important role in tumor progression and the formation of malignant effusions. Further studies are warranted to determine the clinical value of soluble VEGF as a tumor marker, a prognostic factor, and a surrogate indicator of tumor angiogenesis. Cancer 1999;85:178–87. © 1999 American Cancer Society.
    Cancer 11/2000; 85(1):178 - 187. · 5.20 Impact Factor
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    ABSTRACT: We have used the avian chorioallantoic membrane (CAM) to study the interaction of tumor cells with the lymphatics in vivo. The vascular endothelial growth factor-C (VEGF-C) has been shown to be lymphangiogenic. We have therefore grown VEGF-C-expressing human A375 melanoma cells on the CAM. These tumors induced numerous lymphatics at the invasive front, and compressed or destroyed VEGF receptor (R)-3-positive lymphatics were observed within the solid tumors. The lymphatics in the CAM and in the A375 melanomas could also be demonstrated with an antibody against Prox 1, a highly specific marker of lymphatic endothelial cells. Proliferation studies revealed a BrdU labeling index of 11.6% of the lymphatic endothelial cells in the tumors and at their margins. A great number of melanoma cells invaded the lymphatics. Such interactions were not observed with VEGF-C-negative Malme 3 M melanoma cells. Lymphangiogenesis was inhibited to some extent when A375 melanoma cells were transfected with cDNA encoding soluble VEGFR-3 (sflt4), and the BrdU labeling index of the lymphatics in these tumors was 3.9%. Invasion of lymphatics and growth of blood vascular capillaries were not inhibited by the transfection. Therefore, tumor-induced lymphangiogenesis seems to be dependent to some extent on VEGF-C/flt4 interactions, but invasion of lymphatics seems to be a distinct mechanism.
    Histochemie 10/2000; 114(5):373-385. · 2.61 Impact Factor
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    ABSTRACT: Protein ligands and receptor tyrosine kinases that specifically regulate endothelial cell function are mainly involved in physiological as well as in disease-related angiogenesis. These ligand/receptor systems include the vascular endothelial growth factor (VEGF) and the angiopoietin (Ang) families, and their receptors, the VEGF receptor family and the tyrosine kinase with immunoglobulin-like and epidermal growth factor homology domains (Tie) family. In the present study, the contribution of these endothelium-specific ligand/receptor systems to tumor angiogenesis was evaluated. A375v human melanoma cells, which express at least the angiogenic growth factors VEGF, VEGF-C, and Ang-1, were stably transfected to overexpress the extracellular ligand-binding domains of the endothelium-specific receptor tyrosine kinases fms-like tyrosine kinase-1 (Flt-1), Flt-4, Tie-1, and Tie-2, respectively. In vitro proliferation and colony formation assays confirmed that expression of the extracellular receptor domains inhibited neither tumor cell mitogenesis nor the ability to produce anchorage-independent growth. Nude mouse xenografts revealed that interference with either the VEGF receptor pathway or the Tie-2 pathway resulted in a significant inhibition of tumor growth and tumor angiogenesis. In contrast, interference with the Flt-4 pathway or the Tie-1 pathway was without significant effect. Our results show that both the VEGF receptor pathway and the Tie-2 pathway are essential for A375v melanoma xenograft growth. The inhibition of the VEGF receptor pathway cannot be compensated by the Tie-2 pathway, nor vice versa. These findings suggest that the VEGF receptor pathway and the Tie-2 pathway have to be considered as two independent mediators essential for the process of in vivo angiogenesis.
    Cancer Research 08/1999; 59(13):3185-91. · 8.65 Impact Factor
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    ABSTRACT: Vascular endothelial growth factor (VEGF) is an important mediator of tumor-induced angiogenesis and represents a potential target for anticancer therapy. Therefore, we prepared a panel of monoclonal antibodies (mAb) against both the VEGF121 and VEGF165 isoforms. Three of them completely neutralized the mitogenic stimulation by VEGF of human umbilical vein endothelial cells at mAb concentrations below 0.1 microg/ml. The most potent one, with a dissociation constant (Kd) of 8 pM, inhibited, in a dose-dependent manner, VEGF-induced angiogenesis in a growth factor implant model in mice. A complete inhibition of the angiogenic response was obtained by daily intraperitoneal injections of 10 microg mAb/mouse. Angiogenesis induced by basic fibroblast growth factor was not inhibited by the mAb. Epitope mapping of the mAb, performed by competitive enzyme-linked immunosorbent assay and Western blot analysis, showed that it did not bind to the reduced and denatured monomer of VEGF. Substitutions of three residues (Q87R, G88K, Q89K), located on the major surface loop beta5 to beta6 of VEGF, resulted in the complete loss of binding (more than 400-fold reduction). The results suggest that the mAb binds primarily to a conformation-dependent epitope on the VEGF dimeric form, encompassing one of the loop regions involved in KDR receptor binding. The mAb with its strong neutralizing properties represents a useful agent for effective blocking of VEGF-mediated tumor neovascularization.
    Journal of Cancer Research and Clinical Oncology 02/1999; 125(6):336-42. · 2.91 Impact Factor
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    ABSTRACT: Clinical data clearly indicate a correlation between tumor neovascularization, aggressiveness of tumor growth, and metastatic spread. One of the key factors capable of stimulating tumor angiogenesis is vascular endothelial growth factor (VEGF). Using an immunoassay for VEGF, we assessed the levels of soluble VEGF in the sera and effusions of patients with malignant and nonmalignant disease as well as in the sera of healthy controls. Using a sandwich enzyme-linked immunoadsorbent assay, the concentration of VEGF was measured in serum specimens (n=445) and effusions (n=56) collected from a total of 212 patients with various types of cancer, 88 patients with nonmalignant disease, and 145 healthy individuals. Low and rather stable levels of VEGF were detected in the serum of healthy individuals (median, 294 pg/mL; range, 30-1752 pg/mL; 95th percentile, 883 pg/mL). Compared with healthy individuals, serum levels in patients with acute infections were elevated (P=0.03), whereas patients with chronic cirrhosis had lower serum VEGF levels. Among patients with various types of neoplasia, VEGF serum levels in patients with ovarian or gastrointestinal carcinoma were significantly higher than in healthy individuals. Moreover, VEGF concentrations in sera from patients with metastatic disease were higher than in sera from patients with localized tumors. Maximum serum concentrations of VEGF (median, 1022 pg/mL; range, 349-7821 pg/mL) were found in patients with metastatic ovarian carcinoma. Median VEGF levels (and ranges) in malignant effusions were up to 10-fold higher than in matched serum samples: 5528 pg/mL (468-49269 pg/mL) in ovarian carcinoma, 885 pg/mL (77-14,337 pg/mL) in breast carcinoma, and 813 pg/mL (372-18,331 pg/mL) in gastrointestinal carcinoma. In contrast, ascitic fluid from patients with cirrhosis contained only 303 pg/mL (median, range 116-676 pg/mL) of VEGF, corresponding to the low serum levels in this patient group. Depending on the tumor type, elevated levels of VEGF are detectable in the serum of only 0-20% of patients with localized cancer but in 11-65% of patients with metastatic cancer. Of cytology-proven malignant ascites or peritoneal exudates from various malignancies, 46-96% show VEGF levels above the upper limit (95th percentile, 676 pg/mL) of nonmalignant ascites. Maximum VEGF concentrations in malignant effusions indicate abundant local release of VEGF within the pleural or peritoneal cavity. These results suggest that VEGF might play an important role in tumor progression and the formation of malignant effusions. Further studies are warranted to determine the clinical value of soluble VEGF as a tumor marker, a prognostic factor, and a surrogate indicator of tumor angiogenesis.
    Cancer 02/1999; 85(1):178-87. · 5.20 Impact Factor
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    ABSTRACT: The growth of solid tumors and the formation of metastases are dependent on neoangiogenesis. One of the most important factors in inducing the formation of new blood vessels is the vascular endothelial growth factor (VEGF), which acts specifically on endothelial cells. VEGF is expressed and secreted by almost all solid tumors. The molecular mechanisms leading to enhanced production of this angiogenic mitogen are manyfold and have been elucidated to some degree. Two VEGF receptors, fms-like tyrosine kinase 1 (FLT-1) and KDR, have been identified almost specifically on human endothelial cells. They are expressed preferentially in the proliferating endothelium of vessels lining and/or penetrating solid tumors, whereas they are almost undetectable by convenient methods in vessels of healthy tissue. However, the underlying mechanisms are not understood. We could show that media conditioned by various cancer cell lines grown under hypoxic conditions were able to up-regulate expression of FLT-1 mRNA and protein but not of KDR mRNA. Furthermore, up-regulation of a shorter mRNA species was observed that most probably codes for the soluble variant of FLT-1. These effects were completely inhibited by VEGF-neutralizing extracellular VEGF receptor domains. The effect could be mimicked by adding recombinant VEGF instead of conditioned cancer cell medium to the endothelial cell cultures. Both mutant VEGF, which activates only KDR, and placenta growth factor, which activates only FLT-1, were able to enhance FLT-1 expression. VEGF-stimulated FLT-1 mRNA expression was inhibited by actinomycin D. These data suggest that VEGF itself is the main factor secreted by tumor cells that is able to enhance the expression of its receptor FLT-1 and of a soluble variant of FLT-1 in endothelial cells.
    Cancer Research 01/1998; 57(23):5421-5. · 8.65 Impact Factor
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    ABSTRACT: Tumor cells often express antigens that can be recognized by the immune system. Despite induction of an immune response, the tumor cells escape their elimination. We have studied the mechanisms and factors which mediate these events in a syngeneic tumor model. NV2Cd rat schwannoma cells were transplanted into BDIX rats. After injection of 10(7) to 2 x 10(7) cells, tumors grew very slowly for 10 to 12 days. After that time, rapid growth was observed. The tumors consisted of compact areas of spindle-shaped cells with small cysts, many blood vessels and central necrotic areas. During tumor growth, the number of spleen cells and T lymphocytes increased, and cytotoxic T cells with specificity for the NV2Cd tumor cells were detected. The strong specific cellular immune response did not prevent the increase in tumor volume. We studied the biological activity of the fluid present in the cysts of the tumor. At a concentration of 1 ng to 10 microg protein per ml, the cyst fluid inhibited the proliferation of splenic T lymphocytes and B lymphocytes and of lymphoma cells, but enhanced the proliferation of NV2Cd tumor cells. The cyst fluids contain the immunosuppressive transforming growth factors (TGF)-beta1, -beta2 and -beta3, also the vascular endothelial growth factor (VEGF) and epidermal growth factor (EGF). Antibodies directed against TGF-beta relieved the suppression of T-cell growth by cyst fluid, but did not influence the proliferation of NV2Cd cells. The growth-modulating factors present in the tumor cyst fluid were also detected in conditioned medium from NV2Cd cells cultured in vitro. Our data suggest that tumors can escape the cellular immune response by the production of factors that inhibit lymphocytes. They also enhance their own growth environment by secreted factors.
    International Journal of Cancer 04/1997; 70(5):542-50. · 6.20 Impact Factor
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    ABSTRACT: Mutations or loss of both alleles of the von Hippel-Lindau (VHL) tumor suppressor gene has been documented in sporadic renal cell carcinomas and neoplasms that arise in individuals having the VHL syndrome. The well-vascularized phenotype of tumors that form in VHL disease let us consider vascular endothelial growth factor (VEGF) as a mediator of tumor growth in VHL disease. Human renal carcinoma cells that either lacked endogenous wild-type VHL or were transfected with an inactive mutant VHL showed deregulated expression of VEGF on the mRNA and protein level that was reverted by introduction of wild-type VHL. Stimulation of proliferation of endothelial cells by conditioned medium of cells expressing mutant VHL was almost abolished by neutralizing the VEGF. In contrast, expression of basic fibroblast growth factor and of c-myc proto-oncogene was not affected by VHL. Our data suggest VEGF as the key tumor angiogenesis factor in VHL disease.
    Cancer Research 06/1996; 56(10):2299-301. · 8.65 Impact Factor
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    ABSTRACT: Stimulation of NIH 3T3 cells with platelet-derived growth factor (PDGF)-BB and 12-O-tetradecanoylphorbol-13-acetate (TPA) enhances vascular endothelial growth factor (VEGF) gene expression. To address the question of whether Ras and Raf are involved in the induction of VEGF gene expression by PDGF and TPA, we examined the effects of both factors on NIH 3T3 cells stably transfected with v-Ha-ras or v-raf. In serum-starved NIH 3T3 cells, only low levels of mRNA expression can be detected, whereas both ras and raf transformed cell lines express enhanced levels of a 4.3-kilobase VEGF transcript. Stimulation with PDGF or TPA resulted in increased VEGF mRNA in all cell lines, with highest levels found in the transformed cells. Immunofluorescence studies confirmed that the elevated VEGF mRNA expression correlated with enhanced protein levels. Positive immunofluorescence signals could be detected in v-Ha-ras or v-raf transformed cell lines but not in unstimulated NIH 3T3 cells. VEGF from conditioned medium of v-raf transformed NIH 3T3 cells was partially purified by chromatography on heparin-Sepharose. Biological activity of this VEGF protein was demonstrated by competition with binding of recombinant 125I-VEGF165 to human umbilical vein endothelial cells and by its ability to stimulate proliferation of these cells.
    Journal of Biological Chemistry 11/1995; 270(43):25915-9. · 4.65 Impact Factor
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    ABSTRACT: Ovarian hyperstimulation syndrome (OHSS) is a severe complication arising from controlled ovarian stimulation treatment. This iatrogenic condition is potentially lethal and occurs in 0.3-5% of stimulated ovarian cycles. hCG exacerbates OHSS. The pathophysiology of OHSS is still unknown; therefore, treatment regimens are aimed at ameliorating symptoms. Prominent features of OHSS are an elevated risk of thromboembolism due to enhanced production of von Willebrand factor by endothelial cells and ascites, or pulmonary edema due to increased vascular permeability followed by third space fluid accumulation. Both of these sequelae can be evoked by vascular endothelial growth factor (VEGF), also known as vascular permeability factor (VPF). High concentrations of VEGF/VPF have been demonstrated in ascitic fluid from patients with OHSS, but the source of VEGF/VPF in these patients remained unidentified. Here we report that the messenger ribonucleic acid expression of VEGF/VPF in human luteinized granulosa cells (GCs) is dose and time dependently enhanced by hCG in vitro. Furthermore, VEGF/VPF proteins are produced by GCs. Our results suggest that the effects of hCG on the development and course of OHSS may be mediated by the production of VEGF/VPF by GCs.
    Journal of Clinical Endocrinology &amp Metabolism 07/1995; 80(6):1967-71. · 6.43 Impact Factor
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    ABSTRACT: In primary malignant brain tumors increased vascularity and marked edema strongly suggest a possible role of the vascular endothelial growth factor/vascular permeability factor (VEGF/VPF). This was confirmed by earlier in situ hybridization studies, by analysis of the expression of the mitogen in different subsets of glioblastoma cells, and by the fact that the VEGF/VPF receptor flt-1 (fms-like tyrosine kinase) is up-regulated in tumor cells in vivo. To assess and quantify the expression of the VEGF/VPF gene and of the receptor gene, 26 surgical specimens of brain tumor tissue from 24 patients were analyzed. In most malignant gliomas, the expression level of the VEGF/VPF gene is elevated and can be increased up to 20- to 50-fold in comparison with low-grade tumors. Using polymerase chain reaction-based amplification, it could be shown that the messenger RNAs of three different VEGF/VPF forms are synthesized in tumor tissue samples. Northern blot studies revealed that in some samples a significant expression of the gene coding for placenta growth factor, a growth factor closely related to VEGF/VPF, was observed. In addition, using a radioreceptor assay it was possible to detect high VEGF/VPF-like activity in the cyst fluids of brain tumors, indicating the accumulation of the mitogen and permeability factor in brain tumor cysts. Further investigations revealed that astrocytoma and glioblastoma cells in culture express the VEGF/VPF gene and secrete the VEGF/VPF protein, whereas gene expression of the two known VEGF/VPF receptors, kinase insert domain-containing receptor and flt-1, could not be detected. These data support previous reports, which stated that VEGF/VPF acts as a paracrine growth and permeability factor in brain tumors and may contribute to tumor growth by initiating tumor angiogenesis.
    Neurosurgery 10/1994; 35(3):439-48; discussion 448-9. · 2.53 Impact Factor
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    ABSTRACT: Vascular endothelial growth factor (VEGF) is a newly identified growth and permeability factor with a unique specificity for endothelial cells. Recently the flt-encoded tyrosine kinase was characterized as a receptor for VEGF. A novel tyrosine kinase receptor encoded by the KDR gene was also found to bind VEGF with high affinity when expressed in CMT-3 cells. Screening for flt and KDR expression in a variety of species and tissue-derived endothelial cells demonstrates that flt is predominantly expressed in human placenta and human vascular endothelial cells. Placenta growth factor (PIGF), a growth factor significantly related to VEGF, is coexpressed with flt in placenta and human vascular endothelial cells. KDR is more widely distributed and expressed in all vessel-derived endothelial cells. These data demonstrate that cultured human endothelial cells isolated from different tissues express both VEGF receptors in relative high levels and, additionally, that all investigated nonhuman endothelial cells in culture are also positive for KDR gene expression.
    Journal of Cellular Biochemistry 02/1994; 54(1):56-66. · 3.06 Impact Factor
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    ABSTRACT: Vascular endothelial growth factor (VEGF) is an angiogenic growth factor with a target-cell specificity highly restricted to vascular endothelial cells. Recombinant baculovirus were constructed for the production of two different forms of the human VEGF protein in insect cells. VEGF165 and VEGF121 proteins produced by Sf158 cells underwent a similar processing compared with mammalian cells, including efficient glycosylation, formation of a disulfide-linked dimer and secretion into the media. Only one of these forms, VEGF165 had a high affinity for heparin and this characteristic was used to purify this form to homogenicity by a two-step heparin-affinity chromatography. The biological activity of the purified 43-kDa homodimer was demonstrated by high-affinity binding to VEGF receptors, and by the induction of DNA synthesis in vascular endothelial cells. A positive angiogenic activity in vivo was demonstrated by the day-13 chorioallantoic-membrane assay. The mitogenic potency of VEGF121 for human umbilical vein endothelial cells was very similar compared to VEGF165. These results demonstrate that an angiogenic growth factor whose normal processing requires glycosylation and disulfide-bridge formation can be efficiently expressed in high concentration (up to 5 micrograms/ml) in insects cells.
    European Journal of Biochemistry 02/1993; 211(1-2):19-26. · 3.58 Impact Factor
  • K Weindel, D Marmé, H A Weich
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    ABSTRACT: PCR cloning and cDNA sequencing have been used to identify mRNAs of two splice products of the vascular endothelial growth factor (VEGF) gene, VEGF121 and VEGF165, in cells isolated from Kaposi's sarcomas (KS) of AIDS patients (AIDS-KS). As demonstrated by Northern blot analysis, AIDS-KS cells as well as tumor cells show a high expression level of the VEGF gene as compared to primary human vascular cells like smooth muscle cells or endothelial cells. In addition to the lower expression of the gene, vascular cells express a 3.9 kb band together with a 3.2 kb band instead of a 3.9 kb and a 4.3 kb band in AIDS-KS cells. Our data suggest that the angiogenic properties of AIDS-KS cells might be mediated by the secretion of this growth factor and that this factor alone or in combination with other endothelial mitogens may be involved in endothelial proliferation associated with Kaposi's sarcoma.
    Biochemical and Biophysical Research Communications 04/1992; 183(3):1167-74. · 2.28 Impact Factor

Publication Stats

2k Citations
88.38 Total Impact Points

Institutions

  • 1995–2001
    • Clinic for Tumor Biology Freiburg
      Freiburg, Baden-Württemberg, Germany
  • 1992–1994
    • University of Freiburg
      • Institute of Biochemistry and Molecular Biology
      Freiburg, Lower Saxony, Germany