Vascular endothelial growth factor and interleukin-6 in paracrine tumor-stromal cell interactions in multiple myeloma

Vascular endothelial growth factor (VEGF), a multifunctional cytokine, potently stimulates angiogenesis including tumor neovascularization. Although well established in solid tumors, the role of VEGF in bone marrow neoangiogenesis and paracrine tumor-stromal cell interactions in lymphohematopoietic malignancies has not been fully elucidated. In multiple myeloma (MM), marrow neovascularization parallels disease progression. This parallel prompted us to investigate the expression and secretion of VEGF by myeloma cells and its potential effects in myeloma-marrow stroma interactions. The biologically active splice variants VEGF165 and VEGF121 were expressed and secreted by myeloma cell lines and plasma cells isolated from the marrow of patients with MM. As shown by immunocytochemistry or RT-PCR, myeloma cells did not express or weakly expressed the VEGF receptors FLT-1 and FLK-1/KDR, indicating that autocrine stimulation is unlikely. In contrast, FLK-1/KDR was abundantly expressed by marrow stromal cells. Therefore, we studied the effects of VEGF on marrow stroma, focusing on the secretion of interleukin-6 (IL-6), a potent growth factor for myeloma cells and an inhibitor of plasma cell apoptosis. Exposure of stromal and microvascular endothelial cells to recombinant human (rh) VEGF165 or VEGF121 induced a time- and dose-dependent increase in IL-6 secretion (14- to 27-fold at 50 ng/mL after 24 hours, P <.001). Conversely, rhIL-6 stimulated VEGF expression and secretion in myeloma cell lines (40%-60%; P <.05) and to a variable degree (up to 5.3-fold; P <.005) in plasma cells purified from the marrow of patients with MM. This mutual stimulation suggests paracrine interactions between myeloma and marrow stromal cells triggered by VEGF and IL-6. (Blood. 2000;95:2630-2636)     

Macrophage inflammatory protein 1-alpha (MIP-1 alpha ) triggers migration and signaling cascades mediating survival and proliferation in multiple myeloma (MM) cells

Recently, it has been demonstrated that macrophage inflammatory protein 1- alpha (MIP-1 alpha) is crucially involved in the development of osteolytic bone lesions in multiple myeloma (MM). The current study was designed to determine the direct effects of MIP-1 alpha on MM cells. Thus, we were able to demonstrate that MIP-1 alpha acts as a potent growth, survival, and chemotactic factor in MM cells. MIP-1 alpha-induced signaling involved activation of the AKT/protein kinase B (PKB) and the mitogen-activated protein kinase (MAPK) pathway. In addition, inhibition of AKT activation by phosphatidylinositol 3- kinase (PI3-K) inhibitors did not influence MAPK activation, suggesting that there is no cross talk between MIP-1 alpha-dependent activation of the PI3-K/AKT and extracellular-regulated kinase (ERK) pathway. Our data suggest that besides its role in development of osteolytic bone destruction, MIP-1 alpha also directly affects cell signaling pathways mediating growth, survival, and migration in MM cells and provide evidence that MIP-1 alpha might play a pivotal role in the pathogenesis of MM.     

A paracrine loop in the vascular endothelial growth factor pathway triggers tumor angiogenesis and growth in multiple myeloma

BACKGROUND AND OBJECTIVES: In tumors, vascular endothelial growth factor-A (VEGF-A) stimulates angiogenesis and vascular permeability by activating the tyrosine kinase receptor-2 (VEGFR-2 or KDR/Flk-1) and-1 (VEGFR-1 or Flt-1). DESIGN AND METHODS: The distribution and function of VEGF homologs and their receptors on bone marrow plasma cells, endothelial cells, and other stromal cells (residual stromal cells) were examined in patients with multiple myeloma (MM). RESULTS. Plasma cells secrete VEGF-A (and VEGF-B, VEGF-C and VEGF-D, albeit marginally) into their conditioned medium (CM). CM VEGF-A stimulates proliferation and chemotaxis in endothelial cells (both being mandatory for angiogenesis) via VEGF receptor-2 (VEGFR-2), and in residual stromal cells via the VEGFR-1. Residual stromal cells secrete VEGF-C and VEGF-D, but little of the other homologs. Their CM VEGF-C and VEGF-D increase in response to plasma cell CM and trigger plasma cell proliferation via VEGFR-3. Proliferation in all cell types parallels VEGFR and extracellular signal-regulated protein kinase-2 (ERK-2) phosphorylation. The homologs and receptors are weakly or inconstantly expressed in patients with monoclonal gammopathies of undetermined significance or vitamin B12/iron deficiency anemias. INTERPRETATION AND CONCLUSIONS: This study shows that the VEGF pathway is directly involved in tumor angiogenesis and growth in MM. A paracrine VEGF loop for MM progression is suggested. This, in turn, provides a further indication that the VEGF pathway and its signaling proteins may be appropriate targets in the management of MM.     

Novel therapeutic strategies targeting growth factor signalling cascades in multiple myeloma

Multiple myeloma (MM) remains largely incurable despite conventional and high-dose therapies, and novel biologically based treatment approaches are urgently required. Recent studies demonstrate that various growth factors including interleukin (IL)-6, insulin-like growth factor (IGF)-1, vascular endothelial growth factor (VEGF), the tumour necrosis factor (TNF) family proteins, Wnt, and Notch family members play an important role in MM pathogenesis, and mediate tumour cell proliferation, drug resistance and migration in the bone marrow (BM) milieu. Targeting growth factors, therefore, represents a promising therapeutic strategy in MM. Novel agents inhibiting growth factor signalling cascades can target ligands, receptors, and/or downstream signalling cascade proteins in MM cells and the BM microenvironment. Combinations of these novel agents with conventional therapies may not only enhance cytotoxicity, but also avoid drug resistance and thereby improve patient outcome in MM.     

Hepatocyte growth factor. A cytokine mediating endothelial migration in inflammatory arthritis

Objective. Angiogenesis is an integral component of the vasculoproliferative phase of rheumatoid arthritis (RA). Recently, a heparin-binding cytokine termed hepatocyte growth factor (HGF), or scatter factor (due to its ability to disperse cohesive epithelial colonies), was described. We conducted this study to investigate the hypothesis that this cytokine was present in the milieu of the inflamed joint, and that it contributed to the chemotaxis of endothelial cells in the synovial tissue. Methods. We examined synovial fluid, synovial tissue, and peripheral blood from 91 patients with RA and other arthritides. We used 83 total samples in an enzyme-linked immunosorbent assay to quantitate the HGF in synovial fluids and peripheral blood. To determine whether the HGF was biologically active, an epithelial scatter factor assay was performed. Immunohistochemical analysis was used to determine localization in synovial tissues. To define a function for synovial HGF, we preincubated rheumatoid synovial fluids with neutralizing anti-HGF and measured the ability of these synovial fluids to induce endothelial chemotaxis. Results. Synovial fluid from patients with RA contained a mean ± SEM HGF concentration of 2.0 ± 0.3 ng/ml, while synovial fluid from patients with other arthritides (including inflammatory arthritis) contained 2.4 ± 0.7 ng/ml HGF. Osteoarthritis (OA) patient samples contained the smallest quantities of synovial fluid HGF at 0.9 ± 0.1 ng/ml. RA synovial fluid contained significantly more HGF than did RA peripheral blood (1.1 ± 0.2 ng/ml) (P < 0.05). Rheumatoid synovial fluids induced more scattering of cells than did OA synovial fluids, suggesting a role for this cytokine in rheumatoid joint destruction. Interleukin-1β induced expression of rheumatoid synovial tissue fibroblast antigenic HGF and scatter factor activity. Immunohistochemically, HGF, as well as the HGF receptor (the met gene product), localized to significantly more rheumatoid synovial tissue lining cells than normal lining cells (P < 0.05). Both HGF and its receptor immunolocalized to subsynovial macrophages as well. Levels of synovial tissue immunoreactive HGF correlated positively with the number of synovial tissue blood vessels. Anti-HGF neutralized a mean of 24% of the chemotactic activity for endothelial cells found in 10 rheumatoid synovial fluid samples. Conclusion. These results indicate that synovial HGF may contribute to the vasculoproliferative phase of inflammatory arthritides such as RA, by inducing HGF-mediated synovial neovascularization. These findings point to a newly described role for HGF in the fibroproliferative phase of RA-associated synovitis.     

Clinical significance of vascular endothelial growth factor and hepatocyte growth factor in multiple myeloma

Angiogenesis is a crucial process in the progression of multiple myeloma (MM). Vascular endothelial growth factor (VEGF) and hepatocyte growth factor (HGF) are multifunctional cytokines that potently stimulate angiogenesis including tumour neovascularization. Serum levels of VEGF and HGF were measured in 52 patients with MM by enzyme-linked immunosorbent assay (ELISA). Serum levels of VEGF and HGF were elevated in MM patients compared with healthy controls (VEGF: mean 0.31 ng/ml and 0.08 ng/ml respectively, P < 0.01; HGF: mean 2.17 ng/ml and 0.45 ng/ml, respectively, P < 0.001). In serial samples taken after chemotherapy, serum VEGF and HGF levels were correlated with M-protein levels. Serum levels of VEGF were higher in patients with extramedullary plasmacytomas than in patients without them (P < 0.05). They were also significantly higher in a group of patients who showed poor response to chemotherapy (P < 0.01). Serum levels of HGF were higher in patients with complications such as anaemia, hypercalcaemia and amyloidosis than in patients without these complications (P < 0.01, P < 0.05, P < 0.05 respectively). Both serum VEGF and HGF levels were significant predictors of mortality (P = 0.01, P = 0.02, respectively, log-rank test). The present study demonstrated that serum levels of VEGF and HGF are significantly elevated and dependent on the severity of MM, suggesting that measurement of VEGF and HGF may be useful for assessing disease progression and for predicting the response to chemotherapy in MM patients.     

Vascular endothelial growth factor

An understanding of the mechanisms regulating growth and differentiation of vascular endothelial cells is very important for cardiovascular biology and medicine. Several potential regulators of angiogenesis have been identified, including acidic and basic fibroblast growth factors, epidermal growth factor, platelet-derived endothelial cell growth factor, transforming growth factors and β, and tumor necrosis factor (TNF-). Vascular endothelial growth factor (VEGF) is unique among these agents by virtue of its direct and specific mitogenic effects on endothelial cells combined with the fact that it is a secreted polypeptide. By alternative splicing of mRNA, VEGF may exist in four different isoforms that have similar biologic activities but differ markedly in their secretion pattern. VEGF is emerging as an important regulator of developmental and ovarian angiogenesis. Its action is purely paracrine as it is produced by a variety of cell types, but its receptors are only in endothelial cells. There is no evidence that endothelial cells in vivo produce VEGF. The VEGF mRNA is expressed at high level by a variety of human tumors, suggesting that VEGF may be a tumor angiogenesis factor. This hypothesis is supported by the finding that monoclonal antibodies specific for VEGF are able to suppress tumor growth in vivo. Therefore, VEGF antagonists may be used for the treatment of malignancies and, possibly, other angiogenic diseases. The VEGF protein has therapeutic potential as an inducer of neovascularization in conditions characterized by impaired tissue perfusion like obstructive atherosclerosis.     

Vascular endothelial growth factor and microvascular permeability.

Vascular Endothelial Growth Factors (VEGFs) are endogenously produced vascular cytokines which result in angiogenesis, vasodilatation, and increased microvascular permeability in vivo. They are endothelial specific and result in mitosis, migration, stress fiber formation and increased permeability of endothelial cells in culture. They have been critically implicated in a host of pathological conditions including solid tumor growth and diabetes, and been proposed as a therapy for coronary and peripheral ischemic disease. However, the potent permeability-enhancing properties of VEGFs are very poorly understood. The pharmacology, signal transduction pathways, intracellular signaling mechanisms, and ultrastructural changes which result in increased permeability are still not clear. This review discusses the available evidence for how VEGFs increase permeability in vivo, and some of the pitfalls in interpreting experiments which do not take into account the vasoactive properties of VEGFs. It also discusses the clinical implications of the permeability enhancing effect of VEGFs, and the relevance of these studies to development of new therapies.     

血管内皮细胞迁移与肿瘤血管生成

肿瘤生长和转移均依赖于肿瘤的血管生成,而血管内皮细胞迁移是肿瘤血管生成过程的一个重要环节,有着重要的研究意义.现从肿瘤血管生成过程中促血管生成因子、骨架蛋白解聚、细胞外基质的降解三个方面对血管内皮细胞迁移的影响进行综述.     

Vascular endothelial growth factor B, a novel growth factor for endothelial cells.

We have isolated and characterized a novel growth factor for endothelial cells, vascular endothelial growth factor B (VEGF-B), with structural similarities to vascular endothelial growth factor (VEGF) and placenta growth factor. VEGF-B was particularly abundant in heart and skeletal muscle and was coexpressed with VEGF in these and other tissues. VEGF-B formed cell-surface-associated disulfide-linked homodimers and heterodimerized with VEGF when coexpressed. Conditioned medium from transfected 293EBNA cells expressing VEGF-B stimulated DNA synthesis in endothelial cells. Our results suggest that VEGF-B has a role in angiogenesis and endothelial cell growth, particularly in muscle.     

Vascular endothelial growth factor receptor-2-induced initial endothelial cell migration depends on the presence of the urokinase receptor

The angiogenic response of endothelial cells initiated by different growth factors is accompanied by assembly of cell surface-bound proteolytic machinery as a prerequisite for focal invasion. We have shown previously how the vascular endothelial growth factor (VEGF) initiates proteolysis by activation of pro-urokinase (pro-PA) via the VEGF receptor-2 (VEGFR-2). We now show that the cell surface receptor of the uPA-system, the urokinase receptor (uPAR), is redistributed to focal adhesions at the leading edge of endothelial cells in response to VEGF. VEGF165 and VEGF-E, both interacting with VEGFR-2, but not PlGF exclusively stimulating VEGFR-1, induce within minutes internalization of uPAR via an LDL receptor-like molecule, dependent on generation of active uPA and the presence of plasminogen activator inhibitor-1 (PAI-1). uPAR seems to play a pivotal role in VEGFR-2-induced endothelial cell migration because cleavage of surface uPAR impaired the migratory response of endothelial cells toward VEGF-E, but not toward PlGF.     

Insulin-like growth factor I induces migration and invasion of human multiple myeloma cells

Multiple myeloma (MM) is an incurable form of cancer characterized by accumulation of malignant plasma cells in the bone marrow. During the course of this disease, tumor cells cross endothelial barriers and home to the bone marrow. In latter stages, myeloma cells extravasate through blood vessels and may seed a variety of organs. Insulin-like growth factor I (IGF-I) is one of several growth factors shown to promote the growth of MM cells. In the current study, we have assessed the ability of IGF-I to serve additionally as a chemotactic factor affecting the mobility and invasive properties of these cells. Results indicate that IGF-I promotes transmigration through vascular endothelial cells and bone marrow stromal cell lines. Analysis of endogenous signaling pathways revealed that protein kinase D/protein kinase Cmicro (PKD/PKCmicro) and RhoA were both activated in a phosphatidylinositol 3-kinase (PI-3K)-dependent manner. Inhibition of PI-3K, PKCs, or Rho-associated kinase by pharmacologic inhibitors abrogated migration, whereas mitogen-activated protein kinase (MAPK), Akt, and p70S6 kinase inhibitors had no effect. These results suggest that IGF-I promotes myeloma cell migration by activation of PI-3K/PKCmicro and PI-3K/RhoA pathways independent of Akt. The identification of IGF-I as both a proliferative and migratory factor provides a rational basis for the development of targeted therapeutic strategies directed at IGF-I in the treatment of MM.     

Vascular endothelial growth factor in Henoch-Schonlein purpura.

OBJECTIVE: To investigate the possible role of vascular endothelial growth factor (VEGF) in the pathogenesis of Henoch-Schonlein purpura (IHSP). METHODS: Plasma VEGF levels were determined in 22 children by ELISA. Ten age matched healthy children served as controls. VEGF expression was evaluated by immunohistochemistry within the cutaneous vasculitic lesion as well as the nonaffected skin and in the skin specimens during the resolution of the disease. RESULTS. Plasma VEGF levels in pg/ml (mean +/- SE) were significantly higher during the acute phase (407.8 +/- 64.92) when compared with the levels seen during the resolution phase (202.17 +/- 26.6; p < 0.002) and in healthy controls (135 +/- 22.8; p < 0.001). Analysis showed that there was a correlation with erythrocyte sedimentation rate. C-reactive protein, white blood cell and platelet count. In all skin specimens, the intensity of the staining of VEGF in the epidermis, dermis, and vascular endothelial bed were evaluated and scored from (+) to (++++). VEGF expression in the epidermis and the vascular bed was more intense in resolving lesions compared with acute vasculitic lesions (p < 0.05). CONCLUSION: Our results suggest that as a potent permeability, chemotactic, and migratory factor, VEGF may play a crucial role in the morphological and functional changes of the vascular bed and inflammatory reaction in HSP.     

Vascular endothelial growth factor in pleural fluid.

STUDY OBJECTIVES: The purpose of this study was to analyze the relationship of the pleural fluid vascular endothelial growth factor (VEGF) level with the diagnostic category and with the pleural fluid characteristics in a group of 70 patients. DESIGN: The VEGF levels of consecutive patients undergoing therapeutic thoracentesis were determined with an enzyme-linked immunosorbent assay. SETTING: University-affiliated tertiary care center. RESULTS: The median level of pleural fluid VEGF in the patients with congestive heart failure (150 pg/mL) was significantly (p < 0.05) lower than the median level in the patients with coronary artery bypass grafting (357 pg/mL), which in turn was significantly lower (p < 0.05) than the median levels in the patients with malignancy (1,097 pg/mL). The overlap between groups, however, limits the diagnostic usefulness of pleural fluid VEGF levels. The VEGF level was most closely correlated with the lactate dehydrogenase level (r = 0.42, p < 0.001) and was also significantly correlated with the total pleural fluid protein level. The median VEGF levels in the pleural fluid of patients with breast cancer were significantly lower (p = 0.017) than in those with lung cancer. The VEGF level was very high (3,294 pg/mL) in the one patient with pulmonary embolism. CONCLUSIONS: We conclude that the VEGF levels in pleural fluid differ significantly from one diagnostic category to another with the highest median levels occurring in patients with malignant pleural effusions. We speculate that VEGF may be responsible for the pleural fluid accumulation in at least some situations.     

Vascular endothelial growth factor and signaling in the prostate: more than angiogenesis

In cloning tyrosine kinase genes in dog prostate cells, a fragment of the vascular endothelial growth factor (VEGF) receptor 1 or Flt-1 was sequenced. To test for a functional protein, Flt-1 antibodies were used to probe immunoprecipitated tyrosine phosphorylated proteins. Western blotting revealed a major 170-180 kDa band and a few bands below 116 kDa in dog prostate and human prostatic carcinoma PC-3 cells, with higher levels in PC-3. Similar results were obtained with human placental membranes used as a source of Flt-1. That the major Flt-1 tyrosine phosphorylated protein was likely VEGF-R1 and part of VEGF signaling pathways was shown by enhanced level of only this protein when PC-3 cells were exposed to VEGF. Accordingly specific cell surface receptor complexes, displaced by VEGF but not EGF and compatible with Flt-1 in size, were revealed by chemical cross-linking after 125I-VEGF binding. Similarly to the prostatic neuroproduct, gastrin-releasing peptide/bombesin, VEGF directly triggered the tyrosine phosphorylation of focal adhesion kinase and stimulated PC-3 cell motility. The titration of prostate tissue sections with VEGF-A antibodies revealed a confined staining in chromogranin A and/or serotonin positive neuroendocrine (NE) cells, including in primary tumors and lymph node metastases. Given that NE differentiation is associated with advanced disease, that NE cells are a significant source of VEGF in prostatic tumors, and that VEGF directly act on prostate cancer cells in vitro, VEGF-A may be more than angiogenic in prostate cancer and hence favor progression by affecting tumor cells.     

Vascular endothelial growth factor binds to fibrinogen and fibrin and stimulates endothelial cell proliferation

Vascular development and response to injury are regulated by several cytokines and growth factors including the members of the fibroblast growth factor and vascular endothelial cell growth factor (VEGF) families. Fibrinogen and fibrin are also important in these processes and affect many endothelial cell properties. Possible specific interactions between VEGF and fibrinogen that could play a role in coordinating vascular responses to injury are investigated. Binding studies using the 165 amino acid form of VEGF immobilized on Sepharose beads and soluble iodine 125 ((125)I)-labeled fibrinogen demonstrated saturable and specific binding. Scatchard analysis indicated 2 classes of binding sites with dissociation constants (K(d)s) of 5.9 and 462 nmol/L. The maximum molar binding ratio of VEGF:fibrinogen was 3.8:1. Further studies characterized binding to fibrin using (125)I-labeled VEGF- and Sepharose-immobilized fibrin monomer. These also demonstrated specific and saturable binding with 2 classes of sites having K(d)s of 0.13 and 97 nmol/L and a molar binding ratio of 3.6:1. Binding to polymerized fibrin demonstrated one binding site with a K(d) of 9.3 nmol/L. Binding of VEGF to fibrin(ogen) was independent of FGF-2, indicating that there are distinct binding sites for each angiogenic peptide. VEGF bound to soluble fibrinogen in medium and to surface immobilized fibrinogen or fibrin retained its capacity to support endothelial cell proliferation. VEGF binds specifically and saturably to fibrinogen and fibrin with high affinity, and this may affect the localization and activity of VEGF at sites of tissue injury. (Blood. 2000;96:3772-3778)     

Vascular endothelial growth factor gene polymorphisms in giant cell arteritis

OBJECTIVE: To examine potential associations of vascular endothelial growth factor (VEGF) gene polymorphisms with giant cell arteritis (GCA) and disease expression, in particular in patients with and without ischemic complications. METHODS: We enrolled 92 consecutive patients with biopsy-proven GCA residing in Reggio Emilia, Italy. Two hundred healthy blood donors from the same geographic area were selected as controls. All the GCA patients and controls were genotyped by polymerase chain reaction and allele-specific oligonucleotide techniques for 936 C/T and 634 C/G mutations and for an 18 bp insertion/deletion (I/D) polymorphism in the VEGF promoter region. In vitro release of VEGF by peripheral blood mononuclear cells (PBMC) was investigated by ELISA in controls homozygous for the polymorphisms studied. RESULTS: The carriage rates of the alleles I and C634 were significantly more frequent in GCA patients than in controls (p = 0.025, OR 1.9, 95% CI 1.1-3.1 and p = 0.015, OR 2.1, 95% CI 1.1-3.6, respectively). The distribution of allele T936 was similar in GCA patients and controls. No significant differences in the distribution of the polymorphisms studied were observed in patients with ischemic manifestations compared to those without ischemic manifestations. Lipopolysaccharide (LPS)-stimulated VEGF production by PBMC from controls was higher in II homozygous compared to DD homozygous patients. CONCLUSION: Our data indicate that carriers of C634 and I alleles are associated with susceptibility to developing GCA.