Integrin alpha4beta1 promotes monocyte trafficking and angiogenesis in tumors

Monocytes and macrophages extensively colonize solid tumors, where they are thought to promote tumor angiogenesis. Here, we show that integrin alpha4beta1 (VLA4) promotes the invasion of tumors by myeloid cells and subsequent neovascularization. Antagonists of integrin alpha4beta1, but not of other integrins, blocked the adhesion of monocytes to endothelium in vitro and in vivo as well as their extravasation into tumor tissue. These antagonists prevented monocyte stimulation of angiogenesis in vivo, macrophage colonization of tumors, and tumor angiogenesis. These studies indicate the usefulness of antagonists of integrin alpha4beta1 in suppressing macrophage colonization of tumors and subsequent tumor angiogenesis. These studies further indicate that suppression of myeloid cell homing to tumors could be a useful supplementary approach to suppress tumor angiogenesis and growth.     

Crosstalk between tumor and endothelial cells promotes tumor angiogenesis by MAPK activation of Notch signaling

While significant progress has been made in understanding the induction of tumor vasculature by secreted angiogenic factors, little is known regarding contact-dependent signals that promote tumor angiogenesis. Here, we report that the Notch ligand Jagged1 induced by growth factors via mitogen-activating protein kinase (MAPK) in head and neck squamous cell carcinoma (HNSCC) cells triggered Notch activation in neighboring endothelial cells (ECs) and promoted capillary-like sprout formation. Jagged1-expressing HNSCC cells significantly enhanced neovascularization and tumor growth in vivo. Moreover, the level of Jagged1 was significantly correlated with tumor blood vessel content and associated with HNSCC development. Our results elucidate a novel mechanism by which the direct interplay between tumor cells and ECs promotes angiogenesis through MAPK and Notch signaling pathways.     

Morphine stimulates angiogenesis by activating proangiogenic and survival-promoting signaling and promotes breast tumor growth

Morphine is used to treat pain in several medical conditions including cancer. Here we show that morphine, in a concentration typical of that observed in patients' blood, stimulates human microvascular endothelial cell proliferation and angiogenesis in vitro and in vivo. It does so by activating mitogen-activated protein kinase/extracellular signal-regulated kinase phosphorylation via Gi/Go-coupled G protein receptors and nitric oxide in these microvascular endothelial cells. Other contributing effects of morphine include activation of the survival signal PKB/Akt, inhibition of apoptosis, and promotion of cell cycle progression by increasing cyclin D1. Consistent with these effects, morphine in clinically relevant doses promotes tumor neovascularization in a human breast tumor xenograft model in mice leading to increased tumor progression. These results indicate that clinical use of morphine could potentially be harmful in patients with angiogenesis-dependent cancers.     

Oct-3/4 promotes tumor angiogenesis through VEGF production in glioblastoma

Brain Tumor Pathology - Accumulating evidence shows that the expression level of Oct-3/4, a self-renewal regulator in stem cells, is positively correlated with the progression of various solid...     

VEGF receptor signaling in tumor angiogenesis

The growth of human tumors and development of metastases depend on the de novo formation of blood vessels. The formation of new blood vessels is tightly regulated by specific growth factors that target receptor tyrosine kinases (RTKs). Vascular endothelial growth factor (VEGF) and the Flk-1/KDR RTK have been implicated as the key endothelial cell-specific factor signaling pathway required for pathological angiogenesis, including tumor neovascularization. Inhibition of the VEGF tyrosine kinase signaling pathway blocks new blood vessel formation in growing tumors, leading to stasis or regression of tumor growth. Advances in understanding the biology of angiogenesis have led to the development of several therapeutic modalities for the inhibition of the VEGF tyrosine kinase signaling pathway. A number of these modalities are under investigation in clinical studies to evaluate their potential to treat human cancers.     

血管内皮生长因子和Dll4-Notch信号通路在肿瘤血管发生中的作用

抗肿瘤血管发生是一种全新的抗肿瘤治疗策略,目前研究最多的是寻找有效抗血管内皮生长因子(VEGF)信号通路的药物.然而VEGF抑制剂并不是对所有肿瘤有效,因此,有必要进一步探索血管发生的其他信号通路.目前,Dll4-Notch信号通路被认为是抗肿瘤血管发生的新靶点,而且VEGF和Dll4-Notch信号通路在多方面相互作...     

血管内皮生长因子和D114-Notch信号通路在肿瘤血管发生中的作用

抗肿瘤血管发生是一种全新的抗肿瘤治疗策略,目前研究最多的是寻找有效抗血管内皮生长因子（VEGF）信号通路的药物。然而VEGF抑制剂并不是对所有肿瘤有效,因此,有必要进一步探索血管发生的其他信号通路。目前,DH4-Nmch信号通路被认为是抗肿瘤血管发生的新靶点,而且VEGF和DH4-N0tch信号通路在多方面相互作用,在调控血管发生过程中发挥重要作用,对这两条通路的探索和研究,将会使治疗肿瘤的手段更为丰富。     

Notch signaling in developmental and tumor angiogenesis

The discovery that Notch, a key regulator of cell fate determination, is functional in the vasculature has greatly improved our understanding of differentiation and specialization of vessels. Notch signaling has been proven to be critical for arterial specification, sprouting angiogenesis, and vessel maturation. In newly forming vascular sprouts, Notch promotes the distinction between the leading "tip" endothelial cell and the growing "stalk" cell, the endothelial cells that eventually form a new capillary. Notch signaling has also been implicated in vessel stability by regulating vascular mural cell function. More recently, macrophages carrying an activated Notch have been implicated in shaping the course of new sprout formation. Tumor vessels abide by similar principles and use Notch signaling in similar ways. An exciting discovery, made by several researchers, shows that blocking Notch function in tumor vasculature provides a means by which to suppress tumor growth. The authors discuss the developmental and physiological role of Notch in the vasculature and apply this knowledge to an overview of how Notch targeting in the tumor environment can affect tumor angiogenesis and growth.     

Delta-like 4 Notch ligand regulates tumor angiogenesis, improves tumor vascular function, and promotes tumor growth in vivo

The vascular endothelial growth factor (VEGF) plays a key role in tumor angiogenesis. However, clinical trials targeting the VEGF pathway are often ineffective, suggesting that other factors/pathways are also important in tumor angiogenesis. We have previously shown that the Notch ligand Delta-like 4 (DLL4) is up-regulated in tumor vasculature. Here, we show that DLL4, when expressed in tumor cells, functions as a negative regulator of tumor angiogenesis by reducing the number of blood vessels in all five types of xenografts, but acts as a positive driver for tumor growth in two of them (human glioblastoma and prostate cancer). The growth of in vivo models was not related to the effects on growth in vitro. DLL4 expressed in the tumor cells activated Notch signaling in host stromal/endothelial cells, increased blood vessel size, and improved vascular function within tumors. The promotion of tumor growth was, to some extent, due to a reduction of tumor hypoxia and apoptosis. DLL4-expressing tumor cells responded to anti-VEGF therapy with bevacizumab. A soluble form of DLL4 (D4ECD-Fc) blocked tumor growth in both bevacizumab-sensitive and bevacizumab-resistant tumors by disrupting vascular function despite increased tumor vessel density. In addition, we show that DLL4 is up-regulated in tumor cells and tumor endothelial cells of human glioblastoma. Our findings provide a rational basis for the development of novel antiangiogenic strategies via blockade of DLL4/Notch signaling and suggest that combined approaches for interrupting both DLL4 and VEGF pathways may improve antiangiogenic therapy.     

TLR-4 signaling promotes tumor growth and paclitaxel chemoresistance in ovarian cancer

Evidence suggests that an inflammatory profile of cytokines and chemokines persisting at a particular site would lead to the development of a chronic disease. Recent studies implicate bacterial infection as one possible link between inflammation and carcinogenesis; however, the crucial molecular pathways involved remain unknown. We hypothesized that one possible upstream signaling pathway leading to inflammation in carcinogenesis may be mediated by Toll-like receptors (TLR). We describe for the first time an adaptive mechanism acquired by ovarian cancer cells that allows them to promote a proinflammatory environment and develop chemoresistance. We propose that the TLR-4-MyD88 signaling pathway may be a risk factor for developing cancer and may represent a novel target for the development of biomodulators. Our work explains how bacterial products, such as lipopolysaccharide, can promote, directly from the tumor, the production of proinflammatory cytokines and the enhancement of tumor survival. In addition, we provide new evidence that links TLR-4 signaling, inflammation, and chemoresistance in ovarian cancer cells.     

EGFR-AKT-Smad signaling promotes formation of glioma stem-like cells and tumor angiogenesis by ID3-driven cytokine induction

Aberrant activation of receptor tyrosine kinases (RTK) is causally linked to the pathobiological traits of glioblastoma and genesis of glioma stem-like cells (GSC), but the underlying mechanism is still unknown. Here, we show that epidermal growth factor receptor (EGFR) signaling regulates the proliferation, angiogenesis, and acquisition of GSC characteristics by inducing inhibitor of differentiation 3 (ID3) and ID3-regulated cytokines [GRO1 and interleukins (IL)-6 and 8] induction. We found that EGFR-mediated ID3 expression was regulated by Smad5, which was directly phosphorylated by AKT. Furthermore, ID3 alone imparted GSC features to primary astrocytes derived from Ink4a/Arf-deficient mouse, and EGFR-ID3-IL-6 signaling axis gave rise to tumor cell heterogeneity. Conversely, EGFR inhibitors suppressed EGFR-AKT-Smad5-driven induction of ID3, which led to a decrease in the tumorsphere forming ability of GSCs and U87MG cells that possess an active mutant EGFR, EGFRvIII, without obvious cytotoxic effects. However, these cells seemed to regain colonogenic ability after removal of the EGFR inhibitors. Together, the results delineate a novel integrative molecular mechanism in which the RTK-ID signaling pathway governs genesis and maintenance of GBM histopathologic features, such as GSCs-based tumor initiation, progression, and angiogenesis.     

Notch signaling regulates tumor angiogenesis by diverse mechanisms

The Notch signaling pathway is fundamental to proper cardiovascular development and is now recognized as an important player in tumor angiogenesis. Two key Notch ligands have been implicated in tumor angiogenesis, Delta-like 4 and Jagged1. We introduce the proteins and how they work in normal developing vasculature and then discuss differing models describing the action of these Notch ligands in tumor angiogenesis. Endothelial Dll4 expression activates Notch resulting in restriction of new sprout development; for instance, in growing retinal vessels. In agreement with this activity, inhibition of Dll4-mediated Notch signaling in tumors results in hypersprouting of nonfunctional vasculature. This Dll4 inhibition may paradoxically lead to increased angiogenesis but poor tumor growth because the newly growing vessels are not functional. In contrast, Jagged1 has been described as a Notch ligand expressed in tumor cells that can have a positive influence on tumor angiogenesis, possibly by activating Notch on tumor endothelium. A novel Notch inhibitor, the Notch1 decoy, which blocks both Dll4 and Jagged1 has been recently shown to restrict tumor vessel growth. We discuss these models and speculate on therapeutic approaches.     

Integrin alpha(v)beta3 promotes M21 melanoma growth in human skin by regulating tumor cell survival.

Growth and dissemination of malignant melanoma has a profound impact on our population, and little is known concerning the mechanisms controlling this disease in humans. Evidence is provided that integrin alpha(v)beta3 plays a critical role in M21 melanoma tumor survival within human skin by a mechanism independent of its known role in angiogenesis. Antagonists of alpha(v)beta3 blocked melanoma growth by inducing tumor apoptosis. Moreover, M21 melanoma cell interactions with denatured collagen, a known ligand for alpha(v)beta3, caused a 5-fold increase in the relative Bcl-2:Bax ratio, an event thought to promote cell survival. Importantly, denatured collagen colocalized with alpha(v)beta3-expressing melanoma cells in human tumor biopsies, suggesting that alpha(v)beta3 interaction with denatured collagen may play a critical role in melanoma tumor survival in vivo.     

ALK5 promotes tumor angiogenesis by upregulating matrix metalloproteinase-9 in tumor cells

Transforming growth factor beta 1 (TGF-beta1) is a potent tumor suppressor but, paradoxically, TGF-beta1 enhances tumor growth and metastasis in the late stages of cancer progression. This study investigated the role of TGF-beta type I receptor, ALK5, and three mitogen-activated protein kinases (MAPKs) in metastasis by breast cancer cell line MDA-MB-231. We show that autocrine TGF-beta signaling in MDA-MB-231 cells is required for tumor cell invasion and tumor angiogenesis. Expression of kinase-inactive ALK5 reduces tumor invasion and formation of new blood vessels within the tumor orthotopic xenografts in severe combined immunodeficiency (SCID) mice. In contrast, constitutively active ALK5-T204D enhances tumor invasion and angiogenesis by stimulating expression of matrix metalloproteinase MMP-9/gelatinase-B. Ablation of MMP-9 in ALK5-T204D cells by RNA interference (RNAi) reduces tumor invasion and tumor growth. Importantly, RNAi-MMP-9 reduces tumor neovasculature and increases tumor cell death. Induction of MMP-9 by TGF-beta-ALK5 signaling requires MEK-ERK but not JNK, p38 MAPK or Smad4. Dominant-negative MEK blocks and constitutively active MEK1 enhances MMP-9 expression. However, all three MAPK cascades (ERK, JNK and p38 MAPK) are required for TGF-beta-mediated cell migration. Collectively, our results show that TGF-beta-ALK5-MAPK signaling in tumor cells promotes tumor angiogenesis and MMP-9 is an important component of this program.     

A primary tumor promotes dormancy of solitary tumor cells before inhibiting angiogenesis.

Mechanisms that regulate the transition of micrometastases from clinically undetectable and dormant to progressively growing are critically important but poorly understood in cancer biology. Here we examined the effect of a primary tumor on the growth of solitary tumor cells in the mouse liver, as well as on the development of tumor angiogenesis in a dorsal skin-fold chamber. s.c. placement of a CT-26 (BALB/c-derived mouse colon carcinoma) primary tumor markedly inhibited development of liver metastasis in BALB/c mice after subsequent intraportal injection of tumor cells. Dorsal skin-fold chamber experiments showed that this growth inhibition paralleled a strong antiangiogenic effect by the primary tumor. Furthermore, intravital microscopy of the liver after intraportal injection of green fluorescent protein-expressing tumor cells showed that primary tumors promoted dormancy of single tumor cells for up to 7 days. Immunohistological staining for Ki-67 confirmed that these solitary cells were indeed dormant. In contrast, in the absence of a primary tumor, GFP-expressing tumor cells quickly developed into micrometastases. Thus, primary CT-26 tumor implants nearly abrogated tumor metastasis by inhibition of angiogenesis and by promoting a state of single-cell dormancy. Knowledge of the mechanism underlying this dormancy state could result in the development of new therapeutic tools to fight cancer.     

Lymphotoxin-beta receptor immune interaction promotes tumor growth by inducing angiogenesis

Growth of solid fibrosarcoma tumors in mice was inhibited by the release of a solublelymphotoxin-beta receptor inhibitor (LTbetaR-immunoglobulin fusion protein) from the tumor cells. Tumor growth arrest in mice deficient in the ligand LTalpha1beta2 demonstrated the requirement for activation of the LTbetaR on the tumor cells by host cell-derived LTalpha1beta2. Activation of the LTbetaR resulted in enhanced release of macrophage inflammatory protein-2. Blocked angiogenesis was revealed in LTbetaR inhibitor-producing tumor nodules by immunohistochemistry and in vivo microscopy. The growth arrest of LTbetaR inhibitor-producing fibrosarcomas was overcome by forced MIP-2 expression in the tumor cells. Thus, LTbetaR activation on tumor cells by activated host lymphocytes can initiate a novel proangiogenic pathway leading to organized tumor tissue development.     

Integrin signaling in epithelial cells

Although most cells of adult mammals express multiple different integrins, particular types of cells have a characteristic repertoire of integrin expression. Benign and malignant epithelial cells use specific integrins to allow the epithelial microenvironment to modulate a wide variety of cell functions, including cell survival, proliferation, morphogenesis, differentiation, motility, invasion and metastasis. An important concept emerging from the data on integrin signal transduction is that integrin signaling impinges on pathways downstream of other receptors, creating elaborate intracellular signaling networks. This review highlights signal transduction functions of epithelial integrins, with particular emphasis on signaling pathways underlying some of the most important functions of epithelium.     

Postmenopausal obesity promotes tumor angiogenesis and breast cancer progression in mice

Obese postmenopausal women have a 50% higher risk of breast cancer than non-obese women. There is not an animal model that mimics postmenopausal obesity related to breast cancer progression. Using age-relevant C57BL/6 mice, this study determined whether postmenopausal obesity increases VEGF expression, tumor angiogenesis, and breast tumor growth. Ovariectomy (OVX) was performed in 12 sixty week-old female mice, then followed by a low-fat (5%, LF, n=6) or a high-fat (60%, HF, n=6) diet for 12 weeks. In the eighth week of the dietary program, 10(6) E0771 (mouse breast cancer) cells were injected in the left fourth mammary gland. Tumor size was monitored for 4 weeks. Body weights were monitored weekly. At the end of the experiment, blood samples, visceral fat and tumors were collected for measuring VEGF expression using ELISA and intratumoral microvessel density (IMD) using CD31 immunochemistry. Body weight was significantly increased in OVX/HF mice, compared to OVX/LF group (55.3±1.7 vs. 41.5±1.5 g; p < 0.01). There was a two-fold increase in the ratio of visceral fat/BW in OVX/HF mice, compared to those in OVX/LF group (0.062±0.005 vs. 0.032±0.003; p < 0.01). Postmenopausal obesity significantly increased breast tumor weight over the control (4.62±0.63 vs. 1.98±0.27 g; p < 0.01) and IMD (173±3.7 vs. 139±4.3 IM#/mm^2; p < 0.01). Tumor VEGF levels were higher in OVX/HF mice, compared to OVX/LF group (73.3±3.8 vs. 49.5±4.3 pg/mg protein; p < 0.01). Plasma VEGF levels (69±7.1 vs. 48±3.5 pg/ml) and visceral fat VEGF levels (424.4±39.5 vs. 208.5±22.4 pg/mg protein) were significantly increased in OVX/HF mice, compared to OVX/LF group, respectively (n=6; p < 0.01). Interestingly, adipose tissue primary culture showed that subcutaneous fat released more VEGF, compared to visceral fat (6.77±1.14 vs. 0.94±0.16 pg/mg tissue; n=6; p < 0.01). These findings support the hypothesis that postmenopausal obesity promotes tumor angiogenesis and breast cancer progression, possibly through increased adipose tissue mass and adipokines such as VEGF that could systemically and locally affect breast cancer progression.