Importância do domínio extracelular do receptor tirosina quinase Tie1 na angiogênese / The importance of Tyrosine Kinase Receptor Tie1 extracellular domain in angiogenesis

Tie1 é um receptor tirosina quinase expresso em células endoteliais importante em angiogênese, formação de vasos sanguíneos a partir de vasos pré-existentes. Este receptor pertence a uma família pequena composta por apenas dois membros (Tie1 e Tie2) para os quais angiopoietinas foram identificadas como ligantes de Tie2. No entanto, Tie1 continua a ser um receptor órfão, sem ligantes identificados até o momento. Sendo assim, é difícil compreender completamente as propriedades biológicas de Tie1 e seus mecanismos moleculares em angiogênese sem um ligante identificado. Entretanto, como sugerido através de estudos de deleção gênica, este receptor é uma molécula essencial na angiogênese, apresentando um papel importante no desenvolvimento da vascularização da retina e desenvolvimento de tumores. O nosso objetivo foi estudar a participação do domínio extracelular de Tie1 na neovascularização e, no processo, identificar possíveis ligantes para este receptor. Através da tecnologia de phage display, identificamos um peptídeo específico e seletivo para Tie1, sugerindo a existência de um sítio de ligação único neste receptor. Mostramos que este peptídeo é capaz de inibir a proliferação de células endoteliais induzida por Ang1, um ligante bem caracterizado de Tie2 que também modula a atividade de Tie1. Além disso, também mostramos que este peptídeo inibe a angiogênese in vivo num modelo animal bastante relevante para estudo de doenças humanas, o modelo da retinopatia induzida por oxigênio. Uma vez que este peptídeo liga-se a um sítio único e seletivo para Tie1, hipotetizamos que o mesmo poderia mimetizar possíveis ligantes naturais deste receptor. Para identificá-los, proteínas com mimetopo cruzado com este peptídeo foram identificadas em extrato proteico de diferentes linhagens celulares. Tais proteínas são possíveis candidatos a interação com Tie1. Em resumo, demonstramos que o domínio extracelular de Tie1 é importante para a angiogênese patológica e identificamos proteínas como possíveis ligantes deste receptor, o que poderá contribuir para um melhor entendimento da participação de Tie1 na formação de vasos. O peptídeo aqui identificado poderá ser ainda uma ferramenta útil para o desenvolvimento de novas terapias anti-angiogênicas com importantes aplicações à saúde humana

Tie1 is a tyrosine kinase receptor expressed by endothelial cells and important in angiogenesis, the formation of new blood vessels from pre-existing ones. This receptor belongs to a small family of receptors composed of two members only (Tie1 and Tie2) to which angiopoietins have been identified as ligands for Tie2. On the other hand, Tie1 is still an orphan receptor with no ligand identified to date. Thus, it is difficult to assess Tie1 mechanism of action in neovascularization without a known ligand. Nevertheless, gene deletion studies have shown that Tie1 is essential in angiogenesis, and plays an important role in retinal and tumoral vascularization. The aim of our study was to evaluate the participation of Tie1 extracellular domain in angiogenesis, and in the process, to identify putative ligands for this receptor. Utilizing phage display, we have identified and characterized a Tie1 specific and selective ligand peptide, which suggests the existence of a binding site unique to this receptor and not shared by other family members. We show that this peptide prevents endothelial cells proliferation, induced by angiopoetin-1, a ligand for Tie2 but which also modulates Tie1 activity. Using a well-accepted mouse model for human diseases, the oxygen induced retinopathy model, we show that this peptide inhibits angiogenesis in vivo. Since this peptide maps to a unique binding site in Tie1, we hypothesized that it might mimic a natural ligand for this receptor. To identify them, proteins with cross reactive epitopes with an anti-peptide sera were identified by proteomic approaches. These proteins are thus possible ligands for Tie1. In summary, we have shown that Tie1 extracellular domain is important in angiogenesis and we have identified putative ligand for this receptor, which might contribute to a better understanding of the molecular mechanisms associated with Tie1 in blood vessel formation. The peptide here characterized may also be an important tool for the development of novel anti-angiogenesis therapeutic approaches for disesase with an angiogenic component

Expression and function of Angiopoietins and their tie receptors in human basophils and mast cells.

The Angiopoietin/Tie system is a key regulator of vascular remodeling, maturation, angiogenesis and lymphangiogenesis. In humans there are three angiopoietins: Angiopoietin-1 (Ang1), Angiopoietin-2 (Ang2), and Angiopoietin-4 (Ang4). Ang1 and Ang2 are the best characterized angiopoietins. The angiopoietin receptor system consists of two type I tyrosine kinase receptors (Tie1 and Tie2). Tie2 binds all known angiopoietins. We sought to characterize Ang1, Ang2, Tie1 and Tie2 expression and functions in human basophils and mast cells. Basophils, LAD-2 cells and Human Lung Mast Cells (HLMCs) constitutively express Ang1 and Ang2 mRNA. Intracellular staining for Ang1 and Ang2 was stronger in basophils than in mast cells. Immunoelectron microscopy demonstrated Ang1 in cytoplasmic vesicles of basophils. The protein kinase C activators phorbol diester (PMA) and bryostatin 1 (Bryo1) stimulated basophils to rapidly release a large amount of Ang1. PMA-induced Ang1 release was inhibited by brefeldin A. Tie1 and Tie2 mRNAs were expressed in basophils, LAD-2 and HLMCs. Basophils, LAD-2 and HLMCs expressed Tie1 on the cell surface. HLMCs and LAD-2 expressed Tie2 on the cell surface, whereas basophils did not. Ang1, but not Ang2, induced migration of mast cells through the engagement of Tie2. Neither Ang1 nor Ang2 induced basophil chemotaxis. We have identified a novel mechanism of cross-talk between human basophils and mast cells mediated by the Ang1/Tie2 system that might be relevant in the orchestration of inflammatory and neoplastic angiogenesis.

The expression of angiogenic growth factors and their receptors in ovarian follicles throughout the estrous cycle in the ewe.

Healthy follicles are highly vascularized whereas those undergoing atresia have poor vascularity, suggesting a relationship between follicular vascularization and follicular function. Vascularization is regulated by angiogenic factors, and among them vascular endothelial growth factor (VEGF) and angiopoietin-Tie (Ang-Tie) systems are of central importance. The objectives of this study were to determine if VEGF, VEGF receptor-2 (VEGFR-2), and components of the Ang-Tie system are expressed in ovarian follicles at both the protein and mRNA levels and to explore if their expression is related to the stage of the estrous cycle in the ewe. Ovaries from cyclic ewes were collected during the luteal phase (n=5) or before (n=5), during (n=4), and after (n=4) the preovulatory luteinizing hormone (LH) surge. After fixation, ovaries were wax-embedded, serially sectioned, and analyzed for both protein and mRNA expression of VEGF, VEGFR-2, angiopoietin-1 (Ang-1), angiopoietin-2 (Ang-2), Tie-1 (mRNA only), and Tie-2. mRNA was studied by in situ hybridization using digoxigenin-11-UTP-labeled ovine riboprobes. A similar pattern of expression was observed for mRNA and protein for all of the factors. Both mRNA and protein expression of VEGF, VEGFR-2, Ang-1, Ang-2, Tie-1 (mRNA only), and Tie-2 in the granulosa and theca cells of follicles >or=2mm in diameter was significantly different among the stages of the estrous cycle, with the highest expression detected at the post-LH surge stage. Theca cells expressed significantly greater levels of the six angiogenic factors compared with granulosa cells at all stages of the estrous cycle. Expression levels in granulosa and theca cells were comparable between small (2.0 to 2.5mm) and medium (2.5 to 4.0mm) follicles, but large follicles (>4.0mm) expressed higher mRNA and protein levels (all P<0.05) for all factors at all stages of the estrous cycle. These data show (i) that VEGF, VEGFR-2, and the Ang-Tie system are present in both granulosa and theca cells of the ovarian follicle, (ii) that thecal cells consistently express greater levels of all of these factors compared with granulosa cells, and (iii) that their levels of expression are related to the stage of the estrous cycle and to follicle size.

Expression of angiopoietin-1, 2 and 4 and Tie-1 and 2 in gastrointestinal stromal tumor, leiomyoma and schwannoma.

AIM: To investigate the role of angiopoietin (Ang) -1, -2 and -4 and its receptors, Tie-1 and -2, in the growth and differentiation of gastrointestinal stromal tumors (GISTs). METHODS: Thirty GISTs, seventeen leiomyomas and six schwannomas were examined by immunohistochemistry in this study. RESULTS: Ang-1, -2 and -4 proteins were expressed in the cytoplasm of tumor cells, and Tie-1 and -2 were expressed both in the cytoplasm and on the membrane of all tumors. Immunohistochemical staining revealed that 66.7% of GISTs (20 of 30), 76.5% of leiomyomas (13 of 17) and 83.3% of schwannomas (5 of 6) were positive for Ang-1. 83.3% of GISTs (25 of 30), 82.4% of leiomyomas (14 of 17) and 100% of schwannomas (6 of 6) were positive for Ang-2. 36.7% of GISTs (11 of 30), 58.8% of leiomyomas (10 of 17) and 83.3% of schwannomas (5 of 6) were positive for Ang-4. 60.0% of GISTs (18 of 30), 82.4% of leiomyomas and 100% of schwannomas (6 of 6) were positive for Tie-1. 10.0% of GISTs (3 of 30), 94.1% of leiomyomas (16 of 17) and 33.3% of schwannomas (2 of 6) were positive for Tie-2. Tie-2 expression was statistically different between GISTs and leiomyomas (P < 0.001). However, there was no correlation between expression of angiopoietin pathway components and clinical risk categories. CONCLUSION: Our results suggest that the angiopoietin pathway plays an important role in the differentiation of GISTs, leiomyomas and schwannomas.

Mapping of angiogenic markers for targeting of vectors to tumor vascular endothelial cells.

The vasculature of mouse breast tumor spheroids grown on mammary fat pad tissue in an intravital microscopy (IVM) viewing chamber was shown to derive from infiltrating angiogenic mammary vessels. The receptors tissue factor (TF), alpha V beta 3 integrin and Tie-2 were expressed on the vascular endothelium in the periphery but not in the center of the tumor spheroids nor in the mammary tissue nor in smooth muscle tissue, whereas Tie-1 and PCAM-1 were expressed extensively in the entire tumor and in the vascular endothelium of the entire tumor nodule and in normal mammary tissue. TF is a specific target for adenoviral vector-mediated cancer immunotherapy. Subcutaneous injection of the AdfVII/IgG(1)Fc vector leads to the release into the system circulation of a fVII/IgG(1)Fc immunoconjugate molecule that binds specifically and tightly to TF on vascular endothelial cells and tumor cells, activating a cytolytic immune response against the targeted cells. We show that a single administration of the AdfVII/IgG(1)Fc vector destroys the peripheral but not the central vasculature of a tumor spheroid, causing partial tumor regression; additional administrations prevent regeneration of the peripheral vasculature and regrowth of the tumor. These findings indicate that a critical parameter for optimizing tumor damage is the schedule for successive administrations of the AdfVII/IgG(1)Fc, which should coincide with the regeneration of the peripheral vasculature and continue until the tumor is destroyed.

Expression of vascular endothelial growth factor receptor 3 and Tie1 tyrosine kinase receptor on acute leukemia cells.

BACKGROUND: Recent data indicate a role for angiogenesis in hematologic malignancies. In addition to promoting new vessel growth in the bone marrow microenvironment, angiogenic factors are regulators of both hematopoietic and leukemic cells. Activation of vascular endothelial growth factor receptor 3 (VEGFR-3) and Tie1 tyrosine kinase receptor are known to promote leukemia cell survival. The details of this complex angiogenesis-related interaction are still uncertain. PROCEDURE: We studied bone marrow samples from 73 patients with acute lymphoblastic (ALL) or myelogenous (AML) leukemia by using immunological methods. RESULTS: Vascular endothelial growth factor receptor 3 expression was found in 15% of the samples, particularly in samples with pediatric lymphoblastic leukemias and monocytic AMLs. Tie1 protein expression was found in 11% of the samples, all of which were from adult AML patients. CONCLUSIONS: Our findings suggest that there are angiogenesis-related differences between pediatric and adult lymphoblastic leukemias as well as between lymphoid and myeloid leukemias.

Enhanced expression of angiopoietin-2 and the Tie2 receptor but not angiopoietin-1 or the Tie1 receptor in a rat model of myocardial infarction.

Modulation of Tie2 receptor activity by angiopoietin ligands is crucial for angiogenesis, blood vessel maturation, and vascular endothelium integrity. The role of the angiopoietin (Ang) and Tie system in myocardial infarction is not well understood. To investigate the participation of the Ang/Tie in myocardial infarction, adult Sprague-Dawley rats with ligation of the left anterior descending coronary artery to induce myocardial infarction were studied. Ang1, Ang2, Tie1, and Tie2 were measured immediately after ligation of the coronary artery, and at 6 h, 1 and 3 days, and 1, 2, 3 and 4 weeks after ligation by Northern blotting, Western blotting, and immunohistochemical staining. Ang2 mRNA significantly increased from 2 weeks (2.1-fold) to 4 weeks (2.9-fold) after the infarction in the left ventricular free wall. Tie2 mRNA increased significantly from 1 week (2.1-fold) to 4 weeks (3.8-fold) after the infarction. Ang2 protein also significantly increased from 3 days (1.9-fold) to 4 weeks (3-fold) after the infarction in the left ventricular free wall. Tie2 protein increased 2.4-fold at 3 weeks and 2.8-fold at 4 weeks after the infarction. Neither Ang1 nor Tie1 mRNA or protein showed any significant change at any time point after the infarction. The ratio of Ang2/Ang1 mRNA and protein in the study group was higher than that in the control group. Ang2 and Tie2 expression in nonischemic myocardium showed no significant change. Immunohistochemical study also showed increased immunoreactivity of Ang2 and Tie2 at the infarct border. In conclusion, Ang2 and Tie2 expressions significantly increased both spatial and temporal patterns after myocardial infarction in the rat ventricular myocardium, while Ang1 and Tie1 receptor expression did not.