Angiostatin

The Glycosaminoglycan Side Chains and Modular Core Proteins of Heparan Sulphate Proteoglycans and the Varied Ways They Provide Tissue Protection by Regulating Physiological Processes and Cellular Behaviour

This review examines the roles of HS-proteoglycans (HS-PGs) in general, and, in particular, perlecan and syndecan as representative examples and their interactive ligands, which regulate physiological processes and cellular behavior in health and disease. HS-PGs are essential for the functional properties of tissues both in development and in the extracellular matrix (ECM) remodeling that occurs in response to trauma or disease. HS-PGs interact with a biodiverse range of chemokines, chemokine receptors, protease inhibitors, and growth factors in immune regulation, inflammation, ECM stabilization, and tissue protection. Some cell regulatory proteoglycan receptors are dually modified hybrid HS/CS proteoglycans (betaglycan, CD47). Neurexins provide synaptic stabilization, plasticity, and specificity of interaction, promoting neurotransduction, neurogenesis, and differentiation. Ternary complexes of glypican-1 and Robbo-Slit neuroregulatory proteins direct axonogenesis and neural network formation. Specific neurexin-neuroligin complexes stabilize synaptic interactions and neural activity. Disruption in these interactions leads to neurological deficits in disorders of functional cognitive decline. Interactions with HS-PGs also promote or inhibit tumor development. Thus, HS-PGs have complex and diverse regulatory roles in the physiological processes that regulate cellular behavior and the functional properties of normal and pathological tissues. Specialized HS-PGs, such as the neurexins, pikachurin, and Eyes-shut, provide synaptic stabilization and specificity of neural transduction and also stabilize the axenome primary cilium of phototoreceptors and ribbon synapse interactions with bipolar neurons of retinal neural networks, which are essential in ocular vision. Pikachurin and Eyes-Shut interactions with an α-dystroglycan stabilize the photoreceptor synapse. Novel regulatory roles for HS-PGs controlling cell behavior and tissue function are expected to continue to be uncovered in this fascinating class of proteoglycan.

Rutacecarpine Inhibits Angiogenesis by Targeting the VEGFR2 and VEGFR2-Mediated Akt/mTOR/p70s6k Signaling Pathway

This study aimed to investigate the effect of Ru (Rut) on angiogenesis, and the underlying regulation mechanism of signal transduction. 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) assay, adhesion inhibition experiment, migration inhibition experiment, and chick embryo chorioallantoic membrane (CAM) assays were performed on models of angiogenesis. The potential targets of rutaecarpine (Ru) were reverse screened with Discovery Studio 2017. The interaction between the compound and target were detected by surface plasmon resonance (SPR), enzyme-activity experiment, and Western blot assay. The obtained results confirmed that Ru exhibited modest inhibitory activity against human umbilical vein endothelial cells (HUVECs) (IC₅₀ =16.54 ± 2.4 μM) and remarkable inhibitive effect against the migration and adhesion of HUVECs, as well as significant anti-angiogenesis activities in the CAM assay. The possible targets of vascular endothelial growth factor receptor 2 (VEGFR2) were identified by computer-aided simulation. Results showed a good binding relationship between the ligand and target through molecular docking, and this relationship was confirmed by SPR analysis. Furthermore, enzyme-activity experiment and western blot assay showed that Ru remarkably inhibited the activity of VEGFR2 and blocked the VEGFR2-mediated Akt/ (mTOR)/p70s6k signaling pathway in vitro. Ru can be a potential drug candidate for cancer prevention and cancer therapy.

PLASMINOGEN AND ANGIOSTATIN LEVELS IN FEMALE BENIGN BREAST LESIONS

It is known that benign breast tissue exhibit relatively low angiogenic capacity. Activation of angiogenesis in mammary pre-malignant lesions could be associated with disease progression and high risk of transformation into the breast cancer. However, insight into the underlying molecular mechanisms involved in angiogenesis regulation in non-cancerous breast pathologies is still poorly defined. The purpose of the present study was to determine levels of plasminogen and its proteolytic fragments (angiostatins) in mammary dysplasia (mastopathy and breast cyst) and benign neoplasms (fibroadenomas). Plasminogen and angiostatins were analyzed using immunoblotting and quantified by densitometric scanning. The significant increase in plasminogen levels was found in fibrocystic, cysts, and non-proliferatious fibroadenoma masses (4.7-, 3.7-, and 3.5-fold, respectively) compared to healthy breast tissues (control). In the same benign lesions, 6.7-, 4-, and 3.7-fold increase in plasminogen 50 kDa fragment (angiostatin) levels as compared with control were also observed. Activation of matrix metalloproteinase-9, which was detected using gelatine zymography, could be responsible for plasminogen cleavage and abundance of angiostatin infibrocystic and cyst masses. In contrast, dramatic decrease of both plasminogen and angiostatin levels (3.8- and 5.3-folds, respectively) was shown in tissues of proliferatious form of fibroadenoma in comparison with that of the dormant type of this neoplasm. Based on the obtained results, we concluded that angiostatin, a potent vessel growth inhibitor and anti-inflammatory molecule, can play a crucial role in pathophysiology of non-cancerous breast diseases. Further studies are needed to evaluate potential diagnostic and clinical implications of these proteins for prediction and therapy of benign breast pathologies.

Antiangiogenic kringles derived from human plasminogen and apolipoprotein(a) inhibit fibrinolysis through a mechanism that requires a functional lysine-binding site

Many proteins in the fibrinolysis pathway contain antiangiogenic kringle domains. Owing to the high degree of homology between kringle domains, there has been a safety concern that antiangiogenic kringles could interact with common kringle proteins during fibrinolysis leading to adverse effects in vivo. To address this issue, we investigated the effects of several antiangiogenic kringle proteins including angiostatin, apolipoprotein(a) kringles IV(9)-IV(10)-V (LK68), apolipoprotein(a) kringle V (rhLK8) and a derivative of rhLK8 mutated to produce a functional lysine-binding site (Lys-rhLK8) on the entire fibrinolytic process in vitro and analyzed the role of lysine binding. Angiostatin, LK68 and Lys-rhLK8 increased clot lysis time in a dose-dependent manner, inhibited tissue-type plasminogen activator-mediated plasminogen activation on a thrombin-modified fibrinogen (TMF) surface, showed binding to TMF and significantly decreased the amount of plasminogen bound to TMF. The inhibition of fibrinolysis by these proteins appears to be dependent on their functional lysine-binding sites. However, rhLK8 had no effect on these processes owing to an inability to bind lysine. Collectively, these results indicate that antiangiogenic kringles without lysine binding sites might be safer with respect to physiological fibrinolysis than lysine-binding antiangiogenic kringles. However, the clinical significance of these findings will require further validation in vivo.

Inhibition of Angiogenesis and Tumor Metastasis by Targeting a Matrix Immobilized Cryptic Extracellular Matrix Epitope in Laminin

Angiogenesis and tumor metastasis depend on extracellular matrix (ECM) remodeling and subsequent cellular interactions with these modified proteins. An in-depth understanding of how both endothelial and tumor cells use matrix-immobilized cryptic ECM epitopes to regulate invasive cell behavior may lead to the development of novel strategies for the treatment of human tumors. However, little is known concerning the existence and the functional significance of cryptic laminin epitopes in regulating angiogenesis and tumor cell metastasis. Here, we report the isolation and characterization of a synthetic peptide that binds to a cryptic epitope in laminin. The STQ peptide selectively bound denatured and proteolyzed laminin but showed little interaction with native laminin. The cryptic laminin epitope recognized by this peptide was selectively exposed within malignant melanoma in vivo, whereas little if any was detected in normal mouse skin. Moreover, the STQ peptide selectively inhibited endothelial and tumor cell adhesion, migration, and proliferation in vitro and inhibited angiogenesis, tumor growth, and experimental metastasis in vivo. This inhibitory activity was associated with a selective up-regulation of the cyclin-dependent kinase inhibitor P27(KIP1) and induction of cellular senescence. These novel findings suggest the existence of functionally relevant cryptic laminin epitopes in vivo and that selective targeting of these laminin epitopes may represent an effective new strategy for the treatment of malignant tumors by affecting both the endothelial and tumor cell compartments.