Angiogenin enhances actin acceleration of plasminogen activation

Human and mouse angiogenins: Emerging insights and potential opportunities

Angiogenin, a well-known angiogenic factor, is crucial to the angiogenesis in gastrointestinal tumors. Human angiogenin has only one gene, whereas the murine angiogenin family has extended to incorporate six genes. Evolutionary studies have suggested functional variations among murine angiogenin paralogs, even though the three-dimensional structures of angiogenin proteins are remarkably similar. In addition to angiogenesis, the ubiquitous pattern of angiogenin expression suggests a variety of functions, such as tumorigenesis, neuroprotective, antimicrobial activity, and innate immunity. Here, we comprehensively reviewed studies on the structures and functions of human and mouse angiogenins. Understanding the structure and function of angiogenins from a broader perspective could facilitate future research related to development of novel therapeutics on its biological processes, especially in gastrointestinal cancers.

A Graphene Oxide-Angiogenin Theranostic Nanoplatform for the Therapeutic Targeting of Angiogenic Processes: The Effect of Copper-Supplemented Medium

Graphene oxide (GO) nanosheets with different content in the defective carbon species bound to oxygen sp3 were functionalized with the angiogenin (ANG) protein, to create a novel nanomedicine for modulating angiogenic processes in cancer therapies. The GO@ANG nanocomposite was scrutinized utilizing UV-visible and fluorescence spectroscopies. GO exhibits pro- or antiangiogenic effects, mostly attributed to the disturbance of ROS concentration, depending both on the total concentration (i.e., >100 ng/mL) as well as on the number of carbon species oxidized, that is, the C/O ratio. ANG is considered one of the most effective angiogenic factors that plays a vital role in the angiogenic process, often in a synergic role with copper ions. Based on these starting hypotheses, the GO@ANG nanotoxicity was assessed with the MTT colorimetric assay, both in the absence and in the presence of copper ions, by in vitro cellular experiments on human prostatic cancer cells (PC-3 line). Laser confocal microscopy (LSM) cell imaging evidenced an enhanced internationalization of GO@ANG than bare GO nanosheets, as well as significant changes in cell cytoskeleton organization and mitochondrial staining compared to the cell treatments with free ANG.

Characterization and Function of the Interaction of Angiogenin With Alpha-Actinin 2

Angiogenin (ANG) is the first human tumor-derived angiogenic protein, which can promote angiogenesis and tumor growth. In a previous study, we identified alpha-actinin 2 (ACTN2), a cytoskeletal protein, as a direct interacting protein with angiogenin. However, the interaction between ANG and ACTN2 was not characterized in detail, which may provide information on the molecular mechanisms of ANG functions. In this study, we mapped the accurate binding domain and sites in ANG and ACTN2, respectively. In ANG, the residues from 83 to 105 are the smallest motif that can bind to ACTN2. We then use site mutation analysis to identify the precise binding sites of ANG in the interaction and found that the 101st residue arginine (R101) represents the critical residue involved in the ANG–ACTN2 interaction. In ACTN2, the residues from 383 to 632, containing two spectrin domains in the middle of the rod structure of ACTN2, play an important role in the interaction. Furthermore, we validated the interaction of ACTN2-383–632 to ANG by glutathione-S-transferase (GST) pull-down assay. In functional analysis, overexpressed ACTN2-383–632 could impair tumor cell motility observably, including cell migration and invasion. Meanwhile, ACTN2-383–632 overexpression inhibited tumor cell proliferation and survival as well. These data suggest that an excess expression of ACTN2 segment ACTN2-383–632 can inhibit tumor cell motility and proliferation by interfering with the interaction between ANG and ACTN2, which provides a potential mechanism of ANG action in tumor growth and metastasis.

Angiogenin and MMP-2 as potential biomarkers in the differential diagnosis of gestational trophoblastic diseases

BACKGROUND

Gestational trophoblastic diseases (GTDs) are characterized by vascular abnormalities of the trophoblast, but their pathogenesis is unknown. Angiogenin (ANG) and matrix metalloproteinase (MMP)-2, which are molecules implicated in the angiogenic process, may play some role in this process.

MATERIAL AND METHODS

We determined ANG and MMP-2 in the placental tissues of 26 patients who had a benign mole (BM), 12 patients with gestational trophoblast neoplasia (GTN) (1 invasive hydatidiform mole, 10 choriocarcinomas, and 1 placental-site trophoblastic tumor), and 28 normal chorionic villi (NCV) subjects using immunohistochemistry staining. We obtained the serum samples from 20 patients with GTDs and 20 early pregnant women and evaluated them by the enzyme linked immunosorbent assay.

RESULTS

ANG expression in GTN (66.7%) and BM (100%) samples were both significantly higher (strong/intermediate staining) than in NCV (60.7%) samples (P < .001). Similarly, the immunoreactivities of MMP-2 in the GTN (66.7%) and BM (80.8%) samples were significantly elevated compared to that of the NCV (57.1%) samples (P < .001). The levels of ANG and MMP-2 in the maternal serum of the GTN group were both significantly higher than those of the control group (P < .001). ANG and MMP-2 expressions were associated with gestation age, clinical stage, and FIGO stage. A positive correlation between ANG and MMP-2 expression was observed (rs = 0.725; P < .01).

CONCLUSION

ANG and MMP-2 levels were significantly elevated in the placental tissues and maternal serum from patients with GTDs. Further studies with more patients may clarify the vascular abnormalities in GTDs and determine potential biomarkers in the differential diagnosis of GTDs.

Angiogenin and Copper Crossing in Wound Healing

Angiogenesis plays a key role in the wound healing process, involving the migration, growth, and differentiation of endothelial cells. Angiogenesis is controlled by a strict balance of different factors, and among these, the angiogenin protein plays a relevant role. Angiogenin is a secreted protein member of the ribonuclease superfamily that is taken up by cells and translocated to the nucleus when the process of blood vessel formation has to be promoted. However, the chemical signaling that activates the protein, normally present in the plasma, and the transport pathways through which the protein enters the cell are still largely unclear. Copper is also an angiogenic factor that regulates angiogenin expression and participates in the activation of common signaling pathways. The interaction between angiogenin and copper could be a relevant mechanism in regulating the formation of new blood vessel pathways and paving the way to the development of new drugs for chronic non-healing wounds.

Functional roles of the human ribonuclease A superfamily in RNA metabolism and membrane receptor biology

The human ribonuclease A (hRNase A) superfamily is comprised of 13 members of secretory RNases, most of which are recognized as catabolic enzymes for their ribonucleolytic activity to degrade ribonucleic acids (RNAs) in the extracellular space, where they play a role in innate host defense and physiological homeostasis. Interestingly, human RNases 9-13, which belong to a non-canonical subgroup of the hRNase A superfamily, are ribonucleolytic activity-deficient proteins with unclear biological functions. Moreover, accumulating evidence indicates that secretory RNases, such as human RNase 5, can be internalized into cells facilitated by membrane receptors like the epidermal growth factor receptor to regulate intracellular RNA species, in particular non-coding RNAs, and signaling pathways by either a ribonucleolytic activity-dependent or -independent manner. In this review, we summarize the classical role of hRNase A superfamily in the metabolism of extracellular and intracellular RNAs and update its non-classical function as a cognate ligand of membrane receptors. We further discuss the biological significance and translational potential of using secretory RNases as predictive biomarkers or therapeutic agents in certain human diseases and the pathological settings for future investigations.

A novel ligand-receptor relationship between families of ribonucleases and receptor tyrosine kinases

Pancreatic ribonuclease is known to participate in host defense system against pathogens, such as parasites, bacteria, and virus, which results in innate immune response. Nevertheless, its potential impact to host cells remains unclear. Of interest, several ribonucleases do not act as catalytically competent enzymes, suggesting that ribonucleases may be associated with certain intrinsic functions other than their ribonucleolytic activities. Most recently, human pancreatic ribonuclease 5 (hRNase5; also named angiogenin; hereinafter referred to as hRNase5/ANG), which belongs to the human ribonuclease A superfamily, has been demonstrated to function as a ligand of epidermal growth factor receptor (EGFR), a member of the receptor tyrosine kinase family. As a newly identified EGFR ligand, hRNase5/ANG associates with EGFR and stimulates EGFR and the downstream signaling in a catalytic-independent manner. Notably, hRNase5/ANG, whose level in sera of pancreatic cancer patients, serves as a non-invasive serum biomarker to stratify patients for predicting the sensitivity to EGFR-targeted therapy. Here, we describe the hRNase5/ANG-EGFR pair as an example to highlight a ligand-receptor relationship between families of ribonucleases and receptor tyrosine kinases, which are thought as two unrelated protein families associated with distinct biological functions. The notion of serum biomarker-guided EGFR-targeted therapies will also be discussed. Furthering our understanding of this novel ligand-receptor interaction will shed new light on the search of ligands for their cognate receptors, especially those orphan receptors without known ligands, and deepen our knowledge of the fundamental research in membrane receptor biology and the translational application toward the development of precision medicine.

The Levels of Circulating Proangiogenic Factors in Migraineurs

Migraine has been reported as a risk factor for ischemic stroke or cardiovascular events, and dysfunction of endothelial cells has been evidenced in migraine patients. Proangiogenic factors are potential endothelial stimulators, and their disturbances can link abnormalities of endothelium with increased risk of vascular disorders. The aim of this study was to evaluate the levels of circulating proangiogenic factors in sera of migraineurs during interictal period. Fifty-two patients aged 37.9 ± 9.6 years, fulfilling International Headache Society criteria for migraine, were included in this observational case-control study. The control group included 39 healthy volunteers, matched according to age and gender. All subjects underwent full neurological examination and clinimetric evaluation with the use of: MIDAS, MIGSEV, QVM, VAS and VRS scales. Serum concentrations of vascular endothelial growth factor (VEGF), angiogenin, angiopoietin-2, thrombopoietin and Tie-2 were estimated in migraineurs and in the control group with the use of ELISA. In migraineurs during interictal period, we have found decreased serum VEGF and angiogenin concentrations compared with controls. Age of migraine onset correlated with VEGF, angiopoietin-2 and thrombopoietin concentrations. Furthermore, angiopoietin-2 level correlated with QVM score and Tie-2 with pain intensity evaluated using MIGSEV scale. In migraine patients during interictal period, depletion of VEGF and angiogenin, two cooperating proangiogenic factors, can be responsible for endothelial dysfunction and increased risk for vascular disorders.

Extracellular Actin in Health and Disease

This review considers the functions of extracellular actin - cell surface bound, associated with extracellular matrix, or freely circulating. The role of this protein in different pathological processes is analyzed: its toxic effects and involvement in autoimmune diseases as an autoantigen. The extracellular actin clearance system and its role in protection against the negative effects of actin are characterized. Levels of free-circulating actin, anti-actin immunoglobulins, and components of the actin clearance system as prognostic biomarkers for different diseases are reviewed. Experimental approaches to protection against excessive amounts of free-circulating F-actin are discussed.

Three decades of research on angiogenin: a review and perspective

As a member of the vertebrate-specific secreted ribonucleases, angiogenin (ANG) was first isolated and identified solely by its ability to induce new blood vessel formation, and now, it has been recognized to play important roles in various physiological and pathological processes through regulating cell proliferation, survival, migration, invasion, and/or differentiation. ANG exhibits very weak ribonucleolytic activity that is critical for its biological functions, and exerts its functions through activating different signaling transduction pathways in different target cells. A series of recent studies have indicated that ANG contributes to cellular nucleic acid metabolism. Here, we comprehensively review the results of studies regarding the structure, mechanism, and function of ANG over the past three decades. Moreover, current problems and future research directions of ANG are discussed. The understanding of the function and mechanism of ANG in a wide context will help to better delineate its roles in diseases, especially in cancer and neurodegenerative diseases.

Carboxymethylsulfonylated Ribopyrimidines: Rational Design of Ribonuclease A Inhibitors Employing Chemical Logic

Hydrolysis of RNA by ribonuclease A crucially depends on the participation of the 2'-OH group as well as the positioning of the internucleotide bond at two different sites of the enzyme. Therefore, ribopyrimidines were modified with -SO2CH2CO2H, an acidic functional group, which was expected to interact with the phosphate binding site. These ribonucleosides were designed to understand the influence of the 2'-OH group of these inhibitors on ribonuclease A inhibition along with the effect of the -SO2CH2CO2H group. The "down" configuration of the 2'-OH group enhanced the inhibitory properties (Ki =1.75 μm) and also imparted important Val43 H-bonding with the furanose oxygen atom of the inhibitors. One of the most important aspects of this work is that there was no serendipitous discovery of the inhibitors. The inhibitors reported in this manuscript were obtained by design by employing chemical logic.

Circulating monocyte chemotactic protein 1 (MCP-1), vascular cell adhesion molecule 1 (VCAM-1) and angiogenin in type 2 diabetic patients treated with statins in low doses

Statins are known as agents promoting a biphasic dose-dependent effect on angiogenesis under experimental conditions. Dysregulation of angiogenesis plays an important role in the development of atherosclerosis and it may be affected by metabolic factors. The aim of this research was to explain how low doses of statins modify serum concentrations of pro-angiogenic factors MCP-1 and angiogenin in type 2 diabetic patients. Measurements of metabolic control parameters were performed in 30 patients with type 2 diabetes treated with low doses of statin, and in 34 statin-free patients with type 2 diabetes. The serum levels of MCP-1 and VCAM-1 in statin-treated patients were lower than those of the statin-free group. ANCOVA results revealed that these effects were dependent only on the use of statins. In type 2 diabetic subjects, overall positive correlation was found between total cholesterol or LDL serum concentration and MCP-1 serum level. The angiogenin concentration in the serum did not show differences and was comparable in both groups. The angiogenin serum level correlated negatively with HDL, LDL and with HbA1c. Multivariate regression analysis indicated that angiogenin serum levels in type 2 diabetic patients were determined mainly by HbA1c, HDL-cholesterol and diabetes duration. It has been shown that statins used in low doses in type 2 diabetic subjects decrease MCP-1 and VCAM-1serum levels, most likely due to the statins-related effect on the lipid profile, while angiogenin serum levels in this group are determined rather by the current metabolic control.

Angiogenin interacts with the plasminogen activation system at the cell surface of breast cancer cells to regulate plasmin formation and cell migration

Angiogenin (ANG), a 14-kDa pro-angiogenic secreted protein, has been shown to play a role in cell migration and tumor invasion, which involve proteolytic cleavage of plasminogen to generate plasmin. However, the mechanism by which ANG regulates plasmin formation and cell migration was not known. Our studies here detected elevated levels of secreted and cell surface-bound ANG in highly invasive metastatic breast cancer cells. ANG was also detected at very high levels in the tumor cells in infiltrating ductal carcinomas. By immunofluorescence and immunoprecipitation analysis, ANG was detected at the leading edges of the cell surfaces where it colocalized and interacted with members of the plasminogen activation system (PAS) such as annexin A2 (A2), calpactin (S100-A10) and urokinase plasminogen activator receptor (uPAR). Analysis of lipid raft (LR) and non-lipid raft (NLR) regions of the cell membranes showed the predominance of ANG, A2 and S100-A10 in the LR regions. In contrast, uPAR was detected predominantly in the NLR fractions, suggesting that ANG interacts with uPAR at the junctions of LR and NLR regions. ANG knockdown in T47D and MDA-MB-231 breast cancer cell lines did not affect the cellular expression of A2, S100-A10 and uPAR but decreased cell migration and plasmin formation. Neutralization of ANG with monoclonal antibodies similarly decreased the migration of MDA-MB-231 cells. In the presence of ANG, uPAR was observed to interact with uPA, which is necessary for plasmin formation. Conversely, in the absence of ANG, uPAR did not interact with uPA and FAK and Src kinases were observed to be dephosphorylated. Exogenous addition of recombinant ANG to ANG knocked down MDA-MB-231 cells restored FAK phosphorylation, uPAR interactions with uPA, plasmin formation as well as migration of these cells. Taken together, our results identified a novel role for ANG as a member of the uPAR interactome that facilitates the interaction of uPAR with uPA, leading to plasmin formation and cell migration necessary for tumor invasion and metastasis of breast cancer cells.

Kaposi's sarcoma-associated herpesvirus-positive primary effusion lymphoma tumor formation in NOD/SCID mice is inhibited by neomycin and neamine blocking angiogenin's nuclear translocation

Angiogenin (ANG) is a 14-kDa multifunctional proangiogenic secreted protein whose expression level correlates with the aggressiveness of several tumors. We observed increased ANG expression and secretion in endothelial cells during de novo infection with Kaposi's sarcoma-associated herpesvirus (KSHV), in cells expressing only latency-associated nuclear antigen 1 (LANA-1) protein, and in KSHV latently infected primary effusion lymphoma (PEL) BCBL-1 and BC-3 cells. Inhibition of phospholipase Cγ (PLCγ) mediated ANG's nuclear translocation by neomycin, an aminoglycoside antibiotic (not G418-neomicin), resulted in reduced KSHV latent gene expression, increased lytic gene expression, and increased cell death of KSHV(+) PEL and endothelial cells. ANG detection in significant levels in KS and PEL lesions highlights its importance in KSHV pathogenesis. To assess the in vivo antitumor activity of neomycin and neamine (a nontoxic derivative of neomycin), BCBL-1 cells were injected intraperitoneally into NOD/SCID mice. We observed significant extended survival of mice treated with neomycin or neamine. Markers of lymphoma establishment, such as increases in animal body weight, spleen size, tumor cell spleen infiltration, and ascites volume, were observed in nontreated animals and were significantly diminished by neomycin or neamine treatments. A significant decrease in LANA-1 expression, an increase in lytic gene expression, and an increase in cleaved caspase-3 were also observed in neomycin- or neamine-treated animal ascitic cells. These studies demonstrated that ANG played an essential role in KSHV latency maintenance and BCBL-1 cell survival in vivo, and targeting ANG function by neomycin/neamine to induce the apoptosis of cells latently infected with KSHV is an attractive therapeutic strategy against KSHV-associated malignancies.

Genes of the RNASE5 pathway contain SNP associated with milk production traits in dairy cattle

BACKGROUND

Identification of the processes and mutations responsible for the large genetic variation in milk production among dairy cattle has proved challenging. One approach is to identify a biological process potentially involved in milk production and to determine the genetic influence of all the genes included in the process or pathway. Angiogenin encoded by angiogenin, ribonuclease, RNase A family 5 (RNASE5) is relatively abundant in milk, and has been shown to regulate protein synthesis and act as a growth factor in epithelial cells in vitro. However, little is known about the role of angiogenin in the mammary gland or if the polymorphisms present in the bovine RNASE5 gene are associated with lactation and milk production traits in dairy cattle. Given the high economic value of increased protein in milk, we have tested the hypothesis that RNASE5 or genes in the RNASE5 pathway are associated with milk production traits. First, we constructed a "RNASE5 pathway" based on upstream and downstream interacting genes reported in the literature. We then tested SNP in close proximity to the genes of this pathway for association with milk production traits in a large dairy cattle dataset.

RESULTS

The constructed RNASE5 pathway consisted of 11 genes. Association analysis between SNP in 1 Mb regions surrounding these genes and milk production traits revealed that more SNP than expected by chance were associated with milk protein percent (P < 0.05 significance). There was no significant association with other traits such as milk fat content or fertility.

CONCLUSIONS

These results support a role for the RNASE5 pathway in milk production, specifically milk protein percent, and indicate that polymorphisms in or near these genes explain a proportion of the variation for this trait. This method provides a novel way of understanding the underlying biology of lactation with implications for milk production and can be applied to any pathway or gene set to test whether they are responsible for the variation of complex traits.

Transcriptome temporal and functional analysis of liver regeneration termination

Decades of liver regeneration studies still left the termination phase least elucidated. However regeneration ending mechanisms are clinicaly relevant. We aimed to analyse the timing and transcriptional control of the latest phase of liver regeneration, both controversial. Male Wistar rats were subjected to 2/3 partial hepatectomy with recovery lasting from 1 to 14 days. Time-series microarray data were assessed by innovative combination of hierarchical clustering and principal component analysis and validated by real-time RT-PCR. Hierarchical clustering and principal component analysis in agreement distinguished three temporal phases of liver regeneration. We found 359 genes specifically altered during late phase regeneration. Gene enrichment analysis and manual review of microarray data suggested five pathways worth further study: PPAR signalling pathway; lipid metabolism; complement, coagulation and fibrinolytic cascades; ECM remodelling and xenobiotic biotransformation. Microarray findings pertinent for termination phase were substantiated by real-time RT-PCR. In conclusion, transcriptional profiling mapped late phase of liver regeneration beyond 5(th) day of recovery and revealed 5 pathways specifically acting at this time. Inclusion of longer post-surgery intervals brought improved coverage of regeneration time dynamics and is advisable for further works. Investigation into the workings of suggested pathways might prove helpful in preventing and managing liver tumours.

Vascular endothelial growth factor, carbonic anhydrase 9, and angiogenin as urinary biomarkers for bladder cancer detection

OBJECTIVE

To investigate whether elevated urinary levels of vascular endothelial growth factor (VEGF), carbonic anhydrase 9 (CA9), and angiogenin are associated with bladder cancer (BCa).

METHODS

This was a case-control study in which voided urine samples from 127 patients (63 control subjects and 64 patients with BCa) were analyzed. The urinary concentrations of VEGF, CA9, angiogenin, and bladder tumor antigen (BTA) were assessed using enzyme-linked immunosorbent assays. We used the area under the curve of receiver operating characteristic curves to determine the ability of VEGF, CA9, and angiogenin to detect BCa in voided urine samples. Data were also compared with the findings from a commercial enzyme-linked immunosorbent assay-based BCa detection assay (BTA-Trak). The sensitivity, specificity, and positive and negative predictive values were calculated.

RESULTS

The urinary concentrations of VEGF, CA9, angiogenin, and BTA were significantly elevated in those with BCa. VEGF was the most accurate urinary biomarker (area under the curve 0.886, 95% confidence interval 0.8301-0.9418). Furthermore, multivariate regression analysis highlighted VEGF (odds ratio 5.90, 95% confidence interval 2.60-13.40, P < .0001) as an independent variable. The sensitivity and specificity for VEGF (83% sensitivity and 87% specificity) outperformed those for BTA (80% sensitivity and 84% specificity).

CONCLUSION

VEGF could be a valuable addition to voided urine sample analysis for the detection of BCa. Larger, prospective studies are needed to determine the clinical utility of urinary VEGF and angiogenin as biomarkers in the noninvasive evaluation of patients with BCa.

Angiogenin up-regulation correlates with adverse clinicopathological and biological factors, increased microvascular density and poor patient outcome in neuroblastomas

AIMS

As new biomarkers are urgently needed to identify children with high-risk neuroblastoma (NB), we studied the contribution of angiogenin (ANG) to angiogenesis and its association with clinicopathological and biological features and patient outcome in NB.

METHODS AND RESULTS

Ninety NBs and 12 ganglioneuromas (GNs) were immunostained for ANG and CD31. ANG expression in NB tumoral cells (ANG scores) and vessels [ANG microvascular density (MVD)] and total MVD (CD31 MVD) were determined. The ANG score was significantly greater in NBs than in GNs (P = 0.015) and in NBs from children with stage 4 tumours, high-risk disease, unfavourable pathology (P < 0.001 for each), MYCN amplification (P = 0.003), and 1p deletion (P = 0.002). ANG scores correlated with ANG MVD and CD31 MVD (P < 0.001 for each). Total ANG and CD31 protein levels, measured with a sensitive enzyme-linked immunosorbent assay, were highly correlated (P = 0.003). High ANG scores were associated with decreased overall and event-free survival (log-rank test, P = 0.025 and P = 0.018, respectively). High ANG MVD was associated with decreased overall and event-free survival (log-rank test, P = 0.009 and P = 0.026, respectively). High CD31 MVD was associated with decreased event-free survival (P = 0.045).

CONCLUSIONS

The strong correlation of ANG up-regulation with total MVD and adverse clinicopathological and biological factors indicates that ANG supports growth and progression in NB.

New insights into the role of angiogenin in actin polymerization

Angiogenin is a potent stimulator of angiogenesis. It interacts with endothelial cells and induces a wide range of cellular responses initiating a process of blood vessel formation. One important target of angiogenin is endothelial cell-surface actin, and their interaction might be one of crucial steps in angiogenin-induced neovascularization. Recently, it was shown that angiogenin inhibits polymerization of G-actin and changes the physical properties of F-actin. These observations suggest that angiogenin may cause changes in the cell cytoskeleton. This chapter reviews the current state of the literature regarding angiogenin structure and function and discusses the relationship between the angiogenin and actin and possible functional roles of their interaction.

Kaposi's sarcoma-associated herpesvirus latency-associated nuclear antigen and angiogenin interact with common host proteins, including annexin A2, which is essential for survival of latently infected cells

Kaposi's sarcoma-associated herpesvirus (KSHV) infection and latency-associated nuclear antigen (LANA-1) upregulate the multifunctional protein angiogenin (ANG). Our studies demonstrate that silencing ANG or inhibiting its nuclear translocation downregulates KSHV LANA-1 expression and ANG is necessary for KSHV latency, anti-apoptosis and angiogenesis (Sadagopan et al., J. Virol. 83:3342-3364, 2009; Sadagopan et al., J Virol. 85:2666-2685, 2011). Here we show that LANA-1 interacts with ANG and colocalizes in latently infected endothelial telomerase-immortalized human umbilical vein endothelial (TIVE-LTC) cells. Mass spectrometric analyses of TIVE-LTC proteins immunoprecipitated by anti-LANA-1 and ANG antibodies identified 28 common cellular proteins such as ribosomal proteins, structural proteins, tRNA synthetases, metabolic pathway enzymes, chaperons, transcription factors, antioxidants, and ubiquitin proteosome proteins. LANA-1 and ANG interaction with one of the proteins, annexin A2, was validated. Annexin A2 has been shown to play roles in cell proliferation, apoptosis, plasmin generation, exocytosis, endocytosis, and cytoskeleton reorganization. It is also known to associate with glycolytic enzyme 3-phosphoglyceratekinase in the primer recognition protein (PRP) complex that interacts with DNA polymerase α in the lagging strand of DNA during replication. A higher level of annexin A2 is expressed in KSHV+ but not in Epstein-Barr virus (EBV)+ B-lymphoma cell lines. Annexin A2 colocalized with several LANA-1 punctate spots in KSHV+ body cavity B-cell lymphoma (BCBL-1) cells. In triple-staining analyses, we observed annexin A2-ANG-LANA-1, annexin A2-ANG, and ANG-LANA-1 colocalizations. Annexin A2 appeared as punctate nuclear dots in LANA-1-positive TIVE-LTC cells. In LANA-1-negative TIVE-LTC cells, annexin A2 was detected predominately in the cytoplasm, with some nuclear spots, and colocalization with ANG was observed mostly in the cytoplasm. Annexin A2 coimmunoprecipitated with LANA-1 and ANG in TIVE-LTC and BCBL-1 cells and with ANG in 293T cells independent of LANA-1. This suggested that annexin A2 forms a complex with LANA-1 and ANG as well as a separate complex with ANG. Silencing annexin A2 in BCBL-1 cells resulted in significant cell death, downregulation of cell cycle-associated Cdk6 and of cyclin D, E, and A proteins, and downregulation of LANA-1 and ANG expression. No effect was seen in KSHV⁻ lymphoma (BJAB and Ramos) and 293T cells. These studies suggest that LANA-1 association with annexin A2/ANG could be more important than ANG association with annexin A2, and KSHV probably uses annexin A2 to maintain the viability and cell cycle regulation of latently infected cells. Since the identified LANA-1- and ANG-interacting common cellular proteins are hitherto unknown to KSHV and ANG biology, this offers a starting point for further analysis of their roles in KSHV biology, which may lead to identification of potential therapeutic targets to control KSHV latency and associated malignancies.

Vascular disruption and the role of angiogenic proteins after spinal cord injury

Spinal cord injuries (SCI) can result in devastating paralysis, for which there is currently no robustly efficacious neuroprotective/neuroregenerative treatment. When the spinal cord is subjected to a traumatic injury, the local vasculature is disrupted and the blood–spinal cord barrier is compromised. Subsequent inflammation and ischemia may then contribute to further secondary damage, exacerbating neurological deficits. Therefore, understanding the vascular response to SCI and the molecular elements that regulate angiogenesis has considerable relevance from a therapeutic standpoint. In this paper, we review the nature of vascular damage after traumatic SCI and what is known about the role that angiogenic proteins—angiopoietin 1 (Ang1), angiopoietin 2 (Ang2) and angiogenin—may play in the subsequent response. To this, we add recent work that we have conducted in measuring these proteins in the cerebrospinal fluid (CSF) and serum after acute SCI in human patients. Intrathecal catheters were installed in 15 acute SCI patients within 48 h of injury. CSF and serum samples were collected over the following 3–5 days and analysed for Ang1, Ang2 and angiogenin protein levels using a standard ELISA technique. This represents the first description of the endogenous expression of these proteins in an acute human SCI setting.

Angiogenin-mediated ribosomal RNA transcription as a molecular target for treatment of head and neck squamous cell carcinoma

Squamous cell carcinoma of the head and neck (HNSCC) is the eighth most common disease, affecting approximately 640,000 patients worldwide each year. Despite recent advances in surgery, radiotherapy, and chemotherapy, the overall cure for patients with HNSCC has remained at less than 50% for many decades. Patients with recurrent and metastatic disease have a median survival of only 6-10 months. Systemic chemotherapy is the only treatment option for those patients. New treatment options are thus desperately needed to supplement, complement, or replace currently available therapies. New agents that target molecular and cellular pathways of the disease pathogenesis of HNSCC are promising candidates. One class of these new agents is angiogenesis inhibitors that have been proven effective in the treatment of advanced colorectal, breast, and non-small cell lung cancers. Similar to other solid tumors, angiogenesis plays an important role in the pathogenesis of HNSCC. A number of angiogenic factors including vascular endothelial growth factor (VEGF) and angiogenin (ANG) have been shown to be significantly upregulated in HNSCC. Among them, ANG is unique in which it is a ribonuclease that regulates ribosomal RNA (rRNA) transcription. ANG-stimulated rRNA transcription has been shown to be a general requirement for angiogenesis induced by other angiogenic factors. ANG inhibitors have been demonstrated to inhibit angiogenesis and tumor growth induced not only by ANG but also by other angiogenic factors. As the role of ANG in HNSCC is being unveiled, the therapeutic potential of ANG inhibitors in HNSCC is expected.

Targeting abnormal airway vascularity as a therapeutical strategy in asthma

Asthma is a chronic inflammatory disease of airways, characterized by airway hyperresponsiveness and airflow limitation with acute bronchoconstriction, swelling of the airway wall, chronic mucus plug formation and airway wall remodelling. Functional and structural changes in the vasculature of asthmatic airways have been documented, and the signalling mechanisms are complex and have recently attracted much attention. The vascular changes may affect inflammatory cell recruitment, airway hyperresponsiveness and the regulation of airway calibre, and further, the level of disease control. Many critical factors are involved in the pathophysiological regulation of vascular changes in bronchial asthma, and the actions of these factors must be very carefully orchestrated. By better understanding the complicated actions of each factor, we may be able to advance further in asthma treatment.

Binding of human angiogenin inhibits actin polymerization

Angiogenin is a potent inducer of angiogenesis, a process of blood vessel formation. It interacts with endothelial and other cells and elicits a wide range of cellular responses including migration, proliferation, and tube formation. One important target of angiogenin is endothelial cell-surface actin and their interaction might be one of essential steps in angiogenin-induced neovascularization. Based on earlier indications that angiogenin promotes actin polymerization, we studied the binding interactions between angiogenin and actin in a wide range of conditions. We showed that at subphysiological KCl concentrations, angiogenin does not promote, but instead inhibits polymerization by sequestering G-actin. At low KCl concentrations angiogenin induces formation of unstructured aggregates, which, as shown by NMR, may be caused by angiogenin's propensity to form oligomers. Binding of angiogenin to preformed F-actin does not cause depolymerization of actin filaments though it causes their stiffening. Binding of tropomyosin and angiogenin to F-actin is not competitive at concentrations sufficient for saturation of actin filaments. These observations suggest that angiogenin may cause changes in the cell cytoskeleton by inhibiting polymerization of G-actin and changing the physical properties of F-actin.

Kaposi's sarcoma-associated herpesvirus upregulates angiogenin during infection of human dermal microvascular endothelial cells, which induces 45S rRNA synthesis, antiapoptosis, cell proliferation, migration, and angiogenesis

Kaposi's sarcoma (KS)-associated herpesvirus (KSHV) is associated with the angioproliferative KS lesions characterized by spindle-shaped endothelial cells, inflammatory cells, cytokines, growth factors, and angiogenic factors. De novo KSHV infection of human microvascular dermal endothelial cells results in increased secretion of several growth factors, cytokines, chemokines, and angiogenic factors, and the multifunctional angiogenic protein angiogenin is one of them. KS tissue sections were positive for angiogenin, highlighting the importance of angiogenin in KS pathogenesis. Examination of KSHV-mediated angiogenin upregulation and secretion and potential outcomes revealed that during infection of primary endothelial cells, KSHV induced a time- and dose-dependent increase in angiogenin gene expression and protein secretion beginning as early as 8 h postinfection and lasting until the fifth day of our observation period. TIVE latently transformed cells (TIVE-LTC) latently infected with KSHV secreted high levels of angiogenin. Angiogenin was also detected in BCBL-1 cells (human B cells) carrying KSHV in a latent state. Significant induction of angiogenin was observed in cells expressing KSHV ORF73 (LANA-1; latent) and ORF74 (lytic) genes alone, and moderate induction was seen with the lytic KSHV ORF50 gene. Angiogenin bound to surface actin, internalized in a microtubule-independent manner, and translocated into the nucleus and nucleolus of infected cells. In addition, it increased 45S rRNA gene transcription, antiapoptosis, and proliferation of infected cells, thus demonstrating the multifunctional nature of KSHV-induced angiogenin. These activities were dependent on angiogenin nuclear translocation, which was inhibited by neomycin. Upregulation of angiogenin led to increased activation of urokinase plasminogen activator and generation of active plasmin, which facilitated the migration of endothelial cells toward chemoattractants, including angiogenin, and chemotaxis was prevented by the inhibition of angiogenin nuclear translocation. Treatment of KSHV-infected cell supernatants with antiangiogenin antibodies significantly inhibited endothelial tube formation, and inhibition of nuclear translocation of angiogenin also blocked the expression of KSHV-induced vascular endothelial growth factor C. Collectively, these results strongly suggest that by increasing infected endothelial cell 45S rRNA synthesis, proliferation, migration, and angiogenesis, KSHV-induced angiogenin could be playing a pivotal role in the pathogenesis of KSHV infection, including a contribution to the angioproliferative nature of KS lesions. Our studies suggested that LANA-1 and vGPCR play roles in KSHV-induced angiogenesis and that the angiogenic potential of vGPCR might also be due to its ability to induce angiogenin.

Enhanced angiogenesis in porous collagen-chitosan scaffolds loaded with angiogenin

Artificial dermis lacks a vascular network, and angiogenesis is slow in vivo. Controlled delivery of angiogenin (ANG), a potent inducer of angiogenesis, should promote angiogenesis in artificial dermis. In this study, a porous collagen-chitosan scaffold was fabricated and heparinized using N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide (EDC) and N-hydroxysuccinimide (NHS) with a freeze-drying method. Using radioiodine labeling, the effect of heparin on the binding of ANG to the scaffold was studied. The release of ANG from the heparinized scaffold was investigated using a radioiodine labeling method or an enzyme-linked immunosorbent assay method. In vivo angiogenesis of the scaffold was studied for 28 days. All scaffolds possess three-dimensional porous structures, and their mean pore sizes increase upon EDC-NHS cross-linking. The binding of ANG to the scaffold showed a linear correlation with ANG concentration. With ANG concentrations of 160 ng/mL, the binding of ANG to the heparinized scaffold was 36.5%. In vitro, ANG was released from the heparinized scaffold in a controlled manner. The presence of ANG enhanced the angiogenesis of the heparinized scaffold after subcutaneous implantation into rabbits. The results of this study indicate that a porous collagen-chitosan scaffold loaded with ANG may be valuable in the development of artificial dermis requiring enhanced angiogenesis.

Targeting angiogenin in therapy of amyotropic lateral sclerosis

BACKGROUND

Missense heterozygous mutations in the coding region of angiogenin (ANG) gene, encoding a 14 kDa angiogenic RNase, were recently found in patients of amyotropic lateral sclerosis (ALS). Functional analyses have shown that these are loss-of-function mutations, implying that angiogenin deficiency is associated with ALS pathogenesis and that increasing ANG expression or angiogenin activity could be a novel approach for ALS therapy.

OBJECTIVE

Review the evidence showing the involvement of angiogenin in motor neuron physiology and function, and provide a rationale for targeting angiogenin in ALS therapy.

METHODS

Review the current understanding of the mechanism of angiogenin action in connection with ALS genetics, pathogenesis and therapy.

CONCLUSION

ANG is the first gene whose loss-of-function mutations are associated with ALS pathogenesis. Therapeutic modulation of angiogenin level and activity in the spinal cord, either by systemic delivery of angiogenin protein or through retrograde transport of ANG-encoding viral particles, may be beneficial for ALS patients.

Angiogenin-induced protein kinase B/Akt activation is necessary for angiogenesis but is independent of nuclear translocation of angiogenin in HUVE cells

Angiogenin, a potent angiogenic factor, binds to endothelial cells and is endocytosed and rapidly translocated to and concentrated in the nucleolus where it binds to DNA. In this study, we report that angiogenin induces transient phosphorylation of protein kinase B/Akt in cultured human umbilical vein endothelial (HUVE) cells. LY294002 inhibits the angiogenin-induced protein kinase B/Akt activation and also angiogenin-induced cell migration in vitro as well as angiogenesis in chick embryo chorioallantoic membrane in vivo without affecting nuclear translocation of angiogenin in HUVE cells. These results suggest that cross-talk between angiogenin and protein kinase B/Akt signaling pathways is essential for angiogenin-induced angiogenesis in vitro and in vivo, and that angiogenin-induced PKB/Akt activation is independent of nuclear translocation of angiogenin in HUVE cells.

Angiogenin: a review of the pathophysiology and potential clinical applications

Angiogenin is a member of the ribonuclease (RNase) superfamily: enzymes of innate substrate specificity, but divergent functional capacities. Angiogenin is a normal constituent of the circulation and contained in a vasculature that rarely undergoes proliferation, but in some physiological and pathological conditions its levels increase in blood, promoting neovascularization. Hence, angiogenesis is a common pathophysiological attribute of angiogenin. In malignant disease, the most studied pathological state in regard to angionenin, abnormally high levels are seen, which may be of prognostic significance. Angiogenin has also been studied in other non-malignant pathological states. The aim of this review article is to provide an overview of the biochemistry and physiology of angiogenin, specifically in relation to the human pathological states where angiogenin has been implicated and finally, its potential clinical applications.

Influence of angiogenin on the growth of A375 human melanoma cells and the expression of basic fibroblast growth factor

Angiogenin was isolated as a tumor angiogenic factor solely on the basis of its angiogenic activity. Its expression is essential for melanoma progression and metastasis. Many studies have mainly focused on how it induces angiogenesis, which allows further melanoma growth and metastasis. Here, we investigated the effects of angiogenin on melanoma cell growth and studied its influence on the expression and function of the basic fibroblast growth factor. We transfected the angiogenin gene in the sense and antisense orientation into A375 cells, and obtained stable angiogenin under-expressing and over-expressing transfectants. We found that in the angiogenin antisense transfectants, the cell proliferation was decreased and the basic fibroblast growth factor-induced cell proliferation was inhibited, but the expression of basic fibroblast growth factor was increased. In contrast, in the angiogenin sense transfectants, the cell proliferation was increased, and the basic fibroblast growth factor-induced cell proliferation was also increased. The expression of basic fibroblast growth factor, however, was decreased. In conclusion, we demonstrated that, besides its angiogenic activity, angiogenin also directly contributes to A375 cell proliferation and is required for the basic fibroblast growth factor to induce cell proliferation. We also demonstrated that the endogenous angiogenin expression levels affect the expression of basic fibroblast growth factor in A375 cells. By targeting angiogenin, therefore, one may find a potential therapeutic approach to human malignant melanoma.

Genetic and environmental determinants of circulating levels of angiogenin in community-based sample

BACKGROUND

Measurement of angiogenin in plasma provides important prognostic and diagnostic information in variety of malignancies and may even correlate with cancer's progression. Nevertheless, nowadays, specific physiological mechanisms of this protein action as well as major factors regulating its circulating levels normally and in pathology are still poorly understood. The main objectives of this study were to examine the contribution of a number of endogenous factors, such as sex, age, body size and genetic effects on the production of angiogenin in apparently healthy individuals, and to assess the correlations in circulating levels between angiogenin and other molecules involved in angiogenesis.

METHODS

The plasma levels of angiogenin and each of the additional cytokines [interleukin-6 (IL-6), tumour necrosis factor-alpha (TNF-alpha), transforming growth factor-beta (TGF-beta), macrophage-colony stimulating factor (M-CSF), vascular endothelial growth factor (VEGF), epidermal growth factor (EGF), soluble intercellular adhesion molecule-1 (sICAM)] were determined by enzyme-linked immunoassay in a large family based sample.

RESULTS

Angiogenin levels were significantly higher in man than in women (360.64 +/- 104.04 ng/ml vs. 322.15 +/- 100.34 ng/ml, P < 0.01) and significantly correlated with age (P < 0.01) in both sexes. Genetic analysis showed that adjusted for potential covariates, 37.4 +/- 7.1% of angiogenin variation was attributable to putative genetic factors. The results of our study revealed that angiogenin concentrations were positively and significantly (P < 0.05) associated with sICAM, IL-6, TNF-alpha and M-CSF levels in the female cohort.

CONCLUSIONS

Our data provide reliable evidence for the substantial role of genetic factors in the determination of the phenotypic variability of angiogenin plasma levels. These findings of our study, including circulating angiogenin reference limits in healthy population and its correlation with angiogenic cytokines, may be of importance in determination of early stages of pathological angiogenesis.

ACTIBIND, an actin-binding fungal T2-RNase with antiangiogenic and anticarcinogenic characteristics

BACKGROUND

ACTIBIND is an Aspergillus niger extracellular ribonuclease (T2-ribonuclease [RNase]) that possesses actin-binding activity. In plants, ACTIBIND inhibits the elongation and alters the orientation of pollen tubes by interfering with the intracellular actin network. The question rose whether ACTIBIND can also affect mammalian cancer development.

METHODS

Cell colony formation was performed in human colon (HT-29, Caco-2, RSB), breast (ZR-75-1), and ovarian (2780) cancer cells in the presence or absence of 1 muM ACTIBIND. In HT-29 and ZR-75-1 cells, the effect of ACTIBIND on cell migration was studied by microscopic observations and by invasion assay through Matrigel. Tube formation was assessed in human umbilical vein endothelial cells (HUVEC) in the presence of angiogenin or basic fibroblast growth factor (bFGF) (1 microg/mL each) following overnight incubation with 1 or 10 microM ACTIBIND. In an athymic mouse xenograft model, HT-29 cells were injected subcutaneously, followed by subcutaneous (0.4-8 mg/mouse/injection) or intraperitoneal (0.001-1 mg/mouse/injection) injections of ACTIBIND. In a rat dimethylhydrazine (DMH)-colorectal carcinogenesis model, ACTIBIND was released directly into the colon via osmotic micropumps (250 microg/rat/day) or given orally via microcapsules (1.6 mg/rat/day). Aberrant crypt foci, tumors in the distal colon, and tumor blood vessels were examined.

RESULTS

ACTIBIND had an anticlonogenic effect unrelated to its ribonuclease activity. It also inhibited angiogenin-induced HUVEC tube formation in a dose-responsive manner. ACTIBIND was found to bind actin in vitro. It also bound to cancer cell surfaces, leading to disruption of the internal actin network and inhibiting cell motility and invasiveness through Matrigel-coated filters. In mice, ACTIBIND inhibited HT-29 xenograft tumor development, given either as a subcutaneous or intraperitoneal treatment. In rats, ACTIBIND exerted preventive and therapeutic effects on developing colonic tumors induced by DMH. It also reduced the degree of tumor observation.

CONCLUSIONS

This study indicated that ACTIBIND is an effective antiangiogenic and anticarcinogenic factor.

Increased plasma levels of angiogenin and the risk of bladder carcinoma: from initiation ot recurrence

BACKGROUND

Angiogenesis is a well known prerequisite for tumor growth and metastasis. It is believed that angiogenin initiates cell migration and aids cell proliferation. Based on this, the authors hypothesized that individuals who had increased plasma levels of angiogenin were at an elevated risk for carcinoma of the urinary bladder.

METHODS

In this ongoing case-control study, the authors used an enzyme-linked immunosorbent assay to compare plasma levels of angiogenin in 209 patients with bladder carcinoma and in 208 healthy control participants who were matched according to age (+/- 5 years), gender, and ethnicity.

RESULTS

The mean plasma angiogenin concentration was significantly higher in patients compared with controls (343.2 ng/mL vs. 308.0 ng/mL, respectively; P < 0.01). High plasma angiogenin levels were associated with a two-fold increased risk for bladder carcinoma. Moreover, in patients who had superficial bladder carcinoma, plasma angiogenin levels were significantly higher among those who had recurrent disease than in those who were without recurrence (P < 0.01). Similarly, patients who had superficial bladder carcinoma with higher angiogenin levels had a shorter recurrence-free survival than patients who had lower angiogenin levels (P < 0.01). Finally, elevated angiogenin levels were associated with an increased recurrence risk, with hazard ratio of 2.85.

CONCLUSIONS

The results of this study demonstrated that the plasma levels of angiogenin were significantly higher in patients who had bladder carcinoma compared with healthy control participants and in patients with superficial bladder carcinoma who had recurrent disease compared with patients who were without recurrence. Therefore, an elevated plasma level of angiogenin may serve as a novel predictor for the risk of bladder carcinoma.

Endogenous angiogenin in endothelial cells is a general requirement for cell proliferation and angiogenesis

Angiogenin is an angiogenic protein that undergoes nuclear translocation in endothelial cells where it accumulates in the nucleolus and stimulates rRNA transcription, a rate-limiting step in ribosome biogenesis, protein translation, and cell growth. Here, we report that angiogenin is required for cell proliferation induced by various other angiogenic proteins including acidic and basic fibroblast growth factors (aFGF and bFGF), epidermal growth factor (EGF), and vascular endothelial growth factor (VEGF). Downregulation of angiogenin in endothelial cells by small interfering RNA (siRNA) and antisense results in a decrease in rRNA transcription, ribosome biogenesis, and cell proliferation induced by these angiogenic factors. Inhibitors of the nuclear translocation of angiogenin abolish the angiogenic activities of these factors. Stable angiogenin antisense transfection in HeLa cells reduces tumor angiogenesis in athymic mice despite the elevated expression level of bFGF and VEGF. Thus, nuclear angiogenin assumes an essential role in endothelial cell proliferation and is necessary for angiogenesis induced by other angiogenic factors. Angiogenin-stimulated rRNA transcription in endothelial cells may thus serve as a crossroad in the process of angiogenesis induced by various angiogenic factors.

Relation between bone marrow angiogenesis and serum levels of angiogenin in patients with myelodysplastic syndromes

Angiogenesis is implicated in the progression of myelodysplastic syndromes (MDS). Bone marrow microvascular density (MVD), serum angiogenin (ANG) and interleukin 6 (IL-6) were measured in 67 patients with untreated MDS. MVD, ANG and IL-6 were significantly higher in the patient group as a whole when compared to controls (P < 0.01). MVD and ANG were significantly higher in subtypes with a high-risk for leukemic transformation (RAEB, RAEB-t and CMML) than in low-risk subtypes (RA and RARS) (P < 0.01). In the MDS group, a positive correlation was found between ANG and IL-6 (P < 0.001) and also between MVD and IL-6 (P < 0.05). Using multivariate analysis, only IL-6 displayed independent prognostic value and was inversely related to MDS survival.

Cell Surface-Dependent Generation of Angiostatin4.5

Angiostatin4.5 (AS4.5) is a naturally occurring human angiostatin isoform, consisting of plasminogen kringles 1-4 plus 85% of kringle 5 (amino acids Lys78 to Arg529). Prior studies indicate that plasminogen is converted to AS4.5 in a two-step reaction. First, plasminogen is activated to plasmin. Then plasmin undergoes autoproteolysis within the inner loop of kringle 5, which can be induced by a free sulfhydryl donor or an alkaline pH. We now demonstrate that plasminogen can be converted to AS4.5 in a cell membrane-dependent reaction. Actin was shown previously to be a surface receptor for plasmin(ogen). We now show that beta-actin is present on the extracellular membranes of cancer cells (PC-3, HT1080, and MDA-MB231), and beta-actin can mediate plasmin binding to the cell surface and autoproteolysis to AS4.5. In the presence of beta-actin, no small molecule-free sulfhydryl donor is needed for generation of AS4.5. Antibodies to actin reduced membrane-dependent generation of AS4.5 by 70%. In a cell-free system, addition of actin to in vitro-generated plasmin resulted in stoichiometric conversion to AS4.5. Annexin II and alpha-enolase have been reported to be plasminogen receptors, but we did not demonstrate a role for these proteins in conversion of plasminogen to AS4.5. Our data indicate that membrane-associated beta-actin, documented previously as a plasminogen receptor, is a key cell membrane receptor capable of mediating conversion of plasmin to AS4.5. This conversion may serve an important role in regulating tumor angiogenesis, invasion, and metastasis, and surface beta-actin may also serve as a prognostic marker to predict tumor behavior.

The actin binding site on thymosin beta4 promotes angiogenesis

Thymosin beta4 is a ubiquitous 43 amino acid, 5 kDa polypeptide that is an important mediator of cell proliferation, migration, and differentiation. It is the most abundant member of the beta-thymosin family in mammalian tissue and is regarded as the main G-actin sequestering peptide. Thymosin beta4 is angiogenic and can promote endothelial cell migration and adhesion, tubule formation, aortic ring sprouting, and angiogenesis. It also accelerates wound healing and reduces inflammation when applied in dermal wound-healing assays. Using naturally occurring thymosin beta4, proteolytic fragments, and synthetic peptides, we find that a seven amino acid actin binding motif of thymosin beta4 is essential for its angiogenic activity. Migration assays with human umbilical vein endothelial cells and vessel sprouting assays using chick aortic arches show that thymosin beta4 and the actin-binding motif of the peptide display near-identical activity at ~50 nM, whereas peptides lacking any portion of the actin motif were inactive. Furthermore, adhesion to thymosin beta4 was blocked by this seven amino acid peptide demonstrating it as the major thymosin beta4 cell binding site on the molecule. The adhesion and sprouting activity of thymosin beta4 was inhibited with the addition of 5-50 nM soluble actin. These results demonstrate that the actin binding motif of thymosin beta4 is an essential site for its angiogenic activity.

The crystal structure of human angiogenin in complex with an antitumor neutralizing antibody

The murine monoclonal antibody 26-2F neutralizes the angiogenic and ribonucleolytic activities of human angiogenin (ANG) and is highly effective in preventing the establishment and metastatic dissemination of human tumors in athymic mice. Here we report a 2.0 A resolution crystal structure for the complex of ANG with the Fab fragment of 26-2F that reveals the detailed interactions between ANG and the complementarity-determining regions (CDRs) of the antibody. Surprisingly, Fab binding induces a dramatic conformational change in the cell binding region of ANG at the opposite end of the molecule from the combining site; crosslinking experiments indicate that this rearrangement also occurs in solution. The ANG-Fab complex structure should be invaluable for designing maximally humanized versions of 26-2F for potential clinical use.

Extracellular actin impairs glomerular capillary repair in experimental mesangioproliferative glomerulonephritis

Exogenous administration of actin prevents tumour growth in mice by specifically antagonizing angiogenin, a potent inducer of neovascularization. To investigate whether the angiogenin/actin system is also of importance in renal disease, we examined the effect of actin during glomerular capillary repair in anti-Thy-1.1 mesangioproliferative glomerulonephritis. Male Wistar rats were injected intravenously with actin, a control protein, i.e. albumin, or vehicle alone at 8, 16, 24, 32, 40 and 48 h after disease induction. On day 8, actin-treated rats showed significantly more microaneurysms and persistent mesangiolysis as compared to both control groups. This was associated with increased proteinuria in actin-treated rats. Moreover, actin-treated rats showed increased counts of glomerular macrophages (+40%) and polymorphonuclear leukocytes (+100%) on day 3 as well as a decrease in glomerular endothelial area on days 3 and 8. However, no difference in early glomerular endothelial as well as non-endothelial cell proliferation was noted in actin-treated rats as compared to controls. Actin treatment had no apparent influence on mesangial cell activation (i.e. de novo expression of alpha-smooth muscle actin) or glomerular accumulation of fibronectin or type IV collagen. Additional in vitro studies demonstrated that extracellular actin inhibits the angiogenin but not VEGF(165)-induced proliferation of (glomerular) endothelial cells. Moreover, actin inhibited other, yet unidentified, serum-derived angiogenic factors. In conclusion, exogenous actin impairs glomerular capillary repair in experimental mesangioproliferative glomerulonephritis possibly due to interference with angiogenic factors such as angiogenin. Our combined in vivo and in vitro observations suggest that the release of intracellular actin during mesangiolysis is an endogenous pathway by which glomerular capillary damage is augmented.

Angiogenin in sera as an independent prognostic factor in gastric cancer

PURPOSE

The purpose of this study is to elucidate an increased expression of angiogenin (ANG) as a prognostic factor of gastric cancer (GC), against the background of our previous observations of the increased expression of ANG in the more progressed GC.

METHODS

We investigated serum ANG concentrations in 123 GC patients and 63 healthy volunteers as well as the distributions of ANG gene message in 52 GC tissues by in situ hybridization. The prognostic significance of ANG was investigated by the Cox proportional hazards model including variable selection and by survival analysis.

RESULTS

The mean serum ANG concentrations in GC patients (378.3+/-95.5 ng/ml) were significantly higher (P=0.0001) than those in the healthy volunteers (334.1+/-58.2 ng/ml). Either strong, moderate, weak, or no ANG gene message expression was seen in 25, 22, 4, and 1 patients, respectively, in GC cells as well as in interstitial cells in the vicinity of cancer cells, a finding in accord with our previous results of ANG protein localization. The variable selection method selected increased (> or =400 ng/ml) serum ANG concentration (P=0.02), undifferentiated histological type (P=0.01), cancer depth (P=0.001), and third-tier lymph node involvement (P=0.0005) as an independent prognostic factor by the Cox proportional hazards model. A significant correlation was seen between higher serum ANG concentrations (> or =400 ng/ml) and worse disease-free (P=0.003) or disease-specific (P=0.03) survivals. CONCLUSIONS. These results suggest that serum levels of ANG are an independent prognostic factor that could be a predictor of postoperative outcomes of GC patients.

Antiplasmin activity of a peptide that binds to the receptor-binding site of angiogenin

It has been suggested that angiogenin binds to an actin-like molecule present on the surface of endothelial cells. Actin inhibits plasmin activity, but the angiogenin-actin complex is not active. In this report, we found that plasmin inhibits the interaction between angiogenin and actin suggesting a possibility that both angiogenin and plasmin may bind to a similar site on actin. Here we report that chANG, an antiangiogenin peptide that binds to the actin-binding site of angiogenin, inhibits the proteolytic activity of plasmin without any apparent effect on the activities of plasminogen activators and matrix metalloproteases. Its antiplasmin activity is comparable with that of actin. chANG inhibits plasmin activity via its binding to plasmin kringle domains while scrambled chANG does not bind to plasmin. chANG also inhibits the invasion of angiogenin-secreting human fibrosarcoma and colorectal carcinoma cells without effecting migration. Furthermore, chANG blocks angiogenesis induced by fibrosarcoma cells and metastasis of colorectal carcinoma cells to the liver. Therefore, the 11-amino acid peptide chANG has both antiangiogenin and antiplasmin activity, and could be useful in the development of anticancer agents.

Angiogenin activates Erk1/2 in human umbilical vein endothelial cells

Angiogenin is a potent angiogenic factor that binds to endothelial cells and is endocytosed and rapidly translocated to the nucleus where it is concentrated in the nucleolus and binds to DNA. Angiogenin also activates cell-associated proteases, induces cell invasion and migration, stimulates cell proliferation, and organizes cultured cells to form tubular structures. The intracellular signaling pathways that mediate these various cellular responses are not well understood. Here we report that angiogenin induces transient phosphorylation of extracellular signal-related kinase1/2 (Erk1/2) in cultured human umbilical vein endothelial cells. Angiogenin does not affect the phosphorylation status of stress-associated protein kinase/c-Jun N-terminal kinase (SAPK/JNK) and p38 mitogen-activated protein (MAP) kinases. PD98059--a specific inhibitor of MAP or Erk kinase 1 (MEK 1), the upstream kinase that phosphorylates Erk1/2--abolishes angiogenin-induced Erk phosphorylation and cell proliferation without affecting nuclear translocation of angiogenin. In contrast, neomycin, a known inhibitor of nuclear translocation and cell proliferation, does not interfere with angiogenin-induced Erk1/2 phosphorylation. These data indicate that both intracellular signaling pathways and direct nuclear functions of angiogenin are required for angiogenin-induced cell proliferation and angiogenesis.

Human angiogenin is rapidly translocated to the nucleus of human umbilical vein endothelial cells and binds to DNA

Human angiogenin is translocated to the nucleus of human umbilical vein endothelial cells in a time-dependent manner. Exogenous angiogenin appears in the nucleus in 2 min, reaches saturation in 15 min when 85% of the internalized angiogenin is in the nuclei, and remains associated with the nucleus for at least 4 h. Endothelial cells cultured at low density have a much higher capacity to translocate angiogenin to the nucleus than do those cultured at high density. This observation is consistent with previous findings that both the ability of endothelial cells to proliferate in response to angiogenin and the expression of an angiogenin receptor on the cell surface depend on cell density. Nuclear (125)I-angiogenin is not degraded and is neither spontaneously dissociated nor replaced by unlabeled angiogenin. It is, however, released by deoxyribonuclease I, but not by ribonuclease A, suggesting that angiogenin binds to DNA in the nucleus. These results suggest that in addition to acting as a ribonuclease, angiogenin may play a role in regulating gene expression by direct binding to DNA.

Refined crystal structures of native human angiogenin and two active site variants: implications for the unique functional properties of an enzyme involved in neovascularisation during tumour growth

Human angiogenin (Ang), an unusual member of the pancreatic RNase superfamily, is a potent inducer of angiogenesis in vivo. Its ribonucleolytic activity is weak (10(4) to 10(6)-fold lower than that of bovine RNase A), but nonetheless seems to be essential for biological function. Ang has been implicated in the establishment of a wide range of human tumours and has therefore emerged as an important target for the design of new anti-cancer compounds. We report high-resolution crystal structures for native Ang in two different forms (Pyr1 at 1.8 A and Met-1 at 2.0 A resolution) and for two active-site variants, K40Q and H13A, at 2.0 A resolution. The native structures, together with earlier mutational and biochemical data, provide a basis for understanding the unique functional properties of this molecule. The major structural features that underlie the weakness of angiogenin's RNase activity include: (i) the obstruction of the pyrimidine-binding site by Gln117; (ii) the existence of a hydrogen bond between Thr44 and Thr80 that further suppresses the effectiveness of the pyrimidine site; (iii) the absence of a counterpart for the His119-Asp121 hydrogen bond that potentiates catalysis in RNase A (the corresponding aspartate in Ang, Asp116, has been recruited to stabilise the blockage of the pyrimidine site); and (iv) the absence of any precise structural counterparts for two important purine-binding residues of RNase A. Analysis of the native structures has revealed details of the cell-binding region and nuclear localisation signal of Ang that are critical for angiogenicity. The cell-binding site differs dramatically from the corresponding regions of RNase A and two other homologues, eosinophil-derived neurotoxin and onconase, all of which lack angiogenic activity. Determination of the structures of the catalytically inactive variants K40Q and H13A has now allowed a rigorous assessment of the relationship between the ribonucleolytic and biological activities of Ang. No significant change outside the enzymatic active site was observed in K40Q, establishing that the loss of angiogenic activity for this derivative is directly attributable to disruption of the catalytic apparatus. The H13A structure shows some changes beyond the ribonucleolytic site, but sites involved in cell-binding and nuclear translocation are essentially unaffected by the amino acid replacement.