Sequence of the cDNA and gene for angiogenin, a human angiogenesis factor

Effects of Pathogenic Mutants of the Neuroprotective RNase 5-Angiogenin in Amyotrophic Lateral Sclerosis (ALS)

Amyotrophic Lateral Sclerosis (ALS) is a fatal neurodegenerative disease that affects the motoneurons. More than 40 genes are related with ALS, and amyloidogenic proteins like SOD1 and/or TDP-43 mutants are directly involved in the onset of ALS through the formation of polymorphic fibrillogenic aggregates. However, efficacious therapeutic approaches are still lacking. Notably, heterozygous missense mutations affecting the gene coding for RNase 5, an enzyme also called angiogenin (ANG), were found to favor ALS onset. This is also true for the less-studied but angiogenic RNase 4. This review reports the substrate targets and illustrates the neuroprotective role of native ANG in the neo-vascularization of motoneurons. Then, it discusses the molecular determinants of many pathogenic ANG mutants, which almost always cause loss of function related to ALS, resulting in failures in angiogenesis and motoneuron protection. In addition, ANG mutations are sometimes combined with variants of other factors, thereby potentiating ALS effects. However, the activity of the native ANG enzyme should be finely balanced, and not excessive, to avoid possible harmful effects. Considering the interplay of these angiogenic RNases in many cellular processes, this review aims to stimulate further investigations to better elucidate the consequences of mutations in ANG and/or RNase 4 genes, in order to achieve early diagnosis and, possibly, successful therapies against ALS.

Structural mechanism of angiogenin activation by the ribosome

Angiogenin, an RNase-A-family protein, promotes angiogenesis and has been implicated in cancer, neurodegenerative diseases and epigenetic inheritance1-10. After activation during cellular stress, angiogenin cleaves tRNAs at the anticodon loop, resulting in translation repression11-15. However, the catalytic activity of isolated angiogenin is very low, and the mechanisms of the enzyme activation and tRNA specificity have remained a puzzle3,16-23. Here we identify these mechanisms using biochemical assays and cryogenic electron microscopy (cryo-EM). Our study reveals that the cytosolic ribosome is the activator of angiogenin. A cryo-EM structure features angiogenin bound in the A site of the 80S ribosome. The C-terminal tail of angiogenin is rearranged by interactions with the ribosome to activate the RNase catalytic centre, making the enzyme several orders of magnitude more efficient in tRNA cleavage. Additional 80S-angiogenin structures capture how tRNA substrate is directed by the ribosome into angiogenin's active site, demonstrating that the ribosome acts as the specificity factor. Our findings therefore suggest that angiogenin is activated by ribosomes with a vacant A site, the abundance of which increases during cellular stress24-27. These results may facilitate the development of therapeutics to treat cancer and neurodegenerative diseases.

Thermodynamics of the Association of Aminoglycoside Antibiotics with Human Angiogenin

BACKGROUND

The body needs to maintain a firm balance between the inducers and inhibitors of angiogenesis, the process of proliferation of blood vessels from pre-existing ones. Human angiogenin (hAng), being a potent inducer of angiogenesis, is a cause of tumor cell proliferation, therefore its inhibition becomes a vital area of research. Aminoglycosides are linked ring systems consisting of amino sugars and an aminocyclitol ring and are in use in clinical practices for a long time. These compounds have found clinical uses as antibacterial agents that inhibit bacterial protein synthesis.

OBJECTIVE

Gentamycin C1, Kanamycin A, Neomycin B, Paromomycin I, and Streptomycin A are commonly used aminoglycoside antibiotics that have been used for the present study. Among these, Neomycin has reported inhibitory activity against angiogenin-induced angiogenesis on the chicken chorioallantoic membrane. This study focuses on the thermodynamic parameters involved in the interactions of these antibiotics with hAng.

METHODS

Agarose gel-based assay, Fluorescence quenching studies and Docking studies.

RESULTS

Anti-ribonucleolytic effect of the antibiotics was observed qualitatively using an agarose gelbased assay, which shows that Neomycin exhibits the most efficient inhibition of hAng. Fluorescence quenching studies at different temperatures, using Stern-Volmer and van't Hoff equations provide information about the thermodynamics of binding, which furthermore highlights the higher binding constant of Neomycin. Docking studies showed that the antibiotics preferably interact with the nuclear translocation site, except Streptomycin, which shows affinity towards the ribonucleolytic site of the protein with very less affinity value.

CONCLUSION

The study has shown the highly spontaneous formation of Neomycin-hAng complex, giving an exothermic reaction with increase in the degree of freedom of the protein-ligand complex.

Carboxymethyl tethered poly(disubstituted)triazoles built on nucleoside skeletons: A unique class of ribonuclease A inhibitors designed using chemical logic

Molecular docking of N-1,4-disubstituted-1,2,3-triazole tethered carboxymethylated thymidine and uridine with ribonuclease A, indicated their possible binding with the P₁, B₁ and P₂ subsites with varied efficiencies. This theoretical study in combination of our earlier experimental observations was used as the guiding principles for designing a range of 1,4-disubstituted 1, 2, 3- triazole tethered carboxymethylated pyrimidine nucleosides. Triazoles are biologically important molecules and at the same time easily accessible through less complicated synthetic routes as reported about two decades back in the context of "click" reactions. Regioselective propargylation of the nucleosides under controlled conditions followed by the use of CuAAC strategy afforded mono-, bis-, tris- and tetratriazolyl pyrimidine nucleosides. Although the characteristics of nucleosides were lost in these densely functionalized polyheterocycles, the catalytic efficiency of ribonuclease A was significantly reduced by these molecules which were investigated experimentally and by docking studies. Triazoles as linkers helped one or more acidic groups to reach the P₁ subsite of ribonuclease A. Enzyme kinetics showed that the efficiency of inhibition reached the highest point with an optimum number of functional groups and were not linearly dependent on the number of triazole tethered carboxymethyl groups. The location of the triazole ring in the molecule affected the efficiency and nature of inhibition which were the result of the overall structure of the modified nucleosides. Thus, the tris-triazolylated thymidine derivative (T-3', 5', N-tris-CH₂TzCH₂COOH) as opposed to tetra-triazolylated uridine (U-2', 3', 5', N-tetrakis-CH₂TzCH₂COOH) emerged as the best inhibitor with an inhibition constant value of 2.3 ± 0.05 µM.

Structure of angiogenin dimer bound to double-stranded RNA

Angiogenin is an unusual member of the RNase A family and is of great interest in multiple pathological contexts. Although it has been assigned various regulatory roles, its core catalytic function is that of an RNA endonuclease. However, its catalytic efficiency is comparatively low and this has been linked to a unique C-terminal helix which partially blocks its RNA-binding site. Assuming that binding to its RNA substrate could trigger a conformational rearrangement, much speculation has arisen on the topic of the interaction of angiogenin with RNA. To date, no structural data on angiogenin-RNA interactions have been available. Here, the structure of angiogenin bound to a double-stranded RNA duplex is reported. The RNA does not reach the active site of angiogenin and no structural arrangement of the C-terminal domain is observed. However, angiogenin forms a previously unobserved crystallographic dimer that makes several backbone interactions with the major and minor grooves of the RNA double helix.

Dimerization of Human Angiogenin and of Variants Involved in Neurodegenerative Diseases

Human Angiogenin (hANG, or ANG, 14.1 kDa) promotes vessel formation and is also called RNase 5 because it is included in the pancreatic-type ribonuclease (pt-RNase) super-family. Although low, its ribonucleolytic activity is crucial for angiogenesis in tumor tissues but also in the physiological development of the Central Nervous System (CNS) neuronal progenitors. Nevertheless, some ANG variants are involved in both neurodegenerative Parkinson disease (PD) and Amyotrophic Lateral Sclerosis (ALS). Notably, some pt-RNases acquire new biological functions upon oligomerization. Considering neurodegenerative diseases correlation with massive protein aggregation, we analyzed the aggregation propensity of ANG and of three of its pathogenic variants, namely H13A, S28N, and R121C. We found no massive aggregation, but wt-ANG, as well as S28N and R121C variants, can form an enzymatically active dimer, which is called ANG-D. By contrast, the enzymatically inactive H13A-ANG does not dimerize. Corroborated by a specific cross-linking analysis and by the behavior of H13A-ANG that in turn lacks one of the two His active site residues necessary for pt-RNases to self-associate through the three-dimensional domain swapping (3D-DS), we demonstrate that ANG actually dimerizes through 3D-DS. Then, we deduce by size exclusion chromatography (SEC) and modeling that ANG-D forms through the swapping of ANG N-termini. In light of these novelties, we can expect future investigations to unveil other ANG determinants possibly related with the onset and/or development of neurodegenerative pathologies.

RNase A Treatment Interferes With Leukocyte Recruitment, Neutrophil Extracellular Trap Formation, and Angiogenesis in Ischemic Muscle Tissue

Background: RNase A (the bovine equivalent to human RNase 1) and RNase 5 (angiogenin) are two closely related ribonucleases. RNase 5 is described as a powerful angiogenic factor. Whether RNase A shares the same angiogenic characteristic, or interferes with vessel growth as demonstrated for arteriogenesis, has never been investigated and is the topic of this present study.

Methods and Results: To investigate whether RNase A shows a pro‐ or anti-angiogenic effect, we employed a murine hindlimb model, in which femoral artery ligation (FAL) results in arteriogenesis in the upper leg, and, due to provoked ischemia, in angiogenesis in the lower leg. C57BL/6J male mice underwent unilateral FAL, whereas the contralateral leg was sham operated. Two and seven days after the surgery and intravenous injection of RNase A (50 μg/kg dissolved in saline) or saline (control), the gastrocnemius muscles of mice were isolated from the lower legs for (immuno-) histological analyses. Hematoxylin and Eosin staining evidenced that RNase A treatment resulted in a higher degree of ischemic tissue damage. This was, however, associated with reduced angiogenesis, as evidenced by a reduced capillary/muscle fiber ratio. Moreover, RNase A treatment was associated with a significant reduction in leukocyte infiltration as shown by CD45⁺ (pan-leukocyte marker), Ly6G⁺ or MPO⁺ (neutrophils), MPO⁺/CitH₃⁺ [neutrophil extracellular traps (NETs)], and CD68⁺ (macrophages) staining. CD68/MRC1 double staining revealed that RNase A treated mice showed a reduced percentage of M1-like polarized (CD68⁺/MRC1⁻) macrophages whereas the percentage of M2-like polarized (CD68⁺/MRC1⁺) macrophages was increased.

Conclusion: In contrast to RNase 5, RNase A interferes with angiogenesis, which is linked to reduced leukocyte infiltration and NET formation.

Design of configuration-restricted triazolylated β-d-ribofuranosides: a unique family of crescent-shaped RNase A inhibitors

Seven new carbohydrate-bistriazole hybrid molecules were designed taking into consideration the crescent shaped active site of ribonuclease A (RNase A). In this case, the β-d-ribofuranose structure was used as the basic building unit; both the C1 and C4 arms protruding out towards the β-face of the tetrahydrofuran moiety of the ribose sugar provided an overall "U" shape to the basic building block. Several combinations of bistriazole moieties were constructed on the two arms of this basic building block. These mono- and/or bis-substituted 1,2,3-triazole units were linked to acidic functional groups because of the overall basic nature of the hydrolytic site of RNase A. All these compounds were efficient competitive inhibitors of RNase A with inhibition constants (Ki) in the micromolar range. In contrast to the carboxylic acid-modified hybrid molecules, molecules carrying sulfonic acids were found to be more potent because of the stronger interactions with the positively charged active site. The most efficient inhibitor of the series was the disulfonic acid-functionalized carbohydrate-bis-triazole hybrid molecule. Docking studies disclosed that the molecule, because of its well defined "U" shape with flexible arms, fits effectively in the active site; moreover, in all cases, besides the acid groups, the triazole and sugar rings also actively participated in creating the hydrogen bonding network in the cavity of the enzyme active site.

Production and purification of endogenously modified tRNA-derived small RNAs

During particular stress conditions, transfer RNAs (tRNAs) become substrates of stress-induced endonucleases, resulting in the production of distinct tRNA-derived small RNAs (tsRNAs). These small RNAs have been implicated in a wide range of biological processes, but how isoacceptor and even isodecoder-specific tsRNAs act at the molecular level is still poorly understood. Importantly, stress-induced tRNA cleavage affects only a few tRNAs of a given isoacceptor or isodecoder, raising the question as to how such limited molecule numbers could exert measurable biological impact. While the molecular function of individual tsRNAs is likely mediated through association with other molecules, addressing the interactome of specific tsRNAs has only been attempted by using synthetic RNA sequences. Since tRNAs carry post-transcriptional modifications, tsRNAs are likely modified but the extent of their modifications remains largely unknown. Here, we developed a biochemical framework for the production and purification of specific tsRNAs using human cells. Preparative scale purification of tsRNAs from biological sources should facilitate experimentally addressing as to how exactly these small RNAs mediate the multitude of reported molecular functions.

The secretion of the angiogenic and neurotrophic factor angiogenin is COPII and microtubule dependent

The RNaseA superfamily member Angiogenin (ANG) is a secreted protein involved in neovascularization, cell proliferation and stress response. Dysregulation of ANG expression is found in many cancers with poor prognosis and mutations in ANG are associated with neurodegenerative diseases. While the uptake and nuclear translocation of ANG is relatively well characterised, little is known about how it reaches the plasma membrane and its mode of secretion. We generated SH-SY5Y neuroblastoma cell lines constitutively expressing wild type (WT) Hemagglutinin (HA) epitope tagged mouse Ang1 (mAng1), and two amyotrophic lateral sclerosis associated ANG variants (C39W and K40I). Herein, we show that these cell lines secrete mAng1 into the culture media. Using small molecule inhibitors we probed the route taken between the endoplasmic reticulum and trans-Golgi network during secretion and have characterised it as COPII and microtubule dependent. In addition, we show that disruption by the PI3-kinase inhibitor wortmannin of the later stages of transit to the plasma membrane leads to mAng1 trafficking to lysosomal compartments. This suggests an autophagy dependent regulation of secretion.

The catalytic activity and secretion of zebrafish RNases are essential for their in vivo function in motor neurons and vasculature

Angiogenin (hANG), a member of the Ribonuclease A superfamily has angiogenic, neurotrophic and neuroprotective activities. Mutations in hANG have been found in patients with Amyotrophic lateral sclerosis (ALS). The zebrafish (Danio rerio) rnasel-1, 2 and 3 are orthologues of hANG and of these only Rnasel-1 and Rnasel-2 have been shown to be angiogenic. Herein we show that NCI-65828, a potent and specific small molecule inhibitor of hANG inhibits Rnasel-1 to a similar extent. Treatment of early zebrafish embryos with NCI-65828, or with terrein, a fungal metabolite which prevents the secretion of hANG, resulted in spinal neuron aberrations as well defects in trunk vasculature. Our detailed expression analysis and inhibitor studies suggest that Rnasel-1 plays important roles in neuronal migration and pathfinding as well as in angiogenesis in zebrafish. Our studies suggest the usefulness of the zebrafish as a model to dissect the molecular consequences of the ANG ALS variants.

Generation of 2',3'-Cyclic Phosphate-Containing RNAs as a Hidden Layer of the Transcriptome

Cellular RNA molecules contain phosphate or hydroxyl ends. A 2′,3′-cyclic phosphate (cP) is one of the 3′-terminal forms of RNAs mainly generated from RNA cleavage by ribonucleases. Although transcriptome profiling using RNA-seq has become a ubiquitous tool in biological and medical research, cP-containing RNAs (cP-RNAs) form a hidden transcriptome layer, which is infrequently recognized and characterized, because standard RNA-seq is unable to capture them. Despite cP-RNAs’ invisibility in RNA-seq data, increasing evidence indicates that they are not accumulated simply as non-functional degradation products; rather, they have physiological roles in various biological processes, designating them as noteworthy functional molecules. This review summarizes our current knowledge of cP-RNA biogenesis pathways and their catalytic enzymatic activities, discusses how the cP-RNA generation affects biological processes, and explores future directions to further investigate cP-RNA biology.

Circulating Angiogenesis Regulators in Cancer Patients

Background/Aims

To date, numerous studies have demonstrated that several angiogenesis regulators circulate in the blood and may function as endocrine factors in cancer patients. This review aims to give a comprehensive insight into the possible clinical value of circulating angiogenesis regulators, mainly basic fibroblast growth factor (bFGF), vascular endothelial growth factor (VEGF), and hepatocyte growth factor (HGF), angiogenin, pleiotrophin, thrombospondin (TSP) and endostatin (ES) in cancer patients.

Methods

A computerized (MEDLINE) and a manual search based on the reference lists of the publications were performed to identify articles published on this topic.

Results

In a detailed literature search, approximately 100 publications were found up to the end of 1999. Circulating angiogenic factors such as bFGF, VEGF, HGF and angiogenin have been evaluated not only as diagnostic and/or prognostic factors but also as predictive factors in cancer patients. On the other hand, little is known about the clinical significance of negative regulators. Neither the source nor the mechanism of protein externalization has been clarified in detail.

Conclusions

Although there are no known factors with established clinical utility, circulating angiogenesis regulators may be useful in several situations. They could be used to determine the risk of developing cancer, to screen for early detection, to distinguish benign from malignant disease, and to distinguish between different types of malignancies. In patients with established malignancies such factors might be used to determine prognosis, to predict the response to therapy, and to monitor the clinical course. Further investigations are warranted to assess the specific utility of each factor.

The CDI toxin of Yersinia kristensenii is a novel bacterial member of the RNase A superfamily

Contact-dependent growth inhibition (CDI) is an important mechanism of inter-bacterial competition found in many Gram-negative pathogens. CDI⁺ cells express cell-surface CdiA proteins that bind neighboring bacteria and deliver C-terminal toxin domains (CdiA-CT) to inhibit target-cell growth. CDI⁺ bacteria also produce CdiI immunity proteins, which specifically neutralize cognate CdiA-CT toxins to prevent self-inhibition. Here, we present the crystal structure of the CdiA-CT/CdiI^Ykris complex from Yersinia kristensenii ATCC 33638. CdiA-CT^Ykris adopts the same fold as angiogenin and other RNase A paralogs, but the toxin does not share sequence similarity with these nucleases and lacks the characteristic disulfide bonds of the superfamily. Consistent with the structural homology, CdiA-CT^Ykris has potent RNase activity in vitro and in vivo. Structure-guided mutagenesis reveals that His175, Arg186, Thr276 and Tyr278 contribute to CdiA-CT^Ykris activity, suggesting that these residues participate in substrate binding and/or catalysis. CdiI^Ykris binds directly over the putative active site and likely neutralizes toxicity by blocking access to RNA substrates. Significantly, CdiA-CT^Ykris is the first non-vertebrate protein found to possess the RNase A superfamily fold, and homologs of this toxin are associated with secretion systems in many Gram-negative and Gram-positive bacteria. These observations suggest that RNase A-like toxins are commonly deployed in inter-bacterial competition.

Killing of cancer cells through the use of eukaryotic expression vectors harbouring genes encoding nucleases and ribonuclease inhibitor

Cancer gene therapy vectors are promising tools for killing cancer cells with the purpose of eradicating malignant tumours entirely. Different delivery methods of vectors into the cancer cells, including both non-viral and viral, as well as promoters for the targeted expression of genes encoding anticancer proteins were developed for effective and selective killing of cancer cells without harming healthy cells. Many vectors have been created to kill cancer cells, and some vectors suppress malignant tumours with high efficiency. This review is focused on vectors bearing genes for nucleases such as deoxyribonucleases (caspase-activated DNase, deoxyribonuclease I-like 3, endonuclease G) and ribonucleases (human polynucleotide phosphorylase, ribonuclease L, α-sarcin, barnase), as well as vectors harbouring gene encoding ribonuclease inhibitor. The data concerning the functionality and the efficacy of such vectors are presented.

Eosinophil-associated ribonuclease 11 is a macrophage chemoattractant

RNase A is the prototype of an extensive family of divergent proteins whose members share a unique disulfide-bonded tertiary structure, conserved catalytic motifs, and the ability to hydrolyze polymeric RNA. Several members of this family maintain independent roles as ribonucleases and modulators of innate immunity. Here we characterize mouse eosinophil-associated RNase (Ear) 11, a divergent member of the eosinophil ribonuclease cluster, and the only known RNase A ribonuclease expressed specifically in response to Th2 cytokine stimulation. Mouse Ear 11 is differentially expressed in somatic tissues at baseline (brain ≪ liver < lung < spleen); systemic stimulation with IL-33 results in 10-5000-fold increased expression in lung and spleen, respectively. Ear 11 is also expressed in response to protective priming of the respiratory mucosa with Lactobacillus plantarum; transcripts are detected both locally in lung as well as systemically in bone marrow and spleen. Mouse Ear 11 is enzymatically active, although substantially less so than mEar 1 and mEar 2; the relative catalytic efficiency (kcat/Km) of mEar 11 is diminished ∼1000-1500-fold. However, in contrast to RNase 2/EDN and mEar 2, which have been characterized as selective chemoattractants for CD11c(+) dendritic cells, mEar 11 has prominent chemoattractant activity for F4/80(+)CD11c(-) tissue macrophages. Chemoattractant activity is not dependent on full enzymatic activity, and requires no interaction with the pattern recognition receptor, Toll-like receptor 2 (TLR2). Taken together, this work characterizes a divergent RNase A ribonuclease with a unique expression pattern and function, and highlights the versatility of this family in promoting innate immunity.

MicroRNA drop in the bloodstream and microRNA boost in the tumour caused by treatment with ribonuclease A leads to an attenuation of tumour malignancy

Novel data showing an important role of microRNAs in mediating tumour progression opened a new field of possible molecular targets for cytotoxic ribonucleases. Recently, antitumour and antimetastatic activities of pancreatic ribonuclease A were demonstrated and here genome-wide profiles of microRNAs in the tumour and blood of mice bearing Lewis lung carcinoma after treatment with RNase A were analysed by high-throughput Sequencing by Oligonucleotide Ligation and Detection (SOLiD™) sequencing technology. Sequencing data showed that RNase A therapy resulted in the boost of 116 microRNAs in tumour tissue and a significant drop of 137 microRNAs in the bloodstream that were confirmed by qPCR. The microRNA boost in the tumour was accompanied by the overexpression of microRNA processing genes: RNASEN (Drosha), xpo5, dicer1, and eif2c2 (Ago2). Ribonuclease activity of RNase A was shown to be crucial for the activation of both microRNA synthesis and expression of the microRNA processing genes. In the tumour tissue, RNase A caused the upregulation of both oncomirs and tumour-suppressor microRNAs, including microRNAs of the let-7 family, known to negatively regulate tumour progression. Our results suggest that the alteration of microRNA signature caused by RNase A treatment leads to the attenuation of tumour malignancy.

(1)H, (13)C, (15)N backbone and side-chain resonance assignments of rat angiogenin

Angiogenin is an unusual member of the pancreatic ribonuclease superfamily that induces formation of new blood vessels and is a promising anti-cancer target. Here we report backbone and side chain (1)H, (13)C, and (15)N resonance assignments for rat angiogenin (residues 24-145), excluding the N-terminal signal peptide. These data allow nuclear magnetic resonance structure and inhibitor-binding studies with the aim of providing angiogenin antagonists as potential therapeutics.

Evidence for the Presence of Angiogenin in Human Testis

We have reported the expression and possible roles of angiogenin, a potent angiogenic factor, in human female reproductive organs. In this study, we investigated the expression of angiogenin in the human testis, a male reproductive organ. Western blot analysis showed the presence of angiogenin in the human testis, with a single band of the same size as recombinant human angiogenin. Immunohistochemical study and in situ hybridization showed that the angiogenin protein and messenger RNA (mRNA) localized in peritubular myoid cells (PTMCs) and vascular endothelial and smooth muscle cells. PTMCs are known to play various roles in the testes concerned with spermatogenesis, transport of spermatozoa, structural support to the seminiferous tubules, and mediation of Sertoli cell function. The specific localization of angiogenin in PTMCs suggests that angiogenin plays physiologic roles in the human testis.

Motoneurons secrete angiogenin to induce RNA cleavage in astroglia

Amyotrophic lateral sclerosis (ALS) is an incurable neurodegenerative disorder affecting motoneurons. Mutations in angiogenin, encoding a member of the pancreatic RNase A superfamily, segregate with ALS. We previously demonstrated that angiogenin administration shows promise as a neuroprotective therapeutic in studies using transgenic ALS mice and primary motoneuron cultures. Its mechanism of action and target cells in the spinal cord, however, are largely unknown. Using mixed motoneuron cultures, motoneuron-like NSC34 cells, and primary astroglia cultures as model systems, we here demonstrate that angiogenin is a neuronally secreted factor that is endocytosed by astroglia and mediates neuroprotection in paracrine. We show that wild-type angiogenin acts unidirectionally to induce RNA cleavage in astroglia, while the ALS-associated K40I mutant is also secreted and endocytosed, but fails to induce RNA cleavage. Angiogenin uptake into astroglia requires heparan sulfate proteoglycans, and engages clathrin-mediated endocytosis. We show that this uptake mechanism exists for mouse and human angiogenin, and delivers a functional RNase output. Moreover, we identify syndecan 4 as the angiogenin receptor mediating the selective uptake of angiogenin into astroglia. Our data provide new insights into the paracrine activities of angiogenin in the nervous system, and further highlight the critical role of non-neuronal cells in the pathogenesis of ALS.

Mapping, phylogenetic and expression analysis of the RNase (RNase A) locus in cattle

The mammalian secreted ribonucleases (RNases) comprise a large family of structurally related proteins displaying considerable sequence variation, and have been used in evolutionary studies. RNase 1 (RNase A) has been assumed to play a role in digestion, while other members have been suggested to contribute to host defence. Using the recently assembled bovine genome sequence, we characterised the complete repertoire of genes present in the RNaseA family locus in cattle, and compared this with the equivalent locus in the human and mouse genomes. Several additions and corrections to the earlier analysis of the RNase locus in the mouse genome are presented. The bovine locus encodes 19 RNases, of which only six have unambiguous equivalent genes in the other two species. Chromosomal mapping and phylogenetic analysis indicate that a number of distinct gene duplication events have occurred in the cattle lineage since divergence from the human and mouse lineages. Substitution analysis suggests that some of these duplicated genes are under evolutionary pressure for purifying selection and may therefore be important to the physiology of cattle. Expression analysis revealed that individual RNases have a wide pattern of expression, including diverse mucosal epithelia and immune-related cells and tissues. These data clarify the full repertoire of bovine RNases and their relationships to those in humans and mice. They also suggest that RNase gene duplication within the bovine lineage accompanied by altered tissue-specific expression has contributed a survival advantage.

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.

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.

High serum angiogenin at diagnosis predicts for failure on long-term treatment response and for poor overall survival in non-Hodgkin lymphoma

BACKGROUND

Angiogenin is a potent inducer of angiogenesis. We prospectively evaluated the prognostic significance of serum angiogenin from 204 consecutive non-Hodgkin lymphoma (NHL) patients diagnosed and treated in a single institution.

METHODS

Serum angiogenin, VEGF, and bFGF concentrations at diagnosis were determined using a quantitative sandwich enzyme immunoassay technique. Kaplan-Meier survival curves were compared by the log-rank test. Multivariate survival analyses were performed using the parametric model of Weibull and the non-parametric proportional hazards model of Cox.

RESULTS

Patients with a high serum angiogenin at diagnosis (>median; 401 ng/ml) had significantly lower 5-year survival rate than those with a low (≤ median) angiogenin (42% versus 63%, respectively; P = 0.0073). Serum angiogenin provided additional information to the International Prognostic Index (IPI) identifying a subgroup (serum angiogenin >median and IPI>1) with very poor prognosis (5-year survival 19%, P < 0.0001). In receiver operating characteristic (ROC) analyses the accuracy of the IPI to correctly classify patients with favourable or poor survival was improved from fair to good by complementing the IPI with serum angiogenin concentration. With patients who initially achieved complete response (CR) after chemotherapy, a high angiogenin at diagnosis (>median; relative risk (RR) 2.38; P = 0.0077) and an advanced tumour stage (III-IV; RR 2.41; P = 0.0087) were the only independent predictors for patients with unfavourable outcome although first responding well to therapy.

CONCLUSIONS

We conclude that elevated serum angiogenin surfaced as an independent predictor for failure in long-term treatment response and for poor overall survival in a series of 204 NHL patients, and might thus also complement the IPI in identifying the patients with particularly aggressive and/or treatment resistant disease.

Novel endoribonucleases as central players in various pathways of eukaryotic RNA metabolism

For a long time it has been assumed that the decay of RNA in eukaryotes is mainly carried out by exoribonucleases, which is in contrast to bacteria, where endoribonucleases are well documented to initiate RNA degradation. In recent years, several as yet unknown endonucleases have been described, which has changed our view on eukaryotic RNA metabolism. Most importantly, it was shown that the primary eukaryotic 3' --> 5' exonuclease, the exosome complex has the ability to endonucleolytically cleave its physiological RNA substrates, and novel endonucleases involved in both nuclear and cytoplasmic RNA surveillance pathways were discovered concurrently. In addition, endoribonucleases responsible for long-known processing steps in the maturation pathways of various RNA classes were recently identified. Moreover, one of the most intensely studied RNA decay pathways--RNAi--is controlled and stimulated by the action of different endonucleases. Furthermore, endoribonucleolytic cleavages executed by various enzymes are also the hallmark of RNA degradation and processing in plant chloroplasts. Finally, multiple context-specific endoribonucleases control qualitative and/or quantitative changes of selected transcripts under particular conditions in different eukaryotic organisms. The aim of this review is to discuss the impact of all of these discoveries on our current understanding of eukaryotic RNA metabolism.

Optimizing stem cell function for the treatment of ischemic heart disease

BACKGROUND

Stem cell-based therapies for myocardial ischemia have demonstrated promising early clinical results, but their benefits have been limited in duration due to impaired donor cell engraftment and function. Several strategies have emerged for enhancing stem cell function prior to their therapeutic use particularly with regard to stem cell homing, paracrine function, and survival. This review discusses current understandings of stem cell-mediated cardioprotection as well as methods of enhancing post-transplantation stem cell function and survival through hypoxic preconditioning, genetic manipulation, and pharmacologic pretreatment.

MATERIALS AND METHODS

A literature search was performed using the MEDLINE and PubMed databases using the keywords "stem cell therapy," "myocardial ischemia," "hypoxic preconditioning," "paracrine function," and "stem cell pretreatment." Studies published in English since January 1990 were selected. In addition, studies were identified from references cited in publications found using the search terms.

RESULTS

All included studies utilized animal studies and/or in vitro techniques. Stem cell modifications generally targeted stem cell homing (SDF-1, CXCR4), paracrine function (VEGF, angiogenin, Ang-1, HGF, IL-18 binding protein, TNFR1/2), or survival (Akt, Bcl-2, Hsp20, HO-1, FGF-2). However, individual modifications commonly exhibited pleiotropic effects involving some or all of these general categories.

CONCLUSION

These strategies for optimizing stem cell-mediated cardioprotection present unique potential sets of advantages and disadvantages for clinical application. Additional questions remain including those that are most efficacious in terms of magnitude and duration of benefit as well as whether combinations may yield greater benefits in both the preclinical and clinical settings.

Human angiogenin presents neuroprotective and migration effects in neuroblastoma cells

Human angiogenin (ANG) has been highlighted as an angiogenic factor which supports primary and metastatic tumor growth. Recent genetic studies have shown that ANG is presented as a susceptibility gene for amyotrophic lateral sclerosis (ALS) and ALS-frontotemporal dementia (ALS-FTD). They found several missense mutations, including K40I, which present the weakest functional activity in ANG variants. In this study, we investigate whether human wild type ANG (wANG) and its variant K40I (mANG) maintain their divergent functional capacities in neuronal cells. To evaluate this, SH-SY5Y neuroblastoma cells were transfected with wANG and mANG DNA and identified both wild and mutant ANG are localized to nuclei and have no effects on proliferation. We have shown that human wANG prevented cell death under H(2)O(2)-induced oxidative stress in both SH-SY5Y and NSC-34 cells, tested by MTT assay. These effects were more enhanced in motor neuron cell NSC-34. wANG also played a role in cell migration, while mANG decreased these functional activities. Immunoblot analysis revealed that the intracellular signaling of ERK1/2 (at Thr183/Tyr185) was increased following transfection of the wANG gene, and significantly decreased by mANG in neuronal cells. These findings suggest that human ANG plays a critical role in cell protection and migration following alterations in ERK1/2 signaling in SH-SY5Y cells. This may provide the possible relationship between mutations in hANG and other neurodegenerative diseases as well as ALS.

Neamine inhibits prostate cancer growth by suppressing angiogenin-mediated rRNA transcription

PURPOSE

Angiogenin (ANG) undergoes nuclear translocation and stimulates rRNA transcription in both prostate cancer cells and endothelial cells. The purpose of this study is to assess the antitumor activity of neamine, a nontoxic degradation product of neomycin that blocks nuclear translocation of ANG.

EXPERIMENTAL DESIGN

The anti-prostate cancer activity of neamine was first evaluated in a xenograft animal model. It was then examined in the murine prostate-restricted AKT transgenic mice that develop prostate intraepithelial neoplasia (PIN) owing to AKT transgene overexpression.

RESULTS

Neamine inhibits xenograft growth of PC-3 human prostate cancer cells in athymic mice. It blocks nuclear translocation of ANG and inhibits rRNA transcription, cell proliferation, and angiogenesis. Neamine also prevents AKT-induced PIN formation as well as reverses fully developed PIN in murine prostate-restricted AKT mice, accompanied by a decrease in rRNA synthesis, cell proliferation, and angiogenesis and an increase in prostate epithelial cell apoptosis.

CONCLUSION

We confirmed that ANG is a molecular target for cancer drug development and that blocking nuclear translocation of ANG is an effective means to inhibit its activity. Our results also suggested that neamine is a lead compound for further preclinical evaluation.

Three single nucleotide polymorphisms leading to non-synonymous amino acid substitution in the human ribonuclease 2 and angiogenin genes exhibit markedly less genetic heterogeneity in six populations

Angiogenin and ribonuclease 2 (RNase 2) are members of the human RNase superfamily. Although three potential single nucleotide polymorphisms (SNPs) in these genes, which could give rise to an amino acid substitution in the protein, have been identified, relevant population data are not available, and accordingly they have not been applied to clinical-genetic analysis. For this purpose, a novel genotyping method for each SNP using the mismatched PCR-restriction fragment length polymorphism technique has been developed. Using this method, the genotype distribution of each SNP was investigated in six populations: Japanese (n = 167), Korean (n = 90), Mongolian (n = 92), Ovambos (n = 86), Turkish (n = 87), and German (n = 70). In all the populations, only one genotype was found in each SNP. Irrespective of differences in ethnic groups, the angiogenin and RNase 2 genes appear to exhibit markedly less genetic heterogeneity with regard to these SNPs.

Morphological observation of nuclear sub-localization of human angiogenin in HUVECs

Angiogenin, a potent angiogenic factor, was cloned and expressed by Escherichia coli and then purified with gel filtration chromatography. Approximately 90% pure angiogenin was obtained to generate a monoclonal antibody. Using western immunoblotting and ELISA, we confirmed that monoclonal antibody C46 secreted from hybridoma cells stably and specifically binds to angiogenin. The fused protein angiogenin-EGF was then expressed in HUVECs, and the subcellular localization of the recombinant protein was determined by confocal microscopy and TEM assay. Recombinant angiogenin was found to mainly concentrate in the pars granulosa of the nucleus, where the protein accumulates to form ribonucleoprotein particles.

Extracellular matrix-dependent regulation of angiogenin expression in human placenta

Knowledge of the rapidly developing hierarchy of controls affecting vascular development in placenta is required to understand how the growth factors and their receptor-mediated signals actually produce vessels. At the cell biological level, these events clearly require stable interactions between the cells, and cells with the surrounding ECM. The objective of the study was to understand the role of integrins and ECM on the expression and secretion of angiogenin in placentas and from trophoblasts in culture. Functionally active term placental explant culture and trophoblast cultures were used to demonstrate the differential secretion profile of angiogenin and real-time quantitative RT-PCR to demonstrate the mRNA expression in the presence or absence of ECM proteins. In this study, a significant increase in expression and secretion of angiogenin occurred in the presence of vitronectin (VN) and fibronectin (FN). Using antibody-blocking experiments it was also demonstrated that the angiogenin secretion is mediated by placental integrins, alpha(V)beta3 and alpha5beta1. In addition, exposure to hypoxic conditions resulted in diminished angiogenin secretion in the presence of both ECMs suggesting that angiogenin expression in the presence of ECM is modulated by local O2 concentration. In conclusion, this study provides evidence for the regulatory role of ECM and integrins on the mRNA expression and secretion of angiogenin in human placenta. ECMs may have a pivotal role in enhancing secretion of this peptide necessary for placental angiogenesis and provides the impetus as additional targets for the control of angiogenesis in pathological pregnancy.

Angiogenin loss-of-function mutations in amyotrophic lateral sclerosis

OBJECTIVE

Heterozygous missense mutations in the coding region of angiogenin (ANG), an angiogenic ribonuclease, have been reported in amyotrophic lateral sclerosis (ALS) patients. However, the role of ANG in motor neuron physiology and the functional consequences of these mutations are unknown. We searched for new mutations and sought to define the functional consequences of these mutations.

METHODS

We sequenced the coding region of ANG in an independent cohort of North American ALS patients. Identified ANG mutations were then characterized using functional assays of angiogenesis, ribonucleolysis, and nuclear translocation. We also examined expression of ANG in normal human fetal and adult spinal cords.

RESULTS

We identified four mutations in the coding region of ANG from 298 ALS patients. Three of these mutations are present in the mature protein. Among the four mutations, P(-4)S, S28N, and P112L are novel, and K17I has been reported previously. Functional assays show that these ANG mutations result in complete loss of function. The mutant ANG proteins are unable to induce angiogenesis because of a deficiency in ribonuclease activity, nuclear translocation, or both. As a correlate, we demonstrate strong ANG expression in both endothelial cells and motor neurons of normal human spinal cords from the developing fetus and adult.

INTERPRETATION

We provide the first evidence that ANG mutations, identified in ALS patients, are associated with functional loss of ANG activity. Moreover, strong ANG expression, in normal human fetal and adult spinal cord neurons and endothelial cells, confirms the plausibility of ANG dysfunction being relevant to the pathogenesis of ALS.

RNase A ribonucleases and host defense: an evolving story

RNase A (bovine pancreatic RNase) is the founding member an extensive family of divergent proteins that share specific elements of sequence homology, a unique disulfide-bonded tertiary structure, and the ability to hydrolyze polymeric RNA. Among the more intriguing and perhaps counterintuitive findings, at the current state of the art, the connection between RNase activity and characterized host defense functions is quite weak; whether this is a scientific reality or more a reflection of what has been chosen for study remains to be determined. Several of the RNase A family RNases are highly cationic and have cytotoxic and bactericidal properties that are clearly (eosinophil cationic protein, leukocyte RNase A-2) or are probably (RNase 7) unrelated to their enzymatic activity. Interestingly, peptides derived from the leukocyte RNase A-2 sequence are nearly as bactericidal as the entire protein, suggesting that among other functions, the RNase A superfamily may be serving as a source of gene scaffolds for the generation of novel cytotoxic peptides. Other RNase A ribonucleases are somewhat less cationic (mouse angiogenin 4, zebrafish RNases) and have moderate bactericidal activities that have not yet been explored mechanistically. Additional host defense functions characterized specifically for the RNase eosinophil-derived neurotoxin include reducing infectivity of RNA viruses for target cells in culture, which does require RNase activity, chemoattraction of immature human dendritic cells via a G-protein-coupled receptor-dependent mechanism, and activation of TLR2. The properties of individual RNase A ribonucleases, recent experimental findings, and important questions for the near and distant future will be reviewed.

Structural and functional implications of positive selection at the primate angiogenin gene

BACKGROUND

Angiogenesis, the formation of new blood vessels, is a primordial process in development and its dysregulation has a central role in the pathogenesis of many diseases. Angiogenin (ANG), a peculiar member of the RNase A superfamily, is a potent inducer of angiogenesis involved in many different types of cancer, amyotrophic lateral sclerosis and also with a possible role in the innate immune defense. The evolutionary path of this family has been a highly dynamic one, where positive selection has played a strong role. In this work we used a combined gene and protein level approach to determine the main sites under diversifying selection on the primate ANG gene and analyze its structural and functional implications.

RESULTS

We obtained evidence for positive selection in the primate ANG gene. Site specific analysis pointed out 15 sites under positive selection, most of which also exhibited drastic changes in amino acid properties. The mapping of these sites in the ANG 3D-structure described five clusters, four of which were located in functional regions: two in the active site region, one in the nucleolar location signal and one in the cell-binding site. Eight of the 15 sites under selection in the primate ANG gene were highly or moderately conserved in the RNase A family, suggesting a directed event and not a simple consequence of local structural or functional permissiveness. Moreover, 11 sites were exposed to the surface of the protein indicating that they may influence the interactions performed by ANG.

CONCLUSION

Using a maximum likelihood gene level analysis we identified 15 sites under positive selection in the primate ANG genes, that were further corroborated through a protein level analysis of radical changes in amino acid properties. These sites mapped onto the main functional regions of the ANG protein. The fact that evidence for positive selection is present in all ANG regions required for angiogenesis may be a good indication that angiogenesis is the process under selection. However, other possibilities to be considered arise from the possible involvement of ANG in innate immunity and the potential influence or co-evolution with its interacting proteins and ligands.

A new role for angiogenin in neurite growth and pathfinding: implications for amyotrophic lateral sclerosis

Mutations in human angiogenin (hANG), an angiogenic member of the RNase A superfamily, have been recently reported in patients with amyotrophic lateral sclerosis (ALS), a progressive late-onset neurodegenerative disorder. However, very little is known about the expression and subcellular distribution of ANG in the nervous system or its role in differentiation. Here we report that mouse angiogenin-1 (mAng-1) is strongly expressed in the developing nervous system during mouse embryogenesis and neuroectodermal differentiation of pluripotent P19 embryonal carcinoma cells. mAng1 is strongly expressed in motor neurons (MNs) in the spinal cord and dorsal root ganglia as well as in post-mitotic MNs derived from P19 cells. We also show for the first time that ANG expression is in the growth cones and neurites. NCI 65828, an inhibitor of the ribonucleolytic activity of hANG, affected pathfinding by P19-derived neurons but not neuronal differentiation. Our findings clearly show that ANG plays an important role in neurite pathfinding and this has implications for ALS.

RNase T1 mimicking artificial ribonuclease

Recently, artificial ribonucleases (aRNases)—conjugates of oligodeoxyribonucleotides and peptide (LR)₄-G-amide—were designed and assessed in terms of the activity and specificity of RNA cleavage. The conjugates were shown to cleave RNA at Pyr-A and G–X sequences. Variations of oligonucleotide length and sequence, peptide and linker structure led to the development of conjugates exhibiting G–X cleavage specificity only. The most efficient catalyst is built of nonadeoxyribonucleotide of unique sequence and peptide (LR)₄-G-NH₂ connected by the linker of three abasic deoxyribonucleotides (conjugate pep-9). Investigation of the cleavage specificity of conjugate pep-9 showed that the compound is the first single-stranded guanine-specific aRNase, which mimics RNase T1. Rate enhancement of RNA cleavage at G–X linkages catalysed by pep-9 is 10⁸ compared to non-catalysed reaction, pep-9 cleaves these linkages only 10⁵-fold less efficiently than RNase T1 (k_{cat_RNase T1}/k_cat__pep-9 = 10⁵).

Transplantation of angiogenin-overexpressing mesenchymal stem cells synergistically augments cardiac function in a porcine model of chronic ischemia

OBJECTIVE

Accumulated evidence suggests that myogenesis and angiogenesis induced by implanted cells play important roles in restoring cardiac function after a myocardial infarction. The current study investigated the effects of transplanted autologous mesenchymal stem cells overexpressing angiogenin on myocardial perfusion and cardiac function in the porcine chronic ischemic model.

METHODS

Chronic ischemia was generated in Yorkshire pigs by placing an ameroid constrictor around the left circumflex artery. Four weeks after occlusion, the animals were randomly separated into 4 groups: pigs in the MSC(AdAng) or MSC(AdNull) groups were implanted with 6 x 10(8) mesenchymal stem cells infected with adenovirus containing angiogenin gene or null adenovirus, respectively; pigs in the AdAng or AdNull groups were injected intramyocardially with adenovirus (5 x 10(9) plaque forming unit/pig) containing angiogenin gene or null adenovirus, respectively. Four weeks after implantation, mesenchymal stem cells prelabeled with DiI were observed within the implanted area in both cell transplantation groups.

RESULTS

Angiogenin protein levels were significantly greater in the MSC(AdAng) and AdAng groups than in the other 2 groups and were associated with greater neovessel formation than in the other 2 groups. Mesenchymal stem cell transplantation decreased scar size and increased scar thickness. Both the AdAng and MSC(AdNull) groups experienced improved cardiac function compared with that seen in the AdNull group. However, a synergistic effect of mesenchymal stem cells and angiogenin was observed in the MSC(AdAng) group because myocardial perfusion and cardiac function increased significantly (P < .05 for all groups) in this group compared with all the others.

CONCLUSIONS

Transplantation of autologous mesenchymal stem cells transfected with the angiogenin gene revealed a synergistic effect on the improvement of heart perfusion and function after ameroid occlusion.

Cancer gene therapy targeting angiogenesis: An updated Review

Since the relationship between angiogenesis and tumor growth was established by Folkman in 1971, scientists have made efforts exploring the possibilities in treating cancer by targeting angiogenesis. Inhibition of angiogenesis growth factors and administration of angiogenesis inhibitors are the basics of anti-angiogenesis therapy. Transfer of anti-angiogenesis genes has received attention recently not only because of the advancement of recombinant vectors, but also because of the localized and sustained expression of therapeutic gene product inside the tumor after gene transfer. This review provides the up-to-date information about the strategies and the vectors studied in the field of anti-angiogenesis cancer gene therapy.

A therapeutic target for prostate cancer based on angiogenin-stimulated angiogenesis and cancer cell proliferation

Human angiogenin is progressively up-regulated in the prostate epithelial cells during the development of prostate cancer from prostate intraepithelial neoplasia (PIN) to invasive adenocarcinoma. Mouse angiogenin is the most up-regulated gene in AKT-induced PIN in prostate-restricted AKT transgenic mice. These results prompted us to study the role that angiogenin plays in prostate cancer. Here, we report that, in addition to its well established role in mediating angiogenesis, angiogenin also directly stimulates prostate cancer cell proliferation. Angiogenin undergoes nuclear translocation in PC-3 human prostate cancer cells grown both in vitro and in mice. Thus, knocking down angiogenin expression in PC-3 human prostate adenocarcinoma cells inhibits ribosomal RNA transcription, in vitro cell proliferation, colony formation in soft agar, and xenograft growth in athymic mice. Blockade of nuclear translocation of angiogenin by the aminoglycoside antibiotic neomycin inhibited PC-3 cell tumor growth in athymic mice and was accompanied by a decrease in both cancer cell proliferation and angiogenesis. These results suggest that angiogenin has a dual effect, angiogenesis and cancer cell proliferation, in prostate cancer and may serve as a molecular target for drug development. Blocking nuclear translocation of angiogenin could have a combined benefit of antiangiogenesis and chemotherapy in treating prostate cancer.

The RNase a superfamily: Generation of diversity and innate host defense

The Ribonuclease A superfamily includes an extensive network of distinct and divergent gene lineages. Although all ribonucleases of this superfamily share invariant structural and catalytic elements and some degree of enzymatic activity, the primary sequences have diverged significantly, ostensibly to promote novel function. We will review the literature on the evolution and biology of the RNase A ribonuclease lineages that have been characterized specifically as involved in host defense including: (1) RNases 2 and RNases 3, also known as the eosinophil ribonucleases, which are rapidly-evolving cationic proteins released from eosinophilic leukocytes, (2) RNase 7, an anti-pathogen ribonuclease identified in human skin, and (3) RNase 5, also known as angiogenin, another rapidly-evolving ribonuclease known to promote blood vessel growth with recently-discovered antibacterial activity. Interestingly, some of the characterized anti-pathogen activities do not depend on ribonuclease activity per se. We discuss the ways in which the anti-pathogen activities characterized in vitro might translate into experimental confirmation in vivo. We will also consider the possibility that other ribonucleases, such as the dimeric bovine seminal ribonuclease and the frog oocyte ribonucleases, may have host defense functions and therapeutic value that remain to be explored. (190 words).