Ribonuclease/angiogenin inhibitor 1 regulates stress-induced subcellular localization of angiogenin to control growth and survival

Human angiogenin is a potent cytotoxin in the absence of ribonuclease inhibitor

Angiogenin (ANG) is a secretory ribonuclease that promotes the proliferation of endothelial cells, leading to angiogenesis. This function relies on its ribonucleolytic activity, which is low for simple RNA substrates. Upon entry into the cytosol, ANG is sequestered by the ribonuclease inhibitor protein (RNH1). We find that ANG is a potent cytotoxin for RNH1-knockout HeLa cells, belying its inefficiency as a nonspecific catalyst. The toxicity does, however, rely on the ribonucleolytic activity of ANG and a cytosolic localization, which lead to the accumulation of particular tRNA fragments (tRFs), such as tRF-5 Gly-GCC. These up-regulated tRFs are highly cytotoxic at physiological concentrations. Although ANG is well-known for its promotion of cell growth, our results reveal that ANG can also cause cell death.

Immune Modulation by Human Secreted RNases at the Extracellular Space

The ribonuclease A superfamily is a vertebrate-specific family of proteins that encompasses eight functional members in humans. The proteins are secreted by diverse innate immune cells, from blood cells to epithelial cells and their levels in our body fluids correlate with infection and inflammation processes. Recent studies ascribe a prominent role to secretory RNases in the extracellular space. Extracellular RNases endowed with immuno-modulatory and antimicrobial properties can participate in a wide variety of host defense tasks, from performing cellular housekeeping to maintaining body fluid sterility. Their expression and secretion are induced in response to a variety of injury stimuli. The secreted proteins can target damaged cells and facilitate their removal from the focus of infection or inflammation. Following tissue damage, RNases can participate in clearing RNA from cellular debris or work as signaling molecules to regulate the host response and contribute to tissue remodeling and repair. We provide here an overall perspective on the current knowledge of human RNases’ biological properties and their role in health and disease. The review also includes a brief description of other vertebrate family members and unrelated extracellular RNases that share common mechanisms of action. A better knowledge of RNase mechanism of actions and an understanding of their physiological roles should facilitate the development of novel therapeutics.

Stress-induced tRNA cleavage and tiRNA generation in rat neuronal PC12 cells

Transfer RNA (tRNA) plays a role in stress response programs involved in various pathological conditions including neurological diseases. Under cell stress conditions, intracellular tRNA is cleaved by a specific ribonuclease, angiogenin, generating tRNA-derived fragments or tRNA-derived stress-induced RNA (tiRNA). Generated tiRNA contributes to the cell stress response and has potential cell protective effects. However, tiRNA generation under stress conditions in neuronal cells has not been fully elucidated. To examine angiogenin-mediated tiRNA generation in neuronal cells, we used the rat neuronal cell line, PC12, in combination with analysis of SYBR staining and immuno-northern blotting using anti-1-methyladenosine antibody, which specifically and sensitively detects tiRNA. Oxidative stress induced by arsenite and hydrogen peroxide caused tRNA cleavage and tiRNA generation in PC12 cells. We also demonstrated that oxygen-glucose deprivation, which is an in vitro model of ischemic-reperfusion injury, induced tRNA cleavage and tiRNA generation. In these stress conditions, the amount of generated tiRNA was associated with the degree of morphological cell damage. Time course analysis indicated that generation of tiRNA was prior to severe cell damage and cell death. Angiogenin over-expression did not influence the amount of tiRNA in normal culture conditions; however, it significantly increased tiRNA generation induced by cell stress conditions. Our findings show that angiogenin-mediated tiRNA generation can be induced in neuronal cells by different cell stressors, including ischemia-reperfusion. Additionally, detection of tiRNA could be used as a potential cell damage marker in neuronal cells. Cover Image for this issue: doi: 10.1111/jnc.14191.

Proteomic Identification of the Galectin-1-Involved Molecular Pathways in Urinary Bladder Urothelial Carcinoma

Among various heterogeneous types of bladder tumors, urothelial carcinoma is the most prevalent lesion. Some of the urinary bladder urothelial carcinomas (UBUCs) develop local recurrence and may cause distal invasion. Galectin-1 de-regulation significantly affects cell transformation, cell proliferation, angiogenesis, and cell invasiveness. In continuation of our previous investigation on the role of galectin-1 in UBUC tumorigenesis, in this study, proteomics strategies were implemented in order to find more galectin-1-associated signaling pathways. The results of this study showed that galectin-1 knockdown could induce 15 down-regulated proteins and two up-regulated proteins in T24 cells. These de-regulated proteins might participate in lipid/amino acid/energy metabolism, cytoskeleton, cell proliferation, cell-cell interaction, cell apoptosis, metastasis, and protein degradation. The aforementioned dys-regulated proteins were confirmed by western immunoblotting. Proteomics results were further translated to prognostic markers by analyses of biopsy samples. Results of cohort studies demonstrated that over-expressions of glutamine synthetase, alcohol dehydrogenase (NADP⁺), fatty acid binding protein 4, and toll interacting protein in clinical specimens were all significantly associated with galectin-1 up-regulation. Univariate analyses showed that de-regulations of glutamine synthetase and fatty acid binding protein 4 in clinical samples were respectively linked to disease-specific survival and metastasis-free survival.

Angiogenin/Ribonuclease 5 Is an EGFR Ligand and a Serum Biomarker for Erlotinib Sensitivity in Pancreatic Cancer

Pancreatic ribonuclease (RNase) is a secreted enzyme critical for host defense. We discover an intrinsic RNase function, serving as a ligand for epidermal growth factor receptor (EGFR), a member of receptor tyrosine kinase (RTK), in pancreatic ductal adenocarcinoma (PDAC). The closely related bovine RNase A and human RNase 5 (angiogenin [ANG]) can trigger oncogenic transformation independently of their catalytic activities via direct association with EGFR. Notably, high plasma ANG level in PDAC patients is positively associated with response to EGFR inhibitor erlotinib treatment. These results identify a role of ANG as a serum biomarker that may be used to stratify patients for EGFR-targeted therapies, and offer insights into the ligand-receptor relationship between RNase and RTK families.

tRNA fragmentation and protein translation dynamics in the course of kidney injury

Cells under stressful microenvironmental conditions initiate integrated molecular circuitries that aim at reducing general protein translation rates while redirecting protein synthesis toward a selective set of stress-response proteins. The consequence of the activation of this dynamic system is a reduction of the energy expenditure of the cell, and a metabolic rewiring that shapes adaptation under stress, which will, in fine, promote cell survival. In general, the translation initiation step is the prime target of translation reduction, with 2 molcular modules inhibiting translation initiation: the mechanistic target of Rapamycin complex 1, and the stress related kinases eIF2 kinases, which are all involved in the cellular responses to kidney injuries. tRNA (tRNA) dynamics and fragmentation have recently gained a considerable weight in the field of the non-coding RNA biology, and emerge as an important system for protein translation modulation under cellular stress. More precisely, stress-induced tRNA (tiRNA), the cleavage products of the ribonuclease angiogenin, are generated under various stress conditions, including oxidative stress and endoplasmic reticulum stress, and contribute to protein translation reprogramming in mammal cells. Current clinical and experimental evidence indicates that the angiogenin-tRNA fragmentation system is initiated under renal insults, and is involved in the tissue adaptation upon kidney injury. In addition, this system represents a potential source for minimally-invasive or non invasive biomarkers of early kidney injury. Besides RNA interference, tRNA fragments are likely involved in other fundamental cellular functions, including inflammation, and a better understanding of the molecular basis of tRNA functions will drive discoveries on the fundamental role of non coding RNA biology, as exemplified by microRNA, in the regulation of kidney homeostasis.

tRNA-derived small RNAs: New players in genome protection against retrotransposons

Previously believed to be mere random degradation products, tRNA-derived small RNAs have been lately connected to a series of functions that include, surprisingly, genome protection against retrotransposons. tRNAs have been known for a long time to be involved in the replication cycle of retroviruses, pararetroviruses and retrotransposons as primers of their reverse transcription. tRNA-derived small RNAs, as functional small RNAs or as mere tRNA degradation products, have emerged as important players in the regulation of genic transcription. Nevertheless, the involvement of functional sRNAs derived from tRNA transcripts in transposon posttranscriptional control is a regulatory layer that remained elusive until now. Here I review the recent discoveries in the field that connect tRNA-derived small RNAs and retrotransposon control.

Amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS), also known as motor neuron disease, is characterized by the degeneration of both upper and lower motor neurons, which leads to muscle weakness and eventual paralysis. Until recently, ALS was classified primarily within the neuromuscular domain, although new imaging and neuropathological data have indicated the involvement of the non-motor neuraxis in disease pathology. In most patients, the mechanisms underlying the development of ALS are poorly understood, although a subset of patients have familial disease and harbour mutations in genes that have various roles in neuronal function. Two possible disease-modifying therapies that can slow disease progression are available for ALS, but patient management is largely mediated by symptomatic therapies, such as the use of muscle relaxants for spasticity and speech therapy for dysarthria.

Differential processing of small RNAs during endoplasmic reticulum stress

The accumulation of misfolded proteins in the endoplasmic reticulum (ER) lumen due to the disruption of the homeostatic system of the ER leads to the induction of the ER stress response. Cellular stress-induced pathways globally transform genes expression on both the transcriptional and post-transcriptional levels with small RNA involvement as regulators of the stress response. The modulation of small RNA processing might represent an additional layer of a complex stress response program. However, it is poorly understood. Here, we studied changes in expression and small RNAs processing upon ER stress in Jurkat T-cells. Induced by ER-stress, depletion of miRNAs among small RNA composition was accompanied by a global decrease of 3′ mono-adenylated, mono-cytodinylated and a global increase of 3′ mono-uridinylated miRNA isoforms. We observed the specific subset of differentially expressed microRNAs, and also the dramatic induction of 32-nt tRNA fragments precisely phased to 5′ and 3′ ends of tRNA from a subset of tRNA isotypes. The induction of these tRNA fragments was linked to Angiogenin RNase, which mediates translation inhibition. Overall, the global perturbations of the expression and processing of miRNAs and tiRNAs were the most prominent features of small RNA transcriptome changes upon ER stress.

α7β1 Integrin regulation of gene transcription in skeletal muscle following an acute bout of eccentric exercise

The α₇β₁ integrin is concentrated at the costameres of skeletal muscle and provides a critical link between the actin cytoskeleton and laminin in the basement membrane. We previously demonstrated that expression of the α₇BX2 integrin subunit (MCK:α₇BX2) preserves muscle integrity and enhances myofiber cross-sectional area following eccentric exercise. The purpose of this study was to utilize gene expression profiling to reveal potential mechanisms by which the α₇BX2-integrin contributes to improvements in muscle growth after exercise. A microarray analysis was performed using RNA extracted from skeletal muscle of wild-type or transgenic mice under sedentary conditions and 3 h following an acute bout of downhill running. Genes with false discovery rate probability values below the cutoff of P < 0.05 (n = 73) were found to be regulated by either exercise or transgene expression. KEGG pathway analysis detected upregulation of genes involved in endoplasmic reticulum protein processing with integrin overexpression. Targeted analyses verified increased transcription of Rpl13a, Nosip, Ang, Scl7a5, Gys1, Ndrg2, Hspa5, and Hsp40 as a result of integrin overexpression alone or in combination with exercise (P < 0.05). A significant increase in HSPA5 protein and a decrease in CAAT-enhancer-binding protein homologous protein (CHOP) were detected in transgenic muscle (P < 0.05). In vitro knockdown experiments verified integrin-mediated regulation of Scl7a5 The results from this study suggest that the α₇β₁ integrin initiates transcription of genes that allow for protection from stress, including activation of a beneficial unfolded protein response and modulation of protein synthesis, both which may contribute to positive adaptations in skeletal muscle as a result of engagement in eccentric exercise.

Designing the Sniper: Improving Targeted Human Cytolytic Fusion Proteins for Anti-Cancer Therapy via Molecular Simulation

Targeted human cytolytic fusion proteins (hCFPs) are humanized immunotoxins for selective treatment of different diseases including cancer. They are composed of a ligand specifically binding to target cells genetically linked to a human apoptosis-inducing enzyme. hCFPs target cancer cells via an antibody or derivative (scFv) specifically binding to e.g., tumor associated antigens (TAAs). After internalization and translocation of the enzyme from endocytosed endosomes, the human enzymes introduced into the cytosol are efficiently inducing apoptosis. Under in vivo conditions such enzymes are subject to tight regulation by native inhibitors in order to prevent inappropriate induction of cell death in healthy cells. Tumor cells are known to upregulate these inhibitors as a survival mechanism resulting in escape of malignant cells from elimination by immune effector cells. Cytosolic inhibitors of Granzyme B and Angiogenin (Serpin P9 and RNH1, respectively), reduce the efficacy of hCFPs with these enzymes as effector domains, requiring detrimentally high doses in order to saturate inhibitor binding and rescue cytolytic activity. Variants of Granzyme B and Angiogenin might feature reduced affinity for their respective inhibitors, while retaining or even enhancing their catalytic activity. A powerful tool to design hCFPs mutants with improved potency is given by in silico methods. These include molecular dynamics (MD) simulations and enhanced sampling methods (ESM). MD and ESM allow predicting the enzyme-protein inhibitor binding stability and the associated conformational changes, provided that structural information is available. Such "high-resolution" detailed description enables the elucidation of interaction domains and the identification of sites where particular point mutations may modify those interactions. This review discusses recent advances in the use of MD and ESM for hCFP development from the viewpoints of scientists involved in both fields.

Molecular basis for the autonomous promotion of cell proliferation by angiogenin

Canonical growth factors act indirectly via receptor-mediated signal transduction pathways. Here, we report on an autonomous pathway in which a growth factor is internalized, has its localization regulated by phosphorylation, and ultimately uses intrinsic catalytic activity to effect epigenetic change. Angiogenin (ANG), a secreted vertebrate ribonuclease, is known to promote cell proliferation, leading to neovascularization as well as neuroprotection in mammals. Upon entering cells, ANG encounters the cytosolic ribonuclease inhibitor protein, which binds with femtomolar affinity. We find that protein kinase C and cyclin-dependent kinase phosphorylate ANG, enabling ANG to evade its inhibitor and enter the nucleus. After migrating to the nucleolus, ANG cleaves promoter-associated RNA, which prevents the recruitment of the nucleolar remodeling complex to the ribosomal DNA promoter. The ensuing derepression of rDNA transcription promotes cell proliferation. The biochemical basis for this unprecedented mechanism of signal transduction suggests new modalities for the treatment of cancers and neurological disorders.

Proteomics-Based Identification of the Molecular Signatures of Liver Tissues from Aged Rats following Eight Weeks of Medium-Intensity Exercise

Physical activity has emerged as a powerful intervention that promotes healthy aging by maintaining the functional capacity of critical organ systems. Here, by combining functional and proteomics analyses, we examined how hepatic phenotypes might respond to exercise treatment in aged rats. 16 male aged (20 months old) SD rats were divided into exercise and parallel control groups at random; the exercise group had 8 weeks of treadmill training with medium intensity. Whole protein samples of the liver were extracted from both groups and separated by two-dimensional gel electrophoresis. Alternatively objective protein spots with >2-fold difference in expression were selected for enzymological extraction and MS/MS identification. Results show increased activity of the manganese superoxide dismutase and elevated glutathione levels in the livers of exercise-treated animals, but malondialdehyde contents obviously decreased in the liver of the exercise group. Proteomics-based identification of differentially expressed proteins provided an integrated view of the metabolic adaptations occurring in the liver proteome during exercise, which significantly altered the expression of several proteins involved in key liver metabolic pathways including mitochondrial sulfur, glycolysis, methionine, and protein metabolism. These findings indicate that exercise may be beneficial to aged rats through modulation of hepatic protein expression profiles.

Angiogenin Promotes Hematopoietic Regeneration by Dichotomously Regulating Quiescence of Stem and Progenitor Cells

Regulation of stem and progenitor cell populations is critical in the development, maintenance, and regeneration of tissues. Here, we define a novel mechanism by which a niche-secreted RNase, angiogenin (ANG), distinctively alters the functional characteristics of primitive hematopoietic stem/progenitor cells (HSPCs) compared with lineage-committed myeloid-restricted progenitor (MyePro) cells. Specifically, ANG reduces the proliferative capacity of HSPC while simultaneously increasing proliferation of MyePro cells. Mechanistically, ANG induces cell-type-specific RNA-processing events: tRNA-derived stress-induced small RNA (tiRNA) generation in HSPCs and rRNA induction in MyePro cells, leading to respective reduction and increase in protein synthesis. Recombinant ANG protein improves survival of irradiated animals and enhances hematopoietic regeneration of mouse and human HSPCs in transplantation. Thus, ANG plays a non-cell-autonomous role in regulation of hematopoiesis by simultaneously preserving HSPC stemness and promoting MyePro proliferation. These cell-type-specific functions of ANG suggest considerable therapeutic potential.

Knockout of the Ribonuclease Inhibitor Gene Leaves Human Cells Vulnerable to Secretory Ribonucleases

Ribonuclease inhibitor (RNH1) is a cytosolic protein that binds with femtomolar affinity to human ribonuclease 1 (RNase 1) and homologous secretory ribonucleases. RNH1 contains 32 cysteine residues and has been implicated as an antioxidant. Here, we use CRISPR-Cas9 to knock out RNH1 in HeLa cells. We find that cellular RNH1 affords marked protection from the lethal ribonucleolytic activity of RNase 1 but not from oxidants. We conclude that RNH1 protects cytosolic RNA from invading ribonucleases.

Ribonuclease 5 facilitates corneal endothelial wound healing via activation of PI3-kinase/Akt pathway

To maintain corneal transparency, corneal endothelial cells (CECs) exert a pump function against aqueous inflow. However, human CECs are arrested in the G₁-phase and non-proliferative in vivo. Thus, treatment of corneal endothelial decompensation is limited to corneal transplantation, and grafts are vulnerable to immune rejection. Here, we show that ribonuclease (RNase) 5 is more highly expressed in normal human CECs compared to decompensated tissues. Furthermore, RNase 5 up-regulated survival of CECs and accelerated corneal endothelial wound healing in an in vitro wound of human CECs and an in vivo cryo-damaged rabbit model. RNase 5 treatment rapidly induced accumulation of cytoplasmic RNase 5 into the nucleus, and activated PI3-kinase/Akt pathway in human CECs. Moreover, inhibition of nuclear translocation of RNase 5 using neomycin reversed RNase 5-induced Akt activation. As a potential strategy for proliferation enhancement, RNase 5 increased the population of 5-bromo-2′-deoxyuridine (BrdU)-incorporated proliferating CECs with concomitant PI3-kinase/Akt activation, especially in CECs deprived of contact-inhibition. Specifically, RNase 5 suppressed p27 and up-regulated cyclin D1, D3, and E by activating PI3-kinase/Akt in CECs to initiate cell cycle progression. Together, our data indicate that RNase 5 facilitates corneal endothelial wound healing, and identify RNase 5 as a novel target for therapeutic exploitation.

Nucleoside modifications in the regulation of gene expression: focus on tRNA

Both, DNA and RNA nucleoside modifications contribute to the complex multi-level regulation of gene expression. Modified bases in tRNAs modulate protein translation rates in a highly dynamic manner. Synonymous codons, which differ by the third nucleoside in the triplet but code for the same amino acid, may be utilized at different rates according to codon-anticodon affinity. Nucleoside modifications in the tRNA anticodon loop can favor the interaction with selected codons by stabilizing specific base pairs. Similarly, weakening of base pairing can discriminate against binding to near-cognate codons. mRNAs enriched in favored codons are translated in higher rates constituting a fine-tuning mechanism for protein synthesis. This so-called codon bias establishes a basic protein level, but sometimes it is necessary to further adjust the production rate of a particular protein to actual requirements, brought by, e.g., stages in circadian rhythms, cell cycle progression or exposure to stress. Such an adjustment is realized by the dynamic change of tRNA modifications resulting in the preferential translation of mRNAs coding for example for stress proteins to facilitate cell survival. Furthermore, tRNAs contribute in an entirely different way to another, less specific stress response consisting in modification-dependent tRNA cleavage that contributes to the general down-regulation of protein synthesis. In this review, we summarize control functions of nucleoside modifications in gene regulation with a focus on recent findings on protein synthesis control by tRNA base modifications.

Who Regulates Whom? An Overview of RNA Granules and Viral Infections

After viral infection, host cells respond by mounting an anti-viral stress response in order to create a hostile atmosphere for viral replication, leading to the shut-off of mRNA translation (protein synthesis) and the assembly of RNA granules. Two of these RNA granules have been well characterized in yeast and mammalian cells, stress granules (SGs), which are translationally silent sites of RNA triage and processing bodies (PBs), which are involved in mRNA degradation. This review discusses the role of these RNA granules in the evasion of anti-viral stress responses through virus-induced remodeling of cellular ribonucleoproteins (RNPs).

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.

Novel angiogenin mutants with increased cytotoxicity enhance the depletion of pro-inflammatory macrophages and leukemia cells ex vivo

Immunotoxins are fusion proteins that combine a targeting component such as an antibody fragment or ligand with a cytotoxic effector component that induces apoptosis in specific cell populations displaying the corresponding antigen or receptor. Human cytolytic fusion proteins (hCFPs) are less immunogenic than conventional immunotoxins because they contain human pro-apoptotic enzymes as effectors. However, one drawback of hCFPs is that target cells can protect themselves by expressing endogenous inhibitor proteins. Inhibitor-resistant enzyme mutants that maintain their cytotoxic activity are therefore promising effector domain candidates. We recently developed potent variants of the human ribonuclease angiogenin (Ang) that were either more active than the wild-type enzyme or less susceptible to inhibition because of their lower affinity for the ribonuclease inhibitor RNH1. However, combining the mutations was unsuccessful because although the enzyme retained its higher activity, its susceptibility to RNH1 reverted to wild-type levels. We therefore used molecular dynamic simulations to determine, at the atomic level, why the affinity for RNH1 reverted, and we developed strategies based on the introduction of further mutations to once again reduce the affinity of Ang for RNH1 while retaining its enhanced activity. We were able to generate a novel Ang variant with remarkable in vitro cytotoxicity against HL-60 cells and pro-inflammatory macrophages. We also demonstrated the pro-apoptotic potential of Ang-based hCFPs on cells freshly isolated from leukemia patients.

The Many Virtues of tRNA-derived Stress-induced RNAs (tiRNAs): Discovering Novel Mechanisms of Stress Response and Effect on Human Health

In mammalian cells, mature tRNAs are cleaved by stress-activated ribonuclease angiogenin to generate 5'- and 3'-tRNA halves: a novel class of small non-coding RNAs of 30-40 nucleotides in length. The biogenesis and biological functions of tRNA halves are emerging areas of research. This review will discuss the most recent findings on: (i) the mechanism and regulation of their biogenesis, (ii) their mechanism of action (we will specifically discuss their role in the protein synthesis inhibition and the intrinsic pathway of apoptosis), and (iii) their effects on the human physiology and disease conditions.

Angiogenin Mediates Cell-Autonomous Translational Control under Endoplasmic Reticulum Stress and Attenuates Kidney Injury

Endoplasmic reticulum (ER) stress is involved in the pathophysiology of kidney disease and aging, but the molecular bases underlying the biologic outcomes on the evolution of renal disease remain mostly unknown. Angiogenin (ANG) is a ribonuclease that promotes cellular adaptation under stress but its contribution to ER stress signaling remains elusive. In this study, we investigated the ANG-mediated contribution to the signaling and biologic outcomes of ER stress in kidney injury. ANG expression was significantly higher in samples from injured human kidneys than in samples from normal human kidneys, and in mouse and rat kidneys, ANG expression was specifically induced under ER stress. In human renal epithelial cells, ER stress induced ANG expression in a manner dependent on the activity of transcription factor XBP1, and ANG promoted cellular adaptation to ER stress through induction of stress granules and inhibition of translation. Moreover, the severity of renal lesions induced by ER stress was dramatically greater in ANG knockout mice (Ang(-/-)) mice than in wild-type mice. These results indicate that ANG is a critical mediator of tissue adaptation to kidney injury and reveal a physiologically relevant ER stress-mediated adaptive translational control mechanism.

Sex hormone-dependent tRNA halves enhance cell proliferation in breast and prostate cancers

Sex hormones and their receptors play critical roles in the development and progression of the breast and prostate cancers. Here we report that a novel type of transfer RNA (tRNA)-derived small RNA, termed Sex HOrmone-dependent TRNA-derived RNAs (SHOT-RNAs), are specifically and abundantly expressed in estrogen receptor (ER)-positive breast cancer and androgen receptor (AR)-positive prostate cancer cell lines. SHOT-RNAs are not abundantly present in ER(-) breast cancer, AR(-) prostate cancer, or other examined cancer cell lines from other tissues. ER-dependent accumulation of SHOT-RNAs is not limited to a cell culture system, but it also occurs in luminal-type breast cancer patient tissues. SHOT-RNAs are produced from aminoacylated mature tRNAs by angiogenin-mediated anticodon cleavage, which is promoted by sex hormones and their receptors. Resultant 5'- and 3'-SHOT-RNAs, corresponding to 5'- and 3'-tRNA halves, bear a cyclic phosphate (cP) and an amino acid at the 3'-end, respectively. By devising a "cP-RNA-seq" method that is able to exclusively amplify and sequence cP-containing RNAs, we identified the complete repertoire of 5'-SHOT-RNAs. Furthermore, 5'-SHOT-RNA, but not 3'-SHOT-RNA, has significant functional involvement in cell proliferation. These results have unveiled a novel tRNA-engaged pathway in tumorigenesis of hormone-dependent cancers and implicate SHOT-RNAs as potential candidates for biomarkers and therapeutic targets.

Small tRNA-derived RNAs are increased and more abundant than microRNAs in chronic hepatitis B and C

Persistent infections with hepatitis B virus (HBV) or hepatitis C virus (HCV) account for the majority of cases of hepatic cirrhosis and hepatocellular carcinoma (HCC) worldwide. Small, non-coding RNAs play important roles in virus-host interactions. We used high throughput sequencing to conduct an unbiased profiling of small (14-40 nts) RNAs in liver from Japanese subjects with advanced hepatitis B or C and hepatocellular carcinoma (HCC). Small RNAs derived from tRNAs, specifically 30–35 nucleotide-long 5′ tRNA-halves (5′ tRHs), were abundant in non-malignant liver and significantly increased in humans and chimpanzees with chronic viral hepatitis. 5′ tRH abundance exceeded microRNA abundance in most infected non-cancerous tissues. In contrast, in matched cancer tissue, 5′ tRH abundance was reduced, and relative abundance of individual 5′ tRHs was altered. In hepatitis B-associated HCC, 5′ tRH abundance correlated with expression of the tRNA-cleaving ribonuclease, angiogenin. These results demonstrate that tRHs are the most abundant small RNAs in chronically infected liver and that their abundance is altered in liver cancer.

Downregulation of angiogenin inhibits the growth and induces apoptosis in human bladder cancer cells through regulating AKT/mTOR signaling pathway

Angiogenin (ANG) is a multifunctional secreted protein that belongs to the pancreatic ribonuclease A super family, which has been conceived to play a more important role in cell survival, growth and proliferation than the mediation of angiogenesis. Accumulating evidences suggest that the expression and activity of ANG increased significantly in a variety of human cancers. Recent studies showed that ANG activates cell signaling pathway through the putative receptor on endothelial cells. However, the underlying mechanisms remain largely unknown. AKT/mTOR signaling pathway participates in cell growth, cell-cycle progression and cell apoptosis. The purpose of our study was to determine whether ANG implicated in growth and metastasis of bladder cancer cells through regulating AKT/mTOR signaling pathway. In this study, we constructed ANG siRNA plasmids that transfected into human bladder cancer T24 cells. We demonstrated that knockdown of ANG could inhibit cell proliferation, regulate cell cycle and induce apoptosis. We also found that down-regulation of ANG remarkably reduced the phosphorylation of signaling targets AKT, GSK-3β and mTOR. Furthermore, down-regulation of ANG increased expression of ribonuclease inhibitor, which is a cytoplasmic acidic protein with many functions. Finally, ANG siRNA led to the suppression for tumorigenesis and metastasis in vivo. Taken together, these findings highlight for the first time that ANG could play a pivotal role in the development of bladder cancer through regulating AKT/mTOR signaling pathway. The targeting of ANG and associated factors could provide a novel strategy to inhibit human bladder cancer.

Stress granules, P-bodies and cancer

Cancer cells are exposed to adverse conditions in the tumor microenvironment, and utilize post-transcriptional control mechanisms to re-program gene expression in ways that enhance cell survival. Stress granules and processing bodies are RNA-containing granules that contribute to this process by modulating cellular signaling pathways, metabolic machinery, and stress response programs. This review examines evidence implicating RNA granules in the pathogenesis of cancer and discusses their potential as targets for anticancer therapies. This article is part of a Special Issue entitled: Translation and Cancer.

tRNA fragments in human health and disease

Transfer RNA (tRNA) is traditionally considered to be an adaptor molecule that helps ribosomes to decode messenger RNA (mRNA) and synthesize protein. Recent studies have demonstrated that tRNAs also serve as a major source of small non-coding RNAs that possess distinct and varied functions. These tRNA fragments are heterogeneous in size, nucleotide composition, biogenesis and function. Here we describe multiple roles that tRNA fragments play in cell physiology and discuss their relevance to human health and disease.

Oxidative stress diverts tRNA synthetase to nucleus for protection against DNA damage

Tyrosyl-tRNA synthetase (TyrRS) is known for its essential aminoacylation function in protein synthesis. Here we report a function for TyrRS in DNA damage protection. We found that oxidative stress, which often downregulates protein synthesis, induces TyrRS to rapidly translocate from the cytosol to the nucleus. We also found that angiogenin mediates or potentiates this stress-induced translocalization. The nuclear-localized TyrRS activates transcription factor E2F1 to upregulate the expression of DNA damage repair genes such as BRCA1 and RAD51. The activation is achieved through direct interaction of TyrRS with TRIM28 to sequester this vertebrate-specific epigenetic repressor and its associated HDAC1 from deacetylating and suppressing E2F1. Remarkably, overexpression of TyrRS strongly protects against UV-induced DNA double-strand breaks in zebrafish, whereas restricting TyrRS nuclear entry completely abolishes the protection. Therefore, oxidative stress triggers an essential cytoplasmic enzyme used for protein synthesis to translocate to the nucleus to protect against DNA damage.

Overexpression of ribonuclease inhibitor defines good prognosis and suppresses proliferation and metastasis in human colorectal cancer cells via PI3K/AKT pathway

PURPOSE

We aim to evaluate the diagnostic value of ribonuclease inhibitor (RI) in colorectal cancer (CRC) and investigate the important role of RI in cell growth and metastasis of CRC.

METHODS/PATIENTS

In this study, the expression of RI was evaluated in human CRC samples with different histological grade and the association between RI expression and clinicopathological parameters was investigated. Furthermore, the exogenous RI gene was introduced into human HT29 CRC cells and the effects of RI on cell proliferation and metastasis were determined in vitro. The PI3K/Akt signaling pathway and some related protein molecules were detected.

RESULTS

RI is downregulated in CRC tissues compared to adjacent normal tissues and its expression is inversely associated with histological grade, pathological stage, and venous invasion, respectively. Multivariate analysis showed that RI expression was an independent prognostic factor for overall survival. In addition, the exogenous overexpression of RI reduced the proliferation and migration of HT29 CRC cell line in vitro by inhibiting the PI3K/Akt signaling pathway and suppressing the expression of vascular endothelial growth factor (VEGF) and upregulating phosphatase and tensin homolog (PTEN).

CONCLUSIONS

RI represents an important predictor of progression in patients with CRC and suppresses proliferation and metastasis in CRC cells through inhibiting PI3K/AkT pathway.

mTOR regulates the nucleoplasmic diffusion of Xrn2 under conditions of heat stress

Stress induces various responses, including translational suppression and tRNA degradation in mammals. Previously, we showed that heat stress induces degradation of initiator tRNA(Met) (iMet) through 5'-3' exoribonuclease Xrn1 and Xrn2, respectively. In addition, we found that rapamycin inhibits the degradation of iMet under heat stress conditions. Here, we report that the mammalian target of rapamycin (mTOR) regulates the diffusion of Xrn2 from the nucleolus to the nucleoplasm, facilitating the degradation of iMet under conditions of heat stress. Our results suggest a mechanism of translational suppression through mTOR-regulated iMet degradation in mammalian cells.

Plasma autoantibodies against heat shock protein 70, enolase 1 and ribonuclease/angiogenin inhibitor 1 as potential biomarkers for cholangiocarcinoma

The diagnosis of cholangiocarcinoma (CCA) is often challenging, leading to poor prognosis. CCA arises via chronic inflammation which may be associated with autoantibodies production. This study aims to identify IgG antibodies directed at self-proteins and tumor-associated antigens. Proteins derived from immortalized cholangiocyte cell line (MMNK1) and CCA cell lines (M055, M214 and M139) were separated using 2-dimensional electrophoresis and incubated with pooled plasma of patients with CCA and non-neoplastic controls by immunoblotting. Twenty five immunoreactive spots against all cell lines-derived proteins were observed on stained gels and studied by LC-MS/MS. Among these, heat shock protein 70 (HSP70), enolase 1 (ENO1) and ribonuclease/angiogenin inhibitor 1 (RNH1) obtained the highest matching scores and were thus selected for further validation. Western blot revealed immunoreactivity against HSP70 and RNH1 in the majority of CCA cases and weakly in healthy individuals. Further, ELISA showed that plasma HSP70 autoantibody level in CCA was significantly capable to discriminate CCA from healthy individuals with an area under the receiver operating characteristic curve of 0.9158 (cut-off 0.2630, 93.55% sensitivity and 73.91% specificity). Plasma levels of IgG autoantibodies against HSP70 were correlated with progression from healthy individuals to cholangitis to CCA (r = 0.679, P<0.001). In addition, circulating ENO1 and RNH1 autoantibodies levels were also significantly higher in cholangitis and CCA compared to healthy controls (P<0.05). Moreover, the combinations of HSP70, ENO1 or RNH1 autoantibodies positivity rates improved specificity to over 78%. In conclusion, plasma IgG autoantibodies against HSP70, ENO1 and RNH1 may represent new diagnostic markers for CCA.

Functional evolution of ribonuclease inhibitor: insights from birds and reptiles

Ribonuclease inhibitor (RI) is a conserved protein of the mammalian cytosol. RI binds with high affinity to diverse secretory ribonucleases (RNases) and inhibits their enzymatic activity. Although secretory RNases are found in all vertebrates, the existence of a non-mammalian RI has been uncertain. Here, we report on the identification and characterization of RI homologs from chicken and anole lizard. These proteins bind to RNases from multiple species but exhibit much greater affinity for their cognate RNases than for mammalian RNases. To reveal the basis for this differential affinity, we determined the crystal structure of mouse, bovine, and chicken RI·RNase complexes to a resolution of 2.20, 2.21, and 1.92Å, respectively. A combination of structural, computational, and bioinformatic analyses enabled the identification of two residues that appear to contribute to the differential affinity for RNases. We also found marked differences in oxidative instability between mammalian and non-mammalian RIs, indicating evolution toward greater oxygen sensitivity in RIs from mammalian species. Taken together, our results illuminate the structural and functional evolution of RI, along with its dynamic role in vertebrate biology.

An evolutionarily conserved RNase-based mechanism for repression of transcriptional positive autoregulation

It is known that environmental context influences the degree of regulation at the transcriptional and post-transcriptional levels. However, the principles governing the differential usage and interplay of regulation at these two levels are not clear. Here, we show that the integration of transcriptional and post-transcriptional regulatory mechanisms in a characteristic network motif drives efficient environment-dependent state transitions. Through phenotypic screening, systems analysis, and rigorous experimental validation, we discovered an RNase (VNG2099C) in Halobacterium salinarum that is transcriptionally co-regulated with genes of the aerobic physiologic state but acts on transcripts of the anaerobic state. Through modelling and experimentation we show that this arrangement generates an efficient state-transition switch, within which RNase-repression of a transcriptional positive autoregulation (RPAR) loop is critical for shutting down ATP-consuming active potassium uptake to conserve energy required for salinity adaptation under aerobic, high potassium, or dark conditions. Subsequently, we discovered that many Escherichia coli operons with energy-associated functions are also putatively controlled by RPAR indicating that this network motif may have evolved independently in phylogenetically distant organisms. Thus, our data suggest that interplay of transcriptional and post-transcriptional regulation in the RPAR motif is a generalized principle for efficient environment-dependent state transitions across prokaryotes.

Amyloidogenic variant of apolipoprotein A-I elicits cellular stress by attenuating the protective activity of angiogenin

Amyloidogenic ‘gain-of-function' mutations in apolipoprotein A-I (ApoA-I) gene (APOA1) result in systemic amyloidosis characterized by aggregate deposition and eventually cell death. However, how amyloidogenic variants of ApoA-I induce cell death is unknown. Here we report that one of the mechanisms by which amyloidogenic ApoA-I induces cell death is through attenuating anti-stress activity of angiogenin (ANG), a homeostatic protein having both pro-growth and pro-survival functions. Under growth conditions, ANG is located in nucleolus where it promotes ribosomal RNA (rRNA) transcription thereby stimulating cell growth. In adverse conditions, ANG is relocated to cytoplasm to promote damage repairs and cell survival. We find that in cells overexpressing the L75P-APOA1 mutant ANG expression is decreased and normal cellular localization of ANG is altered in response to stress and growth signals. In particular, ANG does not relocate to cytoplasm under stress conditions but is rather retained in the nucleolus where it continues promoting rRNA transcription, thus imposing a ribotoxic effect while simultaneously compromising its pro-survival activity. Consistently, we also find that addition of exogenous ANG protects cells from L75P-ApoA-I-induced apoptosis.

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.