Authors: Felix J Metzner, Simon J Wenzl, Michael Kugler...

Schlafen 11 (SLFN11) is an interferon-inducible antiviral restriction factor with tRNA endoribonuclease and DNA binding functions. It is recruited to stalled replication forks in response to replication stress and inhibits replication of certain viruses such as the human immunodeficiency virus 1 (HIV-1) by modulating the tRNA pool. SLFN11 has been identified as a predictive biomarker in cancer, as its expression correlates with a beneficial response to DNA damage inducing anticancer drugs. However, the mechanism and interdependence of these two functions are largely unknown. Here, we present cryo-electron microscopy (cryo-EM) structures of human SLFN11 in its dimeric apoenzyme state, bound to tRNA and in complex with single-strand DNA. Full-length SLFN11 neither hydrolyses nor binds ATP and the helicase domain appears in an autoinhibited state. Together with biochemical and structure guided mutagenesis studies, our data give detailed insights into the mechanism of endoribonuclease activity as well as suggestions on how SLFN11 may block stressed replication forks.

Topics: Adenosine Triphosphate; Antineoplastic Agents; Antiviral Agents; Apoenzymes; Cryoelectron Microscopy; DNA; Endoribonucleases; Humans; Interferons; Nuclear Proteins; RNA, Transfer

PubMed: 36115853
DOI: 10.1038/s41467-022-33123-0

Authors: Eric J Wolf, Sebastian Grünberg, Nan Dai...

With the rapid growth of synthetic messenger RNA (mRNA)-based therapeutics and vaccines, the development of analytical tools for characterization of long, complex RNAs has become essential. Tandem liquid chromatography-mass spectrometry (LC-MS/MS) permits direct assessment of the mRNA primary sequence and modifications thereof without conversion to cDNA or amplification. It relies upon digestion of mRNA with site-specific endoribonucleases to generate pools of short oligonucleotides that are then amenable to MS-based sequence analysis. Here, we showed that the uridine-specific human endoribonuclease hRNase 4 improves mRNA sequence coverage, in comparison with the benchmark enzyme RNase T1, by producing a larger population of uniquely mappable cleavage products. We deployed hRNase 4 to characterize mRNAs fully substituted with 1-methylpseudouridine (m1Ψ) or 5-methoxyuridine (mo5U), as well as mRNAs selectively depleted of uridine-two key strategies to reduce synthetic mRNA immunogenicity. Lastly, we demonstrated that hRNase 4 enables direct assessment of the 5' cap incorporation into in vitro transcribed mRNA. Collectively, this study highlights the power of hRNase 4 to interrogate mRNA sequence, identity, and modifications by LC-MS/MS.

Topics: Chromatography, Liquid; DNA, Complementary; Endoribonucleases; Humans; Oligonucleotides; RNA, Messenger; Ribonuclease T1; Sequence Analysis, RNA; Tandem Mass Spectrometry

PubMed: 35871301
DOI: 10.1093/nar/gkac632

Review

Authors: Masayuki Nashimoto

TRUE gene silencing is an RNA-mediated gene expression control technology and is termed after tRNase Z-utilizing efficacious gene silencing. In this review, I overview the potentiality of small guide RNA (sgRNA) for TRUE gene silencing as novel therapeutics. First, I describe the physiology of tRNase Z and cellular small RNA, and then sgRNA and TRUE gene silencing. An endoribonuclease, tRNase Z, which can efficiently remove a 3' trailer from pre-tRNA, is thought to play the role in tRNA maturation in the nucleus and mitochondria. There exist various small RNAs including miRNA and fragments from tRNA and rRNA, which can function as sgRNA, in living cells, and human cells appear to be harnessing cytosolic tRNase Z for gene regulation together with these small RNAs. By utilizing the property of tRNase Z to recognize and cleave micro-pre-tRNA, a pre-tRNA-like or micro-pre-tRNA-like complex, as well as pre-tRNA, tRNase Z can be made to cleave any target RNA at any desired site under the direction of an artificial sgRNA that binds a target RNA and forms the pre-tRNA-like or micro-pre-tRNA-like complex. This general RNA cleavage method underlies TRUE gene silencing. Various examples of the application of TRUE gene silencing are reviewed including the application to several human cancer cells in order to induce apoptosis. Lastly, I discuss the potentiality of sgRNA as novel therapeutics for multiple myeloma.

Topics: Endoribonucleases; Gene Silencing; Humans; MicroRNAs; RNA Precursors; RNA, Transfer; RNA, Guide, CRISPR-Cas Systems

PubMed: 35628198
DOI: 10.3390/ijms23105387

Review

Authors: Simon Le Goupil, Hadrien Laprade, Marc Aubry...

The unfolded protein response is a mechanism aiming at restoring endoplasmic reticulum (ER) homeostasis and is likely involved in other adaptive pathways. The unfolded protein response is transduced by three proteins acting as sensors and triggering downstream signaling pathways. Among them, inositol-requiring enzyme 1 alpha (IRE1α) (referred to as IRE1 hereafter), an endoplasmic reticulum-resident type I transmembrane protein, exerts its function through both kinase and endoribonuclease activities, resulting in both X-box binding protein 1 mRNA splicing and RNA degradation (regulated ire1 dependent decay). An increasing number of studies have reported protein-protein interactions as regulators of these signaling mechanisms, and additionally, driving other noncanonical functions. In this review, we deliver evolutive and structural insights on IRE1 and further describe how this protein interaction network (interactome) regulates IRE1 signaling abilities or mediates other cellular processes through catalytic-independent mechanisms. Moreover, we focus on newly discovered targets of IRE1 kinase activity and discuss potentially novel IRE1 functions based on the nature of the interactome, thereby identifying new fields to explore regarding this protein's biological roles.

Topics: Animals; Humans; Endoplasmic Reticulum; Endoribonucleases; Protein Interaction Maps; Protein Serine-Threonine Kinases; Signal Transduction; Unfolded Protein Response; Evolution, Molecular

PubMed: 38494075
DOI: 10.1016/j.jbc.2024.107169

Review

Authors: Yoontak Han, Eun-Jin Lee

Bacterial endoribonuclease toxins belong to a protein family that inhibits bacterial growth by degrading mRNA or rRNA sequences. The toxin genes are organized in pairs with its cognate antitoxins in the chromosome and thus the activities of the toxins are antagonized by antitoxin proteins or RNAs during active translation. In response to a variety of cellular stresses, the endoribonuclease toxins appear to be released from antitoxin molecules via proteolytic cleavage of antitoxin proteins or preferential degradation of antitoxin RNAs and cleave a diverse range of mRNA or rRNA sequences in a sequence-specific or codon-specific manner, resulting in various biological phenomena such as antibiotic tolerance and persister cell formation. Given that substrate specificity of each endoribonuclease toxin is determined by its structure and the composition of active site residues, we summarize the biology, structure, and substrate specificity of the updated bacterial endoribonuclease toxins. [BMB Reports 2020; 53(12): 611-621].

Topics: Antitoxins; Bacteria; Bacterial Proteins; Bacterial Toxins; Endoribonucleases; Gene Expression Regulation, Bacterial; RNA, Messenger; Substrate Specificity

PubMed: 33148377
DOI: 10.5483/BMBRep.2020.53.12.203

Authors: Chantal K Guegler, Gabriella I C Teodoro, Sriram Srikant...

Bacteria harbor diverse mechanisms to defend themselves against their viral predators, bacteriophages. In response, phages can evolve counter-defense systems, most of which are poorly understood. In T4-like phages, the gene tifA prevents bacterial defense by the type III toxin-antitoxin (TA) system toxIN, but the mechanism by which TifA inhibits ToxIN remains unclear. Here, we show that TifA directly binds both the endoribonuclease ToxN and RNA, leading to the formation of a high molecular weight ribonucleoprotein complex in which ToxN is inhibited. The RNA binding activity of TifA is necessary for its interaction with and inhibition of ToxN. Thus, we propose that TifA inhibits ToxN during phage infection by trapping ToxN on cellular RNA, particularly the abundant 16S rRNA, thereby preventing cleavage of phage transcripts. Taken together, our results reveal a novel mechanism underlying inhibition of a phage-defensive RNase toxin by a small, phage-encoded protein.

Topics: Antitoxins; Bacteriophages; Endoribonucleases; RNA, Ribosomal, 16S; Toxin-Antitoxin Systems

PubMed: 38117986
DOI: 10.1093/nar/gkad1207

Review

Authors: Jérémy Cartalas, Léna Coudray, Anthony Gobert...

Mitochondria are the power houses of eukaryote cells. These endosymbiotic organelles of prokaryote origin are considered as semi-autonomous since they have retained a genome and fully functional gene expression mechanisms. These pathways are particularly interesting because they combine features inherited from the bacterial ancestor of mitochondria with characteristics that appeared during eukaryote evolution. RNA biology is thus particularly diverse in mitochondria. It involves an unexpectedly vast array of factors, some of which being universal to all mitochondria and others being specific from specific eukaryote clades. Among them, ribonucleases are particularly prominent. They play pivotal functions such as the maturation of transcript ends, RNA degradation and surveillance functions that are required to attain the pool of mature RNAs required to synthesize essential mitochondrial proteins such as respiratory chain proteins. Beyond these functions, mitochondrial ribonucleases are also involved in the maintenance and replication of mitochondrial DNA, and even possibly in the biogenesis of mitochondrial ribosomes. The diversity of mitochondrial RNases is reviewed here, showing for instance how in some cases a bacterial-type enzyme was kept in some eukaryotes, while in other clades, eukaryote specific enzymes were recruited for the same function.

Topics: Endoribonucleases; Eukaryota; Mitochondria; Mitochondrial Proteins; RNA; Ribonucleases; Transcriptome

PubMed: 35682820
DOI: 10.3390/ijms23116141

Review

Authors: Emily R Garnett, Ronald T Raines

Pancreatic-type ribonucleases (ptRNases) are a large family of vertebrate-specific secretory endoribonucleases. These enzymes catalyze the degradation of many RNA substrates and thereby mediate a variety of biological functions. Though the homology of ptRNases has informed biochemical characterization and evolutionary analyses, the understanding of their biological roles is incomplete. Here, we review the functions of two ptRNases: RNase 1 and angiogenin. RNase 1, which is an abundant ptRNase with high catalytic activity, has newly discovered roles in inflammation and blood coagulation. Angiogenin, which promotes neovascularization, is now known to play roles in the progression of cancer and amyotrophic lateral sclerosis, as well as in the cellular stress response. Ongoing work is illuminating the biology of these and other ptRNases.

Topics: Endoribonucleases; RNA; Ribonuclease, Pancreatic; Ribonucleases

PubMed: 34886717
DOI: 10.1080/10409238.2021.2004577

Review

Authors: Rongxiang Huang, Zhang Hui, Sun Wei...

IRE1 is an important central regulator of unfolded protein response (UPR) in the endoplasmic reticulum (ER) because of its ability to regulate cell fate as a function of stress sensing. When misfolded proteins accumulated in chondrocytes ER, IRE1 disintegrates with BIP/GRP78 and undergoes dimer/oligomerization and transautophosphorylation. These two processes are mediated through an enzyme activity of IRE1 to activate endoribonuclease and generates XBP1 by unconventional splicing of XBP1 messenger RNA. Thereby promoting the transcription of UPR target genes and apoptosis. The deficiency of inositol-requiring enzyme 1α (IRE1α) in chondrocytes downregulates prosurvival factors XBP1S and Bcl-2, which enhances the apoptosis of chondrocytes through increasing proapoptotic factors caspase-3, p-JNK, and CHOP. Meanwhile, the activation of IRE1α increases chondrocyte viability and reduces cell apoptosis. However, the understanding of IRE1 responses and cell death fate remains controversial. This review provides updated data about the role IRE1 plays in chondrocytes and new insights about the potential efficacy of IRE1 regulation in cartilage repair and osteoarthritis treatment.

Topics: Apoptosis; Chondrocytes; Endoplasmic Reticulum Stress; Endoribonucleases; Humans; Osteoarthritis; Protein Serine-Threonine Kinases; Unfolded Protein Response; X-Box Binding Protein 1

PubMed: 34297411
DOI: 10.1002/jcp.30537

Authors: Troy von Beck, Luis Mena Hernandez, Hongyi Zhou...

The emergence of SARS-CoV-1 in 2003 followed by MERS-CoV and now SARS-CoV-2 has proven the latent threat these viruses pose to humanity. While the SARS-CoV-2 pandemic has shifted to a stage of endemicity, the threat of new coronaviruses emerging from animal reservoirs remains. To address this issue, the global community must develop small molecule drugs targeting highly conserved structures in the coronavirus proteome. Here, we characterized existing drugs for their ability to inhibit the endoribonuclease activity of the SARS-CoV-2 non-structural protein 15 (nsp15) via in silico, in vitro, and in vivo techniques. We have identified nsp15 inhibition by the drugs pibrentasvir and atovaquone which effectively inhibit SARS-CoV-2 and HCoV-OC43 at low micromolar concentrations in cell cultures. Furthermore, atovaquone, but not pibrentasvir, is observed to modulate HCoV-OC43 dsRNA and infection in a manner consistent with nsp15 inhibition. Although neither pibrentasvir nor atovaquone translate to clinical efficacy in a murine prophylaxis model of SARS-CoV-2 infection, atovaquone may serve as a basis for the design of future nsp15 inhibitors.

Topics: Animals; Mice; SARS-CoV-2; COVID-19; Atovaquone; Endoribonucleases; Coronavirus OC43, Human

PubMed: 37766247
DOI: 10.3390/v15091841