33 research outputs found
Role Of RNA-Protein Interactions In The Internal Initiation Of Translation Of Plus-Strand RNA Viruses : A Novel Target For Antiviral Therapeutics
No full textInhibition of hepatitis C virus IRES-mediated translation by small RNAs analogous to stem-loop structures of the 5’-untranslated region
No full textTranslation of the hepatitis C virus (HCV) RNA is mediated by the interaction of ribosomes and cellular proteins with an internal ribosome entry site (IRES) located within the 5’-untranslated region (5’-UTR). We have investigated whether small RNA molecules corresponding to the different stem-loop (SL) domains of the HCV IRES, when introduced in trans, can bind to the cellular proteins and antagonize their binding to the viral IRES, thereby inhibiting HCV IRES-mediated translation. We have found that a RNA molecule corresponding to SL III could efficiently inhibit HCV IRES-mediated translation in a dose-dependent manner without affecting capdependent translation. The SL III RNA was found to bind to most of the cellular proteins which interacted with the HCV 5’-UTR. A smaller RNA corresponding to SL e+f of domain III also strongly and selectively inhibited HCV IRES-mediated translation. This RNA molecule interacted with the ribosomal S5 protein and prevented the recruitment of the 40S ribosomal subunit. This study reveals valuable insights into the role of the SL structures of the HCV IRES in mediating ribosome entry. Finally, these results provide a basis for developing anti-HCV therapy using small RNA molecules mimicking the SL structures of the 5’-UTR to specifically block viral RNA translation
COVID-19 and Hyperinflammatory Syndrome
No full text662-669COVID-19, the multifactorial disease caused by the novel coronavirus SARS-CoV-2 is mediated by specific antiviral and inflammatory responses. It is now recognized that in most severe cases of COVID-19 an excessive and uncontrolled inflammatory response exacerbates lung damage caused by viral infection, and contributes to acute respiratory distress syndrome and respiratory failure. This hyperinflammatory syndrome is characterized by multiple cellular and molecular events, including aberrant neutrophil and lymphocyte function, amplification of the inflammatory response by release of damage associated molecular patterns, cytokine storm, lung damage and edema and a pro-fibrotic condition, ultimately leading to respiratory failure. This review discusses these molecular events in correlation with stages of viral infection and disease progression, underscoring the key points that characterize the clinical manifestations of the hyperinflammatory syndrome in COVID-19. Furthermore, it discusses the available or potential therapeutics that target various important mediators of this hyperinflammatory response that are being considered for treatment of COVID-19
La autoantigen is required for the internal ribosome entry site-mediated translation of Coxsackievirus B3 RNA
No full textTranslation initiation in Coxsackievirus B3 (CVB3) occurs via ribosome binding to an internal ribosome entry site (IRES) located in the 5'-untranslated region (UTR) of the viral RNA. This unique mechanism of translation initiation requires various trans-acting factors from the host. We show that human La autoantigen (La) binds to the CVB3 5'-UTR and also demonstrate the dose-dependent effect of exogenously added La protein in stimulating CVB3 IRES-mediated translation. The requirement of La for CVB3 IRES mediated translation has been further demonstrated by inhibition of translation as a result of sequestering La and its restoration by exogenous addition of recombinant La protein. The abundance of La protein in various mouse tissue extracts has been probed using anti-La antibody. Pancreatic tissue, a target organ for CVB3 infection, was found to have a large abundance of La protein which was demonstrated to interact with the CVB3 5'-UTR. Furthermore, exogenous addition of pancreas extract to in vitro translation reactions resulted in a dose dependent stimulation of CVB3 IRES-mediated translation. These observations indicate the role of La in CVB3 IRES-mediated translation, and suggest its possible involvement in the efficient translation of the viral RNA in the pancreas
Ribosome-RNA interaction: a potential target for developing antiviral against hepatitis C virus
No full textHepatitis C virus (HCV), a member of Flaviviridae, encoding a positive-sense single-stranded RNA translates by cap-independent mechanism using the internal ribosome entry site (IRES) present in the 5' UTR of the virus. The IRES has complex stem loop structures and is capable of recruiting the 40S ribosomal subunit in a factor-independent fashion. As the IRES sequence is highly conserved throughout the HCV genotypes and the translation is the first obligatory step of the HCV life cycle, the IRE'S-mediated translation, or more specifically, the ribosome HCV RNA interaction is an attractive target to design effective antivirals. This article will focus on the mechanism of the HCV IRES translation and the various ways in which the interaction of ribosome and IRES has been targeted
Origin and Evolution of Glutamyl-prolyl tRNA Synthetase WHEP Domains Reveal Evolutionary Relationships within Holozoa
No full textTwo internal ribosome entry sites mediate the translation of p53 isoforms
No full textThe p53 tumour suppressor protein has a crucial role in cell-cycle arrest and apoptosis. Previous reports show that the p53 messenger RNA is translated to produce an amino-terminal-deleted isoform from an internal initiation codon, which acts as a dominant-negative inhibitor of full-length p53. Here, we show that two internal ribosome entry sites (IRESs) mediate the translation of both full-length and isoforms. The IRES directing the translation of full-length p53 is in the 5'-untranslated region of the mRNA, whereas the IRES mediating the translation of extends into the protein-coding region. The two IRESs show distinct cell-cycle phase-dependent activity, with the IRES for full-length p53 being active at the G2–M transition and the IRES for showing highest activity at the G1–S transition. These results indicate a novel translational control of p53 gene expression and activity
Origin and evolution of glutamyl-prolyl tRNA synthetase WHEP domains reveal evolutionary relationships within Holozoa.
No full textRepeated domains in proteins that have undergone duplication or loss, and sequence divergence, are especially informative about phylogenetic relationships. We have exploited divergent repeats of the highly structured, 50-amino acid WHEP domains that join the catalytic subunits of bifunctional glutamyl-prolyl tRNA synthetase (EPRS) as a sequence-informed repeat (SIR) to trace the origin and evolution of EPRS in holozoa. EPRS is the only fused tRNA synthetase, with two distinct aminoacylation activities, and a non-canonical translation regulatory function mediated by the WHEP domains in the linker. Investigating the duplications, deletions and divergence of WHEP domains, we traced the bifunctional EPRS to choanozoans and identified the fusion event leading to its origin at the divergence of ichthyosporea and emergence of filozoa nearly a billion years ago. Distribution of WHEP domains from a single species in two or more distinct clades suggested common descent, allowing the identification of linking organisms. The discrete assortment of choanoflagellate WHEP domains with choanozoan domains as well as with those in metazoans supported the phylogenetic position of choanoflagellates as the closest sister group to metazoans. Analysis of clustering and assortment of WHEP domains provided unexpected insights into phylogenetic relationships amongst holozoan taxa. Furthermore, observed gaps in the transition between WHEP domain groupings in distant taxa allowed the prediction of undiscovered or extinct evolutionary intermediates. Analysis based on SIR domains can provide a phylogenetic counterpart to palaentological approaches of discovering "missing links" in the tree of life
Polypyrimidine tract binding protein regulates IRES-mediated translation of p53 isoforms
No full textThe p53 tumor suppressor protein plays a key role in maintaining genomic integrity. Enhanced expression of p53 during genotoxic stress is due to both increased protein stability and translational up regulation. Previous reports have shown that p53 mRNA is translated from an alternative initiation codon to produce N-terminal truncated isoform besides full-length p53. We have demonstrated that two internal ribosome entry sites (IRESs) regulate the translation of p53 and in a distinct cell-cycle phase-dependent manner. Here, we report that polypyrimidine tract-binding protein (PTB) is a p53 IRES interacting trans-acting factor. PTB protein binds specifically to both the p53 IRESs but with differential affinity. siRNA-mediated knockdown of PTB protein results in reduction of activity of both IRESs and also the levels of both the isoforms. It is well known that DNA-damaging agents such as doxorubicin enhance the expression of p53. Our results indicate that during doxorubicin treatment, PTB protein translocates from nucleus to the cytoplasm, probably to facilitate IRES mediated p53 translation. These observations suggest that the relative cytoplasmic abundance of PTB protein, under DNA-damaging conditions, might contribute to regulating the coordinated expression of the p53 isoforms, owing to the differential affinity of PTB binding to the two p53 IRESs
A post-transcriptional pathway represses monocyte VEGF-A expression and angiogenic activity
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