Hepatitis C Virus Reveals a Novel Early Control in Acute Immune Response

Recognition of viral RNA structures by the intracytosolic RNA helicase RIG-I triggers induction of innate immunity. Efficient induction requires RIG-I ubiquitination by the E3 ligase TRIM25, its interaction with the mitochondria-bound MAVS protein, recruitment of TRAF3, IRF3- and NF-κB-kinases and transcription of Interferon (IFN). In addition, IRF3 alone induces some of the Interferon-Stimulated Genes (ISGs), referred to as early ISGs. Infection of hepatocytes with Hepatitis C virus (HCV) results in poor production of IFN despite recognition of the viral RNA by RIG-I but can lead to induction of early ISGs. HCV was shown to inhibit IFN production by cleaving MAVS through its NS3/4A protease and by controlling cellular translation through activation of PKR, an eIF2α-kinase containing dsRNA-binding domains (DRBD). Here, we have identified a third mode of control of IFN induction by HCV. Using HCVcc and the Huh7.25.CD81 cells, we found that HCV controls RIG-I ubiquitination through the di-ubiquitine-like protein ISG15, one of the early ISGs. A transcriptome analysis performed on Huh7.25.CD81 cells silenced or not for PKR and infected with JFH1 revealed that HCV infection leads to induction of 49 PKR-dependent genes, including ISG15 and several early ISGs. Silencing experiments revealed that this novel PKR-dependent pathway involves MAVS, TRAF3 and IRF3 but not RIG-I, and that it does not induce IFN. Use of PKR inhibitors showed that this pathway requires the DRBD but not the kinase activity of PKR. We then demonstrated that PKR interacts with HCV RNA and MAVS prior to RIG-I. In conclusion, HCV recruits PKR early in infection as a sensor to trigger induction of several IRF3-dependent genes. Among those, ISG15 acts to negatively control the RIG-I/MAVS pathway, at the level of RIG-I ubiquitination.These data give novel insights in the machinery involved in the early events of innate immune response

Refractoriness of hepatitis C virus internal ribosome entry site to processing by Dicer in vivo

<p>Abstract</p> <p>Background</p> <p>Hepatitis C virus (HCV) is a positive-strand RNA virus harboring a highly structured internal ribosome entry site (IRES) in the 5' nontranslated region of its genome. Important for initiating translation of viral RNAs into proteins, the HCV IRES is composed of RNA structures reminiscent of microRNA precursors that may be targeted by the host RNA silencing machinery.</p> <p>Results</p> <p>We report that HCV IRES can be recognized and processed into small RNAs by the human ribonuclease Dicer in vitro. Furthermore, we identify domains II, III and VI of HCV IRES as potential substrates for Dicer in vitro. However, maintenance of the functional integrity of the HCV IRES in response to Dicer overexpression suggests that the structure of the HCV IRES abrogates its processing by Dicer in vivo.</p> <p>Conclusion</p> <p>Our results suggest that the HCV IRES may have evolved to adopt a structure or a cellular context that is refractory to Dicer processing, which may contribute to viral escape of the host RNA silencing machinery.</p

Identification of novel RNA secondary structures within the hepatitis C virus genome reveals a cooperative involvement in genome packaging

The specific packaging of the hepatitis C virus (HCV) genome is hypothesised to be driven by Core- RNA interactions. To identify the regions of the viral genome involved in this process, we used SELEX (systematic evolution of ligands by exponential enrichment) to identify RNA aptamers which bind specifically to Core in vitro. Comparison of these aptamers to multiple HCV genomes revealed the presence of a conserved terminal loop motif within short RNA stem-loop structures. We postulated that interactions of these motifs, as well as sub-motifs which were present in HCV genomes at statistically significant levels, with the Core protein may drive virion assembly. We mutated 8 of these predicted motifs within the HCV infectious molecular clone JFH-1, thereby producing a range of mutant viruses predicted to possess altered RNA secondary structures. RNA replication and viral titre were unaltered in viruses possessing only one mutated structure. However, infectivity titres were decreased in viruses possessing a higher number of mutated regions. This work thus identified multiple novel RNA motifs which appear to contribute to genome packaging. We suggest that these structures act as cooperative packaging signals to drive specific RNA encapsidation during HCV assembly

Distribution of larger foraminifera in the reef sediments of Akajima, Okinawa, Japan

This paper examines the bathymetric distribution of larger foraminiferal species on the reef flat and reef slope of Akajima Island, located near Okinawa in the Ryukyu island arc of Japan. It also estimates the total skeletal carbonates contributed by larger foraminifera in the reef. sediments of this island. Three distinct assemblages are recognized with increasing water-depths: (i) Marginopora vertebralis and Baculogypsina sphaerulata are confined to reef flat, occurring at a water depth of 1.5 m (ii) Peneroplis planatus and Neorotalia calcar occur within 30 in bathymetry followed down depth by (iii) Operculina ammonoides, Nummulites venosus, Alveolinella quoyi and Baculogypsinoides spinosus between 30 and 60 in. Cycloclypeus is the deepest dwelling genus, making its first appearance at 60 in. Larger foraminifera contribute about 5.8% of the sediments accumulated on reef flat and reef slope of Akajima, which is significantly higher than the global average. There is considerable variation in relative contributions by miliolids and rotaliids on reef flat and reef slope. On the reef flat, miliolids contribute 64% of the total skeletal carbonates produced by larger foraminifera, whereas on reef slope it contributes only about 5%

An Ancient Chemosensory Mechanism Brings New Life to Coral Reefs

Volume: 191Start Page: 149End Page: 15

Electromagnetic Acoustic Resonance of SiCf/Ti Composites at Elevated Temperatures

We studied electromagnetic acoustic resonance at elevated temperatures up to 1000 K. Using Lorentz-force transduction, we measured the temperature dependence of resonant frequencies and attenuation coefficients in SiC-fiber-reinforced Ti-alloy composites. Evolution of the resonance frequencies is consistent with the changes of elastic constants of the matrix, and attenuation evolution is explained by dislocation damping in the matrix.</p