Search

The influenza A virus polymerase associates with a number of cellular transcription-related factors, including the RNA polymerase II (RNAP II). We previously described that the cellular protein hCLE/ C14orf166 interacts with and stimulates influenza virus polymerase as well as RNAP II activities. Here we show that, despite the considerable cellular shut-off observed in infected cells, which includes RNAP II degradation, hCLE protein levels increase throughout infection in a virus replication-dependent manner. Human and avian influenza viruses of various subtypes increase hCLE levels, but other RNA or DNA viruses do not. hCLE colocalises and interacts with viral ribonucleoproteins (vRNP) in the nucleus, as well as in the cytoplasm late in infection. Furthermore, biochemical analysis of purified virus particles and immunoelectron microscopy of infected cells show hCLE in virions, in close association with viral vRNP. These findings indicate that hCLE, a cellular protein important for viral replication, is one of the very few examples of transcription factors that are incorporated into particles of an RNA-containing virus., This work was supported by the Spanish Ministry of Economy and Competitiveness (MINECO; BFU2011-26175 and BFU2014-57797-R) and the Ciber de Enfermedades Respiratorias (ISCIII).

Background Hepatitis C virus (HCV) proteins interfere with the interferon (IFN)-alpha-induced Jak/signal transducer and activator of transcription (STAT) pathway. Which protein is responsible for this effect and whether this interference results in down-regulation of IFN-induced genes remain controversial. We analyzed the effect of HCV core (HCV-Co) protein on expression of IFN-induced antiviral genes. Methods HepG2 cells were transfected with the plasmid pHCV-Co, and, after treatment with IFN-alpha , levels of MxA, protein kinase R (PKR), and 2'-5' oligoadenylate synthetase (2'-5'OAS) mRNA were determined. Chloramphenycol acethyl transferase (CAT) analysis was performed on cells cotransfected with pHCV-Co and pMx4CAT (containing the MxA gene promoter) and treated with IFN. Electrophoretic mobility shift assays were used, and Western-blot analysis of STAT 1 and 2 was performed. Results Levels of MxA mRNA in pHCV-Co-transfected cells decreased in a dose-dependent manner, by down-regulation of the MxA gene promoter. HCV-Co protein inhibits binding of IFN-stimulated gene factor 3 (ISGF3) to the IFN-stimulated response element (ISRE). Intracellular distribution of STAT 1 and 2 was not modified after treatment with IFN. Expression of HCV-Co protein also results in down-regulation of expression of PKR and 2'-5'OAS genes. Conclusion HCV-Co protein inhibits IFN-alpha-induced transcription of antiviral genes by decreasing binding of ISGF3 to the ISRE.

TT virus (TTV) is an unenveloped, single-stranded, circular-DNA virus which resembles members of the Circoviridae, that is commonly found in humans and which lacks pathological consequences for the infected host. TTV replication has been demonstrated in bone marrow cells but not in peripheral blood mononuclear cells (PBMC), suggesting that hematopoietic cells must be activated to support TTV replication. To test this hypothesis, PBMC from two naturally TTV-infected individuals and from two healthy TTV-DNA negative donors infected in vitro with a TTV-DNA-positive serum were cultured in the presence (stimulated) or absence (unstimulated) of phytohemagglutinin, lipopolysaccharide, and interleukin-2. TTV-DNA was detected in both stimulated and unstimulated PBMC. However, TTV-DNA replicative intermediates and mRNA were detected only in stimulated PBMC. Furthermore, TTV-DNA and mRNA were detected in PBMC from two TTV negative donors reinfected with supernatants from TTV-infected stimulated cells but not when using culture supernatants from unstimulated cells. These results demonstrate that TTV replicates in PBMC only when stimulated.

Cellular messenger RNAs (mRNAs) are associated to proteins in the form of ribonucleoprotein particles. The double-stranded RNA-binding (DRB) proteins play important roles in mRNA synthesis, modification, activity and decay. Staufen is a DRB protein involved in the localized translation of specific mRNAs during Drosophila early development. The human Staufen1 (hStau1) forms RNA granules that contain translation regulation proteins as well as cytoskeleton and motor proteins to allow the movement of the granule on microtubules, but the mechanisms of hStau1-RNA recognition are still unclear. Here we used a combination of affinity chromatography, RNAse-protection, deep-sequencing and bioinformatic analyses to identify mRNAs differentially associated to hStau1 or a mutant protein unable to bind RNA and, in this way, defined a collection of mRNAs specifically associated to wt hStau1. A common sequence signature consisting of two opposite-polarity Alu motifs was present in the hStau1-associated mRNAs and was shown to be sufficient for binding to hStau1 and hStau1-dependent stimulation of protein expression. Our results unravel how hStau1 identifies a wide spectrum of cellular target mRNAs to control their localization, expression and fate.

Double-stranded RNA-binding proteins are key elements in the intracellular localization of mRNA and its local translation. Staufen is a double-stranded RNA binding protein involved in the localised translation of specific mRNAs during Drosophila early development and neuronal cell fate. The human homologue Staufen1 forms RNA-containing complexes that include proteins involved in translation and motor proteins to allow their movement within the cell, but the mechanism underlying translation repression in these complexes is poorly understood. Here we show that human Staufen1-containing complexes contain essential elements of the gene silencing apparatus, like Ago1-3 proteins, and we describe a set of miRNAs specifically associated to complexes containing human Staufen1. Among these, miR-124 stands out as particularly relevant because it appears enriched in human Staufen1 complexes and is over-expressed upon differentiation of human neuroblastoma cells in vitro. In agreement with these findings, we show that expression of human Staufen1 is essential for proper dendritic arborisation during neuroblastoma cell differentiation, yet it is not necessary for maintenance of the differentiated state, and suggest potential human Staufen1 mRNA targets involved in this process.

The influenza A virus genome consists of 8 negative-stranded RNA segments. NS1 is a nonstructural protein that participates in different steps of the virus infectious cycle, including transcription, replication, and morphogenesis, and acts as a virulence factor. Human Staufen1 (hStau1), a protein involved in the transport and regulated translation of cellular mRNAs, was previously identified as a NS1-interacting factor. To investigate the possible role of hStau1 in the influenza virus infection, we characterized the composition of hStau1-containing granules isolated from virus-infected cells. Viral NS1 protein and ribonucleoproteins (RNPs) were identified in these complexes by Western blotting, and viral mRNAs and viral RNAs (vRNAs) were detected by reverse transcription (RT)-PCR. Also, colocalization of hStau1 with NS1, nucleoprotein (NP), and PA in the cytosol of virus-infected cells was shown by immunofluorescence. To analyze the role of hStau1 in the infection, we downregulated its expression by gene silencing. Human HEK293T cells or A549 cells were silenced using either short hairpin RNAs (shRNAs) or small interfering RNAs (siRNAs) targeting four independent sites in the hStau1 mRNA. The yield of influenza virus was reduced 5 to 10 times in the various hStau1-silenced cells compared to that in control silenced cells. The expression levels of viral proteins and their nucleocytoplasmic localization were not affected upon hStau1 silencing, but virus particle production, as determined by purification of virions from supernatants, was reduced. These results indicate a role for hStau1 in late events of the influenza virus infection, possibly during virus morphogenesis.

Background There are patients in whom the etiology of long-standing abnormal results of liver-function tests is unknown (ALF-EU) after exclusion of all known causes of liver diseases. We analyzed the presence of hepatitis C virus (HCV) RNA in liver-biopsy specimens from 100 patients who were negative for anti-HCV antibodies and for serum HCV RNA and who had ALF-EU. Methods HCV RNA status was tested by reverse-transcription polymerase chain reaction (RT-PCR) and by in situ hybridization, in liver and peripheral-blood mononuclear cells (PBMCs). Results HCV RNA was detected in liver-biopsy specimens from 57 of 100 patients negative for anti-HCV antibodies and for serum HCV RNA (i.e., who had occult HCV infection). HCV RNA of negative polarity was found in the liver of 48 (84.2%) of these 57 patients with occult HCV infection. Nucleotide-sequence analysis confirmed the specificity of detection of HCV RNA and that patients were infected with the HCV 1b genotype. Of these 57 patients with intrahepatic HCV RNA, 40 (70%) had viral RNA in their PBMCs. With regard to liver histology, patients with occult HCV infection were more likely to have necroinflammatory activity (P=.017) and fibrosis (P=.022) than were patients without intrahepatic HCV RNA. Conclusions Patients with ALF-EU may have intrahepatic HCV RNA in the absence of anti-HCV antibodies and of serum HCV RNA.

It has not been completely elucidated whether the liver injury induced by the hepatitis C virus (HCV) is due to direct cytopathic damage or to an immune-mediated response against HCV-infected hepatocytes. In this work, we have determined the percentage of HCV-infected hepatocytes, the histological activity index, and the viremia levels in chronically HCV-infected patients with different grades of liver injury to investigate any possible correlation between them. For that purpose, liver biopsies from 27 patients with HCV chronic hepatitis were analyzed by in situ hybridization. This technique revealed that the percentage of infected hepatocytes ranged from 0.04% to 83.6%. Regarding the viremia levels, HCV RNA concentration ranged from 1.8 × 10 3 to 1.4 × 10 6 genome copies/ml. A significant correlation ( r = 0.54; P = 0.003) between the percentage of infected hepatocytes and the viremia levels was found. In contrast, no correlation was observed between the percentage of HCV-infected hepatocytes or the viremia levels and the histological activity index. In conclusion, we have shown that the HCV viremia reflects the extent of the infection in the liver and that the liver injury in chronic HCV infection is not directly related to either the number of infected hepatocytes or the serum HCV RNA concentration.