Efficient formation of influenza virus-like particles: dependence on the expression levels of viral proteins. (49/2752)

It has previously been demonstrated in this laboratory that an influenza virus-like chloramphenicol acetyltransferase (CAT) RNA could be expressed in COS-1 cells that synthesized all ten influenza A virus-encoded proteins from recombinant plasmids. It was also shown that supernatant fluids harvested from these cultures contained virus-like particles (VLPs) that could deliver an enclosed CAT RNA to MDCK cells. Here, it is shown that the levels of expression of the reporter gene in the COS-1 and/or MDCK cells can be altered drastically by modifying the concentrations of the recombinant plasmids transfected in the COS-1 cells. Thus, it was observed that overexpression of NS2 reduced CAT expression in COS-1 cells, whereas overexpression of M2 and NS1 proteins dramatically decreased transmission of the CAT RNA to the MDCK cultures. These results are discussed with reference to the roles of these proteins during virus replication. From these experiments, a ratio of transfected plasmids was found that increased the efficiency of the previously described system by 50-100-fold. Under these optimized conditions, it was demonstrated that VLPs can be formed in the absence of neuraminidase expression and that these VLPs remained aggregated to each other and to cell membranes. Moreover, it is shown that CAT RNA transmission was dependent on specific interactions of the ribonucleoprotein complex with other viral structural polypeptides. These data demonstrate the usefulness of this encapsidation-packaging system for the study of different aspects of the influenza virus life-cycle.  (+info)

A transgene insertion creating a heritable chromosome deletion mouse model of Prader-Willi and angelman syndromes. (50/2752)

Prader-Willi syndrome (PWS) and Angelman syndrome (AS) result from the loss of function of imprinted genes in human chromosome 15q11-q13. The central part of mouse chromosome 7 is homologous to human 15q11-q13, with conservation of both gene order and imprinted features. We report here the characterization of a transgene insertion (Epstein-Barr virus Latent Membrane Protein 2A, LMP2A) into mouse chromosome 7C, which has resulted in mouse models for PWS and AS dependent on the sex of the transmitting parent. Epigenotype (allelic expression and DNA methylation) and fluorescence in situ hybridization analyses indicate that the transgene-induced mutation has generated a complete deletion of the PWS/AS-homologous region but has not deleted flanking loci. Because the intact chromosome 7, opposite the deleted homolog, maintains the correct imprint in somatic cells of PWS and AS mice and establishes the correct imprint in male and female germ cells of AS mice, homologous association and replication asynchrony are not part of the imprinting mechanism. This heritable-deletion mouse model will be particularly useful for the identification of the etiological genes and mechanisms, phenotypic basis, and investigation of therapeutic approaches for PWS.  (+info)

Mapping of the coronavirus membrane protein domains involved in interaction with the spike protein. (51/2752)

The coronavirus membrane (M) protein is the key player in virion assembly. One of its functions is to mediate the incorporation of the spikes into the viral envelope. Heterotypic interactions between M and the spike (S) protein can be demonstrated by coimmunoprecipitation and by immunofluorescence colocalization, after coexpression of their genes in eukaryotic cells. Using these assays in a mutagenetic approach, we have mapped the domains in the M protein that are involved in complex formation between M and S. It appeared that the 25-residue luminally exposed amino-terminal domain of the M protein is not important for M-S interaction. A 15-residue deletion, the insertion of a His tag, and replacement of the ectodomain by that of another coronavirus M protein did not affect the ability of the M protein to associate with the S protein. However, complex formation was sensitive to changes in the transmembrane domains of this triple-spanning protein. Deletion of either the first two or the last two transmembrane domains, known not to affect the topology of the protein, led to a considerable decrease in complex formation, but association was not completely abrogated. Various effects of changes in the part of the M protein that is located at the cytoplasmic face of the membrane were observed. Deletions of the extreme carboxy-terminal tail appeared not to interfere with M-S complex formation. However, deletions in the amphipathic domain severely affected M-S interaction. Interestingly, changes in the amino-terminal and extreme carboxy-terminal domains of M, which did not disrupt the interaction with S, are known to be fatal to the ability of the protein to engage in virus particle formation (C. A. M. de Haan, L. Kuo, P. S. Masters, H. Vennema, and P. J. M. Rottier, J. Virol. 72:6838-6850, 1998). Apparently, the structural requirements of the M protein for virus particle assembly differ from the requirements for the formation of M-S complexes.  (+info)

Association of influenza virus matrix protein with ribonucleoproteins. (52/2752)

To characterize the sites and nature of binding of influenza A virus matrix protein (M1) to ribonucleoprotein (RNP), M1 of A/WSN/33 was altered by deletion or site-directed mutagenesis, expressed in vitro, and allowed to attach to RNP under a variety of conditions. Approximately 70% of the wild-type (Wt) M1 bound to RNP at pH 7.0, but less than 5% of M1 associated with RNP at pH 5.0. Increasing the concentration of NaCl reduced M1 binding, but even at a high salt concentration (0.6 M NaCl), approximately 20% of the input M1 was capable of binding to RNP. Mutations altering potential M1 RNA-binding regions (basic amino acids 101RKLKR105 and the zinc finger motif at amino acids 148 to 162) had varied effect: mutations of amino acids 101 to 105 reduced RNP binding compared to the Wt M1, but mutations of zinc finger motif did not. Treatment of RNP with RNase reduced M1 binding by approximately half, but even M1 mutants lacking RNA-binding regions had residual binding to RNase-treated RNP provided that the N-terminal 76 amino acids of M1 (containing two hydrophobic domains) were intact. Addition of detergent to the reaction mixture further reduced binding related to the N-terminal 76 amino acids and showed the greatest effect for mutations affecting the RNA-binding regions of basic amino acids. The data suggest that M1 interacts with both the RNA and protein components of RNP in assembly and disassembly of influenza A viruses.  (+info)

In vivo replication, latency, and immunogenicity of murine cytomegalovirus mutants with deletions in the M83 and M84 genes, the putative homologs of human cytomegalovirus pp65 (UL83). (53/2752)

We previously identified two open reading frames (ORFs) of murine cytomegalovirus (MCMV), M83 and M84, which are putative homologs of the human cytomegalovirus (HCMV) UL83 tegument phosphoprotein pp65 (L. D. Cranmer, C. L. Clark, C. S. Morello, H. E. Farrell, W. D. Rawlinson, and D. H. Spector, J. Virol. 70:7929-7939, 1996). In this report, we show that unlike the M83 gene product, the M84 protein is expressed at early times in the infection and cannot be detected in the virion. To elucidate the functional differences between the two pp65 homologs in acute and latent MCMV infections, we constructed two MCMV K181 mutants in which either the M83 or M84 ORF was deleted. The resultant viruses, designated DeltaM83 and DeltaM84, respectively, were found to replicate in NIH 3T3 cells with kinetics identical to those of the parent strain. Western blot analysis demonstrated that except for the absence of M83 or M84 protein expression in the respective mutants, no global perturbations of protein expression were detected. When DeltaM83 and DeltaM84 were inoculated intraperitoneally (i.p.) into BALB/c mice, both viruses showed similar attenuated growth in the spleen, liver, and kidney. However, only DeltaM83 was severely growth restricted in the salivary glands, a phenotype that was abolished upon restoration of the M83 ORF. DeltaM83's growth was similarly restricted in the salivary glands of the resistant C3H/HeN or highly sensitive 129/J strain, as well as in the lungs of all three strains following intranasal inoculation. Using a nested-PCR assay, we found that both DeltaM83 and DeltaM84 established latency in BALB/c mice, with slightly decreased levels of DeltaM83 and DeltaM84 genomic DNAs, relative to K181, observed in the salivary glands and lungs. Immunization of BALB/c mice with 10(5) PFU of K181, DeltaM83, or DeltaM84 i.p. provided similar levels of protection against lethal challenge. Although immunization with 200 PFU of DeltaM83 also provided complete protection, this dose allowed both the immunizing and challenge viruses to establish latency in the spleen. Our results show that the two MCMV pp65 homologs differ in their expression kinetics, virion association, and influence on viral tropism and/or dissemination.  (+info)

Signature amino acid changes in latent membrane protein 1 distinguish Epstein-Barr virus strains. (54/2752)

Sequence variations in the Epstein-Barr virus (EBV) latent membrane protein 1 gene have been described in numerous EBV-associated tumors with some of these variations, most notably a 30-base pair deletion in the cytoplasmic carboxyl-terminal domain, suggested as associated with an increase in tumorigenicity. In this study, EBV DNA sequence was determined from 92 tissue specimens or cell lines, including nasopharyngeal carcinoma, oral hairy leukoplakia, post-transplant lymphoma, post-transplant without pathology, mononucleosis, Burkitt's lymphoma, parotid tumor, and normal from distinct geographical regions. The amino- and carboxyl-terminal sequences and, in some cases, the full-length sequences of latent membrane protein 1 were determined. Characteristic sequence patterns distinguished strains, with the carboxyl-terminal sequence being the most informative in distinguishing among the strains. Phylogenetic relationships between strains were determined, as were signature amino acid changes that discriminate between them. A correlation between strain and disease or strain and geographic location was not detected. The sequence variation and signature sequences identified at least seven distinct strains, as well as hybrid strains that apparently result from recombination.  (+info)

Activation of the small GTPase Cdc42 by the inflammatory cytokines TNF(alpha) and IL-1, and by the Epstein-Barr virus transforming protein LMP1. (55/2752)

Cdc42, a Rho-family GTPase, has been implicated in several signal transduction pathways, including organization of the actin cytoskeleton, activation of the c-Jun N-terminal MAP kinase (JNK) and stimulation of the nuclear transcription factor kappa B (NF(kappa)B). We report here that exposure of fibroblasts to the inflammatory cytokines tumor necrosis factor (alpha) (TNF(alpha)) and interleukin-1 (IL-1) triggers the activation of Cdc42 leading first to filopodia formation and subsequently to Rac and Rho activation. Inhibition of Cdc42 completely suppresses cytokine-induced actin polymerization, but not activation of JNK or NF(kappa)B. The latent membrane protein 1 of Epstein-Barr virus, LMP1, is thought to mimic constitutively activated TNF family receptors. When expressed in fibroblasts, LMP1 stimulates Cdc42-dependent filopodia formation as well as JNK and NF(kappa)B activation. Using LMP1 mutants, we show that activation of Cdc42 and JNK/NF(kappa)B occur through distinct pathways and that Cdc42 activation is independent of LMP1's interaction with TRADD and TRAF proteins.  (+info)

Epstein-barr virus-infected resting memory B cells, not proliferating lymphoblasts, accumulate in the peripheral blood of immunosuppressed patients. (56/2752)

When Epstein-Barr virus (EBV) infects B cells in vitro, the result is a proliferating lymphoblast that expresses at least nine latent proteins. It is generally believed that these cells are rigorously controlled in vivo by cytotoxic T cells. Consistent with this, the latently infected cells in the peripheral blood of healthy carriers are not lymphoblasts. Rather, they are resting memory B cells that are probably not subject to direct immunosurveillance by cytotoxic T lymphocytes (CTLs). When patients become immunosuppressed, the viral load increases in the peripheral blood. The expansion of proliferating lymphoblasts due to the suppressed CTL response is believed to account for this increase and is considered to be a major risk factor for posttransplant lymphoproliferative disease (PTLD) and AIDS-associated B cell lymphoma. Here we show that there is an increase in the numbers of latently infected cells in the peripheral blood of immunosuppressed patients. However, the cells are not proliferating lymphoblasts. They are all latently infected, resting, memory B cells-the same population of infected cells found in the blood of healthy carriers. These results are discussed in the context of a model for EBV persistence that explains why PTLD is usually limited to the lymph nodes.  (+info)