Cocaine causes increased type I interferon secretion by both L929 cells and murine macrophages.
(33/771)
Cocaine has been demonstrated to have a number of different effects on immune cell functions. We have reported alterations of cellular functions by macrophages (Mphi) exposed to cocaine in vitro, including the inhibition of mouse hepatitis virus replication. Here, we present evidence that cocaine stimulates the secretion of an antiviral product that is neutralized by anti-interferon (anti-IFN). A dose-dependent increase in the secretion of IFN by both Mphi and L929 cells incubated with cocaine, with a concomitant decrease in virus replication, is also reported. The increase in IFN secretion was most pronounced when cells were cultured in the presence of the IFN inducer poly(I.C). The effect of cocaine on IFN production was found to be primarily at the transcript level in both Mphi and L929 cells. These findings further support our previous research demonstrating an antiviral activity of cocaine in vitro. The relevance of this activity to viral infections in general remains to be determined. (+info)
Four proteins processed from the replicase gene polyprotein of mouse hepatitis virus colocalize in the cell periphery and adjacent to sites of virion assembly.
(34/771)
The replicase gene (gene 1) of the coronavirus mouse hepatitis virus (MHV) encodes two co-amino-terminal polyproteins presumed to incorporate all the virus-encoded proteins necessary for viral RNA synthesis. The polyproteins are cotranslationally processed by viral proteinases into at least 15 mature proteins, including four predicted cleavage products of less than 25 kDa that together would comprise the final 59 kDa of protein translated from open reading frame 1a. Monospecific antibodies directed against the four distinct domains detected proteins of 10, 12, and 15 kDa (p1a-10, p1a-12, and p1a-15) in MHV-A59-infected DBT cells, in addition to a previously identified 22-kDa protein (p1a-22). When infected cells were probed by immunofluorescence laser confocal microscopy, p1a-10, -22, -12, and -15 were detected in discrete foci that were prominent in the perinuclear region but were widely distributed throughout the cytoplasm as well. Dual-labeling experiments demonstrated colocalization of the majority of p1a-22 in replication complexes with the helicase, nucleocapsid, and 3C-like proteinase, as well as with p1a-10, -12, and -15. p1a-22 was also detected in separate foci adjacent to the replication complexes. The majority of complexes containing the gene 1 proteins were distinct from sites of accumulation of the M assembly protein. However, in perinuclear regions the gene 1 proteins and nucleocapsid were intercalated with sites of M protein localization. These results demonstrate that the complexes known to be involved in RNA synthesis contain multiple gene 1 proteins and are closely associated with structural proteins at presumed sites of virion assembly. (+info)
Coronavirus-induced membrane fusion requires the cysteine-rich domain in the spike protein.
(35/771)
The spike glycoprotein of mouse hepatitis virus strain A59 mediates the early events leading to infection of cells, including fusion of the viral and cellular membranes. The spike is a type I membrane glycoprotein that possesses a conserved transmembrane anchor and an unusual cysteine-rich (cys) domain that bridges the putative junction of the anchor and the cytoplasmic tail. In this study, we examined the role of these carboxyl-terminal domains in spike-mediated membrane fusion. We show that the cytoplasmic tail is not required for fusion but has the capacity to enhance membrane fusion activity. Chimeric spike protein mutants containing substitutions of the entire transmembrane anchor and cys domain with the herpes simplex virus type 1 glycoprotein D (gD-1) anchor demonstrated that fusion activity requires the presence of the A59 membrane-spanning domain and the portion of the cys domain that lies upstream of the cytoplasmic tail. The cys domain is a required element since its deletion from the wild-type spike protein abrogates fusion activity. However, addition of the cys domain to fusion-defective chimeric proteins was unable to restore fusion activity. Thus, the cys domain is necessary but is not sufficient to complement the gD-1 anchor and allow for membrane fusion. Site-specific mutations of conserved cysteine residues in the cys domain markedly reduce membrane fusion, which further supports the conclusion that this region is crucial for spike function. The results indicate that the carboxyl-terminus of the spike transmembrane anchor contains at least two distinct domains, both of which are necessary for full membrane fusion. (+info)
Contributions of CD8+ T cells and viral spread to demyelinating disease.
(36/771)
Acute and chronic demyelination are hallmarks of CNS infection by the neurotropic JHM strain of mouse hepatitis virus. Although infectious virus is cleared by CD8+ T cells, both viral RNA and activated CD8+ T cells remain in the CNS during persistence potentially contributing to pathology. To dissociate immune from virus-mediated determinants initiating and maintaining demyelinating disease, mice were infected with two attenuated viral variants differing in a hypervariable region of the spike protein. Despite similar viral replication and tropism, one infection was marked by extensive demyelination and paralysis, whereas the other resulted in no clinical symptoms and minimal neuropathology. Mononuclear cells from either infected brain exhibited virus specific ex vivo cytolytic activity, which was rapidly lost during viral clearance. As revealed by class I tetramer technology the paralytic variant was superior in inducing specific CD8+ T cells during the acute disease. However, after infectious virus was cleared, twice as many virus-specific IFN-gamma-secreting CD8+ T cells were recovered from the brains of asymptomatic mice compared with mice undergoing demyelination, suggesting that IFN-gamma ameliorates rather than perpetuates JHM strain of mouse hepatitis virus-induced demyelination. The present data thus indicate that in immunocompetent mice, effector CD8+ T cells control infection without mediating either clinical disease or demyelination. In contrast, demyelination correlated with early and sustained infection of the spinal cord. Rapid viral spread, attributed to determinants within the spike protein and possibly perpetuated by suboptimal CD8+ T cell effector function, thus ultimately leads to the process of immune-mediated demyelination. (+info)
Subgenomic negative-strand RNA function during mouse hepatitis virus infection.
(37/771)
Mouse hepatitis virus (MHV)-infected cells contain full-length and subgenomic-length positive- and negative-strand RNAs. The origin and function of the subgenomic negative-strand RNAs is controversial. In this report we demonstrate that the synthesis and molar ratios of subgenomic negative strands are similar in alternative host cells, suggesting that these RNAs function as important mediators of positive-strand synthesis. Using kinetic labeling experiments, we show that the full-length and subgenomic-length replicative form RNAs rapidly accumulate and then saturate with label, suggesting that the subgenomic-length negative strands are the principal mediators of positive-strand synthesis. Using cycloheximide, which preferentially inhibits negative-strand and to a lesser extent positive-strand synthesis, we demonstrate that cycloheximide treatment equally inhibits full-length and subgenomic-length negative-strand synthesis. Importantly, following treatment, previously transcribed negative strands remain in transcriptionally active complexes even in the absence of new negative-strand synthesis. These findings indicate that the subgenomic-length negative strands are the principal templates of positive-strand synthesis during MHV infection. (+info)
Genetic manipulation of equine arteritis virus using full-length cDNA clones: separation of overlapping genes and expression of a foreign epitope.
(38/771)
Equine arteritis virus (EAV) is an enveloped, positive-stranded RNA virus belonging to the family Arteriviridae of the order Nidovirales. The unsegmented, infectious genome of EAV is 12,704 nt in length [exclusive of the poly(A) tail] and contains eight overlapping genes that are expressed from a 3'-coterminal nested set of seven leader-containing mRNAs. To investigate the importance of the overlapping gene arrangement in the viral life-cycle and to facilitate the genetic manipulation of the viral genome, a series of mutant full-length cDNA clones was constructed in which either EAV open reading frames (ORFs) 4 and 5 or ORFs 5 and 6 or ORFs 4, 5, and 6 were separated by newly introduced AflII restriction endonuclease cleavage sites. RNA transcribed from each of these plasmids was infectious, demonstrating that the overlapping gene organization is not essential for EAV viability. Moreover, the recombinant viruses replicated with almost the same efficiency, i.e., reached nearly the same infectious titers as the wildtype virus, and stably maintained the mutations that were introduced. The AflII site engineered between ORFs 5 and 6 was subsequently used to generate a virus in which the ectodomain of the ORF 6-encoded M protein was extended with nine amino acids derived from the extreme N-terminus of the homologous protein of mouse hepatitis virus (MHV; family Coronaviridae, order Nidovirales). This nonapeptide contains a functional O-glycosylation signal as well as an epitope recognized by an MHV-specific monoclonal antibody, both of which were expressed by the recombinant virus. Although the hybrid virus had a clear growth disadvantage in comparison to the parental virus, three serial passages did not result in the loss of the foreign genetic material. (+info)
Liver-specific alpha 2 interferon gene expression results in protection from induced hepatitis.
(39/771)
The current therapy for hepatitis B and C is based on systemic administration of recombinant human alpha interferon (r-hIFN-alpha). However, systemic delivery of r-hIFN-alpha is associated with severe side effects, but more importantly, it is effective in only a small percentage of patients. In an effort to maximize IFN-alpha antiviral efficacy, we have explored the therapeutic potential of murine IFN-alpha2 (mIFNalpha2) selectively expressed in the liver. To this end, we have developed a helper-dependent adenovirus vector (HD) containing the mIFN-alpha2 gene under the control of the liver-specific transthyretin promoter (HD-IFN). Comparison with a first-generation adenovirus carrying the same mIFN-alpha2 expression cassette indicates that at certain HD-IFN doses, induction of antiviral genes can be achieved in the absence of detectable circulating mIFN-alpha2. Challenge of injected mice with mouse hepatitis virus type 3 showed that HD-IFN provides high liver protection. Moreover, liver protection was also observed in acute nonviral liver inflammation hepatitis induced by concanavalin A at 1 month postinfection. These results hold promise for the development of a gene therapy treatment for chronic viral hepatitis based on liver-restricted expression of IFN-alpha2. (+info)
Assembly of the coronavirus envelope: homotypic interactions between the M proteins.
(40/771)
The viral membrane proteins M and E are the minimal requirements for the budding of coronavirus particles. Since the E protein occurs in particles only in trace amounts, the lateral interactions between the M proteins apparently generate the major driving force for envelope formation. By using coimmunoprecipitation and envelope incorporation assays, we provide extensive evidence for the existence of such M-M interactions. In addition, we determined which domains of the M protein are involved in this homotypic association, using a mutagenetic approach. Mutant M proteins which were not able to assemble into viruslike particles (VLPs) by themselves (C. A. M. de Haan, L. Kuo, P. S. Masters, H. Vennema, and P. J. M. Rottier, J. Virol. 72:6838-6850, 1998) were tested for the ability to associate with other M proteins and to be rescued into VLPs formed by assembly-competent M proteins. We found that M proteins lacking parts of the transmembrane cluster, of the amphipathic domain, or of the hydrophilic carboxy-terminal tail, or M proteins that had their luminal domain replaced by heterologous ectodomains, were still able to associate with assembly-competent M proteins, resulting in their coincorporation into VLPs. Only a mutant M protein in which all three transmembrane domains had been replaced lost this ability. The results indicate that M protein molecules interact with each other through multiple contact sites, particularly at the transmembrane level. Finally, we tested the stringency with which membrane proteins are selected for incorporation into the coronavirus envelope by probing the coassembly of some foreign proteins. The observed efficient exclusion from budding of the vesicular stomatitis virus G protein and the equine arteritis virus M protein indicates that envelope assembly is indeed a highly selective sorting process. The low but detectable incorporation of CD8 molecules, however, demonstrated that this process is not perfect. (+info)