SCIMP is a spatiotemporal transmembrane scaffold for Erk1/2 to direct pro-inflammatory signaling in TLR-activated macrophages

Immune cells are armed with Toll-like receptors (TLRs) for sensing and responding to pathogens and other danger cues. The role of extracellular-signal-regulated kinases 1/2 (Erk1/2) in TLR signaling remains enigmatic, with both pro- and anti-inflammatory functions described. We reveal here that the immune-specific transmembrane adaptor SCIMP is a direct scaffold for Erk1/2 in TLR pathways, with high-resolution, live-cell imaging revealing that SCIMP guides the spatial and temporal recruitment of Erk2 to membrane ruffles and macropinosomes for pro-inflammatory TLR4 signaling. SCIMP-deficient mice display defects in Erk1/2 recruitment to TLR4, c-Fos activation, and pro-inflammatory cytokine production, with these effects being phenocopied by Erk1/2 signaling inhibition. Our findings thus delineate a selective role for SCIMP as a key scaffold for the membrane recruitment of Erk1/2 kinase to initiate TLR-mediated pro-inflammatory responses in macrophages

New genes from old: redeployment of dUTPase by herpesviruses

Published work (D. J. McGeoch, Nucleic Acids Res. 18:4105-4110, 1990; J. E. McGeehan, N. W. Depledge, and D. J. McGeoch, Curr. Protein Peptide Sci. 2:325-333, 2001) has indicated that evolution of dUTPase in the class of herpesviruses that infect mammals and birds involved capture of a host gene followed by a duplication event that resulted in a coding region comprising two fused dUTPase domains. Some of the conserved residues required for enzyme activity were then lost, resulting in a dUTPase containing a single active site with different elements contributed by each half of the protein. Further conserved residues were lost in one subfamily (the Betaherpesvirinae), yielding a protein that is related to herpesvirus dUTPases but has a different and as yet unrecognized function. Evidence from sequence similarities and structural predictions now indicates that several additional genes were derived from the herpesvirus dUTPase gene, probably by duplication. These are UL31, UL82, UL83, and UL84 in human cytomegalovirus (and counterparts in other members of the Betaherpesvirinae) and ORF10 and ORF11 in human herpesvirus 8 (and counterparts in other members of the Gammaherpesvirinae). The findings clarify the evolutionary history of these genes and provide novel insights for structural and functional studies

Identification of a Varicella-Zoster virus origin of DNA replication and its activation by Herpes Simplex virus type 1 gene products

We have identified and characterized an origin of DNA replication in the genome of the human herpesvirus, varicella-zoster virus (VZV). This origin of replication (VZV ORIS) is located within the major inverted repeats in a position equivalent to that occupied by one of the herpes simplex virus type 1 (HSV-1) replication origins. Products encoded by both VZV and HSV-1 activate cloned copies of VZV ORIS, generating high molecular weight molecules consisting of tandem duplications of the input plasmid. The VZV ORIS region contains a tract of alternating A and T residues located at the centre of symmetry of an almost perfect palindrome of 45 bp, and the use of plasmid deletion mutants has demonstrated that this tract is an important functional element of the origin. Two sequences common to the VZV ORIS region and the regions specifying the two HSV-1 origins (ORIS, located within the TRS/IRS regions, and ORIL, located with in the UL region) were identified and these may represent important recognition sites. One is an 11 bp sequence (CGTTCGCACTT), and the other is represented by the tract of alternating A and T residues. VZV does not appear to contain an origin of replication in a position equivalent to that of HSV-1 ORIL

Blocks to herpes simplex virus type 1 replication in a cell line, tsBN2, encoding a temperature-sensitive RCC1 protein

Circularization of the herpes simplex virus type 1 (HSV-1) genome is thought to be an important early event during the lytic cycle. Previous studies from another laboratory using a cell line, tsBN2, that carries a temperature-sensitive mutation in the gene encoding the regulator of chromatin condensation 1 (RCC1) indicated that functional RCC1 was required for HSV-1 genome circularization and subsequent viral DNA synthesis. Here, HSV-1 infection of tsBN2 cells has been re-examined by utilizing both wild-type HSV-1 and a derivative that enables a direct demonstration of circularization. At the non-permissive temperature, when RCC1 was absent, both circularization and viral DNA synthesis were reduced, but not abolished. However, no infectious progeny virus was detected under these conditions. An impairment in the cleavage of concatemeric DNA and the failure to express at least one capsid protein indicated that HSV-1 replication is also blocked at a late stage in the absence of RCC1. This conclusion was supported by a temperature-upshift experiment, which demonstrated a role for RCC1 at times later than 6 h post-infection. Finally, a virus constitutively expressing β-galactosidase produced the protein in a reduced number of cells when RCC1 was inactivated, suggesting that genome delivery to the nucleus or the initial stages of gene expression may also be affected

The herpes simplex virus type 1 UL37 gene product is a component of virus particles

The herpes simplex virus type 1 UL37 gene encodes a protein with an Mr of 120K that is produced at late times after infection. To study the properties of this protein we have linked a 10 amino acid epitope derived from a human cytomegalovirus protein to the UL37 polypeptide coding sequences by inserting an oligonucleotide at a SpeI site that is unique in the virus genome and lies close to the 3' end of the open reading frame. From studies on the resultant virus recombinant using a monoclonal antibody that recognizes the inserted epitope we find that, contrary to a previous report, the UL37 protein is a structural component of both virions and L particles and is present in the tegument of virus particles. Indirect immunofluorescence analysis revealed that the protein is distributed throughout infected cells but is more abundant in the cytoplasm than the nucleus

Fundamental and accessory systems in herpesviruses

Evolutionary studies have a large theoretical component and will not directly provide therapies for herpesvirus infections. However, they do provide a conceptual framework within which we can evaluate the origins of the various systems that contribute to viral lifestyle. An evolutionary context allows ancient systems that are fundamental to the replication of all herpesviruses to be distinguished from those that have developed relatively recently in order to tailor viruses to particular biological niches. Both categories are in principle accessible to intervention, either to prevent basic replicative capabilities or to reduce the advantages that the virus has in its interactions with the host. Phylogenetic data provide estimates of evolutionary rate for herpesviruses that are only between one and two orders of magnitude greater than those of their hosts. However, it is becoming apparent that certain genes have evolved much faster under selection pressures and by mechanisms that are not well understood. Nonetheless, the mutation rates of even the most highly conserved genes are sufficient to permit herpesviruses to escape from antiviral therapy. Greater understanding of the origins and functions of herpesvirus genes may lead to new insights into the determinants of pathogenesis and hence to new diagnostic and therapeutic targets

The N-terminal 22 amino acids encoded by the gene specifying the major secreted protein of vaccinia virus, strain Lister, can function as a signal sequence to direct the export of a foreign protein

Cells infected with vaccinia virus strain Lister secrete a polypeptide of approximate molecular weight 35,000 (35K) into the medium. Previous studies identified a cleavable, hydrophobic region of 17 amino acids in the 35K protein which could potentially function as a signal peptide to target the protein to the secretory pathway. Here we report the use of the expression-secretion signals derived from the 35K gene to direct export and secretion of a foreign protein. Vaccinia virus recombinants carrying the bacterial chloramphenicol acetyl transferase gene (cat) immediately downstream from the promoter and the N-terminal coding sequences of the 35K gene were constructed. Our studies show that the N-terminal 22 or 42 amino acids of the 35K protein direct efficient secretion of the CAT protein. However, due to a cryptic glycosylation site within CAT, glycosylated protein was secreted, which reduced enzymatic activity. Activity was restored in the presence of tunicamycin. Removal of the glycosylation site by site-directed mutagenesis abolished glycosylation with no effect on secretion, although CAT activity was again reduced, possibly due to an effect on the active site. The results presented here demonstrate the feasibility of using the promoter and the signal sequence of the 35K gene to generate recombinant viruses for overexpression and secretion of foreign proteins

DNA sequence of the gene encoding a major secreted protein of vaccinia virus, strain Lister

Infection of tissue culture cells with vaccinia virus results in the specific secretion of several polypeptides into the medium. Previous studies identified a protein of approximate Mr 35000 (35K) which was secreted in large amounts at both early and late times after infection with the Evans strain. We now show that a related protein is secreted by the Lister strain but not by WR, Wyeth nor Tian Tan. The gene encoding the Lister strain 35K protein was mapped within the inverted terminal repeats of the genome. The DNA sequence of this region showed that the ends of this gene are very similar to previously published sequences flanking a gene of WR which encodes a protein of approximate Mr 7500 (7.5K). Our results suggest that the 7.5K polypeptide of WR may have arisen as a result of a deletion event and is a truncated form of the 35K Lister protein. Site-directed mutagenesis demonstrated that the 35K secreted protein encoded by Lister is not essential for growth in tissue culture

Interaction of the herpes simplex virus type 1 packaging protein UL15 with full-length and deleted forms of the UL28 protein

The UL15 and UL28 proteins of herpes simplex virus type 1 are both required for the packaging of replicated viral DNA into the viral capsid. We have expressed UL28 and a functional epitope-tagged form of UL15 in mammalian and insect cells. Immunoprecipitation experiments confirmed that the two proteins can interact. In agreement with previous results, UL15, when expressed alone, entered the nucleus but UL28 remained cytoplasmic. When co-expressed the two proteins co-localized in the nucleus. Six UL28 deletion mutants were constructed and similarly analysed. The results obtained by immunoprecipitation and immunofluorescence were consistent and demonstrate that at least two separate regions of the UL28 polypeptide chain have the ability to interact with UL15. Surprisingly, three of the mutants prevented the UL15 protein from localizing to the cell nucleus, and these were not functional in a transient DNA packaging assay. Of the three UL28 mutant proteins that entered the nucleus with UL15, one containing an internal deletion of 13 amino acids was able to complement a UL28 null mutant in both DNA packaging and virus yield assays, demonstrating that this region of the protein is not essential for function. In addition to interacting with the UL28 protein we also demonstrated that UL15 molecules can interact with each other, and that sequences within the second exon contribute to this interaction

Nuclear sites of herpes simplex virus type 1 DNA replication and transcription colocalize at early times postinfection and are largely distinct from RNA processing factors

We have visualized the intracellular localization of herpes simplex virus (HSV) type 1 replication and transcription sites in infected HeLa cells by using direct labelling methods. The number of viral transcription foci increases in a limited way; however, the number of replication sites increases in a near-exponential manner throughout infection, and both replication and transcription sites are found buried throughout the nuclear interior. Simultaneous visualization of viral transcription and replication foci shows that the two processes colocalize at early times, but at later times postinfection, there are additional sites committed solely to replication. This contrasts with the situation in adenovirus-infected cells in which, throughout replication, sites of transcription are adjacent to but do not colocalize with sites of viral DNA replication. The data for an increase in HSV transcription sites suggest an initial phase of replication of input genomes which are then transcribed. Sites of HSV replication colocalize with viral DNA replication and packaging proteins but are largely distinct from the punctate distribution of small nuclear ribonucleoprotein particles. Very high multiplicities of infection have shown an upper limit of some 18 viral transcription foci per nucleus, suggesting cellular constraints on transcription site formation. Use of virus replication mutants confirms that the labelled foci are sites of viral RNA and DNA synthesis; in the absence of viral DNA replication functions, no replication foci and only a limited number of transcription foci were present. Absence of a packaging function had no apparent effect on transcription or replication site formation, illustrating that DNA packaging is not a prerequisite for ongoing DNA synthesis. Further, the essential HSV protein IE63 is required for efficient replication site formation at later times postinfection but is not required for transcription foci formation