Identification of two internal signal peptide sequences: critical for classical swine fever virus non-structural protein 2 to trans-localize to the endoplasmic reticulum

CSFV Infection Up-Regulates the Unfolded Protein Response to Promote Its Replication

Classical swine fever (CSF) is an OIE-listed, highly contagious animal disease caused by classical swine fever virus (CSFV). The endoplasmic reticulum (ER) is an organelle in which the replication of many RNA viruses takes place. During viral infection, a series of events elicited in cells can destroy the ER homeostasis that cause ER stress and induce an unfolded protein response (UPR). In this study, we demonstrate that ER stress was induced during CSFV infection as several UPR-responsive elements such as XBP1(s), GRP78 and CHOP were up-regulated. Specifically, CSFV transiently activated IRE1 pathway at the initial stage of infection but rapidly switched off, likely due to the reduction in cytoplasm Ca²⁺ after viral incubation. Additionally, our data show that the ER stress induced by CSFV can promote CSFV production, which the IRE1 pathway play an important role in it. Evidence of ER stress in vivo was also confirmed by the marked elevation of GRP78 in CSFV-infected pig PBMC and tissues. Collectively, these data indicate that the ER stress was induced upon CSFV infection and that the activation of the IRE1 pathway benefits CSFV replication.

Classical swine fever virus nonstructural protein p7 modulates infectious virus production

The classical swine fever virus (CSFV) nonstructural protein p7 is crucial for virus production, yet precisely how the p7 modulates this process is unclear. In this study, we first identified the interactions of p7 with E2 and NS2. The key binding regions of both p7 and NS2 mapped to the first transmembrane (TM1) domain of two proteins. Three amino acid substitutions in the TM1 region of p7 (p7^{TDI18/19/20AAA}, p7^{EVV21/22/23AAA} and p7^{YFY25/26/30AAA}) impaired infectious virus production and reduced the interaction of p7 with the NS2 protein. The E2p7 processing and mature p7, but not the E2p7 precursor, are essential for infectious virus production. Bicistronic mutants (pSM/E2/IRES) with single substitutions at residues 1 to 9 of p7 exhibited a significantly increased infectious CSFV titer compared to their counterparts in the context of pSM. Viral genomic RNA copies of the mutants exhibited similar levels compared with the wt CSFV. Our results demonstrated that CSFV p7 and its precursor E2p7 modulate viral protein interactions and infectious virus production without influencing viral RNA replication.

Follistatin-like protein 1 contributes to dendritic cell and T-lymphocyte activation in nasopharyngeal carcinoma patients by altering nuclear factor κb and Jun N-terminal kinase expression

Follistatin‐like protein 1 (FSTL1) is a newly characterized protein that can regulate the immune response in various ways. Dendritic cells (DCs) are central to immune regulation. In this study, we explored the impact of FSTL1 on DC activity in nasopharyngeal carcinoma (NPC) patients. The surface expression of CD40, CD86, and HLA‐DR on DCs was analyzed and showed significantly elevated expression levels, indicating DC maturity. After FSTL1 was added to DCs collected from NPC patients (n = 50), controls (n = 47), and healthy donors (n = 10), interferon γ secretion and T‐cell receptor expression in cytotoxic T lymphocytes were also investigated. In the experimental groups, the expression of the critical immune protein nuclear factor (NF)‐κb was upregulated, whereas Jun N‐terminal kinase (JNK) was downregulated. Our findings demonstrate that FSTL1 plays a critical role in immune regulation, enhancing the antigen presentation ability of DCs by up‐regulating NF‐κb expression and down‐regulating JNK expression.

The N-terminus of classical swine fever virus (CSFV) nonstructural protein 2 modulates viral genome RNA replication

Pestivirus nonstructural protein 2 (NS2) is a multifunctional, hydrophobic protein with an important but poorly understood role in viral RNA replication and infectious virus production. In the present study, based on sequence analysis, we mutated several representative conserved residues within the N-terminus of NS2 of classical swine fever virus (CSFV) and investigated how these mutations affected viral RNA replication and infectious virus production. Our results demonstrated that the mutation of two aspartic acids, NS2/D60A or NS2/D60K and NS2/D78K, in the N-terminus of NS2 abolished infectious virus production and that the substitution of arginine for alanine at position 100 (NS2/R100A) resulted in significantly decreased viral titer. The serial passage of cells containing viral genomic RNA molecules generated the revertants NS2/A60D, NS2/K60D and NS2/K78D, leading to the recovery of infectious virus. In the context of the NS2/R100A mutant, the NS2/I90L mutation compensated for infectious virus production. The regulatory roles of the indicated amino acid residues were identified to occur at the viral RNA replication level. These results revealed a novel function for the NS2 N-terminus of CSFV in modulating viral RNA replication.

Identification of cytotoxic T lymphocyte epitopes on swine viruses: multi-epitope design for universal T cell vaccine

Classical swine fever (CSF), foot-and-mouth disease (FMD) and porcine reproductive and respiratory syndrome (PRRS) are the primary diseases affecting the pig industry globally. Vaccine induced CD8⁺ T cell-mediated immune response might be long-lived and cross-serotype and thus deserve further attention. Although large panels of synthetic overlapping peptides spanning the entire length of the polyproteins of a virus facilitate the detection of cytotoxic T lymphocyte (CTL) epitopes, it is an exceedingly costly and cumbersome approach. Alternatively, computational predictions have been proven to be of satisfactory accuracy and are easily performed. Such a method enables the systematic identification of genome-wide CTL epitopes by incorporating epitope prediction tools in analyzing large numbers of viral sequences. In this study, we have implemented an integrated bioinformatics pipeline for the identification of CTL epitopes of swine viruses including the CSF virus (CSFV), FMD virus (FMDV) and PRRS virus (PRRSV) and assembled these epitopes on a web resource to facilitate vaccine design. Identification of epitopes for cross protections to different subtypes of virus are also reported in this study and may be useful for the development of a universal vaccine against such viral infections among the swine population. The CTL epitopes identified in this study have been evaluated in silico and possibly provide more and wider protection in compared to traditional single-reference vaccine design. The web resource is free and open to all users through http://sb.nhri.org.tw/ICES.

Antibody screening identifies 78 putative host proteins involved in Cyprinid herpesvirus 3 infection or propagation in common carp, Cyprinus carpio L

Cyprinid herpesvirus 3 (CyHV-3) is the aetiological agent of a serious and notifiable disease afflicting common and koi carp, Cyprinus carpio L., termed koi herpesvirus disease (KHVD). Significant progress has been achieved in the last 15 years, since the initial reports surfaced from Germany, USA and Israel of the CyHV-3 virus, in terms of pathology and detection. However, relatively few studies have been carried out in understanding viral replication and propagation. Antibody-based affinity has been used for detection of CyHV-3 in enzyme-linked immunosorbent assay and PCR-based techniques, and immunohistological assays have been used to describe a CyHV-3 membrane protein, termed ORF81. In this study, monoclonal antibodies linked to N-hydroxysuccinimide (NHS)-activated spin columns were used to purify CyHV-3 and host proteins from tissue samples originating in either CyHV-3 symptomatic or asymptomatic fish. The samples were next analysed either by polyacrylamide gel electrophoresis (PAGE) and subsequently by electrospray ionization coupled to mass spectrometry (ESI-MS) or by ESI-MS analysis directly after purification. A total of 78 host proteins and five CyHV-3 proteins were identified in the two analyses. These data can be used to develop novel control methods for CyHV-3, based on pathways or proteins identified in this study.

Interactive cellular proteins related to classical swine fever virus non-structure protein 2 by yeast two-hybrid analysis

Classical swine fever is caused by the classical swine fever virus (CSFV), which has a special affinity to endothelial cells. This fever is characterized by hemorrhage and necrosis of vascular injury. Very little information is available on the interaction between vascular endothelial cells and CSFV. In the current report, the cDNA library of swine umbilical vein endothelial cell (SUVEC) was constructed by the switching mechanism at 5' end of the RNA transcript approach. The yeast two-hybrid (Y2H) system was adopted to screen non-structure 2 protein (NS2) interactive proteins in the SUVEC line. Alignment with the NCBI database revealed 11 interactive proteins: GOPC, HNRNPH1, DNAJA1, ATP6, CSDE1, CNDP2, FANCL, TMED4, DNAJA4, MOAP1, and PNMA1. These proteins were mostly related to apoptosis, stress response and oxidation reduction, or metabolism. In the protein interaction network constructed based on proteins with NS2, the more important proteins were MOAP1, DNAJA1, GOPC, FANCL, TMED4, and CSDE1. The interactions detected by the Y2H should be regarded only as preliminary indications. However, the CSFV NS2 interactive proteins in the SUVEC cDNA library obtained in the current study provides valuable information for gaining a better understanding of the host protein-virus interactions of the CSFV NS2 protein.

Multiple targeting motifs direct NRAMP1 into lysosomes

Natural resistance-associated macrophage protein 1 (NRAMP1) containing 548 amino acids (AA) and 12 transmembrane domains (TMDs) is localized in membranes of lysosomes. Our study aimed to investigate the targeting motifs of NRAMP1 by expressing GFP-tagged full-length and truncated NRAMP1 proteins and overlapping with the lysosomal marker Lamp1-RFP in Chinese hamster ovary (CHO) cells. The NH(2)-terminal amino acids 73-140 region including TMD2 was essential for NRAMP1 lysosomal targeting. The AA.263-334 region containing the tyrosine-based motif (327)YAPI(330) targeted NRAMP1 into lysosomes. Additionally, two internal signal peptides AA.451-483 and AA.489-522 were identified as lysosomal targeting motifs. Taken together, NRAMP1 consists of multiple targeting motifs for trafficking into lysosomes.

POD1 regulates pollen tube guidance in response to micropylar female signaling and acts in early embryo patterning in Arabidopsis

The pollen tube germinates from pollen and, during its migration, it perceives and responds to guidance cues from maternal tissue and from the female gametophyte. The putative female cues have recently been identified, but how the pollen tube responds to these signals remains to be unveiled. In a genetic screen for male determinants of the pollen tube response, we identified the pollen defective in guidance1 (pod1) mutant, in which the pollen tubes fail to target the female gametophyte. POD1 encodes a conserved protein of unknown function and is essential for positioning and orienting the cell division plane during early embryo development. Here, we demonstrate that POD1 is an endoplasmic reticulum (ER) luminal protein involved in ER protein retention. Further analysis shows that POD1 interacts with the Ca(2+) binding ER chaperone CALRETICULIN3 (CRT3), a protein in charge of folding of membrane receptors. We propose that POD1 modulates the activity of CRT3 or other ER resident factors to control the folding of proteins, such as membrane proteins in the ER. By this mechanism, POD1 may regulate the pollen tube response to signals from the female tissues during pollen tube guidance and early embryo patterning in Arabidopsis thaliana.