Expression and purification of Z protein from Junín virus

The use of novel epitope-tagged arenaviruses reveals that Rab5c-positive endosomal membranes are targeted by the LCMV matrix protein

We report the development of recombinant New World (Junín; JUNV) and Old World (lymphocytic choriomeningitis virus; LCMV) mammarenaviruses that encode an HA-tagged matrix protein (Z). These viruses permit the robust affinity purification of Z from infected cells or virions, as well as the detection of Z by immunofluorescent microscopy. Importantly, the HA-tagged viruses grow with wild-type kinetics in a multi-cycle growth assay. Using these viruses, we report a novel description of JUNV Z localization in infected cells, as well as the first description of colocalization between LCMV Z and the GTPase Rab5c. This latter result, when combined with our previous findings that LCMV genome and glycoprotein also colocalize with Rab5c, suggest that LCMV may target Rab5c-positive membranes for preassembly of virus particles prior to budding. The recombinant viruses reported here will provide the field with new tools to better study Z protein functionality and identify key Z protein interactions with host machinery.

A Proteomics Survey of Junín Virus Interactions with Human Proteins Reveals Host Factors Required for Arenavirus Replication

Arenaviruses are negative-strand, enveloped RNA viruses that cause significant human disease. In particular, Junín mammarenavirus (JUNV) is the etiologic agent of Argentine hemorrhagic fever. At present, little is known about the cellular proteins that the arenavirus matrix protein (Z) hijacks to accomplish its various functions, including driving the process of virus release. Furthermore, there is little knowledge regarding host proteins incorporated into arenavirus particles and their importance for virion function. To address these deficiencies, we used mass spectrometry to identify human proteins that (i) interact with the JUNV matrix protein inside cells or within virus-like particles (VLPs) and/or (ii) are incorporated into bona fide JUNV strain Candid#1 particles. Bioinformatics analyses revealed that multiple classes of human proteins were overrepresented in the data sets, including ribosomal proteins, Ras superfamily proteins, and endosomal sorting complex required for transport (ESCRT) proteins. Several of these proteins were required for the propagation of JUNV (ADP ribosylation factor 1 [ARF1], ATPase, H⁺ transporting, lysosomal 38-kDa, V0 subunit d1 [ATP6V0D1], and peroxiredoxin 3 [PRDX3]), lymphocytic choriomeningitis mammarenavirus (LCMV) (Rab5c), or both viruses (ATP synthase, H⁺ transporting, mitochondrial F1 complex, beta polypeptide [ATP5B] and IMP dehydrogenase 2 [IMPDH2]). Furthermore, we show that the release of infectious JUNV particles, but not LCMV particles, requires a functional ESCRT pathway and that ATP5B and IMPDH2 are required for JUNV budding. In summary, we have provided a large-scale map of host machinery that associates with JUNV and identified key human proteins required for its propagation. This data set provides a resource for the field to guide antiviral target discovery and to better understand the biology of the arenavirus matrix protein and the importance of host proteins for virion function.IMPORTANCE Arenaviruses are deadly human pathogens for which there are no U.S. Food and Drug Administration-approved vaccines and only limited treatment options. Little is known about the host proteins that are incorporated into arenavirus particles or that associate with its multifunctional matrix protein. Using Junín mammarenavirus (JUNV), the causative agent of Argentine hemorrhagic fever, as a model organism, we mapped the human proteins that are incorporated into JUNV particles or that associate with the JUNV matrix protein. Functional analysis revealed host machinery that is required for JUNV propagation, including the cellular ESCRT pathway. This study improves our understanding of critical arenavirus-host interactions and provides a data set that will guide future studies to better understand arenavirus pathogenesis and identify novel host proteins that can be therapeutically targeted.

Tests in mice of a dengue vaccine candidate made of chimeric Junin virus-like particles and conserved dengue virus envelope sequences

Two new vaccine candidates against dengue virus (DENV) infection were generated by fusing the coding sequences of the self-budding Z protein from Junin virus (Z-JUNV) to those of two cryptic peptides (Z/DENV-P1 and Z/DENV-P2) conserved on the envelope protein of all serotypes of DENV. The capacity of these chimeras to generate virus-like particles (VLPs) and to induce virus-neutralizing antibodies in mice was determined. First, recombinant proteins that displayed reactivity with a Z-JUNV-specific serum by immunofluorescence were detected in HEK-293 cells transfected with each of the two plasmids and VLP formation was also observed by transmission electron microscopy. Next, we determined the presence of antibodies against the envelope peptides of DENV in the sera of immunized C57BL/6 mice. Results showed that those animals that received Z/DENV-P2 DNA coding sequences followed by a boost with DENV-P2 synthetic peptides elicited significant specific antibody titers (≥6.400). Finally, DENV plaque-reduction neutralization tests (PRNT) were performed. Although no significant protective effect was observed when using sera of Z/DENV-P1-immunized animals, antibodies raised against vaccine candidate Z/DENV-P2 (diluted 1:320) were able to reduce in over 50 % the number of viral plaques generated by infectious DENV particles. This reduction was comparable to that of the 4G2 DENV-specific monoclonal cross-reactive (all serotypes) neutralizing antibody. We conclude that Z-JUNV-VLP is a valid carrier to induce antibody-mediated immune responses in mice and that Z/DENV-P2 is not only immunogenic but also protective in vitro against infection of cells with DENV, deserving further studies. On the other side, DENV's fusion peptide-derived chimera Z/DENV-P1 did not display similar protective properties.

Antigen vehiculization particles based on the Z protein of Junin virus

BACKGROUND

Arenavirus matrix protein Z plays an important role in virus budding and is able to generate enveloped virus-like-particles (VLPs) in absence of any other viral proteins. In these VLPs, Z protein is associated to the plasma membrane inner surface by its myristoyl residue. Budding induction and vesicle formation properties can be exploited to generate enveloped VLPs platform. These structures can be designed to carry specific antigen in the inner side or on the surface of VLPs.Vaccines based on VLPs are a highly effective type of subunit vaccines that mimic the overall structure of virus particles in absence of viral nucleic acid, being noninfectious.In this work we assayed the capacity of Junin Z protein to produce VLPs carrying the green fluorescent protein (eGFP), as a model antigen.

RESULTS

In this report the Junin Z protein ability to produce VLPs from 293T cells and its capacity to deliver a specific antigen (eGFP) fused to Z was evaluated. Confocal microscopy showed a particular membrane bending in cells expressing Z and a spot welded distribution in the cytoplasm. VLPs were detected by TEM (transmission electron microscopy) and were purified from cell supernatant. The proteinase protection assay demonstrated the VLPs integrity and the absence of degradation of the fused antigen, thus indicating its internal localization. Finally, immunization of mice with purified VLPs produced high titres of anti-eGFP antibodies compared to the controls.

CONCLUSIONS

It was proved that VLPs can be generated from cells transfected with a fusion Junin virus Z-eGFP protein in absence of any other viral protein, and the capacity of Z protein to support fusions at the C-terminal, without impairing its budding activity, allowing vehiculization of specific antigens into VLPs.