Junín virus (JUNV) belongs to the Arenaviridae family and is the causative agent of Argentine hemorrhagic fever (AHF), a severe human disease endemic to agricultural areas in Argentina. At this moment, there are no effective antiviral therapeutics to battle pathogenic arenaviruses. Cumulative reports from recent years have widely provided information on cellular factors playing key roles during JUNV infection. In this review, we summarize research on host molecular determinants that intervene in the different stages of the viral life cycle: viral entry, replication, assembly and budding. Alongside, we describe JUNV tight interplay with the innate immune system. We also review the development of different reverse genetics systems and their use as tools to study JUNV biology and its close teamwork with the host. Elucidating relevant interactions of the virus with the host cell machinery is highly necessary to better understand the mechanistic basis beyond virus multiplication, disease pathogenesis and viral subversion of the immune response. Altogether, this knowledge becomes essential for identifying potential targets for the rational design of novel antiviral treatments to combat JUNV as well as other pathogenic arenaviruses.

Glucosidase I (GI) removes the outermost glucose from protein-linked Glc₃Man₉GlcNAc₂ (G3M9) in the endoplasmic reticulum (ER). Individuals with congenital disorders of glycosylation MOGS-CDG bear mutations in the GI-encoding gene (gls1). Although GI absence has been reported to produce lethality in Schizosaccharomyces pombe yeasts, here we obtained two viable Δgls1 mutants, one with a very sick but not lethal phenotype (Δgls1-S) and the other with a healthier one (Δgls1-H). The sick strain displayed only G3M9 as an ER protein–linked oligosaccharide, whereas the healthier strain had both G3M9 and Man₉GlcNAc₂. The lipid-linked oligosaccharide patterns of the two strains revealed that the most abundantly formed glycans were G3M9 in Δgls1-S and Glc₂Man₉GlcNAc₂ in Δgls1-H, suggesting reduced Alg10p glucosyltransferase activity in the Δgls1-H strain. A mutation in the alg10⁺ gene was indeed observed in this strain. Our results indicated that abrogated G3M9 deglucosylation was responsible for the severe defects observed in Δgls1-S cells. Further studies disclosed that the defects could not be ascribed to disruption of glycoprotein entrance into calnexin-folding cycles, inhibition of the oligosaccharyltransferase by transfer reaction products, or reduced proteasomal degradation of misfolded glycoproteins. Lack of triglucosylated glycoprotein deglucosylation neither significantly prevented glycan elongation in the Golgi nor modified the overall cell wall monosaccharide composition. Nevertheless, it resulted in a distorted cell wall and in the absence of underlying ER membranes. Furthermore, Golgi expression of human endomannosidase partially restored normal growth in Δgls1-S cells. We propose that accumulation of G3M9-bearing glycoproteins is toxic and at least partially responsible for defects observed in MOGS-CDG.

Congenital Disorders of Glycosylation Type I (CDG-I) are inherited human diseases caused by deficiencies in lipid-linked oligosaccharide (LLO) synthesis or the glycan transfer to proteins during N-glycosylation. We constructed a platform of 16 Schizosaccharomyces pombe mutant strains that synthesize all possible theoretical combinations of LLOs containing three to zero Glc and nine to five Man. The occurrence of unexpected LLOs suggested the requirement of specific Man residues for glucosyltransferases activities. We then quantified protein hypoglycosylation in each strain and found that in S. pombe the presence of Glc in the LLO is more relevant to the transfer efficiency than the amount of Man residues. Surprisingly, a decrease in the number of Man in glycans somehow improved the glycan transfer. The most severe hypoglycosylation was produced in cells completely lacking Glc and having a high number of Man. This deficiency could be reverted by expressing a single subunit OST with a broad range of substrate specificity. Our work shows the usefulness of this new S. pombe set of mutants as a platform to model the molecular bases of human CDG-I diseases.

The mammarenavirus Junín (JUNV) is the causative agent of Argentine hemorrhagic fever, a severe disease of public health concern. The most abundant viral protein is the nucleoprotein (NP), a multifunctional, two-domain protein with the primary role as structural component of the viral nucleocapsids, used as template for viral polymerase RNA synthesis activities. Here, we report that the C-terminal domain (CTD) of the attenuated Candid#1 strain of the JUNV NP can be purified as a stable soluble form with a secondary structure in line with known NP structures from other mammarenaviruses. We show that the JUNV NP CTD interacts with the viral matrix protein Z in vitro, and that the full-length NP and Z interact with each other in cellulo, suggesting that the NP CTD is responsible for this interaction. This domain comprises an arrangement of four acidic residues and a histidine residue conserved in the active site of exoribonucleases belonging to the DEDDh family. We show that the JUNV NP CTD displays metal-ion-dependent nuclease activity against DNA and single- and double-stranded RNA, and that this activity is impaired by the mutation of a catalytic residue within the DEDDh motif. These results further support this activity, not previously observed in the JUNV NP, which could impact the mechanism of the cellular immune response modulation of this important pathogen.

Mammarenavirus genus groups viruses causing human haemorrhagic diseases, including the New World (NW) Junín virus (JUNV), and the Old World (OW) viruses Lassa (LASV), among others. The high mortality and morbidity rates associated to pathogenic mammarenaviruses, the absence of vaccines and the constant threat of new emerging species, make these viruses a public health concern in endemic areas. Autophagy is a widely-known intracellular metabolic pathway involved in maintaining the cellular homeostasis in response to several stress conditions.