HSP70 Copurifies with Zika Virus Particles

Chaperones Hsc70 and Hsp70 play distinct roles in the replication of bocaparvovirus minute virus of canines

Minute virus of canines (MVC) belongs to the genus Bocaparvovirus (formerly Bocavirus) within the Parvoviridae family and causes serious respiratory and gastrointestinal symptoms in neonatal canines worldwide. A productive viral infection relies on the successful recruitment of host factors for various stages of the viral life cycle. However, little is known about the MVC-host cell interactions. In this study, we identified that two cellular proteins (Hsc70 and Hsp70) interacted with NS1 and VP2 proteins of MVC, and both two domains of Hsc70/Hsp70 were mediated for their interactions. Functional studies revealed that Hsp70 was induced by MVC infection, knockdown of Hsc70 considerably suppressed MVC replication, whereas the replication was dramatically promoted by Hsp70 knockdown. It is interesting that low amounts of overexpressed Hsp70 enhanced viral protein expression and virus production, but high amounts of Hsp70 overexpression weakened them. Upon Hsp70 overexpressing, we observed that the ubiquitination of viral proteins changed with Hsp70 overexpression, and proteasome inhibitor (MG132) restored an accumulation of viral proteins. In addition, we verified that Hsp70 family inhibitors remarkably decreased MVC replication. Overall, we identified Hsc70 and Hsp70 as interactors of MVC NS1 and VP2 proteins and were involved in MVC replication, which may provide novel targets for anti-MVC approach.

CASC3 Biomolecular Condensates Restrict Turnip Crinkle Virus by Limiting Host Factor Availability

The exon-junction complex (EJC) plays a role in post-transcriptional gene regulation and exerts antiviral activity towards several positive-strand RNA viruses. However, the spectrum of RNA viruses that are targeted by the EJC or the underlying mechanisms are not well understood. EJC components from Arabidopsis thaliana were screened for antiviral activity towards Turnip crinkle virus (TCV, Tombusviridae). Overexpression of the accessory EJC component CASC3 inhibited TCV accumulation > 10-fold in Nicotiana benthamiana while knock-down of endogenous CASC3 resulted in a > 4-fold increase in TCV accumulation. CASC3 forms cytoplasmic condensates and deletion of the conserved SELOR domain reduced condensate size 7-fold and significantly decreased antiviral activity towards TCV. Mass spectrometry of CASC3 complexes did not identify endogenous stress granule or P-body markers and CASC3 failed to co-localize with an aggresome-specific dye suggesting that CASC3 condensates are distinct from well-established membraneless compartments. Mass spectrometry and bimolecular fluorescence complementation assays revealed that CASC3 sequesters Heat shock protein 70 (Hsp70-1) and Glyceraldehyde-3-phosphate dehydrogenase (GAPDH), two host factors with roles in tombusvirus replication. Overexpression of Hsp70-1 or GAPDH reduced the antiviral activity of CASC3 2.1-fold and 2.8-fold, respectively, and suggests that CASC3 inhibits TCV by limiting host factor availability. Unrelated Tobacco mosaic virus (TMV) also depends on Hsp70-1 and CASC3 overexpression restricted TMV accumulation 4-fold and demonstrates that CASC3 antiviral activity is not TCV-specific. Like CASC3, Auxin response factor 19 (ARF19) forms poorly dynamic condensates but ARF19 overexpression failed to inhibit TCV accumulation and suggests that CASC3 has antiviral activities that are not ubiquitous among cytoplasmic condensates.

Expression of HSPA14 in patients with acute HIV-1 infection and its effect on HIV-1 replication

Introduction

Heat shock protein (HSPs) are important intracellular factors, which are often involved in the regulation of viral replication including HIV-1 in infected individuals as molecular chaperone proteins. Heat shock proteins 70 (HSP70/HSPA) family play important roles in HIV replication, but this family contain many subtypes, and it is unclear how these subtypes participate in and affect HIV replication.

Methods

To detect the interaction between HSPA14 and HspBP1 by CO-IP. Simulating HIV infection status in vitro to detect the change of intracellular HSPA14 expression after HIV infection in different cells. Constructing HSPA14 overexpression or knockdown cells to detect intracellular HIV replication levels after in vitro infection. Detecting the difference of HSPA expression levels in CD4+ T cells of untreated acute HIV-infected patients with different viral load.

Results

In this study, we found that HIV infection can lead to changes in the transcriptional level of many HSPA subtypes, among which HSPA14 interacts with HIV transcriptional inhibitor HspBP1. The expression of HSPA14 in Jurkat and primary CD4+T cells infected with HIV were inhibited, overexpression of HSPA14 inhibited HIV replication, while knocking down HSPA14 promoted HIV replication. We also found that the expression level of HSPA14 is higher in peripheral blood CD4+T cells of untreated acute HIV infection patients with low viral load.

Conclusion

HSPA14 is a potential HIV replication inhibitor and may restrict HIV replication by regulating the transcriptional inhibitor HspBP1. Further studies are needed to determine the specific mechanism by which HSPA14 regulates viral replication.

Pathogenesis and virulence of flavivirus infections

The Flavivirus genus consists of >70 members including several that are considered significant human pathogens. Flaviviruses display a broad spectrum of diseases that can be roughly categorised into two phenotypes - systemic disease involving haemorrhage exemplified by dengue and yellow Fever virus, and neurological complications associated with the likes of West Nile and Zika viruses. Attempts to develop vaccines have been variably successful against some. Besides, mosquito-borne flaviviruses can be vertically transmitted in the arthropods, enabling long term persistence and the possibility of re-emergence. Therefore, developing strategies to combat disease is imperative even if vaccines become available. The cellular interactions of flaviviruses with their human hosts are key to establishing the viral lifecycle on the one hand, and activation of host immunity on the other. The latter should ideally eradicate infection, but often leads to immunopathological and neurological consequences. In this review, we use Dengue and Zika viruses to discuss what we have learned about the cellular and molecular determinants of the viral lifecycle and the accompanying immunopathology, while highlighting current knowledge gaps which need to be addressed in future studies.

Chicken Heat Shock Protein 70 Is an Essential Host Protein for Infectious Bursal Disease Virus Infection In Vitro

Infectious bursal disease virus (IBDV) infection causes pathogenicity and mortality in chickens, leading to huge economic losses in the poultry industry worldwide. Studies of host-virus interaction can help us to better understand the viral pathogenicity. As a highly conservative host factor, heat shock protein 70 (Hsp70) is observed to be involved in numerous viral infections. However, there is little information about the role of chicken Hsp70 (cHsp70) in IBDV infection. In the present study, the increased expression of cHsp70 was observed during IBDV-infected DF-1 cells. Further studies revealed that Hsp70 had similar locations with the viral double-stranded RNA (dsRNA), and the result of pull-down assay showed the direct interaction between cHsp70 with dsRNA, viral proteins (vp)2 and 3, indicating that maybe cHsp70 participates in the formation of the replication and transcription complex. Furthermore, overexpression of cHsp70 promoted IBDV production and knockdown of cHsp70 using small interfering RNAs (siRNA) and reducedviral production, implying the necessity of cHsp70 in IBDV infection. These results reveal that cHsp70 is essential for IBDV infection in DF-1 cells, suggesting that targeting cHsp70 may be applied as an antiviral strategy.

Function, Therapeutic Potential, and Inhibition of Hsp70 Chaperones

Hsp70s are among the most highly conserved proteins in all of biology. Through an iterative binding and release of exposed hydrophobic residues on client proteins, Hsp70s can prevent aggregation and promote folding to the native state of their client proteins. The human proteome contains eight canonical Hsp70s. Because Hsp70s are relatively promiscuous they play a role in folding a large proportion of the proteome. Hsp70s are implicated in disease through their ability to regulate protein homeostasis. In recent years, researchers have attempted to develop selective inhibitors of Hsp70 isoforms to better understand the role of individual isoforms in biology and as potential therapeutics. Selective inhibitors have come from rational design, forced localization, and serendipity, but the development of completely selective inhibitors remains elusive. In the present review, we discuss the Hsp70 structure and function, the known Hsp70 client proteins, the role of Hsp70s in disease, and current efforts to discover Hsp70 modulators.

A functional interaction between GRP78 and Zika virus E protein

Zika virus (ZIKV) is a mosquito-transmitted virus that has caused significant public health concerns around the world, partly because of an association with microcephaly in babies born to mothers who were infected with ZIKV during pregnancy. As a recently emerging virus, little is known as to how the virus interacts with the host cell machinery. A yeast-2-hybrid screen for proteins capable of interacting with the ZIKV E protein domain III, the domain responsible for receptor binding, identified 21 proteins, one of which was the predominantly ER resident chaperone protein GRP78. The interaction of GRP78 and ZIKV E was confirmed by co-immunoprecipitation and reciprocal co-immunoprecipitation, and indirect immunofluorescence staining showed intracellular and extracellular co-localization between GRP78 and ZIKV E. Antibodies directed against the N-terminus of GRP78 were able to inhibit ZIKV entry to host cells, resulting in significant reductions in the levels of ZIKV infection and viral production. Consistently, these reductions were also observed after down-regulation of GRP78 by siRNA. These results indicate that GRP78 can play a role mediating ZIKV binding, internalization and replication in cells. GRP78 is a main regulator of the unfolded protein response (UPR), and the study showed that expression of GRP78 was up-regulated, and the UPR was activated. Increases in CHOP expression, and activation of caspases 7 and 9 were also shown in response to ZIKV infection. Overall these results indicate that the interaction between GRP78 and ZIKV E protein plays an important role in ZIKV infection and replication, and may be a potential therapeutic target.

Deciphering flavivirus-host interactions using quantitative proteomics

Flaviviruses are a group of important emerging and re-emerging human pathogens that cause worldwide epidemics with thousands of deaths annually. Flaviviruses are small, enveloped, positive-sense, single-stranded RNA viruses that are obligate intracellular pathogens, relying heavily on host cell machinery for productive replication. Proteomic approaches have become an increasingly powerful tool to investigate the mechanisms by which viruses interact with host proteins and manipulate cellular processes to promote infection. Here, we review recent advances in employing quantitative proteomics techniques to improve our understanding of the complex interplay between flaviviruses and host cells. We describe new findings on our understanding of how flaviviruses impact protein-protein interactions, protein-RNA interactions, protein abundance, and post-translational modifications to modulate viral infection.

Cold Exposure-Induced Up-Regulation of Hsp70 Positively Regulates PEDV mRNA Synthesis and Protein Expression In Vitro

Porcine epidemic diarrhea (PED) is a highly contagious, intestinal infectious disease caused by porcine epidemic diarrhea virus (PEDV). PEDV as an emerging and re-emerging epizootic virus of swine causes substantial economic losses to the pig industry in China and other countries. In China, the occurrence of PED shows significant seasonal variations, usually outbreak during the winter season. The epidemic characteristics of PED may be highly correlated with the changes of ambient temperature. However, molecular mechanism on the seasonal occurrence of PED still remains unclear. It has been widely observed that low ambient temperature up-regulates the expression of host heat shock protein 70 (Hsp70). Here, we showed that nucleotide and protein levels of Hsp70 were up-regulated in the intestinal of cold exposed pig and cold exposed Vero E6 cells. We found that overexpression of Hsp70 could increase PEDV mRNA synthesis and protein expression in Vero E6 and IPEC-J2 cells, while the siRNAs mediated knockdown of Hsp70 and VER155008 mediated inhibition of Hsp70 resulted in inhibition of viral mRNA synthesis and protein expression in Vero E6 cells. These data suggested that Hsp70 positively regulated PEDV mRNA synthesis and protein expression, which being helpful for understanding the seasonality of PED epidemics and development of novel antiviral therapies in the future.

Proteostasis in Viral Infection: Unfolding the Complex Virus-Chaperone Interplay

Viruses are obligate intracellular parasites that rely on their hosts for protein synthesis, genome replication, and viral particle production. As such, they have evolved mechanisms to divert host resources, including molecular chaperones, facilitate folding and assembly of viral proteins, stabilize complex structures under constant mutational pressure, and modulate signaling pathways to dampen antiviral responses and prevent premature host death. Biogenesis of viral proteins often presents unique challenges to the proteostasis network, as it requires the rapid and orchestrated production of high levels of a limited number of multifunctional, multidomain, and aggregation-prone proteins. To overcome such challenges, viruses interact with the folding machinery not only as clients but also as regulators of chaperone expression, function, and subcellular localization. In this review, we summarize the main types of interactions between viral proteins and chaperones during infection, examine evolutionary aspects of this relationship, and discuss the potential of using chaperone inhibitors as broad-spectrum antivirals.