HSPA5 is an essential host factor for Ebola virus infection

Coronavirus replication is closely associated with the endoplasmic reticulum (ER), the primary cellular organelle for protein synthesis, folding, and modification. ER stress is a common consequence in coronavirus-infected cells. However, how the virus-induced ER stress influences coronavirus replication and pathogenesis remains controversial. Here, we demonstrated that infection with the alphacoronavirus transmissible gastroenteritis virus (TGEV) induced ER stress and triggered the unfolded protein response (UPR) and, and ER stress negatively regulated TGEV replication Although TGEV infection activated all three UPR pathways (activating transcription factor 6 [ATF6], inositol-requiring enzyme 1 [IRE1], and protein kinase R-like ER kinase [PERK]), the virus-triggered UPR suppressed TGEV replication in both swine testicular (ST) and IPEC-J2 cells primarily through activation of the PERK-eukaryotic initiation factor 2α (eIF2α) axis, as shown by functional studies with overexpression, small interfering RNA (siRNA), or specific chemical inhibitors. Moreover, we demonstrated that PERK-eIF2α axis-mediated inhibition of TGEV replication occurs through phosphorylated eIF2α-induced overall attenuation of protein translation. In addition to direct inhibition of viral production, the PERK-eIF2α pathway activated NF-κB and then facilitated type I IFN production, resulting in TGEV suppression. Taken together, our results suggest that the TGEV-triggered PERK-eIF2α pathway negatively regulates TGEV replication and represents a vital aspect of host innate responses to invading pathogens. The induction of ER stress is a common outcome in cells infected with coronaviruses. The UPR initiated by ER stress is actively involved in viral replication and modulates the host innate responses to the invading viruses, but these underlying mechanisms remain incompletely understood. We show here that infection with the alphacoronavirus TGEV elicited ER stress and, and the UPR PERK-eIF2α branch was predominantly responsible for the suppression of TGEV replication by ER stress. Furthermore, the PERK-eIF2α axis inhibited TGEV replication through direct inhibition of viral proteins due to global translation inhibition and type I IFN induction. These findings highlight a critical role of the UPR PERK-eIF2α pathway in modulating host innate immunity and coronavirus replication.

Epigallocatechin-3-O-gallate (EGCG) is the major catechin component of green tea (Cameria sinensis), and is known to possess antiviral activities against a wide range of DNA viruses and RNA viruses. However, few studies have examined chemical modifications of EGCG in terms of enhanced antiviral efficacy. This paper discusses which steps of virus infection EGCG interferes with, citing previous reports. EGCG appears most likely to inhibits the early stage of infections, such as attachment, entry, and membrane fusion, by interfering with viral membrane proteins. According to the relationships between structure and antiviral activity of catechin derivatives, the 3-galloyl and 5′-OH group of catechin derivatives appear critical to antiviral activities. Enhancing the binding affinity of EGCG to virus particles would thus be important to increase virucidal activity. We propose a newly developed EGCG-fatty acid derivative in which the fatty acid on the phenolic hydroxyl group would be expected to increase viral and cellular membrane permeability. EGCG-fatty acid monoesters showed improved antiviral activities against different types of viruses, probably due to their increased affinity for virus and cellular membranes. Our study promotes the application of EGCG-fatty acid derivatives for the prevention and treatment of viral infections.

CommentaryAlthough originally thought to be an inhibitor of PDK-1, OSU-03012 (AR-12) was shown in 2005 not to primarily act as a PDK-1 inhibitor in its ability to radio-sensitize tumor cells [1,2]. Subsequently it was shown that the primary mechanism by which AR-12 killed tumor cells was via the PKR-like endoplasmic reticulum kinase (PERK) -dependent induction of endoplasmic reticulum stress signaling [1][2][3]. ER stress signaling in turn promoted a toxic form of autophagy resulting in a necroptotic form of cell death.As AR-12 was causing an ER stress signal, the on-going studies became more focused on defining whether the functions and activities of chaperone proteins, particularly HSP90, HSP70 and GRP78, were being altered by the drug [3]. By western immuno-blotting, AR-12 lowered the expression of HSP90 and GRP78 but stimulated HSP70 expression. These findings were independently confirmed [4]. As AR-12 reduced expression of the PERK inhibitory chaperone GRP78, and as the induction of toxic autophagy was PERK dependent, we investigated in more detail the role of altered GRP78 expression in mediating drug toxicity. AR-12 destabilized GRP78 protein, significantly lowering its half-life as assessed by western blotting from >24 hours to 10 hours [5]. Transfection of cells with a plasmid to force over-expression of GRP78 blunted AR-12 induced PERK activation; autophagosome formation, and tumor cell death.Data published in 2014 and 2015 with AR-12 have additionally underlined the prominence of chaperones and especially GRP78 in the cell biology of OSU-03012. Phosphodiesterase 5 inhibitors including sildenafil (Viagra) and tadalafil (Cialis) were shown to interact with OSU-03012 to facilitate killing in a wide variety of tumor cells. The enhanced killing effect of the drug combination was associated with enhanced PERK-dependent ER stress signaling and autophagosome formation, as well as through death receptor activation [6]. Congruent data were obtained using the parent drug of OSU-03012, celecoxib, and also with the multi-kinase inhibitors sorafenib, regorafenib and pazopanib [7,8]. These pre-clinical studies have resulted in two open clinical trials; in all solid tumor patients (NCT02466802) where patients are receiving increasing once daily dosing with regorafenib and sildenafil; in recurrent glioblastoma patients (NCT01817751) where they receive sorafenib, sildenafil and valproate twice daily.From the research of many laboratories it has been defined that multiple chaperone proteins interact to play key roles in preserving protein stability and signaling, most notably in tumor cells which very often express much higher levels of protein than non-transformed cells. Hence some chaperones, e.g. HSP90, have become a target for developmental therapeutic synthetic chemists and also tumor cell biology scientists. In the area of viral reproductive biology, proteins such as HSPA5/ GRP78/ BiP have for almost 30 years been recognized as playing key facilitator roles in the life cycles of both DNA and RNA viruses [9][10][11...