A Role of Unfolded Protein Response in the Cellular Response to Flavivirus Infection

Flaviviruses are responsible for a myriad of epidemics globally. Factors like movement and climate change perpetuate their spread making control rather challenging. The understanding of host-virus interactions is therefore cornerstone in attempts to produce efficient vaccines and/or therapies. The host immune system is indispensable in fighting infections but viruses have developed evasion strategies which abrogate the response that would otherwise function in virus clearance. The unfolded protein response (UPR), an intrinsic cellular proteostasis pathway is increasingly associated with innate immunity in response to cellular insults including viral infection. UPR activation by external stimuli elicits an earlier induction of IFNβ and antiviral ISGs suggesting UPR as a priming event that potentiates a more robust response against flaviviruses. Prerequisite to the core of this study, an analysis of the effects of TM and TG (UPR chemical inducers) as used in our current experimental settings show that they are only cytostatic but not cytotoxic. Afterwards, I delve into the search for alternative UPR inducers as potential alternatives for the ones currently in use. I show that E, NS1 and NS2B proteins of TBEV can induce UPR and several antiviral ISGs when ectopically expressed, an effect that inhibits TBEV in infection. Of the three proteins studied, NS2B seems to be the most potent inducer of UPR and antiviral ISGs. Furthermore, expression of NS2B together with RIG-I augments the IFNβ promoter activity suggesting a possible role in innate signaling independent of infection. The findings of this work open up possible avenues that require further investigation particularly in the case of NS2B, which is not a well-documented flavivirus protein apart from the context of its function as a protease cofactor. The mechanism by which it induces ER stress is especially intriguing because unlike E and NS1 proteins, it is not a glycoprotei

Viral priming of cell intrinsic innate antiviral signaling by the unfolded protein response

The innate response to a pathogen is critical in determining the outcome of the infection. However, the interplay of different cellular responses that are activated following viral infection and their contribution to innate antiviral signalling has not been clearly established. This work shows that flaviviruses, including Dengue, Zika, West Nile and Tick-borne encephalitis viruses, activate the unfolded protein response before transcription of interferon regulatory factor 3 induced genes. Infection in conditions of unfolded protein response priming leads to early activation of innate antiviral responses and cell intrinsic inhibition of viral replication, which is interferon regulatory factor 3 dependent. These results demonstrate that the unfolded protein response is not only a physiological reaction of the cell to viral infection, but also synergizes with pattern recognition sensing to mount a potent antiviral response

Variant analysis of the sporozoite surface antigen gene reveals that asymptomatic cattle from wildlife-livestock interface areas in northern Tanzania harbour buffalo-derived T. parva

Buffalo-derived Theileria parva can ‘break through’ the immunity induced by the infection and treatment vaccination method (ITM) in cattle. However, no such ‘breakthroughs’ have been reported in northern Tanzania where there has been long and widespread ITM use in pastoralist cattle, and the Cape buffalo (Syncerus caffer) is also present. We studied the exposure of vaccinated and unvaccinated cattle in northern Tanzania to buffalo-derived T. parva using p67 gene polymorphisms and compared this to its distribution in vaccinated cattle exposed to buffalo-derived T. parva in central Kenya, where vaccine ‘breakthroughs’ have been reported. Additionally, we analysed the CD8+ T cell target antigen Tp2 for positive selection. Our results showed that 10% of the p67 sequences from Tanzanian cattle (n = 39) had a buffalo type p67 (allele 4), an allele that is rare among East African isolates studied so far. The percentage of buffalo-derived p67 alleles observed in Kenyan cattle comprised 19% of the parasites (n = 36), with two different p67 alleles (2 and 3) of presumptive buffalo origin. The Tp2 protein was generally conserved with only three Tp2 variants from Tanzania (n = 33) and five from Kenya (n = 40). Two Tanzanian Tp2 variants and two Kenyan Tp2 variants were identical to variants present in the trivalent Muguga vaccine. Tp2 evolutionary analysis did not show evidence for positive selection within previously mapped epitope coding sites. The p67 data indicates that some ITM-vaccinated cattle are protected against disease induced by a buffalo-derived T. parva challenge in northern Tanzania and suggests that the parasite genotype may represent one factor explaining this

Inhibitors of Protein Glycosylation Are Active against the Coronavirus Severe Acute Respiratory Syndrome Coronavirus SARS-CoV-2

Repurposing clinically available drugs to treat the new coronavirus disease 2019 (COVID-19) is an urgent need in the course of the Severe Acute Respiratory Syndrome coronavirus (SARS-CoV-2) pandemic, as very few treatment options are available. The iminosugar Miglustat is a well-characterized drug for the treatment of rare genetic lysosome storage diseases, such as Gaucher and Niemann-Pick type C, and has also been described to be active against a variety of enveloped viruses. The activity of Miglustat is here demonstrated in the micromolar range for SARS-CoV-2 in vitro. The drug acts at the post-entry level and leads to a marked decrease of viral proteins and release of infectious viruses. The mechanism resides in the inhibitory activity toward α-glucosidases that are involved in the early stages of glycoprotein N-linked oligosaccharide processing in the endoplasmic reticulum, leading to a marked decrease of the viral Spike protein. Indeed, the antiviral potential of protein glycosylation inhibitors against SARS-CoV-2 is further highlighted by the low-micromolar activity of the investigational drug Celgosivir. These data point to a relevant role of this approach for the treatment of COVID-19