Orthohantaviruses belonging to three phylogroups all inhibit apoptosis in infected target cells

Carles Solà-Riera,Hans-Gustaf Ljunggren,Shawon Gupta,Jonas Klingström

doi:10.1038/s41598-018-37446-1

Carles Solà-Riera, Hans-Gustaf Ljunggren + Show 2 more

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https://doi.org/10.1038/s41598-018-37446-1

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Abstract

Orthohantaviruses, previously known as hantaviruses, are zoonotic viruses that can cause hantavirus pulmonary syndrome (HPS) and hemorrhagic fever with renal syndrome (HFRS) in humans. The HPS-causing Andes virus (ANDV) and the HFRS-causing Hantaan virus (HTNV) have anti-apoptotic effects. To investigate if this represents a general feature of orthohantaviruses, we analysed the capacity of six different orthohantaviruses – belonging to three distinct phylogroups and representing both pathogenic and non-pathogenic viruses – to inhibit apoptosis in infected cells. Primary human endothelial cells were infected with ANDV, HTNV, the HFRS-causing Puumala virus (PUUV) and Seoul virus, as well as the putative non-pathogenic Prospect Hill virus and Tula virus. Infected cells were then exposed to the apoptosis-inducing chemical staurosporine or to activated human NK cells exhibiting a high cytotoxic potential. Strikingly, all orthohantaviruses inhibited apoptosis in both settings. Moreover, we show that the nucleocapsid (N) protein from all examined orthohantaviruses are potential targets for caspase-3 and granzyme B. Recombinant N protein from ANDV, PUUV and the HFRS-causing Dobrava virus strongly inhibited granzyme B activity and also, to certain extent, caspase-3 activity. Taken together, this study demonstrates that six different orthohantaviruses inhibit apoptosis, suggesting this to be a general feature of orthohantaviruses likely serving as a mechanism of viral immune evasion.

Highlights

Orthohantaviruses, of the order Bunyavirales and previously known as hantaviruses, are small single-stranded negative-sense RNA viruses with a tri-segmented genome (S, M and L segments) encoding four to five proteins
We recently showed that Andes virus (ANDV) and Hantaan virus (HTNV) confer resistance to cytotoxic lymphocyte-mediated killing of infected endothelial cells[51]
Inhibition of apoptosis was observed for ANDV (76.2 ± 3.3% less apoptosis compared to uninfected cells), HTNV (69.5 ± 6.7% less apoptosis), SEOV (79.4 ± 11.3% less apoptosis), Puumala virus (PUUV) (63.2 ± 6.0% less apoptosis), Prospect Hill virus (PHV) (76.2 ± 3.3% less apoptosis), and TULV (80.6 ± 6.6% less apoptosis) (Fig. 1b)

Summary

Introduction

Orthohantaviruses, of the order Bunyavirales and previously known as hantaviruses, are small single-stranded negative-sense RNA viruses with a tri-segmented genome (S, M and L segments) encoding four to five proteins. Mortality rates are generally lower for the Euroasian orthohantaviruses, some of them, such as DOBV, are associated with mortality rates of more than 10%19 Many other orthohantaviruses, such as the Arvicolinae-borne Prospect Hill virus (PHV) and TULV, are believed not to cause disease in immune-competent individuals[20,21]. Given the importance of apoptosis-inducing pathways in cellular anti-viral defense, it is not surprising that some viruses have been shown to interfere with one or more components of these pathways[33,34,35,36,37,38,39,40] Cytotoxic lymphocytes, such as natural killer (NK) cells and cytotoxic T cells (CTL), represent important components of the immune response towards virus infections. Orthohantavirus-infected patients show robust cytotoxic lymphocyte responses encompassing a long-lived NK cell response including specific expansion of NKG2C+ NK cells[45] and strong virus-specific cytotoxic CD8+ T cell responses at onset of disease[46,47,48,49], suggesting that cytotoxic lymphocytes play important roles in human orthohantavirus infections[50]

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