Mobilization of nuclear antiviral factors by Exportin XPO1 via the actin network inhibits RNA virus replication

Abstract

The intricate interplay between +RNA viruses and their hosts involves the exploitation of host resources to build virus-induced membranous replication organelles (VROs) in cytosol of infected cells. Previous genome- and proteome-wide approaches have identified numerous nuclear proteins, including restriction factors that affect replication of tomato bushy stunt virus (TBSV). However, it is currently unknown how cells mobilize nuclear antiviral proteins and how tombusviruses manipulate nuclear-cytoplasmic communication. The authors discovered that XPO1/CRM1 exportin plays a central role in TBSV replication in plants. Based on knockdown, chemical inhibition, transient expression and in vitro experiments, we show that XPO1 acts as a cellular restriction factor against TBSV. XPO1 is recruited by TBSV p33 replication protein into the cytosolic VROs via direct interaction. Blocking nucleocytoplasmic transport function of XPO1 inhibits delivery of several nuclear antiviral proteins into VROs resulting in dampened antiviral effects. The co-opted actin network is critical for XPO1 to deliver nuclear proteins to VROs for antiviral activities. We show that XPO1 and XPO1-delivered restriction factors accumulate in vir-condensates associated with membranous VROs. Altogether, the emerging theme on the role of vir-condensates is complex: we propose that vir-condensate serves as a central battleground between virus and the host for supremacy in controlling virus infection. It seems that the balance between co-opted pro-viral and antiviral factors within vir-condensates associated with membranous VROs could be a major determining factor of virus replication and host susceptibility. We conclude that XPO1 and nuclear antiviral cargos are key players in nuclear-cytoplasmic communication during cytosolic +RNA virus replication.SignificanceTomato bushy stunt virus (TBSV), similar to other (+)RNA viruses, replicates in the cytosol and exploits organellar membrane surfaces to build viral replication organelles (VROs) that represent the sites of virus replication. The authors discovered that XPO1 exportin nuclear shuttle protein inhibited TBSV replication in plants. The conserved XPO1 is a central protein interaction nod, which propelled nucleocytoplasmic transport of several viral restriction factors into the cytosolic VROs that restricted tombusviruses replication. The delivered virus restriction factors provided inhibitory functions within virus-induced condensates associated with membranous VROs. The authors propose that the VRO-associated condensate serves as a central battleground between virus and the host for supremacy in controlling virus infection. Altogether, XPO1 is a critical protein interaction hub with major implications in viral replication. The authors conclude that XPO1 and its nuclear antiviral cargos are key players in nuclear-cytoplasmic communication during cytosolic (+)RNA virus replication.