Cellular endosomal potassium ion flux regulates arenavirus uncoating during virus entry

Lymphocytic choriomeningitis virus (LCMV) is an enveloped and segmented negative-sense RNA virus classified within the Arenaviridae family of the Bunyavirales order. LCMV is associated with fatal disease in immunocompromised populations and, as the prototypical arenavirus member, acts as a model for the many highly pathogenic members of the Arenaviridae family, such as Junín, Lassa, and Lujo viruses, all of which are associated with devastating hemorrhagic fevers. To enter cells, the LCMV envelope fuses with late endosomal membranes, for which two established requirements are low pH and interaction between the LCMV glycoprotein (GP) spike and secondary receptor CD164. LCMV subsequently uncoats, where the RNA genome-associated nucleoprotein (NP) separates from the Z protein matrix layer, releasing the viral genome into the cytosol. To further examine LCMV endosome escape, we performed an siRNA screen which identified host cell potassium ion (K⁺) channels as important for LCMV infection, with pharmacological inhibition confirming K⁺ channel involvement during the LCMV entry phase completely abrogating productive infection. To better understand the K⁺-mediated block in infection, we tracked incoming virions along their entry pathway under physiological conditions, where uncoating was signified by separation of NP and Z proteins. In contrast, K⁺ channel blockade prevented uncoating, trapping virions within Rab7 and CD164-positive endosomes, identifying K⁺ as a third LCMV entry requirement. K⁺ did not increase GP-CD164 binding or alter GP-CD164-dependent fusion. Thus, we propose that K⁺ mediates uncoating by modulating NP-Z interactions within the virion interior. These results suggest K⁺ channels represent a potential anti-arenaviral target.IMPORTANCEArenaviruses can cause fatal human disease for which approved preventative or therapeutic options are not available. Here, using the prototypical LCMV, we identified K⁺ channels as critical for arenavirus infection, playing a vital role during the entry phase of the infection cycle. We showed that blocking K⁺ channel function resulted in entrapment of LCMV particles within late endosomal compartments, thus preventing productive replication. Our data suggest K⁺ is required for LCMV uncoating and genome release by modulating interactions between the viral nucleoprotein and the matrix protein layer inside the virus particle.