Macropinocytosis and Clathrin-Dependent Endocytosis Play Pivotal Roles for the Infectious Entry of Puumala Virus.

: Viruses from the taxonomic family Hantaviridae are encountered as emerging pathogens causing two life-threatening human zoonoses: hemorrhagic fever with renal syndrome (HFRS) and hantavirus cardiopulmonary syndrome (HCPS) with case fatalities of up to 50 %. Here we comprehensively investigated entry of the Old-World Hantavirus Puumala virus (PUUV) into mammalian cells, showing that upon treatment with pharmacological inhibitors of macropinocytosis and clathrin-mediated endocytosis PUUV infections are greatly reduced. We demonstrate that the inhibitors did not interfere with viral replication and that RNA interference, targeting cellular mediators of macropinocytosis, decreases PUUV infection levels significantly. Moreover, we established lipophilic tracer staining of PUUV particles and show co-localization of stained virions and markers of macropinosomes. Finally, we report a significant increase in the fluid-phase uptake of cell infected with PUUV, indicative of a virus-triggered promotion of macropinocytosis.Importance The Hantaviridae family comprises a diverse group of virus species and is considered an emerging global public health threat. Individual hantavirus species differ considerably in terms of their pathogenicity, but also their cell biology and host-pathogen interactions. In this study, we focused on the most prevalent pathogenic hantavirus in Europe, Puumala virus, and investigated the entry and internalization of PUUV into mammalian cells. We show that both, clathrin-mediated endocytosis and macropinocytosis are cellular pathways exploited by the virus to establish productive infections and demonstrate that pharmacological inhibition of macropinocytosis or a targeted knockdown using RNA interference significantly reduced viral infections. We also found indications for an increase of macropinocytic uptake upon PUUV infections, suggesting that the virus triggers specific cellular mechanisms in order to stimulate its own internalization, thus facilitating infection.