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 significantly reduced. We demonstrated that the inhibitors did not interfere with viral replication and that RNA interference, targeting cellular mediators of macropinocytosis, is able to decrease PUUV infection levels significantly. Moreover, we established lipophilic tracer staining of PUUV virus particles and showed co-localization of stained virions and markers of macropinocytic uptake. Cells treated with lysosomotrophic agents were shown to exhibit an increased resistance to infection, confirming previous data suggesting that a low pH-dependent step is involved in PUUV infection. Finally, we observed a significant increase in the fluid-phase uptake of cell infected with PUUV, indicative of a virus-triggered promotion of macropinocytosis.