Macropinocytosis is exploited by many pathogens for entry into cells. 
Coronaviruses (CoVs) such as severe acute respiratory syndrome (SARS) CoV and 
Middle East respiratory syndrome CoV are important human pathogens; however, 
macropinocytosis during CoV infection has not been investigated. We demonstrate 
that the CoVs SARS CoV and murine hepatitis virus (MHV) induce macropinocytosis, 
which occurs late during infection, is continuous, and is not associated with 
virus entry. MHV-induced macropinocytosis results in vesicle internalization, as 
well as extended filopodia capable of fusing with distant cells. MHV-induced 
macropinocytosis requires fusogenic spike protein on the cell surface and is 
dependent on epidermal growth factor receptor activation. Inhibition of 
macropinocytosis reduces supernatant viral titers and syncytia but not 
intracellular virus titers. These results indicate that macropinocytosis likely 
facilitates CoV infection through enhanced cell-to-cell spreading. Our studies 
are the first to demonstrate virus use of macropinocytosis for a role other than 
entry and suggest a much broader potential exploitation of macropinocytosis in 
virus replication and host interactions. Importance: Coronaviruses (CoVs), 
including severe acute respiratory syndrome (SARS) CoV and Middle East 
respiratory syndrome CoV, are critical emerging human pathogens. 
Macropinocytosis is induced by many pathogens to enter host cells, but other 
functions for macropinocytosis in virus replication are unknown. In this work, 
we show that CoVs induce a macropinocytosis late in infection that is 
continuous, independent from cell entry, and associated with increased virus 
titers and cell fusion. Murine hepatitis virus macropinocytosis requires a 
fusogenic virus spike protein and signals through the epidermal growth factor 
receptor and the classical macropinocytosis pathway. These studies demonstrate 
CoV induction of macropinocytosis for a purpose other than entry and indicate 
that viruses likely exploit macropinocytosis at multiple steps in replication 
and pathogenesis.