Coronaviruses induce entry-independent, continuous macropinocytosis

Area of Science:

• Virology
• Cell Biology
• Pathogenesis

Background:

• Macropinocytosis is a cellular process utilized by various pathogens for cellular entry.
• The role of macropinocytosis in coronavirus (CoV) infection, including SARS-CoV and MERS-CoV, remains largely unexplored.
• Understanding alternative roles of macropinocytosis in viral replication is crucial for developing novel therapeutic strategies.

Purpose of the Study:

• To investigate the induction and function of macropinocytosis during coronavirus infection.
• To determine if macropinocytosis plays a role in CoV entry, replication, or cell-to-cell spread.
• To elucidate the molecular mechanisms underlying CoV-induced macropinocytosis.

Main Methods:

• Utilized SARS-CoV and murine hepatitis virus (MHV) infection models in cell cultures.
• Monitored macropinocytosis induction, vesicle internalization, and filopodia formation.
• Investigated the dependence on viral spike protein and epidermal growth factor receptor (EGFR) signaling.
• Assessed the impact of macropinocytosis inhibition on viral titers and syncytia formation.

Main Results:

• Coronaviruses (CoVs) induce macropinocytosis late in infection, independent of viral entry.
• MHV-induced macropinocytosis involves vesicle internalization and filopodia-mediated cell fusion.
• Inhibition of macropinocytosis reduced viral titers in supernatants and syncytia formation, but not intracellular viral loads.
• MHV macropinocytosis requires a fusogenic spike protein and EGFR activation.

Conclusions:

• Coronaviruses exploit macropinocytosis for cell-to-cell spreading, not for initial cell entry.
• Macropinocytosis contributes to increased viral titers and the formation of syncytia, enhancing CoV infection.
• These findings reveal a novel role for macropinocytosis beyond pathogen entry, suggesting broader implications in viral replication and pathogenesis.