Apoptotic mimicry: phosphatidylserine-mediated macropinocytosis of vaccinia virus.

Viruses are obligatory intracellular parasites that rely on cellular processes and factors for most aspects of their replication cycle. For entry, most viruses take advantage of cellular endocytic activities to be transported from the cell surface into the cytoplasm where they penetrate into the host cell cytosol. It has recently emerged that vaccinia virus, the prototypic poxvirus, uses macropinocytosis to gain entry. The incoming virus particles activate a complex signaling network that triggers dramatic changes in the cortical actin network, resulting in membrane blebbing that facilitates virus entry. Phosphatidylserine in the virus membrane is required to trigger the signaling, blebbing, and macropinocytic event, suggesting that the vaccinia virus uses an entry mechanism based on mimicry of apoptotic bodies.