Reovirus Uses Multiple Endocytic Pathways for Cell Entry

Entry of reovirus virions has been well studied in several tissue culture systems. After attachment to junctional adhesionmole-cule A (JAM-A), virions undergo clathrin-mediated endocytosis followed by proteolytic disassembly of the capsid and penetra-tion to the cytoplasm. However, during in vivo infection of the intestinal tract, and likely in the tumor microenvironment, cap-sid proteolysis (uncoating) is initiated extracellularly. We usedmultiple approaches to determine if uncoated reovirus particles, called intermediate subviral particles (ISVPs), enter cells by directly penetrating the limiting membrane or if they take advantage of endocytic pathways to establish productive infection. We found that entry and infection by reovirus ISVPs was inhibited by dynasore, an inhibitor of dynamin-dependent endocytosis, as well as by genistein and dominant-negative caveolin-1, which block caveolar endocytosis. Inhibition of caveolar endocytosis also reduced infection by reovirus virions. Extraction of mem-brane cholesterol with methyl--cyclodextrin inhibited infection by virions but had no effect when infection was initiated with ISVPs. We found this pathway to be independent of both clathrin and caveolin. Together, these data suggest that reovirus virions can use both dynamin-dependent and dynamin-independent endocytic pathways during cell entry, and they reveal that reovirus ISVPs can take advantage of caveolar endocytosis to establish productive infection. To establish infection, viruses must bypass the limiting mem-brane either at the cell surface or through an intracellular com-partment, such as the endosome. Enveloped viruses achieve this through membrane fusion mediated by envelope glycoprotein