Role of the actin cytoskeleton during influenza virus internalization into polarized epithelial cells

The in vivo site of influenza virus infection is a polarized epithelium, and it is well established that the virus preferentially enters from the apical surface of polarized epithelial cells; however, many of the molecular events involved during the endocytosis of the virus into polarized epithelia remain unclear. Here we examined the role of actin microfilaments and the myosin VI motor protein during influenza entry into a panel of polarized and non-polarized cells. By treatment of cells with cytochalasin D and jasplakinolide, we show that influenza virus entry into all the polarized epithelial cells tested requires actin dynamics, with a specific role for the actin cytoskeleton in the process of virus internalization from the plasma membrane. In contrast, influenza could still could efficiently enter and infect all non-polarized cells tested after disruption or stabilization of the actin cytoskeleton. To examine the role of the actin motor protein, myosin VI, we expressed a dominant-negative construct in both polarized and non-polarized cells. Influenza virus infectivity in myosin VI tail mutant-transfected cells was significantly decreased in polarized epithelial cells, but not in non-polarized cells. As a whole, our data suggest indispensable roles of a dynamic actin cytoskeleton for influenza virus entry into polarized epithelial cells, a feature not shared with non-polarized cells.