Early stages of influenza virus entry into Mv-1 lung cells: involvement of dynamin

Viruses generally have one of two mechanisms for entry and uncoating. They can enter the cell either by endocytosis or by direct fusion at the plasma membrane. We have established a novel mink lung (Mv-1) cell line that expresses a dominant-interfering form of dynamin-1 (K44A) under the control of a tetracycline-responsive element and studied the early events in influenza infection using these cells. We found that influenza virus binds equally to both induced and uninduced cells, but in K44A-expressing cells, electron microscopy showed viruses trapped in deep coated pits and irregular-shaped tubular structures that contain discrete coated regions. We also show by immunofluorescence and confocal microscopy that entry of incoming virus into the nucleus is blocked in K44A-expressing cells. Virus replication was assayed by immunofluorescence microscopy and was strongly inhibited at both early and late times postinfection in K44A-expressing cells. Virus infectivity was inhibited by approximately 2 log units in cells expressing K44A dynamin when analyzed by influenza plaque assay. Overall these data show that dynamin is required for efficient influenza virus entry, presumably due to its function in release of vesicles from coated pits.