Early stages of influenza virus entry into Mv-1 lung cells: Involvement ofdynamin

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-l) cell line that expre sses 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 m icroscopy showed viruses trapped in deep coated pits and irregular-shaped t ubular structures that contain discrete coated regions. We also show by imm unofluorescence and confocal microscopy that entry of incoming virus into t he nucleus is blocked in K44A-expressing cells. Virus replication was assay ed by immunofluorescence microscopy and was strongly inhibited at both earl y and late times postinfection in K44A-expressing cells. Virus infectivity was inhibited by similar to 2 log units in cells expressing K44A dynamin wh en analyzed by influenza plaque assay. Overall these data show that dynamin is required for efficient influenza virus entry, presumably due to its fun ction in release of vesicles from coated pits. (C) 2000 Academic Press.