Microtubule-dependent Plus- and Minus End–directed Motilities Are Competing Processes for Nuclear Targeting of Adenovirus

Adenovirus (Ad) enters target cells by receptor-mediated endocytosis, escapes to the cytosol, and then delivers its DNA genome into the nucleus. Here we analyzed the trafficking of fluorophore-tagged viruses in HeLa and TC7 cells by time-lapse microscopy. Our results show that native or taxol-stabilized microtubules (MTs) support alternating minus- and plus end–directed movements of cytosolic virus with elementary speeds up to 2.6 μm/s. No directed movement was observed in nocodazole-treated cells. Switching between plus- and minus end–directed elementary speeds at frequencies up to 1 Hz was observed in the periphery and near the MT organizing center (MTOC) after recovery from nocodazole treatment. MT-dependent motilities allowed virus accumulation near the MTOC at population speeds of 1–10 μm/min, depending on the cell type. Overexpression of p50/dynamitin, which is known to affect dynein-dependent minus end–directed vesicular transport, significantly reduced the extent and the frequency of minus end–directed migration of cytosolic virus, and increased the frequency, but not the extent of plus end–directed motility. The data imply that a single cytosolic Ad particle engages with two types of MT-dependent motor activities, the minus end– directed cytoplasmic dynein and an unknown plus end– directed activity.