Role of kinesins in directed adenovirus transport and cytoplasmic exploration.

Many viruses, including adenovirus, exhibit bidirectional transport along microtubules following cell entry. Cytoplasmic dynein is responsible for microtubule minus end transport of adenovirus capsids after endosomal escape. However, the identity and roles of the opposing plus end-directed motor(s) remain unknown. We performed an RNAi screen of 38 kinesins, which implicated Kif5B (kinesin-1 family) and additional minor kinesins in adenovirus 5 (Ad5) capsid translocation. Kif5B RNAi markedly increased centrosome accumulation of incoming Ad5 capsids in human A549 pulmonary epithelial cells within the first 30 min post infection, an effect dramatically enhanced by blocking Ad5 nuclear pore targeting using leptomycin B. The Kif5B RNAi phenotype was rescued by expression of RNAi-resistant Kif5A, B, or C, and Kif4A. Kif5B RNAi also inhibited a novel form of microtubule-based "assisted-diffusion" behavior which was apparent between 30 and 60 min p.i. We found the major capsid protein penton base (PB) to recruit kinesin-1, distinct from the hexon role we previously identified for cytoplasmic dynein binding. We propose that adenovirus uses independently recruited kinesin and dynein for directed transport and for a more random microtubule-based assisted diffusion behavior to fully explore the cytoplasm before docking at the nucleus, a mechanism of potential importance for physiological cargoes as well.