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 micrometer/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 micrometer/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.

Reinforcing properties of substance P in the lateral hypothalamus revealed by conditioned place preference.

Reinforcing properties of substance P (SP) were investigated in rats using a conditioned place preference paradigm. After three baseline trials one conditioning trial of 10 min duration was performed. Either SP (100 pg, 1 ng, 100 ng) or saline (SI) was injected unilaterally into the lateral hypothalamus or a sham injection (OC) was given. Pairing one compartment with SP (100 pg, 1 ng) significantly increased the time spent in this compartment. Microinjections of 100 ng SP, saline or sham injection had no effect. Locomotor activity was not influenced by either treatment. These data are discussed in terms of (a) the possibility that SP has a role in mediating reinforcement and (b) the relationship between reinforcing effects and post-trial effects on learning and memory of SP applied into the lateral hypothalamus.

Adenovirus-activated PKA and p38/MAPK pathways boost microtubule-mediated nuclear targeting of virus.

Nuclear targeting of adenovirus is mediated by the microtubule-dependent, minus-end-directed motor complex dynein/dynactin, in competition with plus- end-directed motility. We demonstrate that adenovirus transiently activates two distinct signaling pathways to enhance nuclear targeting. The first pathway activates integrins and cAMP-dependent protein kinase A (PKA). The second pathway activates the p38/MAP kinase and the downstream MAPKAP kinase 2 (MK2), dependent on the p38/MAPK kinase MKK6, but independent of integrins and PKA. Motility measurements in PKA-inhibited, p38-inhibited or MK2-lacking (MK2(-/-)) cells indicate that PKA and p38 stimulated both the frequency and velocity of minus-end-directed viral motility without affecting the perinuclear localization of transferrin-containing endosomal vesicles. p38 also suppressed lateral viral motilities and MK2 boosted the frequency of minus-end-directed virus transport. Nuclear targeting of adenovirus was rescued in MK2(-/-) cells by overexpression of hsp27, an MK2 target that enhances actin metabolism. Our results demonstrate that complementary activities of PKA, p38 and MK2 tip the transport balance of adenovirus towards the nucleus and thus enhance infection.

The first step of adenovirus type 2 disassembly occurs at the cell surface, independently of endocytosis and escape to the cytosol.

Disassembly is a key event of virus entry into cells. Here, we have investigated cellular requirements for the first step of adenovirus type 2 (Ad2) disassembly, the release of the fibers. Although fiber release coincides temporally with virus uptake, fiber release is not required for Ad2 endocytosis. It is, however, inhibited by actin-disrupting agents or soluble RGD peptides, which interfere with integrin-dependent endocytosis of Ad2. Fiber release occurs at the cell surface. Actin stabilization with jasplakinolide blocks Ad2 entry at extended cell surface invaginations and efficiently promotes fiber release, indicating that fiber release and virus endocytosis are independent events. Fiber release is not sufficient for Ad2 escape from endosomes, since inhibition of protein kinase C (PKC) prevents Ad2 escape from endosomes but does not affect virus internalization or fiber release. PKC-inhibited cells accumulate Ad2 in small vesicles near the cell periphery, indicating that PKC is also required for membrane trafficking of virus. Taken together, our data show that fiber release from incoming Ad2 requires integrins and filamentous actin. Together with correct subcellular transport of Ad2-containing endosomes, fiber release is essential for efficient delivery of virus to the cytosol. We speculate that fiber release at the surface might extend the host range of Ad2 since it is associated with the separation of a small fraction of incoming virus from the target cells.

The role of the nuclear pore complex in adenovirus DNA entry.

Adenovirus targets its genome to the cell nucleus by a multistep process involving endocytosis, membrane penetration and cytoplasmic transport, and finally imports its DNA into the nucleus. Using an immunochemical and biochemical approach combined with inhibitors of nuclear import, we demonstrate that incoming viral DNA and DNA-associated protein VII enter the nucleus via nuclear pore complexes (NPCs). Depletion of calcium from nuclear envelope and endoplasmic reticulum cisternae by ionophores or thapsigargin blocked DNA and protein VII import into the nucleus, but had no effect on virus targeting to NPCs. Calcium-depleted cells were capable of disassembling incoming virus. In contrast, inhibitors of cytosolic O-linked glycoproteins of the NPC blocked virus attachment to the nuclear envelope, capsid disassembly and also nuclear import of protein VII. The data indicate that NPCs have multiple roles in adenovirus entry into cells: they contain a virus-binding and/or dissociation activity and provide a gateway for the incoming DNA genome into the nucleus.