Nuclear Import of Adenovirus DNA in Vitro Involves the Nuclear Protein Import Pathway and hsc70

Abstract

Adenovirus, a respiratory virus with a doublestranded DNA genome, replicates in the nuclei of mammalian cells. We have developed a cytosol-dependent in vitro assay utilizing adenovirus nucleocapsids to examine the requirements for adenovirus docking to the nuclear pore complex and for DNA import into the nucleus. Our assay reveals that adenovirus DNA import is blocked by a competitive excess of classical protein nuclear localization sequences and other inhibitors of nuclear protein import and indicates that this process is dependent on hsc70. Previous work revealed that the hexon (coat) protein of adenovirus is the only major protein on the surface of the adenovirus nucleocapsid that docks at the nuclear pore complex. This, together with our finding that in vitro nuclear import of hexon is inhibited by an excess of classical nuclear localization sequences, suggests a role for the hexon protein in adenovirus DNA import. However, recombinant transport factors that are sufficient for hexon import in permeabilized cells do not support DNA import, indicating that there are other as yet unidentified factors required for this process.Proteins are imported into the nucleus through aqueous channels that span the nuclear envelope called nuclear pore complexes (NPCs).1 Whereas ions and molecules less than ϳ20 -40 kDa can diffuse passively through the NPC, larger proteins are transported by saturable pathways that are energy-and signal-dependent. The classical signals that specify nuclear protein import (nuclear localization sequences (NLSs)) are short stretches of amino acids rich in basic residues, although other classes of NLSs have been described recently (1, 2). The transport of NLS-bearing proteins into the nucleus requires the participation of soluble cytosolic factors (3). The advent of a cytosol-dependent in vitro assay for nuclear import (3) has led to the identification of a number of these factors (4), namely importin-␣ (also called the NLS receptor and karyopherin-␣), importin-␤ (also called p97 and karyopherin-␤), Ran (TC4), and NTF2 (also called p10 and pp15). An initial step in the import of proteins containing classical NLSs occurs in the cytoplasm, where the substrate binds to the receptor importin-␣. Subsequently, this complex docks at the cytoplasmic face of the NPC together with importin-␤. The complex is then translocated through a central gated channel of the NPC into the nuclear interior. Movement of the import complex through the NPC requires Ran and NTF2 (5-8), but the precise role of these components is unclear. An additional protein, hsp/hsc70, has been shown to be required for import of some substrates (e.g. the large T-antigen protein (9)), but not of others (e.g. the glucocorticoid receptor (10)).Most viruses that replicate in the nucleus must use the NPC to introduce their genome into the nucleoplasm. Although it is known that the gated channel of the NPC can expand up to ϳ25 nm in diameter to allow signal-mediated transport (11), this is still considerably smaller than the diameters of many ...

Herpes Simplex Virus Replication: Roles of Viral Proteins and Nucleoporins in Capsid-Nucleus Attachment

“…It is hypothesized that a loss of capsid integrity precedes DNA release. Following a loss of capsid integrity, the DNA translocates through the NPC as a complex with viral proteins (20,41).…”

Oncolytic viral therapies

“…[72][73][74][75][76][77][78] Receptor binding leads to internalization of the virus by the cell through receptormediated endocytosis, lysis of the endosomal membrane, escape to the cytosol, trafficking along microtubules towards the nucleus, binding the nuclear envelope, and insertion of the viral genome into the nucleus. [79][80][81][82][83][84][85][86][87][88] The adenoviral reproductive cycle is a highly orchestrated process, and gene modification strategies, which enable selectivity, often reduce replication capacity. At the molecular level, completion of the infectious cycle relies on timely expression of a set of viral regulatory proteins that interact with essential endogenous cellular pathways that determine cell viability.…”

Transfection of large plasmids in primary human myoblasts

“…20 The virion is then sequentially disassembled 21 and the adenovirus DNA is directed to the nuclear pores by adenovirus proteins. 22 Nuclear localization signal peptides [23][24][25] and integrinbinding peptides 26 have been proved to enhance transfection. Two peptides, one comprising a SV40 large T antigen nuclear localizing signal (KKPNKKKRKE), the other comprising an integrin binding motif (KKKKKK GRGDTP) were therefore investigated to replace the Gene Therapy adenovirus.…”