A new mechanism for nuclear import by actin-based propulsion used by a baculovirus nucleocapsid.
The transport of macromolecules into the nucleus is mediated by soluble cellular receptors of the importin β superfamily and requires the Ran-GTPase cycle. Several studies have provided evidence that there are exceptions to this canonical nuclear import pathway. Here, we report a new unconventional nuclear import mechanism exploited by the baculovirus Autographa californica multiple nucleopolyhedrovirus (AcMNPV). We found that AcMNPV nucleocapsids entered the nucleus of digitonin-permeabilized cells in the absence of exogenous cytosol or under conditions that blocked the Ran-GTPase cycle. AcMNPV contains a protein that activates the Arp2/3 complex and induces actin polymerization at one end of the rod-shaped nucleocapsid. We show that inhibitors of Arp2/3 blocked nuclear import of nucleocapsids in semi-permeabilized cells. Nuclear import of nucleocapsids was also reconstituted in purified nuclei supplemented with G-actin and Arp2/3 under actin polymerization conditions. Thus, we propose that actin polymerization drives not only migration of baculovirus through the cytoplasm but also pushes the nucleocapsid through the nuclear pore complex to enter the cell nucleus. Our findings point to a very distinct role of actin-based motility during the baculovirus infection cycle.
Department of Zoology, University of British Columbia, Vancouver, British Columbia, Canada.
Shelly
S
Au
Department of Zoology, University of British Columbia, Vancouver, British Columbia, Canada.
Wei
W
Wu
Department of Zoology, University of British Columbia, Vancouver, British Columbia, Canada.
Lixin
L
Zhou
Summerland Research and Development Centre, AAFC, Summerland, British Columbia, Canada.
David A
DA
Theilmann
Department of Zoology, University of British Columbia, Vancouver, British Columbia, Canada pante@zoology.ubc.ca.
Nelly
0000-0002-0926-9378
N
Panté
D051376:Actin-Related Protein 2-3 Complex / Q000378:metabolism; D000199:Actins / Q000378:metabolism*; D021581:Active Transport, Cell Nucleus / Q000187:drug effects; D016367:Baculoviridae / Q000187:drug effects / Q000378:metabolism*; D002463:Cell Membrane Permeability / Q000187:drug effects; D002467:Cell Nucleus / Q000378:metabolism*; D003600:Cytosol / Q000187:drug effects / Q000378:metabolism; D004072:Digitonin / Q000494:pharmacology; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D022022:Nuclear Pore / Q000378:metabolism; D019251:Nucleocapsid / Q000187:drug effects / Q000378:metabolism*; D017924:Nucleopolyhedroviruses / Q000187:drug effects / Q000378:metabolism; D058105:Polymerization / Q000187:drug effects; D011799:Quinazolines / Q000494:pharmacology; D020931:ran GTP-Binding Protein / Q000378:metabolism
D051376:Actin-Related Protein 2-3 Complex; D000199:Actins; D011799:Quinazolines; C568452:importazole; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D020931:ran GTP-Binding Protein; D004072:Digitonin
AcMNPV; Actin; Arp2/3 complex; Baculovirus; Nuclear import