Abstract
Infection of non-enveloped polyomaviruses depends on an intact microtubular network. Here we focus on mouse polyomavirus (MPyV). We show that the dynamics of MPyV cytoplasmic transport reflects the characteristics of microtubular motor-driven transport with bi-directional saltatory movements. In cells treated with microtubule-disrupting agents, localization of MPyV was significantly perturbed, the virus was retained at the cell periphery, mostly within membrane structures resembling multicaveolar complexes, and at later times post-infection, only a fraction of the virus was found in Rab7-positive endosomes and multivesicular bodies. Inhibition of cytoplasmic dynein-based motility by overexpression of dynamitin affected perinuclear translocation of the virus, delivery of virions to the ER and substantially reduced the numbers of infected cells, while overexpression of dominant-negative form of kinesin-1 or kinesin-2 had no significant impact on virus localization and infectivity. We also found that transport along microtubules was important for MPyV-containing endosome sequential acquisition of Rab5, Rab7 and Rab11 GTPases. However, in contrast to dominant-negative mutant of Rab7 (T22N), overexpression of dominant-negative mutant Rab11 (S25N) did not affect the virus infectivity. Altogether, our study revealed that MPyV cytoplasmic trafficking leading to productive infection bypasses recycling endosomes, does not require the function of kinesin-1 and kinesin-2, but depends on functional dynein-mediated transport along microtubules for translocation of the virions from peripheral, often caveolin-positive compartments to late endosomes and ER – a prerequisite for efficient delivery of the viral genome to the nucleus.
Highlights
Mouse polyomavirus (MPyV) is a tumor virus belonging to the Polyomaviridae family, whose members are small non-enveloped DNA viruses replicating in the cell nucleus
Cells expressing EGFPtubulin were infected with fluorescently labeled MPyV and transport of virions along microtubules was followed at early stages post-infection (p.i.) by time-lapse fluorescence microscopy
This observation indicates that MPyV transport to the vicinity of the nucleus is prevalent during a longer time span of trafficking
Summary
Mouse polyomavirus (MPyV) is a tumor virus belonging to the Polyomaviridae family, whose members are small non-enveloped DNA viruses replicating in the cell nucleus. MPyV virions do not escape the endosomal system until they reach the lumen of smooth endoplasmic reticulum (ER) [5,6,9,10], where lumenal enzymes facilitate virus capsid disassembly and uncoating of viral genomes prior to their import into the nucleus [11,12,13]. Two possible ways for viral genome delivery to the cell nucleus have been proposed: either partially disassembled virions translocate from ER to the cytosol and are imported into the nucleus via nuclear pore complexes or, alternatively, they penetrate directly from ER to the nucleoplasm through the nuclear envelope (reviewed in [14])
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