The nuclear lamina is a dense network of intermediate filaments beneath the inner nuclear membrane. Composed of A-type lamins (lamin A/C) and B-type lamins (lamins B1 and B2), the nuclear lamina provides a scaffold for the nuclear envelope and chromatin, thereby maintaining the structural integrity of the nucleus. A-type lamins are also found inside the nucleus where they interact with chromatin and participate in gene regulation. Viruses replicating in the cell nucleus have to overcome the nuclear envelope during the initial phase of infection and during the nuclear egress of viral progeny. Here, we focused on the role of lamins in the replication cycle of a dsDNA virus, mouse polyomavirus. We detected accumulation of the major capsid protein VP1 at the nuclear periphery, defects in nuclear lamina staining and different lamin A/C phosphorylation patterns in the late phase of mouse polyomavirus infection, but the nuclear envelope remained intact. An absence of lamin A/C did not affect the formation of replication complexes but did slow virus propagation. Based on our findings, we propose that the nuclear lamina is a scaffold for replication complex formation and that lamin A/C has a crucial role in the early phases of infection with mouse polyomavirus.

• Keywords
• VP1, lamin A/C, lamin B, mouse polyomavirus, viral replication centres,
• MeSH
• Cell Nucleus metabolism   virology   MeSH
• Phosphorylation MeSH
• Tumor Virus Infections virology   pathology   metabolism   genetics   MeSH
• Nuclear Lamina * metabolism   virology   MeSH
• Nuclear Envelope metabolism   virology   MeSH
• Lamin Type A * metabolism   genetics   MeSH
• Lamin Type B metabolism   genetics   MeSH
• Mice MeSH
• Polyomavirus Infections * virology   metabolism   genetics   pathology   MeSH
• Polyomavirus * genetics   pathogenicity   physiology   MeSH
• Virus Replication * MeSH
• Capsid Proteins metabolism   genetics   MeSH
• Animals MeSH
• Check Tag
• Mice MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Lamin Type A * MeSH
• Lamin Type B MeSH
• Capsid Proteins MeSH
• VP1 protein, polyomavirus MeSH Browser

The tumorigenic potential of mouse polyomavirus (MPyV) has been studied for decades in cell culture models and has been mainly attributed to nonstructural middle T antigen (MT), which acts as a scaffold signal adaptor, activates Src tyrosine kinases, and possesses transforming ability. We hypothesized that MPyV could also transform mouse cells independent of MT via a Toll-like receptor 4 (TLR4)-mediated inflammatory mechanism. To this end, we investigated the interaction of MPyV with TLR4 in mouse embryonic fibroblasts (MEFs) and 3T6 cells, resulting in secretion of interleukin 6 (IL-6), independent of active viral replication. TLR4 colocalized with MPyV capsid protein VP1 in MEFs. Neither TLR4 activation nor recombinant IL-6 inhibited MPyV replication in MEFs and 3T6 cells. MPyV induced STAT3 phosphorylation through both direct and MT-dependent and indirect and TLR4/IL-6-dependent mechanisms. We demonstrate that uninfected mouse fibroblasts exposed to the cytokine environment from MPyV-infected fibroblasts upregulated the expressions of MCP-1, CCL-5, and α-SMA. Moreover, the cytokine microenvironment increased the invasiveness of MEFs and CT26 carcinoma cells. Collectively, TLR4 recognition of MPyV induces a cytokine environment that promotes the cancer-associated fibroblast (CAF)-like phenotype in noninfected fibroblasts and increases cell invasiveness.

• Keywords
• CAF, IL-6, MPyV, TLR4, mouse fibroblasts, mouse polyomavirus, spheroid invasiveness,
• Publication type
• Journal Article MeSH

Viruses have evolved mechanisms to manipulate microtubules (MTs) for the efficient realization of their replication programs. Studying the mechanisms of replication of mouse polyomavirus (MPyV), we observed previously that in the late phase of infection, a considerable amount of the main structural protein, VP1, remains in the cytoplasm associated with hyperacetylated microtubules. VP1-microtubule interactions resulted in blocking the cell cycle in the G2/M phase. We are interested in the mechanism leading to microtubule hyperacetylation and stabilization and the roles of tubulin acetyltransferase 1 (αTAT1) and deacetylase histone deacetylase 6 (HDAC6) and VP1 in this mechanism. Therefore, HDAC6 inhibition assays, αTAT1 knock out cell infections, in situ cell fractionation, and confocal and TIRF microscopy were used. The experiments revealed that the direct interaction of isolated microtubules and VP1 results in MT stabilization and a restriction of their dynamics. VP1 leads to an increase in polymerized tubulin in cells, thus favoring αTAT1 activity. The acetylation status of MTs did not affect MPyV infection. However, the stabilization of MTs by VP1 in the late phase of infection may compensate for the previously described cytoskeleton destabilization by MPyV early gene products and is important for the observed inhibition of the G2→M transition of infected cells to prolong the S phase.

• Keywords
• VP1, histone deacetylase 6, microtubule acetylation, microtubule stabilization, microtubules, mouse polyomavirus, α-tubulin acetyltransferase 1,
• MeSH
• Acetylation MeSH
• Acetyltransferases genetics   metabolism   MeSH
• Cell Line MeSH
• Cell Cycle MeSH
• Cytoplasm metabolism   MeSH
• Fibroblasts virology   MeSH
• Histone Deacetylase 6 genetics   metabolism   MeSH
• Host Microbial Interactions * MeSH
• Microtubules metabolism   virology   MeSH
• Mice MeSH
• Polyomavirus genetics   metabolism   MeSH
• Protein Processing, Post-Translational MeSH
• Tubulin metabolism   MeSH
• Capsid Proteins genetics   metabolism   MeSH
• Animals MeSH
• Check Tag
• Mice MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Acetyltransferases MeSH
• Hdac6 protein, mouse MeSH Browser
• Histone Deacetylase 6 MeSH
• Tubulin MeSH
• Capsid Proteins MeSH
• VP1 protein, polyomavirus MeSH Browser

Microtubules, part of the cytoskeleton, are indispensable for intracellular movement, cell division, and maintaining cell shape and polarity. In addition, microtubules play an important role in viral infection. In this review, we summarize the role of the microtubules' network during polyomavirus infection. Polyomaviruses usurp microtubules and their motors to travel via early and late acidic endosomes to the endoplasmic reticulum. As shown for SV40, kinesin-1 and microtubules are engaged in the release of partially disassembled virus from the endoplasmic reticulum to the cytosol, and dynein apparently assists in the further disassembly of virions prior to their translocation to the cell nucleus-the place of their replication. Polyomavirus gene products affect the regulation of microtubule dynamics. Early T antigens destabilize microtubules and cause aberrant mitosis. The role of these activities in tumorigenesis has been documented. However, its importance for productive infection remains elusive. On the other hand, in the late phase of infection, the major capsid protein, VP1, of the mouse polyomavirus, counteracts T-antigen-induced destabilization. It physically binds microtubules and stabilizes them. The interaction results in the G2/M block of the cell cycle and prolonged S phase, which is apparently required for successful completion of the viral replication cycle.

• Keywords
• T antigens, VP1 capsid protein, cell cycle block, dynein, kinesin, microtubules, molecular motors, polyomavirus, virus, virus trafficking,
• MeSH
• Cell Nucleus virology   MeSH
• Cytosol virology   MeSH
• Endoplasmic Reticulum virology   MeSH
• Endosomes virology   MeSH
• Host-Pathogen Interactions * MeSH
• Humans MeSH
• Microtubules physiology   virology   MeSH
• Mice MeSH
• Polyomavirus genetics   pathogenicity   MeSH
• Virus Replication MeSH
• Protein Binding MeSH
• Capsid Proteins genetics   metabolism   MeSH
• Animals MeSH
• Check Tag
• Humans MeSH
• Mice MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Review MeSH
• Names of Substances
• Capsid Proteins MeSH
• VP1 protein, polyomavirus MeSH Browser