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

DNA virus infections are often lifelong and can cause serious diseases in their hosts. Their recognition by the sensors of the innate immune system represents the front line of host defence. Understanding the molecular mechanisms of innate immunity responses is an important prerequisite for the design of effective antivirotics. This review focuses on the present state of knowledge surrounding the mechanisms of viral DNA genome sensing and the main induced pathways of innate immunity responses. The studies that have been performed to date indicate that herpesviruses, adenoviruses, and polyomaviruses are sensed by various DNA sensors. In non-immune cells, STING pathways have been shown to be activated by cGAS, IFI16, DDX41, or DNA-PK. The activation of TLR9 has mainly been described in pDCs and in other immune cells. Importantly, studies on herpesviruses have unveiled novel participants (BRCA1, H2B, or DNA-PK) in the IFI16 sensing pathway. Polyomavirus studies have revealed that, in addition to viral DNA, micronuclei are released into the cytosol due to genotoxic stress. Papillomaviruses, HBV, and HIV have been shown to evade DNA sensing by sophisticated intracellular trafficking, unique cell tropism, and viral or cellular protein actions that prevent or block DNA sensing. Further research is required to fully understand the interplay between viruses and DNA sensors.

• Keywords
• DNA sensing, DNA viruses, IFI16, IFN, STING, TLR9, cGAS, inflammasome, innate immunity, p204/Ifi-204,
• MeSH
• DNA, Viral metabolism   MeSH
• Herpesviridae * genetics   metabolism   MeSH
• DNA Virus Infections * MeSH
• Humans MeSH
• Polyomavirus * genetics   MeSH
• Immunity, Innate MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Review MeSH
• Names of Substances
• DNA, Viral MeSH

The mechanism by which DNA viruses interact with different DNA sensors and their connection with the activation of interferon (IFN) type I pathway are poorly understood. We investigated the roles of protein 204 (p204) and cyclic guanosine-adenosine synthetase (cGAS) sensors during infection with mouse polyomavirus (MPyV). The phosphorylation of IFN regulatory factor 3 (IRF3) and the stimulator of IFN genes (STING) proteins and the upregulation of IFN beta (IFN-β) and MX Dynamin Like GTPase 1 (MX-1) genes were detected at the time of replication of MPyV genomes in the nucleus. STING knockout abolished the IFN response. Infection with a mutant virus that exhibits defective nuclear entry via nucleopores and that accumulates in the cytoplasm confirmed that replication of viral genomes in the nucleus is required for IFN induction. The importance of both DNA sensors, p204 and cGAS, in MPyV-induced IFN response was demonstrated by downregulation of the IFN pathway observed in p204-knockdown and cGAS-knockout cells. Confocal microscopy revealed the colocalization of p204 with MPyV genomes in the nucleus. cGAS was found in the cytoplasm, colocalizing with viral DNA leaked from the nucleus and with DNA within micronucleus-like bodies, but also with the MPyV genomes in the nucleus. However, 2'3'-Cyclic guanosine monophosphate-adenosine monophosphate synthesized by cGAS was detected exclusively in the cytoplasm. Biochemical assays revealed no evidence of functional interaction between cGAS and p204 in the nucleus. Our results provide evidence for the complex interactions of MPyV and DNA sensors including the sensing of viral genomes in the nucleus by p204 and of leaked viral DNA and micronucleus-like bodies in the cytoplasm by cGAS.

• Keywords
• cGAS sensor, immune sensing of DNA, mouse polyomavirus, p204 sensor, pattern recognition receptors,
• MeSH
• DNA, Viral genetics   immunology   MeSH
• Phosphoproteins antagonists & inhibitors   genetics   metabolism   MeSH
• Phosphorylation MeSH
• Tumor Virus Infections immunology   virology   MeSH
• Host-Pathogen Interactions MeSH
• Interferon-beta metabolism   MeSH
• Nuclear Proteins antagonists & inhibitors   genetics   metabolism   MeSH
• Membrane Proteins antagonists & inhibitors   genetics   metabolism   MeSH
• Mice MeSH
• Nucleotidyltransferases antagonists & inhibitors   genetics   metabolism   MeSH
• Polyomavirus Infections immunology   virology   MeSH
• Polyomavirus genetics   immunology   MeSH
• Immunity, Innate immunology   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
• cGAS protein, mouse MeSH Browser
• DNA, Viral MeSH
• Phosphoproteins MeSH
• Ifi16 protein, mouse MeSH Browser
• Interferon-beta MeSH
• Nuclear Proteins MeSH
• Membrane Proteins MeSH
• Nucleotidyltransferases MeSH
• Sting1 protein, mouse 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

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

The mechanism used by mouse polyomavirus (MPyV) overcomes the crowded cytosol to reach the nucleus has not been fully elucidated. Here, we investigated the involvement of importin α/β1 mediated transport in the delivery of MPyV genomes into the nucleus. Interactions of the virus with importin β1 were studied by co-immunoprecipitation and proximity ligation assay. For infectivity and nucleus delivery assays, the virus and its capsid proteins mutated in the nuclear localization signals (NLSs) were prepared and produced. We found that at early times post infection, virions bound importin β1 in a time dependent manner with a peak of interactions at 6 h post infection. Mutation analysis revealed that only when the NLSs of both VP1 and VP2/3 were disrupted, virus did not bind efficiently to importin β1 and its infectivity remarkably decreased (by 80%). Nuclear targeting of capsid proteins was improved when VP1 and VP2 were co-expressed. VP1 and VP2 were effectively delivered into the nucleus, even when one of the NLS, either VP1 or VP2, was disrupted. Altogether, our results showed that MPyV virions can use VP1 and/or VP2/VP3 NLSs in concert or individually to bind importins to deliver their genomes into the cell nucleus.

• Keywords
• capsid proteins, importin β1, mouse polyomavirus, nuclear localization signal, trafficking into the nucleus,
• MeSH
• Biological Transport MeSH
• Cell Nucleus MeSH
• Cell Line MeSH
• DNA, Viral metabolism   MeSH
• Fluorescent Antibody Technique MeSH
• Nuclear Localization Signals genetics   MeSH
• Karyopherins metabolism   MeSH
• Mutation MeSH
• Mice MeSH
• Polyomavirus Infections metabolism   virology   MeSH
• Polyomavirus physiology   ultrastructure   MeSH
• Virus Assembly MeSH
• Amino Acid Substitution MeSH
• Protein Binding 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
• DNA, Viral MeSH
• Nuclear Localization Signals MeSH
• Karyopherins MeSH
• Capsid Proteins MeSH

To get access to the replication site, small non-enveloped DNA viruses have to cross the cell membrane using a limited number of capsid proteins, which also protect the viral genome in the extracellular environment. Most of DNA viruses have to reach the nucleus to replicate. The capsid proteins involved in transmembrane penetration are exposed or released during endosomal trafficking of the virus. Subsequently, the conserved domains of capsid proteins interact with cellular membranes and ensure their efficient permeabilization. This review summarizes our current knowledge concerning the role of capsid proteins of small non-enveloped DNA viruses in intracellular membrane perturbation in the early stages of infection.

• MeSH
• Adenoviridae physiology   MeSH
• Cell Membrane metabolism   virology   MeSH
• Cell Nucleus metabolism   virology   MeSH
• Endosomes metabolism   virology   MeSH
• Eukaryotic Cells metabolism   virology   MeSH
• Host-Pathogen Interactions MeSH
• Virus Internalization * MeSH
• Humans MeSH
• Papillomaviridae physiology   MeSH
• Parvoviridae physiology   MeSH
• Polyomaviridae physiology   MeSH
• Virus Replication MeSH
• Protein Transport MeSH
• Protein Binding MeSH
• Capsid Proteins chemistry   metabolism   MeSH
• Receptors, Virus metabolism   MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Review MeSH
• Names of Substances
• Capsid Proteins MeSH
• Receptors, Virus MeSH

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.

• MeSH
• Cell Line MeSH
• Endocytosis * MeSH
• Endoplasmic Reticulum metabolism   virology   MeSH
• Endosomes metabolism   virology   MeSH
• Microtubule Proteins metabolism   MeSH
• Microtubules metabolism   MeSH
• Molecular Motor Proteins metabolism   MeSH
• Mice MeSH
• Polyomavirus metabolism   MeSH
• Cell Survival 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
• Microtubule Proteins MeSH
• Molecular Motor Proteins MeSH

Lamins are the best characterized cytoskeletal components of the cell nucleus that help to maintain the nuclear shape and participate in diverse nuclear processes including replication or transcription. Nuclear actin is now widely accepted to be another cytoskeletal protein present in the nucleus that fulfills important functions in the gene expression. Some viruses replicating in the nucleus evolved the ability to interact with and probably utilize nuclear actin for their replication, e.g., for the assembly and transport of capsids or mRNA export. On the other hand, lamins play a role in the propagation of other viruses since nuclear lamina may represent a barrier for virions entering or escaping the nucleus. This review will summarize the current knowledge about the roles of nuclear actin and lamins in viral infections.

• Keywords
• viruses, cytoskeleton, lamin, nuclear actin, nuclear lamina, nucleus,
• MeSH
• Actins metabolism   MeSH
• Baculoviridae metabolism   pathogenicity   MeSH
• Cell Nucleus metabolism   virology   MeSH
• Cytoskeleton MeSH
• Herpesviridae metabolism   pathogenicity   MeSH
• Herpesviridae Infections metabolism   pathology   virology   MeSH
• Lamins metabolism   MeSH
• Humans MeSH
• Virus Replication * MeSH
• Retroviridae metabolism   pathogenicity   MeSH
• Retroviridae Infections metabolism   pathology   virology   MeSH
• Virus Assembly * MeSH
• Virus Diseases metabolism   virology   MeSH
• Animals MeSH
• Check Tag
• Humans MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Review MeSH
• Names of Substances
• Actins MeSH
• Lamins MeSH