Adenovirus early region 4 promotes the localization of splicing factors and viral RNA in late-phase interchromatin granule clusters

Nuclear actin and myosins in adenovirus infection

Adenovirus serotypes have been shown to cause drastic changes in nuclear organization, including the transcription machinery, during infection. This ability of adenovirus to subvert transcription in the host cell facilitates viral replication. Because nuclear actin and nuclear myosin I, myosin V and myosin VI have been implicated as direct regulators of transcription and important factors in the replication of other viruses, we sought to determine how nuclear actin and myosins are involved in adenovirus infection. We first confirmed reorganization of the host's transcription machinery to viral replication centers. We found that nuclear actin also reorganizes to sites of transcription through the intermediate but not the advanced late phase of viral infection. Furthermore, nuclear myosin I localized with nuclear actin and sites of transcription in viral replication centers. Intriguingly, nuclear myosins V and VI, which also reorganized to viral replication centers, exhibited different localization patterns, suggesting specialized roles for these nuclear myosins. Finally, we assessed the role of actin in adenovirus infection and found both cytoplasmic and nuclear actin likely play roles in adenovirus infection and replication. Together our data suggest the involvement of actin and multiple myosins in the nuclear replication and late viral gene expression of adenovirus.

Serine 192 in the tiny RS repeat of the adenoviral L4-33K splicing enhancer protein is essential for function and reorganization of the protein to the periphery of viral replication centers

The adenovirus L4-33K protein is a key regulator involved in the temporal shift from early to late pattern of mRNA expression from the adenovirus major late transcription unit. L4-33K is a virus-encoded alternative splicing factor, which enhances processing of 3' splice sites with a weak sequence context. Here we show that L4-33K expressed from a plasmid is localized at the nuclear margin of uninfected cells. During an infection L4-33K is relocalized to the periphery of E2A-72K containing viral replication centers. We also show that serine 192 in the tiny RS repeat of the conserved carboxy-terminus of L4-33K, which is critical for the splicing enhancer function of L4-33K, is necessary for the nuclear localization and redistribution of the protein to viral replication sites. Collectively, our results show a good correlation between the activity of L4-33K as a splicing enhancer protein and its localization to the periphery of viral replication centers.

A guide to viral inclusions, membrane rearrangements, factories, and viroplasm produced during virus replication

Virus replication can cause extensive rearrangement of host cell cytoskeletal and membrane compartments leading to the “cytopathic effect” that has been the hallmark of virus infection in tissue culture for many years. Recent studies are beginning to redefine these signs of viral infection in terms of specific effects of viruses on cellular processes. In this chapter, these concepts have been illustrated by describing the replication sites produced by many different viruses. In many cases, the cellular rearrangements caused during virus infection lead to the construction of sophisticated platforms in the cell that concentrate replicase proteins, virus genomes, and host proteins required for replication, and thereby increase the efficiency of replication. Interestingly, these same structures, called virus factories, virus inclusions, or virosomes, can recruit host components that are associated with cellular defences against infection and cell stress. It is possible that cellular defence pathways can be subverted by viruses to generate sites of replication. The recruitment of cellular membranes and cytoskeleton to generate virus replication sites can also benefit viruses in other ways. Disruption of cellular membranes can, for example, slow the transport of immunomodulatory proteins to the surface of infected cells and protect against innate and acquired immune responses, and rearrangements to cytoskeleton can facilitate virus release.

Simultaneous detection of adenovirus RNA and cellular proteins by fluorescent labeling in situ

Investigating the cell biology of gene expression requires methodologies for localizing RNA relative to proteins involved in RNA transcription, processing, and export. Adenovirus is an important model system for the analysis of eukaryotic gene expression and is also being used to investigate the organization of gene expression within the nucleus. Here are described the combined in situ hybridization and immunofluorescence staining techniques that have been used to study the localization of viral RNA relative to nuclear structures that contain splicing factors.

Genome concatenation contributes to the late gene expression defect of an adenovirus E4 mutant

Adenovirus mutants that lack the entire E4 region are severely defective for late gene expression. E4 mutant genomes are also concatenated by host double strand break repair (DSBR) proteins. We find that E4 mutant late gene expression improves in MO59J cells that fail to form genome concatemers. DSBR kinase inhibitors interfere with genome concatenation and also stimulate late gene expression. Concatenation of E4 mutant genomes interferes with cytoplasmic accumulation of viral late messages and leads to reduced late protein levels and poor viral yields following high multiplicity infection. However, failure to concatenate viral genomes did not rescue either the DNA replication defect or virus yield following low multiplicity E4 mutant infection. Our results indicate that if the E4 mutant DNA replication defect is overcome by high multiplicity infection, concatenation of the replicated genomes by host DSBR interferes with viral late gene expression.