Viral and cellular subnuclear structures in human cytomegalovirus-infected cells

Abstract

In human cytomegalovirus (HCMV)-infected cells, a dramatic remodelling of the nuclear architecture is linked to the creation, utilization and manipulation of subnuclear structures. This review outlines the involvement of several viral and cellular subnuclear structures in areas of HCMV replication and virus-host interaction that include viral transcription, viral DNA synthesis and the production of DNA-filled viral capsids. The structures discussed include those that promote or impede HCMV replication (such as viral replication compartments and promyelocytic leukaemia nuclear bodies, respectively) and those whose role in the infected cell is unclear (for example, nucleoli and nuclear speckles). Viral and cellular proteins associated with subnuclear structures are also discussed. The data reviewed here highlight advances in our understanding of HCMV biology and emphasize the complexity of HCMV replication and virus-host interactions in the nucleus. IntroductionThe betaherpesvirus human cytomegalovirus (HCMV) is a widespread opportunistic pathogen that severely affects immunocompromised and immunodeficient populations (Mocarski et al., 2007). Like all herpesviruses, HCMV undergoes either productive or latent infection. During productive infection, infectious virus is produced, while in latent infection the virus becomes largely transcriptionally quiescent (Mocarski et al., 2007). Like other herpesviruses, many events that are critical for productive HCMV replication take place within the nucleus. These include essential steps in viral replication, such as: the transcriptional cascade of immediate-early (IE), early and late viral RNA transcripts, synthesis of viral DNA and the production of DNA-containing capsids (Mocarski et al., 2007). Compared with the prototype human herpesvirus, the alphaherpesvirus herpes simplex virus (HSV), certain features of productive HCMV infection are not well characterized. However, it is clear that several subnuclear structures are involved in HCMV genome replication and virus-host interactions. Uncovering the roles of these structures has led to significant advances in our understanding of HCMV biology. This review summarizes the involvement of several viral and cellular subnuclear structures in productive HCMV infection. The participation of each structure in HCMV replication and virus-host interactions is described from entry of the viral genome into the nucleus to the egress of viral capsids through the nuclear membrane. The data discussed highlight recent advances in our understanding of subnuclear structure function, introduce viral and cellular factors associated with subnuclear structures and indicate what questions have yet to be answered.Entry of the HCMV genome into the nucleus: the nuclear pore complex, nuclear speckles, promyelocytic leukaemia protein nuclear bodies and pp150 bodies HCMV genome entry into the nucleus is poorly defined but may be similar to movement of the HSV DNA genome through the nuclear pore complex (NPC) (Kobiler et al., 2012) (Fig. 1a). HCMV capsid ...

Replication Compartments of DNA Viruses in the Nucleus: Location, Location, Location

“…Indeed, it is possible that the upper limit of VRC number is restricted by availability of sites viable for the initiation and growth of VRCs. Interestingly, cellular chromatin is excluded from the VRCs of many DNA viruses, including HSV-1, CMV, and HAdV [11,12,14,15]. This raises the possibility that cellular chromatin must be manipulated to make space for VRC growth.…”

“…In many cases, the accumulation of these viral proteins throughout the nucleoplasm can be detected prior to the formation of VRCs [16,68,85], suggesting that their formation is concentration dependent, which is another feature of LLPS [87][88][89][90]. HSV-1, CMV, PRV, and HAdV VRCs also coalesce as infection progresses and they grow, fusing together in a liquid-like manner [14,15,61,62,65,69,95,[102][103][104]. However, it was recently demonstrated that HSV-1 VRCs are not disrupted by treatment with 1,6-hexanediol, which is a feature of many other cellular BMCs.…”

“…In the case of herpesviruses including HSV-1, HCMV, KSHV, EBV, and VZV, viral proteins involved in DNA replication have been identified at VRCs. These include ssDNA-binding proteins, DNA polymerases, polymerase-associated processivity factors, and primase/helicase proteins [11,15,69,[84][85][86]. Of note, the earliest identification of VRCs resulted from observation of the DNA replication-dependent localization of ICP8 to discrete nuclear sub-domains in HSV-1-infected cells [130].…”

“…Secondly, VRCs typically form at specific sites within the nucleus, suggesting that viral genomes need to be targeted to these sites in order to initiate VRC formation [6,11,12]. Furthermore, it has been hypothesized that the formation and growth of VRCs may require manipulation of the nuclear environment and the re-organization of host chromatin to overcome the spatial restraints of the nucleus [11][12][13][14][15]. In this section, we review key features of VRC initiation and highlight some major challenges to VRC formation.…”

A Role for Nuclear F-Actin Induction in Human Cytomegalovirus Nuclear Egress

“…Assembled capsids are then packaged with DNA before they translocate from the nucleus to the cytoplasm in a process called nuclear egress. To facilitate these steps, herpesviruses impart profound changes to host nuclear architecture, including the formation and expansion of RCs, partitioning of host chromatin, and disruption of the nuclear lamina (1). …”