Human cytomegalovirus proteins PP65 and IEP72 are targeted to distinct compartments in nuclei and nuclear matrices of infected human embryo fibroblasts

Abstract

The cellular distribution of the human cytomegalovirus (HCMV)-specific UL83 phosphoprotein (pp65) and UL123 immediate-early protein (IEp72) in lytically infected human embryo fibroblasts was studied by means of indirect immunofluorescence and confocal microscopy. Both proteins were found to have a nuclear localization, but they were concentrated in different compartments within the nuclei. The pp65 was located predominantly in the nucleoli; this was already evident with the parental viral protein, which was targeted to the above nuclear compartment very soon after infection. The nucleolar localization of pp65 was also observed at later stages of the HCMV infectious cycle. After chromatin extraction (in the so-called in situ nuclear matrices), a significant portion of the pp65 remained associated with nucleoli within the first hour after infection, then gradually redistributed in a perinucleolar area, as well as throughout the nucleus, with a granular pattern. A quite different distribution was observed for IEp72 at very early stages after infection of human embryo fibroblasts with HCMV; indeed, this viral protein was found in bright foci, clearly observable in both non-extracted nuclei and in nuclear matrices. At later stages of infection, IEp72 became almost homogeneously distributed within the whole nucleus, while the foci increased in size and were more evenly spread; in several infected cells some of them lay within nucleoli. This peculiar nuclear distribution of IEp72 was preserved in nuclear matrices as well. The entire set of data is discussed in terms of the necessity of integration for HCMV-specific products into the pre-existing nuclear architecture, with the possibility of subsequent adaptation of nuclear compartments to fit the needs of the HCMV replicative cycle.

Human Cytomegalovirus pUL83 Stimulates Activity of the Viral Immediate-Early Promoter through Its Interaction with the Cellular IFI16 Protein

“…Consistent with previous reports of their separate localizations (3,4,27), immunofluorescent analysis revealed that IFI16 and pUL83 were colocalized within the nucleus and nucleolus in infected cells at 48 hpi following infection at a low multiplicity of infection (Fig. 5A).…”

Cytomegalovirus Immediate-Early Proteins Promote Stemness Properties in Glioblastoma

“…CPMC-041 tissue was processed to generate subcellular fractions; we found IE expressed in the nuclear and cytoplasmic compartments (Figure 1F), which is a pattern distinct from that described in lytic infection of fibroblasts (23). Freshly isolated, CD133+ cells from the same tissue sample (CPMC-041) were grown as neurospheres and processed by double immunofluorescence.…”

Dynamic and Nucleolin-Dependent Localization of Human Cytomegalovirus UL84 to the Periphery of Viral Replication Compartments and Nucleoli

“…How this occurs is unclear, but a direct interaction with nucleolin would provide a simple explanation. Alternatively, it has been reported that several viral proteins, including pp65, can localize to the nucleolus during infection (32)(33)(34)(35). UL84 and pp65 have been reported to interact within the infected cell (16), and thus, pp65 may recruit UL84 to the nucleolus or vice versa, or other viral or cellular factors may be involved.…”