Abstract
Promyelocytic leukemia nuclear bodies, also termed nuclear domain 10 (ND10), have emerged as nuclear protein accumulations mediating an intrinsic cellular defense against viral infections via chromatin-based mechanisms, however, their contribution to the control of herpesviral latency is still controversial. In this study, we utilized the monocytic cell line THP-1 as an in vitro latency model for human cytomegalovirus infection (HCMV). Characterization of THP-1 cells by immunofluorescence and Western blot analysis confirmed the expression of all major ND10 components. THP-1 cells with a stable, individual knockdown of PML, hDaxx or Sp100 were generated. Importantly, depletion of the major ND10 proteins did not prevent the terminal cellular differentiation of THP-1 monocytes. After construction of a recombinant, endotheliotropic human cytomegalovirus expressing IE2-EYFP, we investigated whether the depletion of ND10 proteins affects the onset of viral IE gene expression. While after infection of differentiated, THP-1-derived macrophages as well as during differentiation-induced reactivation from latency an increase in the number of IE-expressing cells was readily detectable in the absence of the major ND10 proteins, no effect was observed in non-differentiated monocytes. We conclude that PML, hDaxx and Sp100 primarily act as cellular restriction factors during lytic HCMV replication and during the dynamic process of reactivation but do not serve as key determinants for the establishment of HCMV latency.
Highlights
Herpesviral latency is defined as a stage in which the viral genome exists as an episome within the nucleoplasm in the absence of lytic gene expression and production of infectious virus [1]
In order to assess if the major nuclear domain 10 (ND10) factors PML, Sp100 and hDaxx are involved in the regulation of the human cytomegalovirus infection (HCMV) major IE promoter (MIEP) in undifferentiated THP-1 monocytes, we wished to analyze HCMV replication in the absence of individual ND10 proteins by generating cells with a stable knockdown of these factors
Previous studies have demonstrated that the ND10-mediated transcriptional repression of HCMV
Summary
Herpesviral latency is defined as a stage in which the viral genome exists as an episome within the nucleoplasm in the absence of lytic gene expression and production of infectious virus [1]. As shown for CD34+ cells, the heterochromatin protein-1 (HP-1) was found to be associated with the MIEP and tri-methylation of histone H3 (lysine 9 and 27) as well as the absence of histone acetylation on histone H4 could be detected, representing a typical repressive chromatin phenotype [8]. This chromatin phenotype is maintained in the monocytes derived from precursor cells [9]. Upon further cellular differentiation robust IE gene expression can be detected allowing for reactivation of infectious virus [10]
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