Virology & Immunology

Ph.D.
Peking Union Medical College (PUMC) & Chinese Academy of Medical Sciences (CAMS)
1997

RESEARCH ACCOMPLISHMENTS-early interactions of virus-hostI have long been fascinated by the interactions between host cells and viruses and by the mechanisms that lead to successful or abortive viral infections. The input genomes of DNA viruses such as papovavirus, adenovirus, and herpes virus can reside anywhere within the nucleus of their hosts, but only those viruses present at promyelocytic leukemia (PML) bodies (also called ND10, or POD) can form transcription foci. The interactions of virus and host cells occur at any different levels including gene regulation, gene splicing regulation and viral DNA replication. My accomplishments in this area are summarized as following. 1. Targeting viral DNA transcription at ND10I studied the factors that determine DNA virus transcription foci formation at ND10 (also called PML oncogenic domain-POD, or PML body) and identified the smallest DNA fragment required and sufficient for SV40 to transcribe at ND10 (Tang Q et al., J. Virol. 2000; 74:9694–9700). The DNA fragment contained the origin of DNA replication and the target sequence for its DNA binding protein, T antigen. To investigate herpesvirus simplex virus (HSV)-1, a large DNA virus, I developed and used the amplicon that contains the HSV-1 origin of DNA replication and a reporter gene to determine the fewest HSV-1 components necessary to localize transcriptionally active DNA to ND10 (Tang Q et al., J. Virol. 2003; 77:5821–5828). However, it has not been determined whether ND10 are the loci favoring viral gene expression. 2. Paradoxical effect of ND10 on viral DNA replicationCytomegalovirus (CMV) transcribes its immediate-early (IE) genes at ND10 (J. Virol. 2003; 77:1357–1367). Since ND10s are comprised of cellular repressors such as PML, SP100, and Daxx, it is easily conceivable that they serve as defense against viral infection. However, this apparently contradicts the fact that only those viral genomes that reside at ND10 appear to transcribe. Setting out from earlier reports that immediate-early protein 1 (IE1) co-localizes with and disperses ND10, I decided to study the interactions between mouse CMV IE1 and ND10 proteins. Finding that IE1 on its own can interact with PML and Daxx was not surprising, but the function of the interaction remains unclear and of interest to me for future studies. The lack of an assay for their activities makes it difficult to elucidate the functions of PML and Daxx. 3. Viral protein-host protein interaction during the immediate-early stageDuring my investigations, I found that CMV IE1 interacts with and reduces the activity of HDAC, a histone deacytelation enzyme (J. Virol. 2003; 77:1357–67). As reported in many publications, chromatin is inactive when deacetylated and activated when acetylated (acetylation and deacetylation are the most important regulators of gene expression in cells). We also observed remodeling and chromatinization of cytomegaloviral DNA after infection in host cells. Moreover, I found that trichostatin A (TSA), an HDAC inhibitor, can rescue IE1 function lost in IE1-deleted mutant virus. Recently, through mutagenesis studies, I identified the minimum length of IE1 peptide that can interact with HDAC and reduce its activity. This work will establish the basis for interference attempts with the viral protein. 4. Functionally interaction of IE3 and E1 (112/113)Both the human CMV immediate-early protein 2 (HCMV-IE2) and its mouse homologue (MCMV-IE3) permit progression of viral transcription, interact with several cellular transcription factors, and activate many viral genes, but they also represses their own promoter. IE3 isan activator of early proteins.If IE3’s repression of its own promoter were to remain unblocked, viral replication would be retarded, and we would not be able to explain why the transcription site of the viral genome is the same site as the greatest accumulation of IE3. Therefore, a factor should exist that can block IE3’s repression of the major immediate-early promoter (MIEP). In MCMV, I found such a factor, the 112/113 gene products (J. Virol. 2005; 79:256–263). Protein interaction most likely occurs between IE3 and the 87-kd spliced form of M112/113, as only the 87-kd component coimmunoprecipitated with IE3. The complex also includes PML. Coexpression of M112/113 products and IE3 results in segregation of IE3 into newly formed M112/113-based domains. Importantly, the complex eliminates the IE3-based repressive effect on MIEP, as determined by MIEP-driven reporter assays. These findings establish a new feedback mechanism between IE and early proteins, a new mechanism of promoter control via segregation of the repressor, and a new function for proteins from the M112/113 locus.  5. Productive MCMV infection in human cells with help of HCMV IE1I examined the molecular basis of the species specificity of CMV in an effort to define conditions under which MCMV can replicate successfully in human cells (J. Virol. 2006; 80:7510-21).Using MCMV producing GFP for in vivo imaging, we did not find localized spread of secondary infection in human fibroblasts. Moreover, viral DNA was degraded, and no apparent loss of infected human fibroblasts was observed. In MCMV-infected human fibroblasts, unlike in mouse cells, histone deacetylase-2 (HDAC2) and MCMV IE1 are segregated into the MCMV replication compartments. These observations suggest that MCMV IE1 functions differently in human cells than in mouse cells. To test whether the HCMV IE1 can restore potentially blocked MCMV progression in human cells, we infected HCMV IE1 expressing human cells with MCMV and found substantial infectious particle formation. This indicates no inherent block exists in the basic transcription, replication, or packaging machinery. In fact, analysis of MCMV microarrays (J. Virol. 2006; 80:6873-82)from normal and HCMV IE1 expressing human fibroblasts revealed 30 more MCMV genes expressed in the HCMV IE1-expressing cells than in the normal human fibroblasts, several of which were late genes. In addition, capsid mRNA was present at relatively low levels, which potentially hinders virus production. HCMV tegument proteins supplied during MCMV infection of human cells promoted infectious MCMV particle production.  6. Gene splicing regulation of HCMV( J. Virol. 2009) The most abundant IE gene, major IE (MIE) gene pre-mRNA, needs to be spliced before being exported to the cytoplasm for translation. In this study, we, for the first time, investigated the regulation of MIE gene splicing. In so doing, we found that polypyrimidine tract-binding proteins (PTBs) strongly repressed MIE gene production in cotransfection assays. In addition, we discovered that the repressive effects of PTB can be rescued by splicing factor U2AF. In intron-deletion mutation assays and RNA detection experiments (RT-PCR and real-time RT-PCR), we further observed that PTBs target all the introns of the MIE gene, especially intron 2, and affect gene splicing, which was reflected by the variation of the ratio of pre-mRNA to mRNA. Using transfection assays, we demonstrated that PTB-knockdown cells induce a higher degree of MIE gene-splicing/expression. Consistently, HCMV can produce more viral proteins and viral particles in PTB-knockdown cells after infection. We conclude that PTB inhibits HCMV replication by interfering with MIE gene splicing through competing with U2AF for binding to the polypyrimidine tract in MIE gene introns. We expect the outcome of this innovative study can be expanded to other viruses so that we can target the viral gene splicing for development of therapeutic drugs. 7. Murine cytomegalovirus IE3 recruits cellular and viral proteins into pre- and replication domains through protein-protein interactions(Martinez et al., J. Gen. Virol. 2010)Murine cytomegalovirus (MCMV) IE3 (a homolog of human CMV IE2) is a phosphorylated nuclear protein and essential for successful viral infection. To study IE3 gene expression and subnuclear distribution, IE3 function, and its interaction with cellular and other viral proteins, we developed MCMVs with GFP-fused IE3 gene using Seamless BAC techniques. The generated viruses included MCMVIE3gfp, in which IE1 was completely removed by in framefusion of exons 3 and 5 which C-terminus was tagged with GFP, and MCMVIE111gfp, in which IE1 was kept intact and GFP was in framefused with C-terminus of IE3. We confirmed by transfection or co-transfection assay that functions of GFP-tagged IE3 remained unchanged in terms of activating E1 promoter and localizing beside PML body. By application of immunofluorescence techniques to MCMVIE3gfp, we revealed the distribution of IE3 and its interaction with viral and cellular proteins, especially proteins pertaining to DNA replication (M44 and E1) and cellular intrinsic defense (PML and HDACs). DNA Fluorescent in situ hybridization(FISH) assay showed that IE3-domains are related to DNA replication. The GFP-fused IE3 can be used to show kinetic formation of viral DNA replication domains. The results also suggested that IE3 might be a key protein to set up pre-replication domains through recruiting viral and cellular proteins for viral DNA replication, and segregate cellular defensive proteins in order to provide the most favorable environment for viral gene expression, viral DNA replication, and, consequently, viral production.  8.Functional Interaction of Nuclear Domain 10 and Its Components with Cytomegalovirus after Infections: Cross-Species Host Cells versus Native Cells. (PlosOne 2011)Species-specificity is one of the major characteristics of cytomegaloviruses (CMVs) and is the primary reason for the lack of a mouse model for the direct infection of human CMV (HCMV). It has been determined that CMV cross-species infections are blocked at the post-entry level by intrinsic cellular defense mechanisms, but few details are known. It is important to explore how CMVs interact with the subnuclear structure of the cross-species host cell. In our present study, we discovered that nuclear domain 10 (ND10) of human cells was not disrupted by murine CMV (MCMV) and that the ND10 of mouse cells was not disrupted by HCMV, although the ND10-disrupting protein, immediate-early protein 1 (IE1), also colocalized with ND10 in cross-species infections. In addition, we found that the UL131-repaired HCMV strain AD169 (vDW215-BADrUL131) can infect mouse cells to produce immediate-early (IE) and early (E) proteins but that neither DNA replication nor viral particles were detectable in mouse cells. Unrepaired AD169 can express IE1 only in mouse cells. In both HCMV-infected mouse cells and MCMV-infected human cells, the knocking-down of ND10 components (PML, Daxx, and SP100) resulted in significantly increased viral-protein production. Our observations provide evidence to support our hypothesis that ND10 and ND10 components might be important defensive factors against the CMV cross-species infection. 9. H2B Homology Region of Major Immediate-Early (MIE) Protein 1 (IE1) Is Essential for Murine Cytomegalovirus to Disrupt Nuclear Domain 10 (ND10), but Not Important for Viral Replication in Cell Culture. (J. General Virol. 2011)Cytomegalovirus (CMV) major immediate-early protein 1 (IE1) has multiple functions and is important for efficient viral infection. As does its counterpart in human CMV, murine CMV (MCMV) IE1 also functions as a disruptor of mouse cell ND10 (nuclear domain 10), where many different gene-regulation proteins congregate. It still remains unclear how MCMV IE1 disperses ND10 and whether this dispersion could have any effect on viral replication. MCMV IE1 has 595 amino acids and multiple functional domains that have not yet been fully analyzed. In this study, we dissected the IE1 molecule by truncation/deletion and found that the H2B homology domain (amino acid sequence NDIFERI) is required for the dispersion of ND10 by IE1. Furthermore, we made additional deletions and point mutations and found that the minimal truncation in the H2B homology domain required for IE1's losing the ability to disperse ND10 is just three amino acids (IFE). Surprisingly, the mutated IE1 still interacted with PML and colocalized with ND10 but failed to disperse ND10. This suggests that binding to ND10 key protein is essential to but not sufficient for the dispersal of ND10 and that some other unknown mechanism must be involved in this biological procedure. Finally, we generated MCMV with IFE-deleted IE1 (MCMVdlIFE) and its revertant (MCMVIFERQ). Although the MCMVdlIFE lost the ability to disperse ND10, plaque assays and viral gene production assays showed that the deletion of IFE did not increase viral replication in cell culture.  10. KSHV K-bZIP protein interacts with HDAC2 via its leucine zipper domain. (submitted to JBC).Kaposi’s sarcoma-associated herpesvrius (KSHV or human herpesvirus-8, HHV-8) encoded protein called K-bZIP (also named K8) was found to be multi-functional. Its roles in KSHV replication during infection or reactivation have been uncertain, but more and more evidences support that it is essential for viral lytic replication and hence viral pathogenesis. Interactions of K-bZIP with other KSHV-encoded proteins have been widely studied, but whether and how K-bZIP has any effects on important KSHV gene promoters (such as ORF50 and OriLyt) remains to be confirmed. In our recent studies, we discovered that K-bZIP interacts with HDAC1/2 (not HDAC3) in 12-O-tetradecanoylphorbol-13-acetate (TPA) stimulated body cavity-based lymphocytes (BCBL-1) cells, which interaction might be crucial for HDAC1/2 to present in viral DNA replication domains. Then, we further dissected the domains of K-bZIP and found that the leucine zipper domain is essential for K-bZIP to interact with HDAC2. We found that the interaction was independent of SUMOylation because the mutated K-bZIP unable to be SUOMOylated can still interact with HDAC2. We also provided evidence that the interaction of K-bZIP with HDAC is important for K-bZIP to inhibit KSHV’s lytic gene promoters (ORF50, ORF59 and Ori-Lytic). Our results suggested that K-bZIP might be a regulator of KSHV gene expression through interacting with HDAC. 11. Evidence of inability of human cytomegalovirus to reactivate Kaposi's sarcoma-associated herpesvirus from latency in body cavity-based lymphocytes. (J. Clin. Virol, 2009)Kaposi's sarcoma-associated herpesvirus (KSHV; also known as human herpesvirus 8 (HHV-8)) has been determined to be the most frequent cause of malignancies in AIDS patients. It is associated primarily with Kaposi's sarcoma (KS) and primary effusion lymphoma (PEL), as well as with multicentric Castleman's disease (MCD).(2) The switch from the latent to the lytic stage is important in the maintenance of malignancy and viral infection. So far, the mechanism of its reactivation has not been fully understood.Human cytomegalovirus (HCMV) and KSHV might infect the same cells, and it was found by other groups that several viruses could reactivate KSHV from latency. We investigate whether HCMV infection could reactivate KSHV from latency in body cavity-based lymphocyte (BCBL-1) cells. STUDY DESIGN AND RESULTS: Laboratory strains of HCMV cannot infect B cells. In this article, we demonstrate that the UL131-repaired HCMV (vDW215-BADrUL131) derived from AD169 strain is able to infect B lymphocytes. We directly infected KSHV latent cells including BCBL-1 with vDW215-BADrUL131 to evaluate the ability of HCMV to reactivate KSHV. Inconsistent with previous reports in human fibroblast cells, our results provide direct evidence that HCMV is unable to reactivate KSHV from latency-to-lytic infection in BCBL-1 cell lines. As a control, herpes simplex virus type 1 (HSV-1) was shown to be able to reactivate KSHV.Our observations, different from others, suggest that reactivation mechanisms for KSHV might vary in different cells.