The LHX2-OTX2 transcriptional regulatory module controls retinal pigmented epithelium differentiation and underlies genetic risk for age-related macular degeneration.

Tissue-specific transcription factors (TFs) control the transcriptome through an association with noncoding regulatory regions (cistromes). Identifying the combination of TFs that dictate specific cell fate, their specific cistromes and examining their involvement in complex human traits remain a major challenge. Here, we focus on the retinal pigmented epithelium (RPE), an essential lineage for retinal development and function and the primary tissue affected in age-related macular degeneration (AMD), a leading cause of blindness. By combining mechanistic findings in stem-cell-derived human RPE, in vivo functional studies in mice and global transcriptomic and proteomic analyses, we revealed that the key developmental TFs LHX2 and OTX2 function together in transcriptional module containing LDB1 and SWI/SNF (BAF) to regulate the RPE transcriptome. Importantly, the intersection between the identified LHX2-OTX2 cistrome with published expression quantitative trait loci, ATAC-seq data from human RPE, and AMD genome-wide association study (GWAS) data, followed by functional validation using a reporter assay, revealed a causal genetic variant that affects AMD risk by altering TRPM1 expression in the RPE through modulation of LHX2 transcriptional activity on its promoter. Taken together, the reported cistrome of LHX2 and OTX2, the identified downstream genes and interacting co-factors reveal the RPE transcription module and uncover a causal regulatory risk single-nucleotide polymorphism (SNP) in the multifactorial common blinding disease AMD.

KSHV genome harbors both constitutive and lytically induced enhancers.

Kaposi's sarcoma-associated herpesvirus (KSHV) belongs to the gamma-herpesvirus family and is a well-known human oncogenic virus. In infected cells, the viral genome of 165 kbp is circular DNA wrapped in chromatin. The tight control of gene expression is critical for latency, the transition into the lytic phase, and the development of viral-associated malignancies. Distal cis-regulatory elements, such as enhancers and silencers, can regulate gene expression in a position- and orientation-independent manner. Open chromatin is another characteristic feature of enhancers. To systematically search for enhancers, we cloned all the open chromatin regions in the KSHV genome downstream of the luciferase gene and tested their enhancer activity in infected and uninfected cells. A silencer was detected upstream of the latency-associated nuclear antigen promoter. Two constitutive enhancers were identified in the K12p-OriLyt-R and ORF29 Intron regions, where ORF29 Intron is a tissue-specific enhancer. The following promoters: OriLyt-L, PANp, ALTp, and the terminal repeats (TRs) acted as lytically induced enhancers. The expression of the replication and transcription activator (RTA), the master regulator of the lytic cycle, was sufficient to induce the activity of lytic enhancers in uninfected cells. We propose that the TRs that span about 24 kbp region serve as a "viral super-enhancer" that integrates the repressive effect of the latency-associated nuclear antigen (LANA) with the activating effect of RTA. Utilizing CRISPR activation and interference techniques, we determined the connections between these enhancers and their regulated genes. The silencer and enhancers described here provide an additional layer to the complex gene regulation of herpesviruses.IMPORTANCEIn this study, we performed a systematic functional assay to identify cis-regulatory elements within the genome of the oncogenic herpesvirus, Kaposi's sarcoma-associated herpesvirus (KSHV). Similar to other herpesviruses, KSHV presents both latent and lytic phases. Therefore, our assays were performed in uninfected cells, during latent infection, and under lytic conditions. We identified two constitutive enhancers, one of which seems to be a tissue-specific enhancer. In addition, four lytically induced enhancers, which are all responsive to the replication and transcription activator (RTA), were identified. Furthermore, a silencer was identified between the major latency promoter and the lytic gene locus. Utilizing CRISPR activation and interference techniques, we determined the connections between these enhancers and their regulated genes. The terminal repeats, spanning a region of about 24 kbp, seem like a "viral super-enhancer" that integrates the repressive effect of the latency-associated nuclear antigen (LANA) with the activating effect of RTA to regulate latency to lytic transition.

Abortive herpes simplex virus infection of nonneuronal cells results in quiescent viral genomes that can reactivate.

Abortive viral infections are usually studied in populations of susceptible but nonpermissive cells. Single-cell studies of viral infections have demonstrated that even in susceptible and permissive cell populations, abortive infections can be detected in subpopulations of the infected cells. We have previously identified abortive infections in HeLa cells infected with herpes simplex virus 1 (HSV-1) at high multiplicity of infection (MOI). Here, we tested 4 additional human-derived nonneuronal cell lines (cancerous or immortalized) and found significant subpopulations that remain abortive. To characterize these abortive cells, we recovered cell populations that survived infection with HSV-1 at high MOI. The surviving cells retained proliferative potential and the ability to be reinfected. These recovered cell populations maintained the viral genomes in a quiescent state for at least 5 wk postinfection. Our results indicate that these viral genomes are maintained inside the nucleus, bound to cellular histones and occasionally reactivated to produce new progeny viruses. We conclude that abortive HSV-1 infection is a common feature during infection of nonneuronal cells and results in a latency-like state in the infected cells. Our findings question the longstanding paradigm that alphaherpesviruses can establish spontaneous latency only in neuronal cells and emphasize the stochastic nature of lytic versus latency decision of HSV-1 in nonneuronal cells.

High-throughput sequencing analysis of a "hit and run" cell and animal model of KSHV tumorigenesis.

Kaposi's sarcoma (KS), is an AIDS-associated neoplasm caused by the KS herpesvirus (KSHV/ HHV-8). KSHV-induced sarcomagenesis is the consequence of oncogenic viral gene expression as well as host genetic and epigenetic alterations. Although KSHV is found in all KS-lesions, the percentage of KSHV-infected (LANA+) spindle-cells of the lesion is variable, suggesting the existence of KS-spindle cells that have lost KSHV and proliferate autonomously or via paracrine mechanisms. A mouse model of KSHVBac36-driven tumorigenesis allowed us to induce KSHV-episome loss before and after tumor development. Although infected cells that lose the KSHV-episome prior to tumor formation lose their tumorigenicity, explanted tumor cells that lost the KSHV-episome remained tumorigenic. This pointed to the existence of virally-induced irreversible oncogenic alterations occurring during KSHV tumorigenesis supporting the possibility of hit and run viral-sarcomagenesis. RNA-sequencing and CpG-methylation analysis were performed on KSHV-positive and KSHV-negative tumors that developed following KSHV-episome loss from explanted tumor cells. When KSHV-positive cells form KSHV-driven tumors, along with viral-gene upregulation there is a tendency for hypo-methylation in genes from oncogenic and differentiation pathways. In contrast, KSHV-negative tumors formed after KSHV-episome loss, show a tendency towards gene hyper-methylation when compared to KSHV-positive tumors. Regarding occurrence of host-mutations, we found the same set of innate-immunity related mutations undetected in KSHV-infected cells but present in all KSHV-positive tumors occurring en exactly the same position, indicating that pre-existing host mutations that provide an in vivo growth advantage are clonally-selected and contribute to KSHV-tumorigenesis. In addition, KSHV-negative tumors display de novo mutations related to cell proliferation that, together with the PDGFRAD842V and other proposed mechanism, could be responsible for driving tumorigenesis in the absence of KSHV-episomes. KSHV-induced irreversible genetic and epigenetic oncogenic alterations support the possibility of "hit and run" KSHV-sarcomagenesis and point to the existence of selectable KSHV-induced host mutations that may impact AIDS-KS treatment.

Kaposi's Sarcoma-Associated Herpesvirus LANA Modulates the Stability of the E3 Ubiquitin Ligase RLIM.

The Kaposi's sarcoma-associated herpesvirus (KSHV)-encoded latency-associated nuclear antigen (LANA) protein functions in latently infected cells as an essential participant in KSHV genome replication and as a driver of dysregulated cell growth. In a previous study, we have identified LANA-interacting proteins using a protein array screen. Here, we explore the effect of LANA on the stability and activity of RLIM (RING finger LIM-domain-interacting protein, encoded by the RNF12 gene), a novel LANA-interacting protein identified in that protein screen. RLIM is an E3 ubiquitin ligase that leads to the ubiquitination and degradation of several transcription regulators, such as LMO2, LMO4, LHX2, LHX3, LDB1, and the telomeric protein TRF1. Expression of LANA leads to downregulation of RLIM protein levels. This LANA-mediated RLIM degradation is blocked in the presence of the proteasome inhibitor, MG132. Therefore, the interaction between LANA and RLIM could be detected in coimmunoprecipitation assay only in the presence of MG132 to prevent RLIM degradation. A RING finger mutant RLIM is resistant to LANA-mediated degradation, suggesting that LANA promotes RLIM autoubiquitination. Interestingly, we found that LANA enhanced the degradation of some RLIM substrates, such as LDB1 and LMO2, and prevented RLIM-mediated degradation of others, such as LHX3 and TRF1. We also show that transcription regulation by RLIM substrates is modulated by LANA. RLIM substrates are assembled into multiprotein transcription regulator complexes that regulate the expression of many cellular genes. Therefore, our study identified another way KSHV can modulate cellular gene expression.IMPORTANCE E3 ubiquitin ligases mark their substrates for degradation and therefore control the cellular abundance of their substrates. RLIM is an E3 ubiquitin ligase that leads to the ubiquitination and degradation of several transcription regulators, such as LMO2, LMO4, LHX2, LHX3, LDB1, and the telomeric protein TRF1. Here, we show that the Kaposi's sarcoma-associated herpesvirus (KSHV)-encoded LANA protein enhances the ubiquitin ligase activity of RLIM, leading to enhanced RLIM autoubiquitination and degradation. Interestingly, LANA enhanced the degradation of some RLIM substrates, such as LDB1 and LMO2, and prevented RLIM-mediated degradation of others, such as LHX3 and TRF1. In agreement with protein stability of RLIM substrates, we found that LANA modulates transcription by LHX3-LDB1 complex and suggest additional ways LANA can modulate cellular gene expression. Our study adds another way a viral protein can regulate cellular protein stability, by enhancing the autoubiquitination and degradation of an E3 ubiquitin ligase.

Latently KSHV-Infected Cells Promote Further Establishment of Latency upon Superinfection with KSHV.

Kaposi's sarcoma-associated herpesvirus (KSHV) is a cancer-related virus which engages in two forms of infection: latent and lytic. Latent infection allows the virus to establish long-term persistent infection, whereas the lytic cycle is needed for the maintenance of the viral reservoir and for virus spread. By using recombinant KSHV viruses encoding mNeonGreen and mCherry fluorescent proteins, we show that various cell types that are latently-infected with KSHV can be superinfected, and that the new incoming viruses establish latent infection. Moreover, we show that latency establishment is enhanced in superinfected cells compared to primary infected ones. Further analysis revealed that cells that ectopically express the major latency protein of KSHV, LANA-1, prior to and during infection exhibit enhanced establishment of latency, but not cells expressing LANA-1 fragments. This observation supports the notion that the expression level of LANA-1 following infection determines the efficiency of latency establishment and avoids loss of viral genomes. These findings imply that a host can be infected with more than a single viral genome and that superinfection may support the maintenance of long-term latency.

Modulation of Cellular CpG DNA Methylation by Kaposi's Sarcoma-Associated Herpesvirus.

Kaposi's sarcoma-associated herpesvirus (KSHV, HHV-8) is a gammaherpesvirus associated with several human malignancies. DNA methylation at CpG dinucleotides is an epigenetic mark dysregulated in many cancer types and in KSHV-infected cells. Several previous studies have analyzed in detail the CpG methylation of the KSHV episomal genomes, but little is known about the impact of KSHV on the human genome. Our knowledge of cellular CpG methylation in the context of KSHV infection is currently limited to four hypermethylated human gene promoters. Therefore, we undertook a comprehensive CpG methylation analysis of the human methylome in KSHV-infected cells and KSHV-associated primary effusion lymphoma (PEL). We performed Infinium HumanMethylation450K and MethylationEpic BeadChip arrays and identified panels of hyper- and hypomethylated cellular promoters in KSHV-infected cells. We combined our genome-wide methylation analysis with high-throughput RNA sequencing (RNA-seq) to add functional outcomes to the virally induced methylation changes. We were able to correlate many downregulated genes with promoter hypermethylation and upregulated genes with hypomethylation. In addition, we show that treating the cells with a demethylating agent leads to reexpression of these downregulated genes, indicating that, indeed, DNA methylation plays a role in the repression of these human genes. Comparison between de novo infection and PEL suggests that the virus induces initial hypermethylation followed by a slow increase in genome-wide hypomethylation. This study extends our understanding of the relationship between epigenetic changes induced by KSHV infection and tumorigenesis.IMPORTANCE In cancer cells, certain promoters become aberrantly methylated, contributing to the phenotype of the tumor. KSHV infection seems to modify cellular CpG methylation, but only a few methylated promoters have been identified in KSHV-infected cells. Here, we investigated the CpG methylation of the human genome in KSHV-associated primary effusion lymphoma (PEL) and KSHV-infected cells. We have identified many hyper- and hypomethylated gene promoters and correlated their methylation with cellular gene expression. These differentially methylated cellular promoters can distinguish KSHV-positive cells from uninfected cells and may serve as the foundation for the use of these differentially methylated regions as potential biomarkers for KSHV-associated malignancies. Drugs that reverse these cancerous methylation patterns have the potential to inhibit tumor growth. Here, we show that treating PEL cells with a demethylating drug (5-aza-2'-deoxycytidine) led to inhibition of cell growth, raising the possibility of testing this drug for the treatment of PEL.

Phosphorylation of the chromatin binding domain of KSHV LANA.

The Kaposi sarcoma associated herpesvirus (KSHV) latency associated nuclear antigen (LANA) is expressed in all KSHV associated malignancies and is essential for maintenance of KSHV genomes in infected cells. To identify kinases that are potentially capable of modifying LANA, in vitro phosphorylation assays were performed using an Epstein Barr virus plus LANA protein microarray and 268 human kinases purified in active form from yeast. Interestingly, of the Epstein-Barr virus proteins on the array, the EBNA1 protein had the most similar kinase profile to LANA. We focused on nuclear kinases and on the N-terminus of LANA (amino acids 1-329) that contains the LANA chromatin binding domain. Sixty-three nuclear kinases phosphorylated the LANA N-terminus. Twenty-four nuclear kinases phosphorylated a peptide covering the LANA chromatin binding domain (amino acids 3-21). Alanine mutations of serine 10 and threonine 14 abolish or severely diminish chromatin and histone binding by LANA. However, conversion of these residues to the phosphomimetic glutamic acid restored histone binding suggesting that phosphorylation of serine 10 and threonine 14 may modulate LANA function. Serine 10 and threonine 14 were validated as substrates of casein kinase 1, PIM1, GSK-3 and RSK3 kinases. Short-term treatment of transfected cells with inhibitors of these kinases found that only RSK inhibition reduced LANA interaction with endogenous histone H2B. Extended treatment of PEL cell cultures with RSK inhibitor caused a decrease in LANA protein levels associated with p21 induction and a loss of PEL cell viability. The data indicate that RSK phosphorylation affects both LANA accumulation and function.

A protein array screen for Kaposi's sarcoma-associated herpesvirus LANA interactors links LANA to TIP60, PP2A activity, and telomere shortening.

The Kaposi's sarcoma-associated herpesvirus (KSHV) LANA protein functions in latently infected cells as an essential participant in KSHV genome replication and as a driver of dysregulated cell growth. To identify novel LANA protein-cell protein interactions that could contribute to these activities, we performed a proteomic screen in which purified, adenovirus-expressed Flag-LANA protein was incubated with an array displaying 4,192 nonredundant human proteins. Sixty-one interacting cell proteins were consistently detected. LANA interactions with high-mobility group AT-hook 1 (HMGA1), HMGB1, telomeric repeat binding factor 1 (TRF1), xeroderma pigmentosum complementation group A (XPA), pygopus homolog 2 (PYGO2), protein phosphatase 2A (PP2A)B subunit, Tat-interactive protein 60 (TIP60), replication protein A1 (RPA1), and RPA2 proteins were confirmed in coimmunoprecipitation assays. LANA-associated TIP60 retained acetyltransferase activity and, unlike human papillomavirus E6 and HIV-1 TAT proteins, LANA did not reduce TIP60 stability. The LANA-bound PP2A B subunit was associated with the PP2A A subunit but not the catalytic C subunit, suggesting a disruption of PP2A phosphatase activity. This is reminiscent of the role of simian virus 40 (SV40) small t antigen. Chromatin immunoprecipitation (ChIP) assays showed binding of RPA1 and RPA2 to the KSHV terminal repeats. Interestingly, LANA expression ablated RPA1 and RPA2 binding to the cell telomeric repeats. In U2OS cells that rely on the alternative mechanism for telomere maintenance, LANA expression had minimal effect on telomere length. However, LANA expression in telomerase immortalized endothelial cells resulted in telomere shortening. In KSHV-infected cells, telomere shortening may be one more mechanism by which LANA contributes to the development of malignancy.

Bortezomib induction of C/EBPß mediates Epstein-Barr virus lytic activation in Burkitt lymphoma.

Epstein-Barr virus (EBV) is associated with a variety of lymphoid malignancies. Bortezomib activates EBV lytic gene expression. Bortezomib, a proteasome inhibitor, leads to increased levels of CCAAT/enhancer-binding proteinß (C/EBPß) in a variety of tumor cell lines. C/EBPß activates the promoter of the EBV lytic switch gene ZTA. Bortezomib treatment leads to increased binding of C/EBP to previously recognized binding sites in the ZTA promoter. Knockdown of C/EBPß inhibits bortezomib activation of EBV lytic gene expression. Bortezomib also induces the unfolded protein response (UPR), as evidenced by increases in ATF4, CHOP10, and XBP1s and cleavage of ATF6. Thapsigargin, an inducer of the UPR that does not interfere with proteasome function, also induces EBV lytic gene expression. The effects of thapsigargin on EBV lytic gene expression are also inhibited by C/EBPß knock-down. Therefore, C/EBPß mediates the activation of EBV lytic gene expression associated with bortezomib and another UPR inducer.

CpG methylation as a tool to characterize cell-free Kaposi sarcoma herpesvirus DNA.

We studied the presence of Kaposi sarcoma herpesvirus sequences in cell-free DNA (cfDNA) isolated from the blood of patients with AIDS-related Kaposi sarcoma (KS) and primary effusion lymphoma (PEL). The use of paramagnetic beads linked to methyl-CpG binding domain protein allowed separation of virion and cell-derived DNA. Only virion DNA was detected in the blood of KS patients, whereas cell-derived DNA was detected in a patient with AIDS-related PEL. The difference in the origins of cfDNA in these settings may in part reflect very different proliferative indices in KS and PEL tumor tissue.

Human cytomegalovirus inhibition by cardiac glycosides: evidence for involvement of the HERG gene.

Infection with human cytomegalovirus (HCMV) continues to be a major threat for pregnant women and the immunocompromised population. Although several anti-HCMV therapies are available, the development of new anti-HCMV agents is highly desired. There is growing interest in identifying compounds that might inhibit HCMV by modulating the cellular milieu. Interest in cardiac glycosides (CG), used in patients with congestive heart failure, has increased because of their established anticancer and their suggested antiviral activities. We report that the several CG--digoxin, digitoxin, and ouabain--are potent inhibitors of HCMV at nM concentrations. HCMV inhibition occurred prior to DNA replication, but following binding to its cellular receptors. The levels of immediate early, early, and late viral proteins and cellular NF-κB were significantly reduced in CG-treated cells. The activity of CG in infected cells correlated with the expression of the potassium channel gene, hERG. CMV infection upregulated hERG, whereas CG significantly downregulated its expression. Infection with mouse CMV upregulated mouse ERG (mERG), but treatment with CG did not inhibit virus replication or mERG transcription. These findings suggest that CG may inhibit HCMV by modulating human cellular targets associated with hERG and that these compounds should be studied for their antiviral activities.

De novo DNA methyltransferase DNMT3b interacts with NEDD8-modified proteins.

DNA methylation and histone modifications play an important role in transcription regulation. In cancer cells, many promoters become aberrantly methylated through the activity of the de novo DNA methyltransferases DNMT3a and DNMT3b and acquire repressive chromatin marks. NEDD8 is a ubiquitin-like protein modifier that is conjugated to target proteins, such as cullins, to regulate their activity, and cullin 4A (CUL4A) in its NEDD8-modified form is essential for repressive chromatin formation. We found that DNMT3b associates with NEDD8-modified proteins. Whereas DNMT3b interacts directly in vitro with NEDD8, conjugation of NEDD8 to target proteins enhances this interaction in vivo. DNMT3b immunoprecipitated two major bands of endogenously NEDDylated proteins at the size of NEDDylated cullins, and indeed DNMT3b interacted with CUL1, CUL2, CUL3, CUL4A, and CUL5. Moreover, DNMT3b preferentially immunoprecipitated the NEDDylated form of endogenous CUL4A. NEDD8 enhanced DNMT3b-dependent DNA methylation. Chromatin immunoprecipitation assays suggest that DNMT3b recruits CUL4A and NEDD8 to chromatin, whereas deletion of Dnmt3b reduces the association of CUL4A and NEDD8 at a repressed promoter in a cancer cell line.

High levels of LINE-1 transposable elements expressed in Kaposi's sarcoma-associated herpesvirus-related primary effusion lymphoma.

Kaposi's sarcoma-associated herpesvirus (KSHV, HHV-8) is a gamma herpesvirus associated with several human malignancies. Transposable elements (TEs) are ubiquitous in eukaryotic genomes, occupying about 45% of the human genome. TEs have been linked with a variety of disorders and malignancies, though the precise nature of their contribution to many of them has yet to be elucidated. Global transcriptome analysis for differentially expressed TEs in KSHV-associated primary effusion lymphoma (PEL) cells (BCBL1 and BC3) revealed large number of differentially expressed TEs. These differentially expressed TEs include LTR transposons, long interspersed nuclear elements (LINEs), and short interspersed nuclear elements (SINEs). Further analysis of LINE-1 (L1) elements revealed expression upregulation, hypo-methylation, and transition into open chromatin in PEL. In agreement with high L1 expression, PEL cells express ORF1 protein and possess high reverse transcriptase (RT)-activity. Interestingly, inhibition of this RT-activity suppressed PEL cell growth. Collectively, we identified high expression of TEs, and specifically of L1 as a critical component in the proliferation of PEL cells. This observation is relevant for the treatment of KSHV-associated malignancies since they often develop in AIDS patients that are treated with RT inhibitors with potent inhibition for both HIV and L1 RT activity.

Global CpG DNA Methylation Footprint in Kaposi's Sarcoma.

Kaposi's sarcoma-associated herpesvirus (KSHV), also familiar as human herpesvirus 8 (HHV-8), is one of the well-known human cancer-causing viruses. KSHV was originally discovered by its association with Kaposi's sarcoma (KS), a common AIDS-related neoplasia. Additionally, KSHV is associated with two B-lymphocyte disorders; primary effusion lymphoma (PEL) and Multicentric Castlemans Disease (MCD). DNA methylation is an epigenetic modification that is essential for a properly functioning human genome through its roles in chromatin structure maintenance, chromosome stability and transcription regulation. Genomic studies show that expressed promoters tend to be un-methylated whereas methylated promoters tend to be inactive. We have previously revealed the global methylation footprint in PEL cells and found that many cellular gene promoters become differentially methylated and hence differentially expressed in KSHV chronically infected PEL cell lines. Here we present the cellular CpG DNA methylation footprint in KS, the most common malignancy associated with KSHV. We performed MethylationEPIC BeadChip to compare the global methylation status in normal skin compared to KS biopsies, and revealed dramatic global methylation alterations occurring in KS. Many of these changes were attributed to hyper-methylation of promoters and enhancers that regulate genes associated with abnormal skin morphology, a well-known hallmark of KS development. We observed six-fold increase in hypo-methylated CpGs between early stage of KS (plaque) and the more progressed stage (nodule). These observations suggest that hyper-methylation takes place early in KS while hypo-methylation is a later process that is more significant in nodule. Our findings add another layer to the understanding of the relationship between epigenetic changes caused by KSHV infection and tumorigenesis.

CpG methylation in cell-free Epstein-Barr virus DNA in patients with EBV-Hodgkin lymphoma.

Epstein-Barr virus (EBV) is associated with a variety of tumors and nonmalignant conditions. Latent EBV genomes in cells, including tumor cells, are often CpG methylated, whereas virion DNA is not CpG methylated. We demonstrate that methyl CpG binding magnetic beads can be used to fractionate among sources of EBV DNA (DNA extracted from laboratory-purified virions vs DNA extracted from latently infected cell lines). We then applied the technique to plasma specimens and showed that this technique can distinguish EBV DNA from patients with EBV-associated tumors (nasopharyngeal carcinoma, Hodgkin lymphoma) and viral DNA from patients without EBV-associated tumors, including immunocompromised patients and patients with EBV(-) Hodgkin lymphoma.

Inhibition of Tip60 Reduces Lytic and Latent Gene Expression of Kaposi's Sarcoma-Associated Herpes Virus (KSHV) and Proliferation of KSHV-Infected Tumor Cells.

Kaposi's sarcoma-associated herpesvirus (KSHV) is an oncogenic virus responsible for the development of Kaposi's sarcoma, primary effusion lymphoma (PEL), and Multicentric Castleman's disease in immunocompromised individuals. Despite the burden of these diseases there are few treatment options for afflicted individuals, due in part to our limited understanding of virus-host interactions. Tip60, a histone aceytltransferase (HAT) has been previously shown to interact with both the KSHV latency associated nuclear antigen protein (LANA), which is the main factor in maintaining the viral latent state, and ORF36, a viral kinase expressed in the lytic phase. We further investigated Tip60-virus interaction to ascertain Tip60's role in the viral life cycle and its potential as a target for future therapeutics. Through modulation of Tip60 expression in HEK293T cells harboring a plasmid containing the KSHV viral episome, Bac36, we found that Tip60 is vital for both lytic replication as well as efficient expression of latent genes. Interestingly, Tip60 small molecule inhibitors, MG149 and NU9056, similarly inhibited latent and lytic genes, and reduced virion production in wild-type KSHV+/EBV- PEL, BCBL-1 cells. Long-term treatment with these Tip60 inhibitors selectively decreased the viability of KSHV-infected B lymphoma cells compared to uninfected cells. From this study, we conclude that Tip60 is important for KSHV infection and its associated cancer development, and Tip60 is therefore a potential target for future antiviral and anticancer therapeutics.

Kaposi's sarcoma-associated herpesvirus LANA protein downregulates nuclear glycogen synthase kinase 3 activity and consequently blocks differentiation.

The Kaposi's sarcoma-associated herpesvirus latency-associated nuclear antigen (LANA) protein interacts with glycogen synthase kinase 3 (GSK-3) and relocalizes GSK-3 in a manner that leads to stabilization of beta-catenin and upregulation of beta-catenin-responsive cell genes. The LANA-GSK-3 interaction was further examined to determine whether there were additional downstream consequences. In the present study, the nuclear GSK-3 bound to LANA in transfected cells and in BCBL1 primary effusion lymphoma cells was found to be enriched for the inactive serine 9-phosphorylated form of GSK-3. The mechanism of inactivation of nuclear GSK-3 involved LANA recruitment of the extracellular signal-regulated kinases 1 and 2 (ERK1/2) and the ribosomal S6 kinase 1 (RSK1). ERK1/2 and RSK1 coprecipitated with LANA, and LANA was a substrate for ERK1 in vitro. A model is proposed for the overall inactivation of nuclear GSK-3 that incorporates the previously described GSK-3 phosphorylation of LANA itself. Functional inactivation of nuclear GSK-3 was demonstrated by the ability of LANA to limit phosphorylation of the known GSK-3 substrates C/EBPbeta and C/EBPalpha. The effect of LANA-mediated ablation of C/EBP phosphorylation on differentiation was modeled in the well-characterized 3T3L1 adipogenesis system. LANA-expressing 3T3L1 cells were impaired in their ability to undergo differentiation and adipogenesis. C/EBPbeta induction followed the same time course as that seen in vector-transduced cells, but there was delayed and reduced induction of C/EBPbeta transcriptional targets in LANA-expressing cells. We conclude that LANA inactivates nuclear GSK-3 and modifies the function of proteins that are GSK-3 substrates. In the case of C/EBPs, this translates into LANA-mediated inhibition of differentiation.

Recruitment of the de novo DNA methyltransferase Dnmt3a by Kaposi's sarcoma-associated herpesvirus LANA.

The Kaposi's sarcoma-associated herpesvirus LANA protein is expressed in all Kaposi's sarcoma-associated herpesvirus-infected cells, including the tumor cells of endemic and AIDS-associated Kaposi sarcoma, primary effusion lymphoma, and Castleman disease. LANA modulates cell gene expression, but the mechanisms of LANA-mediated transcriptional reprogramming are poorly understood. LANA-repressed cell genes were identified by using retroviral-transduced telomerase-immortalized microvascular endothelial cells. Transciptional repression of targeted genes was relieved by treatment with the methyltransferase inhibitor 5-aza-2'-deoxycytidine, suggesting a role for DNA methylation in repression. We found that LANA coprecipitated with DNA methyltransferases (Dnmts) and recruited endogenous DNA methyltransferase activity from the cell extract. LANA preferentially relocalized Dnmt3a from the nuclear matrix into the chromatin fraction. Further, LANA associated with repressed cellular promoters, recruited Dnmt3a to DNA, and facilitated de novo promoter methylation of a down-regulated gene, cadherin 13 (H-cadherin). The data provide an example of promoter-specific epigenetic DNA modification through viral protein recruitment of de novo Dnmt activity.

HBXAP, a novel PHD-finger protein, possesses transcription repression activity.

The PHD/LAP (plant homology domain/leukemia associated protein) finger motif is characteristically defined by a histidine and seven cysteines that are spatially arranged in a C4HC3 consensus sequence. This unique zinc finger, found primarily in a wide variety of chromatin-associated proteins, is considered to mediate protein-protein interactions. We have isolated a novel human PHD-finger protein, HBXAP (for hepatitis B virus x associated protein). HBXAP has three alternatively spliced isoforms. We also identified the Drosophila melanogaster HBXAP ortholog, gene CG8677. Based on alignment of four different proteins, we found a novel conserved domain in HBXAP that we designated the HBXAP conserved domain (XCD). We show that HBXAP represses transcription when recruited to DNA via the DNA binding of GAL4. Furthermore, the PHD finger alone suffices to repress transcription, thus attributing a functional role to this domain. The gene HBXAP is localized to the long arm of human chromosome 11 between q13.4 and q14.1. This region is amplified and rearranged in many tumors, suggesting a role for HBXAP in tumorigenesis similar to that of other PHD-containing proteins.