Lytic Reactivation of the Kaposi's Sarcoma-Associated Herpesvirus (KSHV) Is Accompanied by Major Nucleolar Alterations.

The nucleolus is a subnuclear compartment whose primary function is the biogenesis of ribosomal subunits. Certain viral infections affect the morphology and composition of the nucleolar compartment and influence ribosomal RNA (rRNA) transcription and maturation. However, no description of nucleolar morphology and function during infection with Kaposi's sarcoma-associated herpesvirus (KSHV) is available to date. Using immunofluorescence microscopy, we documented extensive destruction of the nuclear and nucleolar architecture during the lytic reactivation of KSHV. This was manifested by the redistribution of key nucleolar proteins, including the rRNA transcription factor UBF. Distinct delocalization patterns were evident; certain nucleolar proteins remained together whereas others dissociated, implying that nucleolar proteins undergo nonrandom programmed dispersion. Significantly, the redistribution of UBF was dependent on viral DNA replication or late viral gene expression. No significant changes in pre-rRNA levels and no accumulation of pre-rRNA intermediates were found by RT-qPCR and Northern blot analysis. Furthermore, fluorescent in situ hybridization (FISH), combined with immunofluorescence, revealed an overlap between Fibrillarin and internal transcribed spacer 1 (ITS1), which represents the primary product of the pre-rRNA, suggesting that the processing of rRNA proceeds during lytic reactivation. Finally, small changes in the levels of pseudouridylation (Ψ) and 2'-O-methylation (Nm) were documented across the rRNA; however, none were localized to the functional domain. Taken together, our results suggest that despite dramatic changes in the nucleolar organization, rRNA transcription and processing persist during lytic reactivation of KSHV. Whether the observed nucleolar alterations favor productive infection or signify cellular anti-viral responses remains to be determined.

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.

The Portal Vertex of KSHV Promotes Docking of Capsids at the Nuclear Pores.

Kaposi's sarcoma-associated herpesvirus (KSHV) is a cancer-related herpesvirus. Like other herpesviruses, the KSHV icosahedral capsid includes a portal vertex, composed of 12 protein subunits encoded by open reading frame (ORF) 43, which enables packaging and release of the viral genome into the nucleus through the nuclear pore complex (NPC). Capsid vertex-specific component (CVSC) tegument proteins, which directly mediate docking at the NPCs, are organized on the capsid vertices and are enriched on the portal vertex. Whether and how the portal vertex is selected for docking at the NPC is unknown. Here, we investigated the docking of incoming ORF43-null KSHV capsids at the NPCs, and describe a significantly lower fraction of capsids attached to the nuclear envelope compared to wild-type (WT) capsids. Like WT capsids, nuclear envelope-associated ORF43-null capsids co-localized with different nucleoporins (Nups) and did not detach upon salt treatment. Inhibition of nuclear export did not alter WT capsid docking. As ORF43-null capsids exhibit lower extent of association with the NPCs, we conclude that although not essential, the portal has a role in mediating the interaction of the CVSC proteins with Nups, and suggest a model whereby WT capsids can dock at the nuclear envelope through a non-portal penton vertex, resulting in an infection 'dead end'.

Targeting the Kaposi's sarcoma-associated herpesvirus genome with the CRISPR-Cas9 platform in latently infected cells.

BACKGROUND: Kaposi's sarcoma-associated herpesvirus (KSHV) is a transforming gammaherpesvirus. Like other herpesviruses, KSHV infection is for life long and there is no treatment that can cure patients from the virus. In addition, there is an urgent need to target viral genes to study their role during the infection cycle. The CRISPR-Cas9 technology offers a means to target viral genomes and thus may offer a novel strategy for viral cure as well as for better understanding of the infection process. We evaluated the suitability of this platform for the targeting of KSHV. METHODS: We have used the recombinat KSHV BAC16 genome, which contains an expression cassette encoding hygromycin-resistance and a GFP marker gene. Three genes were targeted: gfp, which serves as a marker for infection; orf45 encoding a lytic viral protein; and orf73, encoding LANA which is crucial for latent infection. The fraction of cells expressing GFP, viral DNA levels and LANA expression were monitored and viral genomes were sequenced. RESULTS: We found that KSHV episomes can be targeted by CRISPR-Cas9. Interestingly, the quantity of KSHV DNA declined, even when target sites were not functionally important for latency. In addition, we show that antibiotic selection, used to maintain infection, interferes with the outcome of targeting. CONCLUSIONS: Our study provides insights into the use of this fundamental approach for the study and manipulation of KSHV. It provides guidelines for the targeting CRISPR-Cas9 to the viral genome and for outcomes interpretation.

The KSHV portal protein ORF43 is essential for the production of infectious viral particles.

Herpesvirus capsid assembly involves cleavage and packaging of the viral genome. The Kaposi's sarcoma-associated herpesvirus (KSHV) open reading frame 43 (orf43) encodes a putative portal protein. The portal complex functions as a gate through which DNA is packaged into the preformed procapsids, and is injected into the cell nucleus upon infection. The amino acid sequence of the portal proteins is conserved among herpesviruses. Here, we generated an antiserum to ORF43 and determined late expression kinetics of ORF43 along with its nuclear localization. We generated a recombinant KSHV mutant, which fails to express ORF43 (BAC16-ORF43-null). Assembled capsids were observed upon lytic induction of this virus; however, the released virions lacked viral DNA and thus could not establish infection. Ectopic expression of ORF43 rescued the ability to produce infectious particles. ORF43 antiserum and the recombinant ORF43-null virus can provide an experimental system for further studies of the portal functions and its interactions.

Nucleolar stress enhances lytic reactivation of the Kaposi's sarcoma-associated herpesvirus.

Kaposi's sarcoma-associated herpesvirus (KSHV) is a human tumorigenic virus exhibiting two forms of infection, latent and lytic. Latent infection is abortive and allows the virus to establish lifelong infection, while lytic infection is productive, and is needed for virus dissemination within the host and between hosts. Latent infection may reactivate and switch towards the lytic cycle. This switch is a critical step in the maintenance of long-term infection and for the development of KSHV-related neoplasms. In this study, we examined the effect of nucleolar stress, manifested by failure in ribosome biogenesis or function and often coupled with p53 activation, on lytic reactivation of KSHV. To this end, we induced nucleolar stress by treatment with Actinomycin D, CX-5461 or BMH-21. Treatment with these compounds alone did not induce the lytic cycle. However, enhancement of the lytic cycle by these compounds was evident when combined with expression of the viral protein K-Rta. Further experiments employing combined treatments with Nutlin-3, knock-down of p53 and isogenic p53+/+ and p53-/- cells indicated that the enhancement of lytic reactivation by nucleolar stress does not depend on p53. Thus, our study identifies nucleolar stress as a novel regulator of KSHV infection, which synergizes with K-Rta expression to increase lytic reactivation. This suggests that certain therapeutic interventions, which induce nucleolar stress, may affect the outcome of KSHV infection.

Graphene-Based "Hot Plate" for the Capture and Destruction of the Herpes Simplex Virus Type 1.

The study of graphene-based antivirals is still at a nascent stage and the photothermal antiviral properties of graphene have yet to be studied. Here, we design and synthesize sulfonated magnetic nanoparticles functionalized with reduced graphene oxide (SMRGO) to capture and photothermally destroy herpes simplex virus type 1 (HSV-1). Graphene sheets were uniformly anchored with spherical magnetic nanoparticles (MNPs) of varying size between ∼5 and 25 nm. Fourier-transform infrared spectroscopy (FT-IR) confirmed the sulfonation and anchoring of MNPs on the graphene sheets. Upon irradiation of the composite with near-infrared light (NIR, 808 nm, 7 min), SMRGO (100 ppm) demonstrated superior (∼99.99%) photothermal antiviral activity. This was probably due to the capture efficiency, unique sheet-like structure, high surface area, and excellent photothermal properties of graphene. In addition, electrostatic interactions of MNPs with viral particles appear to play a vital role in the inhibition of viral infection. These results suggest that graphene composites may help to combat viral infections including, but not only, HSV-1.

The Kaposi's-sarcoma-associated herpesvirus orf35 gene product is required for efficient lytic virus reactivation.

Kaposi's sarcoma-associated herpesvirus (KSHV) is implicated in the etiology of several human malignancies. KSHV open reading frame (orf) 35 encodes a conserved gammaherpesvirus protein with an, as yet, unknown function. Employing the bacterial artificial chromosome (BAC) system, we generated a recombinant viral clone that fails to express ORF35 (BAC16-ORF35-stop) but preserves intact adjacent and overlapping reading frames. Using this construct, we studied the role of this previously uncharacterized gene product during lytic reactivation of KSHV. Upon lytic reactivation, the ORF35-stop recombinant virus displayed significantly reduced lytic viral gene expression, viral DNA replication, and progeny virus production as compared to control wild-type virus. Exogenous expression of ORF35-Flag reversed the effects of ORF35 deficiency. These results demonstrate that ORF35 is important for efficient lytic virus reactivation.

Viral Bcl-2 Encoded by the Kaposi's Sarcoma-Associated Herpesvirus Is Vital for Virus Reactivation.

UNLABELLED: The Kaposi's sarcoma-associated herpesvirus (KSHV) open reading frame 16 (orf16) encodes a viral Bcl-2 (vBcl-2) protein which shares sequence and functional homology with the Bcl-2 family. Like its cellular homologs, vBcl-2 protects various cell types from apoptosis and can also negatively regulate autophagy. vBcl-2 is transcribed during lytic infection; however, its exact function has not been determined to date. By using bacterial artificial chromosome 16 (BAC16) clone carrying the full-length KSHV genome, we have generated recombinant KSHV mutants that fail to express vBcl-2 or express mCherry-tagged vBcl-2. We show that the vBcl-2 protein is expressed at relatively low levels during lytic induction and that a lack of vBcl-2 largely reduces the efficiency of KSHV reactivation in terms of lytic gene expression, viral DNA replication, and production of infectious particles. In contrast, the establishment of latency was not affected by the absence of vBcl-2. Our findings suggest an important role for vBcl-2 during initial phases of lytic reactivation and/or during subsequent viral propagation. Given the known functions of vBcl-2 in regulating apoptosis and autophagy, which involve its direct interaction with cellular proteins and thus require high levels of protein expression, it appears that vBcl-2 may have additional regulatory functions that do not depend on high levels of protein expression. IMPORTANCE: The present study shows for the first time the expression of endogenous vBcl-2 protein in KSHV-infected cell lines and demonstrates the importance of vBcl-2 during the initial phases of lytic reactivation and/or during its subsequent propagation. It is suggested that vBcl-2 has additional regulatory functions beyond apoptosis and autophagy repression that do not depend on high levels of protein expression.

Fluorescent tagging and cellular distribution of the Kaposi's sarcoma-associated herpesvirus ORF45 tegument protein.

UNLABELLED: Kaposi's sarcoma-associated herpesvirus (KSHV), also known as human herpesvirus 8 (HHV-8), is a cancer-related human virus, classified as a member of the Gammaherpesvirinae subfamily. We report here the construction of a dual fluorescent-tagged KSHV genome (BAC16-mCherry-ORF45), which constitutively expresses green fluorescent protein (GFP) and contains the tegument multifunctional ORF45 protein as a fusion protein with monomeric Cherry fluorescent protein (mCherry). We confirmed that this virus is properly expressed and correctly replicates and that the mCherry-ORF45 protein is incorporated into the virions. Using this labeled virus, we describe the dynamics of mCherry-ORF45 expression and localization in newly infected cells as well as in latently infected cells undergoing lytic induction and show that mCherry can be used to monitor cells undergoing the lytic viral cycle. This virus is likely to enable future studies monitoring the dynamics of viral trafficking and tegumentation during viral ingress and egress. IMPORTANCE: The present study describes the construction and characterization of a new recombinant KSHV genome BAC16 clone which expresses mCherry-tagged ORF45. This virus enables the tracking of cells undergoing lytic infection and can be used to address issues related to the trafficking and maturation pathways of KSHV virions.

The nucleolar PICT-1/GLTSCR2 protein forms homo-oligomers.

The human "protein interacting with carboxyl terminus 1" (PICT-1), also designated as the "glioma tumor suppressor candidate region 2 gene product", GLTSCR2, is a nucleolar protein whose activity is, as yet, unknown. Contradictory results regarding the role of PICT-1 in cancer have been reported, and PICT-1 has been suggested to function either as a tumor suppressor protein or as an oncogene. In this study, we demonstrate self-association of PICT-1. Through yeast two-hybrid assay, we identified PICT-1 as its own interaction partner. We confirmed the interaction of PICT-1 with itself by direct yeast two-hybrid assay and also showed self-association of PICT-1 in mammalian cells by co-immunoprecipitation and fluorescence resonance energy transfer assays. Furthermore, we confirmed direct self-association of PICT-1 by using in vitro microfluidic affinity binding assays. The later assay also identified the carboxy-terminal domain as mediating self-interaction of PICT-1. Glutaraldehyde cross-linking and gel-filtration assays suggest that PICT-1 forms dimers, though it may form higher-order complexes as well. Our findings add another layer of complexity in understanding the different functions of PICT-1 and may help provide insights regarding the activities of this protein.

Herpes simplex virus type-1 attachment inhibition by functionalized graphene oxide.

Graphene oxide and its derivatives have lately been the subject of increased attention in the field of bioscience and biotechnology. In this article, we report on the use of graphene oxide (GO) derivatives to inhibit herpes simplex virus type-1 (HSV-1) infections, mimicking the cell surface receptor heparan sulfate, and the GO derivatives compete with the latter in binding HSV-1. The inhibition does not affect cell-to-cell spreading. Media content has a significant effect on the inhibition properties of the nanomaterials. These have no cytotoxic effect, suggesting that this is a promising approach for the development of antiviral surfaces and for diagnostic purposes.

Nucleolar localization of GLTSCR2/PICT-1 is mediated by multiple unique nucleolar localization sequences.

The human glioma tumor suppressor candidate region 2 gene product, GLTSCR2, also called 'protein interacting with carboxyl terminus 1' (PICT-1), has been implicated in the regulation of two major tumor suppressor proteins, PTEN and p53, and reported to bind the membrane-cytoskeleton regulator of cell signaling, Merlin. PICT-1 is a nucleolar protein, conserved among eukaryotes, and its yeast homolog has been functionally associated with ribosomal RNA processing. By means of confocal microscopy of EGFP and myc-tagged PICT-1 fusion proteins, we delineate that the nucleolar localization of PICT-1 is mediated by two independent nucleolar localization sequences (NoLS). Unlike most NoLSs, these NoLSs are relatively long with flexible boundaries and contain arginine and leucine clusters. In addition, we show that PICT-1 exhibits a nucleolar distribution similar to proteins involved in ribosomal RNA processing, yet does not colocalize precisely with either UBF1 or Fibrillarin under normal or stressed conditions. Identification of the precise location of PICT-1 and the signals that mediate its nucleolar localization is an important step towards advancing our understanding of the demonstrated influence of this protein on cell fate and tumorigenesis.

Human herpesvirus 8 is not detectable in lesions of large plaque parapsoriasis, and in early-stage sporadic, familial, and juvenile cases of mycosis fungoides.

BACKGROUND: Human herpesvirus (HHV) 8, an essential etiologic agent of Kaposi sarcoma, is also associated with several lymphoproliferative disorders. The involvement of HHV 8 in mycosis fungoides (MF) and large plaque parapsoriasis (LPP) is controversial, with contradictory reports from various countries worldwide. OBJECTIVE: We sought to investigate the presence of the HHV 8 genome in skin lesions of LPP and early-stage sporadic, familial, and juvenile MF in patients in Israel. METHODS: Archival paraffin-embedded and frozen samples from skin biopsies of untreated patients with LPP and early-stage MF performed in 1990 through 2006 were randomly collected from the department of dermatology of a tertiary medical center in central Israel. DNA was extracted, and a TaqMan-based real-time polymerase chain reaction assay specific for the K6 gene region was used to detect the HHV 8 genome. RESULTS: A total of 46 biopsies were sampled from 11 patients with LPP and 35 with early-stage MF (17 adults with sporadic MF, 10 children, and 8 patients with familial MF). In all, 44 samples were negative for HHV 8 DNA; two samples from adults with sporadic MF were positive. LIMITATIONS: The presence of HHV 8 antibodies or virus sequences was not assessed in peripheral blood. CONCLUSION: The results of this study, conducted in a region relatively endemic for HHV 8, support most earlier studies showing a lack of association of HHV 8 infection with LPP and sporadic adult-type MF. To our knowledge, the lack of association of HHV 8 infection with juvenile and familial MF has not been previously reported.

GLTSCR2/PICT-1, a putative tumor suppressor gene product, induces the nucleolar targeting of the Kaposi's sarcoma-associated herpesvirus KS-Bcl-2 protein.

KS-Bcl-2, encoded by Kaposi's sarcoma-associated herpesvirus (KSHV), is a structural and functional homologue of the Bcl-2 family of apoptosis regulators. Like several other Bcl-2 family members, KS-Bcl-2 protects cells from apoptosis and autophagy. Using a yeast two-hybrid screen and coimmunoprecipitation assays, we identified a novel KS-Bcl-2-interacting protein, referred to as protein interacting with carboxyl terminus 1 (PICT-1), encoded by a candidate tumor suppressor gene, GLTSCR2. Confocal laser scanning microscopy revealed nucleolar localization of PICT-1, whereas KS-Bcl-2 was located mostly at the mitochondrial membranes with a small fraction in the nucleoli. Ectopic expression of PICT-1 resulted in a large increase in the nucleolar fraction of KS-Bcl-2, and only a minor fraction remained in the cytoplasm. Furthermore, knockdown of endogenous PICT-1 abolished the nucleolar localization of KS-Bcl-2. However, ectopically expressed PICT-1 did not alter the cellular distribution of human Bcl-2. Subsequent analysis mapped the crucial amino acid sequences of both KS-Bcl-2 and PICT-1 required for their interaction and for KS-Bcl-2 targeting to the nucleolus. Functional studies suggest a correlation between nucleolar targeting of KS-Bcl-2 by PICT-1 and reduction of the antiapoptotic activity of KS-Bcl-2. Thus, these studies demonstrate a cellular mechanism to sequester KS-Bcl-2 from the mitochondria and to downregulate its virally encoded antiapoptotic activity. Additional characterization of the interaction of KS-Bcl-2 and PICT-1 is likely to shed light on the functions of both proteins.

Linking the Kaposi's sarcoma-associated herpesvirus (KSHV/HHV-8) to human malignancies.

In 1994, the Kaposi's sarcoma-associated herpesvirus (KSHV/HHV-8) was identified as the etiologic agent of Kaposi's sarcoma (KS). KSHV has since been associated with two additional malignancies: primary effusion lymphoma and multicentric Castleman's disease. In this chapter, we describe the current understanding of the pathogenesis, transmission, and prevalence of KSHV, and its association mainly with KS. We describe evidence demonstrating that KSHV is a causative agent for KS, and we present other factors that possibly contribute to the incidence of KS. We compare worldwide data on the prevalence of KS and of KSHV infection. Specific viral genes that may induce KS tumors or enable their growth also are described. Finally, we discuss the implications of the transmission modes and epidemiology of this virus on recommendations for KSHV screening of tissues and blood products before transplantation or transfusion.