scholarly journals Raf/MEK/ERK signalling triggers reactivation of Kaposi's sarcoma-associated herpesvirus latency

2006 ◽  
Vol 87 (5) ◽  
pp. 1139-1144 ◽  
Author(s):  
Patrick W. Ford ◽  
Benjaman A. Bryan ◽  
Ossie F. Dyson ◽  
Douglas A. Weidner ◽  
Vishnu Chintalgattu ◽  
...  
Keyword(s):  
Kaposi's Sarcoma ◽  
Primary Effusion Lymphoma ◽  
Kaposi’S Sarcoma ◽  
Lytic Infection ◽  
Lytic Cycle ◽  
Kshv Infection ◽  
Kaposi's Sarcoma Associated Herpesvirus ◽  
Kaposi’S Sarcoma Associated Herpesvirus

Kaposi's sarcoma-associated herpesvirus (KSHV) causes Kaposi's sarcoma, primary effusion lymphoma and multicentric Castleman's disease. KSHV infection of cells produces both latent and lytic cycles of infection. In vivo, the virus is found predominantly in the latent state. In vitro, a lytic infection can be induced in KSHV-infected cells by treating with phorbol ester (TPA). However, the exact signalling events that lead to the reactivation of KSHV lytic infection are still elusive. Here, a role is demonstrated for B-Raf/MEK/ERK signalling in TPA-induced reactivation of KSHV latent infection. Inhibiting MEK/ERK signalling by using MEK-specific inhibitors decreased expression of the TPA-induced KSHV lytic-cycle gene ORF8. Transfection of BCBL-1 cells with B-Raf small interfering RNA inhibited TPA-induced KSHV lytic infection significantly. Additionally, overexpression of MEK1 induced a lytic cycle of KSHV infection in BCBL-1 cells. The significance of these findings in understanding the biology of KSHV-associated pathogenesis is discussed.

scholarly journals Identification and Characterization of the Orf49 Protein of Kaposi's Sarcoma-Associated Herpesvirus

2006 ◽  
Vol 80 (6) ◽  
pp. 3062-3070 ◽  
Author(s):  
Carlos M. González ◽  
Emily L. Wong ◽  
Brian S. Bowser ◽  
Gregory K. Hong ◽  
Shannon Kenney ◽  
...  
Keyword(s):  
Transcription Factor ◽  
Transcriptional Activation ◽  
Kaposi's Sarcoma ◽  
Primary Effusion Lymphoma ◽  
Kaposi’S Sarcoma ◽  
Lytic Cycle ◽  
Transcription Activator ◽  
Kaposi's Sarcoma Associated Herpesvirus ◽  
Factor C ◽  
Kaposi’S Sarcoma Associated Herpesvirus

ABSTRACT Kaposi's sarcoma-associated herpesvirus (KSHV) is the etiological agent of Kaposi's sarcoma, primary effusion lymphoma, and multicentric Castleman's disease. Kaposi's sarcoma is the most common neoplasm among human immunodeficiency virus-positive individuals. Like other herpesviruses, KSHV is able to establish a predominantly latent, life-long infection in its host. The KSHV lytic cycle can be triggered by a number of stimuli that induce the expression of the key lytic switch protein, the replication and transcription activator (RTA) encoded by Orf50. The expression of Rta is necessary and sufficient to trigger the full lytic program resulting in the ordered expression of viral proteins, release of viral progeny, and host cell death. We have characterized an unknown open reading frame, Orf49, which lies adjacent and in the opposite orientation to Orf50. Orf49 is expressed during the KSHV lytic cycle and shows early transcription kinetics. We have mapped the 5′ and 3′ ends of the unspliced Orf49 transcript, which encodes a 30-kDa protein that is localized to both the nucleus and the cytoplasm. Interestingly, we found that Orf49 was able to cooperate with Rta to activate several KSHV lytic promoters containing AP-1 sites. The Orf49-encoded protein was also able to induce transcriptional activation through c-Jun but not the ATF1, ATF2, or CREB transcription factor. We found that Orf49 could induce phosphorylation and activation of the transcription factor c-Jun, the Jun N-terminal kinase (JNK), and p38. Our data suggest that Orf49 functions to activate the JNK and p38 pathways during the KSHV lytic cycle.

scholarly journals Early Events in Kaposi's Sarcoma-Associated Herpesvirus Infection of Target Cells

2009 ◽  
Vol 84 (5) ◽  
pp. 2188-2199 ◽  
Author(s):  
Bala Chandran
Keyword(s):  
Kaposi's Sarcoma ◽  
Kaposi’S Sarcoma ◽  
Target Cells ◽  
Mode Of Entry ◽  
Successful Infection ◽  
Kaposi's Sarcoma Associated Herpesvirus ◽  
Kaposi’S Sarcoma Associated Herpesvirus ◽  
Cell Signaling Pathways

ABSTRACT Kaposi's sarcoma-associated herpesvirus (KSHV), the most recently identified member of the herpesvirus family, infects a variety of target cells in vitro and in vivo. This minireview surveys current information on the early events of KSHV infection, including virus-receptor interactions, involved envelope glycoproteins, mode of entry, intracellular trafficking, and initial viral and host gene expression programs. We describe data supporting the hypothesis that KSHV manipulates preexisting host cell signaling pathways to allow successful infection. The various signaling events triggered by infection, and their potential roles in the different stages of infection and disease pathogenesis, are summarized.

scholarly journals CAK-independent Activation of CDK6 by a Viral Cyclin

2001 ◽  
Vol 12 (12) ◽  
pp. 3987-3999 ◽  
Author(s):  
Philipp Kaldis ◽  
Päivi M. Ojala ◽  
Lily Tong ◽  
Tomi P. Mäkelä ◽  
Mark J. Solomon
Keyword(s):  
Conformational Changes ◽  
Kaposi's Sarcoma ◽  
Cell Cycle Progression ◽  
Kaposi’S Sarcoma ◽  
Binding Assays ◽  
Kaposi's Sarcoma Associated Herpesvirus ◽  
Induced Apoptosis ◽  
Kaposi’S Sarcoma Associated Herpesvirus

In normal cells, activation of cyclin-dependent kinases (cdks) requires binding to a cyclin and phosphorylation by the cdk-activating kinase (CAK). The Kaposi's sarcoma-associated herpesvirus encodes a protein with similarity to D-type cyclins. This KSHV-cyclin activates CDK6, alters its substrate specificity, and renders CDK6 insensitive to inhibition by the cdk inhibitor p16INK4a. Here we investigate the regulation of the CDK6/KSHV-cyclin kinase with the use of purified proteins and a cell-based assay. We find that KSHV-cyclin can activate CDK6 independent of phosphorylation by CAK in vitro. In addition, CAK phosphorylation decreased the p16INK4asensitivity of CDK6/KSHV-cyclin complexes. In cells, expression of CDK6 or to a lesser degree of a nonphosphorylatable CDK6T177Atogether with KSHV-cyclin induced apoptosis, indicating that CDK6 activation by KSHV-cyclin can proceed in the absence of phosphorylation by CAK in vivo. Coexpression of p16 partially protected cells from cell death. p16 and KSHV-cyclin can form a ternary complex with CDK6 that can be detected by binding assays as well as by conformational changes in CDK6. The Kaposi's sarcoma-associated herpesvirus has adopted a clever strategy to render cell cycle progression independent of mitogenic signals, cdk inhibition, or phosphorylation by CAK.

scholarly journals Kaposi's Sarcoma-Associated Herpesvirus LANA2 Is a B-Cell-Specific Latent Viral Protein That Inhibits p53

2001 ◽  
Vol 75 (1) ◽  
pp. 429-438 ◽  
Author(s):  
Carmen Rivas ◽  
Ai-En Thlick ◽  
Carlo Parravicini ◽  
Patrick S. Moore ◽  
Yuan Chang
Keyword(s):  
Kaposi's Sarcoma ◽  
Primary Effusion Lymphoma ◽  
Blot Hybridization ◽  
Human Herpesvirus ◽  
Kaposi’S Sarcoma ◽  
Nuclear Antigen ◽  
P53 Overexpression ◽  
Kaposi's Sarcoma Associated Herpesvirus ◽  
Kaposi’S Sarcoma Associated Herpesvirus

ABSTRACT Kaposi's sarcoma-associated herpesvirus (KSHV), or human herpesvirus 8, is associated with three proliferative diseases ranging from viral cytokine-induced hyperplasia to monoclonal neoplasia: multicentric Castleman's disease (CD), Kaposi's sarcoma (KS), and primary effusion lymphoma (PEL). Here we report a new latency-associated 1,704-bp KSHV spliced gene belonging to a cluster of KSHV sequences having homology to the interferon regulatory factor (IRF) family of transcription factors. ORFK10.5 encodes a protein, latency-associated nuclear antigen 2 (LANA2), which is expressed in KSHV-infected hematopoietic tissues, including PEL and CD but not KS lesions. LANA2 is abundantly expressed in the nuclei of cultured KSHV-infected B cells. Transcription of K10.5 in PEL cell cultures is not inhibited by DNA polymerase inhibitors nor significantly induced by phorbol ester treatment. Unlike LANA1, LANA2 does not elicit a serologic response from patients with KS, PEL, or CD as measured by Western blot hybridization. Both KSHV vIRF1 (ORFK9) and LANA2 (ORFK10.5) appear to have arisen through gene duplication of a captured cellular IRF gene. LANA2 is a potent inhibitor of p53-induced transcription in reporter assays. LANA2 antagonizes apoptosis due to p53 overexpression in p53-null SAOS-2 cells and apoptosis due to doxorubicin treatment of wild-type p53 U2OS cells. While LANA2 specifically interacts with amino acids 290 to 393 of p53 in glutathione S-transferase pull-down assays, we were unable to demonstrate LANA2-p53 interaction in vivo by immunoprecipitation. These findings show that KSHV has tissue-specific latent gene expression programs and identify a new latent protein which may contribute to KSHV tumorigenesis in hematopoietic tissues via p53 inhibition.

scholarly journals Expression in a Recombinant Murid Herpesvirus 4 Reveals the In Vivo Transforming Potential of the K1 Open Reading Frame of Kaposi's Sarcoma-Associated Herpesvirus

2004 ◽  
Vol 78 (16) ◽  
pp. 8878-8884 ◽  
Author(s):  
Jill Douglas ◽  
Bernadette Dutia ◽  
Susan Rhind ◽  
James P. Stewart ◽  
Simon J. Talbot
Keyword(s):  
Kaposi's Sarcoma ◽  
Fluorescent Protein ◽  
Salivary Gland Tumor ◽  
Kaposi’S Sarcoma ◽  
Common Marmoset ◽  
Kaposi's Sarcoma Associated Herpesvirus ◽  
Herpesvirus 4 ◽  
Kaposi’S Sarcoma Associated Herpesvirus

ABSTRACT Murid herpesvirus 4 (commonly called MHV-68) is closely related to Kaposi's sarcoma-associated herpesvirus (KSHV) and provides an excellent model system for investigating gammaherpesvirus-associated pathogenesis. MHV-76 is a naturally occurring deletion mutant of MHV-68 that lacks 9,538 bp of the left end of the unique portion of the genome encoding nonessential pathogenesis-related genes. The KSHV K1 protein has been shown to transform rodent fibroblasts in vitro and common marmoset T lymphocytes in vivo. Using homologous recombination techniques, we successfully generated recombinants of MHV-76 that encode green fluorescent protein (MHV76-GFP) and KSHV K1 (MHV76-K1). The replication of MHV76-GFP and MHV76-K1 in cell culture was identical to that of MHV-76. However, infection of BALB/c mice via the intranasal route revealed that MHV76-K1 replicated to a 10-fold higher titer than MHV76-GFP in the lungs at day 5 postinfection (p.i.). We observed type 2 pneumocyte proliferation in areas of consolidation and interstitial inflammation of mice infected with MHV76-K1 at day 10 p.i. MHV76-K1 established a 2- to 3-fold higher latent viral load than MHV76-GFP in the spleens of infected mice on days 10 and 14 p.i., although this was 10-fold lower than that established by wild-type MHV-76. A salivary gland tumor was present in one of four mice infected with MHV76-K1, as well as an increased inflammatory response in the lungs at day 120 p.i. compared with that of mice infected with MHV-76 and MHV76-GFP.

scholarly journals Exploring the DNA Binding Interactions of the Kaposi's Sarcoma-Associated Herpesvirus Lytic Switch Protein by Selective Amplification of Bound Sequences In Vitro

2006 ◽  
Vol 80 (6) ◽  
pp. 2958-2967 ◽  
Author(s):  
Joseph Ziegelbauer ◽  
Adam Grundhoff ◽  
Don Ganem
Keyword(s):  
Protein Interactions ◽  
Kaposi's Sarcoma ◽  
Genomic Library ◽  
Consensus Sequence ◽  
Kaposi’S Sarcoma ◽  
Genomic Libraries ◽  
Kaposi's Sarcoma Associated Herpesvirus ◽  
Kaposi’S Sarcoma Associated Herpesvirus

ABSTRACT The lytic switch protein RTA of Kaposi's sarcoma-associated herpesvirus (KSHV) can be targeted to DNA by either direct sequence-specific recognition or via protein-protein interactions with host transcription factors. We have searched for sequences capable of direct RTA binding by screening synthetic oligonucleotide pools and KSHV genomic libraries for RTA-interacting elements, using repeated cycles of in vitro binding followed by amplification of the bound sequences. Multiple low-affinity sequences were recovered from the random pools, with generation of only a weak consensus sequence. The genomic library, by contrast, yielded many biologically relevant fragments, most of which could be shown to interact with RTA in vitro and some of which likely play important regulatory roles in vivo. Surprisingly, the most highly selected fragment came from the promoter of a late gene (gB) and contained at least two direct RTA binding sites, as well as one RBP-Jκ binding site. This raises the possibility that some late KSHV genes may also be subject to direct RTA regulation, though indirect models are not excluded.

scholarly journals Identifying cellular genes crucial for the reactivation of Kaposi's sarcoma-associated herpesvirus latency

2006 ◽  
Vol 87 (3) ◽  
pp. 519-529 ◽  
Author(s):  
Benjaman A. Bryan ◽  
Ossie F. Dyson ◽  
Shaw M. Akula
Keyword(s):  
Cell Cycle ◽  
Flow Cytometry ◽  
Kaposi's Sarcoma ◽  
Kaposi’S Sarcoma ◽  
S Phase ◽  
Lytic Cycle ◽  
Kshv Infection ◽  
Cellular Genes ◽  
Kaposi's Sarcoma Associated Herpesvirus ◽  
Kaposi’S Sarcoma Associated Herpesvirus

Kaposi's sarcoma-associated herpesvirus (KSHV) is the latest addition to the long list of human herpesviruses. Reactivation of latent herpesvirus infections is still a mystery. It was demonstrated recently that the phorbol ester TPA was efficient in inducing a reactivation of KSHV infection in the S phase of the cell cycle. In the present study, flow cytometry-sorted, TPA-induced, KSHV-infected haematopoietic cells (BCBL-1) were used to analyse the expression profiles of cancer-related cellular genes in the S phase of the cell cycle compared with the G0/1 phase by using microarrays. Overall, the S phase of the cell cycle seems to provide KSHV with an apt environment for a productive lytic cycle of infection. The apt conditions include cellular signalling that promotes survivability, DNA replication and lipid metabolism, while blocking cell-cycle progression to M phase. Some of the important genes that were overexpressed during the S phase of the cell cycle compared with the G0/1 phase of TPA-induced BCBL-1 cells are v-myb myeloblastosis (MYBL2), protein kinase-membrane associated tyrosine/threonine 1 (PKMYT1), ribonucleotide reductase M1 polypeptide (RRM1) and peroxisome proliferator-activated receptors delta (PPARD). Inhibition of PKMYT1 expression by the use of specific short interfering RNAs significantly lowered the TPA-induced KSHV lytic cycle of infection. The significance of these and other genes in the reactivation of KSHV is discussed in the following report. Taken together, a flow cytometry–microarray-based method to study the cellular conditions critical for the reactivation of KSHV infection is reported here for the first time.

scholarly journals How Kaposi’s sarcoma-associated herpesvirus stably transforms peripheral B cells towards lymphomagenesis

2019 ◽  
Vol 116 (33) ◽  
pp. 16519-16528 ◽  
Author(s):  
Aurélia Faure ◽  
Mitch Hayes ◽  
Bill Sugden
Keyword(s):  
B Cells ◽  
Kaposi's Sarcoma ◽  
Kaposi’S Sarcoma ◽  
Lytic Cycle ◽  
Barr Virus ◽  
Kaposi's Sarcoma Associated Herpesvirus ◽  
Epstein Barr ◽  
Kaposi’S Sarcoma Associated Herpesvirus ◽  
Peripheral B Cells

Primary effusion lymphomas (PELs) are causally associated with Kaposi’s sarcoma-associated herpesvirus (KSHV) and 86% of PELs are coinfected with Epstein–Barr virus (EBV). Understanding how PELs develop has been impaired by the difficulty of infecting B cells with KSHV in vitro, and the inability of KSHV to transform them. We show that EBV supports an optimal coinfection of 2.5% of peripheral B cells by KSHV. This coinfection requires 1 or more transforming genes of EBV but not entry into KSHV’s lytic cycle. We demonstrate that dually infected B cells are stably transformed in vitro and show that while both viruses can be maintained, different cells exhibit distinct, transformed properties. Transformed cells that grow to predominate in a culture express increased levels of most KSHV genes and differentially express a subset of cellular genes, as do bona fide PEL cells. These dually infected peripheral B cells are thus both stably transformed and allow in vitro molecular dissection of early steps in the progression to lymphomagenesis.

scholarly journals ORF73 of Herpesvirus Saimiri, a Viral Homolog of Kaposi's Sarcoma-Associated Herpesvirus, Modulates the Two Cellular Tumor Suppressor Proteins p53 and pRb

2004 ◽  
Vol 78 (19) ◽  
pp. 10336-10347 ◽  
Author(s):  
Sumit Borah ◽  
Subhash C. Verma ◽  
Erle S. Robertson
Keyword(s):  
Cell Cycle ◽  
Kaposi's Sarcoma ◽  
Kaposi’S Sarcoma ◽  
Herpesvirus Saimiri ◽  
Nuclear Antigen ◽  
Kaposi's Sarcoma Associated Herpesvirus ◽  
Kaposi’S Sarcoma Associated Herpesvirus ◽  
P53 Inactivation

ABSTRACT All known DNA tumor viruses are known to target and inactivate two main cell cycle regulatory proteins, retinoblastoma protein (pRb) and p53. Inactivation of pRb promotes host cell cycle progression into S phase, and inactivation of p53 promotes cell immortalization. The DNA tumor virus Kaposi's sarcoma associated herpesvirus (KSHV)-encoded latency-associated nuclear antigen (LANA) was shown to target and inactivate pRb as well as p53. In this report we provide evidence that these functions are conserved in the homologous protein encoded by the related gammaherpesvirus herpesvirus saimiri (HVS). ORF73, the HVS homologue of LANA, is shown to bind both p53 and pRb in vitro and in vivo, to colocalize with p53 in human T cells infected with HVS, and in cells overexpressing both ORF73 and p53, as well as to adversely influence pRB/E2F and p53 transcriptional regulation. The C terminus of LANA, the region most highly conserved in ORF73, is shown to be responsible for both pRb and p53 interactions, supporting the hypothesis that these functions are conserved in both homologues. Finally, the region of p53 targeted by LANA (and ORF73) maps to the domain required for tetramerization. However, preliminary cross-linking studies do not detect disruption of p53 tetramerization by either LANA or HVS-encoded ORF73, suggesting that p53 inactivation may be by a mechanism independent of tetramer disruption.

scholarly journals Kaposi's Sarcoma-Associated Herpesvirus Open Reading Frame 50/Rta Protein Activates the Entire Viral Lytic Cycle in the HH-B2 Primary Effusion Lymphoma Cell Line

2000 ◽  
Vol 74 (13) ◽  
pp. 6207-6212 ◽  
Author(s):  
Lyndle Gradoville ◽  
Jennifer Gerlach ◽  
Elizabeth Grogan ◽  
Duane Shedd ◽  
Sarah Nikiforow ◽  
...  
Keyword(s):  
Cell Line ◽  
Kaposi's Sarcoma ◽  
Primary Effusion Lymphoma ◽  
Kaposi’S Sarcoma ◽  
Open Reading Frame ◽  
Lytic Cycle ◽  
Viral Dna ◽  
Reading Frame ◽  
Kaposi's Sarcoma Associated Herpesvirus ◽  
Kaposi’S Sarcoma Associated Herpesvirus

ABSTRACT Rta, the gene product of Kaposi's sarcoma-associated herpesvirus (KSHV) encoded mainly in open reading frame 50 (ORF50), is capable of activating expression of viral lytic cycle genes. What was not demonstrated in previous studies was whether KSHV Rta was competent to initiate the entire viral lytic life cycle including lytic viral DNA replication, late-gene expression with appropriate kinetics, and virus release. In HH-B2, a newly established primary effusion lymphoma (PEL) cell line, KSHV ORF50 behaved as an immediate-early gene and autostimulated its own expression. Expression of late genes, ORF65, and K8.1 induced by KSHV Rta was eliminated by phosphonoacetic acid, an inhibitor of viral DNA polymerase. Transfection of KSHV Rta increased the production of encapsidated DNase-resistant viral DNA from HH-B2 cells. Thus, introduction of an ORF50 expression plasmid is sufficient to drive the lytic cycle to completion in cultured PEL cells.

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