Differential Expression of Viral Bcl-2 Encoded by Kaposi's Sarcoma-Associated Herpesvirus and Human Bcl-2 in Primary Effusion Lymphoma Cells and Kaposi's Sarcoma Lesions

Widmer, Isabelle; Wernli, Marion; Bachmann, Felix; Gudat, F; Cathomas, Gieri; Erb, Peter C.

doi:10.1128/jvi.76.5.2551-2556.2002

Cited by 26 publications

(17 citation statements)

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“…Further incubation of this blot with antibodies to the lytic gene products ORF45 and ORF65 and to GFP revealed the similar expression of these proteins following lytic induction, suggesting that the efficiency of lytic reactivation of BAC16-mCherry-vBcl-2 is similar to that of wild-type BAC16. Of note, previous studies by others (34) and by our group (data not shown) failed to identify the expression of vBcl-2 protein in cultivated cells, and to the best of our knowledge, the present study is the first to detect endoge- (Fig. 3).…”

Section: Construction Of Bac16-vbcl-2-stopmentioning

confidence: 56%

“…In contrast to the levels of expression of mCherry-tagged ORF45 and of mCherry protein, which was expressed under the control of the same transcriptional control element as mCherry-vBcl-2, the level of vBcl-2 expression was low. This may account for the inability to detect the expression of vBcl-2 in KSHV-infected cell lines by using polyclonal antibodies produced by other groups (34) and in our lab (data not shown). This, together with the abundant cleavage of mCherryvBcl-2, did not allow the use of immunofluorescence to track the expression of mCherry-vBcl-2 within cells.…”

Section: Construction Of Bac16-vbcl-2-stopmentioning

confidence: 60%

“…Thus, inhibition of apoptosis and autophagy by vBcl-2 may provide an attractive mechanism for prolonging the life span of KSHV-infected cells, which in turn enables increased virus production, establishment of latency, and/or efficient reactivation. Of note, transcripts encoding vBcl-2 were detected during lytic infection in various KSHV-infected cell cultures, yet the expression of vBcl-2 protein has been detected only in Kaposi's sarcoma lesions (34). Whether the function of vBcl-2 is necessary for KSHV-mediated oncogenesis is still unknown.…”

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confidence: 99%

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

Gelgor

Kalt

Bergson

et al. 2015

J Virol

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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. IMPORTANCEThe 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. K aposi's sarcoma-associated herpesvirus (KSHV), also referred to as human herpesvirus 8 (HHV-8), is a gamma-2 herpesvirus. KSHV is causally linked to particular human cancers, including Kaposi's sarcoma (KS), primary effusion lymphoma (PEL), and plasmablastic multicentric Castleman's disease (1-7). Among human viruses, KSHV is most closely related to the Epstein-Barr virus (EBV), a tumorigenic gamma-1 herpesvirus known to be associated with lymphomas and nasopharyngeal carcinoma. Like all other herpesviruses, the infectious cycle of KSHV includes two alternative infection phases, latent and lytic. Latent infection allows the virus to establish long-term persistent infection and involves the presence of viral episomes and expression of a small set of viral genes. Lytic infection is needed for the maintenance of viral reservoirs and for virus spread and involves a temporally regulated cascade of viral gene expression and DNA replication, leading to the production and release of new virions. KSHV exists mainly in its latent form in KS lesions and in PEL, yet a small subpopulation of cells undergoes lytic replication. Analogously, most KSHV-infected cultured cells are latently infected. Lytic virus react...

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Section: Construction Of Bac16-vbcl-2-stopmentioning

confidence: 56%

Section: Construction Of Bac16-vbcl-2-stopmentioning

confidence: 60%

mentioning

confidence: 99%

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

Gelgor

Kalt

Bergson

et al. 2015

J Virol

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“…It is expressed in a lytic pattern in spindle cells and monocytes in KS lesions, and its transcript is lytically induced in PEL cells (Fig. 1), although the protein has evaded easy detection there (98,446,533). As predicted by sequence homology, vBcl-2 is antiapoptotic; unlike its cellular counterpart, it can inhibit apoptosis induced by KSHV vCyc in the presence of high cdk6 (378).…”

Section: Orf16/vbcl-2mentioning

confidence: 99%

Molecular Genetics of Kaposi's Sarcoma-Associated Herpesvirus (Human Herpesvirus 8) Epidemiology and Pathogenesis

Dourmishev

Palmeri

et al. 2003

Microbiol Mol Biol Rev

309

367

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Kaposi's sarcoma had been recognized as unique human cancer for a century before it manifested as an AIDS-defining illness with a suspected infectious etiology. The discovery of Kaposi's sarcoma-associated herpesvirus (KSHV), also known as human herpesvirus-8, in 1994 by using representational difference analysis, a subtractive method previously employed for cloning differences in human genomic DNA, was a fitting harbinger for the powerful bioinformatic approaches since employed to understand its pathogenesis in KS. Indeed, the discovery of KSHV was rapidly followed by publication of its complete sequence, which revealed that the virus had coopted a wide armamentarium of human genes; in the short time since then, the functions of many of these viral gene variants in cell growth control, signaling apoptosis, angiogenesis, and immunomodulation have been characterized. This critical literature review explores the pathogenic potential of these genes within the framework of current knowledge of the basic herpesvirology of KSHV, including the relationships between viral genotypic variation and the four clinicoepidemiologic forms of Kaposi's sarcoma, current viral detection methods and their utility, primary infection by KSHV, tissue culture and animal models of latent- and lytic-cycle gene expression and pathogenesis, and viral reactivation from latency. Recent advances in models of de novo endothelial infection, microarray analyses of the host response to infection, receptor identification, and cloning of full-length, infectious KSHV genomic DNA promise to reveal key molecular mechanisms of the candidate pathogeneic genes when expressed in the context of viral infection

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“…Whether the function of KS-Bcl-2 is necessary for KSHV-mediated oncogenesis is still unknown. Nevertheless, the KS-Bcl-2 protein is expressed in late-stage KS lesions but has not been detected in latent or in lytic KSHV-infected PEL cells (39).…”

mentioning

confidence: 99%

GLTSCR2/PICT-1, a Putative Tumor Suppressor Gene Product, Induces the Nucleolar Targeting of the Kaposi's Sarcoma-Associated Herpesvirus KS-Bcl-2 Protein

Kalt

Borodianskiy-Shteinberg

Schachor

et al. 2010

J Virol

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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.

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Differential Expression of Viral Bcl-2 Encoded by Kaposi's Sarcoma-Associated Herpesvirus and Human Bcl-2 in Primary Effusion Lymphoma Cells and Kaposi's Sarcoma Lesions

Cited by 26 publications

References 16 publications

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

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

Molecular Genetics of Kaposi's Sarcoma-Associated Herpesvirus (Human Herpesvirus 8) Epidemiology and Pathogenesis

GLTSCR2/PICT-1, a Putative Tumor Suppressor Gene Product, Induces the Nucleolar Targeting of the Kaposi's Sarcoma-Associated Herpesvirus KS-Bcl-2 Protein

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