Kaposi's sarcoma-associated herpesvirus gene expression in endothelial (spindle) tumor cells

Human herpesvirus 8 (Kaposi's sarcoma-associated herpesvirus) infection in men receiving treatment for HIV-1 infection

OBJECTIVE

To determine the prevalence of human herpesvirus 8 (HHV-8) infection in men treated for HIV-1 infection in Denver, Colorado.

DESIGN

Cross-sectional analysis

METHODS

Blood samples were obtained from 216 HIV-1-infected men. Antibody to latency-associated nuclear antigen (LANA) was detected by an immunofluorescent assay and the presence of HHV-8 in peripheral blood mononuclear cells (PBMC) was detected by polymerase chain reaction amplification.

RESULTS

Among HIV-1-infected men who did not have Kaposi's sarcoma (KS), prevalence of HHV-8 infection was 46% (95% confidence interval [CI], 0.39-0.52). LANA seropositivity was common both among subjects with KS and subjects without KS (69% versus 42%; p = .06), but detection of HHV-8 DNA in peripheral blood was strongly associated with a diagnosis of KS (44% versus 10%; p = .001). In a univariate analysis of study subjects without KS, neither the odds of LANA seropositivity nor detection of HHV-8 DNA in PBMC was significant for CD4+ lymphocyte count, HIV-1 virus load, the use of three drug antiretroviral regimens or the prior occurrence of non-KS AIDS-related conditions.

CONCLUSION

Although antibodies to HHV-8 are common among HIV-1-infected men, detection of HHV-8 DNA in PBMC is uncommon and is associated with a diagnosis of Kaposi's sarcoma.

Transcriptional activation by the product of open reading frame 50 of Kaposi's sarcoma-associated herpesvirus is required for lytic viral reactivation in B cells

Kaposi's sarcoma (KS)-associated herpesvirus (KSHV) is a lymphotropic virus strongly linked to the development of KS, an endothelial cell neoplasm frequent in persons with AIDS. Reactivation from latency in B cells is thought to be an important antecedent to viral spread to endothelial cells during KS pathogenesis. Earlier experiments have posited a role for the transcriptional activator encoded by KSHV open reading frame 50 (ORF50) in such reactivation, since ectopic overexpression of this protein induces reactivation in latently infected B cells. Here we have explored several aspects of the expression, structure, and function of this protein bearing on this role. The ORF50 gene is expressed very early in lytic reactivation, before several other genes implicated as candidate regulatory genes in related viruses, and its expression can upregulate their promoters in transient assays. The protein is extensively phosphorylated in vivo and bears numerous sites for phosphorylation by protein kinase C, activators of which are potent stimulators of lytic induction. The C terminus of the ORF50 protein contains a domain that can strongly activate transcription when targeted to DNA; deletion of this domain generates an allele that expresses a truncated protein which retains the ability to form multimers with full-length ORF50 and functions as a dominant-negative protein. Expression of this allele in latently infected cells ablates spontaneous reactivation from latency and strikingly suppresses viral replication induced by multiple stimuli, including phorbol ester, ionomycin, and sodium butyrate. These results indicate that the ORF50 gene product plays an essential role in KSHV lytic replication and are consistent with its action as a putative molecular switch controlling the induction of virus from latency.

Expression of K13/v-FLIP gene of human herpesvirus 8 and apoptosis in Kaposi's sarcoma spindle cells

BACKGROUND

Human herpesvirus 8 (HHV8) infection is associated with all forms of Kaposi's sarcoma (KS). The HHV8 genome locus ORFK13-72-73 (ORF = open reading frame) encodes proteins that may be important in HHV8-mediated pathogenesis, i.e., the latency-associated nuclear antigen (encoded by ORF73), viral-cyc-D (v-cyc-D), a viral homologue of cellular cyclin D (encoded by ORF72), and viral-FLIP (v-FLIP), a homologue of the cellular FLICE (Fas-associated death domain-like interleukin 1 beta-converting enzyme) inhibitory protein (encoded by ORFK13; is an inhibitor of apoptosis [programmed cell death]). Through differential splicing events, this locus expresses individual RNA transcripts that encode all three proteins (tricistronic transcripts) or just two of them (v-FLIP and v-cyc-D; bicistronic transcripts). We examined expression of these transcripts in KS tissues.

METHODS

We collected tissues from patients with KS of different stages. By use of an optimized in situ hybridization procedure, we examined different ORFK13-72-73 locus transcripts in HHV8-infected cells in skin lesions and in one adjacent lymph node. Apoptosis in KS lesions was determined by use of an in situ assay.

RESULTS AND CONCLUSIONS

Our results indicate the following: 1) Transcripts from the ORFK13-72-73 locus appear to be spliced differentially in latently infected KS cells in skin lesions and in HHV8-infected cells in lymph nodes; specifically, ORFK13-ORF72 bicistronic transcripts were expressed abundantly in KS cells, whereas ORFK13-ORF72-ORF73 tricistronic transcripts were detected only in lymph node cells. 2) Sequences encoding the antiapoptotic protein v-FLIP are expressed at very low levels in early KS lesions, but expression increases dramatically in late-stage lesions. 3) The increase in expression of v-FLIP-encoding transcripts is associated with a reduction in apoptosis in KS lesions.

IMPLICATIONS

These data suggest that functional v-FLIP is produced in vivo and that antiapoptotic mechanisms may be involved in the rapid growth of KS lesions, where only a few cells undergoing mitosis are generally observed.

Characterization of human herpesvirus-8 K8.1A/B glycoproteins by monoclonal antibodies

Human herpesvirus-8 K8.1 gene encodes for two immunogenic class I glycoproteins, K8.1A and B, originating from spliced messages [(1998) Virology 243, 208-217]. The 228-amino-acid-long K8.1A open reading frame (ORF) contains four N-glycosylation sites and the 167-amino-acid-long K8.1B ORF contains three N-glycosylation sites, sharing similar amino- and carboxyl-termini with ORF K8.1A but with an in-frame deletion [(1998) Virology 249, 140-149]. To characterize the K8.1A and B glycoproteins in the infected body cavity-based B cell lymphoma (BCBL-1) cells and in the virion envelopes, monoclonal antibodies (MAbs) recognizing only K8.1A protein or both K8.1A and B proteins were generated. These antibodies reacted with the infected cell membranes and virion envelopes. Stable COS-1 transformant cells expressed the K8.1A and B proteins independently on the plasma membranes. MAbs recognized multiple proteins with molecular weights ranging from 23 to 72 kDa from the BCBL-1 cells and COS-1 cells and the 72 to 68 kDa molecular-weight proteins from the virion particles. The K8.1A is the predominant protein affinity purified from the infected BCBL-1 cells. Digestion with glycosidases show that these proteins contain both N- and O-linked sugars, suggesting that the multiple proteins recognized by the MAbs represent the precursor and product forms of K8.1A and B proteins, and the 72 to 68 kDa molecular-weight proteins represent the virion particle-associated mature forms of these glycoproteins.

Expression of human herpesvirus-8 (HHV-8) encoded pathogenic genes in Kaposi's sarcoma (KS) primary lesions

Transcription of six different HHV-8 specific mRNAs was examined in early- and late-stage KS primary lesions. Expression of the latency-associated T0.7 mRNA and of VP23 mRNA which is a specific marker of lytic/productive infection suggested that HHV-8 is secondarily recruited into the KS lesions by productively infected monocytes, macrophages. From these cells HHV-8 is transmitted to the KS spindle cells, which are latently infected. v-BCL-2, v-MCP-1 and v-IL-6 were not expressed in latently infected KS spindle cells, therefore the impact of these factors in KS pathogenesis appears to be low. By contrast, v-Cyclin D was highly expressed in almost all latently infected spindle cells and may therefore be an important factor triggering progression of late-stage KS lesions.

Virus-associated lymphomas

Epstein-Barr virus, Kaposi's sarcoma-associated herpesvirus/human herpesvirus 8, and human T-cell lymphotrophic virus are viruses that are implicated in lymphoid neoplasia in humans. Their association with specific subsets of lymphomas suggests that they play an important, although not sufficient, etiologic role in their development. Current knowledge suggests that these viruses contribute to lymphomagenesis by subverting the host-cell molecular machinery to deregulate cell growth and survival. In this article, the basic information and recent developments that have contributed to our understanding of viral lymphomagenesis are reviewed.

Human Herpesvirus 8 Infections

Human herpesvirus 8 (HHV-8) or Kaposi's sarcoma (KS)-associated herpesvirus is a recently identified virus that is associated with KS, multicentric Castleman's disease, and body cavity-based lymphomas. KS is the most common kind of cancer in AIDS patients and the initial AIDS-defining condition in over 20% of patients. HHV-8 DNA has now been detected in over 95% of KS tissue samples supporting the concept that HHV-8 has a causal role in KS. The discovery has opened new avenues for understanding the epidemiology, pathogenesis, and treatment of KS and related conditions.

Identification of a spliced gene from Kaposi's sarcoma-associated herpesvirus encoding a protein with similarities to latent membrane proteins 1 and 2A of Epstein-Barr virus

Kaposi's sarcoma-associated herpesvirus (KSHV) or human herpesvirus 8 (HHV-8) is a novel herpesvirus implicated as the causative agent of Kaposi's sarcoma (KS), primary effusion lymphoma, and some cases of multicentric Castleman's disease. KSHV persists in the majority of KS spindle (endothelial tumor) cells and lymphoid cells in a latent form, with only a limited set of viral genes expressed in a tissue-specific manner. Here, we report the identification of a family of alternatively-spliced transcripts of approximately 7.5 kb expressed in latently infected body cavity-based lymphoma (BCBL) cell lines which are predicted to encode membrane proteins with similarities to the LMP2A and LMP1 proteins of Epstein-Barr virus. In two highly divergent sequence variants of the right end of the KSHV genome, alternative splicing of eight exons located between KSHV ORF 75 and the terminal repeats yields transcripts appropriate for proteins with up to 12 transmembrane domains, followed by a hydrophilic C-terminal, presumably cytoplasmic, domain. This C-terminal domain contains several YxxI/L motifs reminiscent of LMP2A and a putative TRAF binding site as in LMP1. In latently (persistently) infected BCBL cells the predominant transcript utilizes all eight exons, whereas in phorbol-ester-induced cells, a shorter transcript, lacking exons 4 and 5, is also abundant. We also found evidence for an alternative use of exon 1. Transfection of an epitope-tagged cDNA construct containing all exons indicates that the encoded protein is localized on cell surface and intracellular membranes, and glutathione S-transferase pull-down experiments indicate that its cytoplasmic domain, like that of LMP1, interacts with TRAF1, -2, and -3. Two of 20 KS patients had antibodies to the hydrophilic C-terminal domain, suggesting that the protein is expressed in vivo.

Comparison of genetic variability at multiple loci across the genomes of the major subtypes of Kaposi's sarcoma-associated herpesvirus reveals evidence for recombination and for two distinct types of open reading frame K15 alleles at the right-hand end

Kaposi's sarcoma (KS)-associated herpesvirus or human herpesvirus 8 (HHV8) DNA is found consistently in nearly all classical, endemic, transplant, and AIDS-associated KS lesions, as well as in several AIDS-associated lymphomas. We have previously sequenced the genes for the highly variable open reading frame K1 (ORF-K1) protein from more than 60 different HHV8 samples and demonstrated that they display up to 30% amino acid variability and cluster into four very distinct evolutionary subgroups (the A, B, C, and D subtypes) that correlate with the major migrationary diasporas of modern humans. Here we have extended this type of analysis to six other loci across the HHV8 genome to further evaluate overall genotype patterns and the potential for chimeric genomes. Comparison of the relatively conserved ORF26, T0.7/K12, and ORF75 gene regions at map positions 0. 35, 0.85, and 0.96 revealed typical ORF-K1-linked subtype patterns, except that between 20 and 30% of the genomes analyzed proved to be either intertypic or intratypic mosaics. In addition, a 2,500-bp region found at the extreme right-hand side of the unique segment in 45 HHV8 genomes proved to be highly diverged from the 3,500-bp sequence found at this position in the other 18 HHV8 genomes examined. Furthermore, these previously uncharacterized "orphan" region sequences proved to encompass multiexon latent-state mRNAs encoding two highly diverged alleles of the novel ORF-K15 protein. The predominant (P) and minor (M) forms of HHV8 ORF-K15 are structurally related integral membrane proteins that have only 33% overall amino acid identity to one another but retain conserved likely tyrosine kinase signaling motifs and may be distant evolutionary relatives of the LMP2 latency protein of Epstein-Barr virus. The M allele of ORF-K15 is also physically linked to a distinctive M subtype of the adjacent ORF75 gene locus, and in some cases, this linkage extends as far back as the T0.7 locus also. Overall, the results suggest that an original recombination event with a related primate virus from an unknown source introduced exogenous right-hand side ORF-K15(M) sequences into an ancient M form of HHV8, followed by eventual acquisition into the subtype C lineage of the modern P-form of the HHV8 genome and subsequent additional, more recent transfers by homologous recombination events into several subtype A and B lineages as well.

Long-term infection and transformation of dermal microvascular endothelial cells by human herpesvirus 8

Human herpesvirus 8 (HHV8) infects Kaposi's sarcoma (KS) spindle cells in situ, as well as the lesional endothelial cells considered to be spindle cell precursors. The HHV8 genome contains several oncogenes, suggesting that infection of endothelial and spindle cells could induce cellular transformation and tumorigenesis and promote the formation of KS lesions. To investigate the potential of HHV8 infection of endothelial cells to contribute to the development of KS, we have developed an in vitro model utilizing dermal microvascular endothelial cells that support significant HHV8 infection. In contrast to existing in vitro systems used to study HHV8 pathogenesis, the majority of dermal endothelial cells are infected with HHV8 and the viral genome is maintained indefinitely. Infection is predominantly latent, with a small percentage of cells supporting lytic replication, and latency is responsive to lytic induction stimuli. Infected endothelial cells develop a spindle shape resembling that of KS lesional cells and show characteristics of a transformed phenotype, including loss of contact inhibition and acquisition of anchorage-independent growth. These results describe a relevant model system in which to study virus-host interactions in vitro and demonstrate the ability of HHV8 to induce phenotypic changes in infected endothelial cells that resemble characteristics of KS spindle cells in vivo. Thus, our results are consistent with a direct role for HHV8 in the pathogenesis of KS.

Unraveling immunity to gamma-herpesviruses: a new model for understanding the role of immunity in chronic virus infection

Murine gamma-herpesvirus 68 (gammaHV68) infection is a new model for understanding how immunity and chronic gamma-herpesvirus infection inter-relate. gammaHV68 is closely related to the human Epstein-Barr virus and Kaposi's sarcoma herpesvirus and is associated with tumors, vasculitis of the great elastic arteries and splenic fibrosis. Advances in the past year have provided an even stronger foundation for believing that gammaHV68 infection of normal and mutant mice will become the pre-eminent animal model for understanding gamma-herpesvirus pathogenesis and immunity. gammaHV68 latency has been characterized employing new assays for quantitating cells carrying the gammaHV68 genome and cells that reactivate gammaHV68 and for detecting the presence of preformed infectious virus in tissues. These advances have fostered the first steps towards a molecular definition of gammaHV68 latency. It appears that gammaHV68 shares latency programs with human gamma-herpesviruses - including the loci for gene 73, v-bcl-2 and the viral homolog of the G-protein coupled receptor. This provides candidate antigens for analysis of the role of T and B cells in regulating latency. Multiple cellular reservoirs for gammaHV68 latency were uncovered with the demonstration that gammaHV68 latently infects macrophages in addition to B cells. A critical role for B cells in regulating the nature of gammaHV68 latency was discovered and the mechanism was shown to be via alteration of the efficiency of reactivation. Studies of the response of CD4(+) and CD8(+) cells during acute and chronic gammaHV68 were performed. These new studies provide key building blocks for further development of this novel and interesting model system.

Comparison of the immunoglobulin-G-specific seroreactivity of different recombinant antigens of the human herpesvirus 8

The open reading frames ORF 52, ORF 65, K12, and K8.1 of the human herpesvirus 8 (HHV8) were expressed as glutathione-S-transferase (GST) fusion proteins and analysed by Western blotting (WB) and enzyme-linked immunosorbent assay (ELISA). The open reading frame (ORF) 65 and K8.1 antigens gave the highest reactivity (71%) in sera from HIV-dependent Kaposi's sarcoma (KS) patients. Therefore both antigens appear to be essential for HHV8 diagnostics, whereas ORF K12 and ORF 52 were of minor importance. Using polymerase chain reaction (PCR) out of the peripheral blood of these KS patients, 48% were detected as positive. By testing an N-terminal-deleted construct (amino acid 80-171) of ORF 65, we could show that the N-terminal region of this protein is essential to mediate full immunogenic reactivity. By analysing different deletion mutants of ORF K8.1, the major epitope was found to be located between aa 29 and 101. The prevalence of antibodies directed against the different antigens was determined for healthy blood donors to be 3-6%. The different antibody patterns obtained in HIV-patients with and without KS support the hypothesis that different antibody profiles develop during the course of KS.

High expression of HHV-8-encoded ORF73 protein in spindle-shaped cells of Kaposi's sarcoma

Human herpesvirus 8 (HHV-8) has been demonstrated previously in Kaposi's sarcoma (KS) tissues by immunohistochemistry, in situ polymerase chain reaction, and in situ hybridization. The HHV-8-encoded protein ORF73 is a 222- or 234-kd protein named latent nuclear antigen (LNA) or latency-associated nuclear antigen (LANA) that is identified in HHV-8-infected cell lines by immunofluorescence assay. In the present study, a rabbit antibody against a recombinant ORF73 protein was developed. Immunofluorescent staining of a HHV-8-infected cell line, TY-1, showed that the staining pattern of the anti-ORF73 antibody overlapped completely the LANA staining pattern obtained using KS patients' sera. Immunoblotting analysis showed that the anti-ORF73 antibody reacted specifically with 222- and 234-kd proteins that were present in TY-1 and BCBL-1 cell lysates. Immunohistochemistry using a catalyzed signal amplification system demonstrated that the anti-ORF73 antibody reacted exclusively with the majority of KS spindle-shaped cells, showing a nuclear dot-like staining pattern. Some of the ORF73 protein-positive cells also expressed CD34 and vimentin but not CD68 or factor-VIII-related antigen. These data indicate that the anti-ORF73 antibody recognizes LANA and that most KS cells are infected with HHV-8 in the latent phase. Our findings also suggest that ORF73 protein plays an important role in the pathogenesis of KS.

Identification of human herpesvirus 8-specific cytotoxic T-cell responses

Human herpesvirus 8 (HHV-8) (or Kaposi's sarcoma-associated herpesvirus) is implicated in the etiopathogenesis of Kaposi's sarcoma (KS) and certain lymphoproliferations. The introduction of more effective therapies to treat human immunodeficiency virus infection has led to a decline in the incidence of KS and also in the resolution of KS in those already affected. This suggests that cellular immune responses including cytotoxic T lymphocytes (CTLs) could play a vital role in the control of HHV-8 infection and in KS pathogenesis. Here we elucidate HLA class I-restricted, HHV-8-specific cellular immune responses that could be important in the control of HHV-8 infection and subsequent tumor development. We show the presence of CTLs against HHV-8 latent (K12), lytic (K8.1), and highly variable (K1) proteins in infected individuals.

A complex translational program generates multiple novel proteins from the latently expressed kaposin (K12) locus of Kaposi's sarcoma-associated herpesvirus

The most abundantly expressed latent transcripts encoded by the Kaposi's sarcoma (KS)-associated herpesvirus derive from the genomic region surrounding open reading frame (ORF) K12 (kaposin A). Here we show that these transcripts, initially described as limited to ORF K12 itself, more frequently encompass upstream sequences spanning two sets of 23-nucleotide GC-rich direct repeats (DRs) (DR1 and DR2). Although the DRs lack AUG codons and were previously presumed to be noncoding, a monoclonal antibody raised to infected cells detected multiple polypeptides encoded by this region. These proteins are expressed during latency and upon induction of lytic viral replication in both primary effusion lymphoma (PEL) cell lines and KS tumors. Biochemical and genetic analyses reveal that these proteins are derived from variant translational initiation at CUG codons. The predominant translation product in the PEL cell line BCBL-1 derives from the 5'-most CUG codon in the transcript, resulting in a protein (termed kaposin B) which is encoded largely by the repeats themselves and which does not include K12 sequences. Other non-AUG codons in alternate reading frames are also used at lower efficiency, including one that initiates translation of a DR-K12 fusion protein (kaposin C) that is predicted to sort to a different subcellular locale than kaposin B. Thus, the products of the K12 region, which is the most abundantly transcribed region in latency, are surprisingly complex and may encompass multiple biological functions.

Detection of human herpesvirus 8 in Korean Kaposi's sarcoma cases by polymerase chain reaction and in situ polymerase chain reaction

Several infectious agents, including herpesvirus-like particles, had been suggested as possible candidates for the development of Kaposi's sarcoma (KS), and a new herpesvirus, human herpesvirus 8 (HHV-8), was recently identified in the vast majority of KS lesions, irrespective of their association with human immunodeficiency virus (HIV) infection. However, the etiologic role of HHV-8 in KS remains controversial. We undertook this study to screen for and localize the presence of HHV-8 in KS in Korea. A total of 46 paraffin-embedded specimens were studied, including KS, hemangioproliferative disorders, and 10 non-KS lesions from HIV-positive patients. We performed nested polymerase chain reaction (PCR) and in situ PCR with HHV-8 specific primers. HHV-8 DNA sequences were detected in 8 of 11 KS specimens. All specimens of hemangioproliferative disorders, non-KS lesions from HIV-positive patients, and other skin samples were negative for HHV-8. When sequencing PCR products, the sequences were almost identical with the prototypic sequence for HHV-8. In PCR-positive tissues, in situ PCR staining of HHV-8 localized to nuclei of endothelial cells and perivascular spindle-shaped tumor cells. The results of this study suggest that HHV-8 is not widespread and has a certain causative role in the development of KS. Further studies, including serological and animal studies, will be helpful to appreciate an epidermiological link and pathogenetic mechanism between HHV-8 and KS.

Expression of the open reading frame 74 (G-protein-coupled receptor) gene of Kaposi's sarcoma (KS)-associated herpesvirus: implications for KS pathogenesis

Kaposi's sarcoma (KS)-associated herpesvirus (KSHV) encodes a G-protein-coupled receptor (GCR) homolog. This protein is a potent, constitutively active signalling molecule that can influence both proliferation and angiogenesis when ectopically expressed in fibroblasts in vitro. Here we have examined the expression of the KSHV GCR gene in virus-infected lymphoid cells and in KS tumors. Our results show that in both situations the gene is expressed primarily during lytic replication; its transcription is unaffected by inhibition of viral DNA synthesis, indicating that it is expressed in the early phases of the lytic program. The major transcript bearing GCR sequences is bicistronic, harboring coding sequences for another viral gene, K14, at its 5' end. Extensive searches for monocistronic GCR mRNAs using nuclease mapping and reverse transcription-PCR failed to detect such species. The 5' end of K14/GCR mRNA maps to nucleotide (nt) 127848, and its poly(A) addition site maps to nt 130546; a 149-nt intron is present in the K14/GCR intergenic region. These results suggest that the KSHV GCR is translated by unconventional mechanisms involving either translational reinitiation, internal ribosomal entry, or leaky ribosomal scanning. The restriction of GCR expression to the lytic cycle has important implications for the potential role(s) of the GCR in KS pathogenesis.

Interleukin-4 receptor-directed cytotoxin therapy of AIDS-associated Kaposi's sarcoma tumors in xenograft model

The elusive and enigmatic origin of AIDS-associated Kaposi's sarcoma (AIDS-KS) makes it a complex tumor and therefore difficult to treat. Here we demonstrate that AIDS-KS cells express surface interleukin-4 (IL-4) receptors, and that IL-4 toxin (IL-4(38-37)-PE38KDEL) is specifically cytotoxic to these cells. Intratumoral, intraperitoneal and intravenous administration of IL-4 toxin in nude mice with established subcutaneous AIDS-KS tumors caused considerable anti-tumor activity in a dose-dependent manner, with highest dose producing durable complete responses. Metabolic changes, including cachexia and lymphopenia, induced by KS tumors were prevented by IL-4 toxin treatment. This report establishes IL-4(38-37)-PE38KDEL as an experimental therapeutic agent for the treatment of AIDS-KS.

Human cytomegalovirus and human herpesvirus 6 genes that transform and transactivate

This review is an update on the transforming genes of human cytomegalovirus (HCMV) and human herpesvirus 6 (HHV-6). Both viruses have been implicated in the etiology of several human cancers. In particular, HCMV has been associated with cervical carcinoma and adenocarcinomas of the prostate and colon. In vitro transformation studies have established three HCMV morphologic transforming regions (mtr), i.e., mtrI, mtrII, and mtrIII. Of these, only mtrII (UL111A) is retained and expressed in both transformed and tumor-derived cells. The transforming and tumorigenic activities of the mtrII oncogene were localized to an open reading frame (ORF) encoding a 79-amino-acid (aa) protein. Furthermore, mtrII protein bound to the tumor suppressor protein p53 and inhibited its ability to transactivate a p53-responsive promoter. In additional studies, the HCMV immediate-early protein IE86 (IE2; UL122) was found to interact with cell cycle-regulatory proteins such as p53 and Rb. However, IE86 exhibited transforming activity in vitro only in cooperation with adenovirus E1A. HHV-6 is a T-cell-tropic virus associated with AIDS-related and other lymphoid malignancies. In vitro studies identified three transforming fragments, i.e., SalI-L, ZVB70, and ZVH14. Of these, only SalI-L (DR7) was retained in transformed and tumor-derived cells. The transforming and tumorigenic activities of SalI-L have been localized to a 357-aa ORF-1 protein. The ORF-1 protein was expressed in transformed cells and, like HCMV mtrII, bound to p53 and inhibited its ability to transactivate a p53-responsive promoter. HHV-6 has also been proposed to be a cofactor in AIDS because both HHV-6 and human immunodeficiency virus type 1 (HIV-1) have been demonstrated to coinfect human CD4(+) T cells, causing accelerated cytopathic effects. Interestingly, like the transforming proteins of DNA tumor viruses such as simian virus 40 and adenovirus, ORF-1 was also a transactivator and specifically up-regulated the HIV-1 long terminal repeat when cotransfected into CD4(+) T cells. Finally, based on the interactions of HCMV and HHV-6 transforming proteins with tumor suppressor proteins, a scheme is proposed for their role in oncogenesis.

Antibodies against human herpesvirus 8 in black South African patients with cancer

BACKGROUND

Infection with human herpesvirus 8 (HHV-8) has been consistently linked to Kaposi's sarcoma, but its mode of transmission, association with other cancers, and interaction with the human immunodeficiency virus type 1 (HIV-1) are largely unknown.

METHODS

Between January 1992 and December 1997, we interviewed 3591 black patients with cancer in Johannesburg and Soweto, South Africa. Blood was tested for antibodies against HIV-1 and HHV-8 in 3344 of the patients. Antibodies against HHV-8 were detected with an indirect immunofluorescence assay. The intensity of the fluorescent signal correlated well with the titers of antibodies (P<0.001). The relations among the presence of anti-HHV-8 antibodies, sociodemographic and behavioral factors, type of cancer, and the presence or absence of coexistent HIV infection were examined with the use of unconditional logistic-regression models.

RESULTS

Among the 3293 subjects with cancers other than Kaposi's sarcoma, the standardized seroprevalence of antibodies against HHV-8 was 32 percent, which did not differ significantly from the standardized seroprevalence among black blood donors. Among these 3293 patients, the prevalence of antibodies against HHV-8 increased with increasing age (P<0.001) and an increasing number of sexual partners (P=0.05) and decreased with increasing years of education (P=0.007); it was not strongly associated with HIV-1 infection. Anti-HHV-8 antibodies were more frequent among black than white blood donors (P<0.001). Among the 51 patients with Kaposi's sarcoma, the standardized seroprevalence of antibodies against HHV-8 was 83 percent, significantly higher than the prevalence among those without Kaposi's sarcoma (P<0.001). For 16 other specific types of cancer, including multiple myeloma (108 cases) and prostate cancer (202 cases), the variation in the standardized seroprevalence of antibodies against HHV-8 was not remarkable. At a given intensity of fluorescence of anti-HHV-8 antibodies, Kaposi's sarcoma was more frequent among HIV-1-positive patients than among those who were HIV-1-negative (P<0.001).

CONCLUSIONS

Among black patients with cancer in South Africa, the seroprevalence of anti-HHV-8 antibodies is high and is specifically associated with Kaposi's sarcoma, particularly at high titers.

The role of HHV-8 in Kaposi's sarcoma

The epidemiology of Kaposi's sarcoma (KS) amongst North American and Northern European patients with AIDS suggests that an infectious agent other than HIV is involved in its pathogenesis. Several lines of evidence indicate that human herpesvirus 8 (HHV-8), also termed Kaposi's sarcoma associated herpesvirus, is the sought after agent. DNA of HHV-8 is invariably found in all forms of KS where the virus is present in the KS spindle cell. In contrast, HHV-8 DNA is not regularly detected in most other malignancies. Antibodies against HHV-8 are more frequently found in groups at risk of KS, and HHV-8 seroconversion precedes KS development. Several HHV-8 genes have been identified that exhibit transforming potential in cell culture systems. In addition, the virus encodes and induces several cytokines and angiogenic factors. This is of particular interest as models of KS pathogenesis developed before the discovery of HHV-8 emphasized the importance of inflammatory cytokines. Although the expression pattern of viral genes in KS is not certain yet, it appears likely that the pathogenetic role of HHV-8 in KS may be rather complex and differs from other virus-induced malignancies. 1999 Academic Press.

The role of Kaposi's sarcoma-associated herpesvirus (KSHV/HHV-8) in lymphoproliferative diseases

The Kaposi's sarcoma-associated herpesvirus (KSHV), also called human herpesvirus 8 (HHV-8), has been found to be present in a limited subset of lymphoproliferative disorders. Among these are the primary effusion lymphomas, formerly designated body cavity-based lymphomas, a rare type of malignant lymphoma which possesses an unusual set of clinical and biologic features, suggesting that they represent a distinct disease entity. This virus is also present in a large proportion of cases of multicentric Castleman's disease, particularly those associated with HIV-infection. In addition, KSHV has been implicated in the pathogenesis of multiple myeloma, where it has been identified in bone marrow adherent cells but not in the neoplastic myeloma plasma cell population. However, the latter finding remains controversial. The discovery of KSHV in a subset of malignant lymphomas has allowed the development of lymphoma cell lines which now serve as biological reagents for propagating the virus, as a substrate for serologic assays, and as a model system for pathobiologic studies. This review discusses the features of KSHV-associated lymphoproliferative disorders and the evidence supporting its role in the pathogenesis of these diseases.

Deregulated signal transduction by the K1 gene product of Kaposi's sarcoma-associated herpesvirus

The Kaposi's sarcoma (KS)-associated herpesvirus is a lymphotropic virus strongly implicated in the pathogenesis of KS and several lymphoproliferative disorders. The KS-associated herpesvirus K1 gene encodes a transmembrane protein bearing a functional immunoreceptor tyrosine-based activation motif (ITAM)-like sequence; it previously has been proposed to be important in viral tumorigenesis because its expression can trigger cell proliferation in vitro and in vivo. Here we show that expression of the full-length K1 protein can initiate calcium-dependent signal transduction in B cells; however, unlike other ITAM-based signal transduction events, K1 signaling occurs constitutively, in the absence of exogenous crosslinking ligands. This property is caused by its cysteine-rich ectodomain, which when transferred to other consensus ITAMs induces constitutive signaling. Although ITAM-based signaling by K1 involves classical syk and phospholipase C gamma2 activation, both ITAM- and syk-independent signaling pathways are activated by K1 expression. These studies indicate that K1 is a deregulated signaling molecule with pleitropic effects that may explain its known growth deregulatory properties.

Cellular tropism and viral interleukin-6 expression distinguish human herpesvirus 8 involvement in Kaposi's sarcoma, primary effusion lymphoma, and multicentric Castleman's disease

Human herpesvirus 8 (HHV-8) infection has been implicated in the etiology of Kaposi's sarcoma (KS), primary effusion lymphoma (PEL), and multicentric Castleman's disease (MCD), three diseases that frequently develop in immunocompromised, human immunodeficiency virus-positive individuals. One hypothesis that would account for different pathological manifestations of infection by the same virus is that viral genes are differentially expressed in heterogeneous cell types. To test this hypothesis, we analyzed the localization and levels of expression of two viral genes expressed in latent and lytic infections and the viral homologue of interleukin-6 (vIL-6). We show that PEL parallels KS in the pattern of latent and lytic cycle viral gene expression but that the predominant infected cell type is a B cell. We also show that MCD differs from KS not only in the infected cell type (B-cell and T-cell lineage) but also in the pattern of viral gene expression. Only a few cells in the lesion are infected and all of these cells express lytic-cycle genes. Of possibly greater significance is the fact that in a comparison of KS, PEL, and MCD, we found dramatic differences in the levels of expression of vIL-6. Interleukin-6 is a B-cell growth and differentiation factor whose altered expression has been linked to plasma cell abnormalities, as well as myeloid and lymphoid malignancies. Our findings support the hypothesis that HHV-8 plays an important role in the pathogenesis of PEL and MCD, in which vIL-6 acts as an autocrine or paracrine factor in the lymphoproliferative processes common to both.

Alpha interferon inhibits human herpesvirus 8 (HHV-8) reactivation in primary effusion lymphoma cells and reduces HHV-8 load in cultured peripheral blood mononuclear cells

Infection by human herpesvirus 8 (HHV-8) is associated with the development of Kaposi's sarcoma (KS). Since regression of KS can be achieved by treatment of the patients with alpha interferon (IFN-alpha), we analyzed the effects of IFN-alpha or anti-IFN-alpha antibodies (Ab) on HHV-8 latently infected primary effusion lymphoma-derived cell lines (BCBL-1 and BC-1) and on peripheral blood mononuclear cells (PBMC) from patients with all forms of KS and from at-risk subjects. IFN-alpha inhibited in a dose-dependent manner the amplification of HHV-8 DNA in BCBL-1 cells induced to lytic infection with tetradecanoyl phorbol acetate (TPA). This effect was associated with the inhibition of the expression of HHV-8 nut-1 and kaposin genes that are induced early and several hours, respectively, after TPA treatment. In addition, IFN-alpha inhibited virus production and/or release from BCBL-1 cells. Inhibition of nut-1 and kaposin genes by IFN-alpha was also observed in BC-1 cells induced with n-butyrate. Conversely, the addition of anti-IFN-alpha Ab to TPA-induced BCBL-1 cells resulted in a larger number of mature enveloped particles and in a more extensive cytopathic effect due to the neutralization of the endogenous IFN produced by these cells. IFN was also produced by cultured PBMC from HHV-8-infected individuals, and this was associated with a loss of viral DNA during culture. However, the addition of anti-IFN-alpha Ab or anti-type I IFN receptor Ab promoted the maintenance of HHV-8 DNA in these cells that was associated with the detection of the latency-associated kaposin RNA. Finally, the addition of IFN-alpha reduced the HHV-8 load in PBMC. Thus, IFN-alpha appears to have inhibitory effects on HHV-8 persistent infection of PBMC. These results suggest that, in addition to inhibiting the expression of angiogenic factors that are key to KS development, IFN-alpha may induce KS regression by reducing the HHV-8 load and/or inhibiting virus reactivation.

Kaposi's sarcoma-associated herpesvirus: a new human tumor virus, but how?

Kaposi's sarcoma-associated herpesvirus, or human herpesvirus 8, the most recently discovered human tumor virus, is involved in the pathogenesis of Kaposi's sarcoma, primary effusion lymphoma and some cases of multicentric Castleman's disease. It is non-pathogenic in the majority of otherwise healthy individuals but highly oncogenic in the context of HIV-1 infection and iatrogenic immune suppression, and other cofactors might exist. Several viral genes can interfere with normal cell growth and differentiation, but their precise role in oncogenesis is still under investigation.

Multicenter comparison of PCR assays for detection of human herpesvirus 8 DNA in semen

Reported prevalences of human herpesvirus 8 (HHV-8) (Kaposi's sarcoma-associated herpesvirus) in semen have ranged widely. This is possibly due to differences in assay sensitivity, geographic or population-based differences in the true presence of the virus in semen, and PCR contamination. This study assessed interlaboratory sensitivity and reproducibility in the analysis of blinded experimental panels, each consisting of 48 specimens and being composed of semen specimens from different healthy artificial-insemination donors (n = 30) and human immunodeficiency virus (HIV)-infected patients (n = 7) plus positive (n = 4) and negative (n = 7) controls. The experimental panels analyzed in each laboratory were identical except for being independently coded. Of 10 experiments done in five laboratories, 5 experiments from three laboratories had evidence of PCR contamination; all instances of contamination were in the context of nested PCR procedures. In the experiments with no false-positive results, HHV-8 DNA was detected in three (8%) of the 37 semen specimens (two from artificial-insemination donors and one from an HIV-positive patient) but in only 3 (1.6%) of the 184 PCRs in which these specimens were analyzed. This suggests that HHV-8 DNA is present in semen at concentrations that can be too low to allow its consistent detection. This study emphasizes the importance of performing blinded, multi-institution experiments to provide a coherent basis for comparing results and to motivate standardization of methods.

Distribution of human herpesvirus-8 latently infected cells in Kaposi's sarcoma, multicentric Castleman's disease, and primary effusion lymphoma

Human herpesvirus 8 (HHV-8, also called KSHV) is linked to the etiopathogenesis of Kaposi's sarcoma (KS), multicentric Castleman's disease (MCD), and primary effusion lymphoma (PEL). The universal presence of HHV-8 in early KS has not yet been shown. We used a mAb (LN53) against latent nuclear antigen-1 (LNA-1) of HHV-8 encoded by ORF73 to study the distribution of the cell types latently infected by HHV-8 in patch, plaque, and nodular KS, MCD, and PEL. In early KS, HHV-8 is present in <10% of cells forming the walls of ectatic vessels. In nodular KS, HHV-8 is present in cells surrounding slit-like vessels and in >90% of spindle cells, but not in normal vascular endothelium. In addition, HHV-8 colocalizes with vascular endothelial growth factor receptor-3 (VEGFR-3), a marker of lymphatic and precursor endothelium. In early KS lesions, VEGFR-3 is more extensively expressed than LNA-1, indicating that HHV-8 is not inducing the proliferation of VEGFR-3-positive endothelium directly. In MCD, HHV-8 is present in mantle zone large immunoblastic B cells. No staining for LNA-1 is seen in samples from multiple myeloma, prostate cancer, and angiosarcoma, supporting the absence of any etiological link between these diseases and HHV-8.

Comparison of human sera reactivities in immunoblots with recombinant human herpesvirus (HHV)-8 proteins associated with the latent (ORF73) and lytic (ORFs 65, K8.1A, and K8.1B) replicative cycles and in immunofluorescence assays with HHV-8-infected BCBL-1 cells

The development of reliable, sensitive, and specific serological methods for the detection of human herpesvirus-8 (HHV-8) antibodies is critical for a thorough understanding of HHV-8 prevalence and pathogenesis. To evaluate the potential usefulness of HHV-8 proteins in measuring the responses against both latent and lytic antigens, we selected 1 latent [open reading frame (ORF) 73] antigen and 3 HHV-8 lytic antigens (ORFs 65, K8.1A, and K8.1B) previously identified as immunogenic [Virology (1998) 243, 208-217]. Full-length genomic ORF 73 and full-length ORFs 65, K8.1A, and K8.1B from the cDNA clones were cloned, expressed in bacterial and baculovirus-insect cell expression systems, and purified as GST fusion proteins. These recombinant proteins were used in Western blot reactions to test sera from 104 human immunodeficiency virus (HIV)+/Kaposi's sarcoma (KS)+ homosexual men, 77 HIV+/KS- homosexual men, and 84 age-matched HIV-/KS- men. These sera were also tested in immunofluorescence assays (IFAs) with uninduced and 12-O-tetradecanoylphorbol-13-acetate-induced B cell lymphoma-1 cells to detect antibodies against latency-associated nuclear antigens (LANA) and antibodies against lytic antigens (cytoplasmic fluorescence). These sera exhibited differential reactivities reflecting different titers of antibodies against HHV-8 proteins, and variable reactivities were seen more commonly with the sera from HIV-/KS- adult men. In the Western blot assay, 89% (93 of 104) of HIV+/KS + sera, 60% (46 of 77) of HIV+/KS- sera, and 7% (6 of 84) HIV+/KS- sera were reactive with both latent and lytic recombinant antigens. Western blot reactions with ORF 73 protein were more sensitive than LANA-IFA results. The lytic IFA and lytic Western blot (ORFs 65 and K8.1A) assays were more sensitive than the ORF 73 Western blots and LANA-IFA. With an exception of 2 sera from the HIV-/KS- group, all sera positive for lytic IFA antibodies and ORF 65 and K8.1A antibodies were also positive for latent antibodies. With few exceptions, sera positive for ORF 65 antibodies were also positive for K8.1A antibodies, and sera recognized the K8.1A protein more often than the K8.1B protein. There is a high degree of concordance between IFA and Western blot reactions, suggesting that this panel of HHV-8 recombinant proteins could detect a majority of the HHV-8-seropositive individuals. These results suggest that IFA followed by confirmation with the Western blot reactions with a panel of latent and lytic immunogenic antigens would provide a reliable, sensitive, and specific method for the detection of HHV-8 antibodies.

Oral ganciclovir for patients with cytomegalovirus retinitis treated with a ganciclovir implant. Roche Ganciclovir Study Group

BACKGROUND

The intraocular ganciclovir implant is effective for local treatment of cytomegalovirus retinitis in patients with the acquired immunodeficiency syndrome (AIDS), but it does not treat or prevent other systemic manifestations of cytomegalovirus infection.

METHODS

Three hundred seventy-seven patients with AIDS and unilateral cytomegalovirus retinitis were randomly assigned to one of three treatments: a ganciclovir implant plus oral ganciclovir (4.5 g daily), a ganciclovir implant plus oral placebo, or intravenous ganciclovir alone. The primary outcome measure was the development of new cytomegalovirus disease, either contralateral retinitis or biopsy-proved extraocular disease.

RESULTS

The incidence of new cytomegalovirus disease at six months was 44.3 percent in the group assigned to the ganciclovir implant plus placebo, as compared with 24.3 percent in the group assigned to the ganciclovir implant plus oral ganciclovir (P=0.002) and 19.6 percent in the group assigned to intravenous ganciclovir alone (P<0.001). As compared with placebo, oral ganciclovir reduced the overall risk of new cytomegalovirus disease by 37.6 percent over the one-year period of the study (P=0.02). However, in the subgroup of 103 patients who took protease inhibitors, the rates of new cytomegalovirus disease were low and of similar magnitude, regardless of treatment assignment. Progression of retinitis in the eye that initially received an implant was delayed by the addition of oral ganciclovir, as compared with placebo (P=0.03). Treatment with oral or intravenous ganciclovir reduced the risk of Kaposi's sarcoma by 75 percent (P=0.008) and 93 percent (P<0.001), respectively, as compared with placebo.

CONCLUSIONS

In patients with AIDS and cytomegalovirus retinitis, oral ganciclovir in conjunction with a ganciclovir implant reduces the incidence of new cytomegalovirus disease and delays progression of the retinitis. Treatment with oral or intravenous ganciclovir also reduces the risk of Kaposi's sarcoma.

Sequence and genomic analysis of a Rhesus macaque rhadinovirus with similarity to Kaposi's sarcoma-associated herpesvirus/human herpesvirus 8

We have sequenced the long unique region (LUR) and characterized the terminal repeats of the genome of a rhesus rhadinovirus (RRV), strain 17577. The LUR as sequenced is 131,364 bp in length, with a G+C content of 52.2% and a CpG ratio of 1.11. The genome codes for 79 open reading frames (ORFs), with 67 of these ORFs similar to genes found in both Kaposi's sarcoma-associated herpesvirus (KSHV) (formal name, human herpesvirus 8) and herpesvirus saimiri. Eight of the 12 unique genes show similarity to genes found in KSHV, including genes for viral interleukin-6, viral macrophage inflammatory protein, and a family of viral interferon regulatory factors (vIRFs). Genomic organization is essentially colinear with KSHV, the primary differences being the number of cytokine and IRF genes and the location of the gene for dihydrofolate reductase. Highly repetitive sequences are located in positions corresponding to repetitive sequences found in KSHV. Phylogenetic analysis of several ORFs supports the similarity between RRV and KSHV. Overall, the sequence, structural, and phylogenetic data combine to provide strong evidence that RRV 17577 is the rhesus macaque homolog of KSHV.

Macrophages are the major reservoir of latent murine gammaherpesvirus 68 in peritoneal cells

B cells have previously been identified as the major hematopoietic cell type harboring latent gammaherpesvirus 68 (gammaHV68) (N. P. Sunil-Chandra, S. Efstathiou, and A. A. Nash, J. Gen. Virol. 73:3275-3279, 1992). However, we have shown that gammaHV68 efficiently establishes latency in B-cell-deficient mice (K. E. Weck, M. L. Barkon, L. I. Yoo, S. H. Speck, and H. W. Virgin, J. Virol. 70:6775-6780, 1996), demonstrating that B cells are not required for gammaHV68 latency. To understand this dichotomy, we determined whether hematopoietic cell types, in addition to B cells, carry latent gammaHV68. We observed a high frequency of cells that reactivate latent gammaHV68 in peritoneal exudate cells (PECs) derived from both B-cell-deficient and normal C57BL/6 mice. PECs were composed primarily of macrophages in B-cell-deficient mice and of macrophages plus B cells in normal C57BL/6 mice. To determine which cells in PECs from C57BL/6 mice carry latent gammaHV68, we developed a limiting-dilution PCR assay to quantitate the frequency of cells carrying the gammaHV68 genome in fluorescence-activated cell sorter-purified cell populations. We also quantitated the contribution of individual cell populations to the total frequency of cells carrying latent gammaHV68. At early times after infection, the frequency of PECs that reactivated gammaHV68 correlated very closely with the frequency of PECs carrying the gammaHV68 genome, validating measurement of the frequency of viral-genome-positive cells as a measure of latency in this cell population. F4/80-positive macrophage-enriched, lymphocyte-depleted PECs harbored most of the gammaHV68 genome and efficiently reactivated gammaHV68, while CD19-positive, B-cell-enriched PECs harbored about a 10-fold lower frequency of gammaHV68 genome-positive cells. CD4-positive, T-cell-enriched PECs contained only a very low frequency of gammaHV68 genome-positive cells, consistent with previous analyses indicating that T cells are not a reservoir for gammaHV68 latency (N. P. Sunil-Chandra, S. Efstathiou, and A. A. Nash, J. Gen. Virol. 73:3275-3279, 1992). Since macrophages are bone marrow derived, we determined whether elicitation of a large inflammatory response in the peritoneum would recruit additional latent cells into the peritoneum. Thioglycolate inoculation increased the total number of PECs by about 20-fold but did not affect the frequency of cells that reactivate gammaHV68, consistent with a bone marrow reservoir for latent gammaHV68. These experiments demonstrate gammaHV68 latency in two different hematopoietic cell types, F4/80-positive macrophages and CD19-positive B cells, and argue for a bone marrow reservoir for latent gammaHV68.

Three distinct regions of the murine gammaherpesvirus 68 genome are transcriptionally active in latently infected mice

The program(s) of gene expression operating during murine gammaherpesvirus 68 (gammaHV68) latency is undefined, as is the relationship between gammaHV68 latency and latency of primate gammaherpesviruses. We used a nested reverse transcriptase PCR strategy (sensitive to approximately one copy of gammaHV68 genome for each genomic region tested) to screen for the presence of viral transcripts in latently infected mice. Based on the positions of known latency-associated genes in other gammaherpesviruses, we screened for the presence of transcripts corresponding to 11 open reading frames (ORFs) in the gammaHV68 genome in RNA from spleens and peritoneal cells of latently infected B-cell-deficient (MuMT) mice which have been shown contain high levels of reactivable latent gammaHV68 (K. E. Weck, M. L. Barkon, L. I. Yoo, S. H. Speck, and H. W. Virgin, J. Virol. 70:6775-6780, 1996). To control for the possible presence of viral lytic activity, we determined that RNA from latently infected peritoneal and spleen cells contained few or no detectable transcripts corresponding to seven ORFs known to encode viral gene products associated with lytic replication. However, we did detect low-level expression of transcripts arising from the region of gene 50 (encoding the putative homolog of the Epstein-Barr virus BRLF1 transactivator) in peritoneal but not spleen cells. Latently infected peritoneal cells consistently scored for expression of RNA derived from 4 of the 11 candidate latency-associated ORFs examined, including the regions of ORF M2, ORF M11 (encoding v-bcl-2), gene 73 (a homolog of the Kaposi's sarcoma-associated herpesvirus [human herpesvirus 8] gene encoding latency-associated nuclear antigen), and gene 74 (encoding a G-protein coupled receptor homolog, v-GCR). Latently infected spleen cells consistently scored positive for RNA derived from 3 of the 11 candidate latency-associated ORFs examined, including ORF M2, ORF M3, and ORF M9. To further characterize transcription of these candidate latency-associated ORFs, we examined their transcription in lytically infected fibroblasts by Northern analysis. We detected abundant transcription from regions of the genome containing ORF M3 and ORF M9, as well as the known lytic-cycle genes. However, transcription of ORF M2, ORF M11, gene 73, and gene 74 was barely detectable in lytically infected fibroblasts, consistent with a role of these viral genes during latent infection. We conclude that (i) we have identified several candidate latency genes of murine gammaHV68, (ii) expression of genes during latency may be different in different organs, consistent with multiple latency programs and/or multiple cellular sites of latency, and (iii) regions of the viral genome (v-bcl-2 gene, v-GCR gene, and gene 73) are transcribed during latency with both gammaHV68 and primate gammaherpesviruses. The implications of these findings for replacing previous operational definitions of gammaHV68 latency with a molecular definition are discussed.

Kinetics of Kaposi's sarcoma-associated herpesvirus gene expression

Herpesvirus gene expression can be classified into four distinct kinetic stages: latent, immediate early, early, and late. Here we characterize the kinetic class of a group of 16 Kaposi's sarcoma-associated herpesvirus (KSHV)/human herpesvirus 8 genes in a cultured primary effusion cell line and examine the expression of a subset of these genes in KS biopsies. Expression of two latent genes, LANA and vFLIP, was constitutive and was not induced by chemicals that induce the lytic cycle in primary effusion lymphoma (PEL) cell lines. An immediate-early gene, Rta (open reading frame 50 [ORF50]), was induced within 4 h of the addition of n-butyrate, and its 3.6-kb mRNA was resistant to inhibition by cycloheximide. Early genes, including K3 and K5 that are homologues of the "immediate-early" gene of bovine herpesvirus 4, K8 that is a positional homologue of Epstein-Barr virus BZLF1, vMIP II, vIL-6, and polyadenylated nuclear (PAN) RNA, appeared 8 to 13 h after chemical induction. A second group of early genes that were slightly delayed in their appearance included viral DHFR, thymidylate synthase, vMIP I, G protein-coupled receptor, K12, vBcl2, and a lytic transcript that overlapped LANA. The transcript of sVCA (ORF65), a late gene whose expression was abolished by Phosphonoacetic acid, an inhibitor of KSHV DNA replication, did not appear until 30 h after induction. Single-cell assays indicated that the induction of lytic cycle transcripts resulted from the recruitment of additional cells into the lytic cycle. In situ hybridization of KS biopsies showed that about 3% of spindle-shaped tumor cells expressed Rta, ORF K8, vIL-6, vMIP I, vBcl-2, PAN RNA, and sVCA. Our study shows that several KSHV-encoded homologues of cellular cytokines, chemokines, and antiapoptotic factors are expressed during the viral lytic cycle in PEL cell lines and in KS biopsies. The lytic cycle of KSHV, probably under the initial control of the KSHV/Rta gene, may directly contribute to tumor pathogenesis.

Characterization and cell cycle regulation of the major Kaposi's sarcoma-associated herpesvirus (human herpesvirus 8) latent genes and their promoter

Retinoblastoma tumor suppressor protein (pRB) inhibition by tumor virus oncoproteins has been attributed to the need for these viruses to promote lytic viral nucleic acid synthesis by unscheduled entry into the S phase of the cell cycle. Kaposi's sarcoma-associated herpesvirus (KSHV or HHV8) encodes a functional cyclin (vCYC) which is expressed during latency and can direct phosphorylation of pRB. We mapped the two major latent transcripts encoding vCYC, latent transcript 1 (LT1) and LT2, by cDNA sequencing, 5' rapid amplification of cDNA ends, and primer extension analyses. Both LT1 and LT2 transcripts are spliced, originate from the same start site, and encode ORF K13 (vFLIP) as well as ORF72 (vCYC). The latency-associated nuclear antigen (LANA, ORF73) is encoded by LT1 but spliced from LT2. While differential expression of the two transcripts was not found, the promoter controlling LT1/LT2 transcription is regulated in a cell cycle-dependent manner. Activities of both KSHV LT1/LT2 and huCYC D1 luciferase promoter reporters transfected into NIH 3T3 cells increase 11- and 4-fold, respectively, after release from cell cycle arrest by serum starvation. Further, vCYC and huCYC D2 mRNA levels are low in naturally infected BCBL-1 cells arrested in late G1 with L-mimosine but increase in parallel during a 24-h period after release from cell cycle arrest. Cell cycle regulation of KSHV vCYC expression mimics cellular D cyclin regulation and may maintain infected cell cycling. This is consistent with an alternative hypothesis that tumor viruses have developed specific responses to innate cellular defenses against latent virus infection that include pRB-induced cell cycle arrest.

Induction of programmed cell death in Kaposi's sarcoma cells by preparations of human chorionic gonadotropin

BACKGROUND

Isolation of the first neoplastic acquired immunodeficiency syndrome-related Kaposi's sarcoma (KS) cell line (KS Y-1) has furthered understanding of the pathogenesis of KS. Studies with KS Y-1 cells have indicated that inhibition of KS cell proliferation occurs in early pregnancy in mice and after treatment with certain commercial preparations of human chorionic gonadotropin (hCG, a pregnancy hormone purified from urine). The activity of the commercial preparations has been attributed to an hCG-associated factor(s) (HAF). While several clinical benefits of HAF are clearly evident, the basis for its anti-KS properties remains unknown. We investigated the apoptosis-inducing effects of HAF and the expression of apoptosis-related proteins in KS cells.

METHODS

KS Y-1 and KS SLK cells were treated with clinical-grade crude preparations of hCG, recombinant hCG, or urine fractions exhibiting anti-KS activity and then examined for features of apoptosis. Levels of proteins associated with apoptosis were monitored by western blot analysis, and cell DNA content was assessed by flow cytometry. Tumors induced in mice by inoculation of KS Y-1 cells were treated with preparations of hCG, and the tumors were examined for cell morphology and also for DNA fragmentation by use of the terminal deoxynucleotidyl transferase-mediated digoxigenin-deoxyuridine triphosphate nick-end-labeling (TUNEL) assay.

RESULTS

The HAF present in some preparations of hCG and in urine fractions has the ability to induce apoptosis in KS cells in vitro and in vivo. HAF-triggered apoptosis was preceded by increased levels of the apoptosis-related proteins c-Myc and c-Rel and cell accumulation in Go/G1 phase of the cell cycle. KS Y-1 cells transfected with a c-Myc complementary DNA showed elevated rates of apoptosis.

CONCLUSION

The anti-KS activity of HAF appears to induce apoptosis. Such activity suggests a role for HAF in pregnancy-related regulation of cell death.

Seroconversion for human herpesvirus 8 during HIV infection is highly predictive of Kaposi's sarcoma

BACKGROUND

The finding of antibodies against human herpesvirus 8 (HHV-8) is associated with the occurrence of Kaposi's sarcoma in persons infected with HIV. However, the predictive value of HHV-8 antibodies for Kaposi's sarcoma in HIV infection is unknown.

METHODS

The Amsterdam Cohort Studies on HIV infection and AIDS started in 1984 for homosexual men and in 1985 for injecting drug users. Serum samples from 1459 homosexual men and 1167 drug users were tested for antibodies to recombinant HHV-8 lytic-phase capsid (ORF65) antigen and latent-phase nuclear (ORF73) antigen. Individuals were retrospectively identified as HHV-8-positive or HHV-8-negative at enrolment or HHV-8 seroconverter during the study. Kaposi's sarcoma-free survival time was compared between HIV-infected men who were positive for HHV-8 at enrolment and those who later seroconverted for HHV-8. Hazard ratios were estimated for Kaposi's sarcoma, lymphoma, and opportunistic infection according to the HHV-8 serostatus.

RESULTS

The incidence of HHV-8 seroconversion among drugs users was 0.7 per 100 person-years based on 31 seroconversions, whereas an incidence of 3.6 was found among homosexual men based on 215 seroconversions. The hazard ratio for Kaposi's sarcoma was 3.15 (95% CI: 1.89-5.25) in HIV-infected individuals if HHV-8 antibodies were present either at enrolment or at HIV seroconversion. In HIV-infected persons who later seroconverted to HHV-8, Kaposi's sarcoma developed more rapidly: hazard ratio of 5.04 (95% CI: 2.94-8.64), an additional risk of 1.60 (95% CI: 1.01-2.53; P = 0.04). Time-dependent adjustment for CD4+ cell count and HIV RNA had no impact on the additional risk, although the CD4+ cell count was an independent risk factor for Kaposi's sarcoma. HHV-8 infection did not increase the risk of AIDS-related lymphoma or opportunistic infections.

CONCLUSIONS

The incidence of HHV-8 infection is higher in homosexual men than in drug users. The presence of HHV-8 antibodies in HIV-infected persons increases the risk of Kaposi's sarcoma. Among HIV-infected persons, those who subsequently seroconvert for HHV-8 are at highest risk. These results strongly confirm the causal role of HHV-8 in Kaposi's sarcoma and emphasize the clinical relevance of HHV-8 seroconversion before and after the HIV infection.

Reactivation of Kaposi's sarcoma-associated herpesvirus infection from latency by expression of the ORF 50 transactivator, a homolog of the EBV R protein

Kaposi's sarcoma (KS)-associated herpesvirus (KSHV), or human herpesvirus 8, is a lymphotropic virus strongly linked to several AIDS-related neoplasms. The primary reservoir of infection consists of latently infected B lymphocytes and possibly other mononuclear cells. Viral reactivation from latency and spread from this lymphoid reservoir is presumably required for development of nonlymphoid tumors like KS. Here we show that deregulated expression of a single viral gene, ORF 50, which encodes a transactivator able to selectively upregulate delayed-early viral genes, suffices to disrupt latency and induce the lytic gene cascade in latently infected B cells. The identification of this gene opens the way to studies of the physiologic mechanisms controlling reactvation of KSHV from latency.

Distinct biology of Kaposi's sarcoma-associated herpesvirus from primary lesions and body cavity lymphomas

The DNA sequence for Kaposi's sarcoma-associated herpesvirus was originally detected in Kaposi's sarcoma biopsy specimens. Since its discovery, it has been possible to detect virus in cell lines established from AIDS-associated body cavity-based B-cell lymphoma and to propagate virus from primary Kaposi's sarcoma lesions in a human renal embryonic cell line, 293. In this study, we analyzed the infectivity of Kaposi's sarcoma-associated herpesvirus produced from these two sources. Viral isolates from cultured cutaneous primary KS cells was transmitted to an Epstein-Barr virus-negative Burkitt's B-lymphoma cell line, Louckes, and compared to virus induced from a body cavity-based B-cell lymphoma cell line. While propagation of body cavity-based B-cell lymphoma-derived virus was not observed in 293 cell cultures, infection with viral isolates obtained from primary Kaposi's sarcoma lesions induced injury in 293 cells typical of herpesvirus infection and was associated with apoptotic cell death. Interestingly, transient overexpression of the Kaposi's sarcoma-associated herpesvirus v-Bcl-2 homolog delayed the process of apoptosis and prolonged the survival of infected 293 cells. In contrast, the broad-spectrum caspase inhibitors Z-VAD-fmk and Z-DEVD-fmk failed to protect infected cell cultures, suggesting that Kaposi's sarcoma-associated herpesvirus-induced apoptosis occurs through a Bcl-2-dependent pathway. Kaposi's sarcoma-associated herpesvirus isolates from primary Kaposi's sarcoma lesions and body cavity-based lymphomas therefore may differ and are likely to have distinct contributions to the pathophysiology of Kaposi's sarcoma.

Purified Tat induces inflammatory response genes in Kaposi's sarcoma cells

OBJECTIVE

Kaposi's sarcoma (KS) is a neoplasm strongly associated with HIV-1 infection and marked by leukocytic infiltration. The infiltrating leukocytes are a possible source of inflammatory cytokines, human herpesvirus 8 (HHV8) and the HIV-1 transactivator protein Tat. This study examines whether Tat directly induces expression of cellular adhesion molecules and cytokines in KS cells and whether this induction differs in kinetics and magnitude from induction by tumour necrosis factor (TNF) alpha.

DESIGN AND METHOD

Changes in gene expression in response to recombinant Tat compared with those to TNFalpha were evaluated at the messenger (m) RNA and protein level using cells that were cultured from KS lesions.

RESULTS

Tat induced the expression of the adhesion molecules vascular cell adhesion molecule 1 (VCAM-1) and intercellular adhesion molecule 1 (ICAM-1) and the cytokines monocyte chemoattractant protein 1 (MCP-1) and interleukin 6 (IL-6). The inductions were observed at both the protein and mRNA levels. The pattern of mRNA induction over time in response to Tat differed from that to TNFalpha, with higher peak levels that occurred earlier in response to Tat. The expression of these genes is, in part, regulated by the transcription factor NF-kappaB. Tat and TNFalpha activated comparable levels of NF-kappaB.

CONCLUSIONS

The ability of the HIV-1 Tat to induce the expression of genes with kinetics that are distinct from those seen in TNFalpha induction suggests that mechanisms in addition to activation of NF-kappaB contribute to the observed induction. Tat may contribute to the pathogenesis of AIDS-related KS through induction of cellular genes that are pro-proliferative and proinflammatory and may enhance the recruitment of leukocytes, which are a possible source of further cytokines, Tat and HHV8.

A cluster of latently expressed genes in Kaposi's sarcoma-associated herpesvirus

Infection with Kaposi's sarcoma-associated herpesvirus (KSHV) is closely associated with Kaposi's sarcoma (KS) and primary effusion lymphoma, with viral genomes present in a latent state in the majority of tumor cells. Here we describe a cluster of latently expressed viral genes whose mRNAs are generated from a common promoter. Two mRNAs in this region encode the latency-associated nuclear antigen, the product of open reading frame 73 (ORF73). The larger RNA, of 5.8 kb, is an unspliced transcript that includes ORF72 and -71 at its 3' end; it initiates at nucleotides (nt) 127880 to 127886 from a promoter lacking recognizable TATA elements. A less abundant mRNA, of 5.4 kb, is a variant of this transcript, in which 336 nt of 5' noncoding information has been removed by RNA splicing. A third, more abundant RNA is generated from the same promoter region via splicing from the common splice donor at nt 127813 to an acceptor 5' to ORF72; this transcript is the presumed mRNA for ORF72, which encodes the viral cyclin D homolog. All three RNAs are 3' coterminal. In situ hybridization analysis with probes that can detect all three transcripts shows that the RNAs are detectable in a large fraction of BCBL-1 cells prior to lytic induction and in >70% of KS spindle cells in primary KS tumors. This confirms that these transcripts are indeed latent RNAs and suggests a role for their products in viral persistence and/or KSHV-associated proliferation.