SV40 replication in human mesothelial cells induces HGF/Met receptor activation: a model for viral-related carcinogenesis of human malignant mesothelioma

Bortezomib inhibits nuclear factor-kappaB dependent survival and has potent in vivo activity in mesothelioma

PURPOSE

Purpose of this study has been the assessment of nuclear factor-kappaB (NF-kappaB) as a survival factor in human mesothelial cells (HMC), transformed HMC and malignant mesothelioma (MMe) cells. We aimed at verifying whether the proteasome inhibitor Bortezomib could abrogate NF-kappaB activity in MMe cells, leading to tumor cell death and may be established as a novel treatment for this aggressive neoplasm.

EXPERIMENTAL DESIGN

In HMC and MMe cells, NF-kappaB nuclear translocation and DNA binding were studied by electrophoretic mobility shift assay, following treatment with tumor necrosis factor-alpha (TNF-alpha). The IKK inhibitor Bay11-7082 was also tested to evaluate its effects on HMC, transformed HMC, and MMe cell viability upon exposure to asbestos fibers. Following Bortezomib treatment, cytotoxicity of MMe cells was evaluated by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide, whereas apoptosis and cell-cycle blockade were investigated by high-content analysis. Bortezomib was also given to mice bearing i.p. xenografts of MMe cells, and its effects on tumor growth were evaluated.

RESULTS

Here, we show that NF-kappaB activity is a constitutive survival factor in transformed HMC, MMe cells, and acts as a survival factor in HMC exposed to asbestos fibers. Bortezomib inhibits NF-kappaB activity in MMe cells and induces cell cycle blockade and apoptosis in vitro as well as tumor growth inhibition in vivo.

CONCLUSIONS

Inhibition of NF-kappaB constitutive activation in MMe cells by Bortezomib resulted in in vitro cytotoxicity along with apoptosis and in vivo tumor regression. Our results support the use of Bortezomib in the treatment of MMe and has led to a phase II clinical trial currently enrolling in Europe.

HGF mediates cell proliferation of human mesothelioma cells through a PI3K/MEK5/Fra-1 pathway

The ligand hepatocyte growth factor/scatter factor (HGF) and its receptor tyrosine kinase, c-Met, are highly expressed in most human malignant mesotheliomas (MMs) and may contribute to their increased growth and viability. Based upon our observation that RNA silencing of fos-related antigen 1 (Fra-1) inhibited c-met expression in rat mesotheliomas (1), we hypothesized that Fra-1 was a key player in HGF-induced proliferation in human MMs. In three of seven human MM lines evaluated, HGF increased Fra-1 levels and phosphorylation of both extracellular signal-regulated kinase 5 (ERK5) and AKT that were inhibited by the phosphatidylinositol 3-kinase (PI3K) inhibitor, LY290042. HGF-dependent phosphorylation and Fra-1 expression were decreased after knockdown of Fra-1, whereas overexpression of Fra-1 blocked the expression of mitogen/extracellular signal-regulated kinase kinases (MEK)5 at the mRNA and protein levels. Stable MM cell lines using a dnMEK5 showed that basal Fra-1 levels were increased in comparison to empty vector control lines. HGF also caused increased MM cell viability and proliferating cell nuclear antigen (PCNA) expression that were abolished by knockdown of MEK5 or Fra-1. Data suggest that HGF-induced effects in some MM cells are mediated via activation of a novel PI3K/ERK5/Fra-1 feedback pathway that might explain tumor-specific effects of c-Met inhibitors on MM and other tumors.

Simian virus 40 in humans

Simian virus 40 (SV40) is a monkey virus that was administered to human populations by contaminated vaccines which were produced in SV40 naturally infected monkey cells. Recent molecular biology and epidemiological studies suggest that SV40 may be contagiously transmitted in humans by horizontal infection, independently from the earlier administration of SV40-contaminated vaccines.SV40 footprints in humans have been found associated at high prevalence with specific tumor types such as brain and bone tumors, mesotheliomas and lymphomas and with kidney diseases, and at lower prevalence in blood samples from healthy donors. Contrasting reports appeared in the literature on the circulation of SV40 in humans by contagious transmission and its association, as a possible etiologic cofactor, with specific human tumors. As a consequence of the conflicting results, a considerable debate has developed in the scientific community. In the present review we consider the main results obtained by different groups investigating SV40 sequences in human tumors and in blood specimens, the putative role of SV40 in the onset/progression of specific human tumors, and comment on the hypotheses arising from these data.

Erionite and asbestos differently cause transformation of human mesothelial cells

Malignant mesothelioma (MM) is an aggressive tumor associated with environmental or occupational exposure to asbestos fibers. Erionite is a fibrous zeolite, morphologically similar to asbestos and it is assumed to be even more carcinogenic. Onset and progression of MM has been suggested as the result of the cooperation between asbestos and other cofactors, such as SV40 virus infection. Nevertheless, several cases of MM were associated with environmental exposure to erionite in Turkey, where SV40 was never isolated in MM specimens. We show here that erionite is poorly cytotoxic, induces proliferating signals and high growth rate in human mesothelial cells (HMC). Long term exposure to erionite, but not to asbestos fibers, transforms HMC in vitro, regardless of the presence of SV40 sequences, leading to foci formation in cultured monolayers. Cells derived from foci display constitutive activation of Akt, NF-kappaB and Erk1/2, show prolonged survival and a deregulated cell cycle, involving cyclin D1 and E overexpression. Our results reveal that erionite is able per se to turn HMC into transformed highly proliferating cells and disclose the carcinogenic properties of erionite, prompting for a careful evaluation of environmental exposure to these fibers. The genetic predisposition to the effect of erionite is a separate subject for investigation.

Expression of cancer-associated molecules in malignant mesothelioma

Malignant mesothelioma (MM) is a malignant tumor derived from mesothelial cells, native cells of the body cavities. Exposure to asbestos is the most strongly established etiologic factor, predominantly for the most common disease form, pleural mesothelioma. The pathogenesis of MM involves the accumulation of extensive cytogenetic changes, as well as cancer-related phenotypic alterations that facilitate tumor cell survival, invasion and metastasis. This review presents current knowledge regarding the biological characteristics of this disease that are linked to the so-called hallmarks of cancer. In addition, data suggesting that the anatomic site (solid tumor vs. effusion) affects the expression of metastasis-associated and regulatory molecules in MM are presented. Finally, recent work in which high-throughput methodology has been applied to MM research is reviewed. The data obtained in the reviewed research may aid in defining new prognostic markers and therapeutic targets for this aggressive disease in the future.

Preliminary data suggestive of a novel translational approach to mesothelioma treatment: imatinib mesylate with gemcitabine or pemetrexed

BACKGROUND

Malignant mesothelioma is a cancer which is refractory to current treatments. Imatinib mesylate is a selective inhibitor of tyrosine kinases such as bcr-abl, c-Kit, c-Fms and platelet derived growth factor receptor beta (PDGFRbeta). PDGFRbeta is often overexpressed in mesothelioma cells and is a therapeutic target for imatinib in some solid tumours. A study was undertaken to assess whether imatinib alone or combined with chemotherapeutic agents may be effective for treating mesothelioma.

METHODS

Cultures from mesothelioma MMP, REN and ISTMES2 cell lines were treated with imatinib alone or in combination with a chemotherapeutic agent.

RESULTS

Imatinib induced cytotoxicity and apoptosis selectively on PDGFRbeta positive mesothelioma cells via blockade of receptor phosphorylation and interference with the Akt pathway. Of the chemotherapeutic agents tested in combination with imatinib, a synergistic effect was obtained with gemcitabine and pemetrexed.

CONCLUSIONS

This study provides a rationale for a novel translational approach to the treatment of mesothelioma which relies on enhancement of tumour chemosensitivity by inhibition of Akt.

Protein encoded by HSV-1 stimulation-related gene 1 (HSRG1) interacts with and inhibits SV40 large T antigen

Herpes simplex virus (HSV)-1 stimulation-related gene 1 (HSRG1) protein expression is induced in HSV-1 infected cells. We found that HSRG1 interacts with SV40 large T antigen (LT) in yeast two-hybrid assay and bimolecular fluorescence complementation (BiFC) assay. This interaction alters LT's regulation of the SV40 promoter and its ability to influence the cell cycle. Choramphenicol acetyl-transferase (CAT) assays revealed that initiation of gene transcription by LT is changed by HSRG1 expression. HSRG1 inhibits the ability of LT to activate SV40 late gene transcription. Further data indicate that the ability of LT protein to stimulate S-phase entry is also inhibited by the expression of HSRG1. The results of a colony-forming assay suggested that expression of HSRG1 in cells transfected by LT gene decreased the rate of colony formation. Yeast two-hybrid beta-galactosidase assay revealed that amino acid residues 132-450 in LT bind HSRG1.

Expression of Cancer-Associated Molecules in Malignant Mesothelioma

Malignant mesothelioma (MM) is a malignant tumor derived from mesothelial cells, native cells of the body cavities. Exposure to asbestos is the most strongly established etiologic factor, predominantly for the most common disease form, pleural mesothelioma. The pathogenesis of MM involves the accumulation of extensive cytogenetic changes, as well as cancer-related phenotypic alterations that facilitate tumor cell survival, invasion and metastasis. This review presents current knowledge regarding the biological characteristics of this disease that are linked to the so-called hallmarks of cancer. In addition, data suggesting that the anatomic site (solid tumor vs. effusion) affects the expression of metastasis-associated and regulatory molecules in MM are presented. Finally, recent work in which high-throughput methodology has been applied to MM research is reviewed. The data obtained in the reviewed research may aid in defining new prognostic markers and therapeutic targets for this aggressive disease in the future.

Gene expression profiling and gene copy-number changes in malignant mesothelioma cell lines

Malignant mesothelioma (MM) is an asbestos-induced tumor that acquires aneuploid DNA content during the tumorigenic process. We used instable MM cell lines as an in vitro model to study the impact of DNA copy-number changes on gene expression profiling, in the course of their chromosomal redistribution process. Two MM cell lines, PMR-MM2 (early passages of in vitro culture) and PMR-MM7 (both early and late passages of in vitro culture), were cytogenetically characterized. Genomic gains and losses were precisely defined using microarray-based comparative genomic hybridization (array-CGH), and minimal overlapping analysis led to the identification of the common unbalanced genomic regions. Using the U133Plus 2.0 Affymetrix gene chip array, we analyzed PMR-MM7 early and late passages for genome-wide gene expression, and correlated the differentially expressed genes with copy-number changes. The presence of a high number of genetic imbalances occurring from early to late culture steps reflected the tendency of MM cells toward genomic instability. The selection of specific chromosomal abnormalities observed during subsequent cultures demonstrated the spontaneous evolution of the cancer cells in an in vitro environment. MM cell lines were characterized by copy-number changes associated with the TP53 apoptotic pathway already present at the first steps of in vitro culture. Prolonged culture led to acquisition of additional chromosomal copy-number changes associated with dysregulation of genes involved in cell adhesion, regulation of mitotic cell cycle, signal transduction, carbohydrate metabolism, motor activity, glycosaminoglycan biosynthesis, protein binding activity, lipid transport, ATP synthesis, and methyltransferase activity.

Pleural mesothelioma in a nine-month-old dog

This paper reports on an unusual case of pleural epitheloid mesothelioma in a nine-month-old male, mixed breed dog. The dog was presented in-extremis and, on post mortem examination, multiple, exophytic, frequently pedunculated, yellowish-red, soft to firm masses ranging from 3 mm to 6 cm in diameter were diffusely distributed over, and attached to, the pericardial and parietal pleural surfaces. Microscopically, these masses consisted of round to partially polygonalshaped, anaplastic cells with minimal cytoplasm and hyperchromatic nuclei covering papillomatous projections or as part of more densely cellular masses. A supporting fibrovascular stroma and mitotic figures were also evident. Constituent tumour cells were labeled positively with antibodies against both vimentin and cytokeratin. In contrast, the same cells exhibited equivocal labeling with an antibody directed against calretinin antigen and did not label with antibodies against carcinoembryonic antigen (CEA) and milk fat globule-related antigen (MFGRA). Such tumours are rare in dogs, particularly in such a young animal.

Cellular and molecular parameters of mesothelioma

Malignant mesotheliomas (MM) are neoplasms arising from mesothelial cells that line the body cavities, most commonly the pleural and peritoneal cavities. Although traditionally recognized as associated with occupational asbestos exposures, MMs can appear in individuals with no documented exposures to asbestos fibers, and emerging data suggest that genetic susceptibility and simian virus 40 (SV40) infections also facilitate the development of MMs. Both asbestos exposure and transfection of human mesothelial cells with SV40 large and small antigens (Tag, tag) cause genetic modifications and cell signaling events, most notably the induction of cell survival pathways and activation of receptors, and other proteins that favor the growth and establishment of MMs as well as their resistance to chemotherapy. Recent advances in high-throughput technologies documenting gene and protein expression in patients and animal models of MMs can now be validated in human MM tissue arrays. These have revealed expression profiles that allow more accurate diagnosis and prognosis of MMs. More importantly, serum proteomics has revealed two new candidates (osteopontin and serum mesothelin-related protein or SMRP) potentially useful in screening individuals for MMs. These mechanistic approaches offer new hope for early detection and treatment of these devastating tumors.

Cross reactivity between many anti-human antibodies for their hamster homologs provide the tools to study the signal transduction pathway activated by asbestos and SV40 in the malignant mesothelioma model

The aim of this study was to test the possibility of using human antibodies to study the pathogenic mechanism of SV40 and asbestos in a hamster mesothelioma model. The cellular lysates from human and hamster primary mesothelial cells were tested by Western blot analysis. All of the antibodies we tested (HGF, Notch, VEGF, Sp1, p53, PP2A, p-ERK1, p-c-jun, Fra1, Fra2, MMP1, MMP9, NFkappaB p65, IkappaB, GAPDH) cross-reacted with their hamster counterparts. These data indicate that hamster mesothelioma model and more in general hamster experimental model, can be used for functional studies because many mouse, rabbit, and goat monoclonal antibodies prepared against human antigens cross-react with their hamster counterparts.

Immortalization of Primary Endothelial Cells by the K1 Protein of Kaposi's Sarcoma–Associated Herpesvirus

Kaposi's sarcoma-associated herpesvirus (KSHV) is linked to three different human cancers: Kaposi's sarcoma, primary effusion lymphoma, and multicentric Castleman's disease. The Kaposi's sarcoma lesion expresses high levels of angiogenic factors and is comprised of a mixed cell population, including endothelial cells that are infected with KSHV. We find that the KSHV K1 protein is expressed in Kaposi's sarcoma lesions and can immortalize and extend the life span of primary human umbilical vein endothelial cells in culture. Vascular endothelial growth factor (VEGF) is critical for the survival of endothelial cells, and we show that expression of K1 in endothelial cells resulted in increased levels of secreted VEGF and the activation of key signaling pathways, including the VEGF/VEGF receptor and the phosphatidylinositol-3'-OH-kinase (PI3K) pathway. The SH2 binding motifs present in the cytoplasmic tail of K1 were critical for K1's ability to activate these pathways. Activation of PI3K by K1 results in activation of Akt kinase and mammalian target of rapamycin and inactivation of the proapoptotic proteins FKHR, glycogen synthase kinase-3, and Bad, which are events indicative of cell survival. Because activation of the PI3K pathway is critical for transformation of many human cells, we suggest that PI3K activation by K1 is involved in endothelial cell immortalization and contributes to KSHV-associated tumorigenesis. We also report that K1 enhances angiogenesis in vivo and increases tumor vasculature and tumor size.

Infrequent existence of simian virus 40 large T antigen DNA in malignant mesothelioma in Japan

Malignant mesothelioma is the most common primary pleural neoplasm. Association of simian virus 40 (SV40) with malignant mesothelioma has been reported, suggesting that SV40 plays an important role in the origin of a subset of these tumors. However, significant geographic variation is present as to how often this association occurs. As no study concerning SV40 in malignant mesothelioma has been reported from Japan, we examined the frequency of SV40 infection in Japanese malignant mesothelioma cases. In pleural malignant mesothelioma tissue from 35 patients in Japan, we sought the presence of SV40 large T antigen DNA using real-time polymerase chain reaction (PCR), as well as expression of the viral protein using immunohistological methods. Real-time PCR demonstrated that two of 35 mesotheliomas contained DNA sequences encoding portions of SV40 large T antigen. None of the 35 malignant mesothelioma specimens showed immunoreactivity for SV40 large T antigen. SV40 infection does not appear to have a major role in the development of malignant mesothelioma in Japan.

SV40-immortalized human fibroblasts as a source of SV40 infectious virions

Human fibroblasts immortalized by Simian Virus 40 (SV40) are widely employed for cell and molecular biology model of study. Indeed, SV40 transmission to humans was believed to occur only under exceptional situations. The oncogenic potential of SV40 in laboratory animals is well established, whereas its involvement in human carcinogenesis is still a matter of active investigations. A recent report links SV40 exposure with the development of a brain tumor in a laboratory researcher. In previous studies, episomal viral DNA was detected in SV40 stably transformed and immortalized fibroblast cell lines. In this study, we report molecular and biological characterizations of SV40 DNA in human fibroblast cells. Our results indicate that SV40 is able to establish a persistent infection in long-term immortalized human fibroblasts, resulting in the production of an infectious viral progeny, which is able to infect both monkey and human cells. These data indicate that SV40-immortalized human fibroblasts may represent a source of SV40 infection. To avoid the SV40 infection, careful attention should be given by operators to this SV40-cell model of study.

Inhibition of the met receptor in mesothelioma

BACKGROUND

Expression of the Met receptor and its ligand, hepatocyte growth factor (HGF), has been observed in 74% to 100% and 40% to 85% of malignant pleural mesothelioma (MPM) specimens, respectively. HGF stimulation has been shown to enhance MPM cell proliferation, migration, cell scattering, and invasiveness.

EXPERIMENTAL DESIGN

To investigate a potential therapeutic role for the Met receptor in MPM, we examined the effects of PHA-665752, a specific small-molecule inhibitor of the Met receptor tyrosine kinase, in a panel of 10 MPM cell lines.

RESULTS

Two of the cell lines, H2461 and JMN-1B, exhibited autocrine HGF production as measured by ELISA (3.9 and 10.5 ng/mL, respectively, versus <0.05 ng/mL in other cell lines). Evaluation of PHA-665752 across the 10 MPM cell lines indicated that despite Met expression in all cell lines, only in cell lines that exhibited a Met/HGF autocrine loop, H2461 and JMN-1B, did PHA-665752 inhibit growth with an IC(50) of 1 and 2 micromol/L, respectively. No activating mutations in Met were detected in any of the cell lines. Consistent with observed growth inhibition, PHA-665752 caused cell cycle arrest at G(1)-S boundary accompanied by a dose-dependent decrease in phosphorylation of Met, p70S6K, Akt, and extracellular signal-regulated kinase 1/2. Growth of H2461 cells was also inhibited by neutralizing antibodies to HGF and by RNA interference knockdown of the Met receptor, confirming that growth inhibition observed was through a Met-dependent mechanism. PHA-665752 also reduced MPM in vitro cell migration and invasion.

CONCLUSIONS

Taken together, these findings suggest that inhibition of the Met receptor may be an effective therapeutic strategy for patients with MPM and provides a mechanism, the presence of a HGF/Met autocrine loop, by which to select patients for PHA-665752 treatment.

Molecular biology of malignant mesothelioma: a review

Malignant mesothelioma (MM) is an uncommon tumor with high mortality and morbidity rates. It arises from mesothelial cells that line the pleural, pericardial, peritoneal, and testicular cavities. This is a disease with an indolent course because tumors arise 20 to 40 years after exposure to an inciting agent. Extensive research has shown that mesothelial cells are transformed into MM cells through various chromosomal and cellular pathway defects. These changes alter the normal cells' ability to survive, proliferate, and metastasize. This article discusses the alterations that occur in transforming normal mesothelial cells into MM. It also details some of the signal transduction pathways that seem to be important in MM with the potential for novel targeted therapeutics.

Human and mouse mesotheliomas exhibit elevated AKT/PKB activity, which can be targeted pharmacologically to inhibit tumor cell growth

Malignant mesotheliomas (MMs) are very aggressive tumors that respond poorly to standard chemotherapeutic approaches. The phosphatidylinositol 3-kinase (PI3K)/AKT pathway has been implicated in tumor aggressiveness, in part by mediating cell survival and reducing sensitivity to chemotherapy. Using antibodies recognizing the phosphorylated/activated form of AKT kinases, we observed elevated phospho-AKT staining in 17 of 26 (65%) human MM specimens. In addition, AKT phosphorylation was consistently observed in MMs arising in asbestos-treated mice and in MM cell xenografts. Consistent with reports implicating hepatocyte growth factor (HGF)/Met receptor signaling in MM, all 14 human and murine MM cell lines had HGF-inducible AKT activity. One of nine human MM cell lines had elevated AKT activity under serum-starvation conditions, which was associated with a homozygous deletion of PTEN, the first reported in MM. Treatment of this cell line with the mTOR inhibitor rapamycin resulted in growth arrest in G1 phase. Treatment of MM cells with the PI3K inhibitor LY294002 in combination with cisplatin had greater efficacy in inhibiting cell proliferation and inducing apoptosis than either agent alone. Collectively, these data indicate that MMs frequently express elevated AKT activity, which may be targeted pharmacologically to enhance chemotherapeutic efficacy. These findings also suggest that mouse models of MM may be useful for future preclinical studies of pharmaceuticals targeting the PI3K/AKT pathway.

SV40-dependent AKT activity drives mesothelial cell transformation after asbestos exposure

Human malignant mesothelioma is an aggressive cancer generally associated with exposure to asbestos, although SV40 virus has been involved as a possible cofactor by a number of studies. Asbestos fibers induce cytotoxicity in human mesothelial cells (HMC), although cell survival activated by key signaling pathways may promote transformation. We and others previously reported that SV40 large T antigen induces autocrine loops in HMC and malignant mesothelioma cells, leading to activation of growth factor receptors. Now we show that SV40 induces cell survival via Akt activation in malignant mesothelioma and HMC cells exposed to asbestos. Consequently, prolonged exposure to asbestos fibers progressively induces transformation of SV40-positive HMC. As a model of SV40/asbestos cocarcinogenesis, we propose that malignant mesothelioma originates from a subpopulation of transformed stem cells and that Akt signaling is a novel therapeutic target to overcome malignant mesothelioma resistance to conventional therapies.

Identification of novel candidate oncogenes and tumor suppressors in malignant pleural mesothelioma using large-scale transcriptional profiling

Malignant pleural mesothelioma (MPM) is a highly lethal, poorly understood neoplasm that is typically associated with asbestos exposure. We performed transcriptional profiling using high-density oligonucleotide microarrays containing approximately 22,000 genes to elucidate potential molecular and pathobiological pathways in MPM using discarded human MPM tumor specimens (n = 40), normal lung specimens (n = 4), normal pleura specimens (n = 5), and MPM and SV40-immortalized mesothelial cell lines (n = 5). In global expression analysis using unsupervised clustering techniques, we found two potential subclasses of mesothelioma that correlated loosely with tumor histology. We also identified sets of genes with expression levels that distinguish between multiple tumor subclasses, normal and tumor tissues, and tumors with different morphologies. Microarray gene expression data were confirmed using quantitative reverse transcriptase-polymerase chain reaction and protein analysis for three novel candidate oncogenes (NME2, CRI1, and PDGFC) and one candidate tumor suppressor (GSN). Finally, we used bioinformatics tools (ie, software) to create and explore complex physiological pathways. Combined, all of these data may advance our understanding of mesothelioma tumorigenesis, pathobiology, or both.

New Agents in the Management of Advanced Mesothelioma

Malignant pleural mesothelioma (MPM) is a seemingly uncommon tumor whose incidence has in fact increased steadily and progressively over the last 30 years. Indeed, an actual "epidemic" is expected in Europe over the next 20 years. Despite unquestionable improvement in the diagnostic methods at our disposal and the availability of new treatment strategies, the prognosis of MPM patients remains dramatically poor (12 to 18 months' median survival from diagnosis), although exceptional cases of long-survivors are reported in all literature series. The current review will cover the dramatic improvements in the treatment of this rare disease that have been recently achieved, as well as the promise that new, molecular-targeted therapies, such as bortezomid, mTOR ( m ammalian t arget o f r apamycin) inhibitors, and Met inhibitors, seem to offer for the next few years. With pemetrexed we now have a drug that is able to impact patient survival. Together with the newer drugs, rapidly emerging from the laboratory to be applied in the clinic, we have the hope of making further advances in the struggle against this disease.

Human mesothelioma cells exhibit tumor cell–specific differences in phosphatidylinositol 3-kinase/AKT activity that predict the efficacy of Onconase

Malignant mesothelioma is an aggressive cancer with no known cure, which has become a therapeutic challenge. Onconase is one of few chemotherapeutic agents that have been studied in patients with malignant mesothelioma that has the advantage of low toxicity and limited side effects. Here, we evaluate the effect of Onconase on killing of malignant mesothelioma cells and how the phosphatidylinositol 3-kinase/AKT (PI3-K/AKT) survival pathway influences this effect. Our results show that Onconase induces apoptosis in malignant mesothelioma cell lines and that this effect is tumor cell specific. Malignant mesothelioma cell lines with the highest AKT activation, which correlated with the presence of the SV40 large and small T antigen (SV40+), were the most resistant to the drug. Finally, a cooperative effect was observed between small molecule inhibitors of PI3-K and Onconase in the killing of malignant mesothelioma cells. Our results suggest that kinase screening of individual malignant mesotheliomas for endogenous levels of activated PI3-K/AKT may be predictive of the efficacy of Onconase and possibly other chemotherapeutic agents.

Simian virus 40 persistent infection in long-term immortalized human fibroblast cell lines

Episomal simian virus 40 (SV40) DNA was detected in various SV40-immortalized human fibroblast cell lines, without rearrangements or mutations. In these cells, SV40 established a persistent infection with the release of a viral progeny. However, electron microscopy analysis showed that virions are morphologically altered, whereas infectivity assay indicated that viral production was hampered. The data suggest that in SV40-infected human fibroblasts, some cells support a complete SV40 productive cycle, whereas other cells resist to the SV40 infection. This sort of "balance" observed within the same human fibroblast population may be responsible for the semipermissiveness of these cells to SV40 infection.

Papilloma and polyoma DNA tumor virus sequences in female genital tumors

Human papillomaviruses (HPVs) and BKV, JCV, and SV40 polyomaviruses (PYVs) are oncogenic viruses associated with different human tumors. Our aim was to determine if PYV and HPV sequences could be detected in human genital tumors. HPV types 6b, 11, 16, and 18 and PYV were investigated in 22 genital tumor samples and the corresponding adjacent normal tissues, by PCR and filter hybridization. HPV and PYV sequences were also searched in six sperm fluid and four peripheral blood cell (PBC) samples. HPV-16 sequences were revealed in 7 of 14 cervical tumors and 1 of 1 vaginal adenocarcinoma, whereas 1 of 14 cervical carcinoma tested positive for HPV-18. Interestingly, each normal cervical tissue surrounding the neoplasm obtained from the same patient was positive for HPV type-16 and -18 with the same prevalence detected in tumors. BKV sequences were found in 9 of 14 cervical tumors, 1 of 7 vulvar tumors, and 1 of 1 adenocarcinoma, but also in normal tissues from cervix (13 of 14), vulva (6 of 7), sperm fluid (5 of 6) and PBC (3 of 4) samples. SV40 sequences were detected in 1 of 14 normal cervical tissue, 2 of 6 sperm fluids and 1 of 4 PBCs. None of the samples were JCV positive. To our knowledge, this is the first investigation reporting on the simultaneous association of both HPV and PYV with human genital tumors. These results suggest that PYV, together with HPV, may be involved as a cofactor in the onset/progression of human genital tumors, and raise the possibility that PYV act synergistically with HPV to enhance their pathogenicity in vivo. In addition, HPV and PYV may complement each other in infecting human genital tissues.

The establishment and characterization of the first canine hepatocellular carcinoma cell line, which resembles human oncogenic expression patterns

Background

Hepatocellular carcinoma (HCC) is one of the most worldwide frequent primary carcinomas resulting in the death of many cirrhotic patients. Unfortunately, the molecular mechanisms of this cancer are not well understood; therefore, we need a good model system to study HCC. The dog is recognized as a promising model for human medical research, namely compared with rodents. The objective of this study was to establish and characterize a spontaneous canine tumor cell line as a potential model for studies on HCC.

Results

Histomorphological, biochemical, molecular biological and quantitative assays were performed to characterize the canine HCC cell line that originated from a dog with a spontaneous liver tumor. Morphological investigations provided strong evidence for the hepatocytic and neoplastic nature of the cell line, while biochemical assays showed that they produced liver-specific enzymes. PCR analysis confirmed expression of ceruloplasmin, alpha-fetoprotein and serum albumin. Quantitative RT-PCR showed that the canine HCC cell line resembles human HCC based on the measurements of expression profiles of genes involved in cell proliferation and apoptosis.

Conclusions

We have developed a novel, spontaneous tumor liver cell line of canine origin that has many characteristics of human HCC. Therefore, the canine HCC cell line might be an excellent model for comparative studies on the molecular pathogenesis of HCC.

Evidence of an important role for SV40 in mesothelioma

The discovery of SV40 DNA in human mesothelioma has evolved from a finding that originally was dismissed as polymerase chain reaction contamination to one that has won approval for a National Cancer Institute Rapid Access to Intervention Development grant to vaccinate SV40-positive tumors with a vaccinia mTag construct. As the credibility of these findings has become imprinted in the literature, the burden of phenomenon dismissal has become more difficult for investigators who have based their arguments on critically flawed validation studies. Mesothelioma is a disease for which novel strategies of detection or treatment should be encouraged, and it is as dangerous as a hungry shark. In the past, the argument always has been whether the finding of SV40 in mesothelioma is credible enough to lead our thinking in another direction to help our patients. Unfortunately, the causality issues have been stuck to the issue like a remora on a shark. It is time to study the remora, but our priorities should be on taming the shark.

Gene expression profiles predict survival and progression of pleural mesothelioma

PURPOSE

Clinical outcomes for malignant pleural mesothelioma (MPM) patients having surgery are imprecisely predicted by histopathology and intraoperative staging. We hypothesized that gene expression profiles could predict time to progression and survival in surgically cytoreduced pleural mesothelioma of all stages.

EXPERIMENTAL DESIGN

Gene expression analyses from 21 MPM patients having cytoreductions and identical postoperative adjuvant therapy were performed using the U95 Affymetrix gene chip. Using both dChip and SAM, neural networks constructed a common 27 gene classifier, which was associated with either the high-risk and low-risk group of patients. Data were validated using real-time PCR and immunohistochemical staining. The 27 gene classifier was also used for validation in a separate set of 17 MPM patients from another institution.

RESULTS

The groups predicted by the gene classifier recapitulated the actual time to progression and survival of the test set with 95.2% accuracy using 10-fold cross-validation. Clinical outcomes were independent of histology, and heterogeneity of progression and survival in early stage patients was defined by the classifier. The gene classifier had a 76% accuracy in the separate validation set of MPMs.

CONCLUSIONS

These data suggest that pretherapy gene expression analysis of mesothelioma biopsies may predict which patients may benefit from a surgical approach.

Evidence against a role for SV40 infection in human mesotheliomas and high risk of false-positive PCR results owing to presence of SV40 sequences in common laboratory plasmids

BACKGROUND

PCR-based evidence of infection by simian virus 40 (SV40) has been reported in varying proportions of pleural mesotheliomas and other tumours, but data are conflicting and reproducibility limited. During a study of SV40 in relation to homozygous deletion of CDKN2A in mesotheliomas, we became concerned by inconsistent results and therefore used several independent techniques to investigate SV40 in these tumours.

METHODS

High-quality DNA and RNA were extracted from 71 frozen mesothelioma samples. DNA PCR was done with four sets of primers for the SV40 T-antigen gene. RNA transcripts were examined by RT-PCR.

FINDINGS

The first two primer sets for DNA PCR gave positive results in proportions similar to those reported in positive studies (56-62%) but there were unusual reproducibility difficulties. These primers were in a region of the T-antigen gene (nucleotides 4100-4713) that is present in many common laboratory plasmids. In assays with PCR primers not included within that region, only four cases (6%) showed products but these were too faint to suggest clonal infection. Further PCR assays confirmed that the SV40 sequences in the tumour samples had a deletion found only in plasmids, not in native functional SV40. Review of previous studies showed a similar pattern of discrepancies between SV40 T-antigen DNA PCR results obtained with primers within and beyond the region 4100-4713. All 71 mesotheliomas were negative for T-antigen transcripts by RT-PCR, and lacked T-antigen-positive tumour cells by immunohistochemistry.

INTERPRETATION

Our data based on three independent experimental approaches do not support a significant role for SV40 in human mesotheliomas. The risk of false-positive results due to contamination by common laboratory plasmids containing SV40 sequences has been underestimated. Studies of SV40 based on PCR methods require careful primer design to reduce this risk.

RELEVANCE TO PRACTICE

This paper presents several lines of evidence against the proposed link between SV40 infection and human mesotheliomas. Studies reporting a high prevalence of SV40 DNA in human tumours have been based on molecular assays prone to false-positive results. Because SV40 appears unlikely to have a major role, if any, in human mesotheliomas, clinicians should continue to consider asbestos exposure as the most likely and most thoroughly established aetiological factor in individuals with this cancer.

Emergent human pathogen simian virus 40 and its role in cancer

The polyomavirus simian virus 40 (SV40) is a known oncogenic DNA virus which induces primary brain and bone cancers, malignant mesothelioma, and lymphomas in laboratory animals. Persuasive evidence now indicates that SV40 is causing infections in humans today and represents an emerging pathogen. A meta-analysis of molecular, pathological, and clinical data from 1,793 cancer patients indicates that there is a significant excess risk of SV40 associated with human primary brain cancers, primary bone cancers, malignant mesothelioma, and non-Hodgkin's lymphoma. Experimental data strongly suggest that SV40 may be functionally important in the development of some of those human malignancies. Therefore, the major types of tumors induced by SV40 in laboratory animals are the same as those human malignancies found to contain SV40 markers. The Institute of Medicine recently concluded that "the biological evidence is of moderate strength that SV40 exposure could lead to cancer in humans under natural conditions." This review analyzes the accumulating data that indicate that SV40 is a pathogen which has a possible etiologic role in human malignancies. Future research directions are considered.

Mesothelial cell proliferation and apoptosis

Mesothelial cells line the pleural and peritoneal surfaces, where under normal conditions they proliferate and undergo cell death at a slow rate, thereby maintaining a constant number of cells. These tightly regulated processes are disrupted in malignancy. By developing a better understanding of the mechanisms that regulate cell proliferation and apoptosis in mesothelial and mesothelioma cells, we may be able to develop more effective therapeutic agents that target specific steps in these pathways to induce apoptosis more efficiently. This paper reviews our current knowledge of the signaling pathways involved in the regulation of mesothelial cell proliferation and apoptosis. The latest advancements in identifying proteins that play key roles in the resistance to apoptosis are highlighted.

Simian Virus 40 Infection Down-Regulates the Expression of Nitric Oxide Synthase in Human Mesothelial Cells

The cytotoxic effects of asbestos are partly mediated by the production of free radicals, including nitric oxide (NO). SV40 has been suggested to synergize with asbestos in the pathogenesis of malignant mesothelioma. Crocidolite asbestos fibers induced in human mesothelial and malignant mesothelioma cells a significant increase of NO synthase activity and expression, which was absent in SV40-infected cells. Furthermore, SV40 infection prevented the NF kappa B activation elicited by crocidolite in both mesothelial and mesothelioma cells. These data suggest that SV40, by inhibiting the synthesis of NO, could favor the survival of transformed, potentially neoplastic cells.

The Kaposi's sarcoma-associated herpesvirus (KSHV/HHV-8) K1 protein induces expression of angiogenic and invasion factors

Kaposi's sarcoma-associated herpesvirus (KSHV/HHV-8) has been linked to Kaposi's sarcoma, primary effusion lymphoma, and multicentric Castleman's disease. In addition to endothelial cells and B lymphocytes, KSHV also has been shown to infect epithelial cells and keratinocytes. The transmembrane glycoprotein K1, encoded by the first open reading frame of KSHV, is a signaling protein capable of eliciting B-cell activation. We show that KSHV K1 can induce expression and secretion of vascular endothelial growth factor (VEGF) in epithelial and endothelial cells. Up-regulation of VEGF was mediated at the transcriptional level because expression of K1 resulted in VEGF promoter activation. We also show that K1 induces expression of matrix metalloproteinase-9 (MMP-9) in endothelial cells. Additional analyses with K1 mutant proteins revealed that the SH2 binding motifs present in the K1 cytoplasmic tail are necessary for VEGF secretion and MMP-9 induction. These results indicate that K1 signaling may contribute to KSHV-associated pathogenesis through a paracrine mechanism by promoting the secretion of VEGF and MMP-9 into the surrounding matrix.

Abrogation of p21 Expression by Flavopiridol Enhances Depsipeptide-Mediated Apoptosis in Malignant Pleural Mesothelioma Cells

PURPOSE

Recent insights regarding the pathogenesis of malignant pleural mesothelioma (MPM) provide new opportunities for targeted molecular therapies for this highly lethal disease. The present study was undertaken to examine the effects of the histone deacetylase inhibitor, Depsipeptide (DP) FK228, in conjunction with the cyclin-dependent kinase inhibitor, Flavopiridol (FLA), in cultured MPM cells.

EXPERIMENTAL DESIGN

Proliferation and apoptosis in drug-treated, virally transduced, or control cells were assessed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide and Apo-bromodeoxyuridine techniques. Western blot and ELISA techniques were used to examine signal transduction and cell cycle-related protein levels in MPM cells exposed to DP and/or FLA in the presence or absence of calphostin, phorbol-12,13-dibutyrate, 5,6-dichloro-1-beta-D-ribofuranosyl-benzimidazole, or adenoviral p21 transduction.

RESULTS

DP (1-50 ng/ml x 6 h) or FLA (100-200 nM x 72 h) alone, mediated low-level, dose-dependent growth inhibition in MPM cells. In contrast, sequential DP/FLA treatment mediated marked growth inhibition and apoptosis in these cell lines. The cytotoxic effects of DP/FLA were considerably less pronounced in cultured normal cells. The proapoptotic effects of DP/FLA treatment coincided with inhibition of DP-mediated induction of p21 by FLA. Overexpression of p21 by adenoviral gene transfer techniques rendered MPM cells refractory to the cytotoxic effects of this treatment regimen. In p21 reporter assays, promoter activation by DP was antagonized by FLA. The magnitude of inhibition of DP-mediated p21 induction by FLA exceeded that observed with the pTEFb antagonist 5,6-dichloro-1-beta-D-ribofuranosyl-benzimidazole. Calphostin C abrogated p21 induction mediated by DP and enhanced DP-mediated apoptosis in a manner comparable with FLA in MPM cells; in contrast, phorbol-12,13-dibutyrate blocked FLA-mediated inhibition of p21 induction by DP and markedly protected these cells from the apoptotic effects of sequential DP/FLA.

CONCLUSIONS

FLA abrogates DP-mediated induction of p21 expression, in part, via inhibition of protein kinase C signaling and markedly potentiates the cytotoxic effects of DP in MPM cells.

Simian virus 40 infection in humans and association with human diseases: results and hypotheses

Simian virus 40 (SV40) is a monkey virus that was introduced in the human population by contaminated poliovaccines, produced in SV40-infected monkey cells, between 1955 and 1963. Epidemiological evidence now suggests that SV40 may be contagiously transmitted in humans by horizontal infection, independent of the earlier administration of SV40-contaminated poliovaccines. This evidence includes detection of SV40 DNA sequences in human tissues and of SV40 antibodies in human sera, as well as rescue of infectious SV40 from a human tumor. Detection of SV40 DNA sequences in blood and sperm and of SV40 virions in sewage points to the hematic, sexual, and orofecal routes as means of virus transmission in humans. The site of latent infection in humans is not known, but the presence of SV40 in urine suggests the kidney as a possible site of latency, as it occurs in the natural monkey host. SV40 in humans is associated with inflammatory kidney diseases and with specific tumor types: mesothelioma, lymphoma, brain, and bone. These human tumors correspond to the neoplasms that are induced by SV40 experimental inoculation in rodents and by generation of transgenic mice with the SV40 early region gene directed by its own early promoter-enhancer. The mechanisms of SV40 tumorigenesis in humans are related to the properties of the two viral oncoproteins, the large T antigen (Tag) and the small t antigen (tag). Tag acts mainly by blocking the functions of p53 and RB tumor suppressor proteins, as well as by inducing chromosomal aberrations in the host cell. These chromosome alterations may hit genes important in oncogenesis and generate genetic instability in tumor cells. The clastogenic activity of Tag, which fixes the chromosome damage in the infected cells, may explain the low viral load in SV40-positive human tumors and the observation that Tag is expressed only in a fraction of tumor cells. "Hit and run" seems the most plausible mechanism to support this situation. The small tag, like large Tag, displays several functions, but its principal role in transformation is to bind the protein phosphatase PP2A. This leads to constitutive activation of the Wnt pathway, resulting in continuous cell proliferation. The possibility that SV40 is implicated as a cofactor in the etiology of some human tumors has stimulated the preparation of a vaccine against the large Tag. Such a vaccine may represent in the future a useful immunoprophylactic and immunotherapeutic intervention against human tumors associated with SV40.

Pregnancy-associated plasma protein-A (PAPP-A) expression and insulin-like growth factor binding protein-4 protease activity in normal and malignant ovarian surface epithelial cells

Pregnancy-Associated Plasma Protein-A (PAPP-A) proteolyses insulin-like growth factor binding protein-4 (IGFBP-4), thereby regulating local IGF availability. Reduced PAPP-A mRNA expression has been reported in ovarian cancer specimens compared to normal ovarian surface epithelial cells (OSE). To characterize PAPP-A expression and proteolytic activity in OSE, we developed a lifespan-extended human cell model using a temperature-sensitive mutant of the SV40 large T antigen (SV40LT). These OSE(tsT) cells proliferate at 34 degrees C (i.e., when SV40LT-positive), but not at 39 degrees C, a temperature at which the SV40LT is unstable (SV40LT-negative). Proteolysis of radiolabeled IGFBP-4 in conditioned media from OSE(tsT) lines was IGF-dependent and blocked by anti-PAPP-A antisera. Temperature shifts that eliminated stable SV40LT induced a 7-fold increase in PAPP-A mRNA and a 4-fold increase in protein. The converse experiment (shifting to SV40LT-positive conditions) resulted in decreased levels of PAPP-A mRNA but little change in PAPP-A protein. Nevertheless, there was a marked reduction in IGF-BP-4 proteolytic activity in medium of SV40LT-positive OSE-(tsT) cells. This decreased PAPP-A activity coincided with a nearly 20-fold increase in mRNA encoding a physiological inhibitor of PAPP-A, the precursor form of eosinophil Major Basic Protein (proMBP), and 4- to 5-fold increases in proMBP protein. Primary cultures of unmodified OSE expressed high levels of PAPP-A and undetectable proMBP, and therefore produced abundant IGFBP-4 protease activity. Short-term ovarian tumor cell cultures expressed variable levels of PAPP-A and high levels of proMBP, and consequently secreted little or no IGFBP-4 protease activity. The concurrent regulation of PAPP-A and its inhibitor, proMBP, suggests that IGFBP-4 proteolysis and local regulation of IGF availability may be altered in malignant ovarian epithelial cells.

High throughput testing of the SV40 Large T antigen binding to cellular p53 identifies putative drugs for the treatment of SV40-related cancers

SV40 has been linked to some human malignancies, and the evidence that this virus plays a causative role in mesothelioma and brain tumors is mounting. The major SV40 oncoprotein is the Large tumor antigen (Tag). A key Tag transforming activity is connected to its capability to bind and inactivate cellular p53. In this study we developed an effective, high throughput, ELISA-based method to study Tag-p53 interaction in vitro. This assay allowed us to screen a chemical library and to identify a chemical inhibitor of the Tag binding to p53. We propose that our in vitro assay is a useful method to identify molecules that may be used as therapeutic agents for the treatment of SV40-related human cancers.

Simian virus 40 and its association with human lymphomas

Simian virus 40 (SV40) is a potent DNA tumor virus that is known to induce cancer in laboratory animals. The neoplasias induced by SV40 in animal models are brain cancers, mesothelioma, bone cancers, and systemic lymphomas. SV40 oncogenesis is mediated primarily by the viral large tumor antigen, which inactivates the tumor suppressor proteins p53 and pRb family members. Evidence indicates that SV40 is an emergent human pathogen and that a significant excess risk of SV40 is associated with primary human brain cancers, malignant mesothelioma, bone cancers, and non-Hodgkin's lymphoma. Therefore, the major types of tumors induced by SV40 in laboratory animals are the same as those human malignancies found to contain SV40 markers. Experimental and clinical data indicate that SV40 may be functionally important in the development of some of those malignancies. Recently, the Institute of Medicine of the National Academies concluded that SV40 infections could lead to cancer in humans under natural conditions (based on moderate strength biologic evidence). This review examines the data implicating SV40 in the pathogenesis of human lymphomas and discusses future directions to define the causative role for SV40 in these malignancies.

New developments about the association of SV40 with human mesothelioma

Simian virus 40 (SV40) has been detected in human tumors in over 40 different laboratories. Many of these reports linked SV40 to human mesotheliomas. The Vaccine Safety Committee of the Institute of Medicine (IOM), National Academy of Sciences, USA, recently reviewed the evidence associating polio vaccines and/or SV40 with human tumors. The IOM conclusions about polio vaccines and human cancer were: (1) 'the evidence is inadequate to accept or reject a causal relation between SV40-containing polio vaccines and cancer' because the 'epidemiological studies are sufficiently flawed'; (2) 'the biological evidence is of moderate strength that SV40 exposure from the polio vaccines is related to SV40 infection in humans'. The epidemiological studies were considered flawed because it was not possible to distinguish reliably among exposed and nonexposed cohorts. Concerning SV40, the IOM concluded that (1) 'the evidence is strong that SV40 is a transforming virus; (2) the evidence is of moderate strength that SV40 exposure could lead to cancer in humans under natural conditions' (IOM, 2002). Similar conclusions were reached at an International consensus meeting on SV40 and human tumors held at the University of Chicago in 2001. G Klein and C Croce, who chaired the final panel that reviewed all the published evidence linking SV40 to human tumors, stated that 'the presence of SV40 in human tumors has been convincingly demonstrated' (Klein et al., 2002). In addition, a workshop organized by the Biological Carcinogenesis Branch of the National Cancer Institute, Bethesda, MD, chaired by J Pagano, has reached similar conclusions (Wong et al., 2002). Therefore, three independent scientific panels have all agreed that there is compelling evidence that SV40 is present in some human cancers and that SV40 could contribute to the pathogenesis of some of them. It should be noted that the presence of SV40 in mesothelioma and other human tumor types has been challenged by a research team that has consistently reported negative findings (Strickler et al., 2001). However, a member of this research team has recently acknowledged - in sworn testimony -sensitivity problems and possible irregularities that raise concerns about these negative reports (MacLachlan, 2002). These revelations, together with the conclusions of the three independent panels mentioned above, appear to bring to an end the apparent controversy about the presence of SV40 in human mesotheliomas and brain tumors.

SV40 in human brain cancers and non-Hodgkin's lymphoma

Simian virus 40 (SV40) is a potent DNA tumor virus that is known to induce primary brain cancers and lymphomas in laboratory animals. SV40 oncogenesis is mediated by the viral large tumor antigen (T-ag), which inactivates the tumor-suppressor proteins p53 and pRb family members. During the last decade, independent studies using different molecular biology techniques have shown the presence of SV40 DNA, T-ag, or other viral markers in primary human brain cancers, and a systematic assessment of the data indicates that the virus is significantly associated with this group of human tumors. In addition, recent large independent studies showed that SV40 T-ag DNA is significantly associated with human non-Hodgkin's lymphoma (NHL). Although the prevalence of SV40 infections in humans is not known, numerous observations suggest that SV40 is a pathogen in the human population today. This review examines the molecular biology, pathology, and clinical data implicating SV40 in the pathogenesis of primary human brain cancers and NHL and discusses future research directions needed to define a possible etiologic role for SV40 in these malignancies.

Oncogenic transformation by BK virus and association with human tumors

BK virus (BKV), a human polyomavirus closely related to JC virus and Simian Virus 40, is ubiquitous in human populations worldwide. After primary infection, BKV establishes a lifelong latent infection in many organs. BKV transforms rodent cells to the neoplastic phenotype and is highly oncogenic in rodents. This review considers the oncogenic potential of BKV in humans and its possible involvement in human tumors. BKV sequences and T antigen (Tag) are detected in several types of human neoplasms, although the viral load is generally low, with less than one copy of the viral genome per cell. The possible causative role of BKV in human oncogenesis rests on the ability of BKV Tag to inactivate the functions of tumor suppressor proteins p53 and pRB family as well as on its ability to induce chromosomal aberrations in human cells. A 'hit and run' mechanism and secretion of paracrine growth factors by BKV Tag-positive cells, recruiting into proliferation neighboring and distant cells, are discussed as possible BKV pathogenic elements in human oncogenesis.

Simian virus 40 in human cancers

BACKGROUND

Many studies have reported the presence of simian virus 40 (SV40) deoxyribonucleic acid (DNA) or protein in human brain tumors and bone cancers, malignant mesothelioma, and non-Hodgkin's lymphoma. However, the small samples and lack of control groups in some reports have made it difficult to assess their reliability.

METHODS

Studies were included in this analysis if they met the following criteria: original studies of patients with primary brain tumors and bone cancers, malignant mesothelioma, or non-Hodgkin's lymphoma; the investigation of SV40 was performed on primary cancer specimens; the analysis included a control group; and the same technique was used for cases and controls. Included reports were published from 1975 to 2002.

RESULTS

Thirteen studies fulfilled the criteria for the investigation of primary brain cancers (661 tumors and 482 control samples). Specimens from patients with brain tumors were almost four times more likely to have evidence of SV40 infection than were those from controls (odds ratio [OR] = 3.9; 95% confidence interval [CI]: 2.6 to 5.8). The association was even stronger for mesothelioma (OR = 17; 95% CI: 10 to 28; based on 15 studies with 528 mesothelioma samples and 468 control samples) and for bone cancer (OR = 25; 95% CI: 6.8 to 88; based on four studies with 303 cancers and 121 control samples). SV40 DNA was also more frequent in samples from patients with non-Hodgkin's lymphoma (OR = 5.4; 95% CI: 3.1 to 9.3; based on three studies with 301 cases and 578 control samples) than from controls.

CONCLUSION

These results establish that SV40 is associated significantly with brain tumors, bone cancers, malignant mesothelioma, and non-Hodgkin's lymphoma. Studies are needed to assess current prevalence of SV40 infections.

Notch-1 induction, a novel activity of SV40 required for growth of SV40-transformed human mesothelial cells

We show that SV40 infection of human mesothelial cells directly causes overexpression of Notch-1, a key cell regulatory gene. Notch-1 induction is achieved at the transcriptional level and requires both the SV40 large T-antigen and the small t-antigen. Notch-1 upregulation is maintained in SV40-transformed human mesothelial clones and in SV40-positive mesotheliomas and derived cell lines. Activation of Notch-1 promotes cell cycle progression and it is required for the growth of SV40-transformed mesothelial cells. Our finding is relevant to the process of SV40-mediated human cell transformation, an effect that cannot be accounted for solely by SV40-Tag inhibition of Rb and p53.

Simian virus 40 sequences in human lymphoblastoid B-cell lines

Human Epstein-Barr virus-immortalized lymphoblastoid B-cell lines tested positive by PCR for simian virus 40 (SV40) DNA (22 of 42 cell lines, 52.3%). B lymphocytes or tissues from which B-cell lines derived were also SV40 positive. In situ hybridization showed that SV40 DNA was present in the nucleus of a small fraction (1/250) of cells. SV40 T-antigen mRNA was detected by reverse transcription-PCR. Lymphoblastoid B-cell lines (n = 4) infected with SV40 remained SV40 positive for 4 to 6 months. SV40-positive B-cell lines were more tumorigenic in SCID mice than were SV40-negative cell lines (4 of 5 [80%] SV40-positive cell lines versus 2 of 4 [50%] SV40-negative cell lines). These results suggest that SV40 may play a role in the early phases of human lymphomagenesis.