Isolation of spindle-shaped cell populations from primary cultures of Kaposi's sarcoma of different stage

A "hit-and-run" affair - A possible link for cancer progression in virally driven cancers

BACKGROUND

It is well-known that certain cancers are caused by viruses. However, viral oncogenesis is complex and only a small fraction of the infected people develop cancer. Indeed, a number of environmental factors can contribute to virally infected cells developing cancer hallmarks, promoting tumorigenesis.

SCOPE OF REVIEW

The hit-and-run theory proposes that viruses facilitate the accumulation of mutations and promote genomic instability until the virus becomes dispensable for tumour maintenance. Indeed, several studies have reported viral genome, episome and/or oncogene loss in tumour cells without losing malignant phenotype.

MAJOR CONCLUSIONS

The current evidence supports the clear contribution of certain viruses to develop cancers. Importantly, the evidence supporting the sustained maintenance of malignancy after the loss of viral "presence" is sufficient to support the hit-and-run hypothesis of viral cancer development. Long-term tracking of vaccination outcome over the decades will test this theory.

GENERAL SIGNIFICANCE

If the hit-and-run theory is true, viruses might cause more cancers than previously thought and will have implications in the prevention of many cancers through implementing vaccination programs.

The Expression of CD154 by Kaposi's Sarcoma Cells Mediates the Anti-Apoptotic and Migratory Effects of HIV-1-Tat Protein

Kaposi's sarcoma (KS) is a malignancy associated to conditions of immune system impairment such as HIV-1 infection and post-transplantation therapy. Here we report that HIV-1-Tat protein, at concentrations well below those detected in AIDS patients, up-regulates the expression of both CD40 and CD154 on KS cells. This occurred also in the presence of vincristine, that at doses shown to induce apoptosis decreased the expression of both CD40 and CD154 on KS cells. The treatment with a soluble CD40-muIg fusion protein (CD40 fp) that prevents the binding of CD154 with cell surface CD40, as well as the transfection with a vector for soluble CD40 (KS sCD40), decreased the anti-apoptotic effect of Tat. Moreover, Tat-induced motility of KS cells was inhibited by soluble CD40 fp. Tat also enhanced the expression of intracellular proteins known to transduce signals triggered by CD40 engagement, in particular TRAF-3. Tat as well as soluble CD154 (sCD154) prevented vincristine-induced reduction of TRAF-3 in KS cells transfected with a vector for neomycin resistance (KS psv-neo), but not in KS sCD40. Immunoprecipitation studies showed that Tat induced CD40 / TRAF-3 association and that this binding was abrogated upon the incubation with the soluble CD40 fp. These data suggest that Tat activates the CD40-CD154 pathway by enhancing the membrane expression of CD40 and in particular of CD154, and by activating the TRAF-3-dependent signaling pathway of CD40. These findings indicate that the CD40-CD154 pathway mediates the anti-apoptotic and migratory effects of HIV-1-Tat, suggesting the potential therapeutic benefits of blocking CD40 activation in HIV-1-associated KS.

In Vitro Models of Angiogenesis: The use of Matrigel

Tumor-induced angiogenesis is a key event for neoplastic progression. In vitro assays are important for identification of potential angiogenic agents and rapid sceening for pharmacological inhibitors. The increased interest in this field of study has generated several in vitro assays that recapitulate the steps of endothelial cell activation and differentiation. In this short report we emphasize the utility of Matrigel, a reconstituted basement membrane, to define two different steps in the angiogenic process: invasion in response to growth factors and organization of microvessels into a network with branching morphology on a Matrigel substrate.

Endothelial cell- and lymphocyte-based in vitro systems for understanding KSHV biology

Kaposi sarcoma (KS), the most common AIDS-associated malignancy, is a multifocal tumor characterized by deregulated angiogenesis, proliferation of spindle cells, and extravasation of inflammatory cells and erythrocytes. Kaposi sarcoma-associated herpesvirus (KSHV; also human herpesvirus-8) is implicated in all clinical forms of KS. Endothelial cells (EC) harbor the KSHV genome in vivo, are permissive for virus infection in vitro, and are thought to be the precursors of KS spindle cells. Spindle cells are rare in early patch-stage KS lesions but become the predominant cell type in later plaque- and nodular-stage lesions. Alterations in endothelial/spindle cell physiology that promote proliferation and survival are thus thought to be important in disease progression and may represent potential therapeutic targets. KSHV encodes genes that stimulate cellular proliferation and migration, prevent apoptosis, and counter the host immune response. The combined effect of these genes is thought to drive the proliferation and survival of infected spindle cells and influence the lesional microenvironment. Large-scale gene expression analyses have revealed that KSHV infection also induces dramatic reprogramming of the EC transcriptome. These changes in cellular gene expression likely contribute to the development of the KS lesion. In addition to KS, KSHV is also present in B cell neoplasias including primary effusion lymphoma and multicentric Castleman disease. A combination of virus and virus-induced host factors are similarly thought to contribute to establishment and progression of these malignancies. A number of lymphocyte- and EC-based systems have been developed that afford some insight into the means by which KSHV contributes to malignant transformation of host cells. Whereas KSHV is well maintained in PEL cells cultured in vitro, explanted spindle cells rapidly lose the viral episome. Thus, endothelial cell-based systems for studying KSHV gene expression and function, as well as the effect of infection on host cell physiology, have required in vitro infection of primary or life-extended EC. This chapter includes a review of these in vitro cell culture systems, acknowledging their strengths and weaknesses and putting into perspective how each has contributed to our understanding of the complex KS lesional environment. In addition, we present a model of KS lesion progression based on findings culled from these models as well as recent clinical advances in KS chemotherapy. Thus this unifying model describes our current understanding of KS pathogenesis by drawing together multiple theories of KS progression that by themselves cannot account for the complexities of tumor development.

Kaposi's sarcoma-associated herpesvirus: clinical, diagnostic, and epidemiological aspects

Kaposi's sarcoma-associated herpesvirus (KSHI) is one of the few viruses proven to be associated with tumorigenesis in humans. Its causal association with all clinical and epidemiological variants of Kaposi's sarcoma (KS) is well established. KSHV is also involved in the pathogenesis of primary effusion lymphoma (PEL) and a subset of multicentric Castleman's disease (MCD). Possible associations of KSHV with other clinical settings have been extensively examined. The findings from several of these studies are contradictory and are yet to be resolved. Concentrated effort over the last decade, since the initial discovery of KSHV, led to the development of several experimental systems that resulted in a better comprehension of the biological characteristics of KSHV and set the stage for the understanding of mechainisms by which diseases are induced by the virus. The development of molecular, histological, and serological tools for KSHV diagnosis allowed researchers to track the transmission and to study the epidemiology of KSHV. These assays have been applied, in particular in ambiguous cases, in order to confirm clinically and pathologically based diagnoses. Here, we review the advances in the clinical, experimental, diagnostic, and epidemiological research of KSHV.

Uncovering the complexities of Kaposi's sarcoma through genome-wide expression analysis

Gene-expression profiling of endothelial cells infected with Kaposi's sarcoma-associated herpesvirus has led to a greater understanding of the histogenesis and pathogenesis of Kaposi's sarcoma.

Gene-expression profiling of endothelial cells infected with Kaposi's sarcoma-associated herpesvirus has led to a greater understanding of the histogenesis of Kaposi's sarcoma and cellular reprogramming events that occur as a result of viral infection and that may play important roles in viral pathogenesis.

Pathogenesis of Kaposi's sarcoma

Kaposi's sarcoma (KS) is a disease characterized by proliferative vascular lesions, which almost invariably contain the KS-associated herpesvirus (KSHV), also called human herpesvirus 8. KSHV is a lymphotrophic and angiotrophic herpesvirus, whose genome encodes several proteins involved in proliferation, antiapoptotic functions, and inflammation. Most KS spindle cells express latent KSHV genes, but a few express lytic genes, which might be involved in angiogenic and paracrine mechanisms that contribute to KS pathogenesis. A number of tissue culture and mouse models have been established, but a comprehensive system that accurately portrays KS pathogenesis still does not exist.

Spectrum of Kaposi's sarcoma-associated herpesvirus, or human herpesvirus 8, diseases

Human herpesvirus 8 (HHV-8), also known as Kaposi's sarcoma-associated herpesvirus (KSHV), discovered in 1994, is a human rhadinovirus (gamma-2 herpesvirus). Unlike other human herpesviruses (herpes simplex virus, Epstein-Barr virus, varicella-zoster virus, cytomegalovirus, HHV-6, and HHV-7), it is not widespread in the general population and has many unique proteins. HHV-8 is strongly associated with all subtypes of Kaposi's sarcoma (KS), multicentric Castleman's disease, and a rare form of B-cell lymphoma, primary effusion lymphoma. In addition, HHV-8 DNA sequences have been found in association with other diseases, but the role of the virus in these diseases is largely unconfirmed and remains controversial. The seroprevalence of HHV-8, based on detection of latent and lytic proteins, is 2 to 5% in healthy donors except in certain geographic areas where the virus is endemic, 80 to 95% in classic KS patients, and 40 to 50% in HIV-1 patients without KS. This virus can be transmitted both sexually and through body fluids (e.g., saliva and blood). HHV-8 is a transforming virus, as evidenced by its presence in human malignancies, by the in vitro transforming properties of several of its viral genes, and by its ability to transform some primary cells in culture. It is not, however, sufficient for transformation, and other cofactors such as immunosuppressive cytokines are involved in the development of HHV-8-associated malignancies. In this article, we review the biology, molecular virology, epidemiology, transmission, detection methods, pathogenesis, and antiviral therapy of this newly discovered human herpesvirus.

Expression of the fibroblast/macrophage marker 1B10 by spindle cells in Kaposi's sarcoma lesions and by Kaposi's sarcoma-derived tumor cells

BACKGROUND

Kaposi's sarcoma (KS) is a tumor whose ontogenic origin remains a matter of contention. KS tissues are characterized by predominant expression of endothelial markers, while KS-derived cell cultures are usually characterized by expression of mesenchymal non-endothelial cell markers.

AIMS

In order to clarify the ontogenic origin of KS cells, we investigated the expression of the fibroblast/macrophage marker 1B10 in KS tissues (AIDS-associated KS, n = 9; classic KS, n = 6; iatrogenic KS, n = 6) and in KS-derived cell cultures.

RESULTS

1B10 was expressed by loosely distributed spindle-shaped cells in early 'patch-stage' KS and by a variable proportion of spindle cells in late 'plaque- and nodular-stage' KS. Using immunohistochemistry and immunoblot analysis, we found that, in vitro, reactivity for 1B10 was uniformly evidenced in fibroblasts and in KS-derived spindle cell cultures, irrespective of their histological or epidemiological setting. By contrast, vascular smooth muscle cells and endothelial cells were negative for 1B10.

CONCLUSIONS

These results suggest that the KS spindle cells isolated in vitro may represent a particular subpopulation of the KS spindle cell compartment.

HIV type 1 Tat protein is a survival factor for Kaposi's sarcoma and endothelial cells

The HIV-1 Tat protein has been directly implicated in the pathogenesis of AIDS-related Kaposi's sarcoma (KS); however, its effects on KS spindle-shaped and endothelial cell apoptosis are largely unexplored. Since susceptibility to apoptosis is relevant for tumor development and response to therapy, we investigated the effects of Tat on KS and endothelial cell survival from apoptosis. The effect of Tat was evaluated in three KS cell lines (KS-imm, KS-C1, and KS-L3) exposed to the chemotherapy agent vincristine, currently used for the treatment of this tumor, and in human umbilical vein-derived endothelial cells (HUVECs) induced to undergo apoptosis by serum withdrawal. Apoptosis was assessed by enzymatic assays, microscopic examination of chromatin and cytoskeleton, evaluation of plasma membrane integrity and subdiploid DNA content, TUNEL assays, and measurement of caspase-3 activity. Tat, in a dose-dependent manner, protected the three KS cell lines and HUVECs from apoptosis induced by vincristine or serum starvation, respectively. This effect appeared to be independent of modulation of Fas, Bcl-2, or Bax expression. In contrast, Tat upregulated Bcl-X(L) expression and induced a relevant decrease in caspase-3 activity in vincristine-treated KS cells. Taken together, these results suggest that the HIV-1 Tat protein may factor KS development and progression by sustaining endothelial and transformed cell survival.

Phenotypic characteristics of Kaposi's sarcoma tumour cells derived from patch-, plaque- and nodular-stage lesions: analysis of cell cultures isolated from AIDS and non-AIDS patients and review of the literature

BACKGROUND

Kaposi's sarcoma (KS) is commonly thought to be derived from endothelial cells because of the predominant expression of endothelial markers in KS lesions. However, the heterogeneity of the spindle-cell compartment makes the precise lineage relationship of KS tumour cells unclear. Cultured KS-derived spindle cells constitutively overexpress antiapoptotic proteins and exhibit invasive properties, which suggests that they may adequately represent the tumour cells of KS.

OBJECTIVES

We aimed to investigate the expression of a wide variety of immunohistochemical markers by spindle cells derived from patch-, plaque- and nodular-stage lesions from patients with iatrogenic, sporadic and acquired immune deficiency syndrome-related KS, and to review the data reported by other laboratories.

METHODS

Cells from six KS cell cultures derived from four subjects were examined by immunostaining.

RESULTS

Comparison of these data indicates that KS-derived spindle cells generally express myofibroblast antigens but lack endothelial and/or leucocyte markers.

CONCLUSIONS

As the myofibroblast phenotype is not the predominant feature of KS tissues, our findings further substantiate the view that the in vivo dominant endothelial population represents a reactive hyperplasia rather than the true KS tumour process.

Kaposi's sarcoma cells of different etiologic origins respond to HIV-Tat through the Flk-1/KDR (VEGFR-2): relevance in AIDS-KS pathology

Kaposi's sarcoma (KS) is an hyperplastic lesion whose main histological features are typical spindle shaped cells with a mixed endothelial-mesenchymal-macrophage phenotype, an intense vascularization and an inflammatory infiltrate. The etiology of KS appears to be linked to activation of a latent HHV8 infection. Sporadic and iatrogenic KS are slow progressing lesions that can undergo spontaneous regression. In contrast, KS, which is frequently associated with HIV infection, is found in a highly aggressive form in AIDS patients. The HIV-1 Tat has been shown to activate the VEGF receptor KDR in endothelial and KS spindle cells, suggesting this HIV protein could contribute to KS pathogenesis. We used primary 'reactive' KS cell culture from sporadic and epidemic KS, and an immortal KS-line (KS-Imm) isolated in our laboratory from a iatrogenic KS lesion, to verify if Tat-induced cell signaling is able to mediate cellular responses. We demonstrate that KS cells migrated in response to Tat and that VEGF is able to compete with the Tat chemotactic activity towards these cells. A function-blocking anti-KDR antibody was able to abrogate both VEGF and Tat-induced KS chemotactic response, indicating a direct involvement of this receptor. Our data show that HIV-Tat can also activate KS cells derived from sporadic or iatrogenic lesions, suggesting that in AIDS patients Tat could cooperate with VEGF in activation of KDS on KS precursor spindle and endothelial cells, and contribute to the aggressiveness of AIDS-KS lesions.

Ultrastructural characterization of human herpesvirus 8 (Kaposi's sarcoma-associated herpesvirus) in Kaposi's sarcoma lesions: electron microscopy permits distinction from cytomegalovirus (CMV)

Kaposi's sarcoma (KS) has been shown by molecular techniques to be associated with infection with human herpesvirus 8 (HHV8/KSHV), but specific ultrastructural characterization of the virus has been impaired by the frequent presence in these lesions of other herpesviruses, particularly cytomegalovirus (CMV). Since the ultrastructural appearance of HHV8/KSHV has been studied in the cell line KS-1 uninfected with other viruses including CMV, it was possible to undertake a comparative study of CMV and HHV8/KSHV in KS lesions. HHV8/KSHV was sparsely present and lytic infection was restricted to endothelial cells. The following specific ultrastructural features allowed distinction between HHV8/KSHV and CMV: the viral particles were more delicate and less numerous in cases of HHV8/KSHV infection; the viral tegument was more electron-dense in CMV than in HHV8/KSHV; dense bodies characteristic of CMV were absent in HHV/KSHV; complete CMV viral particles were more variable in size and generally larger (150-200 nm) than HHV8/KSHV (120-150 nm); and finally, the viral envelope was more pleomorphic in CMV than in KSHV/HHV8. Similarities between CMV and HHV8/KSHV included the basic structure of the nucleocapsids and the presence of capsids lacking central DNA cores (so-called non-infectious enveloped particles). These observations show that electron microscopy can be used to identify HHV8/KSHV and confirm the relationship between HHV8/KSHV and KS.

The beta-core fragment of human chorionic gonadotrophin inhibits growth of Kaposi's sarcoma-derived cells and a new immortalized Kaposi's sarcoma cell line

OBJECTIVE

Kaposi's sarcoma (KS), a condition often associated with HIV infection, is more common in men than in women; pregnancy and sex hormones could be involved. Urinary human chorionic gonadotrophin (hCG) has been reported to inhibit the growth of KS cell lines, with great variability among preparations. Urinary hCG often contains free forms of the hCG subunits and a fragment of the free beta-subunit, the beta-core, which may have biological activity. We compared the effect of the beta-core fragment, the beta-subunit, recombinant and urinary hCG on KS immortal and spindle cells.

DESIGN AND METHODS

A new immortal KS cell line was phenotypically and karyotypically characterized. The effects on growth of this cell line and of primary KS spindle cells by hCG and its purified derivatives were tested. Induction of apoptosis was demonstrated using acridine orange/ethidium bromide staining.

RESULTS

The beta-core fragment harboured the most potent growth inhibitory activity on a molar basis. After 72 h of treatment with the beta-core, 60-70% of KS cells show apoptotic nuclei. No effects were observed on endothelial cells.

CONCLUSIONS

The beta-core fragment of hCG proved to be the most effective part of the hCG molecule, inducing growth inhibition and apoptosis of KS cells. Thus, the beta-core could be the most appropriate hCG derivative for the therapy of KS.

KSHV sequences in biopsies and cultured spindle cells of epidemic, iatrogenic and Mediterranean forms of Kaposi's sarcoma

The pathogenesis of Kaposi's sarcoma (KS) is still unclear, and several factors appear to be involved in the onset of the Kaposi's lesion. Epidemiological studies suggest that a common infective agent may contribute to KS. Sequences which appear to represent a new gammaherpesvirus, currently termed KSHV/HHV8, have recently been identified in KS. To further examine the relationship between this virus and KS, we obtained biopsy samples of KS lesions; these samples, the spindle cells cultured from these lesions and the PBMC of the same patients were tested for the presence of KSHV sequences by PCR. In addition, we tested several "late passage" KS spindle cell lines as well as control samples. The biopsy samples were from lesions of the following forms of KS: one sporadic KS, two epidemic KS and three iatrogenic KS, one of which was in the process of regressing after reduction of immunosuppressive therapy, and two that were at different stages (patch and nodular) from a single patient. The sporadic KS specimen was positive, as were the PBMCs from this patient, and cells grown from this biopsy appeared to contain KSHV viral sequences up to the fifth passage. Both epidemic KS biopsies were positive, but in these cases KSHV sequences were not detected in the cultured cells. The biopsy from the regressing iatrogenic KS lesion was negative, as were the cells cultured from this lesion. However, the PBMCs of this patient were weakly positive for KSHV at the time of biopsy, and PBMCs collected from this patient one month later were completely negative. The samples of both the patch and the nodular KS lesions obtained from another immunosuppressed patient showed amplifiable sequences of KSHV, but both the PBMCs of this patient and primary KS cell cultures from these biopsies were negative. Of the late-passage KS lines tested, only one, IST AIDS KS 12, was positive for KSHV. This line is derived from an early angiomatous-macula lesion. Taken together, these data suggest that an active KSHV infection is associated with KS and that elimination of KSHV from the lesion precedes regression of the lesion, strongly correlating KSHV with KS. In addition, early KS lesions may have a higher KSHV burden, or contain cells more susceptible to KSHV infection, further linking KSHV to KS.