Kaposi sarcoma is a tumor consisting of Kaposi sarcoma herpesvirus (KSHV)–infected tumor cells that express endothelial cell (EC) markers and viral genes like v-cyclin, vFLIP, and LANA. Despite a strong link between KSHV infection and certain neoplasms, de novo virus infection of human primary cells does not readily lead to cellular transformation. We have studied the consequences of expression of v-cyclin in primary and immortalized human dermal microvascular ECs. We show that v-cyclin, which is a homolog of cellular D-type cyclins, induces replicative stress in ECs, which leads to senescence and activation of the DNA damage response. We find that antiproliferative checkpoints are activated upon KSHV infection of ECs, and in early-stage but not late-stage lesions of clinical Kaposi sarcoma specimens. These are some of the first results suggesting that DNA damage checkpoint response also functions as an anticancer barrier in virally induced cancers.

The histogenesis of Kaposi's sarcoma (KS) tumor spindle cells (SC) remains controversial but several immunohistochemical studies favor a lymphatic origin. Twenty KS surgical biopsies were analyzed for the coexpression of LANA, CD34, LYVE-1, D2-40, VEGFR-2, VEGFR3 by using double or triple immunostaining. Most of the SC in both early and late KS expressed the lymphatic markers LYVE-1, D2-40 and VEGFR-3 and the blood vascular endothelial/endothelial precursor cell markers CD34 and endothelial stem cell marker VEGFR-2. All the LANA1 SC in early and late KS were LYVE-11, but only 75% of these LANA1 cells were CD341. The CD341/LANA1 cells increased from early-(68.8%) to late-stage KS (82.2%). However, approximately 18% of the LANA1 SC in early KS were CD342 but were LYVE-11, suggesting that resident lymphatic endothelial cells (LEC) are targeted for primary infection by human herpesvirus-8. This LANA1/LYVE-11/CD342 (resident LEC) cell population clearly decreased during the development of KS from early (18.7%) to late KS (2.9%). Thus, in late stages of KS, most SC were LANA1/CD341/LYVE-11. However, in both early-and late-stage KS, approximately 18% of the SC were CD341/ LANA-/LYVE-12 and could represent newly recruited endothelial precursor cells, which become infected in the lesion and eventually undergo a phenotype switch expressing LEC markers. Our study apparently indicates that KS represents a unique variant of tumor growth with continues recruitment of tumor precursor cells as well as proliferation and decreased apoptosis of SC. ' 2006 Wiley-Liss, Inc.Key words: Kaposi's sarcoma; HHV-8; KSHV; LANA; lymphangiogenesis; lymphatic; vascular endothelium; immunohistochemistry Kaposi's sarcoma (KS) presents as a highly vascularized tumorlike lesion affecting primarily the skin but which during development also disseminates to lymphnodes and viscera. 1 The lesions develop from early stages of patch/plaque to late nodular tumor lesions, 2 with characteristic early infiltration of mononuclear inflammatory cells, formation of atypical small blood vessels and vascular slits (angiogenesis), extravasations of erythrocytes and increased appearance of so-called spindle cells (SC) regarded as the tumor cells. 3 Unlike metastatic cancers, KS may also develop as multicentric tumor lesions, each arising from a focal reactive lesion and appearance of endothelial SC. 4 In 1994, a new herpesvirus was identified, namely, KS-associated herpesvirus or human herpesvirus-8 (KSHV/HHV-8), 5 which subsequently also was found in the other clinicoepidemiological forms of KS, 6-8 i.e., classic KS, iatrogenic KS, endemic KS (EKS) as well as in some rare, often AIDS-associated lymphoid disorders as primary effusion lymphoma 9 and multicentric Castleman's disease. 10 The HHV-8 latency-associated nuclear antigen type 1 (LANA-1) is consistently expressed in infected cells and considered necessary for the maintenance of HHV-8 infection. 11 The histogenesis of KS remains controversial but several immunohistochemical studies favor an endothelial origin...

Purpose: Neoangiogenesis is essential for tumor development. Hypoxia-inducible factor (HIF), a transcriptional factor composed of two subunits (a and h), plays a key role in this process, activating proangiogenic factors such as vascular endothelial growth factor (VEGF). The HIF a subunits are critically regulated by oxygen and are also modulated by growth factors. Kaposi sarcoma (KS) is a highly vascular tumor that releases large amounts of VEGF and for which we have recently described an essential role for the insulin-like growth factor (IGF) system. We therefore investigated the expression of HIF a subunits in biopsies from KS tumors and their modulation by IGF-I in KSIMM, a KS cell line. Results: Both HIF-1a and HIF-2a were expressed in KS biopsies in all tumoral stages. HIF-1a immunopositivity increased through the tumor development with highest expression in the late nodular stages. In KSIMM cells, IGF-I induced accumulation of both HIF a subunits.The induction suggests a translation mechanism as documented by cycloheximide chase experiment coupled with constant RNA levels as evaluated by quantitative real-time PCR. IGF-I^induced HIF a accumulation was followed by an increase in HIF function as assessed both by reporter gene assay and by induction of endogenous target gene expression (VEGF-A). Specific blockade of IGF-I receptor with aIR3 antibody or with picropodophyllin, a specific IGF-IR tyrosine kinase inhibitor, diminishes the basal and IGF-I^dependent induction of both HIF a congeners. Conclusion: These novel findings show the coupling between the IGF and HIF signaling in KS and suggest a coordinated contribution by these pathways to the characteristic vascular phenotype of this tumor.

corresponding to approximately 10% of KS registered during 1990-2005, were diagnosed (ELISA) as HIV-infected (OAKS) (74/78) and endemic KS (4/78). Females were 69.2% (54/78) with median age 31 and males 30.8% (24/78) with median age 38. More males (50%) had systemic KS than females (37%) and 4-times more multicentric OKS. All tested (34) oral KS patients sera had HHV-8 antibodies. Available (31/78) blood showed very low CD4 + T-lymphocyte counts. Most OKS (61.5%) had nodular histology. Immunostaining showed adult male nodular OAKS to have a significantly higher frequency of viral LANA + , endothelial CD34 + tumour spindle-cells (SC) and more Ki-67 + (median =24.1%) proliferating cells compared to females (17.2%). Juvenile nodular OAKS had more LANA + and Ki-67 + cells than corresponding adult cases. Significantly more LANA + and Ki-67 + cells were found in nodular OAKS compared to cutaneous HIV/AIDS Kaposi's sarcoma (CAKS). A positive correlation (60%) was found between the proliferation index (Ki-67 + cell frequency) and LANA + /CD34 + SC. OKS in Tanzania is since 1990, mostly seen in females, associated with HIV/AIDS and advanced (nodular) histopathology. Males have more systemic tumour burden while more females develop primary OAKS. HHV-8 + cells were more frequent in nodular male than female and in juvenile than adult nodular OAKS than cAKS. Higher tumoral HHV-8 content appeared to be correlated to proliferation index.

Kaposi's sarcoma (KS) is a highly and abnormally vascularized tumor-like lesion affecting the skin, lymphnodes and viscera, which develops from early inflammatory stages of patch/plaque to late, nodular tumors composed predominant of spindle cells (SC). These SC are infected with the Kaposi's sarcoma-associated herpesvirus or human herpesvirus-8 (KSHV/HHV-8). KS is promoted during HIV infection by various angiogenic and pro-inflammatory factors including HIV-Tat. The latency associated nuclear antigen type 1 (LANA-1) protein is well expressed in SC, highly immunogenic and considered important in the generation and maintenance of HHV-8 associated malignancies. Various studies favour an endothelial origin of the KS SC, expressing "mixed" lymphatic and vascular endothelial cell markers, possibly representing hybrid phenotypes of endothelial cells (EC). A significant number of SC during KS development are apparently not HHV8 infected, which heterogeneity in viral permissiveness may indicate that non-infected SC may continuously be recruited in to the lesion from progenitor cells and locally triggered to develop permissiveness to HHV8 infection. In the present study various aspects of KS pathogenesis are discussed, focusing on the histopathological as well as cytogenetic and molecular genetic changes in KS.

Kaposi sarcoma (KS) is associated with a herpesvirus (HHV-8/KSHV), which expresses a latency-associated nuclear antigen (LANA). The histopathology of KS is characterized by angiogenesis, inflammatory cells, and the development of CD34+ tumor spindle cells (SCs). However, the cellular basis for the recruitment and dissemination of HHV-8 during the development of KS lesions is not clear. Twenty-nine KS biopsies with AIDS (AKS, n=22) and without HIV infection (endemic KS or EKS, n=7) were immunostained by a triple antibody method to characterize HHV-8-infected and noninfected (LANA+/-) CD34+ SCs, infiltrating CD3+, CD68+, CD20+, and CD45+ leukocytes as well as proliferating (Ki67+) cells. The CD34+/LANA+ SCs were more frequent in late (nodular) as compared with early (patch/plaque) KS stages. However, in late AKS 36.0% of SCs (median of 11 cases) were CD34+/LANA- compared with 20.7% in early cases (median of 11 cases). Furthermore, both AKS and EKS showed, at all stages, a small (4.1-6.5%) population of LANA+/CD34- cells. Proliferating Ki67+ cells were seen (4.5-11.5%) at all KS stages, and were usually more frequent in early AKS, but no significant difference was observed between nodular AKS and EKS. Most of the proliferating cells in the KS lesions were LANA+/CD34+ but a small fraction was LANA+/CD34-. Lesional CD68+ and CD3+ cells varied between AKS (7.3 and 5.2%, respectively) and EKS (4.9 and 3.1%, respectively) but were not clearly stage related. No LANA+ cells were CD3+, CD20+, or CD45+ and very few (<0.5%) were CD68+. These results indicate that not all CD34+ KS SCs were LANA+, suggesting recruitment of noninfected SCs to the lesions. Cell proliferation in general was much higher in early as compared with the late AKS stages. LANA+ SCs could have a proliferative advantage as suggested by higher frequency of cycling (Ki67+) LANA+ SCs. Few macrophages but no lymphocytes are LANA+.

Upregulation of functionally active cyclin E via miR34 with loss of p53 function is associated with cell-cycle checkpoint failure increasing proliferative drive that favors hepatocarcinogenesis.

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