The major transmission route for Kaposi sarcoma-associated herpesvirus (KSHV) infection is the oral cavity through saliva. Kaposi sarcoma (KS) frequently occurs in the oral cavity in HIV-positive individuals and is often the first presenting sign of AIDS. However, the oral target cells for KSHV infection and the cellular origin of Kaposi sarcoma remain unknown. Here we present clinical and experimental evidences that Kaposi sarcoma spindle cells may originate from virally modified oral mesenchymal stem cells (MSC). AIDS-KS spindle cells expressed neuroectodermal stem cell marker (Nestin) and oral MSC marker CD29, suggesting an oral/craniofacial MSC lineage of AIDS-associated Kaposi sarcoma. Furthermore, oral MSCs were highly susceptible to KSHV infection, and infection promoted multilineage differentiation and mesenchymal-to-endothelial transition (MEndT). KSHV infection of oral MSCs resulted in expression of a large number of cytokines, a characteristic of Kaposi sarcoma, and upregulation of Kaposi sarcoma signature and MEndT-associated genes. These results suggest that Kaposi sarcoma may originate from pluripotent MSC and KSHV infection transforms MSC to Kaposi sarcoma-like cells through MEndT. These findings indicate that Kaposi sarcomas, which arise frequently in AIDS patients, originate from neural crest-derived mesenchymal stem cells, with possible implications for improving the clnical treatment of this malignancy. .

Curcumin, a polyphenol, is the main bioactive compound in dietary spice turmeric curcuma longa.It possesses anti-inflammatory, anti-oxidant and anti-neoplastic properties and shows potentials in treating or preventing particular diseases such as oxidative and inflammatory conditions, metabolic syndrome, arthritis, anxiety, hyperlipidemia and cancers. The diverse range and potential health beneficial effects has generated enthusiasm leading to intensive investigation into the phytochemical. However, a concern has been also raised if curcumin has a promiscuous bioassay profile and is a Pan-Assay INterference compound (PAINS). Here we present evidence indicating that curcumin is not a PAINS, but an inhibitor to APE1 redox function that affects many genes and pathways. This discovery explains the wide range of effects of curcumin on diverse human diseases and predicts a potential application in treatment of viral infection and virus-associated cancer. As a proof-of-concept, we demonstrated that curcumin is able to efficiently block Kaposi's sarcoma-associated herpesvirus replication and inhibit the pathogenic processes of angiogenesis and cell invasion.

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Increasing evidence suggests that Kaposi’s sarcoma (KS) arises from Kaposi’s sarcoma-associated herpesvirus (KSHV)-infected mesenchymal stem cells (MSCs) through mesenchymal-to-endothelial transition (MEndT). KSHV infection promotes MSC differentiation of endothelial lineage and acquisition of tumorigeneic phenotypes. To understand how KSHV induces MEndT and transforms MSCs to KS cells, we investigated the mechanism underlying KSHV-mediated MSC endothelial lineage differentiation. Like embryonic stem cells, MSC differentiation and fate determination are under epigenetic control. Prospero homeobox 1 (PROX1) is a master regulator that controls lymphatic vessel development and endothelial differentiation. We found that the PROX1 gene in MSCs harbors a distinctive bivalent epigenetic signature consisting of both active marker H3K4me3 and repressive marker H3K27me3, which poises expression of the genes, allowing timely activation upon differentiation signals or environmental stimuli. KSHV infection effectively resolves the bivalent chromatin by decreasing H3K27me3 and increasing H3K4me3 to activate the PROX1 gene. vIL-6 signaling leads to the recruitment of MLL2 and SET1 complexes to the PROX1 promoter to increase H3K4me3, and the vGPCR-VEGF-A axis is responsible for removing PRC2 from the promoter to reduce H3K27me3. Therefore, through a dual signaling process, KSHV activates PROX1 gene expression and initiates MEndT, which renders MSC tumorigenic features including angiogenesis, invasion and migration.

Kaposi sarcoma (KS) is an angioproliferative and invasive tumor caused by Kaposi sarcoma-associated herpesvirus (KSHV). The cellular origin of KS tumor cells remains contentious. Recently, evidence has accrued indicating that KS may arise from KSHV-infected mesenchymal stem cells (MSCs) through mesenchymal-to-endothelial transition (MEndT), but the transformation process has been largely unknown. In this study, we investigated the KSHV-mediated MEndT process and found that KSHV infection rendered MSCs incomplete endothelial lineage differentiation and formed hybrid mesenchymal/endothelial (M/E) state cells characterized by simultaneous expression of mesenchymal markers Nestin/PDGFRA/α-SAM and endothelial markers CD31/PDPN/VEGFR2. The hybrid M/E cells have acquired tumorigenic phenotypes in vitro and the potential to form KS-like lesions after being transplanted in mice under renal capsules. These results suggest a homology of KSHV-infected MSCs with Kaposi sarcoma where proliferating KS spindle-shaped cells and the cells that line KS-specific aberrant vessels were also found to exhibit the hybrid M/E state. Furthermore, the genetic analysis identified KSHV-encoded FLICE inhibitory protein (vFLIP) as a crucial regulator controlling KSHV-induced MEndT and generating hybrid M/E state cells for tumorigenesis. Overall, KSHV-mediated MEndT that transforms MSCs to tumorigenic hybrid M/E state cells driven by vFLIP is an essential event in Kaposi sarcomagenesis.