Kaposi's sarcoma-associated herpesvirus-encoded interleukin-6 and G-protein-coupled receptor regulate angiopoletin-2 expression in lymphatic endothelial cells

Kaposi's sarcoma (KS) is caused by Kaposi's sarcoma-associated herpesvirus (KSHV) and consists of proliferating spindle cells, which are related to lymphatic endothelial cells (LEC). Angiopoietin-2 (Ang2) is a secreted proangiogenic and lymphangiogenic molecule. Here, we show the expression of Ang2 protein in KS and confirm that KSHV infection upregulates Ang2 in LEC. We show that a paracrine mechanism contributes to this up-regulation. A lentiviral library of individual KSHV-encoding genes, comprising the majority of known latent genes and a selection of lytic viral genes, was constructed to investigate the underlying mechanism of this up-regulation. Two lytic genes, viral interleukin-6 (vIL6) and viral G-protein-coupled receptor (vGPCR), up-regulated Ang2 expression in LEC. Both vIL6 and vGPCR are expressed in KSHV-infected LEC and caused up-regulation of Ang2 in a paracrine manner. KSHV, vIL6, and vGPCR up-regulated Ang2 through the mitogen-activated protein kinase (MAPK) pathway. Gene expression microarray analysis identified several other angiogenic molecules affected by KSHV, including the vascular endothelial growth factor (VEGF)/VEGF receptor (VEGFR) axis, which is also affected by vIL6 and vGPCR in LEC, and matrix metalloproteinases, which could act in concert with Ang2 to contribute to KS development. These findings support the paracrine and autocrine roles of the lytic KSHV-encoded proteins, vIL6 and vGPCR, in KS pathogenesis and identify Ang2 as a potential therapeutic target for this neoplasm.