Abstract
Kaposi's sarcoma (KS) is the most common tumor of AIDS patients worldwide. KS-associated herpesvirus (KSHV) is the infectious cause of this highly vascularized skin tumor. The main cell type found within a KS lesion, the spindle cell, is latently infected with KSHV and has markers of both blood and lymphatic endothelial cells. During development, lymphatic endothelial cells differentiate from preexisting blood endothelial cells. Interestingly, KSHV infection of blood endothelial cells induces lymphatic endothelial cell differentiation. Here, we show that KSHV gene expression is necessary to maintain the expression of the lymphatic markers vascular endothelial growth factor receptor 3 (VEGFR-3) and podoplanin. KSHV infection activates many cell signaling pathways in endothelial cells and persistently activates STAT3 through the gp130 receptor, the common receptor of the interleukin 6 family of cytokines. We find that KSHV infection also activates the phosphatidylinositol 3-OH-kinase (PI3K)/Akt cell signaling pathway in latently infected endothelial cells and that gp130 receptor signaling is necessary for Akt activation. Using both pharmacological inhibitors and small interfering RNA knockdown, we show that the gp130 receptor-mediated activation of both the JAK2/STAT3 and PI3K/Akt cell signaling pathways is necessary for KSHV-induced lymphatic reprogramming of endothelial cells. The induction of the lymphatic endothelial cell-specific transcription factor Prox1 is also involved in KSHV-induced lymphatic reprogramming. The activation of gp130 receptor signaling is a novel mechanism for the differentiation of blood endothelial cells into lymphatic endothelial cells and may be relevant to the developmental or pathological differentiation of lymphatic endothelial cells as well as to KSHV pathogenesis.