Activation of Akt through gp130 Receptor Signaling Is Required for Kaposi's Sarcoma-Associated Herpesvirus-Induced Lymphatic Reprogramming of Endothelial Cells

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.

KSHV and the pathogenesis of Kaposi sarcoma: listening to human biology and medicine

“…But it also poses an important biological question: is the result solely due to lessened immunosuppression, or does inhibition of mTOR signaling have direct antitumor effects? There is reason to believe that the latter might play a role: studies of both PEL cells and KSHV-infected endothelial cells have shown activation of PI3K and Akt phosphorylation (191,192), both of which are events that occur upstream of mTORC1, the principal target of rapamycin action. Thus, viral infection may turn on the mTORC1 pathway.…”

Ets-1 Is Required for the Activation of VEGFR3 during Latent Kaposi's Sarcoma-Associated Herpesvirus Infection of Endothelial Cells

“…VEGFR3 mRNA is upregulated 6-fold in KSHV-infected TIME cells compared to mock-infected cells ( Fig. 2A), as we have described previously (20,23). We next examined the protein expression levels of both Ets-1 and VEGFR3 using Western blot analysis.…”

“…Interestingly, expression of the lymphatic-specific VEGFR3 gene was also knocked down by Ets-1 siRNA in KSHV-infected cells. We previously reported that activation of gp130 by KSHV is required for lymphatic reprogramming and for the expression of lymphatic-specific Prox-1, podoplanin, LYVE-1, and VEGFR3 genes (23). Knockdown of gp130 by siRNA results in a decrease in VEGFR1, VEGR3, and podoplanin but does not significantly alter the expression levels of Ets-1 (Fig.…”

“…KSHV induces the expression of a number of lymphatic endothelial cellspecific markers, including VEGFR3, podoplanin, LYVE-1, and the master regulator of lymphatic differentiation, Prox-1 (11,12,20). Our laboratory previously demonstrated that activation of AKT, through the interleukin 6 (IL-6) cytokine family transmembrane receptor gp130, leads to the expression of the lymphaticspecific markers VEGFR3, LYVE-1, podoplanin, and Prox-1 and that KSHV-induced lymphatic reprogramming requires continued latent viral gene expression (23). We recently demonstrated that the viral homolog of human IL-6 (vIL-6) is sufficient to induce lymphatic reprogramming of blood endothelial cells.…”

Apolipoprotein A-I Limits the Negative Effect of Tumor Necrosis Factor on Lymphangiogenesis

“…Moreover, the Kaposi sarcoma herpes virus depends on the JAK2/STAT3 pathway for Prox-1-mediated lymphatic reprogramming of ECs. 28 On the other hand, the loss of Prox-1 activity results in defective lymphangiogenesis. 13,14 In a murine contact hypersensitivity model, downregulation of Prox-1 is inversely correlated with local TNF and interferon-γ production.…”