Latent Kaposi's Sarcoma Herpesvirus regulates host factors to induce Lymphangiogenesis and Angiogenesis
Gutierrez, Kimberley Diane
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Kaposi's Sarcoma herpesvirus (KSHV), the etiologic agent of Kaposi's Sarcoma, is present in the predominant tumor cells of KS, the spindle cells. Spindle cells express markers of lymphatic endothelium and, interestingly, KSHV infection of blood endothelial cells reprograms them to a lymphatic endothelial cell phenotype. KSHV induced reprogramming requires the activation of STAT3 and PI3/AKT through the activation of cellular receptor gp130. Importantly, KSHV-induced reprogramming is specific to endothelial cells, indicating that there are additional host genes that are differentially regulated during KSHV infection of endothelial cells that contribute to lymphatic reprogramming. In this thesis we explore multiple host factors that contribute to lymphangiogenesis and angiogensis and therefore aid in the tumorogenesis of KSHV infected endothelial cells. In chapter III we explore the host transcription factor Ets-1 and found that Ets-1 is highly expressed in KS spindle cells and is upregulated during KSHV infection of endothelial cells in culture. The latent viral gene vFLIP is sufficient to induce Ets-1 expression in an NF-&kappaB-dependent fashion. Ets-1 is required for KSHV-induced expression of VEGFR3, a lymphatic endothelial cell specific receptor important for lymphangiogenesis, and Ets-1 activates the promoter of VEGFR3. Ets-1 knockdown does not alter the expression of another lymphatic specific gene, podoplanin, but does inhibit the expression of VEGFR3 in uninfected lymphatic endothelium, indicating that Ets-1 is a novel cellular regulator of VEGFR3 expression. Knockdown of Ets-1 affects the ability of KSHV infected cells to display angiogenic phenotypes indicating that Ets-1 plays a role in KSHV activation of endothelial cells during latent KSHV infection. Thus, Ets-1 is a novel regulator of VEGFR3 and is involved in the induction of angiogenic phenotypes by KSHV. We and others have demonstrated that KSHV infected endothelial cells display angiogenic phenotypes such as increased capillary stability. In Chapter IV we show the host cytokine TGF-beta2 is downregulated during latent KSHV infection of endothelial cells. We demonstrate that the addition of TGF-beta2 to KSHV infected cells grown in a three dimensional matrix disrupts capillary stability, indicating that KSHV downregulates TGF-beta2 in order to promote angiogenesis of latently infected endothelial cells. Furthermore, we show that the KSHV microRNAs, miR-K3 and miR-K-8 are sufficient to downregulate transcription of TGF-beta2. In summary, KSHV differentially regulates the expression of many host genes involved in promoting lymphangiogenesis and angiogenesis of latently infected endothelial cells which ultimately may contribute to KS tumorigenesis.
- Microbiology