Kaposi sarcoma (KS), an angioproliferative disease associated with Kaposi sarcoma herpesvirus (KSHV) infection, harbors a diversity of cell types ranging from endothelial to mesenchymal cells of unclear origin. Using a novel three-dimensional (3D) cell model, we have demonstrated that KSHV induces transcriptional reprogramming of primary lymphatic endothelial cells (LEC) to mesenchymal cells via endothelial-to-mesenchymal transition (EndMT). As EndMT induction has been described in response to activation of the TGF-beta or Notch pathways, inhibitor studies were used to decipher their roles in our 3D system. Inhibition of the Notch pathway dramatically attenuated the EndMT in KSHV infected LECs (K-LECs) in 3D whereas inhibition or activation of the TGF-β pathway did not have any effect. Two viral gene products, vFLIP and vGPCR, were found to trigger Notch signaling and lead to the KSHV-induced EndMT. As Notch activation has been shown to inhibit angiogenic and lymphangiogenic sprouting, we assessed the effect of VEGFA or -C stimulation on the 3D K-LECs. Interestingly, VEGFA/C stimulation induced a dramatic outgrowth of (lymph)angiogenic sprouts and inhibited the KSHV-induced EndMT in the 3D K-LECs. This suggests that the KSHV-induced Notch signaling and mesenchymal reprogramming can override the lymphangiogenic properties of LECs in the absence of VEGF-A/C stimulation. These results further corroborate the central role of Notch signaling as a critical determinant for the lymphangiogenic vs. mesenchymal fate of LECs. The 3D K-LEC transcriptome showed significant up-regulation of invasion related genes over the uninfected control. Intriguingly, comparison of the GEM profiles of the 3D K-LECs and KS biopsies, genes with similar co-regulation were found and included those involved both in EMT/EndMT and invasive processes. Using a panel of specific inhibitors we found a membrane associated matrix metalloproteinase MT1-MMP to be the major MMP involved in this process. Our data further identifies Notch as a previously unrecognized upstream regulator of MT1-MMP, and demonstrates that MT1-MMP as such is sufficient to induce EndMT in 3D cultured LECs. Mesenchymal markers and MT1-MMP were found co-distributed in the same cells with LANA in primary KS tumors suggesting that virus-induced EndMT may contribute to development of KS by giving rise to invasive cells, and providing the virus a permissive microenvironment for efficient spread of the viral genomes.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2976. doi:1538-7445.AM2012-2976