Abstract
Blood vessel remodeling is crucial in tumor growth. Growth factors released by tumor cells and endothelium-extracellular matrix interactions are highlighted in tumor angiogenesis, however the physical tumor-endothelium interactions are highly neglected. Here, we report that the physical supports from hepatocellular carcinoma, HepG2 cells, are essential for the differentiation and remodeling of endothelial cells. In a HepG2-HUVEC co-culture model, endothelial cells in direct contact with HepG2 cells could differentiate and form tubular structures similar to those plated on matrigel. By employing HepG2 cell sheet as a supportive layer, endothelial cells formed protrusions and sprouts above it. In separate experiments, fixed HepG2 cells could stimulate endothelial cells differentiation while the conditioned media could not, indicating that physical interactions between tumor and endothelial cells were indispensable. To further investigate the endothelium-remodeling mechanisms, the co-culture model was treated with inhibitors targeting different angiogenic signaling pathways. Inhibitors targeting focal adhesions effectively inhibited the differentiation of endothelial cells, while the growth factor receptor inhibitor displayed little effect. In conclusion, the co-culture model has provided evidences of the essential role of cancer cells in the differentiation and remodeling of endothelial cells, and is a potential platform for the discovery of new anti-angiogenic agents for liver cancer therapy.
Highlights
Blood vessel remodeling is crucial in tumor growth
Many have highlighted the roles of paracrine factors in tumor-induced angiogenesis[2,3], with vascular endothelial growth factor (VEGF) being the key activator in angiogenesis[4]
The underlying mechanism is that common signaling pathways such as PI3K/Akt/mTOR and Ras/Raf/MEK/ERK9 can be activated by multiple angiogenic factors including growth factors, the extracellular matrix (ECM)[10,11], integrins[11,12] and other guidance molecules[12]
Summary
Blood vessel remodeling is crucial in tumor growth. Growth factors released by tumor cells and endothelium-extracellular matrix interactions are highlighted in tumor angiogenesis, the physical tumor-endothelium interactions are highly neglected. Molecular agents such as sorafenib, which targets multiple signaling pathways, provide inhibition to angiogenesis and tumor growth, and have shown promising therapeutic effects against liver cancer[7,8]. Liver cancer cells and ECs labeled with different fluorescence proteins were cultured together to investigate their interactions. This system modeled hepatocellular carcinoma (HCC) angiogenesis much more accurately, and HUVEC-C3 differentiated only in direct contact with HepG2 cells. The physical interactions between HepG2 and HUVEC-C3 are the key factors in tilting the angiogenic balance and the cellular signaling pathways were investigated to understand the molecular mechanisms of this tumor-endothelial interaction. With the expression of a caspase-3 sensor[19] in HUVEC-C3 cells, the survival of ECs as well as the cytotoxic effects[20] of inhibitors and anticancer drugs were investigated concurrently
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
