Figure 4.

Molecular pathways in cancer cells and vascular cells driving angiogenesis. Schematic graph showing the known pathways associated with angiogenesis, the inhibition of which has been associated with vessel co-option. Ang2-Tie signaling: Signaling of Ang-2 through its receptor Tie-2 can cause sprouting angiogenesis if VEGF levels in the tumor microenvironment are high. If VEGF levels are low, Ang-2- Tie-2 signaling leads to regression of co-opted vessels. IRE1 signaling: IRE1 in cancer cells promote VEGF production, which can induce sprouting angiogenesis. On the other hand, it is indicated, that IRE1 impedes cancer cell invasion via inhibition of anti-angiogenic factors, such as SPARC and Decorin. All abbreviations can be found in the list of abbreviations.