Extracellular matrix protein signaling promotes multi-step cancer vasculogenic mimicry formation.

Cancer vasculogenic mimicry (VM) is the formation of vasculature structures in the absence of endothelial cells. We previously established an in vitro model that facilitates the formation of a lumen-containing and fluid-conducting tubular structures after 4 days of cancer cell growth on Matrigel. Herein, we mechanistically characterize this model in breast and ovarian cancer cell lines demonstrating distinct phases of VM formation and the dependence of specific extracellular matrix proteins. We report that VM occurs in four distinct stages. Firstly, alignment, migration then clustering delineate the area of the future tubular structure. Secondly, contraction of aligned structures followed by loss of attachment of some cells and cellular blebbing. Thirdly, a phase of mass proliferation followed by the raising of specific areas of the cancer cell mass above the Matrigel (bridge). Finally, the formation of a cell monolayer closes the tubular structure, forms a glycoprotein-rich luminal lining, then elevates the structure. Only later stages of VM require AKT and FAK signaling, as confirmed by chemical inhibition and phosphorylation analysis. We demonstrate that the lining of the tubular lumen is rich in laminin. Furthermore, the presence of Laminin 111 (but not collagen I) is sufficient in the extracellular matrix (Matrigel) for VM to occur and we confirm that integrin β1, but not integrin β3, is required and this protein changes location during the formation process. RNASeq analysis suggests that VM formation principally occurs through post-transcriptional regulation. As VM is associated with poor patient survival VM, an understanding of the mechanism of VM may bring to light novel biomarkers and anticancer targets.