Regulation of vasculogenic mimicry in melanoma (#4)
Vasculogenic mimicry (VM) is a mechanism whereby tumour cells arrange themselves into patterned networks of basement membrane-lined channels which closely resemble blood vessels. This process is thought to increase perfusion of the tumour and enhance metastatic spread. Accordingly, the presence of VM networks in melanoma tissue biopsies is strongly associated with poor prognosis. Currently, however, little is known about the molecular mechanisms controlling VM. Our recent studies have identified the cadherin desmoglein-2 (DSG2), primarily known for its role in desmosome-mediated adhesion of epithelial monolayers, as a novel marker of vascular potential. Here, we have studied the function of DSG2 in melanoma VM. Gene array analysis of a bank of melanoma cell lines revealed that 47/70 (67%) of these lines expressed intermediate to high levels of DSG2, while expression by the remainder was low to negligible. Based on this data, six DSG2+ and six DSG2- cell lines were selected for further study. Western blot and flow cytometric analyses were used to confirm expression, or lack thereof, of DSG2 surface protein for each cell line. Subsequently, Matrigel-based tube formation assays were used to determine the VM activity of each cell line. Intriguingly, the majority of DSG2+ cell lines readily formed tube-like structures in Matrigel, whereas this activity was rare amongst DSG2-negative cell lines. Time lapse imaging revealed that formation of tube-like structures by DSG2+ cell lines occurred with similar kinetics to human umbilical vein endothelial cells (HUVEC), with the cells beginning to align within 1 hour and peak network formation at ~6hr, followed by consolidation of the structures over the following ~10 hours. Importantly, gene knockdown studies revealed that DSG2 was directly involved in the VM process, with a significant reduction in the number of tubes, branch points and loops after treatment with DSG2-targeting siRNAs. Together, these studies reveal DSG2 as a key regulator of melanoma VM activity, and suggest that this molecule could be targeted by novel cancer therapeutics aimed at reducing tumour perfusion and metastatic spread.