Hypoxia promotes vasculogenic mimicry formation by vascular endothelial growth factor A mediating epithelial-mesenchymal transition in salivary adenoid cystic carcinoma

Objectives To investigate the role of hypoxia in vasculogenic mimicry (VM) of salivary adenoid cystic carcinoma (SACC) and the underlying mechanism involved. Materials and methods Firstly, wound healing, transwell invasion, immunofluorescence and tube formation assays were performed to measure the effect of hypoxia on migration, invasion, EMT and VM of SACC cells, respectively. Then, immunofluorescence and RT-PCR were used to detect the effect of hypoxia on VE-cadherin and VEGFA expression. And pro-vasculogenic mimicry effect of VEGFA was investigated by confocal laser scanning microscopy and Western blot. Moreover, the levels of E-cadherin, N-cadherin, Vimentin, CD44 and ALDH1 were determined by Western blot and immunofluorescence in SACC cells treated by exogenous VEGFA or bevacizumab. Finally, CD31/ PAS staining was performed to observe VM and immunohistochemistry was used to determine the levels of VEGFA and HIF-1 alpha in 95 SACC patients. The relationships between VM and clinicopathological variables, VEGFA or HIF-1 alpha level were analysed. Results Hypoxia promoted cell migration, invasion, EMT and VM formation, and enhanced VE-cadherin and VEGFA expression in SACC cells. Further, exogenous VEGFA markedly increased the levels of N-cadherin, Vimentin, CD44 and ALDH1, and inhibited the expression of E-cadherin, while the VEGFA inhibitor reversed these changes. In addition, VM channels existed in 25 of 95 SACC samples, and there was a strong positive correlation between VM and clinic stage, distant metastases, VEGFA and HIF-1 alpha expression. Conclusions VEGFA played an important role in hypoxia-induced VM through regulating EMT and stemness, which may eventually fuel the migration and invasion of SACC.