Mammalian target of rapamycin signaling is involved in the vasculogenic mimicry of glioma via hypoxia-inducible factor-1α

The mammalian target of rapamycin (mTOR) is a crucial regulator in malignant gliomas. Vasculogenic mimicry (VM) describes functional channels established by highly malignant tumor cells that is different from endothelium-lined blood vessels. Our previous studies confirmed the existence and clinical significance of VM in medulloblastoma and glioblastoma. In the present study, by immunohistochemical and CD34/PAS histochemical double-staining, 34 cases (26.8%) with VM structures were identified among a total of 127 glioma cases, and these VM structures were associated with mTOR expression in the glioma specimens. In vitro, U87 malignant glioblastoma cells formed tube structures similar to HUVECs on Matrigel in 3D culture, and mTOR-specific inhibitor rapamycin inhibited VM formation in the U87 malignant glioblastoma cells under both normoxia and hypoxia. In addition, rapamycin and mTOR siRNA inhibited molecules in the signaling cascade of VM formation, particularly HIF-1α. Taken together, our results demonstrated that mTOR signaling is involved in VM formation, and may be a potential therapeutic target for gliomas.